No-till as a climate aid: If farmers forego plowing before sowing, the carbon dioxide emissions from the soil can be more than halved – with constant crop yields, as field tests with no-till maize now suggest. For a permanently higher carbon storage in the soil, however, no-till must be combined in a crop rotation with the cultivation of arable grass or clover.
Soils are considered to be the world’s largest carbon reservoir: they contain about twice as much carbon as the atmosphere. At the same time, however, they can also become greenhouse gas spinners because the breakdown of organic material by bacteria releases carbon dioxide. This release can be increased by intensive tillage such as plowing. In order to reduce emissions, cultivation techniques are therefore being sought that improve the carbon sequestration of the soil.
What does no-till sowing bring?
One way to do this is to use no-till. Farmers do not plow the fields after the harvest, but rather sow directly into the largely untreated fallow land on which remains of the preculture are still lying. These root and plant residues that remain on the field increase the formation of humus in the soil and thus also the storage of carbon. Researchers working with Inger Struck from the Christian-Albrechts-Universität zu Kiel have determined how the no-till method actually affects soil carbon and CO2 emissions from fields. They also investigated whether direct sowing leads to lower yields, as is often assumed.
To do this, they compared the effects on the yields and emissions of direct corn and traditional plowing. The research team chose a plot in Schleswig-Holstein with sandy loam soil with high to very high yield expectations. Previously, grassland with grasses and herbaceous plants had grown there for ten years, so that the soil was adequately supplied with organic carbon at the start of the experiment. First, the scientists treated this grassland scar with a total herbicide. They then either sowed the maize directly in the former grassland or plowed the soil in the traditional way before sowing. In the two following years, Struck and her team recorded the yields, measured the emissions of the greenhouse gases carbon dioxide, methane and nitrous oxide with the help of special measuring chambers and documented the changes in soil carbon in both test fields. They modeled the long-term effects on carbon stocks.
Emissions more than halved
The result: In comparison to plowed cultivation, the researchers determined 57 percent fewer CO2 emissions per hectare of soil for direct maize sowing. Most of the emissions measured in both plots came from the degradation of soil carbon – but to a much lesser extent in the no-till variant. “Direct sowing of maize offers a good opportunity to reduce greenhouse gas emissions from agricultural soils,” says Struck’s colleague Friedhelm Taube.
In addition, the research team found comparable crop yields in both cultivation systems and there was an adequate supply of nutrients in both fields. The soil water content measured over the course of the year showed greater stability for the direct maize variant. The researchers suspect that this could be due to the better soil structure compared to the plow variant. This soil structure could be particularly advantageous in the future if there is less rainfall during the vegetation period in Schleswig-Holstein due to climate change.
Crop rotation important
However, the emission savings through direct sowing are only temporary: If maize is repeatedly grown in the same field using direct sowing, the positive effect diminishes and the amount of carbon remaining in the soil is reduced: In contrast to permanent grassland with grasses, one Maize monoculture stores around one tonne of CO2 less each year, as the models showed. According to Struck and her colleagues, the cultivation method would have to be improved in order to keep the humus content of the soil at a stable level. For example, by means of a crop rotation in which perennial arable or clover grass is planted again and again as an intermediate crop and the field is not tilled during these years.
“It is crucial that crop rotations in arable farming are made more diverse again,” says Taube. “The inclusion of one to two-year-old arable or clover grass in crop rotations increases the carbon sequestration in the soil by more than three tons of CO2 per hectare and year, which can be retained in the soil longer with the no-till method, even if intensive arable farming follows. If we achieve high yields with low environmental costs at the same time, it would make an effective contribution to climate protection and increase the added value of such systems, ”the scientist sums up.
Alternatives to glyphosate needed
“The results of the project show that there are promising no-till options,” says Struck’s colleague Thorsten Reinsch. “With the combination of perennial field grass or field clover grass and the inserted field use with maize or other crops, a high level of soil humus storage can be achieved. In this way, water and the climate are protected and productivity is still maintained. ”However, the new cultivation method is made more difficult by the impending ban on the total herbicide glyphosate. Because a non-chemical destruction of the sward without tillage is difficult. “Against this background, the development of alternative active ingredients to glyphosate is necessary in order to obtain a sufficient range of adaptation and climate protection measures for agriculture in Germany,” concludes Taube.
Source: Christian-Albrechts-Universität zu Kiel, Article: Soil and Tillage Research, doi: 10.1016 / j.still.2020.104615