Cropping System to Improve Vegetable Production Under Short Crop Rotation
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 yield. 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.
1. Effectiveness of summer and winter cover crops at improving soil fertility under vegetable production systems.
2. Effect of the cropping systems on soil microbial activity.
3. Effects of cropping systems on weed populations.
4. Effects of cropping systems on cucumber yield and yield quality.
Objective 1. In 2004 and 2005, a total of 15 cropping systems, resulting from combinations of summer and winter cover crops, were tested under field conditions at a grower’s farm and at the research station. The summer cover crops included cowpea and sorghum sudangrass and the winter cover crops tested were cereal rye and hairy vetch. A tomato-cucumber rotation was used as the model system. Results indicate that both summer and winter cover crops can be successfully integrated into the cropping system after cucumber harvest. However, only winter cover crops could be grown during tomato years because of its longer growing season. The amount of residue produced by the different summer cover crops varied significantly. The greatest amount of biomass (about 10 t/a) was produced in the sorghum sudangrass system. Biomass produced by cowpea was less than 2 t/a. Rye and vetch produced 4.6 and 3.4 t/a of biomass, respectively. 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 2. Soil microbial activity was assessed as an indicator of the ability of cropping systems to improve soil quality. Soil respiration and microbial biomass showed a clear increase after cover crop incorporation, with about 50% increase in microbial biomass at 4 weeks after cover crop incorporation. Microbial biomass was greater in soils collected from plots previously grown with cereal rye or hairy vetch compared to the system without cover crops. High microbial biomass in the soil is indicative of sustainable management. Therefore, integrating cover crops into short crop rotations could enhance the population of microorganisms in the soil and build a more resilient system.
Objective 3. All cover crop treatments showed lower weed populations compared with the bareground system. Because of the low amount of residue produced in the hairy vetch plots, allelopathy is possibly responsible for the high level of weed suppression. Further studies will be conducted to test the allelopathic potential of hairy vetch.
Objective 4. All cropping systems with cover crops increased cucumber yield. However, the timing of cucumber planting following incorporation of hairy vetch was critical. It appeared that planting cucumber too soon after hairy vetch kill may injure cucumber. The hypothesis is being tested.
All data collected from this study are currently being analyzed for final report.
Impacts and Contributions/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; increase the population of beneficial soil micro organisms, thereby building a more resilient system 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.
Michigan State University
East Lansing, MI 48824