Winter Annual Cover Crops in a Virginia No-till Cotton Production System: I. Biomass Production, Ground Cover, and Nitrogen Assimilation

Abstract

Cotton (Gossypium hirsutum L.) may not provide sufficient surface residue to reduce erosion and protect the soil between crops. A winter annual cover crop might alleviate erosion during the time between cotton crops. This experiment was conducted to evaluate selected winter annual cover crops for biomass production, ground cover, and aboveground N assimilation. Six cover crops, crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia vilosa L.), hairy vetch and rye (Secale cereale L.), rye, wheat (Triticum aestivum L. em.. Thell.), and white lupin (Lupinus albus L.), and two tillage systems (conventional and no-till) were arranged in a split block design with four replications. Percentage ground cover measurements were taken each year prior to desiccation and immediately after cotton planting for 1995 and 1996. In 1997, additional measurements were taken 50 d after cotton planting. Hairy vetch + rye, rye, and wheat provided the most ground cover after cotton planting, while lupin provided the least. All cover crops, with the exception of lupin, provided enough ground cover (>30%) after cotton planting to comply with Natural Resource Conservation Service conservation standards, except during years with below normal winter temperatures. Fifty days after cotton planting, small grain residues provided more (P < 0.05) ground cover compared with legume residues. Averaged over the three experimental years, biomass production from the different cover crops ranged from 946 to 3,047 kg ha-1. The average amount of aboveground N assimilated by cover crops ranged from 32 to 78 kg N ha-1, and was closely related to the amount of cover crop biomass produced. Growth and biomass production of cover crops was greatly affected by the climatic conditions during each season. C is grown on approximately 42,000 ha annually in Virginia. The production area has increased four fold since 1993. Although most of the cotton is grown in the Coastal Plain, cotton acreage is increasing in the southern Piedmont region, where the topography confines agricultural production to small fields with significant slopes that are not well suited for cotton production. Cotton is considered a low residue crop that may not provide sufficient surface residue to reduce erosion and protect the soil. Denton and Tyler (1994) reported the use of winter annual cover crops in a no-till cotton production system as an economically feasible approach to control soil erosion problems. Winter annual cover crops can provide the required surface residue to comply with the Natural Resource Conservation Service (NRCS) conservation tillage Code 329 standards (Bauer and Busscher, 1996). NRCS standards require 60 % ground cover remaining on the soil surface after cotton planting for no-till practices and 30% ground coverage after cotton planting for minimum tillage practices (NRCS, 1992(a)). In addition to erosion control, cover crops can enhance soil productivity and sustain water quality. After many years of conservation tillage research in Tennessee, Bradley (1995) states that cover crops supply significant amounts of organic matter to the soil and, with time, improve soil tilth, moisture holding capacity, cation exchange capacity, and overall productivity of the soil. Surface residues slow the velocity of runoff water and enhance infiltration and percolation of water via improved soil structure (Moseley et al., 1996). Cover crops assimilate N into plant biomass, reducing the potential leaching of nutrients and contamination of surface and ground water (Meisinger et al., 1991). Thompson and Varco (1996) reported that leguminous cover crops can biologically fix N needed for the following cotton crop, decreasing fertilizer expenses. Small grain cover crops recycle residual soil nutrients from the previous growing season (Breitenbeck and Hutchinson, 1994). Smart and Bradford (1996) found in addition to protecting the soil and water by using a conservation tillage system, fuel, labor, equipment expenses, and time are saved by eliminating seedbed preparation and the need for large, high-powered cultivation equipment. The magnitude of the beneficial effects from the cover crops depends on the amount of biomass produced by the cover crop (Holderbaum et al., 1990). Munawar et al. (1990) reported that the amount of biomass (kg ha-1) produced by cover crops and the distribution of the residue remaining on the soil surface is important to the effectiveness of the conservation tillage system. Biomass production directly affects soil properties and water quality in an agricultural system. If the amount of cover crop biomass is too thick it may interfere with proper seed to soil contact at cotton planting. Without proper equipment adjustments, too much 76 JOURNAL OF COTTON SCIENCE, Volume 3, Issue 3, 1999 Table 1. Cover crop desiccation and cotton planting dates, and herbicides used at planting for the 1995, 1996, and 1997 cotton growing seasons in the Piedmont of Virginia.. Year Cover crop desiccation date Cotton planting date Herbicides used at planting for no-till cotton weed management