Plowing and tillage on hilly slopes is depleting soils on farms and threatening future crops, according to a new study published in the journal Nature Food. portal sciencedaily.com.
Scientists from the universities of Lancaster (UK) and Augsburg (Germany) argue that if farmers do not stop working on hillsides, in the long term the soils on the hillsides may become thinner to the point that food crop growth will be seriously threatened.
For centuries, farmers have worked the soil in their fields to create seed beds for growing crops. At one time, traditional animal-drawn plows were used for this purpose, but as agriculture has been mechanized over the past century, tillage has shifted to heavier and faster tractors.
Tillage, including tillage, is known to move significant amounts of soil down slopes and increase weather-induced erosion. On slopes, tillage causes the soil to move down the hills and settle on the bottom of the valleys.
As soil is depleted on slopes, material from the subsoil mixes with the topsoil, reducing crop quality due to nutrient deficiencies, biological activity and reduced water availability.
The scientists note that the role of tillage in reducing soil depth remains an under-recognized threat to crop production. Although tillage is known to move significant volumes of soil downslopes, often exceeding the volumes moved by water and wind erosion, little has been known so far about how the result of such action affects crop yields. As tractor power continues to increase and climate change increases the frequency of droughts, the impact of tillage soil erosion on crop yields in sloping terrain is likely to become more severe in many parts of the world.
The researchers studied crops of wheat and corn grown in the northern German region of Uckermark, which is a highly mechanized and productive agricultural area in Europe. The researchers used published information on the effect of cultivation on crop yields and applied soil redistribution and crop growth models to study the effect of tillage at a regional landscape scale.
This allowed them to determine whether the yield gains in those parts of the landscape that received soil from erosion outweighed the losses caused by soil depletion on the slopes.
Their calculations show that if the usual approach to tillage on slopes is maintained, farmers in the Uckermark region will face a cumulative decline in winter wheat yields of up to 7,1% over 50 years and up to 10% per cent over a century (in normal and dry years).
For corn, the researchers predict a yield reduction of 4% over 50 years and 5,9% over 100 years (in normal and dry years).
The effects of soil depletion will be most pronounced during a drought, as depleted soils are less able to retain moisture and nutrients. In wetter years, although not as much as in normal and drier years, yields will also decline over 50-100 years.
This decline in yields is equivalent to thousands of tons of wasted food in the Uckermark region alone. The researchers believe that reduced yields due to soil erosion are likely to be seen worldwide where tillage is carried out on slopes.
They argue that this projected increase highlights the need for urgent action to reduce tillage-induced soil depletion.
Farmers may consider measures such as adapting the tillage rate to the position of the slope and generally reducing the tillage depth to slow down the erosion process. But in fact, according to scientists, farmers should stop tilling on slopes to protect their soils and future crops.
Although the researchers did not model the effects of climate change, they believe that tillage-induced soil erosion pressures will increase as climate change increases the frequency of dry spells during crop growing seasons.