Crop rotation and tillage system effects on reducing ryegrass occurrence in spring wheat
Under the Mediterranean climatic conditions of the Western Cape province, the Swartland region is intensively cropped, producing spring wheat (Triticum aestivum L.), but due to ryegrass competition, yield is reduced. In addition, ryegrass has developed resistance to herbicides. This necessitates the use of integrated weed management practices for suppressing ryegrass in wheat fields. The objectives were to quantify and qualify the impact of crop rotation and tillage systems used in combination with reduced herbicide input and to determine whether these could reduce ryegrass population numbers. Analyses of variance of data were used to determine crop rotation × tillage system response in field and shade-netting experiments. Wheat monoculture, in both tillage systems, was associated with the highest ryegrass population increase in both years. The results of both the field and shade-netting experiments showed that there was no significant difference between minimum-tillage and no-tillage in reducing ryegrass numbers. Results obtained from the shade-netting experiment indicated that the three crop-rotation treatments under minimum-tillage differed significantly from the control. In the field wheat–medic–wheat–medic rotations under no-tillage out-performed all other rotations, followed by wheat–lupin–wheat–canola under minimumtillage. It is essential to use competitive crop sequences that decrease particular weed population numbers.
Keywords: crop rotation, ryegrass reduction, ryegrass seedling emergence, tillage system