Cover Crop Integration Into Conservation Production Systems For Cotton and Sorghum

Cover Crop Integration Into Conservation Production Systems For Cotton and Sorghum

Summary

This project will make cover crops more attractive by reducing their cost and developing easier ways of managing them. Specific objectives are:
1) Identify legume cover crop germplasm with superior reseeding characteristics
2) Demonstrate practical management systems that reduce the need for herbicides in no-till and low-till crop production.

Approach
Cover Crop Nursery Evaluations: Legume cover crop germplasm were screened at several locations representing a range of soil types and climatic zones varying from the gulf coast to northern Tennessee, and from Georgia to western Arkansas. ‘Tibbee’ crimson clover was used as a standard against which 17 other cover crops are compared seeking a superior combination of winter hardiness, vigor, early maturity and hard seededness. Additionally, over a two-year period seed of one promising new legume cover crop, balansa clover (Trifolium balansae), which was identified in this project as possessing superior reseeding potential, was distributed to fifteen farmers who responded to articles in Common Ground and Agriculture Research magazines for evaluation on acre-sized areas. A follow up survey was sent to these producers to obtain input and many responded.

Seed increase of another promising reseeding, spotted burclover (Medicago arabica (L.) Hudson) continued in cooperation with the USDA-NRCS Jamie Whitten Plant Materials Center in Coffeeville, MS. Detailed observations were made of the growth of spotted burclover in order to relate time after flower blooming to the production of hard seed.

Management System Evaluations: Management systems being evaluated in replicated-plot and on-farm studies include demonstrating mechanical killing cover crops ahead of no-till planting of cotton and other crops, testing planter attachments to facilitate the planting of cotton through the cover crop residues, and evaluating the ability of the residue mulches to reduce weed competition with summer crops. A Mowing Date Study compared mowing vetch, rye, or rye plus vetch 0, 2, 6, 14, or 26 days ahead of no-till cotton planting in early May and tested four commercial residue management planter attachments. A Cover Crop X Weed Control Study compared four winter cover crops (vetch, rye, rye plus vetch, or volunteer vegetation) and four weed control treatments (ranging from no-till with broadcast preemergence and postemergence herbicides to a minimum herbicide treatment involving mechanical and flame cultivation) for cotton production. Soil temperature, cotton growth, and weed populations were conducted in cooperation with Steve McKaskle in Braggadocio, MO; Steve Parks and Lorna McMahon in Tiptonville, TN; David Denton in Tyronza, AR; and Jim Whitfield in Yazoo City, MS.

A video describing the work done in this project was finalized and distributed. The project coordinator participated as an editor of the revision of the SAN cover crop book so that the information gained in this project are reflected there.

Results
Reseeding legume cover crops: This work identified two promising new legume cover crops: southern spotted burclover and ‘Paradana’ balansa clover. Both these cover crops mature seed slightly earlier than crimson clover, although they often do not produce as much biomass. Their big advantage over crimson clover is their ability to reseed for several years from a single seed crop. Both have volunteered back for four years following maturation of a seed crop in 1993 in Senatobia, MS and they have also reseeded successfully for at least two years at several other locations in AL, GA, and MS. Neither Tibbee nor ‘AU Robin’ crimson clover reseeded for more than one year at any location.

Unlike crimson, clover, whose flowers open nearly at one time, spotted burclover, like other medics and subterranean clover, flower over a period of several weeks, producing clusters of three to five flowers on successive main stem nodes about 2.5 to 3 days apart. Although burs reached nearly maximum size by 14 days after bloom, seeds continued to accumulate mass for about 50 days. About 50% of seeds became viable and hard after about 30 days. This percentage increases to nearly 90% by 40 days.

Insect pests, the clover leaf weevil (Hypera punctata Fabricius) and the alfalfa weevil (Hypera postica Gyllenhal), preferentially attack medics over other winter legume cover crops and delay and reduce seed development. Cold and insect damage to the local spotted burlclover accession has not been as severe as to the commercial (Australian) annual burclovers.

Because insect feeding often damages later burclover flowers, most of the productive flowers open within the first 10 days of first bloom. Thus most seed is formed by 40 to 50 days after first bloom. If first bloom occurred on 23 March, this translates into a viable seed crop by 2 May, and maximum seed formation by 12 May. By allowing the cover crop to grow until the 40 to 50 days after first bloom and managing the cropping system without tillage that would bury burclover seeds too deeply, spotted burclover should successfully reseed for several years.

Although no insect control measures were taken and insect damage did not eliminate reseeding in these studies, in a commercial seed production enterprise or in the first year of seeding a cover crop, insect control when weevils are in their second instar growth state, possibly using pyrethroid insecticides or parasitic wasps, would significantly increase seed yield if weevil pressure is heavy.

Regional evaluation of balansa clover by producers resulted in mostly favorable reviews. Most farmers managed the clover as a forage crop rather than as a cover crop. Several correspondents also noted that it seemed to be favored by honey bees.

Mechanical control of cover crops: Mowing was effective in killing rye and vetch over crops during late April. Cover crop residues dry rapidly after mow-killing. Use of tined-wheel row cleaners enabled successful no-till cotton planting only two to six days after mow-killing dense cover crops, but row cleaners became wrapped up with vegetation when planting was done same day as mowing while the residues were still moist and flexible at Steve McKaskle’s farm.

Heavy cover crop mulches did not eliminate the need for supplemental chemical and/or mechanical weed control. However, cover crops permitted no-till cotton to be produced using a banded herbicide application comparable to that used in conventional-tilling culture.

Impact and Benefits
These studies demonstrate two ways that farmer can increase their production efficiency and build their soil quality without increasing their production costs. The farm and society both benefit from decreased run-off and erosion losses and improved water quality.

Reseeding cover crops offer the benefits of increased organic matter inputs to soil and reductions in needs for purchased nitrogen fertilizer without the expense of seeding a cover crop each fall. If the cover crops are planted on time and managed to produce a heavy seed crop the first spring, the farmer could save $25/acre cover crop seeding costs plus $15/acre in fertilizer savings (50 lb/a) for the following three to four years even in crop rotations where the cover crops cannot make seed each year.

Alternatively, planting heavy residue-producing cover crops like rye and hairy vetch can offset herbicide costs in no-till systems. These cover crops mature seed too late in the spring to reseed by themselves, so they must be planted each fall. However, they shade out undesirable species and can themselves be killed by mowing or rolling and so can permit no-till planting without the need for burndown herbicides. The resulting mulches assist with weed control so that total herbicides can be restricted to a band over the row at rates no higher than are used with conventional tillage culture. In this system, the farmer can get the soil and water conservation benefits of no-till using cover crops and pay for the cover crop planting costs with savings in herbicide expenses.

Both of these approaches benefit consumers by maintaining a cleaner environment while producing crops with maximum efficiency and minimum cost.

December 1997