Climate sequences – winter rain washes nitrogen out

Fifty years ago, it was common in Germany to plow the harvested arable floor in late autumn in order to suspend it for several months of the cold. The frostgar that started in winter made the ground loose and fine -crumbly, so that the farmers were able to sow again successfully in spring.

From the past, many still know the autumn picture: behind the mechanized plowing that were pulled by tractors, large, thrown earth floes remained. In December at the latest, they were covered by a thick layer of snow that gradually thawed in spring. The melting water moistened the floor, expanded during the night frosts and blew up the soil crumbs. This process, called Frostgare, hardly took place in the past ten years, especially in northwestern Germany, states Uwe Kalthoff, coordinator of a model consultant team that developed strategies for water protection together with farmers in North Rhine-Westphalia.

In the Allgäu, too, the number of frost days in the winter months from an average of 17.8 days in the 1970s decreased to an average of 12.6 days a year between 2013 and 2022. The middle winter temperatures have often been above three degrees plus since 2013.

The lack of frost in winter also has a negative impact on nutrients such as nitrogen and phosphorus, which are still released in the months with less light intensity. This leads to great loads of the groundwater as well as surrounding rivers and lakes.

Always green is better

Changed weather conditions require different approaches in agriculture. This applies above all to the areas in the north and northwest of Germany, but partly also to the low mountain ranges in the south and southeast. Between September and October, winter cereals or a snack such as mustard are sown. On the one hand, the young plants should protect the otherwise bare ground from soil erosion by wind or glossing of mud for heavy rain. On the other hand, in -line crops can take advantage of the remaining remains of fertilizer containing nitrogen. This is to prevent too many nutrients washed out of the ground with the beginning of wet cooling, rainy weather in the autumn and winter months.

Nd.Diewoche – Our weekly newsletter

With our weekly newsletter . We’re Doing Look at the most important topics of the week and read them Highlights our Saturday edition on Friday. Get the free subscription here.

Nitrogen that comes into the groundwater in a mineralized form as a nitrate with the rainwater is highly stressed by the drinking water obtained from it. In Germany, around two thirds of the drinking water requirement made of groundwater are covered.

Danger for infants

If nitrate gets into the drinking water, newborns and infants under six months are particularly at risk. Due to its stomach colonization with other bacteria than in adults, a nitrate can be converted into the harmful nitrite.

This leads to the oxidation of the blood pigment hemoglobin to methemoglobin, which cannot bind and transport oxygen. An enzyme that builds up this methemoglobin in the body is not yet so effective in newborns. As a result, infants suffer an acute lack of oxygen, which is evident in a blue coloring of your skin and can be fatal.

Not all babies are so sensitive to nitrate in the prepared infant food, but the vulnerable children need to be protected. With the limit of 50 milligrams of nitrate per liter of water, a risk should be excluded.

The problem of nitrate pollution of waters in areas of the European Union has been known since the 1970s. However, Directive 91/676/EEC was only issued in December 1991 to protect the waters from nitrate from agricultural sources.

Over -fertilization of waters

In order to protect the ecosystems in streams, ponds, rivers and ultimately in the North and Baltic Sea, measures were determined that affect the storage and spending of all nitrogen compounds on agricultural areas.

Otherwise there is a further eutrophication of waters – that is, the enrichment with nutrients – which is also accelerated by heating the water. More nitrogen compounds in the water make algae grow more. Dead algae are in turn broken down by microorganisms that consume a lot of oxygen. As a result, the ecosystem collapses in the eutrophied waters due to lack of oxygen. In the Baltic Sea there have already been low -oxygen death zones in which fish do not survive.

In areas where the limit of 50 milligrams of nitrate per liter of groundwater is exceeded, only 80 percent of the need for fertilizers containing nitrogen may be brought into the field in accordance with the fertilizer regulation. Organic fertilizers such as manure or fermentation substrate must be subjected to a nutrient analysis. Purified regions are located in North Rhine-Westphalia, Mecklenburg-Western Pomerania, Lower Saxony, Hesse, Franconia and in Central Germany. This flat -rate restriction is not enough to protect the groundwater like the surrounding waters.

Dry main season

Climate change additionally tightens the problem. The summer months tend to remain too dry. It rains more in autumn and winter. If there is a longer drought at the main growth period in spring and summer, the plants cannot optimally utilize the nitrogen in the soil. At the beginning of autumn, too much nitrogen remains in the soil and can be washed out with the rain.

In Germany, around two thirds of the drinking water requirement made of groundwater are covered.

Lighter sand floors, especially in the north German regions characterized by the milder naval class, are significantly warmer in the winter months and are therefore more affected by the problem. There, organically bound nitrogen of soil bacteria is sometimes converted into the mineral nitrate that is slightly available for plants all year round. It is therefore crucial to have a timely sowing from midruptcy until mid -September or immediately after the harvest of the forecast.

Uwe Kalthoff explains in a first record of the model project on groundwater -friendly cultivation process: “Until a more adapted management influences the groundwater values, it can take up to 25 years.” In the project to implement the European Water Framework Directive, improvement options for dealing with nitrogen are to be recognized faster and be implemented in practice.

Model projects show alternatives

For this purpose, special suction plates in a depth of up to 115 centimeters were used in the arable land in a depth of up to 115 centimeters to take samples of seepage water in twelve farms. Bores up to 16 meters are also carried out. In this way, concrete measures and changes in soil processing, crop rotation and fertilization can tend to be rated after just a few years and faster recommendations for farmers can be made in order to avoid nitrogen losses.

There are different ways to supply the plants with nitrogen. In Germany with the currently still extensive and intensive animal husbandry, this is the business fertilizer such as manure, crap or fermentation substrate that arises from manure and herbal by-products when creating biogas. In addition, synthetically generated ammonium nitrate and ammonium phosphate are used.

In organic farming, in addition to the animal economic fertilizer, the so -called green manure is used. For this purpose, plants from the family of legumes – also called leguminoses – such as peas, beans, lentils, lupins, lucerne or clover are sown. Cleep plants and other legumes live in symbiosis with the nodules bacteria, which convert the nitrogen from the air into a shape that can be used for the plants.

Green manure instead of manure

If, for example, clover grass is broken down in the field in spring, this contributes significantly to nitrogen supply to the subsequent planting. “Up to 200 kilograms of nitrogen per hectare can be released within two months of the Kleegraskrasskrasschrucht,” says Pascal Gerbauget in a conversation published on the Oekolandbau.de internet portal. As part of the model project on groundwater protection, he advises seven organic farms.

After that, early white cabbage plants can be placed, potatoes placed or corn sown, which the ammonium ions produced by the nodel bacteria benefit. In vegetable cultivation, the transfer of Kleeschnitt from the “Geberfeld” to a “recipient field” with needy young plants promises success.

Especially after the harvest of potatoes that consume a little less nitrogen, interim fruits are important, which use the nitrogen residues before they seep into useless, and on the other hand in an environmentally harmful way. This leaves a mustard seed, which can be used as green fodder, a well -loosened floor, the so -called floor guarantee due to its deep roots.

Technical solutions are also tested in the project in North Rhine -Westphalia, how liquid business fertilizers can be targeted by means of a fertilization fertilization and quickly incorporated into the upper layer of earth. Measuring mineralized nitrogen in the arable floor can contribute to a more conscious handling of valuable fertilizer.

In organic farming there is basically a lower fertilization level, but the quantities of nitrogen are more difficult to calculate, Pascal gerbaubeet admits. Climate change makes it more complicated for all farmers.