Mineralizable Carbon, Nitrogen, and Water‐Extractable Phosphorus Release from Stockpiled and Composted Manure and Manure‐Amended Soils

Abstract

Dissolved N and P transfer to runoff water may increase with surface applications and shallow soil incorporation of animal manure. Information is needed regarding water‐extractable nutrient release during manure decomposition to quantify that potential transfer to runoff in permanent pastures and conservation tillage systems. Release of net mineralizable C (MIN_C), net mineralizable N (MIN_N), and dissolved reactive P (DRP) was determined in stockpiled and composted cattle ( Bos taurus ) manure and manure‐amended soils at 4, 20, and 35°C for 322 d at about 60% water‐filled pore space. Flushes of CO 2 –C exceeding 100 mg kg −1 d −1 , inorganic N, and DRP were released rapidly from both manures when incubated alone or as soil amendments. Dissolved P release varied inversely with sorption capacity and degree of P saturation in an Aridic Paleustalf and Torrertic Paleustoll. Net mineralizable C, MIN_N, and DRP flux densities were lognormally distributed during the 322‐d incubation. Results from the lognormal modeling approach suggest that incubations needed to be performed only for as long as needed to attain the 50% maximal flux density beyond the maximum to predict MIN_C, MIN_N, and DRP release flux density distributions. Significant nonlinear relationships exist between ln(cumulative CO 2 –C) and inorganic N or DRP and have an inflexion point between 14 and 20 d. The nonlinearity of the C‐to‐N and C‐to‐DRP relationships indicates multiple substrate pools and supports the use of lognormal distributions to describe MIN_C, MIN_N, and DRP release from manures and manure‐amended soils and to shorten laborious incubations.