Potassium Fertility Effects Yield Components and Seed Potassium Concentration of Determinate and Indeterminate Soybean

Indeterminate maturity group (MG) IV soybean [Glycine max (L.) Merr.] cultivars may be more susceptible to yield loss from K deficiency due to the shorter growing season and earlier onset of reproductive growth than MG V determinate soybean cultivars. Our objective was to identify whether indeterminate MG IV or determinate MG V soybean are affected differently by K deficiency. Seed yield and selected yield components were evaluated from a determinate (MG 5.3) and indeterminate (MG 4.7) soybean cultivar grown under three K fertility levels (low, medium, and high). The trial was conducted in long-term plots that receive 0, 75, or 150 kg K ha(-1) yr(-1). Yield and yield components of both the determinate and indeterminate cultivars responded similarly to K deficiency. Seed yield for soybean grown with low K averaged 3.4 Mg ha(-1) and was 13 to 15% lower than the yields of soybean grown with medium and high K fertility. The yield loss associated with K deficiency was from fewer pods (16-25%) and seeds (22-30%) plant(-1), higher seed abortion (5-7%), and lower individual seed weight (8-10%) than soybean with medium or high K fertility. Seed K concentration increased with each increase in K fertility level averaging 15.8, 18.7, and 19.8 g K kg(-1) for soybean grown under low, medium, and high K levels, respectively. Regardless of growth habit, the yield loss caused by K deficiency was attributed to the same primary mechanisms of reduced pod number and increased seed abortion.