DESEMPENHO DA LAVOURA DE TRIGO E ATRIBUTOS DO SOLO EM RAZÃO DE FONTES E DOSES DE NITROGÊNIO EM SEMEADURA E COBERTURA

Abstract

Nitrogen fertilization of wheat remains under discussion, especially in no tillage (PD), whereupon the management nitrogen (N) rates in sowing and as topdressing may alter yield, depending on N source used. The objective with this work was to evaluate the Management of wheat nitrogen fertilization under PD using the sources urea, urea treated with urease inhibitor (ureia + NBPT) and ammonium nitrate (NA), applying 0, 40 and 80 kg ha?¹ of N in sowing furrow and/or as topdressing. The managements with growing total N rate resulted in increasing N levels on wheat flag leaf, whose values with source NA were never overcome by other sources. The thousand grain weight (MMG) for NA source was inferior to that obtained with other sources in 2011, and in 2013 the MMG with urea + NBPT was higher in relation to urea alone, and the managements with lower N rates had higher MMG. Grain yield and N accumulation in grains had similar behavior in relation to the sources, with NA being superior to other sources in 2012, under a water deficit condition, and urea + NBPT being superior to NA in 2013, under normal water condition. The managements with growing N rates resulted in higher yield and N accumulation in grains. The addition of NBPT to urea decrease soil pH in relation to urea alone, in different evaluated soil layers, but without difference to NA source. This behavior of soil pH was influenced by climatic variation in the crop seasons. Among N managements, 0+40 and 80+40 kg ha?¹ of N normally acidified the soil in relation to other treatments. For the NO3- and NH4+ levels into the soil, no differences were observed until 20 cm depth in 2011, but in 2012 and 2013 the urea + NBPT source showed lower NH4+ levels in relation to NO3- in comparison to urea, due to nitrification. At the 20-40 cm layer, no source effect was observed. In 2011 and 2013, when yield and N exportation were high with managements of 40+40 and 80+80 kg ha?¹ of N, the NH4+ and NO3- soil levels decreased to the levels observed with control (0+0 kg ha?¹ de N), low in this case because no N was applied with mineral fertilizer. In 2012, control revealed soil N levels normally lower in relation to other managements, for NO3- and NH4+, once with water deficit there was lower plant absorption, causing mineral fertilization to maintain higher N levels in the soil.