NITROGEN-CYCLE PROCESSES AND ACIDIFICATION OF SOILS IN GRAZED PASTURES RECEIVING OR NOT RECEIVING EXCRETA FOR 23 YEARS

Soil acidification in agricultural systems can be related to production and consumption of protons during nutrient cycling processes. Carbon and nitrogen cycles are particularly important in this respect for grazed pastures. Rates of acidification were calculated for grazed pastures that had received animal exreta in the normal way and for areas that had been free from excreta for 23 years. Acidification rates were 3.59 and 0.86 kmol H+ ha-1 yr-1 respectively. Measurement indicated that the areas were not diverging in pH. Short term effects of excreta caused a significant increase in pH over much of the area receiving excreta. When these effects were eliminated, no indication of decreasing pH or titratable acidity in the areas receiving excreta was apparent; a decrease in buffer capacity in the 150-300 mm horizon was noted, however. The calculation of acidification rates is discussed and the possible need to account for movement of NH4+ and inputs of CO3(2-) in faeces is identified.