Effect of High Rates of N, P, K Fertilizer on Corn (Zea mays L.)1

Abstract

AbstractThis experiment was conducted to observe the effects on corn (Zea mays L.) grown on soils which received annual applications of fertilizer at rates above those normally recommended. Annual applications of high rates of N, P, and K fertilizer to Clarion‐Webster Soil Association soils in central (Ames) and north central (Kanawha) Iowa planted to corn produced variable yield results. Incremental rates of N, P, and K fertilizers up to 1,344, 504, and 1,008 kg/ha, (1,200, 450, and 900 lb/a), respectively, were applied annually for 3 consecutive years. The grain yields were analyzed statistically using analyses of variance and regression techniques. Three regression functions, a second order quadratic, a logarithmic to the base e, and a square root function were used to estimate the response surfaces and compared for goodness of fit. The yields were the dependent variable and the applied fertilizer nutrients were the independent variables.It was observed that the logarithmic function fitted the data best in all three years at both sites. A second order quadratic yield prediction equation was developed which included independent variables for fertilizer N, K, N2, interactions of N with soil p, K with soil k and K with soil pH, a variable for soil n supplying power and a variable for measuring climatic influences. Increases in yields resulted from N fertilization. Yield decreases the final year were attributed to high salt concentrations and acid soil reactions. The surface soil pH decreased at a rate of 0.05 pH units per 112 kg/ha (100 lb/a) of N and yields decreased the final year as salt concentrations increased. Yields decreased at N rates above 224 kg/ha (200 lb/a) at the Ames site and above 448 kg/ha (400 lb/a) at the Kanawha site.