Nitrogen-cycle processes and acidification of soils in grazed pastures receiving or not receiving excreta for 23 years

Abstract

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 NH+4 and inputs of CO2-3 in faeces is identified.

Effects of fertiliser application on nutrient status and organic matter content of hill soils

“…Sinclair et al (1993) suggested that where it is not financially viable to lime hillcountry, long-term sustainability of farming is questionable. Despite this, there is no clear evidence for acidification of soils in legume-based pastures in New Zealand (Carran & Theobold 1995). Sakadevan et al (1993) measured only small annual NO3-N leaching losses (1.3 to 3.7 kg N ha" 1 ) within the trial described here.…”

“…The effect of intensification on soils and pastures was generally viewed as being beneficial, resulting in increases in soil organic matter quantity and quality (Haynes & Williams 1993), although some negative consequences were quantified, e.g., the effects of soil slip erosion on pastures and soils (Trustrum et al 1984) and the influence of intensification on nutrient and soil losses (Lambert et al 1985). More recently, the potential for soil acidification has been debated (Bolan et al 1991;Carran & Theobold 1995).…”

Soil acidification: A provisional model for New Zealand pastoral systems

“…(2) where DMin is the dry matter intake (kg/SU), CC Monaghan et al (1996) Monaghan et al (1996) Monaghan et al (1996) Monaghan et al (1996) Sinclair (1995) Carran & Theobald (1995) a In mg NO3" -N per kg soil. b When an additional 150 kg MCP-P was applied, the EC contents were 0.64, 0.54, 0.47, and 0.42 mol c /kg DM for the 4 N rates, respectively.…”

Monitoring long‐term changes in reserve potassium in some New Zealand soils using a modified sodium tetraphenyl‐boron method

“…Dry matter production estimates from the Aorangi site were approximately 6 and 15 tonnes DM/ha per year from fence-line and paddock plots, respectively (Carran & Theobald 1995). Net differences in DM and excreta returns between sites of over 200 kg K/ ha per year was considered a reasonable assumption with total net K removal from fence-line locations at the Aorangi site over the last 23 years estimated at c. 6000 kg K/ha or c. 260 kg K/ha per year.…”