Maintaining soil fertility
Revitalising the soil
In Europe, we lose 2.46 tonnes of soil per hectare through erosion every year. Worldwide, it is estimated that 224 billion tons are lost. Fallow land is particularly at risk. The lack of vegetation makes the soil more susceptible to drying out and to erosion by wind and rain. Due to hydrophobicity, dry soils cannot absorb water during heavy rainfall events. Permanent vegetation or very short fallow periods make it possible to retain more moisture in the soil. The leaves reduce evaporation and water is fed back into the soil as a result of dew formation. This makes the soil capable of absorbing water.
Another positive effect of evergreen systems is the promotion of soil life and, consequently, the formation of stable soil aggregates. Site-specific measures can also provide a solution to prevent or loosen up compaction. Some crops, such as field beans, sunflower seeds, and melioration radish, manage to break up compaction with their strong root growth and improve the fertility of the soil. (Bio Austria, Bioland. Bio Suisse, Demeter, Naturland, IBLA, FiBL (2013): Principles of soil fertility - Shaping the relationship with soil. 2nd edition)
If fallow periods are kept short, there are numerous advantages for crop production:
Reducing unproductive water evaporation (evapotranspiration)
Preventing the soil from overheating
Promoting soil microorganisms
Improving infiltration capacity
Forming stable soil particles
Providing food for earthworms
Earthworms as an indicator of fertile soils
The earthworms in the soil can convert up to 6 tonnes of organic matter per hectare every year. In order to provide them with sufficient food, it is an advantage to maintain plant cover all year round. Varied cover crop mixtures that also include deep-rooted plants are particularly favourable. This can break up compaction and expand the earthworm habitat. (Bio Austria, Bioland. Bio Suisse, Demeter, Naturland, IBLA, FiBL (2013): Principles of soil fertility - Shaping the relationship with soil. 2nd edition)
Because earthworms are very sensitive, they move to deeper layers, especially in winter and summer, to protect themselves from the heat or cold. This behaviour can be put to good use in order to make the soil more earthworm-friendly.
Ploughs and power harrows should only be used when necessary and should be avoided altogether during the active phases of the earthworm in spring and autumn. Shallow ploughing with the on-land plough is an advantage here.
It is essential to avoid compaction in deeper layers, because earthworms can only break these up very slowly. Even after 70 years, compacted layers are often still visible in soil profiles.
The best thing for earthworms is to minimise tillage and conserve the soil. Light and soil-friendly mechanisation that exerts less pressure on the ground and minimises compaction is also important. Moreover, processing steps should only be carried out on well-dried soil that is able to bear the weight of the machines.
Cover crops to improve the soil
Using cover crops or companion crops can help to keep the soil covered permanently and promote soil life.
Cover crops shorten or avoid fallow periods and have a number of positive influences depending on their composition. The roots of the plants promote the formation of soil particles, and plant root exudates are a source of food for soil life. Wilted organic material contributes to the nutrition of earthworms and the formation of humus. If legumes are included in the cover crop mixture, they store nitrogen in the soil. Sowing a cover crop quickly, especially after a crop that has been harvested early in the season, helps to reduce the soil temperature over the summer months and reduce dehydration.
Companion crops have a similar effect. In this situation, the faster growth of the companion crop can bridge the time until row integration and prevent erosion. In addition, when oil seed rape is used as a companion crop, for example, it acts as a decoy plant to reduce flea beetle damage to the primary crop.
What the plants need from the soil
If all the plants in a crop are to develop evenly, they all need the same starting conditions. That is where the placement depth of the seed comes in. Seeds should not lie too deep or too shallow.
There are three factors that are key deciders on the emergence of our plants: temperature, moisture and oxygen. These parameters are determined primarily by the type of soil, the location and the weather.
In terms of farming, these three parameters are difficult to influence. One of the biggest influencing factors is the pore volume of the soil. A loose, crumbly tilth structure with many medium-sized pores can absorb water better and ensure the exchange of gases. It can also warm up evenly and quickly, creating optimum germination conditions. A disease-free environment is also important, which is achieved through a varied crop rotation, sufficient fallow periods, and a rapid conversion rate of organic matter.
Preparing a bed for the seed
The seedbed needs to provide the seed material with the best conditions for rapid germination and even development. The most important properties are a stable structure that can absorb precipitation and prevent ponding. At the same time, it has to protect the water from evaporation and supply the seedling with sufficient capillary water.
The profile of an optimum seedbed could look like this: coarser clods on the surface that protect against drying out and crusting and can slow down the effects of wind and rain. This tapers into finer particles, which provide the capillary lift to supply the seed with water and nutrients. It is also important to ensure the seed is well covered following sufficient consolidation so that the supply of soil water is made available as soon as possible.
Plant nutrition
Most of the substances that the plant needs are provided by the reserves in the soil. However, the soil reserves can be limited, especially in terms of the nutrition provided by nitrogen, phosphorus and potassium. That is why these substances need to be replenished by fertilisation. Another factor is that these substances are not emitted endlessly by the source rock in the soil. Nutrients such as nitrogen can also be washed out or shifted to deeper layers where they are no longer available to the plants. Phosphorus, on the other hand, is a soil-immobile substance. It is released during a process called chemical weathering that makes it available to the plants and their roots.
Nutrients in the soil continue to decline as a result of decades of cultivation. That is why it is a good idea to analyse the composition of the soil at regular intervals and get an idea of the supply levels in the soil, and take the necessary measures.
Yields and soil fertility can be improved by implementing a varied crop rotation, planting mixed crops, and applying fertilisers and micro-granules at the time of drilling.
Crop rotation
Crop rotation plays an important role in soil health and fertility. Crops that improve the quality of the humus are alternated with crops that deplete the humus, and there is an alternation between summer and winter crops or leaf and stalk crops. On top of that, the effects of the previous crop and plant disease management also need to be taken into consideration when choosing crop rotation plants. Many harmful pathogens have a similar host plant cycle and can thrive in one-sided crop rotations.
Furthermore, there needs to be sufficient breaks in planting between each crop. Cover crops play a decisive role here, because they can have a healing effect when mixed correctly. On the other hand, they can also cause problems if, for example, mustard plants are grown as a crop in crop rotation and as a component of a cover crop mixture. A varied crop rotation offers a great deal of potential for keeping the soil healthy and optimising yields.