Effect of tillage systems and nitrogen application rates on selected physical and biological properties of a clay loam soil in KwaZulu-Natal, South Africa

Abstract

The effects of agricultural management practices on soil physical and biological parameters provide fundamental information for assessing sustainability. Tillage (annual conventional tillage and no-till) and nitrogen fertiliser (limestone ammonium nitrate at rates of 0, 100 and 200 kg N ha⁻¹) were evaluated for their effects on bulk density, water retention characteristics, saturated hydraulic conductivity, soil penetration resistance and microbiological activity (hydrolytic and cellulolytic) on a clay loam soil (Typic Haplustox) at a field experiment initiated in 2003 and planted to dryland maize. Tillage regime and nitrogen application rate significantly (p < 0.05) affected soil physical properties and microbial activity in the 0–5 cm layer. Under no-till the saturated water content and saturated hydraulic conductivity were significantly lower than under annual conventional tillage while plant available water was greater under no-till. Penetration resistance, bulk density and microbial activity were greater under no-till than annual conventional tillage. At 200 kg N ha⁻¹ microbial activity, bulk density, water retention and saturated hydraulic conductivity were significantly lower than at the lower rates of application, especially under no-till. These results indicate that no-till improved soil physical properties and suggest there is a need to re-evaluate the sustainability of using high rates of nitrogen to increase maize yields, especially under a no-till system.