In the 1990’s, research at the University of Missouri-Delta Center at Portageville showed significant cotton yield increases from planting wheat cover crops in the row middles for wind protection (Stevens, et al, 1996). Cover crops protect cotton seedlings from blowing sand and minimize replanting. The objective of our current study is to evaluate mixtures of cover crops including radishes and cereal rye for increasing rainfall and irrigation infiltration, enhancing nutrient availability, and reducing root knot nematodes.
Field trials at Portageville and Clarkton showed that achieving a clover stand and keeping it through a cold winter is easier on silt loam than on sandy soils. Seedling survival was improved when clover was mixed with wheat. Generally, vetch was more winter hardy than clover. On large-scale strip tests at Clarkton over three years, cotton with 40 lb N/acre after vetch cover crop was compared to cotton with100 lb N/acre after wheat. Each year, cotton yields were either higher or the same using vetch with 60% less N fertilizer. However, vetch is difficult to kill and is a problem weed in wheat fields.
The Natural Resource Conservation Service is promoting soil quality programs with “cocktail” mixtures of cover crops. The idea is to have some type of live root growing in the soil 12 months a year to provide uninterrupted favorable conditions for symbiotic fungi such as mycorrhiza and predators to nematodes. Widmer et al. (2002) summarized research on cover crops and soil health management to reduce plant-parasitic nematodes. Myers (2002) cited anecdotal evidence that compounds in canola residue suppress nematode growth. Canola is in the mustard family with turnips and radishes. In Burleigh County, North Dakota, farmers plant a mixture of cover crops for grazing and hay rotated in alternate years with row crops such as corn. By minimizing soil disturbance with conservation tillage, farmers have created a healthy environment for microorganisms and earthworms. Beneficial fungi also help with crop phosphorus uptake and nematode control. The mucous secretions from the soil organisms increase soil aggregate stability which helps rainfall percolation and reduces runoff. Over the long-term, the farmers are using less fertilizer.
This project is evaluating new crop cover management practices. In North Carolina, boot growth stage cereal rye was killed without herbicide by snapping the stalk with a roller. Small seeded weeds such as pigweed often require light to sprout. The thick matt of rye residue laying on the soil surface helps prevent their germination. Radishes may be good cover crop for helping P uptake in cotton. It is easy to kill and produces good fall growth. White and Weil (2011) found that available soil P is concentrated in soil surrounding radish holes left by decaying taproot roots. In Northeast Missouri radishes are being used in corn/soybean rotations.
We learned from past cover crops tests that small plots do not provide a good evaluation of the effects of wind protection. Often “upwind” cover crop treatments have as much effect on the cotton seedling as the cover in the actual plot.
Plan of Work
Research is being conducted on sandy soil at Clarkton Missouri at the MU Rhodes Farm. Cover crop seeds were broadcast in September before cotton defoliation in wide strips across two ranges with the rows running with the prevailing southwest wind. A smaller test with radishes will be conducted beginning next fall on range which has high root knot nematode levels. Background and seasonal soil quality parameters will be measured for organic matter content, aggregate stability, water infiltration, soil CO2 respiration, bulk density, and residue cover. Soil pH, N, P, K and micronutrients and earthworms and nematode eggs will also be sampled. Cover crops will include wheat, Abruzzi rye, crimson clover, rapeseed, tillage radishes, and Austrian winter peas. Some rye plots will be rolled and some left standing before planting cotton. Strips will be maintained in the same location over the life of the study. Cotton plant population, growth stage dates, and yield will be recorded for each treatment.
Field Notes on March 20, 2012
Rainfall was low in September and October 2011 when we established the cover crops. This was our first experience with Austrian winter peas as a winter legume crop. Pea seeds are much larger in size than clover. They sprouted on the soil surface after a light rain but had a difficult time rooting into the dry soil. Ideally, they should be planted into the soil and covered rather than broadcast. But, to our surprise, the winter peas produced a better stand with more growth than crimson clover. Plant height of the peas is 3 to 10 inches and clover is 1 to 3 inches.
The winter of 2011/12 had above normal temperatures which probably helped the winter peas (left). Mid March is a rapid growth stage for winter cover crops. The closer that we wait to kill the peas with burndown herbicides the more N they will fix from the atmosphere. But they will pull more moisture from the soil which may inhibit cotton seed germination. Another potential problem is the vines on the pea plants could wrap around the planter row cleaners.
There is significant variability within plots in the stands of tillage radishes and rapeseed plants. Both brassica (mustard) species are flowering now. The radishes are 3 to 24 inches tall and the rapeseed is 3 to 38 inches tall. Although the radishes have long roots, part of the tap roots are above the soil surface and will not help loosen the subsoil.
The radishes roots that we cut with knives were hollow in the centers. We don’t know it this was caused by a pest or is normal for the crops. The above ground foliage looked healthy.
Some radish roots are completely dead in the middle of and others just had necrosis in the centers of the roots.
No nitrogen fertilizer has been applied to the cover crops other than residual N from last year’s cotton crop. Abruzzi rye is hardier and producing more biomass than the winter wheat. The rye is 7 to 32 inches tall versus wheat that is 4 to 9 inches tall.
In a multi-species cover crop mixture, domination of the grass crop at the expense of legumes and mustards may not be a good thing. Peas produce vines and can climb on rye or wheat which clover cannot do. We had a hard time finding the small clover crops in mixtures with grass species.
Austrian winter peas growing with Abruzzi rye.
Crimson clover, wheat, rapeseed mixture.
Because of the large, open fields, cotton farmers typically plow as little as possible to prevent loose soil from blowing in the spring. Ridge-tillage is a common practice. To improve drainage and soil temperature in the seed furrow, fields are typically hipped (rebedded) in the fall when wheat cover crop seeds are broadcast. In the current test, we not disturb the beds in the fall from the 2011 season. This helped promote a natural stand of henbit cover in our untreated check plots. We are looking at alternative management practices that will keep the height of the beds by running strip tillage equipment at planting or light cultivation in the row middles during the season.
Stevens, G., B. Phipps, and J. Mobley. 1996. Managing cotton for reduced wind damage with ridge till systems. In P. Dugger and D.A. Richter (ed.) Soil Management and Plant Nutrition Conf., Proc. Beltwide Conf., Vol. 2, p. 1403-1405. Nashville, TN, Jan 9-12, Natl. Cotton Council, Memphis, TN.
Myers, R. 2002. Canola-an emerging oilseed alternative. Jefferson Institute. Columbia, MO
White, C. and R. Weil. 2011. Forage radish cover crops increase soil test phosphours surrounding radish holes. Soil Sci. Society of America 75:121-130.
Widmer, T. N. Mitkowski, and G.S. Abawi. 2002. Soil organic matter and management of plant-parasitic nematodes. J. Nematology 34:289-295.