Climate change may be leading to a decline in the humus content of soils, affecting agricultural production worldwide. Scientists from the Technical University Munich (TUM) suspect that the input of organic matter into the soil, the crucial source for humus formation, will decrease as a result of stagnating crop yields in Europe. For the study, which was published in the journal Science of the Total Environment, they analysed crop yield statistics provided by the UN Food and Agriculture Organisation (FAO) which are dating back to the 1960s. The statistics indicate that yields of wheat, barley and maize have been stagnating in Central and Northern Europe since the 1990s. According to soil expert Dr Martin Wiesmeier, the lead author of the study, the stagnation in yields must also have an impact on the humus stocks in soils due to the strong link between crop yields and the input of organic substances into the soil. Given that rising temperatures cause higher levels of humus decomposition while, at the same time, the supply of organic substances is stagnating, the scientists expect a depletion of the humus content in the long term. This could negatively impact the fertility and water storage capacity of soils, which in turn could result in poorer harvests – a “vicious circle” according to Wiesmeier. The authors of the study attribute the stagnation of yields to different factors. One reason could be a shift in priorities in the EU common agricultural policy of the 1990s, due to which less fertiliser was used and leguminous plants were often excluded from crop rotation cycles. However, climate change could have a major impact with temperatures increasingly exceeding the optimum level for plant growth, shifting vegetation periods and more frequent droughts. Other studies had predicted an increased organic matter supply to soils as a result of climate change. In order to prevent the loss of humus, the scientists call for the promotion of agricultural practices that increase soil organic matter: “These include the diversification of crop rotation, the application of green manure and winter greening to reduce soil erosion, optimised soil cultivation, organic farming, agroforestry, and leaving crop residues on fields,” explains co-author Dr Rico Hübner. (ab)