Distance and Distribution Effects of Phosphorus Fertilizer on Corn

Fertilizer P distribution and distance of application from the plant can affect fertilizer P efficiency. Ammonium polyphosphate solution tagged with 32 P was injected into Sharpsburg sicl (Typic Argiudoll) 10‐cm deep on circle located 16, 32, 48, and 64 cm from five corn seeds ( Zea mays L.) planted in the center. The P fertilizer for each plot was divided into 10 equal parts and was injected into 10 spots on the circle's circumference at five different spacings. To study the movement of P in the soil, seven concentrations of P fertilizer were injected into the soil 5‐cm deep. Results indicate that after 90 d P fertilizer moves outward from the injected point to form a near perfect sphere whose volume was related in a quadratic manner to the P application rate. At early stages of growth, seed placement of P fertilizer and placement up to 16 cm resulted in greater plant P from fertilizer than other P distances. At maturity little or no effect of P application distance was observed. Plant P from fertilizer increased as the surface area of the fertilizer P‐effected soil increased, indicating surface area is an important factor involved in determining the probability of root‐fertilizer contact. Plant P from fertilizer increased as the spacing between injection points increased because surface area of the fertilizer P‐effected soil was increasing. Plant P from fertilizer decreased with time indicating that a greater proportion of plant P was from soil P late in the growing season.