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Animal manure contains significant amounts of nitrogen (N) and phosphorus (P) that can be utilized as fertilizer. However, manure application rates are generally set to meet crop N demand, which results in excess P application which increases the risk of P loss into bodies of water. We examined the application method of manure compost based on crop P demand on the dry matter yield of silage corn (Zea mays L. var. indentata), on nutrient uptake and on soil P accumulation in an upland Andosol with a high P-fixing capacity. Cattle and poultry manure composts (CMC and PMC) with different P solubility were applied to meet the crop's N requirements (N-based application) or P requirements (P-based application) in 3 consecutive years. Supplemental N was applied using polyolefin-coated urea in the P-based treatments. The dry matter yields and nutrient uptakes of silage corn in the P-based CMC and PMC application systems were similar to those in the corresponding N-based systems. The average relative efficiency of N in CMC (33%) was close to the predicted value (30%) during the study. On the other hand, the relative efficiency of N in PMC (42%) was higher than the predicted value (28%). The average relative efficiency of P from CMC and PMC was 109% and 50%, respectively. These were higher than the predicted values based on the available P proportion (the sum of water-and sodium bicarbonate-soluble P) for CMC (78%) and PMC (34%), indicating that the available P fraction in the manure composts was more effective than that in P fertilizer for corn growth or that the other P fractions were also effective for corn. P-based manure compost application lowered the soil P accumulation to between 41 and 43% of the value in the N-based accumulation (versus a value of between 31 and 40% of that value for soil Truog-P). Compared to N-based manure compost application, P-based manure compost application with supplemental N fertilizer produced similar dry matter yields of corn and suppressed soil P accumulation in the upland Andosol field.

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Swine manure compost (SMC) contains a significant amount of phosphorus (P). In this study, the characteristics of P compounds in SMC were investigated by the nondestructive X-ray diffraction (XRD) method, chemical extraction, and a cultivation experiment. Only magnesium ammonium phosphate hexahydrate (MAP or struvite, MgNH 4 PO 4 ·6H 2 O) was detected as crystal P compound by XRD in most SMC. Furthermore, MAP crystal was observed by scanning electron microscope (SEM) image. The amount of ammonium nitrogen in MAP (MAP-NH 4 -N) was 3.38 ± 2.24 mg-N g -1 on average, equivalent to 54% of total NH 4 -N (hydrochloric acid-extractable NH 4 -N) in SMC. The content of P in MAP (MAP-P) in SMC calculated backward from MAP-NH 4 -N was 7.5 ± 4.5 mg-P g . Sequential water extraction demonstrated that MAP in SMC was dissolved in water. The ratio of MAP-P to water-extractable P (WEP) was 66%, indicating that the amount of WEP was controlled by MAP existence in SMC. The amount of P uptake by the Japanese mustard spinach (Komatsuna; Brassica rapa var. perviridis) plant accorded with WEP content in SMC.

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