Soil requirements – the basis for land use

Prof. Mats Olsson clarifies the concepts

World-wide there are more than 30 major soil units. Each one of them provides unique properties with specific prerequisites for biomass production, agricultural crops, energy crops, range land and forestry. The soil properties are determined by the combination of geology, climate, topography, land-use and soil age. Thus, each soil type has its own ability and capacity to produce biomass. A system analysis perspective is needed for the comparison and evaluation of different options.

Thin soils, cold climate & limited availability of water

About 10% of the globally available 15,300 million hectares of land are located in mountainous areas and are characterised by very thin soils (Leptosols) as a result of heavy erosion. These soils are not suitable for intense biomass production and should be preserved by keeping a permanent vegetation cover. Potential land uses are forestry, preferably uneven aged forestry with a continuous tree cover, or extensive grazing. Another 12% of the land is located in cold climates with permafrost. Low temperatures and frozen ground make intense biomass production impossible. No less than 23% of the world land area consists of soil types characterised by limited availability of water, either owing to drought, groundwater levels that are too deep for roots and/or low water retention capacity in the soil. Many of these soils are rich in nutrients but need substantial irrigation to sustain high yields. The potential for irrigation and agricultural production will most likely be even more limited in the future because of declining water resources and competing water use caused by urbanisation.

A high water content & poor mineralogy

In about 10% of the world soils the water content is too high for intense biomass production. Some of these soils are very fertile and may after some water regulation provide excellent agricultural conditions. However some soils have dense subsoil and drainage has to be combined with deep ploughing and even fertilisation. About 25% of the land area consists of soil types that, on account of poor mineralogy and/or intense weathering, have a low nutrient content. Many of these soils occur in tropical conditions and are characterised by excellent structure, but in particular by limited phosphorus availability. The production of agricultural crops could be doubled or tripled by the application of commercial fertilisers or compost and manure.

20% consists of naturally fertile soils

Finally, almost 20% of the land area consists of naturally fertile soils with respect to nutrient levels, texture and climate. Nonetheless, these soils are frequently fertilised with nitrogen and phosphorus. It should be stressed that, owing to high application rates, the marginal effect of changes in application might be rather small.

The water availability is often the limiting factor

A re-allocation of fertilisers from countries where application rates are at present high to countries with low application rates could be beneficial when it comes to yields and effective use of resources. On the other hand, in many of the countries with low application rates water availability is low, and, at the same time, demand for water per unit of produced crop is high.

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Text and Photo: Mats Olsson, SLU