Fixação biológica de nitrogênio e fertilizantes nitrogenados no balanço de nitrogênio em soja, milho e algodão

Abstract

Resumo -O objetivo deste trabalho foi avaliar os efeitos da fixação biológica de nitrogênio (FBN) da cultura da soja, e a eficiência do uso de fertilizantes nitrogenados (EUFN) pelas culturas de milho e algodão, no balanço de N de um Latossolo Vermelho distroférrico, sob plantio direto, em Dourados, MS. O estudo foi feito em dois anos, concentrando-se nas safras de verão. A contribuição da FBN para a soja foi avaliada pela técnica de abundância natural de 15 N. A EUFN foi avaliada mediante a substituição dos fertilizantes nitrogenados convencionais pelos enriquecidos com 15 N, nas culturas do milho e algodão. No primeiro ano, foram adicionados 115 kg ha -1 de N, de forma parcelada, para ambas as culturas; somente a parte aérea das plantas foi avaliada. No segundo ano, somente a cultura do milho foi avaliada, tendo recebido 70 kg ha -1 de N aos 29 DAE. Nesse ano, além da parte aérea do milho, amostrou-se também o solo, na profundidade de 0-20 cm. Nos dois anos de avaliação, a FBN foi superior a 80% do N nas plantas de soja, o que resultou em alta produtividade e em balanço positivo de N para o solo. A EUFN na parte aérea de milho e algodão, no primeiro ano, foi de 48 e 61%, respectivamente. No segundo ano, a EUFN, na parte aérea do milho, foi de 46%, tendo-se observado que 24% do N do fertilizante permaneceu nos primeiros 20 cm de solo. Para os níveis de produtividade das culturas de milho e algodão, o manejo do fertilizante nitrogenado resulta em balanços negativos de N para o solo.Termos para indexação: 15 N, eficiência do uso de N, plantio direto. Biological nitrogen fixation and nitrogen fertilizer on the nitrogen balance of soybean, maize and cottonAbstract -The subject of this work was to evaluate the effect of biological nitrogen fixation (BNF) of soybean, and the nitrogen fertilizer use efficiency (NFUE) by maize and cotton, on the N balance of an Oxisol (Typic Haplorthox) under no-tillage, in Dourados, MS. The study was carried out for two consecutive years, focusing the summer crops. The BNF contribution to soybean was evaluated by the 15 N natural abundance technique. The NFUE was evaluated by the substitution of conventional N fertilizers used for maize and cotton crops by 15 N enriched ones. In the first year, both crops were fertilized with 115 kg N ha -1 split in three doses; only plant aerial parts were evaluated. In the second year, only the maize crop was evaluated and received 70 kg ha -1 N, as a dressing fertilization at 29 DAE. In that year, the aerial part of maize plants and the soil of a 0-20 cm layer were evaluated. For two consecutive harvests, the BNF contribution to soybean was over 80%, bringing about high yields and a positive N balance to the soil. In the first year, NFUE for aerial parts of maize and cotton were 48 and 61%, respectively. In the second year, NFUE for maize was 46%, and the soil layer of 0-20 cm also retained 24% of de N fertilizer applied. For the yield levels of maize and cotton, the fertilizer management results in negative N balances to the soil.Index-terms: 15 N...

Effect of fertilization at sowing on nutrition and yield of crambe in second season

“…According to Broch et al (2010), soybean residues provide successive crops with N remaining from biological fixation. Even though N exportation in soybean is relatively high, the N balance in the soil is positive after growing this leguminous crop (Alves et al, 2006). The K concentration was not affected by fertilization, probably because of the initial soil K contents of 4.4 mmol c dm 3 in 2010 and 3.7 mmol c dm 3 in 2011 in the experimental area, which is considered high (Raij et al, 1997).…”

Bradyrhizobium strain and the 15N natural abundance quantification of biological N2 fixation in soybean

“…Assuming an N content of the grain of 6.5% N, this means that this crop would accumulate 163 kg N ha -1 in the grain, or approximately 500 mg N per plant. As both the proportion of N in the grain compared to the whole shoot (the N harvest index) and the %Ndfa are both usually close to 80% (Alves et al, 2002(Alves et al, , 2003(Alves et al, , 2006, ideally soybeans used to determine 'B' value should accumulate approximately this amount of N from BNF. In the present study N derived from BNF by the soybeans inoculated with the 4 different Bradyrhizobium strains accumulated between 460 and 620 mg N per plant (910 to 1240 mg N per pot) from BNF (mean %Ndfa = 97%) very close to this value.…”

“…The 'B' values for the Bradyrhizobium strains 29 W (SEMIA 5019 -B. elkanii) and CPAC 7 (SEMIA 5080 -B. japonicum), respectively, were -4.54 and -2.39 ‰ for the shoot tissue. These two strains are both recommended for inoculant manufacture in Brazil and proportional BNF inputs to soybean are generally high (Alves et al, 2003(Alves et al, , 2006. Therefore, the objective of this study was to determine the 'B' values in soybean plants grown in an open field soil inoculated with of all four recommended strains of B. elkanii and B. japonicum.…”

Nitrogen fertilization on cotton cropped under straw formed by seed proportions of crotalaria and brachiaria

“…Similarly, there was no significant difference in total N content of straw from the association with more or less participation of crotalaria (Table 2). Alves et al (2006) found negative balance of N or near neutrality after the cultivation of soybeans, i.e. BNF is sufficient to ensure high productivity and demand just for itself.…”

“…Similarly, it is observed that even in the subplots without application of N, the yield obtained was high and there was no N deficiency in the leaves (Table 3), as part of N may have been from the mineralization of organic matter. However, high cotton yield with low doses of nitrogen can promote soil depletion over time, since the quantity exported by the harvest is greater than the amount added (Alves et al, 2006). According to Carvalho et al (2011), the average N exported is 33.9 kg N for each ton of cotton seed produced.…”