Mineralizable phosphorus, nitrogen, and carbon relationships in dairy manure at various carbon-to-phosphorus ratios

Phosphorus (P) in animal manure can be an important nutrient for crops or an environmental contaminant if in excess. Organic P in dairy manure may add to the environmentally bioactive P pools upon mineralization. A 353 d incubation study of manures containing C:P between 83 and 130:1 was conducted to determine linkages between C and P transformations and the effects of C:P on the immobilization–mineralization of manure P. As C:P widened from 83:1 to 130:1, P mineralization increased and phosphate accumulated at rates between 0.013 and 0.021 mg kg−1 d−1. Water-extractable C was positively correlated with N:P, particularly at narrow C:P (P < 0.001). Absence of a negative feedback by phosphate suggested that P mineralization occurred with degradation of organic P-containing C substrates and appeared incidental to microbial P needs. Carbon content in manure may be managed to lower risks of elevated soluble P and C losses under non-limiting N conditions.