The evaluation of three ground floor management systems for organic apple orchards suggests that the Swiss Sandwich System (SSS) is the most promising for Michigan and other states with similar climate. Mulching (alfalfa hay) increases significantly the amount of available nitrogen and organic matter in the soil compared with the other two systems. Flaming and SSS release the same. Mulching actually releases too much nitrogen risking leaching problems.
Root dynamics were affected from the treatments under evaluation behaving differently depending on time of the year, position related to the tree, and depth in the soil profile.
The systems affect the soil food web with mulching and SSS creating a comparable environment while flame has the lowest population numbers.
Organic agriculture focuses on soil management systems and a common phrase used to characterize organic growing is, “Feed the soil, not the plant”. Organic matter plays a central role in the building of a healthy and productive soil (Magdoff and van Es, 2000). In organic fruit production, in contrast to conventional production that relies on regular fertilization, one of the main goals is to build organic matter in the soil (Bloksma, 2000). Organic matter is also an indicator of carbon sequestered in the soil (Stevenson, 1994).
A goal in organic agriculture is the development and implementation of an integrated approach to agriculture that considers potential impacts on the environment and the soil (FAOa).
Consideration of biological, chemical and physical implications of land use and management practices and of ecological principles will allow agricultural productivity to be sustained in low and high input agricultural systems. Effective soil biological management will provide opportunities for enhancing productivity and for the restoration of degraded soils (FAOb). Orchard floor management systems are the main tool to implement these concepts.
Unlike herbaceous crops, limitations exist in woody perennial crops that restrict the incorporation of soil amendments. Also, in organic fruit production there is the need for a more sustainable approach to weed management compatible with organic protocols that provides careful utilization instead of suppression (Sooby, 1999).
Orchard floor management systems (OFMS) affect soil conditions and consequently nutrient availability, tree growth and yield (Yao et al, 2005). Organic growers have to rely on the soil food web to obtain the nutrient availability for the plants since the N release from different sources varies with the quantity and quality of the material used and the soil environment (Myers et al., 1997; Wardle and Lavelle, 1997; Magdoff and van Es, 2000; Brady and Weil, 2002). Orchard floor management systems will change the microbial composition of the soil (Yao et al, 2005).
There have been several studies on the effects of soil management systems on soil microbes and the structure of the soil food web (Mader et al., 2002; Ferris et al., 2004; Yao et al., 2005). Most of these studies were on herbaceous crops (Ferris et al., 1996; Robertson et al., 1997) and very few on apples (Forge et al., 2003; Yao et al, 2005).
Rhizosphere microorganisms may affect the hormonal balance and competitive ability of the plant, which will modify the soil biology community and the soil ecosystem (El-Shatnawi and Makhadmeh, 2001). Factors that are more likely to enhance stability of the soil microbial biomass are more likely to enhance nutrient conservation in the soil (Wardle and Nicholson, 1996).
Alleviating stress on the microbial community has stabilizing effects (Wardle, 1998). Factors which stabilize the microbial biomass reduce turnover, and are likely to have important consequences for soil nutrient dynamics and ultimately plant growth and ecosystem productivity (Wardle, 1998).
The microorganism activity in the organic system influences the release of available nitrogen to the trees in the soil (Forge et al., 2003).
Orchard floor management systems can provide organic forms of C and N which are quickly metabolized to inorganic nitrogen and other nutrients, primarily by bacteria and fungi (Ferris et al., 1998). Nitrogen is also mineralized as predators of bacteria and fungi, such as protozoa and microbivorous (“microorganism eating”) nematodes, graze on prey which contain more N than required by the predators (Ferris et al., 1998). Although more research attention is given to the plant parasitic nematodes, microbivorous organisms make up a large portion of the nematode community. Excess N generated by grazing is released to the soil and becomes available for plant uptake (Ferris et al., 1998). Nematodes feeding types play an overall positive contribution to soil and thus ecosystem processes (Yeates, 1987; Bongers and Ferris, 1999; Bardgett et al., 1999).
Nematodes can be used as indicators of soil functional and biodiversity aspects (Yeates, 2003) since they reflect the soil and ecological processes (Yeates, 1999). Most of the studies on the benefits of nematodes on nutrient release and availability in the soil have been done on the bacterial and fungal feeder nematodes. Bacterial feeders are responsible for a greater release of N when soil conditions are closer to optimal (Ferris et al., 1996; Ferris et al, 1997; Laakso et al., 2000; Forge et al., 2003) while fungal feeders have a higher effect when soil conditions are not optimal (Ingham et al., 1985; Ferris et al., 1998; Ferris and Chen, 1999; Ferris et al., 2004). A food web becomes more beneficial with increased structure and diversification (Power, 1992; Paine, 1996; Sugihara et al., 1997; Garlaschelli, 2004).
The interaction between the OFMS and the soil food web has an impact on edaphic conditions and nutrient availability. The degree to which kinetics of nutrient uptake or other potential adjustments are expressed would ultimately depend on soil nutrient availability and soil factors that determine nutrient transport to the root surface (Bassirirad, 2000). The retention of nutrients within an ecosystem depends on temporal and spatial synchrony between nutrient availability and nutrient uptake (Tierney et al., 2001).
Orchard floor management systems that support the most diversified food web will be able to reach a balance in time with an increased probability of a self sustainable environment, thus increasing the long term productivity of the plants.
Organic horticulture is becoming one of the fastest growing sectors in the agriculture economy (Dimitri, 2002). There is a worldwide growing interest in the development of sustainable production systems for food production (Yussefi, 2004).
Organic agriculture limits the inputs used to those considered environmentally and economically sustainable when compared with conventional methods. It becomes then, a challenge to overcome issues such as pest, weed control, and fertilization.
There is the need to identify management systems that are productive under these constraints.
In tree fruit production, Orchard Floor Management Systems (OFMS) are developed to create the best environment for tree growth allowing the maximization of its performance (Weibel, 2002). A successful OFMS needs to increase soil fertility, physical and biological properties, to supply nutrients to the trees, while suppressing the competitive effects of weeds without the use of traditional herbicides, and minimizing insect and disease pressure.
Orchard floor management practices have been developed and adopted by commercial fruit growers to satisfy practical needs. Mulching (with organic or inorganic material) keeps the soil free from vegetation competition, conserves soil moisture, keeps temperature constant, increases organic matter through its decomposition (in the case of organic mulches), releases nutrients to the soil, and improves the soil environment enhancing the microbial activity (Merwin and Stiles, 1994; Merwin et al., 1995; Marsh et al., 1996; Lloyd et al, 2000).
Tillage also keeps the soil free from vegetation competition but can impede internal water drainage, cause surface organic matter losses (Merwin and Stiles, 1994) and disrupt surface roots (Cockroft and Wallbrink, 1996).
Additionally, tillage can cause surface water run-off and soil erosion. It is still widely used globally even if it is expensive, uses precious petrol fuel and requires specialized machinery.
Recently a modified tilling system has been implemented in Switzerland, called the Swiss Sandwich System. It consists of a strip where spontaneous vegetation is allowed to grow on the tree row and two shallow tilled strips at each side of the tree row. This system encourages predator insects to complete their cycle in the volunteer vegetation that grow on the tree row, becoming more efficient in limiting pests and diseases, and increasing biodiversity (Luna and Jepson, 1998; Horton, 1999; Schmid and Weibel, 2000; Galoach, 2002). The resulting vegetation in the tree row can be considered as cover crops, contributing to the system their significant benefits to organic production systems aiding in the prevention of soil erosion, increased soil organic matter, facilitation in the recycling of soil nutrients, and reduction in the amount of nitrate runoff and leaching from the soil (Miles and Chen, 2001). The Swiss system is easy to manage since there is no need to reach under the tree canopy to mow weeds or till (Schmid and Weibel, 2000; Weibel, 2002; Weibel and Haseli, 2003). The two strips of shallow tilled bare soil have the effect of reducing vegetation competition for water and nutrients (Merwin and Ray, 1997).
Flaming is another effective practice in use by organic growers (Gourd, 2002; Robertson, 2003), with relative little known regarding the effects of this system, besides vegetation suppression. It has, however, drawbacks associated with its practice, such as fires, damage to the trees (Zoppolo, 2004) and the need of special equipment.
All of these systems achieve the goal to keep a certain amount of soil surface free from competitive vegetation which can have a negative impact on tree growth (Parker, 1990; Welker and Glenn, 1991; Merwin and Ray, 1997). Without the use of herbicides, vegetation management requires more thought and management skills by growers in organic production (Webster, 2000).
It is clear, that all of these OFMS have a different approach and will have different results, since they are difficult to standardize or compare, even if they somewhat achieve the same results. It will then be left to the trees to overcome eventual stressful situations created in the soil from the OFMS.
Another form of management that growers can use to overcome this problem is the selection of appropriate rootstock, irrigation and nutrient management. There is a wide variety of specifically selected apple rootstocks that have been developed and released over many years. Each rootstock differs in its ability to adapt to soil conditions (Ferree and Carlson, 1987), disease resistance, and influenced vigor and production characteristics of the scion. There are extensive research programs that center on rootstock evaluation for the above mentioned characteristics. The evaluation is performed with conventional practices and under optimal growing conditions unless different conditions are strictly required. This factor alone reduces the utility of the rootstock outside of those conditions, thus inducing the growers to adapt their orchard conditions to the optimal one in which the rootstocks were tested. Environmental factors seem to be more influential on the uptake of nitrogen and phosphorus than the rootstock genotype (Kennedy et al., 1980) but not enough is known on the subject. There is a strong relationship between genetic (vigor) and environmental factors in determining the adaptability of the root system and consequently its capability of nutrient uptake and tree performance under adverse conditions.
Since organic OFMS do create environmental conditions that are different from the conventional practices in which rootstocks are evaluated, perhaps rootstock selection can compensate and overcome these differences.
It will then be of great value to obtain information on rootstock performance as a response to OFMS. In this study we evaluated three rootstocks of different vigor managed with three different organic OFMS (mulching, flaming and the new Swiss sandwich system).
One of the major challenges in organic fruit production is the implementation of successful orchard floor management systems (OFMS). The lack of herbicides in organic horticulture requires OFMS that limit or restrict ground cover competition so tree performance does not suffer.
Whichever the OFMS selected, organic growers rely primarily on soil microbial processes to obtain the nutrients for plants; thus, OFMS are extremely important because they have an effect on soil conditions and consequently on nutrient availability, tree growth and yield (Yao et al, 2005). Orchard floor management systems will change the microbial composition and food web of the soil (Yao et al, 2005). The absorption of nutrients within an ecosystem depends on temporal and spatial synchrony between nutrient availability and nutrient uptake (Bassirirad, 2000; Tierney et al., 2001).
Plant roots can alter their water and nutrient acquisition capacity by adjusting their physiological longevity, morphological and/or architectural characteristic to meet changes in shoot nutrient demand (Chapin, 1980; Clarkson and Hanson 1980; Clarkson 1985). Therefore, it is useful to evaluate root characteristics that play a role such as lifespan and turnover, as indicators of growth potential of the plant and its actual nutrient acquisition (Bakker, 1999).
Roots, and fine roots in particular, play a central role (Schulze et al., 1997) in soil chemicals (pH, O2, CO2 and other ions), physical (moisture and aeration), and biological (soil pathogens, beneficial microorganisms and allelopathy) composition (El-Shatnawi and Makhadmeh, 2001) with important consequences for plant growth and productivity, plant competition, biological activity, and carbon and nutrient cycling at an ecosystem scale by releasing in the soil a wide variety of exudates (Makhadmeh and El-Shatnawi, 2001; Bertin et al., 2003; Walker et al., 2003). Plants expend a substantial proportion of photosynthate below ground in the annual production of fine roots (Eissenstat et al., 2000) and release of exudates (Walker et al., 2003). In many cases, more than 50% of annual net primary production (NPP) is allocated below ground, and nutrient return to the soil by tree fine root death may exceed that by the above ground litterfall (Kasuya N., 1997). Tree root turnover may return four to five times more carbon to the soil than above ground litter (Zech and Lehrmann, 1998). Consequently there is a need to include the effects of root turnover in models of carbon and nutrient cycling (Cox et al., 1978; Vogt et al., 1986; Hendricks et al., 1993; Jackson et al., 1997; Norby and Jackson, 2000).
Moreover, through the exudation of a wide variety of compounds, roots regulate the soil microbial community in their immediate vicinity, cope with herbivores, and encourage beneficial symbioses (Nardi et al., 2000, Walker et al., 2003).
Assessing root turnover becomes then, very important as an indicator of plant productivity and a measurement of carbon return to the soil. In the last decade the most common technique to measure fine root turnover is by minirhizotrons installed in the ground. They can be used to characterize fine root production, phenology, growth, mortality and lifespan, and are useful in developing ecosystem carbon budgets (Hendrick and Pregitzer, 1996; Majdi, 1996). Their reliability depends on the accuracy of assessing physiological status of the roots (alive or dead) (Wang et al, 1995; Tingey et al, 2000) mostly based on color (Hendrick and Pregitzer 1992a, b; Comas et al, 2000).
However, the determination of fine root physiological status is a common problem (Comas et al., 2000). Also, there is a certain inconsistency in the definition of the proper diameter for fine roots. Several authors reported that fine roots, for woody perennials, should be ≤ 1 mm in diameter (McCrady and Comerford, 1998; Eissenstat et al, 2000; Comas and Eissenstat 2001).
Processes and responses vary not only with root diameter but with other root characteristics as well (Norby and Jackson, 2000). It is necessary to couple the total size of the root system with physiological information on the response of root specific nutrient uptake efficiency (Norby and Jackson, 2000). The size of the root system and its efficiency to deploy roots at the time and place nutrients are present (Fitter et al., 1991), as well as the efficiency by which a particular root segment can take up a nutrient from the soil solution (Norby and Jackson, 2000), are fundamental for the plant uptake capacity (Tjeerd et al., 2001). The degree to which kinetics of nutrient uptake or other potential adjustments are expressed would ultimately depend on soil nutrient availability (Tjeerd et al., 2001) and soil factors that determine transport to the root surface (Bassirirad, 2000). Nutrient adsorption, and eventually absorption within an ecosystem, depends on temporal and spatial synchrony between nutrient availability and nutrient uptake, and disruption of fine root development (Tierney et al., 2001).
In general, increased N concentrations in the soil decrease fine root turnover because of their increased lifespan (Pregitzer et al., 1993; Ostonen et al., 1999; Burton et al., 2000; Hendricks et al., 2000; King et al., 2002) allowing the plant to reduce carbon costs. However, several authors reported that with increased N concentration in soil, root turnover rates increase, reducing fine root lifespan (Aber et al, 1985; Nadelhoffer et al., 1985; Persson and Ahlström, 2002). Burton et al. (2000), in an experiment on fine roots (<1 mm) dynamics within and across forest species with different N availability, found that, across species root lifespan decreases with increased N availability, while within species there is the opposite trend. Tjeerd et al. (2001) found that in P depleted soils citrus fine roots life span was diminished.
In any case, all the authors agree on the importance of the interaction between N availability and fine root dynamics, especially for the effects on organic matter (McClaugherty et al, 1982), on the organic N pool in the soil (Ehrenfeld et al., 1997), and on the control of the substrate quality (Hendricks et al., 2000).
Root turnover has been extensively studied in grasslands and forests ecosystems but there is not much literature on fruit trees and none in organic tree production.
The established interaction between OFMS, food web, and root processes could create a different response from the roots that needs to be studied and compared between conventional and sustainable conditions.
In this experiment we evaluated three different OFMS for their rationale and input of organic material to the soil. One has a constant addition of N containing organic material (alfalfa hay mulch added twice yearly), another has the constant destruction of organic material on the soil surface (flaming), and the last one is a combination between modified cover crop (natural vegetation never mowed) and tillage.
We hypothesize that these differences in management will have an impact on the soil N concentration and organic matter content and therefore will impact the soil food web structure and diversity, tree productivity, rootstock adaptation, and fine root dynamics.
Investigate the behavior of apple trees fine roots (timing and rate of growth, and their turnover) subjected to two different ground managements under the organic protocol.
Amount of carbon sequestered in the soil by the trees.
Effects of fine root turnover on nutrient cycling, food-web and soil sustainability.
Introduction of the best ground floor management system for the desired growing conditions.
The experiment was conducted in an orchard of cultivar “Pacific Gala” (Malus x domestica Borkh.) apple established in April 2000 at the Clarksville Horticultural Experiment Station. The orchard was certified organic by the Organic Crop Improvement Association (OCIA) in 2003 and 2004 and Organic Grower of Michigan (OGM) in 2005.
The predominant soil type of the orchard is Kalamazoo sandy clay loam (Typic Hapludalfs) with 53.1% sand, 23.1% silt, and 23.8% clay. The orchard presents mild slopes (less than 3%).
Drip irrigation with drippers of 2.3 L/h every 0.6 m was installed in May 2001 and suspended from the lowest wire of the trellis on the tree row. All orchard floor management systems received equal irrigation throughout the season. Soil moisture was measured by time domain reflectometry (TDR) using a Mini Trase 6050X3 (Soilmoisture Equipment Corp., Goleta, CA) with 45 cm long stainless steel rods permanently installed in the tree rows in 2001, halfway between two trees and in the middle of the tilled strip in 2002. Measurements were taken for each of the 6 plots per treatment weekly in 2002 and every other week in 2003-2005.
Orchard floor management
The site was previously farmed with conventional soybean-corn-corn-alfalfa rotation for two cycles until 1998. Subsequent soil preparation consisted of sowing of buckwheat and chicken compost (1250 kg/ha) and lime (2250 kg/ha) application in 1999 on the entire surface. At plantation (April 2000) a mixture of red mammoth clover and endophytic rye was sown in the alleys.
The three orchard floor management systems (OFMS) under study were established in the beginning of the second growing season (2001) and maintained for the entire study. The treatments consisted of mulch (MU) of alfalfa hay, the Sandwich System (SS) and Flaming (FL) with a propane burner. The alfalfa hay mulch was laid underneath the tree canopy in a strip of 1 m on each side of the tree and kept 15-20 cm thick. 105 round alfalfa bales/ha were used with a C:N ratio of 15:1. The treatment was hand-applied every spring and fall to keep the thickness of the mulch constant in order to provide a shading effect for weed suppression, and to maintain soil moisture.
The flaming treatment consists of the burning of weeds underneath the tree canopy and 1 m on each side of the tree with propane gas (estimated 56 L/ha). A custom engineered burner, consisting of 4 burners (200000 BTU/burner) in a row, and covered with a metal protective shield to concentrate the heat and to prevent its escaping and damaging the canopy. On the back of the shield was also mounted a sprinkler system to extinguish eventual fires occurring during the burning. To reach the weeds underneath the canopy on the tree row, a hand burner (150000 BTU) was used. The burner was mounted on the side of a tractor on a hydraulic arm to better control the application of the treatment. The treatment was applied five to six times during the year, starting at the end of April – beginning of May and ending at the end of August. The treatment was repeated every time the weeds would reach 10 cm high. Tractor speed was kept between 1.6 and 3.2 km/h depending on the density of the weeds to be controlled.
The Sandwich System is an adaptation of the Swiss system (Weibel, 2002) and consists of an area 25-30 cm on each side of the tree, underneath the canopy, where spontaneous vegetation is allowed to grow undisturbed (SVA). On each side of this vegetated area, two strips of soil were kept free of vegetation (STS) by shallow tilling (5-10 cm deep). The strips were 70 cm wide from tree planting till 2003 and expanded to 90 cm wide in 2004. Timing of the treatment application was the same as the flaming treatment. The tilling was accomplished from 2001 through 2004 with a spring-tooth (three teeth 2001-2003, 5 teeth 2004) harrow mounted on a side-bar of a tractor. To improve tillage effectiveness, a modified notch-disk tiller, mounted on the tractor side-bar, was deployed during the 2005 growing season (Picture 1; 2).
The alley consisted of an equal mixture of endophytic rye and mammoth clover established soon after planting the orchard in 2000. Clover was also reseeded in 2005 to keep the proportion constant. The alleys were managed equally in all treatments by periodical mowing (3-4 times year).
Soil sampling and measurements
Soil samples, from which the effect of OFMS on soil conditions and microbial communities were measured, were collected for the three OFMS by mixing 20 soil core sub-samples from the tree row. Soil samples from the alleys and the tilled strip of the SS were obtained by mixing 10 soil core sub-samples from each side of the tree row. Soil samples were collected four times per year (from April till November) at 0-10 and 0-30 cm depth starting from April 2001 till November 2005 to measure the temporal effect on the soil conditions. The two depths have been chosen to represent the surface soil, where most of the microbial processes take place (0-10 cm), and the most frequently explored part of soil by roots (0-30 cm). The two depths also provided an indication of the effect of depth on the soil conditions. Soil samples were stored at 4ºC until the analyses were performed.
The effects of the OFMS on the soil conditions were monitored through:
• Soil nitrate (NO3-), from 2001 till 2005, and ammonium (NH4+), from 2003 till 2005, concentration (ppm) in the soil, to check the immediate available nitrogen released from the treatments available to the trees. The addition of the two forms of nitrogen gave us the total available mineral nitrogen concentration. Soil samples were air dried at 105ºC for 24 hrs. Nitrates and ammonium concentration was extracted from the soil by 100 ml of KCl 1 M on 10 g of dried soil, placed for 1 hour on a shaker and then filtered with filter paper. The extraction liquid was sent to the MSU soil lab for the analysis of NH4+ and NO3- following the procedure described by (Kenney, 1982) using a Lachat automated colorimetric analyzer (Lachat Instruments Inc. Milwaukee, WI).
• Soil organic matter content, from 2002 till 2005, was measured by loss on ignition of 3g of dry soil, from the above described soil samples, at 400 °C for 8 hours in a muffle furnace.
• Soil carbon content was calculated from the organic matter values and divided by 1.724. This value is based on the organic matter containing 58% carbon (Stevenson 1994). Values obtained from the organic matter were corrected for the relative surface covered from each segment of the treatments (alley, tree row, and in case of the sandwich, vegetated area and tilled strip) and reported as the treatments were covering the entire surface of an orchard. Corrected values were then related to the volume of soil, respectively at 0-10 and 0-30 cm depth, contained in a hectare and showed as t/ha. Data were reported for the year 2005 and as average of the period 2002-2005 for both sampling depths (0-10 and 0-30 cm).
The effects of OFMS on microbial communities were measured two times during the growing season (April and November) starting from November 2003 until April 2005. Nematode populations’ composition were utilized as indicators of soil functional and biodiversity aspects (Yeates, 2003) since they reflect the soil and ecological processes (Yeates, 1999). To better understand these effects, apple and grass roots were examined for mycorrhizal infection (November 2004) and root lesion nematodes inside the roots (August 2005). Mycorrhizae spores in the soil were correlated with mycorrhizal root infection to determine eventual relationship between the two.
After collection, soil samples were transported to the soil nematode analysis facility of Dr George Bird at Michigan State University in East Lansing, MI. The extraction of nematodes and mycorrhizal spores from the soil was performed by the centrifugal-flotation (Jenkens, 1964). Nematodes were then sequentially sieved into a counting plate, and identified at 50•x magnification to families, genera and trophic group levels. Nematode communities’ composition was calculated as percentage of each group feeding behavior on the total number of nematodes in the soil (Bird personal communication, 2006).
Apple roots from the four treatment positions (mulch row, flame row, sandwich vegetated area, and sandwich tilled strip), as well as a composite sample of weed roots from the vegetated area in the sandwich tree row, were collected in November 2004 were sent to the Dr. Amarantus lab (Grant Pass, Or) to determine the percent of endomycorrhizal infection. The percent of endomycorrhizal colonization was determined using a grid intercept method. This method includes examination for the development of spores, vesicles, arbuscules and fungal hyphae along the sample roots. Sampled roots are placed in capsules in a 10% KOH solution in a water bath at low heat for 24 hours. The KOH is poured off and capsules rinsed in three complete changes of tap water. Capsules are placed in a 1% HCL mixture for 30 minutes then immediately transferred into a water bath of Tri Pan blue for 3 hours and repeatedly rinsed. Roots from each capsule are rinsed and chopped in segments. Segments from each capsule are examined and tallied for percent colonization and presence of arbuscular spores of mycorrhizal fungi using a dissecting microscope. Roots are examined on a graduated Petri dish and each root intersection tallied as mycorrhizal or non mycorrhizal at 100 grid line crossings. Apple roots from the four treatment positions (mulch row, flame row, sandwich row, and sandwich tilled strip) were collected in August 2005 to determine the number of root lesion nematodes in the roots. Root lesion nematodes were extracted with the shake method (Bird 1971) from 1 g of roots and then counted with a counting plate at 50•x magnification.
Plant material and measurements above ground
The orchard consists of 468 trees grafted on three rootstocks depending on their vigor.
The rootstocks under evaluation are the dwarfing M9. NAKB 337 (40% of the size of a seedling. Marini et al., 2000), the semi-dwarfing M9. RN 29 (Perry, 2000a), and Supporter 4 (semi-vigorous) (Perry, 2000b).
Spacing between the trees is dependant of the rootstock vigor (Perry, 2002) and are 4.6 x 1.4 m for M9. NAKB 337, 4.6 x 1.7 m for M9. RN 29, and 4.6 x 2.0 m for Supporter 4.
Trees were trained to a vertical axe system. Rubber bands and clothes pin were used to bend branches in early years (Perry, 2000c). Minimal pruning was applied to allow the tree to grow as natural as possible mainly singularizing the leader or main branches. A two wire trellis with galvanized metal poles was installed as support system.
Rootstock performances were measured by growth, production, and nutritional status parameters of the trees while OFMS effect on the soil was measured by periodically checking the soil conditions.
Growth parameters measured were:
• Trunk cross sectional area (TCA) at dormancy as well as its differential since establishment (TCAI) during the years. This methodology has been proven to be highly correlated with the tree growth (Westwood and Roberts, 1970).
• Shoot growth (extension) was measured every week on three representative shoots plus the leader during all the vegetative season to measure the growth rate. Shoots were selected to represent the bottom, middle and top part of the tree. Selected shoots were comparable in size and insertion angle at the time of selection.
• Canopy volume was calculated measuring the total height as well as two orthogonal diameters of the canopy at 0.7 m from the soil.
Production parameters measured were:
• Yield (kg/tree) and number of fruits to obtain the average fruit weight (g), as well as cumulative yield during the years. Values were also corrected to the actual number of trees to obtain productions/ha.
• “Yield efficiency” (kg/cm2), or ratio of fruit yield to trunk vigor (TCA) was calculated by dividing the yield of the year by the TCA of the previous year, as well as the cumulative yield efficiency (kg/cm2) calculated by dividing the cumulative yield by the TCAI of the current year.
Tree nutritional status parameters measured were:
• Relative chlorophyll content of a composite sample of 10 leaves per data tree collected from the middle portion of one year old branches. Relative chlorophyll content was measured using a SPAD-502 meter (Spectrum Technologies Inc, Plainfield IL) in early August.
• Mineral nitrogen concentration of the previously described composite sample of leaves. Leaves were rinsed with distilled water, air dried at 60ºC for 48 hrs, ground and sent to the MSU soil and plant nutrition lab to be analyzed for N concentration.
Measurements on trees belowground
Root development was monitored using minirhizotrons installed during summer 2002. Minirhizotrons consisted of clear butyrate plastic tubes 13 cm in diameter and 182 cm long. Four tubes for each tree in trial were installed at a 45˚ angle facing the tree at 40 cm from the tree trunk parallel to the tree row, and 122 cm deep. To evaluate the effect of the OFMS on root development the tubes were installed at the same fixed intervals from the tree trunk in each treatment (2 at 13 cm on each side the tree trunk perpendicular to the tree row, 1 at 53 cm, and the last one at 68 cm) (Fig. 1 A and 1 B). Two trees for each treatment were utilized in the experiment with four replicates for a total of 32 tubes for each treatment.
Images of roots were recorded at fixed time intervals (2-3 weeks) during the growing season with a digital camera developed by Bartz Technology Corp., CA. Thirteen images were collected for each tube and recorded every 10 cm along the length of the tube starting at 10 cm depth. Data were collected in 2003 and 2004.
Root parameters (number, length, diameter, area, volume, number of branches, and angle of branch insertion) were measured through a software program especially designed from our department. The software utilizes an algorithm (claimed in U.S. Patent Number 6,690,816 which has been assigned to the University of North Carolina at Chapel Hill. Used with permission) specifically modified for root studies. The program is copyrighted by the MSU Board of Trustees, and is currently not commercially available.
Root data from each image was segregated into four classes (0-30 cm, 30-60 cm, 60-90 cm, and below 90 cm) to evaluate development within the soil horizons. Distances from the tree trunk were kept separated to evaluate the effect of distance on root development.
Fig 1A. Minirhizotron location for apple tree root development study in the mulch treatment. Fig 1B. Minirhizotrons location for apple tree root development study in the Swiss Sandwich treatment.
We also performed a limited maintenance cost comparison of the systems deployed for the 2005 growing season utilizing our experimental plot as unit (Table 7).
Experimental design and statistical analysis
The treatments were applied in a complete randomized split plot design with OFMS as main plots as CRBD and the rootstocks as sub-plots with 6 replicates. Four trees for each rootstock were planted in each sub-plot. Only the two central trees for each rootstock were utilized as data trees for a total of 84 trees under evaluation. Each data row was alternated with buffer rows consisting of trees of same rootstocks and distances arranged in single rows.
For the soil data the experiment design was CRBD. All the soil data statistical analysis was considered separately (to determine the effect on microbial populations) as well as repeated measures (to determine the overall effect on microbial dynamics). Repeated measures were preformed using block*OMFS as the subject.
For the root experiment data were log transformed to maintain homogeneity before the analysis. The experimental design was CRBD.
In all the experiments analysis of variance was performed using the MIXED procedure to detect the different treatments under evaluation effects, as well as their interactions. Where appropriate, means were separated using the Least-square means test (LSMEANS) with p≤0.05.
Effect on soil organic matter and carbon content.
The soil organic matter content was similar between the plots prior to the establishment of the treatments. Over the duration of the experiment the treatments did have an effect on organic matter content. Within each year soil organic matter (SOM) content was always significantly higher in the alfalfa hay Mulch (MU) than in the other treatments, except in 2002 where it was similar to the Swiss Sandwich tilled strip (STS) for the depth of 0-10 cm (Figure 1A). Soil organic matter increased during the years in MU, remained constant in the Swiss Sandwich vegetated area (SVA) and decreased in Flame (FL) and in STS. For the deeper sampling (0-30 cm) there is no difference between treatments within the year, however SOM increases during the years in MU and STS while it remains constant in FL and SWA (Fig. 1B). No treatment effect occurred in the alleys at any depth during the experiment period.
Carbon sequestered in the soil was different between the treatments at 0-10 cm depth with MU showing the highest value, FL the lowest and sandwich not differing between the two both in 2005 and as average during the evaluation period (2002-2005) (Table 1). The amount of carbon sequestered in 2005 was not different from the average of the evaluation period at 0-10 cm depth (Table 1). For the deeper sampling (0-30 cm) FL presented the lowest value of carbon sequestered with no differences between the other two treatments in the year 2005. No differences were measured in the average 2002-2005 between the treatments (Table 1). However both mulch and sandwich treatments presented an increase in carbon sequestered during 2005 when compared with the average 2002-2005 (Table 1).
Effect on soil Nitrogen concentration.
Since the implementation of the treatments the NO3- – N, at both depths, concentration in the soil of the MU treatment was significantly higher than the other two treatments. Between the years, only SVA shows a decrease in NO3- concentration at both depths (Figure 2 A-B). The total mineral N follows the same pattern of NO3-, with MU showing the highest concentration between the treatments for the duration of the experiment at both depths (Figure 3 A-B). However all the treatments show a significant increase in 2005, mostly due to the high concentration of NH4+ (data not shown).
Effect on Nematode community structure.
Nematode community structure was affected by the treatments during the 18 months of the duration of the experiment (November 2003 – April 2005). MU presented the highest number of total nematodes between the treatments. Bacterivores represented the highest percentage in the community structure in all the treatments followed by the fungivores, except for the vegetated area of the Swiss Sandwich where herbivores presented the same percentage as the fungivores (Table 2). However, between the treatments some differences in the structure composition were noted. While MU presented the highest percentage of bacterivores between the treatments, FL and STS presented the highest percentage of fungivores and omnivores, and SWA presented the highest percentage of herbivores (Table 2). No differences were noted between treatments for the carnivores. Mulch presented the lowest percentage of herbivores. This result was confirmed from the number of lesion nematodes in the apple roots where MU presented the lowest with no differences between the other treatments (Figures 5).
A direct correlation was found between the amount of mycorrhizal spores in the soil and the percentage of roots colonized from arbuscular mycorrhizae with an r2 value of 0.7059 (Figure 6). However, the percentage of root colonization from arbuscular mycorrhizae was higher in SVA and FL, followed by MU and STS. The weeds present in the vegetated area of the Swiss Sandwich treatment presented the lowest percentage of infected roots (Figure 7).
Temporal effect on the nematode community structure.
Inside of each collecting date the nematode community structure followed the general structure presented in Table 2. With some exceptions, Swiss Sandwich vegetated area always presented the highest number of herbivores during the experiment period (Figure 8). Mulch had the lowest percentage of fungivores in November 2003 and April 2005 and the highest percentage of bacterivores (entire period) (Figure 8).
There was a temporal effect on the community structure inside of each treatment. In all the treatments the total number of nematodes increased in time, except for STS, where it remained constant (Table 3). All the treatments presented an increase in bacterivores during the duration of the experiment, except for STS where there is a decrease (Figure 9). However the feeding groups that compensate this increase in bacterivores vary between treatments (Figure 9). In flame the herbivores diminished, in mulch, herbivores and fungivores, and in SVA there is not a clear variation (Figure 9). In STS, at the diminishing of the bacterivores, there is an increase of fungivores (Figure 9). Omnivores and carnivores did not seem affected by temporal variation during the experiment period (Figure 9).
Soil water content.
Measurements performed with TDR (Figure 10) demonstrated that most of the time there were no differences between OFMS. When some difference was present MU had always the highest values while the SVA had the lowest. Flame and the STS did not differ from the other two.
Rootstock and Orchard Floor Management Systems Evaluation.
In 2005, for all the growth parameters considered, there was no effect of the treatments and no interaction between the treatments and rootstocks (Figure 11; Table 4). Only during training years (2001-2003) did the treatments present some effect on branch growth, trunk cross sectional area (TCA) and its increase (TCAI) with mulch (MU) showing the highest values (Zoppolo, 2004). However, since the trees entered in full production (2004) the treatment effect has ceased to be noticeable.
Among rootstocks, Supporter 4 had the highest values in most of the growth parameters considered, presenting the same trend as Figures 11, with no differences between the other two rootstocks (M.9 RN 29 and M.9 NAKB 337) except for branch growth in 2004 (data not shown) and 2005 where no differences were noticed. Branch growth in 2005 ranged between 38 cm (M.9 RN 29 in mulch) and 43 cm (M.9 NAKB 337 and Supporter 4 in sandwich).
Rootstock did not influence the nitrogen status of the leaves. Since 2003 MU presented the highest values in leaf nitrogen concentration (Table 5).
Cropping was not influenced by OFMS but differences among rootstock exist (Table 6). Rootstock did not impact cropping in mulch treatment, while M.9 RN 29 was most productive (with no differences between the other two rootstocks) in both of the other treatments (Figure 12). Yield efficiency, as the ratio of fruit yield to trunk vigor, presented the same trend as the yield values (Figure 12).
The same production parameters behaved differently when corrected for the number of trees to obtain values per hectare. There was still no influence of the treatments on any of the parameters, but there was an influence from the rootstocks and their interaction with the treatments (Table 6). All the parameters considered had the same trend as the cumulative yield (t/ha) in which there was no difference between the rootstocks in the treatments flame (Figure 13). Supporter 4 presented the lowest production in both mulch and sandwich while M.9 NAKB 337 had the highest yield/ha in mulch and M.9 RN 29 in sandwich (Figure 13).
Effect on root parameters.
In general there were no differences between the two years of observation (2003-2004) in any of the fine root parameters measured. Also, the only fine root parameters that were affected from the treatments were the fine root numbers, area, and the rate of growth.
Effect on fine root number
There were more fine roots per image in SS than MU in both years (Figure 14). Fine root number in SS declined during the growing season and approached values of MU towards the beginning of July and then no differences were measured between the treatments for the rest of the measurements (Figure 14).
Fine root number was not affected by depth in the soil profile but was affected by distance from the trunk in SS, which had a higher number of fine apple roots closer to the trunk in the vegetated area than MU (Figure 15).
When the fine root number was segregated by classes of diameter and checked for their frequency (expressed as the percentage of fine roots in each diameter class), there was significant difference among the diameter classes, with a greater proportion of apple roots being 0.4 to 0.8 mm (Figure 16). Orchard floor management systems did not affect root diameters. Roots generated near the trunk (13 cm) are larger in MU than SS (Figure 17). Sandwich presented the opposite in the middle position that is closer to the transition between the vegetated area and the tilled strip, and a much higher percentage of very fine roots (0.2-0.4 mm) farther from the trunk (corresponding to the middle of the tilled strip) (Figure 17).
Larger roots were found developing deeper in the soil profile in MU (Figure 18).
Effect on fine root area
The amount of fine root area for both treatments varied, depending on the distance from the trunk and soil depth. Closer to the surface (0-30 cm) SS presented a higher fine root area closer to the trunk (in the vegetated area) than mulch for most of the duration of the experiment, both in 2003 and 2004 (Figure 19). No differences were measured between the treatments in any other position in both years.
Below 30 cm there was a lot of variation during the experiment that nullified differences between positions inside of the treatments and between them in both years (Figure 20). Differences did not exist deeper in the soil profile (below 60 cm) (Figure 21; 22).
Effect on growth rate
The growth rate (expressed as number of roots/day -1) was different between the two treatments. In the literature, root length is normally used to establish root turnover rates and life span. According to Tracey et al. (2003), root number can be substituted for root length if there is a direct correlation between the two. The correlation found in this experiment allowed us to use root number as an indicator of fine root turnover and lifespan (Figure 23).
There was a decline in fine root number greater for SS than MU. The amount of re-growth was similar between the treatments, but SS always had a higher fine root reduction than MU (Figure 24). Additionally, the turnover rate was greater in SS than MU when expressed as fine root mortality (Figure 24) following the methodology utilized by Joslin et al. (2000). The amount of time between active growth and fine root disappearance was used as an estimation of fine root life span. Sandwich had an estimated lifespan of around 30 days compared with the 50-60 for mulch (Figure 24).
Growth rate was not affected by the depth in the soil profile or by the distance from the trunk; also, there were no interactions with the treatments.
The different classes of fine root diameter considered did not differ in growth rate.
Nematode populations structure and Soil parameters
In our study, Orchard Floor Management Systems (OFMS) did have an impact on soil organic matter (SOM), even if it is largely believed that the process should take several years unless large quantities of organic matter are added. The greatest impact occurred under the mulch treatment near the surface (0-10 cm), where it increased during the experiment. Similar results were reported by Merwin et al. (1994), Sanchez et al. (2003) and Zoppolo (2004). At the deeper sampling (0-30 cm), the SOM increased but to a lesser degree, this is probably caused from the fact that the alfalfa mulch was layered on the soil surface without disturbance. Soil organic matter was the highest for the entire duration of the experiment under the mulch treatment. When differences occurred, water content in the soil was also the highest under alfalfa mulch.
The SOM varied in the sandwich treatment depending on the position in the orchard. In the vegetated area SOM content remained constant during the experiment at both sampling depths, while in the tilled area SOM decreased at 0-10 cm depth but increased at 0-30 cm depth. This result is normal for tilled soils where the increased aeration provoked by tilling initiates loss of organic matter (Brady and Weil 2002). When differences occurred, water content in the soil was the lowest in the vegetated area due to weed competition.
In the flame treatment, SOM decreased only at the shallow depth, probably due to the constant burning of the vegetation leaving only ashes on the soil surface.
In the alleys, where vegetation was mowed regularly and left on the soil, SOM remained more or less constant during the experiment.
Organic matter in the soil is mostly responsible for the carbon sequestration in the soil (Stevenson 1994). It is interesting to notice that when we consider the treatments as if applied to the entire surface of an orchard, taking into consideration the relative surface covered from each segment of the treatments (alley, tree row, and in case of the sandwich weeded area and tilled strip), we did not find the same differences reported for the SOM in each single segment. At 0-10 cm depth, mulch is still sequestering the highest amount of carbon/ha, flame the least and sandwich is in the middle, and the values are remaining constant during the years. At 0-30 cm depth, mulch and sandwich sequestered the same, and highest, amount of carbon and it increased during the experiment, while for flame it decreased. If we consider the fact that mulch is the only treatment with continuous addition of external sources of carbon, it appears that the sandwich system is the treatment with the highest potential of sequestering more carbon in the soil.
The effect of the treatments on the SOM correlated with soil nitrogen concentration (Powlson and Jenkinson, 1990; Díaz Rossello, 1992b; Bloksma, 2000) to a certain degree. The highest soil nitrogen concentration (almost double), for both nitrates and total mineral concentration was in the mulch treatment, while ammonium was the same between treatments. Nitrate concentration fluctuated during the years under the mulch treatment ending up being more or less constant compared with the beginning of the experiment. Only the vegetated area of the sandwich had a decrease in NO3- concentration. The NH4+ concentration increased for all treatments, especially in 2005, resulting in a general increase in total mineral nitrogen concentration. This shows that the treatments reached a sort of equilibrium because even if there was not an increase in SOM (treatments flame and sandwich), there was an increase in nitrogen concentration.
Organic floor management systems change the microbial composition (Yao et al, 2005) that is responsible for the nutrient availability in the soil (Forge et al., 2003; Yao et al, 2005).
Our experiment supports previous studies (Mader et al., 2002; Ferris et al., 2004; Yao et al., 2005) affirming that OFMS has an impact on the soil biology composition that we represented by the relative abundance (% on the total) of nematode populations (Ritz and Trudgil, 1999; Ferris et al., 2001; Yeates, 2003; Zoppolo, 2004) with different feeding habits.
The total number of nematodes was highest in mulch treatment followed by the vegetated area of the Swiss Sandwich (SVA). The difference between these two and the others is probably caused by the continuous decomposition of the vegetative material on the soil (Cookson et al., 2002).
In all the treatments, the bacterivores dominated the nematode population, which was highest in mulch treatment and had no differences between the other treatments. The composition of the remaining nematode populations varied depending on the treatment. According to Ingham et al. (1985) the more stressful the environment, lacking in nutrients (N and P) and/or water, the higher will be the amount of fungal feeding nematodes. This was corroborated in our experiment, where flame and Sandwich Tilled Area (STA) showed the highest number of fungal feeding nematodes, followed by SVA and mulch.
The number of herbivore nematodes (root feeding) in the soil is very important because it could create damage to the crops (Merwin and Stiles, 1989). The percentage of this nematode feeding population in the soil was affected by the OFMS. In fact, the SVA had the highest percentage followed by flame, STA and mulch. This result was not however, confirmed from the number of root feeding nematodes inside the roots where flame, STA, and SVA presented the same number, with mulch showing the lowest. It is not clear if the difference in percentage in the soil and the number inside the roots is due to the fact that the herbivore nematodes measured in the soil are a more expanse composition of populations than those in the roots. Another factor could be that the highest values measured in SVA could be due to the higher number of weed roots present in the treatment, since we did not measure the root feeding nematodes in the weeds.
Most of the current ecological research agrees that the most beneficial food webs are those which are highly structural and diversified (Power, 1992; Pain, 1996; Sugihara et al., 1997; Garlaschelli, 2004). Based on trends, overtime, in this study we suggest an impact, and through the evolution of the populations’ diversification, on structure. Populations fluctuated according to treatments. Bacterial feeder nematodes increased in flame treatment to the detriment of herbivores. In contrast there was a decrease in herbivore nematodes in mulch with no clear tendency in other populations. The fluctuation was high in SVA of all the populations and STA showed an increase in fungal feeder nematodes with no clear tendency of which population was decreasing. If we consider the last sampling date (April 2005) as an indicator of the treatments to reach a balance in their structure it appears that mulch has the highest percentage of bacterivores, STA the highest of fungivores with mulch the lowest, and that SVA has the highest percentage of herbivores.
To have a better comprehension of the food web structure we measured the amount of endomycorrhizal spores in the soil as well as the percentage of infection from said mycorrhizae in the roots. It is established that mycorrhizae are of extreme importance in aiding the plant to absorb nutrients from the soil in low N conditions (Miller et al., 1985; Grange et al., 1994; Newsham et al., 1995). There is a clear correlation between the amount of spores in the soil and the percentage of infection in the roots indicating that the amount of spores in the soil could be utilized as an indicator of infection. Additionally, mycorrhizal infection in the roots was highest in SVA and flame, with the weeds in the SVA showing the lowest (probably due to a species-host issue). Mulch and STA presented the same percentage of infection in between the other treatments. This could be due to mulch associated with a high nutritional status of the soil and for STA to the disturbance generated from tillage.
All of these results suggest that the mulch treatment has the lowest diversified soil biology among the treatments.
OFMS and rootstock evaluation.
The mulch treatment created the most favorable soil conditions for the tree growth having higher concentration of SOM, N and water in the soil while the other two treatments had similar soil conditions. This was reflected in the foliar N concentration, as has been reported by Nielsen and Hogue (1985), and Merwin and Stiles (1994). It is not clear which is the optimal N concentration in the leaves to determine eventual deficiency, since it has not been measured for each available variety but only in general. In our study, in fact, branch growth, TCA, TCAI and canopy volume have not been affected from the OFMS treatments, suggesting that foliar N was still sufficient.
Despite the effect of the treatments on the soil conditions, they did not have an effect on any of the growth parameters measured (TCA, TCAI, branch growth, and canopy volume) except in early years (2001-2003) where sandwich presented the least growth probably due to the vegetation competition exerted by the vegetated area underneath the canopy (Glenn and Welker, 1989; Parker 1990; Merwin and Ray, 1997; Giovannini et al., 1998; Zoppolo, 2004). An expansion of the width of the tilled strip from 2004 probably compensated and reduced vegetation competition.
Trees on Supporter 4 were more vigorous than the M.9 clones used in the experiment, as noted in previous studies (Marini, 2000).
While there has been no effect of OFMS on the vigor, there is an interaction between treatments and rootstocks regarding cropping. In the mulch, which had the most favorable growing conditions, there were no differences measured between the rootstocks while in both flame and sandwich M.9 RN 29 was the rootstock with the highest yield and “yield efficiency”, with no differences between the other two rootstocks. Generally, trees on vigorous rootstocks are less precocious than less vigorous rootstocks. M.9 RN 29 appears to be a rootstock that adapts better to the less favorable growing conditions presented by SS and FL (lower SOM, N, and water content in the vegetated area of the sandwich) as expressed from the higher “yield efficiency” measured in these two treatments when compared with MU.
When we consider cropping per hectare, we have to adapt the results to relative tree density. The lowest cumulative yield per hectare is the flame treatment with no differences among the rootstocks. Yield and Yield efficiency per tree as well as the cumulative production per hectare (even if somewhat diminished by the reduced number of trees) make M.9 RN 29 and the low cost sandwich system a very interesting combination that should be considered by growers that wish to plant Pacific Gala under organic protocol in Michigan and related climates.
Fine root parameters.
We did not find a clear correlation between fine root parameters and amount of nitrogen present in the soil, except for the fine root lifespan and turnover. The literature present is contradictory regarding the effect of nitrogen on fine roots. Some authors report that with increased N concentration in soil, root production and length, as well as their life span increases (Aber et al, 1985; Nadelhoffer et al., 1985; Persson and Ahlström, 2002) while others (Pregitzer et al., 1993; Ostonen et al., 1999; Burton et al., 2000; Hendricks et al., 2000; King et al., 2002) reported the opposite. Our work aligns with the correlation of higher N concentration and increased life span, thus reducing carbon costs of the root system (Nadelhoffer and Raich, 1992).
In any case, all the authors agree on the importance of the interaction between N availability and fine root dynamics especially for the effects on organic matter (McClaugherty et al, 1982), on the organic N pool in the soil (Ehrenfeld et al., 1997), and on the control of the substrate quality (Hendricks et al., 2000).
McClaugherty et al (1982) reported that increased organic matter in the soil increased root lifespan while we found the opposite. The difference in SOM in our experiment was probably not enough to exert an effect.
The 30 days of root lifespan found in the mulch treatment is similar to the finding by Bouma et al. (2001) for apples. The same author also states that nutrient depleted systems increase not only the fine root lifespan but also their nutrient efficiency uptake, thus implying that the sandwich system is more efficient.
This theory also explains the higher number of fine roots measured in SS compared with MU early in the season when the trees are in higher demand. It also explains the higher amount of fine roots and area found closer to the trunk in the first 30 cm of soil in the sandwich system. The higher competition for nutrients and water exerted from the vegetation present in this area of the SS is probably responsible for this finding, since it will increase the system nutrient depletion (Schenk and Jackson, 2002).
It is not clear which factors are responsible for the lack of response in fine root area in the other positions and depths between the treatments.
Wells and Eissenstat (2001), reported that 55-60 % of apple roots in their study have a diameter of 0.5-1.1 mm and 30 % of 0.3-0.5 mm. Our findings, even if the divisions in classes of diameter are slightly different, support their observation. We did not, however, find an association between root diameter and mortality, as found in their report.
We did instead find an interaction between the diameter class frequency and both depth in the soil profile and distance. This interaction was different for the two treatments. It is not clear which factors are responsible for these results. Closer to the trunk (the vegetated area in the sandwich), MU tends to show a higher frequency of larger diameters than SS, especially both, near to and the farthest distance to the trunk. Sandwich presented the opposite in the middle position that is closer to the transition between the vegetated area and the tilled strip, and a much higher percentage of very fine roots (0.2-0.4 mm) farther from the trunk (corresponding to the middle of the tilled strip). A similar tendency was noticed for soil profile depth. Mulch tends to have higher frequency of larger root classes deeper in the soil profile, even if the most represented classes are still the two mid size roots in both treatments.
The reason why SS tends to show a higher frequency of very fine roots farther from the trunk and deeper in the soil profile than MU could be explained by lower carbon cost for very fine root, thus reducing the demand of the root system and allowing SS to be equally productive as MU.
More research should be done trying to link root diameters with efficiency of nutrient absorption, response to water content, SOM, and carbon cost of their production.
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Educational & Outreach Activities
In 2003, 60 growers attended the field day. Four talks were given on the project at local and national conferences.
In 2004 65 growers attended the field day. Five talks were given on the project at local, national and international conferences.
In 2005 68 growers attended the field day. Five talks were given on the project at local, national and international conferences.
In 2006 68 growers attended the field day. Two talks were given on the project at local and national conferences.
• ASHS 2006, New Orleans, Louisiana. D. Stefanelli, R.L. Perry – Effect of Ground Floor Management Systems on Root Architecture of Pacific Gala on M.9 NAKB 337 under organic protocol.
• APS 2005, Austin, Texas. D. Stefanelli, R. L. Perry, G. W. Bird – Impact of orchard ground cover management on nematode community structure.
• ASHS 2005, Las Vegas, Nevada. D. Stefanelli, R.J. Zoppolo, R.L. Perry – Fine root dynamics in organic apple orchard under two ground floor management systems.
• ASHS 2003, Providence, Rhode Island. D. Stefanelli, R.L. Perry, R.J. Zoppolo – Effect of two ground floor management systems on apple fine root dynamics under organic protocol in Michigan.
Invited speaker oral presentations
• November 2-4, 2005. D. Stefanelli, R.L. Perry – Ground floor management systems for organic apple
orchards. Great Lake Fruit Workers Conference. MSU, East Lansing, MI.
• November 2-4, 2005. D. Stefanelli, R.L. Perry – Effects of ground floor management on rootstocks and soil in apple orchards. Great Lake Fruit Workers Conference. MSU, East Lansing, MI.
• February 28 – March 2, 2005. D. Stefanelli, R.L. Perry, M. Whalon, R.J. Zoppolo. – Organic apple production in Michigan, an update from Michigan State University. Benzie-Manistee Horticultural Society, Thompsonville, Michigan.
• December 7-9, 2004. R.L. Perry, R.J. Zoppolo, D. Stefanelli. – Challenges in producing organic apples in eastern North America. Great Lakes Fruit, Vegetables and Farm Market Expo. Grand Rapids, Michigan.
• March 6, 2003. R.J. Zoppolo, R.L. Perry, D. Stefanelli. – The Michigan State University organic apple project. Fruit crop ecology – The living soil. Traverse City, Michigan
• May 28-30, 2003. D. Stefanelli, R.J. Zoppolo, R.L. Perry. – Ground floor evaluation in organic apple production. 2nd National organic tree fruit symposium. Grand Junction, Colorado.
• D. Stefanelli, 2006. Evaluation of orchard floor management systems for apple under organic protocol: effect on soil organic matter and nitrogen, nematode community, root architecture and development, and rootstock performance. PhD Thesis dissertation, Michigan State University.
• R.J. Zoppolo, D. Stefanelli, R.L. Perry. Soil Properties Under Different Orchard Floor Management Systems for Organic Apple Production. Targeted journal. American Journal Horticultural Science. (in press).
• D. Stefanelli, G.W. Bird, R.L. Perry. Nematode Communities as Affected from Orchard Floor Management Systems in Apple under Organic Protocol. Targeted journal. American Journal Horticultural Science.
• D. Stefanelli, R.J. Zoppolo, R.L. Perry. The Response of “Pacific Gala” on three Rootstocks to three Orchard Floor Management Systems under Organic Protocol. Targeted journal. American Journal Horticultural Science.
• D.Stefanelli, R.L. Perry. Root Development of Apple as Affected by Orchard Floor Management Systems under Organic Protocol. Targeted journal. American Journal Horticultural Science.
• D. Stefanelli, R.L. Perry. Effect of Orchard Floor Management Systems on Root Architecture of “Pacific Gala” on M.9 NAKB 337 under Organic Protocol. Targeted journal. American Journal Horticultural Science.
With these experiments we asserted that the Orchard Floor Management Systems (OFMS) under evaluation were able to change the soil conditions regarding organic matter, carbon sequestration and nitrogen concentration.
The highest soil organic matter (SOM) concentration was found in the mulch treatment (MU), which increased over the duration of the experiment, especially near the soil surface where litter was added twice yearly. Soil organic matter decreased near the soil surface for flame (FL) and the tilled strip of the sandwich system (SS) where there was continuous burning of the vegetation (in the flame treatment) and the effect of tillage (in the tilled strip of the sandwich, STA). Soil organic matter in the vegetated area of the sandwich system (SVA) remained constant for the duration of the experiment due to the continuous degradation of the on site vegetation. Soil organic matter was less significant deeper in the soil profile (0-30 cm), where MU increased overtime and was the highest in soil organic matter. The tilled strip of the sandwich also increased in SOM. There was no change at this depth over time for the other systems/positions sampled.
A very similar trend was found for all treatments regarding Nitrogen (N) concentration in the soil.
When some difference was present MU had always the highest water content values in the soil while the SVA had the lowest. Flame and the tilled strip in the sandwich did not differ from the other two.
The trend for carbon sequestration per hectare at orchard level was inverse in relation to SOM for the systems. The greatest potential for carbon sequestration was at 0-30 cm depth, for MU and SS.
The different nematode populations present in the soil were changed by the OFMS. There were more bacteria feeding nematodes (84%) in the mulch system which accelerated over time and eventually dominated nematode populations. In contrast, bacteria feeding nematodes stabilized (around 60%) in SS and FL, while the fungal feeding populations strengthened. Fungal feeding nematodes usually develop in depleted soil conditions but at the same time have an enhanced effect on nitrogen release in the soil. This may have occurred here where there was a measured increase in nitrogen concentration in the soil, even with decreasing or stable SOM. Also, a higher percentage of roots were infected by mycorrhizae in FL and SS, which is commonly associated with poor soil conditions. These results suggest that these two treatments found a balance to overcome the lower SOM concentration, thus increasing their efficiency. Mycorrhizal infection enhances root lifespan in woody roots (Hooker et al., 1992).
There were less root feeding nematodes in the soil in MU than FL and SS. Levels in FL and SS were similar but below damage threshold.
There was a direct correlation between mycorrhizal spores in the soil and percentage of roots infected by mycorrhizae.
It appears that trees managed in all system treatments were equally efficient regarding plant growth and development (TCA, TCAI, canopy volume, and shoot growth). Perhaps the different performances of plants under the OFMS improved root system efficiency. This was demonstrated when we measured the fine root development under MU and SS by minirhizotrons. Fine root turnover life span was increased under SS (from 30 days of MU to 50-60 days), suggesting an improved efficiency of nutrient uptake and reducing the carbon cost of new root production. The adaptation of the root system to the OFMS was not confined only to a physiological but also to a physical one.
Weed presence influenced root architecture measured by trench soil profile. Apple roots were confined to the weed free area in MU and FL and relatively closer to the soil surface. In contrast, very few roots were found in SS closer to the trunk (vegetated area), and more were found extended into the tilled strip (vegetation free), and reached farther into the alley. It was also found to have a greater frequency of roots deeper in the soil profile. The lower water content found in the vegetated area of the sandwich could have also played a role in the root distribution.
In total, there were more roots found in MU than the other two treatments. This fact coupled with the fact that no differences were measured in the tree growth parameters suggests that there is a better carbon allocation for trees in FL and SS.
The trench profile data contradicts the spatial results from the minirhizotrons regarding between MU and SS. The soil and root interface sampling in the minirhizotrons is very limited and thus data is not applicable in assessing spatial distribution. This technique is reliable in monitoring root growth development. With the trenches, a selected part of the root system is measured and it is assumed representative of the totality. The general trends of the results should still be considered valid.
During the minirhizotron experiment we found some unique results that linked the treatment diameter class of fine roots with the depth in the soil profile and distance from the trunk. The Sandwich system had higher frequency of very fine roots (0.2-0.4 mm) closer and farthest from the trunk, as well as deeper in the soil profile when compared with mulch. The reason of this finding is not clear and more research should be done on the subject.
As part of the OFMS evaluation we also measured the performance of three rootstocks (the dwarfing M.9 NAKB 337, the semi-dwarfing M.9 RN 29, and the semi-vigorous Supporter 4) to the different conditions created.
The OFMS treatments did not have an effect on tree growth, but nitrogen concentration of leaves was lowest in sandwich and flame. This suggests that the growing conditions were still sufficient but should still be monitored because the values were in the lowest acceptable range.
As expected, trees on Supporter 4 rootstock were most vigorous.
There was an interaction between treatments and rootstocks regarding the crop yield with M.9 RN 29 having the highest yield and yield efficiency per tree in flame and sandwich while no differences were noticed between the rootstocks in mulch despite its better growing conditions. This suggests that M.9 RN 29 is a rootstock that is better adapted to the more stressful conditions imposed by sandwich and flame treatments (lower SOM, N and in case of the sandwich vegetated area less water content). This is probably due to RN 29 being slightly more vigorous than NAKB 337 and more precocious than Supporter 4. It could also depend on its higher efficiency in nutrient and water absorption.
When considering the values per hectare and especially the cumulative yield, the flame treatment cropped least with no differences between the rootstocks. Mulch and sandwich treatments had similar cumulative production per hectare with Supporter 4 having the lowest values with no differences between the other two rootstocks.
The low production per hectare in FL, despite its higher “yield efficiency” per tree, and the low level of nitrogen in the leaves, suggests that this OFMS could not be sufficient anymore without implementation of fertilization. This is interesting since this system is equivalent to conventional orchards where a weed free zone is maintained with herbicides.
Implementation of each of these OFMS is quite different and should be considered during the selection and implementation for the growers.
The flame system presents high risk of fires, damage to the lowest branches due to heat convection, and requires specialized equipment. It is however, relatively inexpensive to maintain ($218). In my opinion, this treatment is not particularly desirable to organic growers.
The mulch is expensive ($788), difficult to apply, requires multiple redressing to maintain adequate thickness, subject to rodent damage and wild fires during the summer. In my opinion this treatment is slightly more desirable to organic growers than flame. More research should be done on the kind of mulching material to use, in relation to SOM and soil food web.
The sandwich system is easy to implement, it does not damage tree trunks, it is less expensive to manage ($91), and it requires only an easily modified notch disk tiller. The drawback of this system is that vegetation competes with tree growth and soils are lower in SOM and N concentration than mulch. Therefore, irrigation and soil fertility must be monitored. Also the ideal width of the tilled strip requires more research for various soil types.
Overall, the sandwich system coupled with the M.9 RN 29 rootstock appears to be a suitable choice for growers that want to grow Pacific Gala under organic protocol in Michigan and similar climates. More research is still necessary, especially to confirm these results in a longer term study and under commercial orchard operations.
We performed a tentative economic analysis, utilizing our plot as unit, since the randomization of the blocks made it impossible to make a correct relationship to commercial scale. However they could be compared, since there were the same number of turns and space between the blocks.
The cost evaluation of the application of the different ground floor management systems during 2005 is reported in the below table.
14 round bales of alfalfa $420
Labor for application by hand 30 hrs * $ 12.25/hr = $367.5
30 gal LPG * $1.33/gal = $39.9
Labor 9hr 45′ * $12.25/hr = $119.44
Tractor 25 hp 9hr 45′ * $6.0 hr = $58.5
Labor 4hr 05′ * $12.25/hr = $50
Tractor 55hp 4hr 05′ * $10/hr = $40.83
In 2004 a grower volunteered 10 acres to try the Swiss Sandwich System (one of the systems under evaluation in the project) to try it at a commercial scale. We have been contacted from another grower that wants to install the Swiss Sandwich System in his three acres orchard.
In 2005 a grower volunteered 5 acres to try the Swiss Sandwich System (one of the systems under evaluation in the project) to try it at a commercial scale.
A total of 261 farmers have been informed of our research and results during the years through our field days.
The systems implemented were very different and it is difficult to give absolute suggestions to growers.
Trees on Supporter 4 rootstock were most vigorous. M.9 RN 29 is a rootstock that is better adapted to the more stressful conditions imposed by sandwich and flame treatments (lower SOM, N and in case of the sandwich vegetated area less water content). This is probably due to RN 29 being slightly more vigorous than NAKB 337 and more precocious than Supporter 4. It could also depend on its higher efficiency in nutrient and water absorption.
The low production per hectare in Flame, despite its higher “yield efficiency” per tree, and the low level of nitrogen in the leaves, suggests that this Orchard Floor Management Systems (OFMS) could not be sufficient anymore without implementation of fertilization. This is interesting since this system is equivalent to conventional orchards where a weed free zone is maintained with herbicides.
Implementation of each of these OFMS is quite different and should be considered during the selection and implementation for the growers.
The flame system presents high risk of fires, damage to the lowest branches due to heat convection, and requires specialized equipment. It is however, relatively inexpensive to maintain. In my opinion, this treatment is not particularly desirable to organic growers.
The mulch is expensive, difficult to apply, requires multiple redressing to maintain adequate thickness, subject to rodent damage and wild fires during the summer. In my opinion this treatment is slightly more desirable to organic growers than flame.
The sandwich system is easy to implement, it does not damage tree trunks, it is the least expensive to manage between the three, and it requires only an easily modified notch disk tiller. The drawback of this system is that vegetation competes with tree growth and soils are lower in SOM and N concentration than mulch. Therefore, irrigation and soil fertility must be monitored.
Overall, the sandwich system coupled with the M.9 RN 29 rootstock appears to be a suitable choice for growers that want to grow Pacific Gala under organic protocol in Michigan and similar climates.
Areas needing additional study
More research should be done on the kind of mulching material to use, in relation to SOM and soil food web.
The ideal width of the tilled strip requires more research for various soil types.
More research is still necessary, especially to confirm these results in a longer term study and under commercial orchard operations.
More studies should be done regarding the natural vegetation in the vegetated area of the Sandwich system, especially in regard to their ability to host beneficial insects and/or be repellent to pests.
Both Flame and Sandwich systems seemed suitable in completely destroying the fallen leaves during the winter, thus reducing scab inoculums. This should be further researched.
Eventual fertility trials should be conducted, especially regarding the long term performance for the Flame and Sandwich treatments, particularly in poor soil conditions.
Adaptations studies of the Sandwich system to different soil types and climates are necessary, as well as to different fruit species.
More research should be done trying to link root diameters with efficiency of nutrient absorption, response to water content, SOM, and carbon cost of their production.