Agricultural fertilisation in maize – optimal support for an ideal development

The fermentation residue left behind in the biogas plant is a popular fertiliser in agriculture due to its high nutrient content. It can be solid or liquid and is also referred to as biogas slurry.
KWS has summarised for you what effect fermentation has on dry matter and nutrient content. These effects always depend on the dwell time of the substrates in the fermenter, the temperature in the fermenter, the volumetric load of the fermenter and the physical and chemical conditions.

How many nutrients are in which fertiliser?

Selecting the right fertiliser with adequate nutrients is important in order to ensure an optimal supply of nutrients for the plant. KWS has collated the nutrient content of various farm fertilisers.

Source: Chamber of Agriculture

Nitrogen is essential for plant growth, plant health and therefore also for the yield. Adhering to the right doses here is crucial not only from an environmental point of view but also when it comes to plant health. A needs-based approach must be adopted.

In general, a quantity of nitrogen of approximately 140 - 200 kg N/ha (depending on the expected yield) is recommended.
In the early development phase of the maize, there is a high risk that nitrogen is relocated into the deeper soil layers by rainfall in the form of nitrate. Nitrogen in the form of ammonium is not bound in the soil and thus is not subject to the risk of leaching. In addition, maize is able to absorb ammonium at a very early stage. For economic, ecological and structural optimisation of the supply of nitrogen to plants, both the Nmin contents as well as nitrogen replacement must be considered in the course of the vegetation. To determine the amount of nitrogen fertilisation, in addition to the desired yield volume, the various sources of nitrogen supply and causes for nitrogen losses must be considered.

The use of nitrogen fertilisers is regulated by the Fertiliser Ordinance.

For phosphate, fertilisation on soils with a medium supply level of 40 - 80 kg/ha p₂0₅ is recommended.

Early in its development, especially under cold conditions, maize exhibits poor phosphate acquisition. In this growth stage, the root system of the maize plant is not yet fully developed and the phosphate-acquiring ability is low, especially on cold, inactive soils or in cold weather. As a rule, phosphate deficiency is a temporary deficiency.

A phosphate supply sufficient at this stage is best achieved by under-root fertilisation along with an initial nitrogen additive. NP fertilisers (e.g. DAP, MAP) are primarily used in practice. At locations with a high P-supply level (level D, E), the phosphate content can be reduced without adverse effect. Nitrogen-boosted NP fertilisers (e.g. N/P ratios 20 + 20, 25 + 15) are suitable. Under-root fertilisation can be dispensed with altogether only with very high supply stages. A dose of 30 kg of phosphate plus the corresponding amount of nitrogen ensures the supply for young plants in well-supplied locations.

For potassium, a fertilisation quantity of 200 - 240 kg/ha K₂O is recommended.

Potassium is involved in the activation of numerous enzymes in the metabolism of plants and influences the formation of ingredients and carbohydrates. In addition, potassium is responsible for maintaining the osmotic pressure of the cells and thus for regulating water balance. Potassium deficiency inhibits water absorption and increases unproductive water consumption. Potassium deficiency combined with excess nitrogen further reduces pest and disease resistance. Plants optimally supplied with potassium will survive drought periods much better.

A good supply of potassium increases standability and resistance to stalk rot and is important for full cob formation. Like all carbohydrate-rich plants, maize has a very high potassium requirement. As far as the edge of the tassels, an average of 240 kg K₂O is absorbed per hectare. The results of the current soil survey must also be taken into account in order to determine the fertiliser requirement. Fertiliser recommendation on locations supplied with normal levels of potassium: Korn-Kali to grain and silage maize in spring. At an average yield level of 5 - 6 dt/ha, at a high yield level of 6 - 7 dt/ha (source: K + S Kali GmbH).

For magnesium, fertilisation of 40 - 70 kg/ha MgO is recommended.

Most of the magnesium (two-thirds) is absorbed between row closure and flowering. For under-supplied soils, the recommendation is to spread 2 - 5 dt/ha kieserite or 1 - 2 dt/ha kieserite (under-root) in combination with NP fertilisers (source: K + S Kali GmbH).

For normally supplied soils, the magnesium requirement of maize is most easily met by the use of magnesium-containing mineral fertilisers (e.g. Korn-Kali) and lime. Burnt or cottage lime contain about 5 - 15% MgO. The magnesium supply cannot be ensured merely by fertilisation with liquid slurry, since slurry has a potassium-magnesium ratio of around 4, which is too high: 1.

Fertilisation of 30 - 40 kg/ha S is ideal, depending on the nutrient requirement.

Due to decreasing sulphur inputs via the air (<10 kg / ha), in recent years sulphur fertilisation has increased in importance for ensuring yield and quality. The majority (up to 90%) of sulphur in the soil is in organic form and is only available after mineralisation. The dynamics of nutrient conversion of sulphur are comparable to that of nitrogen. On light soils, leaching can be expected. Sulphur fertilisation must be adapted to the needs of the crops and should be done together with nitrogen fertilisation. Sulphur also improves nitrogen utilisation.

In farms with livestock, a sulphur deficiency is relatively unlikely because for example, via slurry, sulphur gets into the soil at a rate of 0.3 - 0.5 kg/m³ .

A good lime supply promotes the soil structure, soil life and gives yield reliability. The risk of soil compaction or sedimentation is reduced, which has a positive effect on plant growth. The recommended fertiliser always depends on the soil type and the pH-value of the soil.

Positive effects by pre-calcification with 1.5 - 2 t/ha CaO:

• Promotion of soil structure and warming
• Prevention of silting and acidification

Depending on the soil type, certain pH-values should be aimed for.

Consequences of pH-values that are too high:
The availability of micronutrients tends to decrease with increasing pH-value levels.

Consequences of pH-values that are too low:

• Determination of nutrients
• Release of toxic elements
• Reduction of biological activity
• Occurrence of structural damage

Causes of soil acidification:

• Excretions of plant roots and soil organisms
• Withdrawal through the plants
• Leaching (100-400 kg CaO/ha per year)
• Use of acidic fertilisers (e.g. ammonium sulphate nitrate, urea)

A supply of trace elements is discussed especially at high yield and dry sites.

Fertilisation can be done as soil or foliar fertilisation. In soil fertilisation, the spreading technique is the limiting factor; in foliar fertilisation, it is the developmental stage of the maize. In addition, various location and weather factors have an effect on the efficacy of the micro elements as shown in the following table.