Phosphorus Fertilizer Carriers and Their Placement for Minimum Till Corn Under Sprinkler Irrigation

Several methods of placement and sources of P were evaluated for sprinkler irrigated corn (Zea mays L.) grown under minimum tillage on a Sharpsburg silty clay loam (Typic Argiudoll) and a Coly silt loam (Typic Ustorthent). Nitrogen and P, dual placed in a localized band (anhydrous ammonia applied with liquid P sources), accomplished greater P uptake and higher corn grain yields on a P deficient calcareous soil than P banded to the side of the seed or banded below the seed, although both methods increased early plant growth compared to either broadcast or P dual placed with NH₃. Broadcast preplant applications of P were equally as effective as dual placed P in this study. Explanation of yield and P uptake enhancement by dual placement may lie in the synergistic effect of ammoniacal N and P placed together. The superior performance of the broadcast method of P application was apparently due to root activity near the surface of the soil or in the soil residue interface. In contrast, starter band applications gave higher yields than broadcast or dual placed methods of P application on a slightly acid medium P soil. While it is not known why differences were obtained between the performance of methods of P application on these two soils, low subsoil P levels in the calcareous soil compared to the acid soil was believed to be a contributive factor. Enhanced early P uptake with such row applications may increase yields where high subsurface P levels exist. Urea phosphate (UP) provided greater yields, grain P uptake, and total P uptake than ammonium polyphosphate (APP) and diammonium phosphate (DAP) at the calcareous site—especially when band (side), broadcast, and dual placement methods of P application were used. Total P concentration from plant tissue taken at the eight-leaf stage was greater for UP than APP and DAP on the slightly acid soil, but no yield differences could be attributed to sources at this site.