2007 Beltwide Cotton Conferences, New Orleans, Louisiana, January 9-12, 2007 6633 1832 2007 Beltwide Cotton Conferences, New Orleans, Louisiana, January 9-12, 2007 COVER CROP MANAGEMENT PRACTICES: IMPLICATIONS FOR EARLY SEASON WEED CONTROL IN CONSERVATION TILLAGE CORN COTTON ROTATION Monika Saini Auburn University Auburn, AL Andrew J. Price USDA-ARS Auburn, AL Edzard Van Santen Auburn University Auburn, AL Abstract Use of the winter cover crops is an integral component of the conservation systems in corn (Zea mays L.) and cotton (Gossypium hirsutum L.). A field experiment was initiated in 2004 to evaluate weed suppression provided by winter cover crops in a conservation tillage corn and cotton rotation. Rotation for winter cover crops included clover (Trifolium incarnatum L.) preceding corn and rye (Secale cereale L.) preceding cotton. Both covers were planted at five different planting dates with the median date corresponding to the thirty year average first frost. Termination dates in the spring were 4, 3, 2 and 1 week prior to cash crop planting, based on thirty year average soil temperature. Results showed a dramatic impact on biomass production with even a week’s delay in winter cover crop planting and corresponding reduction in summer annual weed suppression. More than ten times difference in biomass produced by clover was observed when clover was planted on the earliest and terminated on last date compared to late planting and early termination. Rye produced almost eight times more biomass in the same comparison. Correspondingly, weed biomass was 556 kg/ha in the treatment with least rye biomass, 8 times higher compared to the treatment with greatest rye biomass. Weed populations observed in clover were less than in rye even though the difference was only 34 kg/ha in case of clover. The data for the first two years show no significant relationship between cover crop biomass and the cash crop yield. Introduction Use of conservation tillage systems for cotton and corn production has become increasingly popular in the last two decades primarily to address concerns of decreasing air and water quality and soil productivity. Use of high residue cover crops is an integral component of conservation tillage systems. Cover crop residue provides soil with a cover which plays a vital role in reducing erosion, improving infiltration, soil moisture retention carbon sequestration, increasing soil organic matter and nutrient recycling (Blevins et al. 1971; Bradley 1995; Kaspar et al. 2001; Reeves 1997). Raper et al. (2003) in research conducted on Coastal Plain soils in southeastern USA established that it is essential to include cover crops as an integral part of conservation tillage cotton systems. Effective weed management throughout the growing season is a critical component in cotton production. Cotton can not compete effectively with weeds early in the season and presence of weeds late in the season can reduce the harvesting efficiency and can also adversely impact the lint quality. Approximately 90% of the cotton grown in United States in 2001 received herbicides (Anonymous 2002). Development of herbicide resistant weed species and shift in the weed populations are the results of such extensive chemical control. Practical alternatives to the intensive use of herbicides for controlling weeds in cotton production therefore offers economical as well as environmental benefits. Winter cover crops also play an important role in weed suppression. Weed control by using cover crops is gaining more importance in today’s conservation tillage systems when an increasing number of weed species are acquiring resistance to herbicides. Previous research has shown that early season weed control by using cover crops with conservation tillage systems is comparable to chemical control in many situations (Teasdale and Mohler, 1992; Johnson et. al. 1992). The degree of weed control provided by a cover crop depends on the management strategies.