Seed protein, oil, fatty acids, and minerals concentration as affected by foliar K-glyphosate applications in soybean cultivars

Previous studies showed that glyphosate (Gly) may chelate cation nutrients, including potassium (K), which might affect the nutritional status of soybean seed. The objective of this study was to evaluate seed composition (protein, oil, fatty acids, and minerals) as influenced by foliar applications of K + Gly. A greenhouse experiment was conducted at Mississippi Valley State University, using two glyphosate-resistant soybean cultivars DK 4968 and Pioneer 95Y70 grown in a randomized complete block design. The treatments were foliar applications of K alone, Gly alone, K + Gly combined, and nontreated control (C). A single application of potassium (1.75% as K2SO4) was applied, and Gly was applied at a rate of 0.75 ae/ha at V5 stage. Leaf samples were harvested one week after treatment (1WAT) and 3WAT. Mature seeds were collected at harvest maturity (R8). The results showed that K, nitrogen (N), and phosphorus (P) concentrations increased in leaves in K alone and K + Gly treatments at 1WAT, but significantly increased at 3WAT in all treatments. The concentration of iron (Fe) and zinc (Zn) showed a decrease in leaf concentration in Gly and K + Gly treatments compared to C. Boron (B) concentration increased in Gly treatment. Seed protein percentage was higher in all treatments in cultivar DK 4968, and the increase was about 4.0% in K treatment, 6.9% in Gly treatment, and 3.5% in K + Gly treatment compared to C. The opposite trend was observed in oil concentration, especially in Gly treatment where the percentage decrease was 11.2% compared to C. Stearic fatty acid was significantly higher in K + Gly treatment compared to K treatment for DK 4968. A higher percentage increase in linolenic acid was observed in DK 4968 in K treatment (an increase of 24.5%) and in K + Gly treatment (an increase of 29.5%) compared to C. In Pioneer 95Y70, the decrease in oil was 2.7% in K treatment and 2.3% in K + Gly treatment compared to C. Stearic acid in Pioneer 95Y70 was significantly higher in Gly treatment, an increase of 8.3%, compared to C. Our research demonstrated that foliar application of K and Gly altered mineral concentration in leaves and shifted seed composition towards protein and stearic concentration. Further research under field conditions is needed before final conclusions are made.