Assessing Soil Quality in Intensive Organic Management Systems

Assessing Soil Quality in Intensive Organic Management Systems

Summary

We are evaluating the effects of cover crop, amendment, and tillage strategies on soil quality in organic vegetable and tree fruit production. Amendment had the greatest short-term effect across a range of soil properties in the vegetable crop experiment. Spader tillage reduced compaction compared with conventional tillage. Improved soil quality has not yet led to improved yield. In the orchard system, wood chips provided greater overall soil quality and production benefits than living mulches or cultivation. The economic benefit covered the cost of wood chip application. Tillage appears to be degrading soil quality.

Objectives/Performance Targets

• 1. Compare the effects of selected organic row crop and orchard management systems on soil quality as measured by field and laboratory tests and field observations.
  2. Evaluate the NRCS Soil Conditioning Index as a tool for soil quality assessments.
  3. Develop underseeded cover crop guidelines for humid Northwest environments.
  4. Share findings with organic vegetable and fruit producers and other producers interested in sustainable practices in the Northwest.

Accomplishments/Milestones

Objective 1. Compare the effects of selected organic row crop and orchard management systems on soil quality as measured by field and laboratory tests and field observations.

This project includes soil quality measurements in an organic vegetable crop systems experiment at WSU Puyallup (established 2003), two orchard weed and soil management experiments established in Wenatchee in 2004 and 2005, and six on-farm sites in western Washington. Five of the cooperating farmers grow organic vegetables, while the sixth farmer grows organic vegetables and small fruit (raspberry, strawberry, and blueberry). One farm also has small poultry flocks for egg and meat production.

Vegetable crop systems experiment.

Tables and figures providing more information on the procedures and results of the vegetable crops systems experiment are on our website at: http://www.puyallup.wsu.edu/soilmgmt/SusAg_Sum_SoilQual.htm

Outline of procedures.

The organic systems experiment at Puyallup compares 12 combinations of organic management systems, consisting of three cover crop treatments, two tillage treatments, and two soil amendment treatments arranged in a split-split plot design, with cover crops as the main plots. The cover crop treatments include 1) a traditional fall-seeded cereal rye-hairy vetch mix, 2) relay-intercropped hairy vetch planted into the standing cash crop, and 3) a short-term ryegrass-clover pasture that is rotated with cash crops in alternating years. The tillage treatments include conventional (plow, disc, rototill as needed), and modified (spader) tillage. Soil amendments are broiler litter compost applied at 1.5 dry tons/acre (low carbon) and on-farm mixed compost applied at 14 dry tons/acre (high carbon). The crop rotation for the first three years was snap bean (2003), spinach following summer cover (2004), and winter squash (2005). Beginning in 2006, 4 rotation crops were grown in each plot each year, by dividing the plots into narrow beds, typical of those used by local organic mixed vegetable growers. The rotation across beds is: 1) double crop of spring broccoli followed by fall spinach, 2) snap bean, and 3) winter squash.

The plots with the pasture cover crop are in cash crops each odd-numbered growing season (2003, 05, 07 etc.) and in pasture at all other times. We raise Cornish Cross pastured poultry during the growing season of the pasture years.

Soil quality measurements include soil physical properties (compaction using Rimik penetrometer, bulk density, infiltration using single-ring falling head, and aggregate stability); biological indicators (b-glucosidase and dehydrogenase enzymes, nematodes, collembola, microbial community assessment via phospholipid fatty acid analysis, and substrate induced respiration to estimate total, fungal, and bacterial activity); and chemical properties (total and particulate organic matter carbon, and basic soil nutrients). Most samples were collected pre-plant (2 to 3 weeks following incorporation of cover crops and amendments) and mid-season (at the time of canopy closure of the squash crop). Some measurements were made post-harvest.

These measurements are more extensive than those originally proposed, and have been supported through this SARE project and other funding sources. We are seeking funding to continue this project for at least another 3-4 years.

Results.

Bulk density. Soils with low bulk density are generally more porous and contain more organic matter than soils with high bulk density. Bulk density measured in mid season of 2004, 2005, and 2006 was significantly lower in plots receiving the high C amendment (on-farm compost) compared with the low C amendment (broiler litter). Differences between the amendments increased each year. Mean bulk density in 2006 was 1.07 g/cm3 for the low C treatment and 0.99 g/cm3 in the high C treatment. Cover crop affected bulk density in 2004 and 2006, with higher bulk density in the pasture treatment. There was no difference among cover crops in 2005, when the pasture treatment was in cash crop production. In 2006 there was an interaction between cover crop and amendment, with a larger amendment effect in the relay and post-harvest treatments than in the pasture treatment. This was to be expected, because the pasture treatment receives amendments biennially compared to annual applications for the other treatments, and the compaction that occurs in the pasture cycle can mask some of the differences from amendment. Nonetheless, there was a significant, albeit small, amendment effect in the pasture treatment, indicating long-lasting effects of compost applications. Tillage did not affect bulk density.

Soil compaction (0 to 40 cm depth) was measured twice each year using a recording cone penetrometer. Soils have been consistently less compact at the 15 to 30 cm depth in the plots tilled with the spader, in part because of the greater depth of tillage done by the spader. Soil in the pasture (ley) treatment was significantly more compact in the upper part of the profile in 2004 and 2006 (pasture years), but not in 2005 (cash crop year). There was a cover crop x tillage interaction in 2004 and 2006. In 2004 there was no tillage effect in the pasture treatment, while in 2006 there was a smaller tillage effect in the pasture treatment than observed in the other cover crops. The tillage effect in the 2006 pasture treatment was noteworthy, indicating tillage effects persisting more than one growing season. We measured a small amendment effect in 2006, with less compaction in the high C treatment in the upper part of the profile. This was the first year that an amendment effect was seen.
Infiltration measurements were made at planting and mid season in 2005 and 2006 using a simple single ring infiltrometer with falling head. Infiltration rate was greater with the high C amendment and spader tillage in the spring of 2005, but the differences were no longer significant by mid season. In 2006 the infiltration rate was much lower in the pasture treatment, because it was in the pasture rather than row-crop phase. Infiltration rate was greater with the high C amendment in the relay and post-harvest cover crop treatments, and the effect was significant in both the early-season and mid-season measurements. This suggests that the effect of amendment on infiltration persisted longer into the growing season in 2006 than in 2005.

Aggregate stability. No differences in aggregate stability were observed among treatments analyzed through 2005. Data analysis for 2006 is still in progress. We have evaluated aggregate stability as mean aggregate diameter and % water stable aggregates. Because biological activity plays an important role in the creation of stable aggregates, we would expect differences in aggregate stability to develop more slowly than for many of the other physical measurements. Mean aggregate diameter over all treatments was 2.37 mm in 2005.

Particulate organic matter (POM) C was greater in the plots receiving the high C amendment, indicating the short-term effect of amendment addition on soil C when large amounts of amendments are applied. POM levels were 4.52 g/kg soil in High C vs. 3.49 g/kg in Low C in 2004, and 6.60 vs. 4.49 g/kg in 2005. Analysis for 2006 is in progress.

b-glucosidase and dehydrogenase. Enzyme analyses for 2006 are not complete. A summary of 2004-05 results follows. These enzymes were the most responsive biological indicators in our study. B-glucosidase activity was affected by cover crop all three dates sampled (pre-plant and mid-season 2005, as well as mid-season 2004), with the relay vetch plots tending to have the greatest activity and the post-harvest rye vetch the lowest. This is probably a result of the different qualities of the cover crop residues, with the most succulent residue being the relay vetch. Dehydrogenase activity was lowest for the post-harvest cover crop in 2004, which was the time when there were the greatest differences in the quality of the cover crops. The high C amendment increased dehydrogenase activity in the 2004 and 2005 mid season samples, while spader tillage increased dehydrogenase in the pre-plant 2005 samples. Spader tillage also increased b-glucosidase on one date, suggesting that the lower intensity of the spader may have some effect on soil biological activity. More data are needed to evaluate this hypothesis.

PLFA and Biolog plates. We used phospholipid fatty acid (PLFA) analysis and Biolog plates to evaluate the effects of the different systems on microbial community structure. Principal component analysis of the PLFA data showed a separation among cover crops mid-season 2004, when differences in the cover crop environment were greatest, but no substantial differences were seen on other dates (data not shown). Effects of treatment on Biolog activities were small. Together, these data suggest that that there is little short-term difference in biological community structure among the organic systems. Biolog analyses were dropped after 2005, and 2006 PLFA analyses are not complete.

Nematodes, collembola, and microbial biomass. Analysis of nematodes and collembola allows examination of the soil food web at a higher trophic level, while microbial biomass provides information on the lower levels of the soil food web. Microbial biomass measurements began in 2006. In the spring, following tillage of the relay and post-harvest plots, biomass was greater in the tilled plots compared with the untilled pasture treatment, probably a result of incorporation of fresh biomass into the soil. Microbial biomass was also higher in conventionally tilled plots compared with the spader treatment. No differences among treatments were observed in the mid-season sample, suggesting that biomass showed a short-term response to introduction of fresh organic residues. We are refining techniques for comparison of bacterial and fungal biomass via substrate-induced respiration. Collembola and nematode measurements began in 2005. The only significant treatment effect observed in 2005 was a greater number of collembola in the relay treatment in the fall compared to the post-harvest and pasture treatments. The relay treatment was the only one that was not tilled in the fall of 2005, and higher collembola numbers reflect a positive response to reduced tillage. Collembola data for 2006 have not been analyzed. No significant effects of treatment on nematodes were observed in 2005, but in mid-season 2006 more nematodes were observed in the broiler litter treatment (input of labile organic N). Nematodes decreased in the order: Post-harvest cover crop > Relay cover crop > Pasture. The post-harvest cover crop had the greatest input of organic matter in the spring, while the only organic matter from the pasture treatment was from decaying root tissue and exudates from the living pasture grass and clover. The same cover crop trend occurred in the October 2006 sampling, six months after incorporation of cover crops.

Soil pH, exchangeable K, and organic matter (0-30 cm depth) were higher with the High C amendment (on-farm compost) compared with the Low C amendment (broiler litter). Cover crop affected the amount of difference in pH, K and OM between the two amendments, with the smallest difference occurring in the pasture, the treatment that receives amendments on a biennial rather than annual basis.

Weeds. There have been no significant differences in weed density among treatments at any time since measurements began in 2004.

Crop yield. The only crop affected by treatment in 2006 was broccoli, yielding 5.5 tons/acre following broiler litter compared with 4.6 tons/acre following on-farm compost. This may have been the result of more early-season N available from the broiler litter. Acorn squash, spinach, and snap bean yields were not affected by treatment.

Post-Harvest Soil Nitrate averaged 6 mg/g soil in the 0-30 cm depth in 2005, with no differences among treatments. This indicates that excess N was not present in the soil following the 2005 growing season.

Conclusions.

The amendments provided a larger volume of C (especially the compost), but it is less labile than C provided by the cover crops. Tillage affected the depth of incorporation of amendments and the degree of disturbance of the soil. The spader tills deeper than conventional tillage and it incorporates residues more completely, but we believe that is nonetheless less disruptive than conventional tillage because the tillage action is slower, and there are fewer passes over the field. The main cover crop effects were related to the timing and amounts of tillage, and to a lesser extent the amount and quality of cover crop biomass.

Amendment had the greatest effect on soil properties. The High C amendment (on-farm compost) decreased bulk density and increased POM C, total OM, dehydrogenase activity, soil pH, and exchangeable K compared with the low C amendment (broiler litter). All of these effects were measured each year, and were the result of an immediate response to incorporation of the compost. The High C amendment also increased infiltration rate, with a transient increase observed in 2005 and a long-term increase in 2006. Amendment did not affect compaction until 2006, when a significant decrease in compaction in the surface 15 cm was observed with the High C amendment. Amendment has not yet affected aggregate stability, B-glucosidase activity, PLFA, or collembola. Nematodes were increased by the low C amendment (broiler litter), probably as a response to N rather than C. Crop yield also showed occasional responses to amendment, which were also related to N. The amendment effects were greater in the relay and post-harvest cover crop treatments, which received amendments every year, compared with the pasture treatment, which received amendments every other year.

Cover crop effects were often related to the frequency and timing of tillage in each cover crop rotation. The post-harvest cover crop treatment was fully tilled every spring and fall, while the relay treatment was tilled in the spring only, and the pasture was tilled spring and fall every other year. During the years in pasture, the pasture treatment had higher bulk density, greater compaction in the surface soil, and slower infiltration. Collembola responded negatively to tillage, while nematodes appeared to respond positively to residue volume, and b-dehydrogenase responded to residue quality.

The type of tillage affected soil compaction, with consistent differences between spader and conventional tillage in the 15-30 cm depth occurring every year. Plots tilled with the spader also showed occasional, transient improvements in infiltration and enzyme activity.

Work remaining. In 2007 will complete analysis of all data from 2006, including aggregate stability, biochemical measurements, enzyme activities, PLFA, collembola counts, and evaluation of nematode ecology using Structure, Enrichment, and Channel Indices. We will also create a spatial map of soil texture. We will prepare a final report and a paper focused on short term effects of different organic management systems on soil quality, and present results at workshops, field days, and farm walks focused toward organic and small-acreage farmers. If we obtain new funding, we will continue the same series of measurements made in 2006.

On-farm cooperators.

Results. In 2005 we measured bulk density, aggregate stability, infiltration rate, penetrometer resistance, and texture at multiple points on each of the six cooperating farms. At two of the farms we made measurements at two different farm sites under their management. We also collected composite samples for soil organic matter, pH, Bray P and exchangeable K. Each sampling location was logged into a GPS system so that we can return to the same points in subsequent years. In 2006 we completed measurements at four of the six farms. The fifth farm was in a fallow cycle and we only did partial measurements, and we did not sample the sixth farm because we became limited by fall weather.

Soil test values showed a wide range in organic matter, reflecting both native soil properties current and past management, and length of time in organic production. P and K levels also varied widely, with four locations having excessive levels of P. Post-harvest nitrate levels were measured at only three farms, but all suggest conservative N management, with low levels of nitrate-N available for leaching at the end of the growing season. One of the farms had visible signs of N deficiency in the crops. Infiltration rates reflected soil texture and to a lesser extent management. Infiltration data for 2005 (not shown) and 2006 were similar. Penetration resistance had different patterns among farms, but was generally within the range of that observed in the systems experiment.

Work remaining. We will complete analysis of the 2006 data and summarize all data for the final report. We were not able to incorporate conventional farms into this study in 2006, but are seeking other funding to continue long-term evaluations of soil quality on these farms and add several conventional vegetable farms.

Orchard mulches and weed management experiments.

The objective of these experiments is to evaluate soil quality differences related to in-row weed control methods in orchards including mechanical tillage (different rates and types), wood chip mulch, living mulch or control treatments applied to the weed strip. Soil infiltration rate and resistance to penetration were measured to monitor the soil quality impacts of repeated mechanical tillage compared to untilled or mulched soil. Our overarching hypothesis for these two trials is that the wood chip mulch improves soil physical properties, and tillage degrades them relative to a bare or mowed control. Additionally, we hypothesized that a living mulch planting would also increase soil quality over tillage or control treatments.

Tables and figures showing data from the orchard experiments are on our web site at http://organic.tfrec.wsu.edu/OrganicIFP/OrchardFloorManagement/Index.html

Procedures:

1. Tillage Comparison Trial. In April 2004, a 2-year trial was set out in an 8-year-old block of Gala/M26 in transition to organic certification at the Wenatchee Valley College teaching orchard near East Wenatchee, WA. Treatments included control (no tillage, mowing to keep weeds down), wood chip mulch (applied 6” thick,), Cultivator Y (3x), Cultivator Z (2x), Cultivator Z (3x), and Cultivator Z (4x), with 5 replicates, where “x” denotes the number of times plots were tilled. In Year 2 Cultivator Y treatment was tilled once only, in early August. Cultivator Y is a hydraulically driven unit with a vertical axis cultivating head. Cultivator Z is a ground-driven rolling cultivator with a spring blade that works in between the trees. Infiltration and soil penetration resistance data were collected in both years, and in 2005 soil samples were taken for organic matter and microbial tests. Resistance data were collected using a Rimik® recording cone penetrometer with readings from 0-425 mm depth, at 15 mm intervals, and nine measurements were made per plot. Infiltration was collected using brass rings in 2004, and Mini Disk Infiltrometers (Decagon, Inc. Pullman, WA) in 2005.

2. Integrated mulch trial. In April 2005, a trial was set up in a new apple (Pinata/M7) block to test the following understory treatments during orchard establishment: bare ground control, bare ground with Brassica meal, wood chip mulch, cultivation, Sandwich system (tillage each side of the tree line and a 45-cm strip of living mulch in the tree line, see Photo 1), and a Living Mulch (LM) treatment filling the 150 cm wide tree row. The living mulch and sandwich had separate legume and non-legume treatments to test the nitrogen impacts. The LM and Sandwich legume treatments are a species mix of Mt. Barker subclover, black medic, burr medic, birdsfoot trefoil, and bentgrass. The Sandwich non-legume treatment is transplanted sweet woodruff and Corsican mint, while the living mulch non-legume mix contains sweet alyssum, five spot, mother of thyme and bentgrass. Experimental design is a randomized complete block with 5 replicates. Tillage rates were uniform for all tilled plots, and as needed throughout the growing season. Soil measurements included volumetric soil moisture using both a Moisture Meter® and Hydrosense® meter (Decagon, Pullman WA), resistance, and nutrient and carbon status. Resistance data were collected as in the tillage trial. Infiltration data were collected with Mini-Disk® infiltrometers (Decagon).

Results:

Tillage Comparison Trial. This trial was continued for a third year, but with a simplification to the three maximum contrasting treatments – wood chip mulch, mow (control), and tillage (3 times). Organic matter was measured in the top 5 cm (Loss on Ignition) and no differences were seen among treatments. Active C measurement is scheduled for January using an aerobic incubation. The most striking soil quality finding was that provided by tree growth and yield, arguably the most useful bioassay of soil quality. In year 2 (2005), we measured a significant increase in optimum fruit size with wood chip mulch, which led to an economic increase that covered the cost of the mulch application. The same fruit measurements were done in year 3 (2006), and tree growth was also measured (Trunk Cross Sectional Area [TCSA] increase, and canopy volume). The same pattern for fruit size was detected but it was not significant at p<0.05. However, wood chip mulch led to a significant increase in TCSA compared to the control, and tillage led to a significant decrease. Canopy volume followed a similar pattern.

Integrated multiple mulch (IMM) trial. In the IMM trial we monitored performance of the orchard in the second year. Tilled trees exhibited statistically more leaning than all other treatments (data not shown), suggesting that cultivation was interfering with tree anchoring either by root pruning or loosening soil. These trees still exhibited the best growth, but are more susceptible to blowing over in strong winds. Initial soil quality analyses by Lori Hoagland are showing that plots with the living mulches exhibit improved soil quality over two years using a number of soil C, N, and microbial measures. But trees in these plots had the lowest growth again. Thus, the results to date support our hypothesis that tillage to eliminate weed competition in a new organic apple planting would improve tree growth but at a cost to soil quality. Over time, this would likely lead to leakier nutrient cycling with tillage and more need for external nutrient inputs to maintain the system. Our bare ground control plots have been difficult to maintain weed free since no effective herbicide is available for organic systems, but would clearly make it more feasible to maintain soil quality and tree growth.

Portable EC probe and soil N. We also tested a novel method to monitor soil N mineralization from amendments or other sources using a portable EC probe from Spectrum Technologies. This probe is designed to give an instantaneous EC readout (temperature compensated) directly from soil. We “mapped” the IMM plots with the probe, taking a reading at 0, 15, 30, 45, and 60 cm soil depth . We also had soil samples from selected depths analyzed for EC and nitrate in the USDA-ARS lab (courtesy Dr. Jeff Smith) and correlations of r2 = 0.7-0.8 were calculated. The dramatic effect of tillage in increasing available N (due to increased mineralization) is evident, as is the impact of increasing fertility rate (0.5x, 1x, 1.5x for compost rate). The probe appears useful at least as a relative indicator, considering the consistent readings of background EC in the unfertilized control plots of 0.2 dS/m, which is in line with previous lab analyses of this soil. We have taken soil samples from 0-15 cm, 15-30 cm, 30-45 cm, and 45-60 cm in November 2006 (3 reps only due to weather) and will analyze these for EC with the probe and nitrate using the Cardy meter to further validate this approach and develop data for comparison with spring nitrate to estimate over-winter losses under the various orchard floor systems. Initial nitrate measurements in surface soil indicated very large losses, but it is not known if the nitrate is moving below the rooting zone.

Work remaining: In the months remaining we will complete analysis and reporting of 2006 data. We will analyze soil samples from IMM for EC and nitrate to further validate the EC probe and provide a baseline for overwinter movement of nitrate to 60 cm depth. Active C will be measured in the 0-5 cm soil from the Tillage Comparison Trial.

Objective 2. Evaluate the NRCS Soil Conditioning Index as a tool for soil quality assessments.

Procedure:

We ran a series of scenarios based on field data (crop yield, cover crop biomass, amendment application rates, and field operations) for the different systems in the WSU Puyallup organic systems experiment. We evaluated 1-year (2005) and 2-year (2004-05) simulations for the 6 cover crop and amendment combinations, but did not compare tillage systems, because the Soil Conditioning Index (SCI) database does not contain field operation inputs for spaders.

Results:

Preliminary results indicate a wide range of soil conditioning indices among the experimental treatments. One-year results ranged from –0.13 to +0.12, while 2-year results ranged from –0.02 to +0.36. The two-year results were higher because they included a year with more time spent in cover crops and less in cash crops. This range of values suggests that relatively large differences in soil quality may become apparent over time in the experiment. A problem with adapting the SCI to use with small-scale organic farms is that many of the common equipment and tillage operations on these farms are not part of the current SCI database. Also, it is clear that accurate record keeping is needed to gain confidence in the SCI results.

Work Remaining: Completing this objective will be the thrust of our work this winter. We will work with the SCI developers to including tillage and cover crop operations that are applicable to small-scale organic vegetable production. We will refine the erosion factor for our own experimental site using RUSLE inputs, and expand the scenarios to three (2003-2005) and four (2003-2006) years. If we can include new tillage and cover crop operations in the model, we will then run simulations on selected partner farms, based on the quality of input and field operations records from those farms. We plan to continue to run SCI simulations for our own systems experiment over the long term (beyond this SARE project), and determine if relative changes in soil quality predicted by the model are supported by field measurements.

Objective 3. Develop underseeded cover crop guidelines for humid Northwest environments.

Relay planting or interseeding of legume cover crops is designed to overcome some of the drawbacks of legumes, such as slow establishment in the fall, poor winter ground cover, and poor weed suppression, while improving N accumulation. Relay-cropping presents its own challenges, however, including shading by the cash crop, competition with the cash crop, weed management, and effects on winter hardiness. We are determining which cash crops, cover crops, and conditions are most amenable to successful relay cropping of legumes.

Procedure:

This experiment began in 2003 using other funding, and has been jointly funded by SARE and WSU Center for Sustaining Agriculture and Natural Resources since 2004. Legume cover crops are interseeded into snap bean (Jade) and sweet corn (Blaze) approximately 30 days after planting the cash crop. Following cash crop harvest, the residue is mowed and the cover crop must grow through the residue. Specific treatments have changed each year as we have narrowed the focus of our experiment based on previous years’ results. Measurements include cash crop fresh yield, cover crop stand at intervals during the winter and spring, cover crop biomass at the time of incorporation, and soil inorganic N three weeks after cover crop incorporation.

In 2005 we moved the location of the experiment to increase the size of the plots and alleys. New plot sizes are 30 ft by 15 ft with 20 ft alleys between each plot along the direction of planting. Each experiment has five treatments and three replicates.

Results:

Summary of 2003-04 experiment. The hairy vetch and woolypod vetch were well established by late October. Red clover had a fair stand, but common vetch and crimson clover performed poorly and were dropped from the trial. Some winter damage occurred to the vetch in January during a week-long period of snow cover and cold temperatures, but the vetch recovered by spring. Cover crops were harvested in early April 2004 and biomass was similar in the corn and bean experiments. Hairy vetch had the greatest biomass (2170 lb/acre dry weight) followed by woolypod vetch (1760 lb/acre) and red clover (720 lb/acre). Hairy vetch significantly increased early season inorganic N over the control treatment, but red clover did not. Later incorporation would likely have substantially increased biomass and N.

2004-05 experiment. Establishment of the cover crops was poorer than the previous year. Heavy crop residue from the corn, followed by early rains that compacted the crop residue reduced the fall stand of the interseeded cover crops. Cover crops partially recovered during the fall, and by January ground cover averaged 40-50% for hairy vetch and 30-35% for red clover in both corn and bean plots. Cold night temperatures (10 consecutive nights between 20 and 25 F) and lack of insulation by snow in February reduced ground cover to 10 to 20% for hairy vetch by early March, while red clover ground cover was not affected. This illustrates one of the potential problems with interseeded hairy vetch – reduced winter hardiness when planted in mid-summer. Red clover had the greatest biomass at incorporation (12 May), averaging 1980 lb/acre dry matter (mean of corn and bean experiments), while average hairy vetch yields were only 900 lb/acre. The post-harvest rye vetch (planted 4 October) yielded nearly 6000 lb/acre of dry matter.

2005-06 experiment. The design was modified to make a direct comparison of interseeded vs. post-harvest plantings of hairy vetch and red clover. Fall stand of the interseeded hairy vetch and red clover was much improved over the poor stands 2004-05, and similar to 2003-04. Stand ratings over the winter showed trends similar to those observed in previous years: better initial stands with hairy vetch compared to red clover, better initial stands following beans than corn, a decline in the hairy vetch stand during the winter, and a recovery in the spring. Post-harvest plantings of hairy vetch and red clover (done on October 4) had weak stands and never caught up to the interseeded plantings. Biomass yield at harvest averaged 2800 lb/acre dry wt for hairy vetch and 1900 lb/acre for red clover. Soil nitrate-N at 2 weeks after cover crop incorporation greatest for interseeded hairy vetch (9 mg/kg) and 3-4 mg/kg for other treatments. The trend was similar in mid July, with only interseeded hairy vetch (26 mg/kg) approaching an adequate level for a pre-sidedress nitrate test. No differences in weed pressure were observed during the 2006 cash crop season. Neither were differences in cash crop yield observed, although this may have been the result of high yield variability across the plots.

2006-07 experiment. Fall growth of red clover and hairy vetch was similar to the previous year, with some damage to hairy vetch during cold (20F) nights at the end of October. Fall-seeded legumes were not planted until late October, and emergence to date has been poor.

Work remaining. Final cover crop harvest will be done in the spring of 2007, followed by soil nitrate sampling and data analysis for the 2007 season. We have applied for other funding to move this experiment to a new phase focused on nitrogen contribution of the interseeded cover crops and guidelines for nitrogen management.

Objective 4. Share findings with organic vegetable and fruit producers and other producers interested in sustainable practices in the Northwest.

We held field days in February and July 2006 at WSU Puyallup focused on organic agricultural systems, cover cropping, and soil quality. Combined attendance was more than 100. These were the fourth and fifth field days held in conjunction with this project. A 1-evening soils module was taught at five locations as part of WSU classes for small farms operators. Total attendance was 120. In addition we presented two posters at the American Society of Agronomy national meetings, which brought our work to a national audience. Information on our soil quality and organic systems research is available on our web site: http://www.puyallup.wsu.edu/soilmgmt/SusAg.htm The website is revised each January with current information, including portions of this report. Presentations on the orchard understory management were given at 3 grower meetings, the Washington Horticulture Association annual meeting, the American Society of Horticultural Science annual meeting, and the International Horticulture Congress, reaching over 200 growers, researchers, and consultants. Project reports are posted at http://organic.tfrec.wsu.edu/OrganicIFP/OrchardFloorManagement/Index.html . The PIs were participants in the Building Soils for Better Crops workshop and field day in the Columbia Basin in February and July 2006 respectively.

Work remaining. In 2007 we will prepare articles on interseeded cover cropping, soil quality, and soil testing for farmer-oriented publications. In the long run (after the conclusion of this grant) we will prepare an extension bulletin on interseeded cover cropping and a refereed scientific manuscript on effects of organic vegetable cropping systems on soil quality. A journal article on orchard understory management has been submitted to HortScience.

Impacts and Contributions/Outcomes

Our work is leading to strategies and recommendations for relay planted cover crops in irrigated vegetable production systems. Organic growers at our field days have responded enthusiastically to our work on relay planted cover crops. Our research site gives growers an opportunity to compare different relay cover crop strategies. Growers are eager to obtain additional information from our research, to make informed decisions on adopting relay-planted cover crops. One of our cooperating farmers has integrated interseeded cover crops into his farming system on his 15-acre farm, and a second is ready to test interseeding on his 300-acre farm. Several of the other cooperators are interested, but do not yet have plans for implementation.

Our soil quality research is still in early stages, so we do not have on-farm impacts to report yet. We have demonstrated that different organic management systems affect soil quality in different ways in the short run; we plan to continue this research to gain a better understanding of long-term effects. We expect that long-term assessment of soil quality in our experiment and on participating farms will encourage farmers of intensively managed high-value organic crops to adopt practices that provide more long-term benefits to soil quality. Even though the measurable effects of modified tillage using the spader are small at this point, growers are impressed by the quality of seedbed that it can produce after a single pass. The spader appears to be most suitable for small farms and light- to medium-textured soils. We have applied for funding to conduct economic analyses of the different cropping systems in our experiment so that long-term soil quality gains can be better assessed in terms of economic costs and benefits.

Orchardists are keenly interested in soil quality, especially as the number and acreage of organic orchards increases. They typically rely on tillage for weed control and incorporation of fertility amendments. However, a few more growers each year begin using mulches, particularly on low performing parts of the orchard, and report favorable results. The ability to provide more nitrogen internal to the farm via legumes is a priority interest, which this work is helping to address.

Collaborators: