What has an influence on Soil Fertility?

Farmers know that the fertility of the soil depends on many factors. For the plants to grow they
need to get from the soil suitable conditions for root growth, appropriate supply of water and
nutrients available for uptake by roots. If certain soil conditions are not suitable, plant growth can
be inhibited. For example water logging, acidity, compaction or shortage of nutrients can tremendously
decrease the yields of some crops.

Why organic matter is so important?

Soil organic matter helps to build up a loose and soft soil structure with a lot of cavities
(pores). This leads to better aeration, better infiltration of rain or irrigation water and an easier
penetration of roots.
The visible parts of organic matter act like tiny sponges which can hold water up to five times
their own weight. Therefore in dry periods more water is available for the plants for a longer
time. This is especially important in sandy soils.
The non-visible parts of organic matter act like a glue, sticking soil particles together thus forming
stable crumbs. Such aggregates improve the soil structure, especially in clay and sandy
soils.
Beneficial micro-organisms and other soil organisms such as earthworms also feed on organic
material thus decomposing it. As these organisms require sufficient humidity and aeration,
soil organic matter provides a suitable environment for them.
Organic matter has a great capacity to retain nutrients and release them continuously. It thereby
increases the capacity of the soil to supply the plants with nutrients and reduces nutrient
losses by leaching. This is especially important in sandy soils as they naturally retain very few
nutrients.
Organic matter also prevents soils from becoming too acidic.

Soil Testing

Most people have strong trust in any scientific work. Therefore, when it comes to soil fertility,

farmers might also think of getting their soil analysed in a laboratory. Though chemical soil

testing may yield valuable information to specific questions, farmers should not expect too

much of it.

For example there are some inherent problems related to analysing nutrient contents: For

the plant, the total content of a certain nutrient in a sample is not always relevant, as the

nutrient may be absorbed to minerals so strong that it is not available to the plant roots (e.g.

Phosphorus, see chapter 4.1.3). Therefore, some tests treat the sample with solvents in

order to simulate the fraction of the nutrient available to plants. This might be a realistic

simulation for conventional farming. In organically managed soils, however, the higher activity

of soil organisms can result in a better availability of the nutrient, thus the result of the test

is not fully appropriate. The content of other nutrients such as nitrogen is extremely fluctuating

within few days, so that it highly depends on the point of time when the sample is taken.

Still, chemical soil analysis can be useful in some cases, e.g. to analyse the level of acidity

of the soil (pH) or to detect deficiency of nutrients such as Potassium (K) or Zinc (Zn).

Organic farmers might be especially interested in knowing and monitoring the content of soil

organic matter.

Chemical soil analysis on pesticide residues is highly complicated as one must know which

pesticide to look for, and they are very costly. Physical testing, e.g. related to water retention

capacity or soil structure can yield interesting information, but samples must be taken very

carefully. Biological analysis, e.g. of the activity of soil organisms, must be done in specially

equipped laboratories and is rather costly. Altogether, the use of soil analysis on the farm

level is limited due to the scientific methods, the availability of suitable laboratories and the

costs involved. If soil tests are used, make sure that the relevant aspects are investigated