|Pande, Manju -|
|Goli, Mudlagiri -|
|Epps, Tyneiseca -|
Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 10, 2012
Publication Date: N/A
Interpretive Summary: Potassium is a major essential nutrient for crop growth, yield, and seed quality. Potassium is involved in seed protein and oil production, and sugars transport from leaves to seed. Potassium enhances the ability of crop to resist biotic (diseases, pests, and insects) and abiotic (drought and heat) stresses. Deficiency of potassium leads to yield reduction, low seed quality, and sensitivity to disease and drought and heat stresses. Although the application of glyphosate herbicide (Roundup) has been effectively used to control weed, literature reported that glyphosate can bind to cation nutrients (nutrients that have the ability to form a positive charge such as potassium). This binding can inhibit the movement of potassium, resulting in reduction of potassium accumulation in seed, lowering seed quality. Therefore, the objective of this experiment was to evaluate the effects of potassium and glyphosate on soybean seed composition (protein, oil, fatty acids, and minerals). A greenhouse experiment was conducted on Roundup Ready soybean, and the treatments were foliar applications of potassium alone, glyphosate alone, potassium and glyphosate combined, and nontreated control. Application of potassium and glyphosate were applied at commercial rates at vegetative stage. The results showed that the application of potassium and glyphosate treatment resulted in an increase in some nutrients such as potassium, nitrogen, phosphorus, and boron concentrations, and resulted in a decrease in some nutrients such as iron and zinc concentrations. However, this increase or decrease depended on the variety. Seed protein and stearic fatty acid percentages increased, and oil and linolenic acid decreased, and this alteration depended on the variety as well. Our research demonstrated that foliar application of potassium and glyphosate can alter (increase or decrease) mineral concentration in leaves and seed composition, but this alteration did not lead to a deficiency level of these nutrients in seed. This research provides useful information on potassium fertilizer and glyphosate management in relation to seed mineral nutrition and quality.
Technical Abstract: 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 3.97% in K treatment, 6.94% in Gly treatment, and 3.51% in K+Gly treatment compared to C. The opposite trend was observed in oil concentration, especially in Gly treatment where the percentage decrease was 11.19% 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 24.49%) and in K+Gly treatment (an increase of 29.51%) compared to C. In Pioneer 95Y70, the decrease in oil was 2.74% 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 8.33%, 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.