Final Report for LS06-190
Project Information
The contribution of perennial leguminous shrubs in an alley cropping system to soil carbon and nutrients was measured in 36 experimental plots. Soils in plots with leguminous shrubs had approximately 100 % more carbon and 90% more nitrogen than in plots without the shrubs. Pot experiments in which the shrub was labeled with stable isotopes showed that root sloughing was the source of the increased carbon and nitrogen. An economic analysis of three different cash crops in an organic alley cropping system showed that only chili peppers Capsicum annum were economically profitable, because of their relatively high market value.
Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
sueblum@uga.edu for a hard copy.
Research Objectives
To compare crop yield, soil organic matter, and soil properties of an alley cropping system plus winter cover crops and composts with a more conventional organic farming system that uses composts plus winter cover crops but no perennial leguminous shrubs..
To measure the time and effort needed to manage the two systems.
To determine whether pruning of above ground biomass of a perennial legume causes an increase in root sloughing, and if so, to quantify the contribution of root sloughing to soil organic matter and nitrogen.
Outreach and Educational Objectives:
To develop an outreach component that will disseminate research results, establish on-farm trials, conduct workshops and internships, and provide feedback to researchers;
To continue, expand, and integrate the Agroecology Lab's current educational program for undergraduates and graduate students into the outreach program.
The purpose of this project was: to evaluate a strategy of soil organic management for organic farming systems that includes perennial leguminous shrubs in an alley cropping system as a sustainable source of nutrients; to analyze the contribution of root sloughing to soil organic matter and nutrient concentration; to develop an outreach component that will disseminate research results, establish on-farm trials, conduct workshops and internships, and provide feedback to researchers.
Most agricultural soils in the Southeast are derived from highly weathered parent material of the ancient Appalachians or Coastal Plain sand. When early pioneers first arrived in the Southeast, they found soil relatively rich in organic matter. Clearing of the forests in the 1800s followed by over 100 years of intensive cropping exposed the once-fertile soils of the Tennessee Valley, Southern Piedmont and Inner Coastal Plain to leaching, erosion and loss of soil organic matter (Langdale et al 1979, Yoo and Touchton 1989). For example in the Piedmont region, continuous cultivation has destroyed the O and A horizons leaving only the subsoil, high in Iron and Aluminum, and low in Organic matter, N, Ca and Mg, and in available P (Perkins et al. 1973).
Because most organic farmers of today in the South begin operations on this remnant subsoil, management techniques to build up soil organic matter (SOM) are particularly important. Because the hot, humid climate causes rapid decomposition, organic matter amendments must be supplied in greater quantities than in other regions of the U.S. Compounding the problem, organic farmers typically till their soil to control weeds. The problem here is that the tillage disturbs the soil, with concomitant increase in microbial respiration and consequent rapid decomposition of the SOM. Conservation tillage or no-till planting are possible solutions because they reduce the aeration of the soil and thereby slow decomposition. Although conservation tillage is being increasingly practiced by commodity farmers in the South (NeSmith et al. 1987, Truman et al. 2003) and there is extensive research on the subject (Rhoton et al. 2002, Feng et al. 2003, Boquet et al. 2004), organic farmers usually till their soil because organic agriculture does not permit the herbicides used by commodity farmers, and because no-till equipment for small-scale farms is generally expensive or not available.
Organic farmers in the South often use winter cover crops to supply SOM and nutrients in the spring, but later in the growing season as the residue decomposes, other amendments are necessary to supply nutrients for the economic crops. The majority of amendments and fertilizers available to organic practitioners are economically expensive. Compost dependent systems can be labor and time intensive, and usually require many years before the organic matter content of the soil is substantially increased. Not only is the process slow, it is logistically inefficient, because gathering a high-nitrogen component such as cow or pig manure and collecting a low-nitrogen component such as wood chips, and then composting them is logistically complicated and heavy equipment dependent, and thus economically expensive. In addition, there are potential problems with imported of manures or grasses carrying weed seeds, or being contaminated. Green manures can eliminate some of these problems. They may reduce weeds, and provide habitat for beneficial organisms. However, most green manures must be cut, raked, transported to the crop, and spread. To supply an equal amount of nutrient elements as inorganic fertilizers, 40 or more times as much bulk must be applied to the soil. (Natural Resource Conservation Service 2003).
These functional, yet expensive and time consuming practices for supplying organic matter to the carbon-depleted soils of the Southeast translates into regional growers charging prices that are not competitive, lack of solvency, and increased grower burn out. To meet the challenge of growing organically in the Southeast in a price-competitive fashion, techniques must be developed to make organic farming more cost and labor efficient, while meeting fertility and weed control requirements. What is needed is a perennial “in situ” source of organic matter and nitrogen. The advantage of perennials in preserving soil organic matter is well recognized For example, a primary goal of the Land Institute, Salina Kansas (Cox et al. 2004) is to develop perennial grains. A promising strategy to achieve more efficiency in managing organic matter is to incorporate in-situ production of organic amendments by perennial legumes (Jordan, 2004). To minimize the logistical problems of transporting organic amendments, there is a need to research perennial sources of organic matter, and methods to manage these sources to maximize organic matter input into the soil and minimize competition with the commercial crop.
The major issue that we are addressing by incorporating perennial legumes in an organic matter management system is to simplify the logistics, while increasing the long-term efficiency of supplying organic matter to where it is needed most, the cropping zone. The idea is to substitute, as much as possible, organic matter produced “in situ”, for organic matter hauled in from off-site or off-farm. This can be done with alley cropping systems, where legumes are planted in hedgerows, and the crop is planted in the “alley” between the hedges. Establishing alley cropping systems can be time and labor intensive, but the primary costs are incurred during the first year. It is after the first year that the advantage of perennial legumes over other input systems becomes apparent, because from then on, management is simpler and consequently more cost effective. All that has to be done is prune, and this is easily and quickly accomplished with a power hedge trimmer or tractor-mounted brush-cutter. Not only will alley cropping reduce the time and labor required for supplying organic matter to crop beds, it would reduce the amount of petroleum products needed to transport the organic matter from distant sources. However, there have been no studies done on the time and effort required for an alley cropping system compared to that for organic systems that are managed with cover crops and/or composts. This project asked whether an organic cropping system that uses a perennial legume in an alley cropping configuration plus a winter cover crop would be more effective in supplying organic matter and nutrients to soil as an organic farming system that employs winter cover crops and compost additions alone.
Another question was, if alley cropping does indeed increase carbon and nutrients in the soil, what is the mechanism? Matta-Machado and Jordan (1995) showed that after two years, an alley cropping system plus winter cover crops had a carbon input to the soil of 6831 kg/ha/yr, an N input of 258 kg/ha/yr,, and a P input of 18.8 kg/ha/yr compared to a system with only winter cover crops that had inputs of 4308 kg/ha/yr of C, 121 of N, and 13.1 of P. The question arises, did some of this input come from death and sloughing of roots? In a review of the role of roots of leguminous hedgerows, Akinnifesi et al. (2004) stated that “the role of the tree roots as a source of nutrients for the crop (resulting from root decay and the release of decomposition products), cannot be over looked or ruled out in agroforestry associations.” Haggar et al.(1993) suggested that nutrient build-up in alley-cropping systems may come from readily decomposable roots. Smucker et al. (1995) found that as much as 193 kg/ha of N was recycled from root turnover of both maize and leucaena during a growing season. A major objective of this project was to determine whether sloughing of roots of a perennial hedgerow contributes to soil organic matter, and whether pruning the hedgerows during the growing season increases the supply of nutrients to the crop plants compared to non-pruned hedgerows.
It has been suggested that root sloughing results from a physiological imbalance within the plants caused by the pruning of above-ground biomass. Nygren and Campos (1995) found that severe pruning or pollarding of trees to a height of 1.5 meters caused a decline in the fine root mass of Erythrina poeppigiana. Chesney and Nygren (2002), Peter and Lehmann (2000) and Hartley and Amos (1999) found root sloughing following above-ground pruning. Sloughed roots may represent a considerable input of organic matter to the soil, as determined by plants labeled with 15-N (Albrecht et al. 2004). Input of nutrients and carbon to the soil via root sloughing may be particularly effective because the input is within the soil, not on the soil surface, so the problem of incorporating the organic matter into the soil is eliminated. In addition, decomposition of the organic matter within the soil will be much slower than OM on the surface. An objective of the work proposed here was to determine whether root sloughing occurs as a result of above-ground pruning, and if so, what the contribution is toward soil carbon and nitrogen. If indeed root sloughing of perennial legumes can make a significant contribution to the soil organic matter, it could mean that alley cropping could be a more effective way of increasing soil organic matter and nutrients, and that after the leguminous hedgerows are established, an alley cropping system would be a less expensive and more sustainable system to manage.
A frequent problem for organic farmers in the Southeast is lack of information on improved methods of soil organic matter management. Particularly lacking is guidance on how to restore soils degraded by intensive tillage and erosion so that these soils become suitable to sustain an agricultural production system. There are no extension agents in Georgia to serve the critical needs and questions of the burgeoning southern sustainable agricultural community. Also, there is little research and outreach to guide growers on this topic. Interviews by personnel of the Agroecology Laboratory (the entity that proposed this project) with organic farmers in the Southeast indicated that soil organic matter management is a problem of greatest concern. It was clear that there are many innovative practices being employed throughout the region, but no adequate channels for growers to share and learn from each other's unique, yet corresponding experiences. Georgia Organics (the umbrella organization of organic farmers in Georgia), SARE, ATTRA (Appropriate Technology Transfer for Rural Areas), SAWG (Southern Agricultural Working Group) and others have made initiatives, but there is much more that can be done. The rationale for the outreach component of this project is to improve and organize organic matter management by organic growers in the Southeast.
Another problem is lack of educational programs for entrants into organic agriculture. While there are a number of Universities in the U.S. that have begun major programs of education and outreach for organic agriculture, there is only one in Southeastern U.S., The Center for Environmental Farming Systems sponsored by NC State Univ. and NC A&T State Univ. The lack of centers or programs dedicated to education in organic agriculture in the Southeast is especially critical because without a strong educational platform to inform future growers the possibility of creating a more sustainable agriculture will be limited.
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Cooperators
Research
Field experiment
Site description
The study site is located in the Georgia Piedmont, near Athens, Georgia USA (33°57’N
lat. 83°19’W long). The soil is classified as a Pacolet sandy clay loam (kaolinitic, thermic typic
hapludults). The soil of the experimental plots was highly eroded, and consisted only of a B
horizon, heavily compacted red clay. The site was chosen to test the methods on an extremely
poor soil. The site is on a 100-acre historic farm that has been in cultivation since 1864, with
cotton, cattle, sorghum and soybeans grown on the site until 1993. At this time, the site began to
be managed as a mowed fallow of pasture grasses and weeds. In 2001, an alley cropping system
was planted along an east facing slope on the site, with hedgerows of Albizia julibrissin spaced 5m apart. Between 2001 and 2004, the alley ways were planted with a variety of vegetables and
cotton, to test various cultivation techniques. In summer of 2004, the alleys were surface tilled
with a rototiller to a depth of 5 cm to expose mineral soil. A summer cover crop of sunn hemp
(Crotalaria juncea) was broadcast sown, and killed with a mechanical grass roller (a “roller crimper”) in September, when this work began.
Experimental Design
In early October, summer vegetation was killed using the roller crimper, and a blend of
legume and grass cover crops was broadcast sown. The cover crop blend and seeding rates were:
Crimson clover (Trifolium incarnatum), 18 lbs/acre (20.17 kg/ha); Austrian winter pea (Pisum sativum) 36 lbs/acre (22.61 kg/ha); cereal rye (Secale cereale), 48 lbs/acre (53.80 kg/ha).
Following broadcast seeding, a cultipacker was passed over the soil to shake any cover crop seed
from surface litter, ensuring seed contact with the mineral soil. In the spring (mid-April), the
winter cover crop was mechanically killed using the roller crimper, which rolls the vegetation
down and crimps the vascular tissue of the plant, killing the shoots and leaving a uniform layer
of cover crop residue on the soil surface. Winter cover crops were managed identically in both
the AC and OST cropping systems.
After approximately 2 weeks, plots were strip-tilled using a disc followed by a 2.5” wide
shank. The strip tillage created a planting furrow approximately 25 cm wide by 15 cm deep.
Vegetable crops were direct seeded (Years 1 and 3) or transplanted (Year 2) into the furrow by
hand. All plots were hand weeded. Conventionally tilled treatments were disked and roto-tilled
approximately 1 week prior to vegetable planting. All vegetable crops were irrigated using drip
irrigation, which was installed prior to planting each spring and removed each fall. Following standard practice for diversified organic vegetable production in the region,
summer vegetables were rotated annually, with the following crops:
Year 1: Okra (Abelmoschus esculentus, ‘Clemson spineless’),
Year 2: Hot peppers (Capsicum annum, ‘Long cayenne’)
Year 3: Corn and winter squash intercrop (Zea mays, ‘Reid’s yellow dent’ and Cucurbita
moschata, ‘Waltham butternut’).
Within the AC (Alley Cropping) system, 6 treatments with combinations of compost applications of 0, 10 and 20 tons/acre with and without straw mulch were randomly distributed, with 4replicates per treatment. AC plots were 5 m wide (the spacing between the hedgerows) by 4.8m– 7.3m in length. The OST (Organic Strip Till) cropping system consisted of 3 treatments with compost applications of 0, 10 and 20 tons/acre, with all treatments receiving straw mulch, and 4 replicates per treatment randomly distributed throughout the system. OST plots were 5m by 5m. Complete treatment descriptions are listed in Table 2.1. Compost and straw mulch were applied by hand in all treatments. Conventional treatments were broadcast fertilized with inorganic fertilizers (10-10-10 percent N, P and K respectively) in bands adjacent to crop rows within 10 cm of crop plants, according to the University of Georgia College of Agriculture Cooperative Extension guidelines for N requirements for each crop species. After broadcasting, fertilizer was lightly raked into the soil without disturbing the transplants or seedbed. Albizia hedgerows were pruned 1-3 times each summer to a height of 1m when they
began to shade crop plants. Prunings were evenly applied to the cultivated plots in adjacent
alleys. The AC, CT and Fallow cropping systems were established in 2004 and studied for 3
years, and the OST system was established in 2005, and studied for 2 years.
Sampling
Soils were sampled for C and N at 0-5 cm and 5-15 cm depths in the fall of each year,
prior to fall compost application and winter cover crop planting. Soils were sampled for NH4+
and NO3 - 6 times over 3 years from 0-30 cm depths, in the spring prior to mechanically killing the cover crop, and in the fall prior to mechanically killing the summer crop. Soil microbial biomass was sampled 6 times over 3 years from 0-5 cm depths, in the winter (February) and spring (late April) of each year. These dates were chosen because they approximate base and peak microbial biomass estimates, respectively. Soil microbial biomass and NH4+ and NO3-samples were placed in a cooler with ice prior to transport to the laboratory. For each sampling period, three cores from a 2 cm diameter soil probe were collected randomly from the middle
portion of each plot, oven dried at 50° C, and bulked for a single analysis. Bulk density was
sampled according to the USDA Soil Quality Test Kit Guide (National Resource
ConservationService, 1999), with one sample collected from the middle portion of each plot,
with care taken not to sample in a planting furrow. A PVC ring 6” in diameter was place on the
mineral soil surface, a wooden block placed over the ring and a rubber mallet used to hammer
the ring 5 cm deep into the soil. The sample was carefully removed, and a flat-bladed knife used
to scrape excess soil from the bottom of the PVC ring. Aggregate stability was sampled in the
spring of 2004 in the AC treatments, and in the fall of 2005, 2006 and 2007 in all treatments,
according to the USDA soil quality test kit protocol (National Resource ConservationService,
1999). Three 0-5 cm cores were bulked from each plot, carefully collected so as not to disturb
the soil aggregates, and air dried.
Vegetation was sampled in the spring and fall, corresponding to the end of the winter cover crop and summer cropping seasons. One .25 m2 sample was collected randomly from the middle portion of each plot. Roots were carefully excavated with a shovel and left attached to plant shoots. Loose dirt was gently shaken off each sample, and roots and shoots transported in paper bags to the lab for further processing. In 2005 and 2006, crop yields were recorded throughout the summer. Crop fruits from 4 marked plants were weighed in the field from 4 marked plants per plot, and yields from 1 marked plant transported to the lab for dry biomass determination and nutrient analysis. Fruits harvested throughout the season were bulked for each marked plant at the end of the season for a single nutrient analysis. In 2007, this methodology was modified, due to the sampling difficulty of isolating 4 individual winter squash plants per plot. In 2007, all winter squash fruits in each plot were weighed for yield determinations, and 1 fruit per plot was collected for nutrient analysis. Corn yields were estimated from kernel counts on 10 ears of corn per plot, total number of corn plants per plot were recorded, and yields determined by assuming an average of 90,000 kernels/bushel and average mass of 24.36 kg/bushel, determined by dry weights of a known quantity of oven dry kernels. Corn nutrient content was obtained from ears collected in .25m2 vegetation samples. Albizia and straw mulch additions were sampled at the time of application, with one, 1 m2 sample collected from the middle portion of each plot.
Laboratory Analysis
Soils C and N samples were oven dried at 50° C to a constant mass, passed through a
2mm sieve, ground on a Spex mill to a particle size <250um. They were weighed into tin
capsules and analyzed for C and N by micro-Dumas combustion assay at the University of
Georgia (UGA) School of Ecology Analytical Chemistry Laboratory (ACL). pH was determined
from these samples in a solution of equal volumes of soil and water. NH4+ and NO3- samples
were extracted within 1 week of field sampling, and were stored in sealed plastic bags in
refrigeration until time of extraction. Samples were extracted by placing 4 g of wet weight
sample in 20 mL of 2 M KCl solution, placed on a shaker for 1 h at medium speed, and filtered
through Whatman #42 filter paper into scintillation vials. Samples were analyzed by continuous flow colorimetry at the UGA School of Ecology ACL.
Soil microbial biomass was determined by the chloroform fumigation extraction method
(Vance, Brookes & Jenkinson, 1987). Samples were processed within 24 hours of collection,
and hand sorted to remove visible roots and rocks. Hand sorted was preferred to the standard
practice of passing through a 2-mm sieve because during the initial sampling date soils were too
wet and clayey to pass through the sieve and thus processing was handled identically at
succeeding sampling dates. 10 g of each sample were fumigated with chloroform under a
vacuum for 5 days, because this duration maximizes extraction of microbial biomass C in wet,clayey soils (Motavalli, 1994). After fumigation, desiccation chambers were allowed to vent overnight and TOC extracted by adding 40 mL 0.5M K2SO4 to the fumigated sample. Beakers
with the soil in the K2SO4 solution were placed on a shaker for 1 hour at medium speed, and the
solution filtered through Whatman #42 filter paper into scintillation vials. Non-fumigated
samples were extracted by same procedure immediately after sorting. Extracted samples were
stored frozen until they were analyzed on a Shimadzu 500 Total Organic Carbon analyzer at the
UGA School of Ecology ACL. Microbial biomass C was calculated as the difference between
fumigated and non-fumigated samples using a kc value of 0.45 (Joergensen, 1996).
Aggregate stability was measured by wet sieving by hand, according to procedure in the
USDA Soil Quality Test Kit (National Resource Conservation Service, 1999). A 10g subsample
of air dry soil from each plot were passed through a 2mm sieve, gently wetted, and wet
sieved in a deionized water bath through a vertical distance of 1.5cm at a rate of 30 oscillations per minute for 3 min. After wet sieving, samples were dried in a 100° C drying oven for 24 h, weighed, and then dispersed in soap (Calgon) solution. Sieves were soaked for 5 minutes, during which time they periodically moved up and down. After 5 min, sieves were rinsed with running water until only sand remained. Samples were again dried in a 100° C drying oven and weighed.
Water stable aggregates were calculated as % of soil > 0.25mm = (mass of dry aggregates –
sand)/ (mass of dry soil – sand).
Roots from .25m2 vegetation samples were carefully washed over a 2-mm sieve before
drying to remove adhered soil. Dried samples were sorted into weed and crop categories. Spring
cover crop samples were sorted into legume and rye categories. Above and below-ground
biomass for each category was recorded, then sorted samples were bulked into root and shoot
categories for each plot for nutrient analysis. Albizia, straw mulch, vegetation biomass, and
crop yields except winter squash were dried in a 50° C drying oven until a constant mass was
achieved, and dry mass recorded before nutrient analysis. Winter squash was dried in an
American Harvest Food Dehydrator to a constant mass, because samples tended to mold in the
drying oven due to high moisture content and sugar content. All biomass from vegetation
samples were first passed through a Wiley mill with a 2-mm screen to homogenize the sample
and reduce particle size. Subsamples from the entire milled biomass were ground to less than
250 um particle size in a Spex mill. Samples were weighed into tin capsules and analyzed by
micro-Dumas combustion assay for C and N at the UGA School of Ecology ACL.
Isotope Tracer Study
This study was to determine whether pruning of above ground biomass of a perennial legume causes an increase in root sloughing, and if so, to quantify the contribution of root sloughing to soil organic matter and nitrogen.
In January of 2007, 1 year old seedlings of Amorpha fruticosa were transplanted into 5 gallon pots. In June 2007 plants were prepared for isotopic labeling by covering the soil with plastic to prevent direct contact of soil with the label solution. Dual isotopic labeling (13C and 15N) started on June 7. Labeling was done by spraying the leaves with a urea solution prepared by dissolving 2 g 99 atom % 13C urea and 4 g 99 atom % 15N per liter of deionized water. Control unlabeled plants were also sprayed with non-enriched urea solution of equal concentration. Plants were kept in hoop houses which remained covered for the 24 h immediately after spraying but otherwise were kept open. Plants were sprayed every week for 9 weeks. On August 3rd, after the final spraying, half of the plants were pruned (all leaves removed except for one). Pruning was repeated on September 6 and October 17. A set of unlabeled control pots was only pruned one time. Beginning on August 14th and ending in April 2008 we destructively sampled 5 replicate pots of each treatment twice after the first pruning, twice after the second pruning and three times after the third pruning. Destructive sampling involved separating the soil from the plant material and subsequently into roots, leaves and stems. All plant material was freeze-dried and weighed. Soil was homogenized and a sample was collected to be processed within 24 h for dissolved carbon and microbial biomass carbon and nitrogen by chloroform fumigation extraction in K2SO4. Remaining soil was freeze-dried within 24 h of collection. For obtaining nitrogen isotopic ratios, an aliquot of the liquid extracts was digested through persulfate oxidation to convert all forms of nitrogen into nitrate. Digested and undigested extracts were subjected to a diffusion method to capture nitrate in solution into acidified glass fiber disks and have been sent for analysis. Isotopic ratios of the microbial biomass were estimated by mass balance from the ratios of the fumigated and unfumigated extracts.
Roots of plants collected at the last sampling date (pruned, unpruned and only pruned once) were used to estimate the ratio of live to dead roots. After washing the whole root system of each plant, all <1mm roots were removed, homogenized and a 1-g subsample was sorted into live and dead tissue. Live roots had an elastic and white to slightly brown stele and had light and turgid root tips. In dead roots the stele was brownish and easily broken and root tips did not appear active. To directly assess the effects of pruning on total and root-derived nitrogen availability we grew corn in re-hydrated freeze-dried soils from pruned and unpruned plants simultaneously in soils from three of the sampling dates. Eight corn seeds were planted into 100 g of soil from each original pot and harvested two weeks later. Total plant dried weight (50ºC) including roots was recorded and plant material was ground and analyzed for total N and C, d13C and d15N.
Field Experiment
Statistical Analysis
Data were analyzed using a repeated measures mixed model in SAS Version 9.1 for PC
(SAS Inc., 1989-2007). Least squares means were estimated using the restricted maximum
likelihood method. Significance was determined for all results at p < 0.05. The experiment was
analyzed as a randomized block, with plot as the random variable. Treatment effects were nested
within cropping system (AC, OST, CT and Fallow). The nested effect was necessary to account
for the placement of plots of each treatment within adjacent cropping systems and not randomly
throughout the complete block. Separation of cropping systems was necessary to separate the
effects of hedgerow roots from other treatments.
Soil Characteristics
Bulk density (g/cm3) from 0-5 cm differed significantly by treatment over time (F[17, 67] =
1.90, p = 0.0332), decreasing in AC treatments, remaining relatively constant in Fallow and CT
treatments, and increasing in the OST treatments (Figure 2.1). Within AC treatments, bulk
density increased in Year 2 in treatments not receiving compost or mulch additions, but declined
to values comparable to the other treatments by Year 3. Mean values for all treatments were
uncharacteristically low for the region.
Water stable aggregates (WSA’s) > 250 μm in the 0-5 cm soil depth changed significantly over time (F[2, 61] = 27.12, p = <0.001) but not by treatment. Mean WSA’s from all
treatments increased from Year One (65.97% + 7.12%) to Year 3 (80.17% + 1.66%), then
decreased from Year 3 to Year 4 (58.45% + 6.17%).
pH was higher in the 0-5 cm depth than in 5-15 cm depths, (F[1, 235] = 117.55, p =
<0.0001), with significant effect by treatment over time with depth (F[31, 235] = 1.79, p = 0.0086).
All AC and the OST3 treatment increased in pH from 0-5 cm. OST 1, OST2 and Fallow
treatments decreased, and the CT increased in Year 3, but fell to initial levels by Year 4 (Figure 2.2). pH in all organic treatments decreased in their first year in cultivation, but AC treatments rapidly increased after the initial drop, whereas, OST treatments did not. From 5-15 cm, all treatments increased in pH, except the fallow (Figure 2.3).
Percent total soil C was greater from 0-5 cm than from 5-15 cm in all treatments (F[1, 161]
= 284.02, p = <0.0001) and significantly different by treatment by depth (F[10,161] = 2.32, p = 0.0140) (Figures 2.4 and 2.5, respectively). Changes in soil total % C were significant over time (F[3,161] = 5.71, p = 0.0010), as were treatment by time interactions (F[24, 161] = 1.97, p = 0.0073), but not by depth. Irrespective of depth, AC1, AC2, AC4, OST1 and OST3 decreased over time.
AC3 and AC5 increased, while AC6 and OST2 did not change significantly. The CT treatment
decreased, while the Fallow treatment increased (Figure 2.6). Soil microbial biomass carbon (μg
C/g dry soil) fluctuated seasonally, with higher biomass C in spring than in winter (F[5, 151] =
6.58, p = <0.0001), but did not differ significantly by treatment or by treatment over time.
Soil total soil percent nitrogen was higher from 0-5cm than 5-15cm in all treatments
(F[10, 146] = 2.39, p = 0.0116) (Figure 2.7 and Figure 2.8, respecitively). Total %N differed
significantly by treatment over time (F[24, 146] = 2.12, p = 0.0035), but not by treatment by time by
depth. Irrespective of depth, the AC and Fallow treatments had consistently higher %N than
OST treatments. Percent N declined in treatments AC1, AC2, OST3 and CT. Percent N
increased in AC4 and AC6 during the experiment, but after the third year of cultivation, changes
were not different from the initial treatment means. AC3 and AC5 increased significantly. OST
treatments all declined in after 2 y of cultivation, but OST1 and OST2 increased in Year 3. The Fallow was relatively unchanged (Figure 2.9).
Data for NH4+-N from 0-30 cm were highly variable, but were significant by date (F[5, 161]
= 3.56, p = 0.0045), generally with higher values in the spring than in the fall (Figure 2.10).
Changes in soil NO3--N (μg NO3-/g dry soil) from 0-30 cm were significant by treatment (F[10,
161] = 11.37, p = <.0001), date (F[5, 161] = 29.89, p = <0.0001) and treatment by date (F[44, 161] = 3.99, p = <0.0001). Treatment responses were variable, but in general all treatments increased between spring and fall sampling dates each year. All cultivated treatments were higher in NO3-at the end of the 3 years than their initial values. During all spring sampling dates, AC treatments had higher NO3- than OST and CT treatments (Figure 2.11). Means and standard
errors for NO3- and NH4+ date appear in Table 2.2.
Vegetation characteristics
Spring vegetation samples consisted of above and below ground biomass of winter cover
crops and weeds. Spring vegetation data were only available for 2005 and 2007, as 2006
samples molded in storage prior to analysis. Spring above ground biomass (kg/ha), differed
significantly by treatment (F[10,19] = 11.14, p = <0.0001) and date (F[1, 19] = 9.76, p = 0.0056), but not treatment by date. In general, AC treatments planted in winter cover crops had greater vegetation biomass than CT and Fallow treatments. The latter was comprised of volunteer
vegetation. Above ground biomass decreased from 2005 to 2007 in all treatments except AC3.
Declines in AC5 and AC6 were less precipitous than other treatments (Figure 2.12).
In addition to biomass changes, the composition of the spring vegetation community
shifted from 2005 to 2007. The weed above ground biomass increased significantly over the 3
year experiment (F[1, 19] = 6.86, p = 0.0168). In 2007, after 3 years of the AC experiment,
mulched treatments had less weeds than non-mulched treatments. Rye above ground biomass
declined in all treatments over time (F[1, 19] = 6.86, p = 0.168) and differed significantly by
treatment (F[10, 19] = 6.28, p = 0.0003) not did not differ significantly by treatment by date.
Clover above ground biomass generally decreased from 2005 to 2007 (F[1, 19] = .0168), and
varied significantly by treatment (F[10, 19] = .0003), but not by treatment over time. In the CT and Fallow treatments, the biomass of leguminous and forb plants increased, while grass biomass decreased.
Above ground biomass C (kg C/ha) production in spring vegetation decreased in all
treatments (except AC3) over time (F [1, 19] = 15.00, p = 0.0010) (Figure 2.13), with responses
varying by treatment (F[10, 19] = 6.06, p = 0.0004) but not by treatment by time (F[7, 19] = 2.20, p = 0.0812). In 2005, C production was significantly higher in AC treatments compared to the CT and Fallow, with the exception of AC3. In 2007, C production was more variable, but in general,treatments receiving compost (AC3, AC5, AC6, OST3) had higher C production than those not
receiving compost additions (Figure 2.13). Above ground biomass N production (kg N/ha)
decreased in all AC treatments over time except AC3 (F[1, 19] = 11.18, p = 0.0034 ). N production
in AC treatments differed significantly by treatment (F [10, 19] = 4.66, p = 0.0020) and treatment by date (F[7, 19] = 2.75, p = 0.0374). AC treatments not receiving compost (AC1 and AC2)
decreased more than those receiving compost. In the year of data available for the OST
treatments. N production increased with increasing levels of compost application (Figure 2.14). Shoot C/N ratio did not differ significantly by treatment or date.
Fall vegetation above ground biomass (kg/ha) consisted of crop plants and weeds, and
differed significantly by treatment (F[9, 51] = 2.85, p = 0.0085), but not by date. Crop biomass
(kg/ha) differed significantly by treatment (F[10, 51] = 2.15, p = 0.0368) and over time (F[2, 51] = 12.43, p = <0.0001), but not treatment by time. In 2005, AC treatments produced more above
ground biomass than the CT treatment, with mulch treatments generally producing more biomass
than non-mulched treatments (Figure 2.15). In 2006, there was less of a visible mulch effect, and biomass in CT treatments was on par with the AC treatments, although the CT treatment had
more weed biomass. The less marked differences between mulched and non-mulched treatments
is probably an outbreak of Fusarium wilt in mulched treatments, which lead to higher mortality, as discussed further below. Weed biomass (kg/ha) decreased in all treatments over time (F[15, 51] = .0549), with significant differences by treatment (F[10, 51] = 2.94, p = 0.0054), with lower weed biomass in mulched treatments. Changes in weed biomass over time were significant (F[15, 51] =
1.84, p = 0.0549). By the final vegetation sampling date, fall weeds in mulched treatments were nearly non-existent. Shoot C/N ratio differed by treatment (F[10, 49] = 0.0039), date (F[2, 49] = <0.001), and treatment by date (F[15, 49] = <0.0001) (Figure 2.16). Shoot C (kg/ha) differed significantly by date (F [2, 51] = <.0001), but not by treatment or treatment and date. Shoot N differed by treatment (F[10, 51] = 0.0004), but not by treatment or date.
Below ground biomass data was incomplete in spring vegetation biomass samples,
because root samples were not taken in 2005, and samples molded prior to analysis in 2006.
Below ground fall vegetation biomass (kg/ha) increased significantly from 2006 to 2007 (F[1, 30] = 24.36, p = < 0.0001), reflecting changes in biomass with different species in the crop rotation.
Differences were not significant by treatment or treatment by date, but differences were
significant when looking specifically at weed and crop root biomass. Differences in crop and
weed below ground biomass were variable, but significant by treatment over time (F[9, 30] =
12.87, p = < 0.0012, F[9, 30] = 2.30, p = 0.0356, respectively). In 2006, differences between crop
and weed root biomass were not striking, other than that OST treatments had higher weed
biomass than the AC and CT treatments. In 2007, weed and crop below ground biomass
increased in all treatments, the crop due to the deep and prolific rooting of the corn plants and the weeds due to an outbreak of crab grass late in the season. Of note is the decreased root biomass in the mulched treatments compared to the non-mulched treatments (AC3, AC5). If the mulch
was retaining significant moisture, as we hypothesize, in non-mulched treatments, plant roots would have to root deeper to access water, and increase in root biomass. Weed root biomass was higher in non-mulched treatments (Figure 2.17).
Crop yields (fruit biomass) did not differ significantly by treatments, but differed
significantly by year (F[5, 258] = 10.29, p = 0.0002), due to differences in biomass of crop fruits in
the various crop species in the crop rotation. Mean yields (+ standard error) for all treatments by year were: Okra (2005) = 3535 + 360 kg/ha, hot peppers (2006) = 4633 + 272 kg/ha, and corn
and winter squash intercrop (2007) = 2718 + 255 kg/ha. Although treatment differences were
not significant, there were trends based on mulch applications. Non-mulched AC treatments had
lower yields than mulched treatments in 2005 and 2007, but higher yields in 2006, due to disease
damage. Crop yields (mean + std. dev.) for all treatments from 2005 to 2007 are presented in
Table 2.3. Yield nutrient data is not presented here, as 2005 yields were damaged in storage by
pests prior to analysis, and data from corn yields in 2007 was incomplete.
Albizia pruning biomass ranged from 578.57 + 211.29 kg/ha to 2780.00 + 935.31kg/ha,
corresponding to inputs of 15.93 + 6.91 and 75.77 + 22.74 kg N/ha, respectively. Pruned
biomass varied over significantly over time (F[5, 48] = 15.44, p = <0.0001), with greater biomass
from the first annual prunings than succeeding prunings. C and N inputs (kg/ha) varied
significantly over time (F[5, 48] = 15.73, p = <0.0001 and F[ 5, 48] = 14.88, p = <0.0001,
respectively), as did the C:N ratio (F[5, 48] = 10.29, p = <0.0001). During 2005, biomass and C/N
ratios declined throughout the season over the course of 3 prunings. In 2006, biomass and C/N
ratios increased. On April 9, 2007, a hard spring frost severely damaged the Albizia and killed
developing new shoots. The frost, combined with a severe drought, led to very slow Albizia
development in 2007, and pruning was only necessary in the late summer. Mean values for each
pruning date are presented in Table 2.4.
Discussion
Field Experiment
The decline in aggregate stability (WSA’s > 250 μm) is likely a function of severe drought in the last year of the experiment. In 2007, drought conditions in Georgia deteriorated to
“exceptional” levels, a condition expected only once every 100 years (Stooksbury, 2008), and
soils were exceedingly dry, friable and compacted during the fall sampling date. Differences in
pH between 0-5cm and 5-15cm soil depths are to be expected, as pH generally decreases deeper
in the soil profile. The pH increases in alley cropping treatments were incremental. However,
they demonstrate that alley cropping with no-till management can increase surface soil pH
beyond organic no-till without alley cropping, except for in the heavily composted no-till
treatment. All cultivated treatments increased in pH from 5-15cm, probably due to root-derived
organic matter inputs.
Changes in total soil %C may be explained by the quantity of organic matter additions
and the presence or absence of mulch. All AC treatments increased in %C from 0-5 cm, except
for AC1 and AC2, which did not receive compost. All other AC treatments increased in %C,
however, the mulched treatments increased less than non-mulched treatments receiving the same
level of compost. While the straw mulch treatment was initially assumed to improve weed
suppression, it probably also helped to conserve moisture during dry, hot conditions. The
additional moisture present under the mulch may have increased decomposition of compost
and/or soil organic matter, leading to less marked increases in %C in the mulched treatments.
When comparing AC treatments with OST treatments with the same level of compost and mulch
additions, AC treatments accumulated soil % C, while OST were just able to maintain soil %C.
These results demonstrate that for this site, alley cropping can maintain surface soil %C (0-5 cm)beyond that of organic, conservation tillage systems. At deeper soil depths (5-15 cm) %C in the
AC treatments declined in all mulched treatments, but increased in AC treatments with compost
additions without mulch. In OST treatments, %C was maintained only in OST3, which received
20 tons/acre compost application, but the trends indicate a decline in this treatment as well. This
indicates that biomass additions and potential sequestration under conservation tillage cannot
compensate for higher decomposition rates under mulch.
It is well established that conservation tillage conserves soil C (West et al., 1992;Hendrix, Franzluebbers & McCracken, 1998; Jarecki & Lal, 2003). However, it is possible in this case that root biomass additions may have created a “microbial priming effect,” hypothesized by Fontaine (Fontaine et al., 2004). Root exudates and dead root biomass additions may have activated the microbial community, which then consumed the root carbon as well as
existing soil C. While it was assumed the conservation tillage would slow organic matter cycling and conserve, and perhaps increase soil C, it is unknown whether some tillage would have
increased soil C at deeper depths by incorporating organic amendments. These results indicate that alley cropping and conservation tillage with moderate compost application are enough to maintain and build surface soil C. However, winter cover crops and compost additions are not enough to maintain soil C at deeper depths in alley cropping or conservation tillage organic systems in clayey soils, and that these conclusions are confounded by the interactions between compost and mulch additions. The increase in the Fallow treatment was also expected, as the
soil was not disturbed as heavily as the other systems, and mowed biomass remained within the
plots.
While soil %N results did not have significant treatment by time by depth interactions,
treatment by time interactions followed similar patterns as soil %C results. In AC treatments,
compost additions were required to maintain %N. The lack of increase in %N in mulched
treatments supports the hypothesis that higher decomposition rates were occurring under the
mulch, and that slowing decomposition through moisture limitation can sequester soil N.
Because all OST treatments were mulched, it is unknown whether organic, conservation tillage
practices without mulch additions would have similar effects to AC treatments with identical
compost applications. With the current experimental design, it is impossible to determine
whether the declining trends in soil N in OST treatments are due to lack of organic matter inputs from hedgerows, or from high decomposition rates under the mulch.
Throughout the course of the study, the OST treatments had lower soil %N than the AC
and Fallow treatments at both 0-5 cm and 5-15 cm depths. Difference in initial %N between the
cropping systems may be explained by the establishment period of the alley cropping treatment.
The hedgerows were planted 3 years prior to initiation of this experiment. During this time,
inputs from occasional Albizia prunings, root sloughing, and crop and weed residues may have
contributed soil N. Alternatively, while they are the same soil type, the soils in the OST
treatment were slightly sandier than the AC soils, which could lead to higher NO3- leaching rates in OST treatments, and/or interactions between soil type and organic matter dynamics.
Albizia biomass production and C/N of prunings were variable, and probably a function
of plant response to pruning, precipitation and temperature. The biomass from the first pruning
in 2005 was quite woody, with many large branches as the plants had not been pruned regularly
since establishment. The succeeding growth consisted of more lush, green growth, but by the
third pruning the hedgerows were developing more woody growth. In 2006, biomass was similar
between the two prunings, but again the biomass from the second prunings was considerably
more nitrogenous than the first. As only pruned biomass was sampled for this work, nutrient
input estimates are likely underestimates of actual C and N inputs from the hedgerows.
Hedgerows could contribute additional N and C inputs from root biomass, including root
exudates and large pulses of dying fine roots that may senesce after pruning (“root sloughing”),
as well as above and below ground inputs from seasonal senescence in the fall (Kass, Sylvester-Bradley & Nygren, 1997).
It was initially theorized that the Albizia pruning biomass would also to weed suppression
(Jordan, 2004). Pruning biomass was not sufficient to suppress weeds for any length of time, in part due to the wide spacing of the hedgerows, and in part due to leaf morphology. It is possible that with less space between the hedgerows, and thus additional hedgerows, biomass production would have been sufficient to suppress weeds. However, additional hedgerows would also
reduce available cropland. It is possible that Albizia residues do not have the capacity to
suppress weeds at any planting density due to its extremely fine leaflets. Leaflets fell from the
rachis of the compound leaf within 48 hours of pruning, leaving sparse woody material on the
surface with insufficient biomass to smother weeds.
Weed biomass increases in spring vegetation in the AC treatments can be explained by a
build up of pernicious early season weeds in the plots, such as Carolina horse nettle (Solanum
carolinense), crab grass (Digitaria genus) and perennial ryegrass (Lolium perenne). More
diligent, timely weed management in the early season could have minimized this problem. That
said, organic farmers identified weed control as their biggest management challenge (Stockdale
et al., 2001) and tillage is considered the most effective method of weed suppression in organic
farming (Pekrun, El Titi & Claupein, 2003) Successful weed suppression in organic,
conservation tillage systems depends upon dense spring cover crop production, and timely
transplant and quick establishment of vegetable crops (Infante & Morse, 1996; Carrera et al.,
2005). In this work, weeds declined in fall biomass sampling, as mature crop plants could better compete with weeds, and as the late summer weed community shifted from spring grasses
towards easier to manage forbs.
Declines in spring vegetation shoot biomass, C, and N production could be due to
decreased cover crop seed germination in the increasingly thick no-till litter layer. However, this hypothesis is inconsistent with the increased spring biomass found in mulched treatments, which had a thicker litter layer than non-mulched treatments. Thus, it is more likely that declines spring growth were a function of depleted nutrient content in the fall at the end of the summer growing season. This is supported by the results from treatments receiving fall compost (AC5,AC6), which had less marked declines than treatments no receiving fall compost.
Fall crop biomass and yield results may be partially explained by rainfall and crop
susceptibility to soil-borne pathogens. In 2005, okra yields in mulched treatments were higher
than in non-mulched treatments receiving the same quantity of compost. This is probably due to
the water conserving effect of the mulch and that okra is susceptible to few soil borne pathogens.
Yield results in 2007, a drought year, showed similar trends. However, in 2006, yields in the
mulched treatments were lower, as the pepper plants in these treatments had a higher incidence
of Fusarium wilt. It is possible this fungal disease was exacerbated under wetter soil conditions and in the organic matter rich litter layers of the composted treatments.
As discussed above, the presence of mulch influenced both the nutrient dynamics and
vegetation growth of the cropping systems. It is also likely influenced interactions between plant
and soil. In mulched treatments, increased moisture content could have increased microbial
activity, which led to greater nutrient mineralization and plant growth. Similarly, increased moisture would have improved the ability for root penetration into the soil, increasing the plants’ ability to uptake nutrients, but also increasing sloughing of root exudates as the roots move through the soil. This would create a positive feedback loop, as the soil food web feeds on root exudates, and then excretes mineralized nutrients that would available for plant uptake.
Results:
Isotope tracer study:
Roots collected 12 days after pruning showed significant enrichment (P<0.0001) of 15N and 13C (d15N= 20.17 +/- 1.47 in labeled plants vs 0.28 +/- 0.22 in unlabeled plants; d13C= -24.31 +/- 0.31 in labeled plants vs -26.13 +/- 0.14 in unlabeled plants). There was no significant effect of pruning on the isotopic ratios of roots (P>0.05). Eight months after the first pruning roots had significantly lower (P< 0.0001) levels of enrichment (d13C= -25.42 +/- 0.36 and d15N= 11.46 +/- 2.1) but still showed significant enrichment (P< 0.05) of both isotopes relative to the roots of unlabeled plants sampled 12 days after pruning.
Effect of pruning on root biomass:
Root biomass was considerably reduced due to pruning (by ca. 20%) even only 12 days after the first pruning event. This effect was further enhanced with the two subsequent prunings so that biomass was about 70% lower in pruned plants six months after the last pruning (Figure 1). Plants that were pruned only once had an average root biomass 46% lower than plants that were never pruned (Figure 2).
Effect of pruning on the ratio of dead to live roots:
Nine months after the first pruning and six months after the last one the ratio of live to dead roots was lower in plants that had been pruned three times compared to those never pruned and those pruned only one time (Figure 3). This increase in the proportion of dead roots suggests greater mortality of roots associated with pruning.
Effect of pruning on soil microbial biomass and its isotopic composition:
Microbial biomass carbon was positively impacted by pruning over the first six months after the first pruning (Figure 4). Twelve days after the first pruning, the microbial biomass in soils from unpruned plants was more enriched in 13C (d13C= -26.12 +/-0.08 in unpruned plants vs d13C=-26.97 +/-0.24 in pruned plants; P=0.02). Three weeks after pruning however, this difference had disappeared (d13C= -27.82 +/-0.29 in unpruned plants vs d13C=-27.39 +/-0.13 in pruned plants; P=0.27). Over the 8 months following the first pruning, the microbial biomass in soil from pruned plants tended to be more enriched in 15N than soils from unpruned plants (Figure 5).
Effect of pruning on N availability for corn:
There was no significant difference in total nitrogen uptaken by corn plants at either sampling date (Figure 6a). There was no difference in the amount of root-derived N (15N) 12 days and 9 weeks after the first pruning, however seven months later there was a greater amount of 15N uptaken by corn plants grown in soils from A. fruticosa plants that had not been pruned (Figure 6b).
The field experiment was established to see to what extent an “ecologically ideal” cropping
system, based up proven and experimental approaches recommended for the region, can reduce
off-farm inputs, maintain and sequester nutrients, and effectively manage weed populations. No
cultivated treatments were able to maintain soil %C or %N without the of addition compost. In
alley cropping treatments with compost additions of both 10 and 20 tons/acre, %C was
maintained, and increased in non-mulched treatments. In non-alley cropped organic treatments
(OST), soil %C declined, even at the 20 tons/acre application rate. Similarly, %N did not change
in treatments receiving compost and mulch in either the OST or AC system. Percent N increased
in non-mulched AC treatments receiving compost additions, and all AC treatments maintained
greater %N than OST treatments. Thus, alley cropping can maintain and sequester soil C and N
beyond organic conservation tillage and certainly more than conventionally tilled, chemically
fertilized treatments. However, interactions between compost additions and mulch treatments
are non-additive. That is, if effects were additive, we would expect to see twice the N and C
increases in the 20 tons/acre compost additions than in the 10 tons/acre addition. While the
increases in soil %C and %N are larger in 20 tons/acre treatments than in 10 tons/acre without
mulch, differences between the two levels of compost in mulched AC treatments are not
significant. The OST shows an even more pronounced trend, with lower %C and %N in the
higher level of compost application. The declines in %N under higher compost applications may
be explained by increased shoot biomass N (kg/ha) in heavily composted treatments, as N was
mineralized and taken up by crop plants. However, lack of change in %C may be evidence of
microbial priming.
Both the OST and AC systems involved considerable organic amendments in the form of
winter cover crop residue, compost additions, and Albizia inputs, in the latter system. The
mechanisms for incorporation of nutrients from these surface applied amendments would be
through alluviation into the soil during rainfall or irrigation events and translocation of nutrients
and organic material by soil organisms. It is unknown what quantity of nutrients were volatilized
or respired from the surface amendments, and if nutrients could have been better sequestered
through incorporation. While tillage is generally considered to decrease soil %C through
increased decomposition rates, it is possible that incorporation of carbon in lignified materials,
such as Albizia residue, could have sequestered more carbon deeper into the soil profile and
appropriately timed tillage could have offered more weed control.
While the spring cover crop residue provided an effective weed barrier for 4 to 6 weeks
after cover crop kill, it was not enough to suppress weeds throughout the season. The mulched
treatments required considerably less labor to weed in summer. Labor and production economics
are considered in further detail in the economic analysis of this experiment. Briefly,
the trade-offs in labor and nutrient dynamics driving the decision of whether or not to mulch are
ultimately dependent on the resources available to the grower and the paramount land
management goal. If a farmer is labor-limited, as many small, diversified organic farmers in the
region are (Estes, Kleese & Lauffer, 2003), mulching to reduce labor may outweigh the effects of
increased decomposition under mulch on C and N sequestration.
Similar trade-offs must be weighed when interpreting the results from the mowed fallow
treatment. This treatment was included in this work, as it is a common alternative land use for
nutrient and SOM depleted agricultural lands in the Southeast. Ultimately the efficacy of mowed
fallow for soil restoration is subject to the subsequent land use. While mowed fallows may
increase soil C and keep N-cycling relatively tight, mowing favors grasses and grazing adapted
forb species, which can be aggressive weeds in agricultural systems. Thus, if the fallowed land
is intended for agriculture, particularly organic, where herbicide use is not allowed, an improved
fallow, such as alley cropping with winter cover crops may more effective at preparing a future
cropping system for cultivation.
Our results demonstrate that alley cropping with compost additions, while resource and
labor intensive, may provide farmers on degraded Southeastern US soils a cropping system that
can restore soil C and keep lands in cultivation.
An important result of this project was the discovery that Amorpha fruticosa is better suited as a hedgerow in organic agriculture than is Albizia julibrissin. The latter is a tree, and while it sprouts readily, the ratio of leaves to wood is relatively high. As a result, prunings are high in wood content, and interfere with crop growth. In contrast, Amorpha fruticosa is a shrub, and the ratio of wood to leaves in the prunings is relatively low, resulting in a more desirable mulch.
The field experiment was carried out using Albizia julibrissin. However, when the superiority of Amorpha fruticosa was realized, it was used instead of Albizia julibrissin for the isotope tracer study. It was also the species used for trials in three farms outside of the experimental farm.
Educational & Outreach Activities
Participation Summary:
Carrillo, Dulia Yolima. 2007. Linking litter quality, the soil microbial and faunal communities and soil processes. Ph.D. Dissertation, University of Georgia.
Jacobsen , Krista. 2008. Turning Red Clay Brown: The Ecological Effects and Economic Viability of a Restorative Agroecosystem in the Georgia Piedmont. Ph.D Dissertation, University of Georgia.
Carrillo, Y., C.F. Jordan. 2008. Modeling green manure additions in alley cropping systems:
linking soil community dynamics and nitrogen mineralization. Pp 267-283 in S. Jose
and A. Gordon Eds. Toward Agroforestry Design: an Ecological Approach. Springer.
Jacobsen, K , Jordan CF. Effects of a restorative agroecosystem on soil characteristics and plant production on a degraded soil in the Georgia Piedmont. Renewable Agriculture and Food
Systems. In Press.
Jordan, C.F., and J. Mann. 2007. Georgia Organics and UGA’s Agroecology Lab join forces. The Quarterly Newsletter of Georgia Organics, Summer 2007: pg 4.
Jordan, C.F. and J. Mann. 2007. Conservation of the Soil Food Web … or why organic agriculture is so difficult in the Southeast and what can be done about it. The Quarterly Newsletter of Georgia Organics, Fall 2007: pg 8.
Jordan, C.F. and J. Mann. 2008. Advancing Organic Agriculture in Georgia. The Dirt. The
Quarterly Newsletter of Georgia Organics. Winter 2007-8. p.15.
Carrillo, Y., Ball, B., Molina, M., Jordan, C. Chemical quality of litter as a driver of
detrital community assemblage in mineral soil. To be submitted to Soil Biology and Biochemistry
Carrillo, Y., Ball, B., Molina, M., Jordan, C. Mediation by soil fauna on the effect of
litter quality on nitrogen mineralization. To be submitted Soil Biology and Biochemistry
Carrillo, Y., Jordan, C., Ball, B. Modeling the effect of the interaction of soil community
structure and plant litter quality on C and N mineralization. To be submitted to Soil Biology
and Biochemistry
Jacobsen, K, Escalante, C. Economic analysis of an experimental organic agricultural system on a highly eroded soil of the Georgia Piedmont. In Prep.
Jacobsen, K. A Soil organic matter model of a diversified organic vegetable farming system on a degraded soil in the Georgia Piedmont, USA. In Prep.
Outreach
The outreach and education capacity of the Agroecology Laboratory has grown significantly over the last three years due to the direct support from this SARE grant. The outreach and education objectives have been strategically achieved in diverse and adaptive ways that have far exceeded our initial expectations and projections. To realize the fullest potential of our ambitions, and decidedly integrated education and outreach programs, we opted to employ an overarching adaptive management philosophy to guide the direction and redirection of our service programs. Utilizing an adaptive management framework, in which the research and education priorities were driven and refined by the feedback of our diverse set of collaborators allowed us to allocate our energies and resources effectively and responsibly. As well, this process proved to be highly effective in keeping our research and education personal in synch with the evolving needs and knowledge of our farmer stakeholders. One of the most important and enduring results that will emerge from the outreach and educational dimensions will be the quality of the relationships developed and the potential for those relationships to contribute substantially to the future development of ecological agricultural in the Southeast.
Building upon our Lab’s general research concentration on soil organic matter management and systems ecology we prioritized our outreach efforts on gaining a more comprehensive understanding of the practices and problems facing southeastern growers in order to tailor our research program. We accomplished this by first creating a diverse (by scale, crop, and region) practitioner advisory group that was selected based upon a survey that was issued to key actors in Georgia’s sustainable agriculture community. Upon organization, it was utilized to select a broader group that gathered at the Georgia Organic 2008 annual conference to participate in an intensive facilitated focus group aimed at achieving consensus concerning the major issues facing growers. The results and transcript of this session are included in the addendum. The rich data collected in this session and the relationships born from it have and will be valuable in to the unforeseeable future.
Over the last three years the Agroecology Laboratory’s educational programming and infrastructure has experienced significant development in its capacity to reach and serve diverse agricultural practitioners across multiple operational scales, geographies, and cropping systems. Due to the unique relationship and positioning between the Lab and our onsite commercial farming operation (FullMoon Farms) we have been able to provide a truly unique experiential learning environment for students, farmers, researchers, and professional educators.
All research presented in this final report was carried out at “Spring Valley Ecofarms”, a privately owned farm near Athens, Georga, and managed by Spring Valley Ecofarms, a 501C NGO. SARE sponsored research featured on its website, www.springvalleyecofarms.org click on “Site Projects”.
Every years, approximately 2000 (two thousand) undergraduate students from the Univ. of Georgia, Gainesville State College, and UGA Gwinnett campus visit Spring Valley Ecofarms as one of their course lab exercises.
Twelve interns went through our program from 2006-2009.
Every year, Approximately 20 University of Georgia Students take a UGA accredited intensive 3-week “Maymester” course in organic agriculture at Spring Valley Ecofarms.
Spring Valley Ecofarms Hosted training sessions in Ecological Agriculture for extensions agents, 4-H teachers, and environmental education teachers
March 19, 2009. Demonstration of alley cropping system at Glover Family Farms as part of Georgia Organics field trip.
April, 2007. Georgia Organics held a Field Day at Spring Valley Ecofarms. Research and application of perennial legumes in organic production systems was featured. Approximately 60 people in attendance.
Jordan, C.F. 2008. An Ecosystem Approach to Organic Agriculture. Invited lecture, Penn State Univ., Nov. 5, 2008. Approximately 75 attendees.
Jordan, C.F. and J. Mann. 2008. Priorities in Organic Agriculture. Poster session, Sustainable Agriculture Summit, June 12, Fort Valley State College. Attendance estimated at 200.
Mann J, Jordan C.F. Priorities for Organic Farmers in Georgia. The Agroecology Laboratory of the Odum School of Ecology held a workshop entitled “Managing the Southeastern Organic Farm: Establishing Priorities for a UGA/Georgia Organics Research and Development Program”. The forum was held as part of the Georgia Organics annual conference at Dalton, Georgia, on Feb. 29th, 2008. 40 participants. Results are included in an appendix to the printed copy.
Alley cropping using Amorpha fruticosa was incorporated into overall farm plan at:
Full Moon Farms, Athens Georgia (approximately 1 acre in alley cropping).
Root Farm, Ogelthorpe County, Georgia (approximately 1 acre in alley cropping)
Glover Family Farms, Carrollton, Georgia (approximately 2 acres in alley cropping).
Specific recommendations:
Distance between hedgerows is a compromise between soil enrichment (hedgerows planted closer together) and land use for crops (hedgerows planted farther apart). In the experimental plots, the hedgerows were planted at 5-meter intervals. Farmers that adopted the alley cropping system, planted the hedgerows at intervals of 10-15 meters.
Farmers should seedlings in hedgerows one year before the area is used for vegetable cropping, to avoid mechanical damage to seedlings by the cropping. Thus alley cropping is better for fallow areas that areas to be brought into cropping than it is for areas actively cropped.
Amorpha fruticosa can easily be pruned by running a tractor- mounted bush hog (brush cutter) over the hedgerows. To avoid competition between Amorpha fruticosa and crop plants, Amorpha fruticosa should be pruned several times during the growing season, and kept to an ideal height of about .7 meters or less.
Project Outcomes
The field experiment was established to see to what extent an “ecologically ideal” cropping
system, based up proven and experimental approaches recommended for the region, can reduce
off-farm inputs, maintain and sequester nutrients, and effectively manage weed populations. No cultivated treatments were able to maintain soil %C or %N without the of addition compost. In alley cropping treatments with compost additions of both 10 and 20 tons/acre, %C was maintained, and increased in non-mulched treatments. In non-alley cropped organic treatments (OST), soil %C declined, even at the 20 tons/acre application rate. Similarly, %N did not change in treatments receiving compost and mulch in either the OST or AC system. Percent N increased in non-mulched AC treatments receiving compost additions, and all AC treatments maintained greater %N than OST treatments. Thus, alley cropping can maintain and sequester soil C and N beyond organic conservation tillage and certainly more than conventionally tilled, chemically fertilized treatments. However, interactions between compost additions and mulch treatments are non-additive. That is, if effects were additive, we would expect to see twice the N and C increases in the 20 tons/acre compost additions than in the 10 tons/acre addition. While the increases in soil %C and %N are larger in 20 tons/acre treatments than in 10 tons/acre without mulch, differences between the two levels of compost in mulched AC treatments are not
significant. The OST shows an even more pronounced trend, with lower %C and %N in the
higher level of compost application. The declines in %N under higher compost applications may
be explained by increased shoot biomass N (kg/ha) in heavily composted treatments, as N was
mineralized and taken up by crop plants. However, lack of change in %C may be evidence of
microbial priming.
Both the OST and AC systems involved considerable organic amendments in the form of winter cover crop residue, compost additions, and Albizia inputs, in the latter system. The
mechanisms for incorporation of nutrients from these surface applied amendments would be
through alluviation into the soil during rainfall or irrigation events and translocation of nutrients and organic material by soil organisms. It is unknown what quantity of nutrients were volatilized or respired from the surface amendments, and if nutrients could have been better sequestered through incorporation. While tillage is generally considered to decrease soil %C through increased decomposition rates, it is possible that incorporation of carbon in lignified materials, such as Albizia residue, could have sequestered more carbon deeper into the soil profile and appropriately timed tillage could have offered more weed control.
While the spring cover crop residue provided an effective weed barrier for 4 to 6 weeks
after cover crop kill, it was not enough to suppress weeds throughout the season. The mulched
treatments required considerably less labor to weed in summer. Labor and production economics
are considered in further detail in the economic analysis of this experiment. Briefly,
the trade-offs in labor and nutrient dynamics driving the decision of whether or not to mulch are ultimately dependent on the resources available to the grower and the paramount land
management goal. If a farmer is labor-limited, as many small, diversified organic farmers in the
region are (Estes, Kleese & Lauffer, 2003), mulching to reduce labor may outweigh the effects of increased decomposition under mulch on C and N sequestration.
Similar trade-offs must be weighed when interpreting the results from the mowed fallow
treatment. This treatment was included in this work, as it is a common alternative land use for
nutrient and SOM depleted agricultural lands in the Southeast. Ultimately the efficacy of mowed
fallow for soil restoration is subject to the subsequent land use. While mowed fallows may
increase soil C and keep N-cycling relatively tight, mowing favors grasses and grazing adapted
forb species, which can be aggressive weeds in agricultural systems. Thus, if the fallowed land
is intended for agriculture, particularly organic, where herbicide use is not allowed, an improved fallow, such as alley cropping with winter cover crops may more effective at preparing a future cropping system for cultivation.
Our results demonstrate that alley cropping with compost additions, while resource and
labor intensive, may provide farmers on degraded Southeastern US soils a cropping system that
can restore soil C and keep lands in cultivation.
An important result of this project was the discovery that Amorpha fruticosa is better suited as a hedgerow in organic agriculture than is Albizia julibrissin. The latter is a tree, and while it sprouts readily, the ratio of leaves to wood is relatively high. As a result, prunings are high in wood content, and interfere with crop growth. In contrast, Amorpha fruticosa is a shrub, and the ratio of wood to leaves in the prunings is relatively low, resulting in a more desirable mulch.
The field experiment was carried out using Albizia julibrissin. However, when the superiority of Amorpha fruticosa was realized, it was used instead of Albizia julibrissin for the isotope tracer study. It was also the species used for trials in three farms outside of the experimental farm.
Economic Analysis
Production input costs for okra, hot peppers, and the corn/winter squash intercrop are
presented in Tables 3.1, 3.2 and 3.3, respectively. Budgeting periods for each crop begin with
sowing of winter cover crop seed in October of the fall preceding the summer crop, and ends
with the final harvest of the summer crop. While the site was not certified organic, it was
organically managed and production costs reported here are for USDA Certified Organically approved materials. Production inputs were calculated on a 1 acre scale. Estimates for AC
treatments include a 25 percent loss of production acreage to space occupied by hedgerows,
which is equivalent to 134 beds (3’ wide by 100’ long) per acre with 3’ wide hedgerows
between. Spacing for OCT and CT treatments included 194 beds (3’ wide by 100’ long) beds,
as these did not include hedgerows.
Production Input Costs
Organic crop and cover crop seed prices reflect 2007 costs from the lowest price of 5
common organic farming supply sources and did not include shipping and delivery charges.
Estimates from the Georgia Vegetable Budgets (Economics, 2008b) were used for conventional
corn and okra seed costs. Conventional winter squash and pepper seeds costs were the lowest
price from three common farm supply sources for the region, as no data were found for the
region with these figures.
Compost costs were calculated from the only organically-approved compost provider in
the state, and do not include delivery costs, as these vary by distance from the supplier. Straw
mulch costs are the price paid local to the experimental site for an approximately 1 short ton
round bale, delivery included. Costs for conventional fertilizers were based on estimates from
the Georgia Vegetable Budgets (Economics, 2008b).
Irrigation costs for each crop include annual purchase of drip tape, and a life span of
mainline and connectors of 3 years. Connector and mainline costs were distributed evenly over 3
years. Irrigation system costs for pumps and buried infrastructure are included in the Whole
Farm Costs (Table 3.5).
The straw mulch estimates are based on application rates calculated from a 1 m2 sample
taken from experimental plots that had mulch applied to a depth of approximately one inch.
Extrapolating application rates from this sample size yielded application rates of approximately 1
short ton round bale per acre, which is an underestimate of mulch used over the entire
experimental area, and is likely a function of variation in the depth of mulch applied and does not
account for mulch lost in the spreading process. Thus, mulch costs reported here are probably
less than actual costs.
Tractor variable costs include fuel and lubrication, based on an average diesel price of
$3.00 per US gallon and a fuel consumption rate of 1 US gallon per hour for the 40 hp tractor.
Irrigation pump costs were based on an average gasoline price of $3.00 per US gallon and pump
gasoline consumption rate of 0.5 US gallons per hour (Jordan, personal communication).
Lubrication costs were calculated as a standard 15 percent of fuel costs (Born & Baier, 2005).
Conventional herbicides and pesticides were not used in this work, as the experimental
farm is primarily an organically-managed, diversified operation with a large community outreach
component. It was decided that the use of agrochemicals for experimental purposes needed to be
minimal and limited to nutrient application only. Therefore the production input budgets do not
include the use of these chemicals, considered standard in conventional farming operations, and
are underestimates of actual agrochemical costs. Under realistic production scenarios, the CT
enterprise budget would include costs for herbicide, and labor and equipment costs for
application.
Labor
Labor estimates were calculated from recorded labor for each experimental plot (25-45
m2) throughout the season, and the mean total labor value for each treatment converted to hours
per acre estimates. Due to the experimental nature of this work, consistency from plot to plot
was needed for all management practices. Practices such as compost and fertilizer application,
hedgerow pruning application, seeding and weeding were all conducted by hand, and probably
overestimate labor requirements for these practices on a production-oriented farm. All
harvesting was done by hand, with harvest labor calculated by the same method as non-harvest
labor, described above.
An hourly wage was not applied to all labor costs, because the labor supply on organic
farms in the region is highly variable, consisting of family, paid farm workers, interns and
volunteer labor under a heterogeneous blend of compensation schemes (Estes, Kleese &
Lauffer, 2003). Instead, it was decided to only apply a dollar value to hired labor when it would
be required for each treatment. In their 2004 National Organic Farmers Survey, the Organic
Farming Research Foundation estimated that 67% of organic farmers worked on the farm fulltime, with an average of 2 full-time, year-round household employees. Additional costs for
hourly hired labor wages were included in the enterprise budgets when labor for any 7 day period
exceeded 80 hours (40 hours per week per household employee). No wage labor was found for
workers on organic farms in Georgia, but wage data from surveys of organic farms in Wisconsin
and California estimated wages ranging from $3.32 - $14.90 per hour and $9.00 - $11.25 per
hour, respectively. Based on these ranges, a wage of $10.00 per hour was applied to hired labor.
Labor and production costs do not include marketing costs or associated labor.
For production practices requiring tractor work, 15 minutes per task (the average from
this study) was added to each task to allot for time spent changing equipment, refueling, etc., and
spread evenly across all treatment that task was performed upon.
Whole Farm Equipment Costs
Equipment costs for items used throughout the farm are reported in Table 3.4. These
include tractor and irrigation infrastructure, which have a straight line depreciation and 10%
salvage value. Fuel and lubrication required for production of specific crops is accounted for in
the production input costs for each crop. A number of operations were performed by hand, as
previously discussed. Whole farm costs accounted for here include only equipment used in the
production methods outlined, and not common equipment costs that are part of standard
operations in the region, such as seeders, manure spreaders, and storage buildings.
Yields and Returns
As was previously discussed, budgetary information for organic, conservation tillage
systems is sparse. Some yield and production cost information exists for either organic
production or conservation tillage, but rarely the two. A few notable exceptions were found that
used living mulches interplanted with vegetables in organically-managed treatments (Infante &
Morse, 1996; Biazzo & Masiunas, 2000; Carrera et al., 2005). While yields from the field
experiment were not statistically different between treatments in each year (Chapter 2),
differences in returns between treatments, discussed further below, may be significant to the
farmer.
Okra yields averaged 3395 lbs/acre, categorized as “worst production category” yield
estimates for conventional okra production by University of Georgia Extension Agriculture
Economics Department budget estimates (Flanders & Flanders, 2001). However, yields were
comparable to organically-managed, conservation tillage experimental yields the Midwest
(Biazzo & Masiunas, 2000). Hot pepper yields averaged 4187 lbs/acre, and were comparable to
yields in some of Biazzo and Masiunas (2000) treatments in the same study. It should be noted
the yields from the conservation tillage, living mulch treatments in Biazzo and Masiunas (2000)
work were 1/5th to ½ of the yields of their conventional treatments. In our work, conventional
treatments generally had lower yields than the organic treatments. Experimental corn yields
averaged 13 bushels per acre, and were a fraction of estimates for strip tilled conventional yields
(UGA Department of Agricultural Economics 2008a). According to the UGA Agricultural
Economics Department yield estimates, yields for strip tilled conventional corn average 185/bu
acre for a corn monoculture in South Georgia. This would equate to yields of 92.5 bushels per
acre when reducing the production space by ½ to account for the area in which winter squash
was grown. The low yields of corn can be attributed to low germination in all treatments, due in
part to the severe drought in 2007, as well use of an heirloom corn variety that was not
particularly drought tolerant. Table 3.5 presents a modification of yield data for the corn crop,
based on complete germination, using the kernel weights from the existing yields to modify the
bushels per acre estimates. No studies including winter squash or hot pepper yields for either
conservation tillage or organic production were found for the southeast.
All yield data in this study must be interpreted in light of the degraded soils in which
experiment took place. Frequently, yield estimates in enterprise budgets are from agricultural
experiment stations where the soil is often the best in the region, which may be misleading to
farmers seeking to duplicate these results. The soils in this study were chosen because they were
the worst soils on the experimental farm to test these techniques, and are characteristic, if not
worse, than sandy, clay loams in the region.
Organic crop prices for okra, hot peppers and winter squash were determined from an
average of prices from 3 organic farmers in the region and the average market price at a certified
organic market in Atlanta, GA, the nearest major metropolitan market. The organic corn price
was an average value for #2 yellow corn from 9 nationwide markets reported on the New Farm
Organic Price Index (New Farm, 2008) for the 2007 crop. Conventional prices for okra and corn
were prices reported in the University of Georgia Vegetable Budgets (UGA Extension and
Applied Agricultural Economics 2008b). No prices for conventional winter squash or hot
peppers were found for the state. Instead, winter squash and cayenne pepper prices from the
Louisiana State University Research and Extension Ag Center were used (LSU AgCenter 2006).
It is worth noting that while okra and hot peppers had the highest net returns, harvest labor
requirements were 10 to 15 fold higher with these crops than the corn/winter squash intercrop
when averaged across all treatments. While these crops may have lower net returns per acre, the
decreased labor requirements may allow for planting of larger acreages. The highest returns
were for labor intensive crops, with the greatest differences between organic and conventional
treatments in crops that commanded a significant price premium over conventional produce.
Previous alley cropping research in the region has suggested that due to higher labor and
land requirements, alley cropping systems may be best suited for high value horticultural and/or
organic crops (Rhoades, Nissen & Kettler, 1998). However, the labor associated with hedgerow
management was not as great as was expected, and was spread throughout the season, averaging
12 hours per pruning event per acre. This time includes application of residues, and is probably
overestimates of actual labor requirement due to experimental design necessity.
Discussion
Organic farming frequently takes a long-term systems approach to nutrient and pest
management, by incorporating the use of winter cover crops, fallow periods and organic
amendments to increase soil organic matter and thus the long-term productive capacity of the soil
(Altieri, 1995). The term “building soil” refers to shifting the soils capacity from a lowproductivity soil to a high one through conscientious management (Magdoff & van Es, 2000). In the Southeast, building soil is often referred to in the context of restoration of soil organic matter on the highly degraded, weathered soils characteristic of the region. Reducing tillage and the use of composts, cover crops and mulches is considered beneficial for increasing soil organic matter content and controlling erosion. Mulches are frequently used to provide a vegetative cover to smother weeds and thus reduce weeding labor. In 2005 and 2006, mulched AC treatments required 23% less labor than non-mulched treatments, due to effective weed suppression. In 2007, mulch only reduced labor requirements by 4%, due to a lack of weed pressure in the extreme drought. All OST treatments were mulched, so there is no way to compare labor in mulched versus non-mulched labor requirements. However, analysis of soil carbon levels after 3years of study in the AC system and 2 years in the OST system indicates that there may be tradeoffs in balancing short term reductions in labor and weed pressure and long-term carbon sequestration and soil restoration.
Applications of mulch in the AC and OST treatments resulted in significantly lower soil
carbon levels than non-mulched treatments receiving the same level of compost. Carbon
comprises about 58 percent of soil organic matter, and is often a more accurate measure of soil
organic matter than direct assays, especially in clay soils (Nelson & Sommers, 1996). In the hot,
subtropical climate of the Southeastern US, evapotranspiration rates in the summer are high and
soils dry down rapidly, decreasing biological function. Increased soil moisture under mulch
could have lead to increased soil food web activity and root growth, and thus higher
decomposition rates of organic amendments and soil organic matter.
Evidence of effects of moisture conservation was also apparent in yields. While yields
were not significantly different between treatments, in 2005 (okra) and 2007 (corn/winter
squash), there was a trend towards higher yields in mulched treatments versus non-mulched
treatments. In 2006, non-mulched treatments had higher yields, due to an outbreak of Fusarium
wilt in mulched peppers, which proliferated more readily in the moist soil under the mulch. This
indicates that mulch in addition to the roller crimper killed cover crop residue may be best suited
for dry years and for plants that are not susceptible to soil borne pathogens.
The goal of this work was to document the costs and labor requirements for an
experimental agroecosystem, and compare the ecological effects and economic costs of
production practices designed to restore degraded soils. Organic conservation tillage treatments
had less tractor costs and labor than conventional treatments because the conventional treatments
required multiple types of tillage using different of pieces of equipment, which increased labor
and fuel costs . The organic treatments had little pest and pathogen pressure, with the exception
of Fusarium wilt in some treatments. The winter cover crop residue layer suppressed weeds for
up to 4-6 weeks, but was not enough to effectively suppress weeds throughout the season and
thus required additional weeding labor. Mulches to suppress weeds reduced labor requirements
by an average of 23% during non-drought years, but moisture conservation under the mulch lead
to higher decomposition rates and reduced already depleted soil carbon levels. Thus, this short
term reduction in labor could compromise long term soil restoration in organic, conservation
tillage systems with high decomposition rates.
Farmer Adoption
Alley cropping using Amorpha fruticosa was incorporated into overall farm plan at:
Full Moon Farms, Athens Georgia (approximately 1 acre in alley cropping).
Root Farm, Ogelthorpe County, Georgia (approximately 1 acre in alley cropping)
Glover Family Farms, Carrollton, Georgia (approximately 2 acres in alley cropping).
Specific recommendations:
Distance between hedgerows is a compromise between soil enrichment (hedgerows planted closer together) and land use for crops (hedgerows planted farther apart). In the experimental plots, the hedgerows were planted at 5-meter intervals. Farmers that adopted the alley cropping system, planted the hedgerows at intervals of 10-15 meters.
Farmers should seedlings in hedgerows one year before the area is used for vegetable cropping, to avoid mechanical damage to seedlings by the cropping. Thus alley cropping is better for fallow areas that areas to be brought into cropping than it is for areas actively cropped.
Amorpha fruticosa can easily be pruned by running a tractor- mounted bush hog (brush cutter) over the hedgerows. To avoid competition between Amorpha fruticosa and crop plants, Amorpha fruticosa should be pruned several times during the growing season, and kept to an ideal height of about .7 meters or less.
Areas needing additional study
Hedgerows may provide habitat for beneficial insects. A preliminary study showed that there more beneficial insects in field with hedgerows than in field without.
An important parameter regarding competition between hedgerows and crops is the depth and lateral extent of the roots of the hedgerow species. The stable isotope techniques described in this report could be used to determine depth and lateral extent of roots of Amorpha fruticosa in alley cropping system.