Distribution of Nitrogenous Compounds in a Rhodic Paleudult Following Heavy Manure Application

Agriculture faces the problem of animal manure disposal while maintaining crop yields and soil water quality. There is an economic advantage of manure disposal at elevated rates close to the source. This in turn increases the potential for groundwater contamination. This study was conducted to determine the effect of high rates of cattle and poultry manure application on the N balance and on the distribution of NH₄⁺, NO₃⁻, NO₂⁻, and total N to a depth of 6 m in a Davidson clay loam soil (Rhodic Paleudult, clayey, kaolinitic, thermic). Average dry weights of manure added per year (from 1972 to 1976) were 32, 61, and 121 Mg ha⁻¹ for cattle and 94 and 184 Mg ha⁻¹ for poultry waste. In addition to manure treatments, a fertilizer treatment and a control were also present. A N balance showed that while 36% of the inorganic fertilizer N applied was removed by the crop, with manure application < 10% of the total was crop recovered. The percentage of the total N in the upper 6 m of the soil profile generally decreased with increased manure N application, although N present increased with increased N applications. The unrecovered N, attributed primarily to denitrification losses, increased with increased N application and ranged from 6% for the fertilizer check to 58% for the highest rate of poultry manure. The primary inorganic N component in the soil profile was NO₃⁻-N and the zone of maximum accumulation is between 2 and 2.5 m. The organic N fractions remaining in the soil profile could be adequately estimated using existing decay constants. The present study shows that the most feasible means of determining the quantity of manure to apply for crop growth and simultaneously reduced N leaching would be the use of decay series for manure decomposition combined with an estimate of atmospheric loss.