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Worldwide soil quality of different tillage systems receives attention worldwide. However, studies which attempt to link soil quality to yield are uncommon. The authors of the study referenced below aimed to identify the soil quality properties which best model pasture yield by relating those soil quality indicators with variations in pasture yield as a result of a soil disturbance gradient caused by tillage. The study was conducted on kikuyu pasture over-sown with annual ryegrass using different tillage methods. The methods were over-sowing kikuyu with ryegrass (1) using a minimum-tillage seed-drill, (2) eradication of kikuyu with herbicide and ryegrass sown with a minimum-till planter, (3) shallow (less than 150 mm) and (4) deep (more than 150 mm) disturbance with a cultivator or conventional tillage, respectively, and (5) a control.
Most changes in soil quality indicators as a result of soil tillage were observed shortly after tillage, and occurred mostly at the 0 – 100 mm soil layer. Few of these effects were still visible 420 days after tillage. Microbiological indicators were most sensitive. The contribution of individual soil quality indicators to the pasture productivity could not be isolated, probably because they interact as a complex which involves multi-faceted processes, the outcome of which is a particular yield. Thus, although the mechanism of how some soil quality indicators affect yield is well-described, more research is required to determine the ways of how a combination of multiple soil quality indicators affect yield.
Reference:
P. A. Swanepoel, C. C. du Preez, H. A. Snyman, P. R Botha, & J. Habig. 2016. Tillage effects, soil quality and production potential of kikuyu-ryegrass pastures in South Africa. Proc. of the 51st Annual Congress of the Grassland Society of Southern Africa, Wilderness, 4-8 july 2016.