COTTON YIELD AND FIBER QUALITY RESPONSE TO GREEN MANURES AND NITROGEN

The quantity and availability of N from green manures will considerably affect the N management of a succeeding cotton (Gossypium hirsutum L.) crop. This study was conducted to determine the N supplying capacity of crimson clover (Trifolium incarnatum L.), Austrian winter pea [Pisum sativum subsp. arvense (L.) Poir.], and rye (Secale cereale L.) to cotton and their influence on cotton yield and fiber properties. Green manure treatments (and a fallow check) with fertilizer N levels of 0, 56, 112, and 168 kg ha-1 were compared for 3 yr on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Kandiudult). Soil moisture at planting was similar among the four green manure treatments. At the 0 N level, the legumes generally had higher soil NO3-N than rye or fallow. Cotton grown following clover and pea with 0 kg ha-1 added N had petiole NO3-N levels similar to those of rye and fallow with 56 kg N ha-1. Fertilizer N had no influence on cotton yield in the pea winter cover treatment. A quadratic regression equation best described the lint yield response following clover. For both rye and fallow treatments, yield plateaued at 56 kg N ha-1. Green manures had little influence on fiber properties. The results indicate that legumes supply adequate but not excessive N for modern cotton production and that incorporation of rye into the production system does not affect N fertilization requirements.