It’s a mild summer evening in Vierkirchen, where around 30 farmers from southern Bavaria have gathered around Michael Pabst. Tonight, he and Max Stadler from the Society for Conserving Soil Treatment (GKB) will be presenting the cultivation method of the transverse dam greening for potatoes, which is intended to protect the arable soil from erosion. Since Bavaria is Germany’s second largest potato region after Lower Saxony and potatoes are grown in almost every region, the topic discussed at the Mitterwiedenhof is of great interest.
Tim Meier, also from the GKB, and Martin Gruber from the Ingolstadt-Pfaffenhofen Agricultural Office will open the event: Erosion in potato cultivation is a problem that most farmers in Bavaria have to contend with, explains Meier. Gruber then thanks farmer Pabst for his “pioneering work and providing valuable soil”. He hopes that this new cultivation method will reduce the problem of erosion in potato cultivation and “the soil will stay where it belongs”. Here Stadler takes the floor and explains the theory behind this cultivation method. He got to know her in Austria, where farmers also sown oats between the transverse dams in order to strengthen the dams with the roots of the oats, to better hold back the water with the additional plants and to make the soil more absorbent.
Transverse dams slow down the flow of water
Because of the way they are cultivated, potato fields are very susceptible to damage caused by heavy rainfall, such as erosion and waterlogging. First, dams are built on the potato fields, into which the tubers are then planted. After settlement, the soil is very sensitive to erosion by water and even on gently sloping surfaces, a heavy rain event can cause water to pool in the valleys between the levees, taking soil with it. Another consequence is uneven water supply in the field. One solution are transverse dams that are also created. As a result, the water flow can be significantly slowed down and kept at the place of precipitation.
Pabst grows his potatoes exclusively with this method of cultivation. This type of cultivation has paid off for him because he has many fields with slopes. But the transverse dams alone are not effective enough. That’s what he found out when he tried greening the transverse embankment on an area of three hectares for the first time last year. At that time he planted oats and spring barley between the transverse dams and found that the additional plants made the water run off more slowly, less soil was washed away and everything was “much more stable”.
Winter barley stabilizes the potato dam
This year he laid new transverse dams with greening on 30 hectares, the remaining area remains without greening. This time he planted winter barley instead of oats and spring barley, as this crop is slower growing when the field is planted with it in spring. In contrast to spring barley, this type of barley does not represent any competition for the potato plants. Winter barley also has the advantage that it first grows in width instead of driving up like oats. This way they hold the water more effectively.
Pabst and Stadler can show the direct comparison on the adjacent field this evening and simulate heavy rain with a watering can. The amount of water roughly corresponds to the amount that occurs during heavy rain. “During the last heavy rain I had almost 30 liters in 15 minutes,” says Pabst. “I found that the winter barley slowed down the flow of water considerably.” For him, the sown barley was a success.
Without greenery, the rain rushes through
The difference is clearly shown in the experiment with the watering can: the flow of the water is interrupted by the sown winter barley between the dams. In the transverse dams – without greening – the water simply rushes through quickly and without hindrance. Here the dry soil cannot absorb the water as fast as it flows over it. And on the sides of the heaped-up dams, the water takes small clods of earth with it: “With such an amount of water, there isn’t much soil left,” Pabst points out during the performance. “Erosion is a gradual process, by the time you notice it it’s usually too late.”
In the future, heavy rainfall will increase, which is due to climate change, says Stadler: “You can’t change the weather, but you can change the fields and with this cultivation method you can protect the soil from erosion.” For Pabst, this cultivation method has led to higher yields and is the only sustainable solution to the erosion problem. He implemented the experiment as simply as possible, every farm has the necessary technology. “I can only advise everyone to try it out. Anything is better than watching the bottom float away,” are Pabst’s final words.