Harnessing the forces of nature and agricultural practice in all its variety - that is diversification. Diversification brings benefits - positive impacts on yields and environmental protection. This is the conclusion of an international study in which Agroscope researchers took part, and which was recently published Advances.
Agriculture produces our grains, meat, vegetables and fruit. But in large agricultural countries, wheat or maize, cultivated in vast monocultures, tends to dominate. This leads to soil erosion, loss of biodiversity, and water pollution. By contrast, Swiss agriculture is already much more diverse - diversification is the catchword, and is also being promoted by the Swiss federal government. "It’s about various measures, for example, cultivating different crops in the rotation, planting flower strips and hedges, or spreading organic fertilisers and compost instead of mineral fertilisers" says Marcel van der Heijden, a soil ecologist at Agroscope and co-author of the study.
5000 studies evaluated: the positive effects predominate
Tamburini, van der Heijden and their co-authors statistically analysed over 5000 studies from throughout the world. Their conclusion: in two-thirds of the studies, diversification leads to positive effects on yield, species diversity or water balance. It also reduces greenhouse gases such as CO2 and methane, keeps pests in check, and favours pollinating insects. Moreover, diversification maintains or even improves soil quality by preventing the humus-rich topsoil from becoming increasingly thin, as occurs when it is used intensively without soil-improvement measures like the spreading of manure. Year-round soil cover also has a positive effect, since it promotes useful soil microorganisms which ensure that the soil and the plants growing in it remain healthy.
In around 15% of the studies, there were reductions in yield, despite diversification. Van der Heijden’s response: "In order to avoid negative effects, it is important to choose site-appropriate options."
Examples of good solutions
Instead of fertilising a field with artificial fertilisers alone, a green manure of clover or vetch could be used, or meadows with grass-clover mixtures could increasingly be incorporated in the crop rotation. Clover fixes atmospheric nitrogen in its roots and converts it to fertiliser. Wildflower strips on the edges of fields can also markedly increase biodiversity, repelling pests and promoting ecological services such as the pollination of field crops and fruit trees.
Conclusions of the study
"The opportunities for sustainable production offered by nature are already there for the taking" says van der Heijden. "Diversity helps to prevent future environmental damage - in most cases without yield losses."
In large agricultural countries such as the USA, France and Germany, diversification has not yet become widespread, and large monocultures often predominate. This has long-term consequences for the environment: water pollution, soil erosion, loss of biodiversity and excessive greenhouse gas emissions. This study shows how diversification offers opportunities for preventing these problems.