Phosphorus Source Effects on Corn Utilization and Changes in Soil Test

Estimating crop availability of manure P and changes in soil test P (STP) with manure application are essential components of nutrient management planning. The objectives of this field study were to (i) evaluate manure P availability to crop growth through crop P uptake and yield; (ii) determine if second‐year residual P availability from manure application is different than fertilizer; and (iii) evaluate the effect of P source on changes in STP levels. Research plots were established at Arlington and Marshfield, WI, in 2005 on fields with low STP. All P sources (dairy slurry, dairy solid, swine slurry, pelletized poultry litter, and fertilizer) were applied at three target rates of 39, 79, 118 kg total P ha −1 in spring 2005 before planting corn ( Zea mays L.). No additional P was applied in 2006. Phosphorus application increased early season biomass, silage and grain yield, and P uptake. In 2005, all manures had silage and grain yields and P uptakes, along with silage P recoveries, that were not significantly different than fertilizer. In 2006, the residual effect of 2005 P applications rates were observed; however, there was no significant difference in any measure of crop response between any manure and fertilizer. These data suggest that manure total P is as available to corn as fertilizer P in the year of application and in the following year. Manure application changed STP levels as much as fertilizer in terms of total P applied.