Crop rotation and tillage effects on phosphorus distribution in the central Great Plains

The fate and availability of soil P in the central Great Plains may become less predictable with less tillage and more intensive crop rotations that produce more crop residue and litter than conventional-till (CT) wheat (Triticum aestivum L.)-fallow (W-F). We need to evaluate these new systems relative to new P distribution patterns that may be occurring, We determined P changes in a Weld silt loam soil (fine, montmorillonitic, mesic aridic Paleustoll) in predetermined plots from a 5-year rotation-tillage experiment where 45 kg P ha(-1) was applied in 1990, and 18 kg P ha(-1) was applied to the wheat phase of the rotation thereafter, We determined changes in water-soluble P, resin-extractable P, total organic P, bicarbonate-extractable P, and phosphomonoesterase activity as a function of tillage and cropping intensity in soil from the 0- to 5-cm and 0- to 15-cm depths. Phosphorus concentration in wheat tops at an early stage was also determined lo assess soil P availability. Generally, P. availability indices increased significantly in the 0- to 5-cm depth with continuous cropping treatments compared with wheat-fallow treatments. The results suggest that under more intensive cropping systems P recycling through residue and litter could be an important mechanism resulting in additional plant-available P.