The Swedish journal “Greppa Näringen” recently released an article based on ten years of research in Switzerland, claiming that different levels of reduced tillage mitigates effects on erosion compared with conventional seedbed preparation. The research shows that the soil losses decreased by 90 percent when reduced tillage replaced ploughing and harrowing.
Different levels of reduced tillage mitigated erosion compared with conventional seedbed preparation
In the unique study “On-farm effects of tillage and crops on soil erosion measured over 10 years in Switzerland”, erosion from ordinary arable farming of over 200 fields was investigated for a 10-year period. The crops grown, the slope of the land and precipitation amounts in the study area are similar to those experienced in some Swedish agricultural areas. The contribution of arable land to phosphorus losses to water environments mainly takes place via erosion of topsoil.
203 fields over 10 years
The investigation included 203 fields on 52 farms. The crops grown were winter wheat, grass ley, maize, sugar beet, winter barley and potatoes. Mean annual precipitation was just over 1 000 mm and the topsoil is described as free-draining clay with a moderate risk of erosion.
The farmers were interviewed about the crops grown on the actual fields during the period 10 years, with the emphasis on how they tilled the soil. Soil tillage was divided into four classes, the first of which was conventional tillage, with ploughing and one or two harrowings. The other classes comprised reduced tillage of different forms, with direct drilling at the other end of the scale.
Farmers plough less
During the 10-year period, the farmers decreased conventional seedbed preparation (ploughing plus 1-2 harrowings) by as much as half. Instead, all forms of reduced tillage increased. This had great significance for soil erosion. For fields with conventional tillage the estimated soil losses were 1 240 kg per hectare and year. For the two different forms of reduced tillage that leave more than 30 percent of the soil covered with crop residues, the corresponding losses were 70 to 120 kg per hectare and year, a reduction in the order of 90 percent.
The crop grown was also very significant, with ley of course having the lowest erosion (70 kg soil per hectare and year). The greatest soil losses, of almost 3 000 kg per hectare and year, occurred in the year in which potatoes were grown, with an unexpectedly high proportion of these losses occurring during the summer half-year.
Two to four tons ’acceptable’
On average, the losses were 750kg soil per hectare and year. This is equivalent to around one cubic metre of soil. According to official Swiss guidelines, soil losses of less than 2-4 tons per hectare and year are ’acceptable’. The combined erosion from the 203 fields studied varied greatly between years, from around 50 to around 500 tons per year. There was no correlation between annual precipitation and erosion within years. Instead, the amount of soil lost was determined by how long and how intensively it rained in individual rainfall events and the state of the soil surface at the time.
Prasuhn, Volker 2012. On-farm effects of tillage and crops on soil erosion measured over 10 years in Switzerland. Soil and Tillage Research, vol. 120.