Soybean response to starter nitrogen and Bradyrhizobium inoculation on a Cerrado oxisol under no-tillage and conventional tillage systems

Abstract

SUMMARYIn Brazil, Bradyrhizobium inoculation has successfully replaced the use of N fertilizer on soybean [Glycine max (L) Merr.] crops. However, with the expansion of no-tillage cropping systems in the Cerrados region, the idea that it is necessary to use small N rates at the sowing to overcome problems related with N immobilization has become widespread, mainly when soybean is cultivated after a non-legume crop. In this study we examined soybean response to small rates of N fertilizer under no-tillage (NT) and conventional tillage (CT) systems. Four experiments (a completely randomized block with five replicates) were carried out in a red yellow oxisol, during the periods of 1998/1999 and 1999/ 2000, under NT and CT. The treatments consisted of four urea rates (0, 20, 30 and 40 kg ha -1 N). All treatments were inoculated with Bradyrhizobium japonicum strains SEMIA 5080 and SEMIA 5079, in the proportion 1 kg of peat inoculant (1,5 x 10 9 cells g -1 ) per 50 kg of seeds. In both experiments, soybean was cultivated after corn and the N fertilizer was band applied at sowing. In all experiments, N rates promoted reductions of up to 50 % in the nodule number at 15 days after the emergence. Regardless of the management system, these reductions disappeared at the flowering stage and there was no effect of N rates on either the number and dry weight of nodules or on soybean yields. Therefore, in the Brazilian Cerrados, when an efficient symbiosis is established, it is not necessary to apply starter N rates on soybean, even when cultivated under notillage systems.Index terms: soybean, Bradyrhizobium japonicum, inoculation, zero-tillage, biological nitrogen fixation.(

Combination of inoculation methods of Azospirilum brasilense with broadcasting of nitrogen fertilizer increases corn yield

“…The second mechanism relates to the production of plant hormones such as auxins, gibberellins and cytokinins (OKON & VANDERLEYDEN, 1997) that act on root morphology and physiology enhancing absorption of surface water and nutrients (PERIN et al, 2003). Nitrogen fixation is a process with high energy cost for the plant (FAGAN et al, 2007), so when large quantities of the nutrient are available in the soil, there is a reduction of the biological fixation (MENDES et al, 2003). Based on the previous evidences and the results obtained in this study, the effect on the plant hormones seems to be the main factor responsible for the increases in corn yield.…”

Adubação nitrogenada suplementar tardia em soja cultivada em latossolos do Cerrado

“…Assim, deve-se garantir que as novas cultivares de soja estabeleçam simbioses altamente efi cazes no processo de FBN (Nicolás et al, 2006), inclusive no caso de materiais transgênicos.…”

“…Mesmo em solos com grande quantidade de resíduos vegetais (26 Mg ha -1 ), não é observada resposta da soja à aplicação de fertilizantes nitrogenados na semeadura, para a superação de possíveis problemas relacionados à imobilização do N mineral do solo ou à competição inicial com ervas daninhas (Vargas et al, 1982). Mais recentemente, Hungria et al (1997) e Mendes et al (2003) confirmaram que não há necessidade da utilização de doses de "arranque" com adubo nitrogenado na semeadura, tanto em áreas de plantio direto, quanto de plantio convencional da soja.…”

Nitrogen uptake, fixation and response to fertilizer N in soybeans: A review

“…Because some studies on N fertilization did not concurrently quantify N 2 fixation and other studies did not evaluate response to N fertilizer when quantifying N 2 fixation, data analyses were performed for two data sub-sets: Data set A was used to examine relationships between N uptake, N 2 fixation and grain yield; Data set B was used to evaluate yield response to fertilizer-N. Data set A comprised 61 studies in which N 2 fixation was quantified. Several different techniques were used: (1) the N difference method (Dashti et al, 1998, Israel and Burton, 1997, Israel and Mikkelsen, 2001, Saxena and Chandel, 1997, Thies et al, 1995, Wagner and Zapata, 1982, Weber, 1966; (2) Ureides determination in the xylem sap (Gan et al, 2002, Guafa et al, 1993, Herridge, 1982, Herridge et al, 1990, Hughes and Herridge, 1989, Hungria et al, 2003, Peoples et al, 1995a, Reis et al, 2002, Takahashi et al, 1992, Yinbo et al, 1997, Ying et al, 1992, Zotarelli, 2000; (3) 15 N dilution and abundance techniques (Afza et al, 1987, Alvarez et al, 1995, Alves et al, 2006, Amarger et al, 1979, Bergersen et al, 1989, Bergersen et al, 1992, Boddey et al, 1990, Chapman and Myers, 1987, Coale et al, 1985, Eaglesham et al, 1982a, Eaglesham et al, 1982b, George and Singleton, 1992, Guffy et al, 1989, Hardarson et al, 1984, Hardarson et al, 1989, Kucey et al, 1988a...…”