Has agricultural soil really been reached?

Sustainably managed and healthy soil is invaluable. Vital soils provide a large number of ecosystem services for agricultural entrepreneurs, water managers and other land users. Recent studies suggest that the quality of our soils is bad and link it to land use.

Intensive agricultural management would ensure that the majority of soils suffer from acidification, eutrophication, desiccation, compaction and all kinds of soil-related diseases. This in turn leads to lower yields, a reduction in biodiversity, eutrophication of surface water, less water storage and higher greenhouse gas emissions.

This seems justified in the conclusion that the quality of rural soils is deteriorating and urgent measures are needed to achieve national and international targets. However, is this conclusion correct? Is it really that bad with agricultural soil in the Netherlands? I have great hesitations...

Poor soil quality poorly substantiated
It strikes me that the above conclusion is only shared by agricultural entrepreneurs to a very limited extent. And they are the people who walk around and use the soil every day. Their business operations depend on the quality of the soil. The agricultural tests carried out by the NMI and PPO also only moderately support the conclusion that the Dutch agricultural soil is doing dramatically badly. What about the agricultural soil?

I will substantiate the statement that our agricultural soils are still among the most fertile and that for the most part they are also sustainably managed. In other words, the earlier conclusion of poor soil quality is a poorly substantiated hypothesis for agricultural soils. In a second part of this article, I hope to discuss some possible explanations for the common negative tone of studies that claim the opposite.

What is sustainable managed agricultural soil?
Let's start by pre-defining the term soil quality. This determines how we interpret changes in soil analyses. Without a clear vision on soil quality, it is impossible to specify when a soil is getting worse or better. More does not always equal better and less does not always equal decline.

In my view the quality of the soil can be defined as 'the capacity of the soil to function as a vital living system, within ecosystem and land use limits, to maintain or improve plant and animal productivity, to improve water and air quality, and to promote of plant and animal health.'

Quantifying Soil Features
Soil functions are used in scientific literature as well as in farming practice to make this capacity measurable. Soil functions quantify 'the role of the soil in fulfilling certain objectives'. Soil functions include supplying water, nutrients, providing a stable medium for growth, and suppressing natural pests and diseases. Chemical soil processes as well as soil life play a crucial role in this. In order to appreciate a change in soil quality, insight is therefore needed into the goal and the associated soil functions.

For an agricultural soil, the first goal is that a good and healthy crop can grow with a high crop yield. For the current year, but also for future years. Second, agricultural soils can also contribute to other services such as water retention, carbon sequestration, water purification, and so on. In practice, these goals often go hand in hand. In order to be able to assess whether the quality of an agricultural soil is decreasing, we must therefore see a decrease in crop yields or a change in (measurable) soil functions. Is that also the case?

Why is the soil bad?
Let's take a look at the recent study by the Council of the Environment, entitled 'reached the bottom?!' Based on a number of fact-finding papers and discussions with various soil scientists, the report concludes that a large part of the soil has been compacted and that a large part of the natural soil has become acidified and dried up. The micronutrient content in the soil also decreases, as does the nutrient content in crops.

In addition, the supply of nutrients from manure disrupts the balance in the natural soil, the amount of nutrients in the surface water is almost everywhere too high for the desired ecological goals and the nitrate content in the groundwater is often still above the standard. The content of organic matter (fractions) also decreases in European agricultural soils, there are differences in biodiversity between agriculture and nature and the risk of diseases and pests is increasing.

The main causes mentioned are the high intensity of soil use as well as the use of crop protection agents, fertilizers, monocultures, heavy machinery and lowering water levels. Please note: many of these original studies do not deal with the current agricultural soil in the Netherlands and only very slightly on the most important function of an agricultural soil: producing healthy crops to feed people. But still... the trend has been set.

Why is the soil doing well?
There are a number of reasons why the Dutch agricultural soil is doing well. I will mention 7. First of all, the majority of farmers are aware of the importance of good soil management, they actively work to maintain and improve soil quality and experience few problems. 

Secondly, a large number of field studies have been carried out in recent years that, based on thousands of measurements on individual agricultural plots (with data from agricultural laboratories), show that almost all relevant soil parameters are in 'good' to 'very good' agricultural status. . Thirdly, long-term trend analyzes are available that show no relevant decreases in parameters related to physical, chemical and biological soil functions.

Positive Carbon Balance
For almost all investigated soil parameters and functions, the soil quality remains the same or even improves. Fourth, on most farms there is a positive carbon balance, the organic matter content is far above the agricultural optimum and the organic matter content remains the same or even increases. Fifthly, there is an enormous amount of animal manure, compost and organic residual flows available in the Netherlands. Products that are used as basic fertilizer or soil improver.

The doses used and the composition of the most commonly used animal fertilizers are largely in line with the mineral requirements of growing agricultural crops. In the current practice of fertilization and soil management, a large-scale decrease (to below the agricultural optimum) in the content of meso- and micronutrients is unrealistic. In addition to animal manure and compost - where necessary - artificial fertilizers are used to compensate for any shortage of these nutrients. Soil life is also stimulated through compost, slurry, fertilizer and lime. 

Sixth, long-term analyzes show that crop yields have remained stable or even increased for years, despite the fall in application standards. Finally, it is a serious practical experience that common soil quality problems can be managed with good soil management and sophisticated fertilization in such a way that any damage can be prevented or repaired within the period of a construction plan.

What is wrong with soil quality analysis?
What then goes wrong with studies that nevertheless conclude that the soil quality in the Netherlands is very bad? In the follow-up article I will discuss some common causes. In anticipation of this, one substantive argument: many conclusions are drawn on the basis of extrapolations without an agricultural assessment framework.

And extrapolations are always risky, especially when it comes to soil quality, where landscape factors in combination with (historical) management and management together determine the soil quality. Looking at the studies in the aforementioned RLI report, I note that a large part of the observed acidification, eutrophication and desiccation was observed in nature reserves or in agricultural parcels within a European context.

No comparable goal
Agricultural plots and nature plots do not have a comparable goal, and the soil functions needed to achieve the goals vary. In addition, the soil quality on nature plots is maintained to a very limited extent. Many natural processes also take over the role of the farmer in influencing soil quality. In addition, compared to other European countries, Dutch agricultural soils have an intensive history of organic fertilization, which means that soil processes and functions operate in a completely different equilibrium.

In order to make generic statements about the soil quality of Dutch agricultural soils, insight is needed into the soil functions in relation to the desired construction plan. Only in this way is it possible to substantiate the statement 'the soil is doing well or badly'. So customization and no generic statements based on a number of field trials or monitoring data.

Demonstrating differences
More importantly, many publications do not go further than demonstrating differences between fields or differences between farm systems or over different measurement periods. A decrease or an increase in a soil parameter (because these are measured) does not in itself provide information as long as there is not an evident response with crop growth or stability of crop growth.

A valuation of the soil is therefore not possible without a vision of soil quality in relation to the agricultural function of the plot. A different biodiversity, a higher or lower P-availability or the sludge sensitivity of a plot cannot be interpreted without an agricultural assessment framework. For example, a decrease in P stocks is not a problem at all, as long as the P buffering is sufficient to make enough phosphate available for crop uptake. It is precisely this link with functionality that is missing and is not as clear-cut as it is often suggested.

How further?
On the basis of the arguments described above, I would like to plead for a positive view of soil quality, building on the concept of the Opportunity Map. Soil management offers opportunities to contribute to a more sustainable agricultural system. This statement does not become less valid if we start with good quality agricultural soil.

That is why I also share the advice of the RLI report that soil quality can (and must) play a central role in the policy instruments. The further valorisation of sustainable soil management can also be stimulated via the CAP or initiatives from the market, such as the initiative of the Soil Coalition or the PPP Better Soil Management.

In my opinion, the observation that the agricultural soil is now in bad shape is not necessary for this, even unjustly and can even demotivate the end users to take extra measures that increase the quality of the soil in relation to services other than agricultural production.

Bottom not reached
This is not to say, however, that there are no challenges: there are certainly and especially with regard to soil structure (and the use of heavy machines) and diseases (in specific crops). But in my view, these challenges do not lead to the conclusion that the bottom has been reached. Through sustainable management we can stay on top and possibly even increase quality. Via the route of extensification or via the route of precision agriculture.

In my opinion, the soil quality for agricultural production is in order on most plots in the Netherlands. I compliment the agricultural sector with this, because they show that - despite all kinds of developments in the market and legislation - they work with care to maintain and improve soil quality.

And I admire the hundreds of farmers who actively respond to the desire to contribute to the challenges for climate, biodiversity, water quality and water quantity through sustainable soil management. Opportunities lie there, enormous opportunities themselves. Because measures have a positive effect on a more sustainable agricultural system. And we should encourage that.

Gerard Rose

Senior project manager in soil, water and agriculture at the Nutrient Management Institute (NMI).

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