Soil fertility trends and management in Conservation Agriculture: a South African perspective

Conservation Agriculture (CA) is an integrated approach that consists of a suite of practices, namely no-till farming, cover crops, and crop rotation that includes at least three crops. In the global context, CA is implemented widely in South America (Argentina and Brazil) and North America (United States and Canada), with smaller proportions in Australia and New Zealand. There is little implementation of CA elsewhere in the world mainly because of natural resource constraints. Benefits of the system include increases in soil organic matter and related increases in organic N in soils. Experimental results show extremely strong stratification of important plant nutrients, particularly P, K and Ca, at very shallow soil depths (<5 cm) under a no-tillage system due to their low mobility in soil. Results to date have demonstrated poor root development near the soil surface under the extreme conditions in the marginal cropping areas that dominate most of South Africa’s crop production areas. Plant nutrient uptake is thus much lower under no-till farming than under conventional tillage. Furthermore, scarce movement of lime was found under no-tillage, hampering amelioration of soil acidity. Research in South Africa has confirmed international data that indicate maize requires much higher N application under no-tillage than under conventional tillage.