Agronomic effectiveness of calcium phosphate recovered from liquid swine manure

A new manure treatment technology developed as an alternative to anaerobic lagoons on swine (Sus scrofa domesticus) farms includes solid-liquid separation and subsequent recovery of soluble P as calcium phosphate from the wastewater. The objective was to determine the agronomic effectiveness of this calcium phosphate material. A greenhouse study was conducted with annual ryegrass (Lolium multiflorum Lam.). Three fertilizer materials were evaluated: the recovered P in two particle sizes (0.5-1.0 and 2.0-4.0 mm), and commercial triple superphosphate (TSP). Fertilizer rates were 0, 22, 44, 88, and 176 mg P kg(-1) soil. Three harvests of the ryegrass were made at 2-wk intervals. Total P uptake increased linearly with application rate for all three fertilizer materials. At the highest application rate, total P uptake was 37.8 mg pot(-1) for TSP, 26.2 mg pot(-1) for the recovered P with small particle size, and 9.0 mg pot(-1) for the recovered P with large particle size. Chemical analysis of the recovered P material revealed that over 99% of the P2O5 in the recovered calcium phosphate was plant available P, mostly as citrate-soluble. Mehlich-3 extractable soil P at the end of the experiment indicated that little of the large particle size of recovered P material dissolved and became available during this short 10-wk study. The recovered calcium phosphate appears to have potential as a fertilizer source.