Keeping the soil fit

Productive soils are not only of key importance for agriculture, but form the basis for clean drinking water and help to protect against flooding and landslides as well. They also play a major role as sinks and sources of the most important greenhouse gases – carbon dioxide, methane and nitrous oxide. Several NRP 68 projects have investigated what affects soil productivity – in other words, soil quality. They focussed in particular on the loss of soil organic matter (humus) and compaction. Other projects looked for ways of maintaining and improving soil quality through soil management or alternative crop protection measures.

Humus depletion due to insufficient farmyard manure

Humus plays a fundamental role in soils, helping to store nutrients and water, improving the soil structure and feeding soil organisms. But in many agricultural soils, a decrease in humus has been observed. This is having an impact on soil functions and can jeopardise agricultural production in the long term. Humus depletion also causes carbon dioxide (CO2) to escape into the atmosphere from the soil, which acts as a huge carbon sink. This exacerbates the greenhouse effect. Humus depletion is particularly marked in drained peatland, from which most of the CO2 emissions in Swiss farming result. Climate change will probably increase humus depletion even further. One of the reasons for humus depletion on arable farm land is that arable and livestock farming are increasingly being carried out in physically separate locations. There is therefore a shortage of organic fertilisers such as manure on the fields, which would offset the depletion. The removal of crop residues and the absence of grasslands in crop rotation are also contributory factors. “It is therefore important to encourage farming practices – such as cover crops or grassland in crop rotation – which enable the humus content to be maintained, and to restrict practices such as the removal of crop residues that accelerate humus depletion,” stresses Dr Raphaël Charles, Head of the Western Switzerland Branch of the Research Institute of Organic Agriculture (FiBL).

The long-term consequences of soil compaction

Driving across land with heavy machinery or when the soil is wet – in farming, forestry or during construction projects – can severely damage the soil structure. After such a compaction, it is virtually impossible for water or air to permeate the soil. One long-term experiment specially set up to test this in Zurich-Reckenholz showed that the resulting damage extended deep into the soil and reduced the yield by 20 to 80 per cent in the first year after compaction. In the case of severe compaction, the damage is irreversible and, even with suitable regeneration measures, it takes years for the soil to regain its healthy structure. This underscores the importance of preventative measures. In particular, it is advisable to use heavy machinery only when the conditions are favourable, and to reduce its use in general. Conformance testing for heavy agricultural machinery should also beconsidered.

Optimising fertilising strategies

The large amounts of fertiliser used in certain areas of Swiss agriculture are also overburdening the soil, leading to nutrients being washed into water courses and nitrous oxide being released into the atmosphere. It is therefore contributing to water pollution and the greenhouse effect. The use of nitrogen fertilisers can be reduced by means of location-appropriate fertilising and the inclusion of pulses, catch crops and perennial clover and grass dominated grasslands in crop rotation plans.

Site-specific, regionally adapted agriculture

The agricultural reform of the 1990s guided Swiss farming in a direction that is significantly better adapted to the natural conditions. However, the specialisation of farms, the trend towards larger farms and also market requirements have once again placed an increased burden on the soil. Looking to the future, it therefore makes sense to adopt site-specific, regionally adapted agriculture that focusses on soil quality, manages with the fewest possible auxiliary materials and reduces the use of machinery to a minimum. Elements of this farming might include ploughless tillage techniques, permanent ground cover and the use of multi-functional catch crops in crop rotation plans. “Repeatedly measuring humus content would be one way of checking how sustainable farming is,” emphasises Dr Frank Hagedorn from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).

In the case of drained peatland, however, some fundamental decisions need to be taken, particularly since the existing drainage systems needs renewing in many locations, and the humus will soon have decomposed as far down as the subsoil in some areas. No strategy has yet been found for farming this land in a sustainable manner. If it continues to be farmed, this drained peatland will become a significant source of CO2 emissions in the agricultural sector.

Charles Raphaël, Wendling Marina, Burgos Stéphane (2018): Soil and food production. Thematic synthesis report TS4 for the National Research Programme “Sustainable Use of Soil as a Resource” (NRP 68), Bern.
ISBN: 978-3-907087-28-2 (German); ISBN 978-3-907087-29-9 (French)
Obtainable from:www.nrp68.chandnfp68@snf.ch

Hagedorn Frank, Krause Hans-Martin, Studer Mirjam., Schellenberger Andreas, Gattinger Andreas (2018): Soil and environment - soil organic matter, greenhouse gas emissions and physical pressures on Swiss soils. Programme “Sustainable Use of Soil as a Resource” (NRP 68), Bern.

ISBN: 978-3-907087-30-5 (German); ISBN 978-3-907087-31-2 (French)
Obtainable from:www.nfp68.chandnfp68@snf.ch

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Links

• Thematic synthesis report “Soil and food production” (in German) (PDF)
• Thematic synthesis report “Soil and environment” (in German) (PDF)
• Graphics (all graphics in German or French only) (PDF) (PDF)
• Cover photo: Soil is the basis of food production (JPEG)  (JPEG)
• Graphic 1: Modelled spatial distribution of nitrous oxide emissions in Switzerland in 2014 (JPEG)   (JPEG)
• Graphic 2: Rising winter wheat in cover crops on a field near Leuzigen BE (JPEG) (JPEG)
• Graphic 3: Signs of soil compaction after heavy rainfall on Swiss arable land (JPEG) (JPEG)
• Graphic 4: Soil types suitable and unsuitable for food production (JPEG) (JPEG)
• Graphic 5: Peat settlement on a field at Créssier NE (JPEG) (JPEG)