Phosphorus release from cattle manure ash as soil amendment in laboratory-scale tests

Excessive application of animal manure to farmland leads to phosphorus (P) loss into the surrounding water. Manure is incinerated to convert it to P-rich ash as a slow-release P fertilizer. However, the potential P loss and P availability for plants from cattle manure ash (CMA) have not been fully understood. The aims of this study were to determine the P release mechanism from CMA and to propose appropriate application rates that mitigate P loss and increase available P to soil in Fukushima, where the soil is deficient in nutrients after the replacement of cesium-137-contaminated soil with sandy mountain soil. Different P fractions in CMA were sequentially extracted with H2O, 0.5M NaHCO3, 0.1M NaOH, and 1M HCl. Phosphorus contents in different fractions of CMA were in the order of HCl-P>NaHCO3-P>H2O-P>NaOH-P. Water-soluble P release of CMA was also determined by kinetic experiments for 120h. Results showed that total water-soluble P accounted for a maximum of 2.9% of total P in CMA over 120h due to recalcitrant P compounds formed through incineration. The Fukushima sandy soil amended with CMA at three application rates, 94, 157, and 314mgPkg(-1) (corresponding to 300, 500, 1000kgP(2)O(5)ha(-1)) was incubated for 56days. Cattle manure compost and KH2PO4 were applied at 157mgPkg(-1) for comparison. Phosphorus release in water and CaCl2 solution from ash-amended soil was significantly lower than those from compost and KH2PO4-amended soil at the same P application rate of 157mgPkg(-1) (p<0.05). Available P in ash-amended soil, determined by Fe-oxide impregnated strips, was not significantly different from those in compost-amended soil after day 7 and KH2PO4-amended soil on day 56 at the same P application rate. Thus, CMA reduces P losses from soil to the surrounding water while it increases P availability for plants. In comparison of different rates of CMA, P release in water or CaCl2 was significantly greater at 314mgPkg(-1) than at 94 or 157mgPkg(-1), while the percentage of available P to total P was the lowest at the highest application rate (p<0.05), suggesting that the best application rates were 94 and 157mgPkg(-1) in this experiment.