Phosphate and soil carbon

High yields generally require sufficient fertilizer, e.g. phosphate. Phosphorus is an element essential to plant growth. But whereas nitrogen fertilizer is synthesized, the only way to produce fertilizer containing phosphorus, is to mine it as phosphate. World phosphate resources are limited, peak production is imminent, and contrary to crude oil (peak oil), phosphate does not have substitutes. Therefore, we need to use phosphate conservatively in order to forgo depletion as long as possible.

The main phosphate reserve is in the part of Morocco which used to be Spanish Sahara. There are just a few other good reserves. Up to the eighties, Morocco was the main supplier to the European fertilizer industry.

Moroccan phosphate has a relatively high cadmium content. In the long run, this will accumulate on the land and in surface waters. Encouraged by stricter regulation, the European industry asked Delft Technical University and Dutch TNO to develop a process to remove cadmium from the ore.

European industry never used this technology. In the end, they had lower production costs using more expensive Florida ore. Moroccan phosphate ore subsequently found its way to developing countries, e.g. to the Nile delta, where it contributes to heavy metal poisoning.

Return minerals to the land directly
One of the main advantages of ‘forward integration’ in agriculture (process the yield at the farm), is direct minerals recovery, not in the least phosphate. The farmer could process potatoes and sugar beet to a storable intermediate product, allowing minerals to be returned to the land directly (in liquid form). Projects with similar goals carry names like the self-fertilizing land.

Carbon – in the form of humus – is essential to agricultural soil structure. Humus tends to decompose, and hence the farmer has to return organic material to the land: harvest waste, green manure crops, organic fertilizer, or soil improvement material. If organic material should become more valuable (e.g. in the biobased economy), this could pose problems.

Western European soils have decreasing carbon contents. This is because:
•    stricter manure regulation results in less organic matter being returned to the land;
•    moreover, farmers tend to fertilize less in order to lower the nitrate residue;
•    organic matter decomposes more quickly: because fields low in pH are treated with chalk, because of intensification (for example in vegetable cropping), because less straw or other agricultural waste  remains on the land, because of deeper ploughing, and because of meadow shearing.

Courtesy WTC, Dutch Scientific and Technological Committee for the biobased economy

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