Fate of 15N-urea applied to wheat-soybean succession crop

Abstract

The wheat crop in São Paulo State, Brazil, is fertilized with N, P and K. The rate of applied N (0 to 120 kg.ha -1 ) depends on the previous grown crop and the irrigation possibility. The response of wheat to rates and time of N application and the fate of N applied to irrigated wheat were studied during two years. Residual N recovery by soybean grown after the wheat was also studied. The maximum grain productivity was obtained with 92 kg.ha -1 of N. The efficiency of 15 N-urea utilization ranged from 52% to 85%. The main loss of applied 15 N, 5% to 12% occurred as ammonia volatilized from urea applied on soil surface. The N loss by leaching even at the N rate of 135 kg.ha -1 , was less than 1% of applied 15 N, due to the low amount of rainfall during the wheat grown season and a controlled amount of irrigated water, that were sufficient to moisten only the wheat root zone. The residual 15 N after wheat harvest represents around 40% of N applied as urea: 20% in soil, 3% in wheat root system and 16% in the wheat straw. Soybean recovered less than 2% of the 15 N applied to wheat at sowing or at tillering stage. No Estado de São Paulo, a cultura do trigo é adubada, além de P e K, com N, cuja dose (0 a 120 kg ha -1 ) depende do cultivo anterior e da possibilidade de irrigação. A resposta do trigo às doses e épocas de aplicação e o destino do N aplicado foi estudada em dois cultivos de trigo, seguidos pela soja. Também se avaliou a recuperação do N residual pela soja cultivada nas mesmas parcelas após o trigo. A produtividade máxima estimada de grãos seria obtida com a dose de 92 kg.ha -1 de N. A eficiência de absorção 15 N-uréia variou de 52% a 85%. A principal perda de N, que variou de 5% a 12%, ocorreu através de volatilização de amônia proveniente da uréia aplicada na superfície do solo. Por lixiviação foi perdido menos que 1% do N aplicado, pois a água da chuva ou da irrigação foi suficiente para molhar somente a camada do solo onde se encontrava o sistema radicular do trigo. O N residual após o cultivo do trigo correspondeu a 40% do total aplicado, posto que 20% permaneceu no solo, 3% na matéria vegetal radicular do trigo e 16% na matéria vegetal da palha do trigo, depositada sobre o solo. A soja recuperou menos que 2% do 15 N aplicado no solo na semeadura ou no perfilhamento do trigo.Palavras-chave: adubação nitrogenada, eficiência, amônia, volatilização.A.E. Boaretto et al.

Ammonia volatilization from nitrogen fertilizers in no-till wheat and maize in southern Brazil

“…These mean air temperatures observed in winter in SP (Boaretto et al, 2004) were close to the mean temperatures recorded in the summer experiment with maize. In the first maize crop (2009/10), volatilization losses were highest in treatments with urea application in the morning and the afternoon with 13.2 and 12.2 % of applied N, respectively.…”

“…In an experiment with wheat in the winter in São Paulo State, Boaretto et al (2004) found N volatilization losses ranging from 5 to 12 % of N applied as urea, higher than those recorded in the winter in the South-Central region of Paraná. Possibly, the lower volatilization losses recorded in south-central of Paraná were related to lower daily temperatures (~14 °C), than in the Southeast region (~21 °C).…”

Nitrogen fertilizer (15N) leaching in a central pivot fertigated coffee crop

“…As already mentioned, in other regions and other experiments the N leaching component was always of minor importance. Reichardt et al (2009) also working with coffee found N leaching of 2.3% of the total N applied, Gava et al (2006) for corn and Boaretto et al (2004) for wheat reported losses of 1%, and Quiñones et al (2005 and for citrus under controlled environment found only 0.1% of N losses.…”

15N-labeled nitrogen from green manure and ammonium sulfate utilization by the sugarcane ratoon

“…Other authors have reported low recovery (about 3.5% of the N) by the second crop after sunn hemp cover crop (Silva et al, 2006) or hairy vetch (Vicia villosa Roth) plowed into the soil (Seo et al, 2006). Low recovery of residual N has also been observed for inorganic fertilizer sources: less than 3% of the N derived from fertilizers was taken up by soybeans (Glicine max (L) Merril) (Boaretto et al, 2004), maize (Silva et al, 2006), Seo et al (2006) or sugarcane (Saccharum spp.) (Basanta et al, 2003).…”