Distribution and Chemical Speciation of Phosphorus in Manure-Amended Saskatchewan Soils for One to Eleven Years.

There is very limited information on the specific P forms that accumulate in manured soils over the short and long term. To address this knowledge gap, detailed speciation of soil phosphorus (P) was assessed using a variety of chemical soil test phosphorus (STP) extraction methods and a synchrotron- based technique. Soils were collected from short- and long-term manure addition field research plots in the Black soil zone of Saskatchewan. The long-term research plots had an 11-year history of either solid cattle manure (SCM) or liquid hog manure (LHM) application, whereas the short-term research plots had a 1-2 year history. The research site soil is classified as a Black Chernozem with loamy surface texture. Soil samples were collected from an unmanured control, low and high rate manure application treatments. The low rate of SCM and LHM application in this study site was 7.6 T ha^-1 yr^-1 (dry weight) and 37,000 L ha^-1 yr^-1, respectively. The high rate was four times this amount. The SCM application resulted in significant increase in the labile P concentration over control regardless of application rate and time. With LHM, a small but significant increase of labile P fraction was observed only after long-term application at the high rate compared with the control. This is attributed to the lower amount of P added with the LHM than the SCM. In soil amended with SCM for one year, the X-ray absorption near edge structure (XANES) spectra showed the dominance of brushite and adsorbed P. Long-term SCM application resulted in a dominance of soluble Ca-P minerals and evidence of transformation of free and weakly bound adsorbed P minerals to more stable Ca-P minerals such as apatite. In contrast, phosphate in short-term LHM (two years) amended soil was mainly associated with Mg compounds such as struvite and adsorbed P compounds. Long-term LHM soils revealed mainly poorly crystalline dicalcium phosphate. This suggests that transformations of P minerals are important in soil nutrient cycling for P.