Agronomic Management Innovations Improve Soybean Yield By Lengthening Seed-Filling Duration at Different Canopy Regions.

Increasing average soybean yield will require a better understanding of the agronomic, genetic, and environmental factors that influence soybean yield. These factors also influence the rate and duration of seed filling, and therefore, a greater understanding of all physiological yield determinants are necessary to fully achieve the maximum yield potential of soybean. The objective of this research was to quantify the effect of agronomic production practices on the physiological determinants of soybean yield and the effective filling period (bean filling rate and duration) at different regions of the soybean canopy.

Field experiments were conducted during 2013 at the Department of Crop Sciences Research and Education Center in Urbana, Illinois. Three agronomic factors including variety selection (S34-N3 vs S36-M8), balanced mineral nutrition (with and without preplant banded phosphorus at 84 kg P₂O₅ ha^-1 as Microessentials SZ; 12-40-0-10S-1Zn), and foliar crop protection (with and without foliar insecticide + fungicide applied at R3) were used to further evaluate the physiological determinants of soybean yield. Using weekly time intervals beginning at R5 (beginning seed), five plants plot^-1 were sampled and the number and mass of beans were determined. Measurements were conducted at three nodes, each indicative of a different region of the soybean canopy: node 4 or 5 (bottom third of canopy), node 10 or 11 (middle third), and node 15 or 16 (upper third).

The trial yield average measured 3,558 kg ha^-1 (0% moisture concentration) with significant increases due to agronomic management. Variety S36-M8 was most responsive to management where yield improvements of 212 and 282 kg ha^-1 were realized with supplemental fertility and foliar protection, respectively. Regardless of management practice used, seed mass was the primary yield component responsible for observed yield gains (+10 – 13%; P < 0.05). Interestingly, the increase in seed mass as a result of these practices when compared to the control varied throughout the canopy. Supplemental fertility resulted in a 29 mg increase in seed mass in the bottom region of the canopy, nearly twice that of the middle and upper regions. In contrast, the primary increase in seed mass due to foliar protection occurred in the upper canopy where the advantage was nearly 50% greater than observed in the middle and lower canopy regions. The duration of active seed-filling was lengthened by nearly two weeks and may explain these results. These data suggest that agronomic management can be used to improve soybean yield through seed mass, and that these practices act at specific regions of the soybean canopy.