Tillage and its temporal effects on soil organic matter and microbial characteristics in the semi-arid central South Africa

Abstract

Context Tillage has temporal effects on soil organic matter and microbial attributes. Aim Three tillage systems (NT, no-tillage; MT, mulch tillage; MP, mouldboard ploughing) were used to assess the impact on soil quality indicators such as gravimetric soil water content (GSWC), soil organic carbon (SOC), total nitrogen (TN), easily extractable-glomalin (G EE), dehydrogenase (DHA), β-glucosidase (β-glu), urease (URE), acid-(AcP) and alkaline-(AlP) phosphatase over time in a sandy-loam Plinthustalf cropped annually with winter wheat and occasionally oat in eastern Free State. Methods Samples were collected during oat (October 2010, November 2010), fallow (February 2011, April 2011, May 2011) and wheat (August 2011, September 2011, October 2011) phases at 0–5 and 5–10 cm depth. Results When averaged over sampling dates, GSWC, SOC, TN and enzyme activities were 6–85% higher under NT than in MT and MP in the upper 5 cm soil. Trends changed at the 5–10 cm depth, with 20–32% higher enzyme activities recorded under MT. Soil quality indicators exhibited different trends over time, with GSWC, TN, DHA, AcP and AlP generally increasing during the fallow period and decreasing during oat and wheat phases, while β-glu was higher during both crop phases than at fallowing. URE was 33.6–174.3% higher during the oat phase than at the fallow and wheat phases. The opposite was observed with SOC, C/N ratio and G EE. Conclusions Enzyme activities were sensitive indicators, but SOC and TN can be used to assess temporal changes in soil quality in resource-limited countries. Implications However, temporal effects on SOC and TN were probably built in the long-term, hence further research focusing on multiple seasons is required.