Scientific studies usually investigate individual soil management practices, which makes it difficult to compare their different effects and keep track of things. Here, the results of over 10,000 observations on soil-management and cropping-system practices and their effect on hydrological soil properties were collected from scientific studies and then analysed.
Many farmers, enterprises and governments are dealing with the impacts of climate change on agriculture. Although soil is clearly important for agricultural production, the role of soil management in climate-change adaptation has received scant attention from policy-makers and farmers. One reason for this is that many studies were conducted under site-specific conditions that have not yet been incorporated into a wider context. The CLIMASOMA project synthesised the results of 36 meta-analyses covering 2803 individual studies from the past 100 years. These included numerous studies investigating the impact of soil and crop-management practices on climate-change adaptation with a specific focus on soil hydrological function.
Continuous soil cover with living plants stimulates soil life and carbon storage. Both are essential for developing a good soil structure, which in turn ensures good water infiltration and storage. This soil cover can be achieved in different ways: catch crops such as oilseed rape or phacelia can be grown post-harvest in the winter, grass can be undersown in maize fields and grass strips planted between rows of fruit trees. However, all agricultural practices come with their disadvantages as well as advantages: cover crops, for example, will take additional water from the soil, which can be a problem in regions struggling with year-round drought. Site-specific soil management is thus essential.
Although experiments focusing on reduced or no-tillage farming have been conducted for many years, the results of these experiments present a mixed picture. Reduced tillage tends to increase soil water availability, but also soil compaction, which leads to reduced water infiltration and a greater risk of soil erosion. It also encourages weed growth, which usually results in increased herbicide use. Reducing soil compaction, on the other hand, has only positive effects. Rather than enacting tillage bans, we might want to work towards using less, better-timed and lighter machinery on the land in general – and towards restoring compacted soils in the process.
According to some studies, organic carbon is to soil as mortar is to the bricks of a house, holding soil particles together and improving soil structure. Research on what farmers can add to their fields to improve soil structure is often interwoven with questions about other practices such as reduced tillage. In such studies, it is difficult to distinguish the effects of adding organic material from those of tillage. Still, the benefits of adding organic matter such as plant residues, compost, manure, wood chips and biochar are undeniable. Local availability of these materials, preferably in large quantities, remains the big challenge.
Although some practices were clearly shown to be beneficial, the main takeaway remains that farming is very context-specific. No single practice is ideal in every combination of soil, climate and crops, and no single practice can be viewed separately from the wider context of the agroecosystem in which it exists. Regardless of the amount of organic material added to the soil, the effect will be minimal if you proceed to destroy your soil structure by driving over it with heavy machinery while it is wet. We therefore need to avoid generalisations and to continue investigating the implications of these context-specific correlations between farming practices and water-regulating soil functions.
