Soil water and mineral nitrogen content as influenced by crop rotation and tillage practice in the Swartland subregion of the Western Cape

Abstract

Adoption of conservation agricultural practices, reduced tillage and crop rotation in the grain-producing areas of the Western Cape, South Africa, resulted in a gradual build-up of organic matter on the soil surface. It was expected that the increase in organic matter cover would influence soil water content and nitrogen mineralisation potential of the topsoil. The effect of crop rotation and tillage practice on soil water (g g⁻¹) and mineral-N content (mg kg⁻¹) in the 0–200 mm soil layer during 2010 and 2011 was assessed. Crop rotation, wheat monoculture (WWWW), lupin–wheat–canola–wheat (LWCW) and wheat–medic rotation (McWMcW) and tillage, conventional-till (CT), minimum-till (MT), no-till (NT) and zero-till (ZT) were studied. Crop rotation did not influence soil moisture content. Soil water content in CT tended to be lower compared with the other tillage treatments tested. A tendency of higher mineral-N in CT was observed, although not for all sampling dates. Mineral-N content did not differ between ZT, NT and MT. It is concluded that tillage influenced soil water and mineral-N content, whereas crop rotation only influenced mineral-N if the system included a legume crop (medic). Results obtained could be valuable in developing management strategies for wheat grown under different production systems.

Keywords: crop rotation, nitrogen mineralisation, soil tillage, soil water content