Loose, clump-free, crumbly and reconsolidated – these are the optimum characteristics of cultivated soils. Tillage is becoming increasingly important in achieving this, particularly in view of fertiliser regulations and the restricted use of plant protection products. The main options for tilling are stubble cultivation, primary tillage and seedbed preparation. In general, as with all field work but especially tillage, it is important to avoid damage from soil compaction. In this context, stubble cultivation becomes highly significant.
Goals of stubble cultivation
The primary goal of stubble cultivation is to reduce the amount of residual seeds in the soil, and to encourage weed seeds and volunteer cereals to germinate by incorporating them just below the surface. This involves incorporating the organic matter into the soil at a shallow depth and disrupting capillary action in the soil, which prevents rising water from evaporating. It usually requires at least two passes. The first pass is shallow and the second is at a medium depth, which enables the crop residues to be distributed within the soil. To optimise the mixing effect and to break up tyre tracks, it is recommended to work at a 15-degree angle to the direction of the stubble during cultivation (around two threshing widths). The timing of stubble cultivation is highly weather-dependent. There should ideally be no rainfall between the first, very shallow cultivation pass and the following, deeper cultivation pass. If the cultivator is set too deep during the first pass, the incorporated soil horizon can dry out, causing the opposite effect. On the other hand, to retain as much ground water as possible, the ground should be tilled promptly after harvesting.
Any residual seeds from weeds or the previous crop can be eradicated either mechanically or chemically before sowing the next crop. This requires them to germinate evenly. Shallow cultivation has additional positive effects, such promoting a crumbly, well-consolidated soil texture. When controlling weeds and unwanted plants mechanically, the weather should be dry – including on the subsequent days – to prevent the plants that are pulled out from continuing to grow. Controlling some particular weeds, however, requires multiple passes of deep cultivation to bring their subterranean rhizomes up to the surface. Tillage encourages the organic matter in the soil to rot. By mixing soil into the crop residues, it facilitates their conversion, which prevents pathogens from being transferred to the new crop.