Soil fertility is the ability of the soil to meet the needs of plants in the form of nutrients necessary for their proper functioning and development. Soil fertility depends on a number of factors, mainly the abundance of plant-useful minerals in the soil, the structure of the soil profile and the chemical, physical and biological properties of the soil. Soil fertility is a soil characteristic that builds up over decades and determines agricultural suitability.
Soil fauna inhabit the soil and also influence and create it. The most important function of the fauna is the decomposition of organic matter. Without the decomposition of plant remains, the chemical elements and other nutrients they contain would be unavailable to plants. During decomposition, stable organic matter is converted to complex humic substances, which in turn are capable of sorbing various nutrients and ions and then gradually releasing them. Soil humus is capable of holding these nutrients and protecting them from leaching, thus counteracting the eutrophication of surface and groundwater.
The current efficiency of agricultural production is always some consequence of past events, so we need to take into account the impact of previous crops and our actions on the soil.
The farmer’s impact on the soil organic matter content considered in the balance depends on the type of crops grown and the organic fertilisers used.
The role of crops in the humus balance:
| Plants that reduce humus | Plants that increase humus |
| – cereals – maize – leafy and root vegetables – root crops (no manure) | – oleaginous bean crops (lucerne, clover, peas, vetches, broad beans, soybeans) – mixtures of grasses with faba bean plants – mixtures of cereals and faba bean plants |
In contrast, the crop-dependent rates of increase or decrease in soil organic matter are as follows:
One recurring and growing problem is the loss of soil fertility. Conventional intensive agriculture has significantly decoupled livestock production from crop production, resulting in less frequent use of organic fertilisers to ensure the return of organic matter and macro- and micronutrients to soils. Intensification of soil cultivation and mineral fertilisation, simplification of crop rotations, loss of biomass (e.g. straw as an energy resource) deplete the diversity of soil organisms and reduce humus-forming processes. Furthermore, biomass depletion causes soil microorganisms to start decomposing humus instead of using fresh organic matter. At this point, a vicious circle is created – the loss of soil humus makes it necessary to increase mineral fertilisation, which accelerates humus mineralisation processes and further loss of fertility.
Any action not based on the actual fertility of the soil, but only on the use of mineral fertilisation and plant protection, may have short-term effects, but lead to further deterioration. The main causes of declining fertility of arable soils are:
- simplifying crop rotations,
- intensive mineral fertilisation with reduced use of organic fertilisers,
- neglect of pH regulation (liming),
- plough tillage – excessive mixing and movement of soil,
- water and wind erosion,
- surface runoff – also as a result of soil cultivation errors and lack of protection,
- salinisation – a derivative of mineral over-fertilisation,
- waterlogging and soil crusting – derived from loss of structure and degradation of soil aggregates.
Soil fertility is not synonymous with fertility. Soil fertility is the ability of the soil to satisfy the needs of the crop leading to a harvest. It is the result of soil fertility and the agronomic measures taken by the farmer. Fertility determines the productive value of the soil.
The distinctions are:
- potential fertility, which depends on the habitat in which the soil is found,
- current fertility, which can vary due to water availability, temperature, etc.
The primary measure of fertility is the yield of the crop.
In addition to soil fertility and fecundity, there is also the concept of soil productivity, which refers to the ability of the soil to produce biomass produced in a specific unit of time on a corresponding area of land, expressed in dry matter. Soil productivity is closely linked to a specific plant or set of plants, a specific rotation, etc.
The needs of plants can only be met if the nutrients required for them are available in the soil. The availability of nutrients to plants varies over time and depends on many factors. Among these are:
- water availability and the amount of precipitation – water is essential for the processes of uptake of nutrients from the soil, but can also lead to their being washed into the profile, leaching from the soil altogether, and washing into watercourses, for example;
- soil and air temperature – too low or too high temperatures impair the uptake of nutrients from the soil, e.g. phosphorus. Extreme temperatures limit the use of already uptaken nutrients for plant growth;
- soil mineral composition – depending on the content and nature of the soil’s fluvial minerals shapes its nutrient capacity, as well as the water required for uptake;
- distribution of nutrients in the soil – e.g. phosphorus is best taken up at a distance of 1 mm from the root hair zone, calcium and magnesium ions at a distance of 5 mm, potassium ions at a distance of 7.5 mm and nitrogen ions at a distance of 20 mm;
- soil pH – depending on the crop:
- the chemical mechanisms of nutrient uptake by the roots are strongly dependent on the pH of the environment and specific to each nutrient and plant;
- soil transformation of mineral and organic matter – soil matter undergoes constant changes leading to the binding and release of nutrients from mineral matter as well as from organic matter, depending on humidity and temperature. However, higher temperatures can also accelerate the decomposition and mineralisation of organic matter in the soil, resulting in a decrease in organic carbon content (fao.org/3/a0100e/a0100e07.htm). Increasing atmospheric carbon dioxide concentrations may cause microorganisms in the soil to decompose organic matter more rapidly, potentially releasing even more carbon dioxide (EEA Report No 12/2012, Climate change, impacts and vulnerability in Europe 2012);
- soil microbial activity – a number of micro-organisms have the ability, for example, to fix atmospheric nitrogen or convert phosphorus compounds to plant-available forms;
- plants previously growing on the soil – due to specific requirements (brassica plants – sulphur uptake) or symbiosis with microorganisms (faba bean plants – nitrogen retention), the availability of components can change significantly;
- elements entering the soil from the atmosphere – with precipitation and particles falling on the soil, various components enter the soil, depending on the composition of air pollutants.
A large proportion of these factors are beyond human influence (e.g. precipitation, temperature, bedrock), and there are some that human activity can change rapidly (e.g. pH) or support long-term (organic matter transformation).