Nutrient Uptake and Partitioning in High-Yielding Soybean.

Patterns of nutrient uptake, partitioning, and remobilization in soybean have been researched from the 1940’s to 1970’s in an effort to better understand the physiology of nutrient accumulation. While most studies quantified only macronutrients, they also were conducted with varieties and agronomic management practices typical of lower yielding conditions. The objective of this study was to quantify nutritional requirements, including total nutrient uptake, removal, and use, in elite commercial germplasm using modern fertilizer source and placement technologies. Locally adapted varieties were grown at central (Champaign) and northern (DeKalb) Illinois locations in 2012. Plots were sampled at seven incrementally spaced growth stages and total nutrient content was determined among four plant fractions for soybean yielding 2.9 Mg ha^-1 (Champaign) and 3.6 Mg ha^-1(DeKalb).

By quantifying total nutrient uptake and removal, key nutrients for soybean production were identified. Total dry weight production (DW) and nutrient uptake at DeKalb were generally greater than observed at Champaign (difference relative to Champaign shown in parenthesis): 9950 kg DW (+1372 kg), 304 kg N (+62 kg), 56 kg P₂O₅ (+13 kg), 202 kg K₂O (+101 kg), 21 kg S (+4 kg), 0.6 kg Zn, and 0.06 kg Cu per hectare. Regardless of locational differences in total nutrient uptake, similar harvest index values were determined for DW (35%), N (72%), P (~79%), S (~60%), Zn (~25%), and Cu (~55%). These results suggest that N, P, K, and S are required in high quantities for soybean production and are also important in developing grain tissue.

In contrast to nutrient uptake in corn, where maximum rates of nutrient accumulation occur during late vegetative growth, a more stable and season-long pattern of nutrient uptake occurred for soybean growth. An approximate 50-day period from V5 to R5 accounted for as much as 75% of total DW production and N, P, K, and S acquisition. Although the timing of micronutrient acquisition was more intricate than macronutrients, maximum rates of micronutrient accumulation were observed during early reproductive development (e.g., R2-R5). This reevaluation of nutrient uptake and utilization in soybean will provide essential information to help design a balanced nutritional program that maximizes the inherent yield potential of soybean.