Cover Cropping and Residue Management for Weed Suppression, Soil Fertility and Organic Crop Production
Following edamame soybean harvest and summer mowed fallow, cereal rye winter annual cover crops was planted in 5 of 7 treatment plots in the fall of 2003. The rye was killed in early May and the residue managed as per protocols (strip-till, mow, roll, incorporate, herbicide). The other two treatments (crimson and subteranean clover) reestablished from previous season volunteer seed. An heirloom flint corn, ‘Abenaki Calais’, was seeded in late May. Plots were split, and the equivalent of 120 lbs of N per acre of composted dairy manure and feather meal were applied to organically managed sub-plots. Herbicide plots received 120 lbs of N as ammonium nitrate. Rainfall was limited and germination and early season growth poor. The corn was quickly overtaken by weeds, primarily nutsedge, spiny amaranth, and lambsquarter. Much of the weed pressure derived from seed in the poorly composted dairy manure. In an effort to save the corn crop, harvest interrows were mowed with rotary mowers and string trimmers in mid-June. Weed pressure was only temporarily relieved and soon thereafter, the corn crop completely overtaken in crimson and suberanean clover treatments and in all rye treatments except the herbicide treatment. However, even in the herbicide treatment, the crop was stunted due to weed pressure and limited rainfall early in the season. Because of poor overall grain yields due to weed, drought, and disease (smut) pressures, no yield data was collected. In this season, organic weed control treatments were a total failure. The third year of this project envisioned demonstrations of successful organic weed control strategies at three locations (Fletcher, Goldsboro, Clemson). The principal investigators felt that these demonstrations would not be advisable given limited weed control effectiveness of the experimental treatments. The project protocols were changed to add an additional year in the field, planting edamame soybean following winter annual cover crop treatments. In an effort to reduce weed seed stocks, all plots were deep plowed to bury weed seed deposited on the surface. Additional effort (timing, seeding rate, soil preparation) was made to ensure a better stand of the winter cover crops so that biomass and allelopathic potential was maximized for the 2005 growing season.
1. Investigate the weed suppression of crimson clover, rye, and crimson clover/rye biculture cover crops prior to the establishment of principal crops and in the subsequent vegetable soybean and corn crops.
2. Evaluate techniques for mechanically killing cover crops as alternatives to use of herbicides.
3. Investigate the reseeding capacity of crimson clover left to mature in a strip crop tillage system.
4. Investigate the N contribution of a cover crop biculture (crimson clover/rye) in a cereal rye-edamame-crimson clover/rye biculture-corn rotation.
5. Characterize N cycling in a cereal rye-vegetable soybean-crimson clover/rye biculture-corn rotation.
6. Publish results, demonstrate successful production practices to growers, produce written production guidelines, and discuss results at professional and county meetings, conferences, and field days.
With regard to the accomplishment of the project objectives, the following observations can be made. Weed suppression of crimson clover, rye, and crimson clover/rye biculture cover crops in the subsequent vegetable soybean and corn crops is minimal, particularly with poor, cereal rye stands. Mechanical kill of cover crops with mowing, rolling, incorporation and strip-tilling is a viable alternative to herbicides for killing cover crops in no-till systems. Allowing crimson and subteranean clover to mature seed in interrows between strip-tilled planting rows is a viable means for reseeding those cover crops in the subsequent fall. Full stands can be expected (though subsequent pressure from curly dock reduced stand). No bicultures were planted in the cereal rye-corn treatments and plots were split instead with the equivalent of 120 lbs N ac-1 organic fertilizer. These fertilizer treatments were very effective in promoting weed growth. Nutrient budgets are currently under study. No publications or additional outreach activities have been conducted at this time.
Impacts and Contributions/Outcomes
At this point, with one growing season remaining, no outcome metrics have been evaluated. However, results to this point indicate that outcomes might be quantified in terms of growers NOT attempting to control weeds in organic no-till systems with winter annual cover crops.
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