First: shred it
It is sometimes said that harvesting is not the last stage of cultivation, but the first. There is a lot of truth in this, because the effects of further straw management and its use as fertilizer depend on the solutions used in the combine harvester.
The first rule of good straw management is to chop it well. This is especially important in the case of cereal straw. Straw that is well cut into small pieces undergoes better microbiological and chemical decomposition in the soil and does not hinder subsequent cultivation treatments and the emergence of subsequent plants.
But what does "well crushed" mean? The length of straw sections should not exceed 8-10 cm. It is best that most of the chaff, i.e. 70-80 percent. all straw fragments were 1-4 cm long. If the straw chopper in the combine harvester cannot cope with cutting the straw into such fragments, any subsequent chopping of the straw after harvest, e.g. with a mulcher, will not fully remedy the problems at the combine harvesting stage. This is a solution rarely found in Poland.
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Second: scatter it
This is the next step in straw management, which is largely determined by the combine harvester. The best results are achieved with equipment equipped with a straw chopper with a chaff spreader and a chaff spreader. It is best if the shredded straw is spread over the entire mowing working width, although this is not always possible in practice.
The distribution of residues can be assessed visually – at least 70%. the field surface should be evenly covered with shredded straw, without visible "rolls" or "mounds". This definitely facilitates subsequent cultivation operations and allows subsequent plants to emerge without any obstacles.
Uneven straw spreading can be compensated to some extent by spreading it on the stubble using, for example, a mulch harrow. However, this requires some skill, for example in setting the appropriate angle of attack of the tines, so as not to drag a row of straw behind the machine, which will leave a heap in one place when the harrow is lifted. The use of a mulch harrow can also be treated as an initial, shallow mixing of straw with the soil and stimulating the germination of weeds and self-sowing plants.
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Third: accelerate decomposition
The third step on the way to good straw management is the appropriate addition. Straw, especially cereal straw, is characterized by a wide carbon to nitrogen ratio, which may lead to periodic immobilization of nitrogen by microorganisms. The addition of 5-8 kg N/1 ton of straw allows you to narrow the carbon to nitrogen ratio and ensure efficient straw decomposition.
There are also supporters of adding lime to straw, the addition of which eliminates the phytotoxic effects of straw decomposition products and has a beneficial effect on cariogenic processes. If a given site does not require significant soil pH correction, the so-called the dose for straw decomposition is 500-1500 kg CaO/ha or according to another conversion factor: 45-55 kg CaO/t dry matter of straw.
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Fourth: mix
The last step in straw management is, of course, mixing it with the soil. Shredding and evenly distributing straw fragments makes this stage much easier. We have various technologies and machines to use, including disc harrows and stubble cultivators. It is recommended that post-harvest cultivation be performed diagonally, at an angle of 30-45° in relation to the direction of travel of the combine harvester.
The depth of mixing the straw with the soil is important. It is assumed that for each ton of straw there is 1.5-2 cm of cultivation depth. On heavy soils, we work a little shallower so as not to impede the access of air, which interferes with the decomposition of straw. A greater mixing depth can be used on light and dry soils. For example: assuming a cereal straw yield of 4.5 t on light soil, the mixing depth should be approximately 9 cm.
