A Decade Plus of Monoculture Wheat Compared to Wheat/Legume Pastures – Long-term Effects of Management Practices on Some Soil Physicochemical and Microbial Properties in the Winter Rainfall Region of South Africa

The quest for sustainable agriculture has increased along with the ever increasing demand for food and fibre by the growing human population. It has been realised that monoculture is probably not sustainable and has a detrimental influence on the soil’s capability to produce food and fibre. In 2010, we reported on a four year study that was conducted in the wheat producing area of the Western Cape, South Africa, in which we compared the effects of monoculture wheat to wheat in a legume/pasture rotation, with regards to soil physicochemical characteristics and culturable microbial populations. In order to determine the long-term effects of the two management systems on these parameters, the site was revisited in 2019. Soil biological aspects measured were aggregate stability, active carbon levels, microbial activity as well as carbon substrate utilisation as measured by Biolog EcoplatesTM. Physicochemical properties measured included soil moisture on the day of sampling, as well as the levels of organic carbon, boron, sulphur and phosphorous in the soil. It was found that the carbon substrate utilisation patterns in 2019 were significantly different from those recorded in 2006. When the variables tested in 2019 were analysed, the different management systems separated clearly. Interestingly, substrate utilisation was higher in the monoculture system. This could be attributed to the possibly higher plant diversity and the associated root exudates of these systems, should the weed infestation that was occurred, be considered. Further long-term research is needed in the quest for sustainable agriculture and healthy soils.