Effect of Potassium Application on Soybean Seed Protein and Oil Composition.

Soybean is an important crop because of high protein and desirable oil content of soybean seed.  Potassium (K) is necessary for carbohydrate and protein metabolism, which is essential for growth, and pod and seed formation. The objective of this research was to study the effectiveness of soil and foliar application of K on seed protein, oil and fatty acid content. The study was conducted in our greenhouse facility. Soybean cultivar (Pioneer 95470) of maturity group 5.7 was grown in pots in a repeated experiment in a randomized complete block design. Treatment consisted of two different concentrations of K₂SO₄ of foliar and soil applications.  The foliar application had two K concentrations (T1, 1.75%; T2, 2.5%). For  soil application, K was also applied at two concentrations (T3, 190mg/kg;  T4, 380mg/kg). The two applications were performed  at V3 (vegetative) and R3 (beginning of seed pod initiation)  stages. Mature seeds were analyzed for protein, oil and fatty acid content using Infra-red (NIR) instrument at USDA-ARS in Stoneville, MS. The results  were analyzed using SAS. As no significant interaction was found between the repeated experiments, our results from both experiments were compiled. Seed protein concentration in T3 (soil application with 190mg K/kg) had a significant increase (3.09%) in protein compared to control. Seed oil percentage  showed a general  decrease in all the treatments except for in T4 (soil application with 380mg K/Kg), where a significant increase in oil percentage (19.36%) was found compared to control (18.76%). Palmitic and stearic acid percentages show significant increase in both T2 (11.15%) and T4 (12.12%) treatments  versus  control (10.37%). Linoleic acid percentage increased in both foliar treatments (T1 and T2). Linolenic acid percentage also increased in soil application T4 (8.6%), but significant decrease (6.45%) in foliar application T2 when compared with control (7.66%). In contrast, oleic acid did not show any significant changes except  in T4, where a significant decrease was observed. In conclusion, K application to soil or foliar can alter seed composition. The increase of protein occurred at the expenses of oil. Further research is needed to understand the mechanisms of K effects on seed composition in soybean. This research is beneficial for soybean growers; it may provide them with the possible effect of K management on seed quality.