Since Biblical times it has been clear that soils are different. Jesus told the parable of the sower, where some of the seed fell on good soil, leading to a bumper crop, while some seed fell on poor soil, leading to a poor crop (Figure 1).

Good Soil vs Bad Soil

Figure 1: Since Biblical times it has been known that good soils produce good crops, while poor soils produce poor crops.

The need to differentiate between good and poor soils is even more important today, with 95% of the world’s food being produced in soil (FAOSTAT, 2003). When looking at soils, it is easy to see that soils are different (Figure 2). They look different, because they have different properties (such as texture, chemical composition, mineral composition and water regimes). These differences in properties lead to different abilities in performing various functions, such as crop production in the Bible passage. In ecology, although often neglected, the importance in understanding differences between soils could be even more important. The soil is the only medium where air, water, plants, animals and rocks occur simultaneously, and is thus a good indicator of ecological health and resilience. Nearly all rainwater (except for that which evaporates directly from plant and water surfaces) comes into contact with the soil, and the soil’s properties determine the final destination of that water and as such how that ecosystem will function.

Different Soil Properties

Figure 2: Soils look different, because they possess different properties leading to fulfilling different functions.

So be it for agricultural of ecological use, environmental managers should take note of soils differences and know where the different soils are situated. The key to knowing your areas soils distribution is having an accurate soil map created by a trained soil surveyor. In a case study for 19 000 ha of land in Mozambique (Figure 3), the standard Nitrogen fertilizer application rate for Mozambique was compared to soil specific Nitrogen fertilizer application using a soil map.

Mozambique Soil Map

Figure 3: Soil map of 19000 ha in Mozambique. Soil map units are based on the South African soil classification system (Soil Classification Working Group, 1991).

Using the standard Nitrogen fertilizer application rate, 92 726 tonnes or 6 tonnes/ha of maize per year is potentially attainable, by applying 2077 tonnes or 128 kg/ha of elemental Nitrogen. In contrast, when fertilising according to the soil map, the attainable yield is 116 538 tonnes or 7.2 tonnes/ha, when using 2403 tonnes or 148 kg/ha elemental Nitrogen. The differences are because the standard application rate applies enough fertilizer to obtain a yield of 6.3 tonnes/ha, while the production potential according to the soil properties varies between 3 and 8.1 tonnes/ha. The standard Nitrogen application rate leads to smaller yields due to the under-fertilizing of top producing areas, while it also allows for the over fertilization in lower producing areas. some areas, leading to eutrophication and unnecessary emission of NOx gasses. Fertilization of other nutrients will follow the same trends.