nitrogen fertilization in top dressing for wheat crop in succession to soybean under a no-till system

ABSTRACT Agricultural intensification to improve wheat yield has increased the demand for nitrogen fertilizers. This study aimed to investigate the wheat response in succession to soybean due to application of nitrogen rates and sources in top dressing, as well as to determine the N rates of maximum technical yield (MTY) and maximum economic yield (MEY). A field experiment was carried out in Ponta Grossa, Paraná State, Brazil, on a clayey Typic Hapludox (Oxisol) under a continuous no-till. A randomized block design was used, with 3 replications in a 4 × 3 complete factorial arrangement. The treatments consisted of a control and 3 N rates at 40; 80 and 120 kg∙ha−1 as calcium nitrate (CN), ammonium sulfate (AS), and urea (UR) in top dressing at tillering of wheat crop. Increasing N rate in top dressing increased plant height, 1,000-grain mass, and grain yield, but it also favored the plant lodging and reduced the hectoliter mass of wheat. The N, P, Ca, and S concentrations in grains increased with N fertilization. MTY would be obtained at 96; 69 and 67 kg N∙ha−1 in top dressing, respectively, as CN, AS, and UR. Although CN proved to be an effective source of N for application in top dressing, its use was infeasible by the high cost of fertilizer. Both AS and UR showed economic viability, and MEY with these 2 sources would be obtained at a rate of 45 kg N∙ha−1 in top dressing for wheat yield of 4.0 t∙ha−1 in succession with soybean.