Maximum rates of seed placed fertilizer for corn for three soils

Fertilizer is placed in the seed row with corn (Zea mays L.) to increase plant growth. Fertilizers contain salts that have the potential for damaging roots and reducing plant emergence. The objective of this study was to determine the rates of fertilizer sources that can safely be placed with the corn seed for three soils with differing chemical properties. Eleven liquid and dry fertilizer sources were tested at five rates in the greenhouse on three soils: clay loam (CL), fine sand (FS), and silt loam (SiL). After 14 d of plant growth, final stand counts and plant mass were used to develop damage index values using the mean and product of relative plant emergence and plant mass. Predicted rates indicated that 10.6 kg N + K ha^-1 could be applied for CL and SiL soils while the rate was 5.7 kg for the FS. Predicted rates using total N plus K agreed with rates predicted when using the salt index of the fertilizer times the rate applied except for ammonium thiosulfate (ATS) and a low-salt N-P-K fertilizer source. Better predictions were made when N and S were considered for ATS and only N for the low-salt fertilizer. Both models predicted rates similarly for the FS, but the N plus K model was more conservative for the CL and SiL soils. The data indicate that a single model could be used for predicting seed-safe rates for multiple fertilizer sources; however, care must be taken because predicted rates may assume optimal soil moisture.