Effects of Soybean Release Year and Intensive Management on Seed Fill.

Advances in the latest soybean varieties and management practices aim to improve production through yield potential, protection, and consistency. One method of attaining high yields is to maximize the duration of the seed fill period and the rate of dry matter accumulation. The objective of this research was to quantify the changes of seed fill duration and rate, over the past 50 years as factored by fertility and foliar protection. Two studies were initiated in 2016 for maturity group (MG) II and MG III, with two varieties chosen from the 1970s, 1990s, and 2010s for each MG. The six varieties were factored across six management series resulting in 36 treatments that were replicated three times. Treatments were arranged in a split-plot design with management as the main plot and variety as the subplot. Studies were planted May 20, 2016 near Lafayette Indiana and repeated in 2017. Three of the six management levels (Untreated, Enhanced Fertility, Enhanced Fertility + Foliar Protection) were sampled every 7-10 d from R4 (full pod) through R8 (maturity) to determine dry matter accumulation in the seeds. Samples were fully partitioned at R4, R6, and R8 into stems, leaves, fallen leaves, pods, and seeds to track nutrient and dry weight allocation in the plant and over seed fill. The duration from R4 to R7 was about four days longer for modern varieties compared to the older varieties. Maximum seed fill rate also increased across the decades. Within MG II study, varieties from 1970s deposited 14.3 g/m²/d (20 d after R4), varieties from 1990s deposited 17.2 g/m²/d (25 d after R4), and varieties from 2010s deposited 20.8 g/m²/d (28 d after R4). Management levels had minimal influence on seed fill rate and duration, but maximum seed weight tended to be highest with the enhanced fertility + foliar protection.