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.
ASJC Scopus subject areas
- Agronomy and Crop Science