Comparative response of corn and soybean to seed-placed phosphorus over a range of soil test phosphorus

The responses of corn and soybean to seed-placed fertilizer were compared over NaHCO3-extractable soil phosphorus (P) levels ranging from 3 to 35 ppm in a two-year experiment. Early season corn and soybean shoot-P concentrations were increased with increasing soil test P and were increased with seed-placed P regardless of soil test P, although the increases were greater for corn than soybean. Corn grain yield increased with increasing soil test P to a plateau level and increased with seed-placed P regardless of soil test P. A side-band (5 cm x 5 cm) application of 39 kg P ha(-1) at a low soil test P increased yield more (P<0.15) than application of 7 kg P ha(-1) with the seed. A side-band application of 9 kg P ha(-1) at a medium soil P test did not increase yield, Soybean yield was increased with increasing soil test P one year out of two, but did not respond to seed-placed P in either year. The yield response of corn was attributed to the increased P concentration prior to the 6-leaf stage.