Effects of Increasing the Rates of Potassium and Nitrapyrin on Nitrogen Uptake by Corn

Plant uptake of NH⁺₄ is competitive with the uptake of K⁺. This relationship is of interest because fertilizer N is commonly applied in the NH⁺₄ form and K is either present in large quantities in the soil or is applied as fertilizer. This study was conducted to determine the effects of high K rates and a nitrification inhibitor on the uptake of N and yields of corn (Zea mays L.). Corn (Landmark C747X) was grown in a field experiment during 2 years. Anhydrous ammonia was applied to all plots at 112 kg N/ha. Treatments consisted of three rates of KCI (0, 90, and 360 kg K/ha) applied in all combinations with three rates of nitrapyrin [2-chloro-6-(trichloromethyl) pyridine] (0, 0.56, and 2.24 kg/ha) to a Kokomo silty clay loam soil (fine, mixed, mesic Typic Argiaquoll). Plant samples were taken 1 week after tasseling during one growing season for chemical analysis. Grain yields and N analyses of leaf tissue at harvest were averaged over 2 years. Soil samples were collected from the surface, 30 cm of soil surrounding the anhydrous ammonia band at 2-week intervals for 12 weeks. The soil was analyzed for inorganic N to monitor the predominant ionic form available to the plants. Nitrapyrin application kept a higher concentration of NH⁺₄ in the soil as compared to the checks for 4 to 6 weeks. Increased rates of K decreased yields and decreased the percent total N in leaves 6 through 10 at 12 weeks. Total N in grain was not affected by K rate or nitrapyrin rate, however, it was very low (0.95%) indicating an N deficiency in all treatments. Total nutrient analysis indicated that the concentration of Ca, Mg, Cu, and P decreased as K rate increased. The study indicated that increasing K rates may decrease yields if N is a limiting factor, due to a competition for uptake. The competition was confirmed by low total N in the grain and the decreased total N in leaves 6 through 10 at tasseling as K rate increased.