Quantification of N₂ fixation and annual N benefit from N₂ fixation in soybean accrued to the soil under soybean‐wheat continuous rotation

Abstract

PNSS P89/2BSummary A computational exercise was undertaken to quantify the percent N derived from atmosphere %Ndfa) in soybean and consequent N benefit from biological N 2 -fixation process annually accrued to the soil by the soybean crop using average annual N-input/-output balance sheet from a 7 yr old soybean-wheat continuous rotational experiment on a Typic Haplustert. The experiment was conducted with 16 treatments comprised of combinations of four annual rates of farmyard manure (FYM @ 0, 4, 8, and 16 t ha ±1 ) and four annual rates of fertilizer N (@ 0, 72.5, 145, and 230 kg N ha ±1 ) applications. The estimated N contributed through residual biomass of soybean (RBN S ) consisting of leaf fall, root, nodules, and rhizodeposition varied in the ranges of 7.02±16.94, 11.65±28.83, 3.31± 8.91, and 11.3±23.8 kg N ha ±1 yr ±1 , respectively. A linear relationship was observed between RBN S and harvested biomass N (HBN S ) of soybean in the form of RBN S = 0.461 HBN S ± 20.67 (r = 0.989, P < 0.01), indicating that for each 100 kg N assimilated by the harvested biomass of soybean, 25.4 kg N was added to the soil through residual biomass. The Ndfa values ranged between 13% and 81% depending upon the annual rates of application of fertilizer N and FYM. As per the main effects, the %Ndfa declined from 76.4 to 26.0 with the increase in annual fertilizer-N application from 0 to 230 kg N ha ±1 , whereas %Ndfa increased from 40.8 to 65.8 with the increase in FYM rates from 0 to 16 t ha ±1 , respectively. The N benefit from biological N 2 fixation accrued to the soil through residual biomass of soybean ranged from 7.6 to 53.7 kg N ha ±1 yr ±1 . The treatments having %Ndfa values higher than 78 showed considerable annual contribution of N from N 2 fixation to the soil which were sufficient enough to offset the quantity of N removed from the soil (i.e., native soil N / FYM-N / fertilizer-N) with harvested biomass of soybean.

Soybean Response to Single or Mixed Soil Amendments in Kashmir, Pakistan

“…The low N 2 fixation in UN 100 may be explained by the inhibitory effect of applied mineral N fertilizer on nodule formation and activity. In earlier studies, a significant reduction in N 2 fixation of soybean (lower than the control) was observed at each increased level of fertilizer N, as a result of which Ndfa values declined from 76% at N 0 to 27% at 230 kg N ha −1 (Singh et al, 2004). The possibility of substantial accumulation of NO 3 − –N in the soil under the N fertilizer treatment in this research severely suppressed nodulation, thereby decreasing N 2 fixation, consistent with many other studies (Peoples and Herridge, 1990).…”

“…The maximum amount of N 2 fixed was 43 kg N ha −1 at Hajira, while 73 kg N ha −1 was fixed at Rawalakot site the treatment supplemented with PM 100 . It has been recognized that a high level of organic matter buildup in soil due to the addition of organic amendments improves soil physical conditions and enhances nutrient levels and microbial activity that eventually increases N 2 fixation in soybean (Singh et al, 2004). The integrated use of UN with PM or WMR in our research improved N 2 fixation of soybean, suggesting that continuous use of organic amendments (PM and WMR) with mineral N had a beneficial effect on N 2 fixation.…”

“…Oberson et al (2007) estimated symbiotic N 2 fixation of soybean under organic and conventional cropping systems and reported that N 2 fixation was lower in conventionally than organically grown soybean. Quantification of N 2 fixation by soybean was examined in India, and the results indicated a significant reduction in %Ndfa at each increased level of fertilizer N, whereas farmyard manure (FYM) and integrated treatments displayed progressive increases in N 2 fixation (Singh et al, 2004). The organic matter buildup in soil due to the addition of organic amendments improved soil physical conditions and enhanced microbial activity that eventually increased nodulation and N 2 fixation (Singh et al, 2004; Singh and Shivakumar, 2010).…”

Biological Nitrogen Fixation: Importance, Associated Diversity, and Estimates

“…In addition, another major problem is that the root system is routinely not included in the BNF estimates, which may lead to soybean going from a net exporter (Di Ciocco et al 2011 ) to a net fi xer of soil N (Singh et al 2004 ). When considering the importance and number of agricultural systems in which soybean participates, this change may have signifi cant effects on overall N balance.…”

Effect of biological fertilizer on the growth and nodules formation to soya bean (Glicine max (L.) merrill) in ultisol under net house conditions

“…According to Sanginga et al (2010) this plant can fix annually 11-120 kg atmospheric nitrogen in the form of Nitrate. Further, Handarson et al (1989) reported that nitrogen fixation ability of the soybean crop is influenced by several factors such as plant varieties, soil types, climatic conditions, crop management practices, availability of organic matter (Kundu et al, 1996) and the availability of Phosphorus and Sulfur (Kris Joko, 2001;Singh, 2004).…”