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

Abstract

Although relationships among soybean (Glycine max [L.] Merr) seed yield, nitrogen (N) uptake, biological N 2 fixation (BNF), and response to N fertilization have received considerable coverage in the scientific literature, a comprehensive summary and interpretation of these interactions with specific emphasis on high yield environments is lacking. Six hundred and thirty-seven data sets (site-year-treatment combinations) were analyzed from field studies that had examined these variables and had been published in refereed journals from 1966 to 2006. A mean linear increase of 0.013 Mg soybean seed yield per kg increase in N accumulation in above-ground biomass was evident in these data. The lower (maximum N accumulation) and upper (maximum N dilution) boundaries for this relationship had slopes of 0.0064 and 0.0188 Mg grain kg −1 N, respectively. On an average, 50-60% of soybean N demand was met by biological N 2 fixation. In most situations the amount of N fixed was not sufficient to replace N export from the field in harvested seed. The partial N balance (fixed N in above-ground biomass − N in seeds) was negative in 80% of all data sets, with a mean net soil N mining of −40 kg N ha −1 . However, when an average estimated below-ground N contribution of 24% of total plant N was included, the average N balance was close to neutral (−4 kg N ha −1 ). The gap between crop N uptake and N supplied by BNF tended to increase at higher seed yields for which the associated crop N demand is higher. Soybean yield was more likely to respond to N fertilization in high-yield (>4.5 Mg ha −1 ) environments. A negative exponential relationship was observed between N fertilizer rate and N 2 fixation when N was applied on the surface or incorporated in the topmost soil layers. Deep placement of slow-release fertilizer below the nodulation zone, or late N applications during reproductive stages, may be promising alternatives for achieving a yield response to N fertilization in high-yielding environments. The results from many N fertilization studies are often confounded by insufficiently optimized BNF or other management factors that may have precluded achieving BNF-mediated yields near the yield potential ceiling. More studies will be needed to fully understand the extent to which the N requirements of soybean grown at potential yields levels can be met by optimizing BNF alone as opposed to supplementing BNF with applied N. Such optimization will require evaluating new inoculant technologies, greater temporal precision in crop and soil management, and most importantly, detailed measurements of the contributions of soil N, BNF, and the efficiency of fertilizer N uptake throughout the crop cycle. Such information is required to develop more reliable guidelines for managing both BNF and fertilizer N in high-yielding environments, and also to improve soybean simulation models.

Fontes de nitrogênio e caule decomposto de Mauritia flexuosa na nodulação e crescimento de Enterolobium contortsiliquum

“…Os tratamentos com e sem inoculação apresentaram resultados semelhantes e o com adubação nitrogenada produziu menor número na raiz. Na literatura são vários os estudos que comprovam a inibição da nodulação por proporções de N aplicadas na forma mineral (SALVAGIOTTI et al, 2008;SILVA et al, 2009). Já espécies como sabiá (Mimosa caesalpiniaefolia Benth.)…”

“…As leguminosas apresentam uma vantagem competitiva em relação à aquisição desse nutriente, pois têm capacidade de estabelecerem simbiose com bactérias diazotróficas. Portanto, elas são importantes sob o ponto de vista ecológico e econômico, podendo dispensar total ou parcialmente os fertilizantes nitrogenados (SALVAGIOTTI et al, 2008;XAVIER et al, 2008;SILVA et al, 2009), contribuindo para viabilizar reflorestamentos, principalmente em áreas degradadas (SANTOS et al, 2001) e minimizar possíveis impactos ambientais decorrentes da utilização destes insumos.…”

Drivers of spatial and temporal variation in soybean yield and irrigation requirements in the western US Corn Belt

“…For example, based on average irrigated yield levels of 3.7 to 4.4 Mg ha −1 found in across regions in this study, total N uptake requirements would range from 300 to 360 kg N ha −1 and the contribution from N 2 fixation would be 50-55% of total crop N uptake (Salvagiotti et al, 2008).…”

Soybean susceptibility to manufactured nanomaterials with evidence for food quality and soil fertility interruption

“…Soybean provides more edible oil and protein than any other food crop, with most of the seed meal after oil extraction used for livestock feed (14). Soybean agriculture requires comparatively less nitrogenous fertilizer (e.g., in 2006, 18.5% of soybean acres in the United States were treated with N vs. 96.6% for corn in 2005, per the US Department of Agriculture Agricultural Resource Management Survey Farm Financial and Crop Production Practices; http://www.ers.usda.gov/Data/ARMS/ app/default.aspx?survey_abb=CROP) as a result of N 2 -fixing symbioses (i.e., nodules) arising on soybean roots in soil (15). Fertilizer production is fossil fuel-intensive (16), and N is significantly lost from fertilized fields (17) to increasingly hypoxic coastal zones (18).…”