A Quantitative Method for Analyzing Nitrogen Assimilation in Soybeans

Abstract

Seed yield in soybeans [Glycine max (L.) Merr.] strongly depends on nitrogen (N) assimilation (NA). The NA in nodulated soybeans is based on two N sources, soil and N fixation. Hence, the controlling NA in soybean to increase seed yield is more difficult than in many other crops that depend on fertilizer. The objective of this study was to establish a quantitative relationship between NA by plants and N applied via fertilizer (NF) to increase soybean seed production. The NA was modelled as a function of NF with two parameters: amount of available soil N (NS) and maximum N assimilation (NAmax), both to be determined experimentally, and one equation to describe fixed N (NFIX), would be maximum under nonfertilizer conditions (NFIXmax). It is assumed that NA is equal to NAmax when NF ≥ NAmax − NS and that, below this threshold, NA decreases in proportion with NFIX + NS. To obtain variable datasets, different rates of N fertilizer were applied to nodulated and non‐nodulated isolines under pot and field conditions from full bloom to beginning of maturity. Seed yields were found to be highly dependent on NA regardless of nodulation type or genotype. In non‐nodulated isolines, NA − NF was a good estimate of NS. In nodulated soybeans, NFIX could be modelled as a liner function of NF. These results indicate that the relationship between NA and NF with NS and NFIX can be modelled in a simplified way. The relationships between NFIX, NF, and NFIXmax indicate key traits for determining NA for seed production in nodulated soybeans.

A quantitative analysis of the relationship between absorbed and applied phosphorous and their contribution to seed production in soybeans under various applied nitrogen conditions

“…Case 1 is that P A continuously and linearly increases with P F , where the slope = 1 (no phosphorus retention and no remaining P in soils) and all P F is apparently absorbed by plants, and P A at P F = when P F is partially xed by and/ or retained in the soil. Case 3 is that the increasing P A in Case 2 has a ceiling; this relationship depends on Blackman's law (Thornley 1976), including observations of the relationship between N A and N F (Kakiuchi and Kobata 2017). In Cases 1 and 2 and the phase below the ceiling in Case 3, the slope [SLOPE = (P A − P S ) / P F ] of the line representing the relationship between P A and P F with an intercept of P S can be used to represent P F use e ciency for P A .…”

“…To estimate N S , the maximum N A , and N FIX in soybeans, a quantitative N model indicating the relationship between N A and N F was used for each P application rate (Fig. 2, upper graph) (Kakiuchi and Kobata 2017). The relationship between N F and N A was incorporated into the model to estimate the maximum N A (N Amax ) and N FIX .…”

Nutrition Diagnosis for Nitrogen in Winter Wheat Based on Critical Nitrogen Dilution Curves

“…RESEARCH I ncreasing crop yield per unit area is of considerable significance because of the rapidly expanding global population and gradual reduction in farmland area (Xiao et al, 2013), as well as the limited availability of natural resources. The addition of nitrogen (N) fertilizer to agricultural systems is a necessary facet of modern agricultural practices, and such applications can generate ~30 to 50% increases in crop yield (Erisman et al, 2008;Kakiuchi and Kobata, 2017). Generally, in the effort to enhance crop production, the quantities of N applied in China are often larger than the recommended and threshold levels (Yin et al, 2016).…”