To achieve the Dutch government's objective of realising a circular economy in the Netherlands, it is essential to maintain the productivity of the country's farmland. Healthy soil produces renewable raw materials for biobased products. However, declining carbon levels in arable Dutch soil is inhibiting our ability to meet this objective, and continued global warming is standing in the way of a circular economy. Lijbert Brussaard, professor of Soil Biology and Biological Soil Quality at Wageningen University & Research, addressed this issue in his valedictory speech on 6 October.
The amount of organic matter in Dutch soil appears to be relatively stable, particularly in grasslands, with only sandy soils experiencing a net loss. 'But appearances can be deceiving,' says the soil biologist. 'The depletion of organic matter is being masked by the manure surplus we've experienced in recent years. And that surplus is largely the result of the large-scale import of animal feed, such as soya, from foreign countries. The declining level of soil organic matter will therefore manifest itself soon in the Netherlands. This will undoubtedly be the case if climate change worsens, as higher temperatures accelerate the breakdown of soil organic matter and increase CO2 emissions,' says the Wageningen professor.
In order to achieve the Dutch government's objective of achieving a circular economy by 2015 without depleting our natural resources, and to achieve the 50% interim target by 2030, we need to exchange fossil fuels for renewable biobased resources derived largely from farmland crops. This not only includes crops intended for human consumption, animal feed and fibres, but also green raw materials for fuel, flavours, fragrances and so on. 'In order to meet increasing demands, we need to maintain the productivity of the soil. To do so, we need to take into account the quality and the quantity of residual materials to be returned to the farmland. This needs to be anticipated on throughout the chain,' explains Professor Brussaard. 'Failure to do so will cause the biobased economy to miss the circular economy boat.'
Rich soil life
Organic matter derived from plant residues is extremely important for maintaining healthy soil. This soil organic matter determines the structure and porosity of the soil and ensures the gradual release of water and nutrients for plants as mediated by the soil biota. Stimulation of the soil biota can in a natural way reduce the impact of human interventions, such as ploughing and drainage. 'Maintaining soil organic matter is an important part of sustainable soil management,' says Professor Brussaard in his valedictory speech titled, De bodem onder ons bestaan ('The ground beneath our feet').
Professor Brussaard also stresses that increasing the carbon content of the soil can help reduce the greenhouse effect, as the French demonstrated during last year's COP21 climate negotiations in Paris. They are committed to achieving a global annual increase of 0.4% in soil organic matter stock for the upper 40 cm of the soil. According to their calculations, this seemingly minor increase can offset the greenhouse effect in the long term. This demonstrates the enormous potential of good soil management. In The Netherlands examples are known of carbon storage as high as 1.5% per year. 'This is an outstanding achievement in terms of reducing the amount of CO2 in the atmosphere,' says Professor Brussaard.
In the past, underground CO2 storage in the deeper geological strata has generated considerable unrest. 'If the government and the industry are willing to invest in reducing atmospheric CO2 levels, an obvious step would be to support the agricultural sector in increasing the organic matter content of the soil and include this in the EU's Common Agricultural Policy,' says Professor Brussaard.