Cropping System Effects on Soil P Availability to Corn

A field study was established with the objectives to determine the influence of crop rotation, tillage and residual P on several soil and plant parameters. Parameters measured were incidence of vesicular-arbuscular mycorrhizae (VAM), early growth response to P, early P uptake, soil P availability, soil solution and labile inorganic and organic P fractions, and grain yield of corn. Crop rotation and tillage influenced the early growth and P uptake of corn. Early drymatter [sic] production and P uptake in the check plots were highest in the ridge plant (RP) com-soybean system and lowest in the moldboard (MP) corn-fallow system. Generally the VAM infection rates were significantly higher in the RP systems than in the MP systems. Considerable reduction in VAM infection rates were found with P fertilization (P\u3c0.01) in all cropping systems. Relative early growth response to P and VAM infection were inversely related. The check plots of com-soybean in the RP system had greater total P uptake, grain yield, soil solution, and labile inorganic and organic fractions than the other cropping systems. The residual effect of P fertilizer caused significant increases in soil solution and labile inorganic P fractions, ear leaf P concentration and total P uptake, in almost all cropping systems. Significant grain yield responses to P occurred [sic] in com-fallow and continuous corn in MP systems and in continuous corn in the RP systems in 1987. In 1988, yields were markedly reduced due to drought conditions, whereby P x systems and P effects were insignificant. Grain yield responses in 1987 were inversely related to NaHCO3 -Po at all sampling times. The NaHCO3 -Po appeared to play an important role in determining grain yield response in these systems. Soil samples were collected from P x Tillage experiments from three locations (South East, SE; East Central, EC; western South Dakota) to study the spatial distribution and solubility status of applied P. Stratification of P occurred in fertilized and check plots in all tillage systems across all sites. Fertilizer treatments and soil pH influenced P solubility at the SE site. In -the 5.8 to 6.6 pH range (0.01M CaCl2) all treatments plotted near hydroxyapatite [sic] (HA) and at 7.5 to 7.6 solubility was similar to that of B-tricalcium phosphate (TCP). At the SE site irrespective of the P placement method, the P solubility appears to be set by the adsorbed phase with an upper limit approaching fluorapatite (FA). Solubility data from the calcareous soils of the western site, indicated significant TCP buffering of soil solution P