IMPACT OF FERTILIZER PLACEMENT AND TILLAGE SYSTEM ON PHOSPHORUS DISTRIBUTION IN SOIL

Repeated use of band applications, both surface and subsurface, of imm obile nutrients applicable to a variety of tillage systems raises conc erns about the collection of soil samples used for making fertilizer r ecommendations. This study was conducted to measure the effect of till age system and fertilizer placement on soil test P in a major part of the root zone. Soil samples were collected from control treatments and from treatments where phosphate fertilizer supplying 29 kg P ha(-1) y r(-1) had been broadcast, applied as a surface band, or applied in a s ubsurface band for three consecutive years in a corn (Zea mays L.)-soy bean [Glycine max (L.) Merr.] rotation. These placements were used in both a chisel and a ridge-till planting system. Soil samples were coll ected from depths of 0 to 7.5, 7.5 to 15.0, 15.0 to 22.5, 22.5 to 30.0 , and 30.0 to 45.0 cm at distances of 0, 7.5, 15.0, 22.5, 30.0, and 37 .5 cm from the row. Soil test P, to a depth of 15 cm at each position from the row, was significantly affected by fertilizer placement. Plac ement also had a significant effect on soil test P to a depth of 30 to 45 cm at a distance of 30 cm from the row. Tillage system had a signi ficant effect on measured soil test P at sampling positions near the r ow. These results indicate that both tillage system and fertilizer pla cement could have a major effect on soil test values. If band location s are known, they should be avoided, if possible, during sample collec tion.