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Significant reduction in sulphur concentrations in Dutch soil

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Monday, January 2, 2017

The concentration of sulphur (S) in Dutch soil has decreased markedly over the last 10 years. This is evident from the analysis of average results performed by Eurofins Agro. Eurofins Agro performs soil analysis for 90% of the Dutch plots, so this offers reliable insight.

The average reduction in clay soils is 15%, whilst in sandy soils the concentration has reduced by more than 30% in the period 2005-2015. Sulphur is one of the most important nutrients for crops. It is one of the so-called main elements. Sulphur is required for the formation of proteins in plants. It therefore plays a role in both the yield and quality of crops.

Supplies of sulphur

A crop can obtain sulphur via deposition (precipitation), organic manure, ground water, mineralisation of soil organic matter and of course via fertilisers. A sulphur deficiency was almost unheard of at the end of the previous century. Sulphur was continuously supplied via deposition (precipitation) (up to more than 50 kg per hectare). However, this has not happened in recent years: the supply ‘from the air’ is almost non-existent now thanks to environmental measures. It is very likely that the same applies to other parts of the world, particularly the rest of north-western Europe.

The source of sulphur from rain, to which Dutch farmers and horticulturists had become accustomed, no longer exists. The supply via animal manure has reduced, due to the environmental policy relating to manure. Furthermore, sulphur in manure is mainly organically bound and will barely contribute to the sulphur supply for crops, particularly in the early spring. What the soil is able to supply is becoming increasingly important.

Declining concentrations

Eurofins Agro concluded that total sulphur concentrations in Dutch soils are declining significantly (figure 1). The capacity of the soil to supply sulphur to crops is thereby reduced. We can also see this in the C/S ratio.

Reduced supply from mineralisation

The C/S ratio has increased particularly in sandy soils (figure 2). The C/S ratio is a measure of the amount of sulphur that is released through the decomposition of organic matter. The higher the C/S ratio, the lower the amount of sulphur released during decomposition. ‘Not only is there a reduced supply of sulphur from the air (deposition), there is also a reduced supply from mineralisation,’ according to dr. Arjan Reijneveld, product manager at Eurofins Agro.

Figure 1: Total S is reducing in both sandy and clay soils in the Netherlands.

Figure 2: An increasing C/S ratio; less sulphur is being released by mineralisation.

Quality of organic matter

According to dr. Reijneveld, the increase in the average C/S ratio is an indicator that something is has changed in the quality of organic matter. ‘On average, we have not seen a reduction in the concentration of organic matter in the soil yet. So the quantity is still the same, but the quality is changing.’ Eurofins Agro is currently conducting further research - in the form of pyrolysis - into the quality of organic matter in the soil. This method can measure the various fractions of organic matter (quality). ‘We expect to generate lots of new insights for the farmer, but also for specialists and scientists.’

Adjusting sulphur concentrations during the season

In the soil survey, Eurofins Agro measures both total S and the C/S ratio and this season they also started measuring mineral sulphur (bio-available to plants). This allows the user to determine whether the sulphur concentration needs to be adjusted. An application of fertiliser early in the season (when the mineralisation process has not started yet) can be cost effective, particularly for crops with a high sulphur requirement, such as grass and winter wheat.