Soybean seed yield distribution within the canopy as affected by nitrogen supply

Abstract

Soybean (Glycine max [L.] Merr.) seed yield is influenced by the seasonal availability of resources (i.e., nutrients, light, and water). While nitrogen (N) supply is becoming a soybean yield-limiting factor, the N-induced effect in seed yield components is still unclear. The objective of this research was to assess the effect of N supply on soybean yield components distribution within the canopy. A ‘Full-N’ treatment, which provided the crop with ample N supply, was compared against a ‘Zero-N’ treatment in which the crop relied on soil N and biological N fixation at nine high-yielding irrigated soybean environments in Nebraska, with known levels of N limitation. Soybean seed yield components were determined at every node and grouped into five canopy sections. Seed yield ranged from 4378 to 7314 kg ha⁻¹ across environments and treatments. The greater N availability in the Full-N increased yield by 984 kg ha⁻¹ in comparison to Zero-N; via +253 seeds m⁻² (7%) and +16 mg seed⁻¹ (11%). N-induced responses in seed yield occurred in the lower (nodes 0–4), middle (nodes 9–13), and middle-upper sections (nodes 13–18). Seed number and pod number increased in the middle-upper section. Notably, individual seed weight increased in all node sections. The seed number per pod response to N was negligible. The seed abortion within pods was 8%, but the Full-N treatment reduced it by one percentage point. This study comprehensively examined the effects of N availability on soybean yield components within the canopy during their sequential establishment.