Is potash fertilization profitable?

As a result of the currently high prices for fertilizers and other production inputs, their application is being examined even more closely in terms of economic viability. For nitrogen (N), these questions appear to be comparatively easy to answer. The relevant “N optimum curves” are used, which are available for many locations and crops.

For potassium (K), the correlation between the level of fertilization and the expected yield is less close than for nitrogen. The exception to this are constellations in which the potassium content in the soil is at a very low level (e.g., content class A) or there are other reasons for a drastic undersupply of the plants. Since potassium, as an essential plant nutrient, has a central function in yield formation, a sufficient supply must always be ensured through basic fertilization. For potassium, too, it is possible to calculate which fertilizer costs are economical due to the additional yield.

Soil supply is the most important starting point when calculating the recommendation for basic potash fertilization. In principle, fertilization is recommended even with an optimum soil content (C). This is known as maintenance fertilization. This nutrient supply compensates for the assumed losses due to harvested products and losses and, therefore, ensures the targeted yield level. At the same time, an undesirable drop in soil content is avoided. Restoring the optimum nutrient content in the soil may require considerably more effort.

Naturally, the yield effect of potassium fertilization in the area of optimal supply is lower than at a sub-optimal level. This is often the starting point for considerations that take a reduction in fertilization measures into account. Here, however, it is not a gut feeling that should decide, but a profitability calculation.

The following factors are relevant for calculating the profitability of a basic fertilization measure:

• Fertilizer costs, calculated in euros per kg of nutrient, e.g., euros per kg of K₂O

• Quantity of the nutrient to be used

• Producer prices that can be achieved with these additional yields

• Additional yields per ha to be expected from the fertilization

In the following table, the additional yields were calculated for varying fertilizer and producer prices, which would be required to cover costs with an exemplary average potassium fertilization of 60 kg K₂O/ha.

For comparison: If 65% grain, 10% rapeseed, 10% sugar beet, and 10% silage corn as well as 2.5% potatoes are cultivated on one hectare, an average yield of approx. 80 kg K₂O/ha would be applied with the harvested products alone. In practice, however, even lower average amounts of potassium are sometimes applied [1]. The specific amount of fertilizer applied to the individual crop remains variable.

The higher the producer prices and the lower the nutrient costs, the lower the additional yields required to cover the costs of the potassium fertilizer. The additional yields that can be expected, however, depend on various factors.

The probability of achieving higher yields through fertilization increases with a decreasing potassium soil content. Fertilization on the fields or parts of fields that actually need it (!) unlocks the full yield potential. Blanket “withdrawal fertilization” does not bring any certain advantages on soils with a high potassium content, but is not sufficient for optimum yields in content classes A and B. 

Our advice: Use targeted fertilization measures based on detailed and up-to-date information about the soil supply!

The ability to appropriate potassium and the quantities required vary greatly from crop to crop. Potatoes, sugar beet, and corn, for example, have a high demand and at the same time a limited ability to utilize the available soil reserves. The difference to grain can even be demonstrated over many years on a black loess soil (see figure).

With high mineral fertilizer prices, the nutrients contained in organic fertilizers are particularly valued. These fertilizers are multi-nutrient fertilizers with different nutrient ratios. They must be applied correctly for reasons of environmental protection and economic viability. Particular attention should be paid to the corresponding nutrient requirements.

It is important to know that only two nutrient fractions in organic fertilizers such as digestate or liquid manure are actually immediately available to plants: These are potassium and ammonium (NH₄) nitrogen. All other nutrients are only fully utilized after mineralization.

This is particularly important on fields that have hardly ever been fertilized organically. The frequently used phrase “...can be fully taken into account in fertilization planning” is, therefore,not always likely to lead to an optimal result when covering an acute need in spring. Particular attention must be paid to a sufficient supply of available magnesium to counteract ion antagonism when there is a high supply of highly soluble cations such as K⁺ and NH₄⁺.

Our advice: Apply organic fertilizers as required, taking into account the availability of nutrients. Supplement missing nutrients, especially magnesium and sulfur (e.g., with ESTA Kieserite).
 

An economic analysis of potash fertilization includes both the cost and the revenues side. The applicator is initially confronted with the costs of rising mineral fertilizer prices. Higher prices are also being charged for organic fertilizers, however. Due to the likewise increased application costs (e.g., 4-9 €/m³ liquid manure [2]), the costs per nutrient unit are also rising here with relatively low nutrient density. This applies similarly to transportation and almost all other factors (energy, seed, crop protection).

Although the total cost of production per hectare has increased significantly, this is fortunately also the case for many agricultural producer prices. This increases the leverage effect of the individual production factors. his naturally also applies to potash fertilization. Blanket savings do not lead to optimal results.

[1]Marketing year 2020/21. Germany: approx. 27 kg K₂O/ha, Lower Saxony: 41 kg K₂O/ha, Saxony-Anhalt: 18 kg K₂O/ha LF.

[2] Macke, A. “Suddenly manure is in demand like never before”. DLG-Mitteilungen, 02/2022