Cover crop, nitrogen, and tillage effects on cotton as indicated by petiole analysis

Soil erosion is a major problem in the Southeast. This, coupled with the increasing cost of nitrogen fertilizer, has made no-tillage and the use of leguminous cover crops more attractive. Many problems have been solved in no-till grain crop production, whereas very little research has been done in no-till cotton production, especially involving legume covers. Field experiments were conducted at Jackson and at Milan, Tennessee, during 1981 and 1982. Objectives of these experiments were to determine the effect of different cover crops, tillage systems, and nitrogen rates on cotton height and lint yield. The tillage systems were conventional (CT) and no-tillage (NT). The covers were no winter cover (NC), rye (R), vetch (V), or a rye-vetch (RV) mixture. The four nitrogen rates were 0, 34, 67, or 101 kg/ha. Petiole analysis was used as a possible indicator of the plant N status. Ammonium nitrate or foliar urea (F) was applied based on this analysis. Petioles of cotton grown in vetch had high NO₃-N content, while those of cotton following rye were low. No cover and rye-vetch produced cotton petioles with intermediate NO₃-N content. In 1981 cover affected petiole NO₃-N content at Jackson, and cover by tillage interactions and N rate affected petiole NO₃-N content at Milan. In 1982 cover, tillage, and nitrogen interacted to affect petiole NO₃-N at both locations. Petiole NO₃-N content increased with increasing N rate; however, even at higher N rates, petioles of cotton grown in rye were deficient in NO₃-N. Cotton grown in NC produced the highest yields followed by R and RV. Where cover was present, CT cotton outyielded NT. Cotton grown in V grew more vegetatively, matured later, and had lower lint yields.as compared to other treatments. Cotton grown in NC and R matured earliest, with that grown in RV being intermediate in maturity. Foliar fertilization had no consistent effect on lint yield. Changes in lint yield were minimal and were of no practical significance. Yields were not significantly different in the NT-NC cotton and CT-NC cotton. Yields were reduced when cotton was no-tilled into a heavy mulch. Tillage in the absence of a heavy mulch was not necessary for maximum yields.