Parcelamento da cobertura nitrogenada do algodoeiro

The advantage of parcelling out the side dressed nitrogen in cotton crop was studied in twenty four-field experiments, conducted on different soils of the major producting regions of the State of Sao Paulo, Brazil, during the period from 1975 to 1984. Doses of 0, 25, and 50kg/ha of N were side dressed, just after thinning, with the purpose of studying the effect of rate of nitrogen application. In other three treatments, the highest dose was splitted, half at thinning and half at delayed stages, at 45-55, 65-75 and 85-95 days after plant emergency. Ammonium sulphate was used in those treatments. In an extra treatment urea was side dressed at thinning at the rate of 50kg/ha of N. A Latin square experimental design was used. Generally the effect of nitrogen on cotton yield was related more with the intensity of previous cultivation than with soil texture. Cotton grown after pasture, on sandy soils, presented low response to nitrogen application, whereas on sandy-clay and heavy-clay soils intensely cultivated, the effect of nitrogen fertilization was positive and highly significant. Split application of nitrogen did not show any advantage over one side dressing even in the groups of soils of high response to fertilization. Otherwise, a tendency to lower yields was observed with the delay of the split application. Thus, for cotton grown on sandy-clay and heavy-clay soils, it is recommended that the nitrogen be side dressed just after thinning, provided that the soil moisture is adequate. Further studies are needed on the use of nitrogen fertilizers on sandy soils.