It's no secret that the organic growing process is harder on the environment, with more toxic pesticides, less efficient use of the land, and lower yields, but some practices are exceptionally harmful, like growing crops in organic (peat) soil.
When organic soils are drained and cultivated the organic matter in the soil will decompose which leads to emissions of greenhouse gases, finds a study in Denmark, and that makes up as much as 6 percent of Denmark's total greenhouse gas emissions.
Agricultural management practices affect emissions of the three greenhouse gases: carbon dioxide, nitrous oxide and methane. Nitrous oxide is produced during the conversion of nitrogen in the soil. Methane is formed when organic matter decomposes under oxygen-depleted conditions.
Nitrous oxide is a 298 times more powerful greenhouse gas than CO2. Methane is 25 times more powerful than CO2. Both have much shorter lifespans, which is why CO2 is the big concern, but the other two have gained in fundraising popularity as CO2 levels have dropped. Still, since CO2 is what environmental activists have lobbied quite heavily on, so total greenhouse gas emission is calculated as CO2 equivalents, where the effect of the climate is converted into a CO2 effect. Drained, peaty soils emit CO2 and nitrous oxide because the decomposition of the organic matter takes place in the presence of oxygen, while methane is emitted from anoxic wetland areas.
Decomposition of organic matter releases greenhouse gases
Organic soils and raised bogs have a high organic matter content due to detritus from plant roots and other residues. The reason is because these soils have a naturally high water content which limits the amount of oxygen available and that limits decomposition. Over the last couple of centuries most of the Danish organic peat soils have been drained and cultivated. These soils have often initially been very fertile, but because some settling of the soil takes place over time, the water table on these areas is often very high, which can create problems for their further cultivation or means they have to be re-drained.
An inventory of the land uses on organic soils in 2013 shows that roughly 81,000 ha are in rotation and 27,000 are used for permanent grassland. Around 67,000 ha of this area have an organic carbon content of more than 12 percent where the greenhouse gas emissions are particularly large if cultivated.
When organic soils are drained and cultivated, the organic content in the soil will start to decompose, which, as previously mentioned, will lead to the emission of greenhouse gases. In 2013 the total emission from drained organic soils was 3.3 million tonnes CO2-equivalents, which corresponds to 6 percent of the total greenhouse gas emission in Denmark. The methane and nitrous oxide emissions from livestock and manure management in farming make up 19 percent of total emissions.
Organic soils should be taken out of rotation
The climate can be given a helping hand by taking the organic soils out of rotation. Danish farmers can get compensation for taking fields out of rotation or putting them under extensive farming if certain stipulations for their organic matter content are met. Once the fields have been set aside, they cannot officially be tilled, fertilized or treated with pesticides.
The effect depends on the land use and soil carbon content prior to the start of the project as well as the water level after the change in land use. The climate effect can be up to 100 times higher compared to taking mineral soils out of rotation. This requires that the land is removed from agricultural land use, that a high water level is reestablished on this land, and that the removal is targeted organic soils with a high carbon content.