“Maximizing Fertilizer Value from Cereal Straw: Strategies for Potassium, Nitrogen, and Phosphorus”

2023-06-01 07:28:00

In addition to being a source of carbon, cereal straw contains potassium and, to a lesser extent, nitrogen and phosphorus. Its future, returned or exported, depends on many factors, including the rotation, the potassium requirement of the following crop and its nitrogen needs, especially in the fall.

50 kg/ha of potassium

According to the references, one tonne of common wheat straw contains 1.7 kg of phosphorus (P₂O₅), 12,3 kg de potassium (K₂O) and 5.7 kg of nitrogen (N). These fertilizing values ​​vary according to the richness and availability of soil elements.

The “richer” the soil, the more elements the plant absorbs and the more it then restores in its residues left on the ground, says Christine Le Souder, fertilization engineer at Arvalis. Four tons of straw harvested per hectare export about fifty units of potassium from the soil. This data is to be taken into account in the calculation of the fertilization of the following crop and in the agronomic projections of the plot. Without compensation, the potassium content of the soil is likely to decrease and be penalizing for demanding crops.

Analyze to better fertilize

The soil analysis remains the best tool to know the situation of the soil. It makes it possible to check where the PK content of the plot is in relation to the reference threshold and whether it is advisable to skip PK fertilization or to reinforce the application rate.

This is assessed according to a grid established by Comifer. It takes into account the return or export of the straw, the requirement of the crop (more important for beets or potatoes), the type of soil, etc.

In soil poor in organic matter (OM) and potassium, the return of straw is justified, explains Rémy Ballot, engineer at Inrae. In this specific situation, with crops requiring potassium, the addition of potassium amendments may be unavoidable. Conversely, if the soil is well supplied with OM and potassium, then the export of straw is possible, especially if it returns in the form of organic effluents.

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