Final Report for GNC04-036
Project Information
A comparison of various cropping systems suggests that cover crops could improve vegetable production under short-term crop rotation. Integrating cover crops into short-term vegetable crop rotation improved soil fertility, reduced weed population, increased soil microbial activity, and enhanced cucumber and tomato yields. Use of legume cover crops like hairy vetch or cowpea showed potentials to help reduce nitrogen fertilizer inputs in subsequent crops. A cropping system that includes cover crops would improve the long-term viability of the farm while protecting the environment from nutrient leaching.
Introduction:
Intensive vegetable production is generally achieved by high fertilizer and pesticide inputs in order to meet the ever growing market demand for quality produce. There is a wide variety of vegetables produced in Michigan (Michigan Department of Agriculture, 2006). Michigan is ranked first in the U.S. for processing cucumbers and fourth in the nation for fresh market cucumbers (Michigan Department of Agriculture, 2006). Over the years, it has become increasingly difficult for growers to maintain high yields and quality. This can be attributed to factors such as increased incidence of soil-borne diseases, weed pressure, reduction in soil fertility levels, limited availability of good land, and economic constraints. Over the past few years, Michigan vegetable growers have been interested in adopting sustainable agronomic practices which can serve a two-fold purpose: cost reduction and quality improvement. Most vegetable growers understand the benefit of long-term crop rotations. However, lack of good land and the need for crop specialization has forced them to adopt short-term rotations. Cover crop usage is well documented and its benefits include: erosion control, reduced runoff, improved infiltration, soil moisture retention, and improved soil tilth, (Blevins et al. 1990; Hall et al. 1984; Robinson and Dunham 1954; Teasdale 1996; Teasdale and Mohler 1993; Utomo et al. 1990). In addition, cover crops can also provide weed control (Gallandt et al. 1999; Mohler and Teasdale 1993; Ngouajio et al. 2003; Teasdale and Daughtry 1993; Williams et al. 1998), and improve soil fertility (Kuo and Jellum 2002; Kuo et al. 1997; Ranells and Wagger 1996). In Michigan, cucumber – tomato rotation is a common rotation followed by vegetable fresh market growers on an intensive scale. Because of the short growing cycle of cucumber, harvest is usually completed by Mid July, allowing a short window for growth of summer cover crops such as sorghum sudangrass [Sorghum bicolor (L) x S. sudanense (P) Stapf.] and cowpea [Vigna unguiculata (L.) Walp.]. In addition, both tomato and cucumber could allow planting of winter hardy cover crops like cereal rye (Secale cereale L.), and hairy vetch (Vicia villosa) after harvest of a cash crop. Management practices that include cover cropping have been reported to affect soil quality parameters (Gregorich et al., 1996; Kou et al 1997). Cover crops provide increased vegetative cover, facilitating reduction in soil erosion levels and enhancing soil C and N levels (Kuo et al., 1997). Fall seeded winter cover crops especially, cereal rye, are the most commonly used cover crops in Michigan (Ngouajio and Mennan, 2004). They are planted in fall after cash crop harvest and killed by cultivation or herbicide application in late spring (Mutch and Martin, 1998). Rye has been shown to increase soil organic C and N (Kuo et al., 1997) as well as impact weeds and disease levels in cropping systems (Bottenberg et al., 1997 a,b; Ngouajio et al. 2003). Cover crops may also increase tomato yield as compared to a bare ground fallow system (Shennan, 1992). Legume cover crops such as hairy vetch has shown enhanced soil N levels as well as increased tomato yield in comparison with systems with no cover crop inputs (Teasdale and Abdul-Baki, 1995; Sainju et al., 2001). Legume cover crops also increase soil C levels and improve tomato shoot and root growth (Sainju et al., 2000). If cover crops were successfully integrated into short-term tomato-cucumber rotations, they could improve the cropping systems with minimal change on growers’ practices. Our general goal was to integrate warm season (summer) and cool season (winter) cover crops into a short-term tomato-cucumber rotation.
- Evaluated the effectiveness of summer and winter cover crops at improving soil fertility under vegetable production systems.
Measure the effect of the cropping systems on soil microbial activity.
Determine the effects of cropping systems on weed populations.
Quantify the effects of cropping systems on cucumber yield and yield quality.
Cooperators
Research
Experimental site and design
The experiments were conducted at a commercial farm in Benton Harbor, MI and at Michigan State University Horticulture Teaching and Research Center (HTRC) in East Lansing. The trial at Benton Harbor had a randomized complete block design with four replications. Each experimental unit was of 10 m by 6 m with six raised beds. One of the two middle beds was used for destructive harvest and the other for yield. The treatments were:
1. Sorghum sudangrass grown throughout summer
2. Cowpea grown throughout summer
3. Sorghum sudangrass sown after cucumber harvest,
4. Cowpea planted after cucumber harvest
5. Cereal rye sown after cucumber
6. Hairy vetch sown after cucumber
7. No cover crop
The two treatments where sudangrass and cowpea were grown throughout summer simulated a scenario where a grower would like to fallow its farm every two years (to grow a cover crop), a practice common for those who have enough land. The seeding rates for the cover crops were 70, 35, 80, and 40 kg/ha for sorghum sudangrass, cowpea, rye, and hairy vetch, respectively. The soil type was sandy loam with 6.4 pH and 1.3 % organic matter. The short rotation sequence used in the study was slicing cucumber var ‘Dasher II’ planted in 2002 followed by tomato var ‘Mountain Spring’ in 2003 followed again by slicing cucumber in 2004. In early April of each year, the winter cover crops or residues left from the summer cover crops were incorporated into the soil using a plow. The cash crop was then planted about four weeks later on a raised bed system covered with black plastic mulch, drip irrigated and fertigated. The experiment at HTRC had four treatments (Sorghum sudangrass, hairy vetch, cereal rye, and control with no cover crop). This study was conducted from 2001 to 2005. The soil was a Hillsdale sandy loam (Coarse-loamy, mixed, mesic Typic Hapludalfs) with 1.1% organic matter and 6.9 pH. The experiment was established on land that had been fallow for over three years. All cover crops were sown after harvest of pickling cucumber variety ‘Vlaspik’.
Cover crop biomass. Cover crop biomass was estimated using two 50 cm by 50 cm quadrats randomly tossed in each treatment. Above and below ground plant material were collected within each quadrat. All fresh plant materials were dried in an oven at 120 ºF for 2 weeks, then the dry weight was measured and converted to metric tons/ha.
Weed biomass and species composition .Weeds were collected from the different treatments once during late spring of each year and during the cash crop growing season. The weeds were then sorted by different species for all treatments. Dry biomass was also estimated after drying the weeds for one week.
Yield and fruit quality. Tomato and cucumbers were harvested multiple times at Benton harbor and graded according to market specification. Pickling cucumber was harvested once by destroying all plants to simulate machine harvest. Data were recorded on cucumber fruits total soluble solids (Brix %), specific gravity, and firmness. For all measurements 3 cucumbers fruits of grade No1 were used. Brix measurements were conducted using a digital refractometer (Palette PR-32, National Microscopic Exchange, 11405 West Lake Joy Dr. NE Carnation, WA 98014). Specific gravity was conducted by estimating the mass and volume of the fruits. Fruit firmness was conducted using a pressure tester (Imada Digital Force Gauge DPS-11R, Imada Inc, Northbrook, 60062, Illinois, U.S.A).
Soil chemical properties. Soil analyses were conducted on soils collected 4 weeks after cover crop incorporation in 2003 and on soils collected at all three stages (4 weeks before 2 days after and 4 weeks after) of cover crop incorporation in 2004. An initial soil analyses was also conducted on soil before establishing the experiment in 2002. The soil samples collected at each stage were analyzed for water holding capacity as well as moisture content. Soil pH was measured in a saturated paste using 1:1 (deionized water:soil). Cation exchange capacity was measured by centrifugation method. Organic matter was determined using the Loss-on-Ignition method. Nitrate –N was analyzed using an automated Flow Solution IV Ion Analyzer (Cadmium reduction method). P was analyzed using Bray and Kurtz P-1 Test. K, Mg, Ca were analyzed using 1 M Ammonium acetate extractant.
Soil biological properties. Microbial biomass C was determined using the chloroform fumigation incubation method (CFI) described by Paul et al. (2001), including the partial control subtraction equation for microbial in the unfumigated sample (Sarig et al. 1999). Soils from each treatment in pairs (50g dry wt equivalent) were put into 50 ml glass jars, then adjusted to 50% water holding capacity using distilled water, and preincubated for a period of 5 days at 25ºC. One sample from each pair was fumigated using a dessicator under a fumehood and the other sample was left unfumigated. After a 24 hr period the chloroform was evacuated from the desiccators and the samples transferred into 970 ml canning jars with a rubber septum on the lit. The jars were closed tightly and subsequently incubated a period of 10 days at 25ºC. At the end of the 10th day, the CO2 content in the headspace of the fumigated as well as the unfumigated jar for each treatment was measured by injecting 1ml of the headspace sample into an Infra Red Gas Analyzer (IRGA, Qubit Systems,Inc.4000 Bath Rd, Kingston Ontario) (Lundquist et al. 1999). Microbial Biomass C was then estimated using the following equation proposed by Horwath et al. (1996):
MBC (µg g-1soil) = 1.73 (Cf) - 0.56(Cc)
where MBC is microbial biomass carbon, Cf is CO2-C from fumigated soil, Cc is CO2-C from unfumigated soil, and 1.73 and 0.56 are correction factors.
Soil respiration was measure as indicated above using unfumigated soil samples incubated for 10 days. The respiration was computed on a day basis as µgCO2-C/g soil/day.
Statistical Analyses Statistical analyses were completed using SAS (SAS Institute, 1999). Analysis of variance (ANOVA) was carried out for a randomized complete block design. Treatment means were separated using LSD at 5% significance level. No significant interaction between the summer cover crops (main plot factor) and the winter cover crop (subplot factor) was observed. Therefore only main effects are presented.
Cover crop biomass production
Among the summer cover crop treatments, sorghum sudangrass grown all summer produced the greatest dry biomass of 24.9 t/ha followed by sorghum sudangrass planted after harvest of cucumber (6.6 t/ha). Biomass production by cowpea was generally low, with less than 3 t/ha in all treatments.
For the winter cover crops, cereal rye produced a dry biomass of 11.3 t/ha which was greater than hairy vetch biomass of 8.4 t/ha. Because of the large biomass produced, sorghum sudangrass may be an excellent cover crop for soil building during fallow years. However, most growers may not afford to leave the land fallow due to limited availability of good land.
Objective 1. Effect of cover crops on soil fertility.
Soils collected prior to experimental setup showed no significant differences among soil chemical properties in all treatments. This indicated that the experimental plot had uniform fertility levels. Soil collected 4 weeks after incorporation of cover crops in 2003 exhibited differences among winter treatments (rye and vetch) in pH, NO3-N, K and Mg parameters but no significance difference in soil fertility was observed among the summer cover crop treatments. Hairy vetch increase soil nitrogen content compared with the other treatments.
Objective 2. Effects of the cover crops on soil microbial activity.
Microbial biomass C (MBC) from soil samples collected in 2003 and 2004 exhibited a clear increase following cover crop incorporation. There was an increase in MBC production by approximately (50 %) at 4 weeks after incorporation compared with samples collected before or 2 days after incorporation. Among warm season cover crop treatments, sorghum sudangrass (grown all summer) produced significantly higher MBC in comparison to cowpea. In the case of cool season cover crop treatments, cereal rye exhibited a significantly greater MBC production in comparison to hairy vetch. Microbial respiration rates were higher in 2004 in comparison to 2003 suggesting that environmental conditions may play a key role in soil microbial activity. The 2003 season was significantly dryer compared with 2004. Soil moisture has been shown to affect soil microbial activity in cropping systems (Lundquist, 1997, Ross, D.J., 1987). High microbial biomass in the soil is indicative of sustainable management. Therefore, integrating cover crops into short-term crop rotations could enhance the population of microorganisms in the soil and build a more resilient system. The ability of the cover crops to enhance soil microbial activity in a short-term (1 to 2 years) is very encouraging.
Objective 3. Effects of cropping systems on weed populations.
Broadleaved weeds accounted for 87.9% and 95.6% of the total population in both years. The most prominent species were Amaranthus retroflexus (redroot pigweed.), Portulaca oleracea (common purslane), Chenopodium album (common lambsquarters), and Conyza canadensis (horseweed). Weed density varied with year and cover crop treatment. Weed density was low before cover crop kill and was similar in all treatments in the first year. During the following year, however, the bare ground system had more weeds than any of the cover crops early in the season. Weed densities measured during the cucumber growing season were higher in the bare ground system than in any of the cover crop systems. A total of 372 and 151 weed seedlings m-2 emerged in the bare ground treatment at 43 and 73 days after cover crop kill (DAK) respectively. At the same time, less than 70 weeds m-2 emerged in any of the cover crops used. In the second year, the weed populations were also different among cover crops. During the cucumber growing season, hairy vetch and sorghum sudangrass provided the greatest weed suppression. At 22 DAK, weed density was 3, 26, 118, and 202 plants m-2 for hairy vetch, sorghum sudangrass, rye, and bare ground, respectively. Similar results were observed at 40 DAK for weed density and weed biomass alike.
Sudangrass residue reduced weed density by 89.2% and 75.1% in year 1 and year 2 respectively, compared with no-cover crop treatment after 43 and 40 DAK. Rye and hairy vetch reduced weed densities by 84.94% and 82.5%, respectively. Generally weed suppression is correlated with biomass production of the cover crop. Decomposing residues provided physical and allelopathic effects that reduced both weed germination and growth. Plant residues were shown to lower soil temperatures, reduce diurnal temperature fluctuations, and act as a physical barrier to reduce weed seed germination (Teasdale, 1996). Residues of several legumes have been shown to have allelopathic potential (Weston, 1996) and the high weed suppression observed in hairy vetch plots could be due to this phenomenon.
Objective 4. Effects of cropping systems on yield and yield quality.
Benton Harbor Trial. In 2003, tomato yield was affected by the precious cover crop. This was observed for No1 large yield as well as total marketable yield. The cover crops used enhanced tomato yield at the exception of cowpea when it was grown throughout the previous summer. Tomato yield was 55 kg/plot in the control system and 60-62 kg/plot with the following cover crops: Cowpea and sorghum sudangrass (grown all summer) and cowpea sown after cucumber. When cowpea was grown the entire summer, yield was reduced to 45 kg/plot. Tomato was the first crop in the rotation after establishment of the cover crop treatments. In 2004, fresh market cucumber followed tomato in the rotation sequence. Unlike the cool season cover crops (rye and vetch), warm season cover crops (sudangrass and cowpea) affected yield of cucumber. Differences among treatments were observed after the 5th harvest. The greatest fruit yield was obtained in plots that were fallow with cowpea in 2002. This treatments produced the greatest number of fruits (148 000 fruits ha-1) compared to sudangrass (117 000 fruits ha-1). Our results suggest that the effect of cover cropping can last beyond one growing season. This observation supports the importance of crop rotation and cover cropping in developing sustainable cropping systems.
HTRC Trial. Among the cover crop treatments, marketable cucumber yield was generally highest in hairy vetch and lowest in and no-cover crop plots. In 2004, total marketable yield was 28, 24, 34, and 19 lbs/plot (100 square feet) in the sorghum sudangrass, rye, hairy vetch, and bare ground plots, respectively. In 2005, total marketable yield was 16, 18, 21, and 11 lbs/plot in the sorghum sudangrass, rye, hairy vetch, and bare ground plots, respectively.
There was little effect of the cover crop treatments on fruit quality parameters such as Brix value, specific gravity, and fruit firmness. The only difference observed was enhanced firmness of fruits from the cowpea treatments. But this effect was recorded only at the 6th harvest of the slicing cucumber in the Benton Harbor trial.
References cited
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Bottenberg, H., J.B. Masiunas, C. E. Eastman, and D.M. Eastburn. 1997a. The impact of rye cover crops on weeds, insects, and diseases in snap bean cropping systems. Journal of Sustainable Agriculture 9(2/3):131-155
Bottenberg, H., J. Masiunas, C. Eastman, and D. Eastburn. 1997b. Weed management effects on insects and diseases of cabbage and snapbean. HortTechnology 7(4):23-26
Gallandt, E. R., M. Liebman, and D. R. Huggins. 1999. Improving soil quality: implications for weed management. J. Crop Prod. 2:95-120.
Gregorich, E.G., Ellbert, B.H., Drury, C.F., Liang B.C., 1996. Fertilization effects on soil organic matter turnover and corn residue C storage. Soil Science Soc of Am. J. 60, 472-476.
Hall, J. K., N. L. Hartwig, and D. L. Hoffman. 1984. Cyanazine losses in runoff from no-tillage corn in living and dead mulches vs. unmulched conventional tillage. J. Environ. Qual. 13:105-110.
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Kuo, S., U. M. Sainju, and E. J. Jellum. 1997. Winter cover cropping influence on nitrogen in soil. Soil Sci. Soc. Am. J. 61:1392-1399.
Lundquist, E.J., 1997. Rapid changes in soil microbial biomass and carbon and nitrogen pools in response to agricultural practices. Unpublished Ph.D. thesis, University of California, Davis.
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Sainju, U.M. Singh ., B.P. Whitehead, W.F., 1998. Cover crop root distribution and its effect on soil nitrogen cycling. Agron. J. 90, 511-518.
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Educational & Outreach Activities
Participation Summary:
Thesis and dissertation
1. Selvaraj M. 2007. Cropping systems to improve cucumber-tomato production under short rotations. Master of Science Thesis, Michigan State University (in progress).
Papers and Presentations at Scientific Meetings
1. Ngouajio M and G Wang. 2006. Effects of planting density on canopy dynamics and yield of pickling cucumber grown for once-over machine harvest. Proceedings 5th National Integrated Pest Management Symposium, April 4-6 St. Louis Missouri. P. 83 (Abstract, poster presentation).
2. Ngouajio M., M. Selvaraj and E. Hill. 2005. Effects of cropping system on cucumber yield and quality. Pickling Cucumber Research Reporting Session. Jan 7, 2005 MSU (Oral presentation).
3. Ngouajio M., E. Hill, M. Selvaraj, and K. Charles. 2004. New research trends in weed science in the USA. Proceedings of the First Plant Protection Congress of Turkey, September 8-10, 2004 Samsun, Turkey P.1-7.
4. Selvaraj M. and M. Ngouajio. 2004. Effects of Cover Crops on Soil Microbial Biomass in Vegetable Cropping Systems. HortScience (Abstract) 39:871, (Abstract, oral presentation)
5. Selvaraj M., M. Ngouajio, D. Warncke, D. Mutch, and J. Ernest. 2003. Integrating Summer Cover Crops into Cucumber–Tomato Rotation. HortScience 28:808. (Abstract, poster, presentation).
Papers Published in Magazines and Newsletters
1. Ngouajio 2006. Pickle Field Productivity: Cover crops can help maintain high yields, but they should not be a substitute for crop rotation. American Vegetable Growers Magazine. April issue P. 16
2. Ngouajio 2006. Pest of the Month: Common Dandelion A.K.A. Taraxacum officinale G. H. Weber ex Wiggers. American Vegetable Growers Magazine. P. 8
3. Ngouajio M. 2006. Cover crop management in a warm spring for vegetable production. Vegetable Crop Advisory Team Alert newsletter Vol. 21, No. 3, May 10, 2006 P.1
4. Ngouajio M. 2005. Manage soil, manage weeds. The Organic Report. American Vegetable Grower. August 2005 P4. Note Permission was granted to the following Magazine to publish this article.(1) American Fruit Growers (Published in the August 2005 Issue), (2) Western Fruit Growers (Published in the August 2005 Issue), (3) Florida Grower (No feedback on publication process), and (4) Productores de Hortalizas (permission granted to Ana Reho, Managing Editor to translate and publish the article in Spanish)
5. Ngouajio M. 2005. Pest of the Month: Carpetweed (Mollugo verticillata L.). American Vegetable Grower. January 2005 P9.
6. Ngouajio M. 2004. Pickle Quality Starts in the Field. The vegetable Growers News November issue P. 64-65
7. Ngouajio M. 2004. It is time to put on the cover: Protect the soil after crop harvest. CAT Alert August 11, 2004 19(16):5-6
8. Ngouajio M. 2004. Know your cucumber plant for improved management. CAT Alert June 2, 2004 19(9):3-4.
9. Ngouajio M. 2004. Pest of The Month: Common lambsquarters (Chenopodium album L.). American Vegetable Grower Magazine April 2004, P. 8
Reports
1. Ngouajio M, E. Hill, G. Wang, and W. R. Chase. 2006. Long Term Effects of Soil Management with Cover Crops on Pickling Cucumber Production. 2005 Annual Report. Cucumber reporting session P.1-4
2. Ngouajio M. 2005. Using Cover Crops to Extend Productivity in Pickle Fields. Great Lakes Expo Proceedings 3p. http://www.glexpo.com/abstracts/2005abstracts/picklingcucumber.pdf
3. Ngouajio M., M. Selvaraj and E. Hill. 2005. Effects of cover crops on pickle production. Pickling Cucumber Research Reporting Session Report. MSU P.7-14. (REPORT).
4. Hausbeck M.K., R. Grumet and M. Ngouajio. 2005. Developing a cucurbit Production System that minimizes fruit rot. Pickling Cucumber Research Reporting Session Report. MSU P.22-25. (REPORT).
5. Ngouajio M., M. Selvaraj, D. Warncke, R. Goldy, D. Mutch and G. McManus. 2005. Cropping system to improve vegetable production under short crop rotation. 2004. SWMREC Annual Report. 6p. Available at URL: http://www.maes.msu.edu/swmrec/publicationsfolder/Annualreports/04annualrpt/croppingsystem_mathieu.pdf
6. Hausbeck M., R. Grumet, M Ngouajio and J. Breinling. 2004. Developing a Cucurbit Production System that Minimizes Fruit Rot. Project GREEEN # GR03-023 Final Report. 5 pages. Available at: http://www.greeen.msu.edu/July_04_Final/GR03-023.pdf
7. Hausbeck M., R. Grumet, M Ngouajio and J. Breinling. 2005. Reducing the Risk of Phytophthora Fruit Rot on Pickles. Project GREEEN No. GR04-023. 5 p. Available at: http://www.greeen.msu.edu/July_2005_FINAL/GR04-023_FINAL.pdf
8. Ngouajio, M., M. Hausbeck, D. Warncke, D. Mutch, S. Snapp, B. Zandstra, R. Goldy, J. Breinling, and G. McManus. 2005. Cropping System to Improve Vegetable Production Under Short Crop Rotation. Project GREEEN No. GR02-057. 6 p. Available at: http://www.greeen.msu.edu/July_2005_FINAL/GR02-057_FINAL.pdf
9. Ngouajio M. and W. Chase. 2004. Effect of Cover crops on pickle production: 2002-2003 report. Pickling Cucumber Research Report 2004, Michigan State University p.12-16.
Over 20 extension presentations at the local, regional, national and international levels
Project Outcomes
- Integrating cover crops into current rotation systems will be more attractive to the 1,550 Michigan vegetable growers than any technology that proposes major changes to their production system. Protecting the soil with cover crops between cash crop seasons has multiple benefits.
Our results have clearly shown that by using cover crops, vegetable growers can significantly reduce weed pressure in their farm. Reducing initial weed pressure improves subsequent weed control strategies like herbicide applications or cultivation.
Cover crops protect the environmental from nitrate leaching by trapping residual nutrients left in the soil after harvest of the cash crop and recycling these nutrients to the following crop.
Cover crops protect the ground from erosion, which is a major cause of loss of productivity on most agricultural lands.
Cover crops improve biodiversity; increased soil microbial activity, which could promote more resilient systems for long-term productivity.
Hairy vetch, a legume cover crop, fixed 50 pounds of nitrogen per acre. With a total of about 177,000 acres of vegetables in Michigan, this will correspond to 4,000 tons of nitrogen. This will result in significant savings to the industry and 4,000 fewer pounds of synthetic fertilizers applied.
Our findings were presented at the Great Lakes Fruits, Vegetables and Farm Market Expo in 2004 and 2005, American Society for Horticultural Sciences meeting in 2004 and 2005, and Weed Science Society of America Annual meeting in 2005, North Central Weed Science Society meeting in 2004 and 2005, and at various growers meetings.
Economic Analysis
Not Applicable
Farmer Adoption
- This study was conducted at a commercial farm. The year following initiation of the experiments, the grower cooperator planted 7 acres of cowpea cover crop and was highly satisfied with the results. In 2004, another grower who attended one of our presentations on the project requested our expertise to help him design a cover crop program for his organic farm. As a result of our effort, that grower received a SARE Producer Grant to work on cowpea and sorghum sudangrass cover crops. The work was successfully completed in summer 2005.
Other farmers, including carrot, celery, onion, growers have adopted our results and are using cover crops when ever the conditions allow.
The most challenging thing so far has been availability of seeds with some of the cover crops that growers are interested in. This includes cowpea, mustard, oilseed radish, and sorghum sudangrass.
Areas needing additional study
- The cover crops tested in this study allowed to improve crop yield in most cases, however, several questions remain unanswered.
Tomato yield was reduced following a system where cowpea was grown throughout the previous summer. Also, we found that planting cucumber shortly after hairy vetch kill tended to reduce yield despite the large amount of nitrogen fixed by the hairy vetch cover crop. These two observations strongly suggest that cowpea and hairy vetch might produce allelopathic compounds.
The cover crops used increase soil microbial activity. Studies to understand changes in soil microbial community structure in response to various cover crops would help better understand and improve the role of cover crops in cropping systems.
This study looked at the short-term (two years) effects of the cover crops. Long-term studies may help better understand how cover crops affect soil chemical and biological properties.