Phosphorus availability to wheat from manures, biosolids, and an inorganic fertilizer

A greenhouse study was conducted to assess phosphorus (P) availability (as measured by plant uptake) from various P sources using Kaskaskia winter wheat (Triticum aestivum L.). The phosphorus sources included feces with low, medium, and high P concentrations from a dairy feeding study, whole (unfractionated) manure, fiber manure from a liquid-solid separator, biosolids from a municipal waste treatment facility, and calcium phosphate (CaHPO4). All P sources were applied at 0, 101, and 202 kg total P ha(-1) to a sand medium. A randomized complete block design with four replicates was used. Top growth was harvested three times and roots were collected at the final harvest. An identical set of treatments was applied to a growing medium of sand plus 5% Ringwood silt loam soil. Additionally, a sub-experiment was conducted using Ringwood silt loam soil as the growing medium with whole manure, biosolids, and CaHPO4 as the P sources. Wheat total P uptake and total dry matter yield were determined for each treatment. In the sand medium, whole and low P manures produced the lowest P availability; medium P, high P, and fiber manures had intermediate P availability; and biosolids and CaHPO4 had the highest P availability. In contrast, the sand + soil experiment showed that CaHPO4, biosolids, and fiber manure produced the lowest P availability, while the other P sources (whole, low P, medium P, and high P manures) were significantly higher and similar to each other. In the soil sub-experiment, biosolids and whole manure produced significantly higher total P uptake and total dry matter yield than CaHPO4. In these studies P availability from sources with high soluble P contents was reduced in soil or sand + soil growing media possibly by reaction with Fe, Al, Mg, or Ca in the soil or adsorption of P to clay and mineral surfaces. This observation emphasizes the importance of growing media characteristics in greenhouse experiments to assess P availability. These results suggest that soluble P sorption by soil, available P contributions from soil, and mineralization of organic P from the P source treatments masked initial differences in P availability among these P sources.