Soil Fertility. Decline not proven

The declining soil fertility is receiving a lot of attention from agricultural politicians and interest groups. This is due to fertilization standards that are being tightened up more and more. However, it remains to be seen whether this is correct and whether this is in any case the main concern.    

Soil and crop laboratory Eurofins does not measure decreasing organic matter contents in the soil and soil compaction deserves at least as much attention. Working as many hectares as possible at the lowest possible cost is an important cause of soil compaction. It is better to work twice with low tire pressure than once with too high tire pressure, is the remedy. 

It was one of the conclusions of the theme afternoon of the Committee on Fertilization for Agricultural Fields (CBAV). Specialist Harm Brinks from Delphy led the debate following the presentations given by Wageningen UR employees. Brinks: ‘I would rather have a soil with one percent less organic matter and a good structure with a lot of air, than one percent extra organic matter and a compacted soil.’

According to Brinks, you cannot accurately determine what happens to the organic matter percentage of the soil on the basis of the course of organic matter over a series of years. ‘The available series of measurements is too limited to prove that soil fertility is declining.â€

Lease contracts sometimes contain a provision that requires that the organic matter content does not decrease during the lease period. Brinks: ‘Understandable, but you cannot determine this accurately with soil samples. What you can do is demonstrate with organic matter accounting that you are supplying more than you are removing.’ Working as many hectares as possible at the lowest possible cost is an important cause of soil compaction. 

Not only the course of the organic matter in the Dutch soil contradicts the farming practice that soil fertility decreases, the soil fertility also does not appear to decline when balanced fertilization is applied. WUR employee Philip Ehlert investigated this. ‘It is logical that the phosphate status of soils that fall into the ‘high’ phosphate class falls. It is government policy to prevent over-fertilization’, says Ehlert. 

The use of soil improvers was also discussed during the study afternoon. The WUR research, which shows that soil improvers have no demonstrably positive effect on crop yield, has caused quite a stir, says Brinks. Critics are of the opinion that the research at WUR experimental farm locations in the Netherlands does not concern soil types that could really benefit from soil improvers. 

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