Liquid Swine Manure Application Timing and Nitrification Inhibitor Impacts on Soil N Transformations and Corn Growth.

Nitrogen (N) is one of the most expensive variable input costs for corn production. Optimized manure management is essential to ensure maximum crop N utilization and to reduce the risk of N loss. A field study was conducted in central Indiana from 2011-2013 to assess liquid swine (Sus scrofa L.) manure N availability when applied at different times or co-applied with Instinct^TM, a microencapsulated form of nitrapyrin. Soil inorganic N contents, soil N mineralization, corn yield, grain N uptake, whole plant N concentrations of corn V6 growth stage, and ear leaf N concentrations of R1 growth stage differed from year to year and were greatly influenced by manure application timing and climate conditions.

A static cup incubation was used to assess N mineralization from soil samples collected at two depths at various times (early winter, planting and corn V6 growth stage). The cumulative net N mineralization was fitted to a first-order exponential model to determine potentially mineralizable N (N₀) and N mineralization rate constant (k).The results showed that at both soil depths, cumulative mineralizable N up to 16 weeks was not affected by liquid swine manure application timing or the use of Instinct^TM. Differences in total soil inorganic N after incubation were mainly due to soil initial inorganic N differences. Negligible amounts of NH₄⁺-N were recovered from soil extracts in all treatment plots during incubation study, indicating that nitrification occurred and that there was little efficacy from Instinct^TMat controlling nitrification at the time of soil sample collection.

Spring liquid swine manure showed higher corn productivity and grain N uptake (6.9 Mg/ha and 61.2 kg N/ha) compared to early fall applications (5.1 Mg/ha and 44.6 kg N/ha) only at Location 3 during 2013 growth year, while during 2012 growth year corn yield appeared to be unaffected by manure application timing. Distinct climate conditions of these two years were considered as a main source of yearly inconsistence. Corn growth and yield was not affected by the addition of Instinct^TM at any location. Primary factors that could have affected efficacy of this nitrification inhibitor include: i) the release rate and concentration of nitrapyrin from Instinct^TM with time in soil; ii) sorption of released nitrapyrin by organic matter and clay minerals in soils; and iii) efficacy of released nitrapyrin on nitrifiers under the varying soil moisture and temperatures encountered during this field study.