Evaluating the impact of manure application timing on corn uptake and losses of nitrogen
The agronomic value of livestock manures as a nitrogen (N) source and the potential environmental losses of N in corn ('Zea Mays' L.) production were compared over different manure types, application rates and the times of application throughout the year. Corn N-uptake response to spring applications of liquid hog manure (LHM) and liquid cattle manure (LCM) were greater than the late-summer and fall applications. Spring applications of LHM and LCM had an increased proportion of N recovered than the late-summer and fall applications. A pulse of mineral N after the late-summer and fall applied LHM and LCM was found at lower soil depths indicating that the reduction in N recovery may be attributed to leaching losses. Solid poultry manure (SPM) and solid cattle manure (SCM) had a greater proportion of N as organic-N. Since the late-summer and fall applications were greater in N-uptake than the spring applications, this may be due to the mineralization of the organic N. No increases in mineral N concentrations at lower depths were detected for each manure type over the application times. The proportion of available mineral N present within manure types may more directly affect the potential for livestock manures to serve as an N source. Environmental losses of manure N due to application timing may be a function of the proportion of manure as mineral N and seasonal conditions associated with application times. In particular, applications during seasonal patterns of downward water movement increase the potential for mineral N leaching to lower soil depths and to groundwater sources.