The formation of acidic subsurface layers in soil under stock urine patches with special emphasis on nitrogen transformations

The cause of the formation of acidic subsurface layers in urine patches was examined.The rate and magnitude of N processes occurring under simulated urine patches in column studies in the glasshouse and laboratory were examined in 2 cm depth increments and related to the observed changes in soil pH. A H+ balance model was used to determine the magnitude of the soil pH change attributed to the N processes of urea hydrolysis, NH3 volatilisation, nitrification, and net mineralisation/ immobilisation in a soil column study in the absence of plants. The influence of plant growth on soil pH change after application of simulated urine was investigated in a soil column system. The effect of varying concentrations of simulated urine constituents (urea-N and KCl) on soil pH after application to soil under actively growing plants was also determined. A field study was conducted to substantiate the formation of acidic subsurface layers in a ryegrass pasture during two varying environmental seasons. Acidic subsurface layers were produced in both spring and summer as a result of N transformations occurring after the application of simulated urine solutions.