Weed Control in Reduced Tillage Cropping Systems: Use of Overseeded Cover Crops
Technologies are urgently needed by farmers for ecological weed control in cropping systems that allow them to conserve soil and water resources and observe conservation compliance guidelines. The principles tested in these unique systems include shading weeds with standing cover crops, smothering weeds with mown cover crops, and generally preempting the niches that weeds tend to fill when the ground is left bare, as in conventional cropping systems. In this project, collaborators at four locations spanning the climatic range of the northeastern US are performing experiments to determine the feasibility of controlling weeds in no-till and reduced-till cropping systems with the use of fall-sown cover crops.
The work at Cornell University is focused on developing no-till grain and soybean production systems without the use of herbicides. The basic strategy is to use relay cropping to keep weeds suppressed by crop competition. They are also exploring methods for improving establishment of aerially overseeded crops. Preliminary results indicate that direct overseeding of winter grains into standing corn can approach commercial yields, even under less than ideal weather conditions.
Although buckwheat is notoriously hard to establish by surface sowing, both pelletized and presoaked buckwheat seed established well. Unfortunately, subsequent growth was poor, apparently due to competition rather than to soil or weather conditions.
Establishment success of aerial overseedings into corn and beans tends to be inconsistent between years and even from one part of a field to another. Several satellite trials run to test methods for improving establishment of oversown small grains and legume cover crops indicated that pelletizing the seed of buckwheat and spring barley (Birka) greatly improved the germination of both species in all watering regimes. Weed control by rye mulch was very good.
In experiments conducted at USDA/ARS in Beltsville, MD, investigators found that planting corn in 15-inch rows rather than the standard 30-inch rows improved performance of low-input treatments. Use of higher corn plant densities may be an effective safeguard against years when cool, wet soils predominate and can provide additional competition for weed suppression.
Rye as a cover crop appears to suppress soybeans, dry beans, and corn. One of the highest-yielding treatments was corn no-till planted into hairy vetch (not significantly different from conventional treatments). Weather conditions and soil drainage properties play a large role in achieving success with cover crops.
The Low-Input Reduced Tillage experiment at Rodale Research Center is attempting to combine what farmers are learning about reduced tillage, ridge tillage, and especially no-till (mow-sow) planting into cover crops with what has been learned about how to grow crops without purchased fertilizer or pesticides. Once the experiment has gone through one or two rotation cycles and the tillage systems are well established, this trial will be a valuable testing ground where agronomic questions can be answered about system feasibility, and energy and economic comparisons can be calculated from a realistic, multi-year data set.
(1) Develop reduced-tillage systems without herbicide that provide adequate weed control, reasonable yields, and improved net profits for farmers. Such systems will eliminate risk of groundwater contamination from herbicides.
(2) Use mulch and relay cover crops to significantly reduce the establishment of annual and perennial weed seedlings and the spread of perennial weeds from vegetative propagules.