Tillage update - The value of Chopped Straw
Mark Plunkett, Soil & Plant Nutrition Specialist discusses P and K values of chopped straw. In 2022 there will be ~ 52,000ha of straw chopped under the DAFM Straw Incorporation Scheme (SIM) combining both cereals and oilseeds.
Incorporating chopped straw is a relatively new practice on Irish farms. It brings many benefits from the addition of organic matter / carbon to tillage soils plus a return of valuable P and K. Straw contains mainly potassium (K) and a small proportion of phosphorus (P). Table 1 below shows the levels of P and K returned depending on the crop type. The majority (90%) of P is removed in the grain at harvest time and ~ 10% of total crop P remains in the straw. Approximately 50% of the K remains in the straw for barley and wheat, while for oats ~ 65% of the K remains in the straw at harvest time.
Spring barley and wheat cereals remove 11.4 kg K /tonne while a winter barley and wheat removes slightly less at 10 kg K/t. Winter and spring oats remove 14.4 kg K / tonne of grain yield. Crop P and K removals can be calculated based on grain yield at harvest time. Table 1 below shows P and K levels removed for a range of crops based on typical grain yields.
Table 1: Chopped straw P and K values for a range of crops based on grain yields (t/ha)
|Crop yield - t/ha
|P - kg/ha
|K - kg/ha
|Winter Oilseed Rape
|Spring Oilseed Rape
Chopped straw can reduce reliance on imported P and K
In the current year with high fertiliser prices and prices forecasted to remain relatively high, chopping straw offers the opportunity to reduce our reliance on imported P and K’s. This is especially true as ~ 50% of the crops K remains in the straw at harvest time and can reduce crops K requirements annually as K off takes will be lower. The K in straw is relatively available as it is water-soluble and will be available to the soils reserve of potassium. The amount of P that is returned is relatively low but will add to the soil P reserves and not as available as the K in the short term.
Soil organic matter
The chopping of straw will also add soil organic matter / carbon (C) to the soil. The addition of organic matter will help improve the soils ability to retain and recycle nutrients and will improve the soil structure. Organic matter will also provide a food source for soil biology and improve soil health and function. Building soil organic matter is a slow process and takes time. For example take a 10t/ha crop of winter wheat which will return ~ 2.4t C/ha of which ~ 15 to 20% of the C is retained in the soil. Research from Teagasc at the Knockbeg site showed that after 8 years of straw incorporation the soil organic carbon levels increased from 1.63% to 1.75% in the top 15cm of soil.
Incorporating straw will also take up nitrogen (N) in the decomposition process by the soil microorganisms. It is very important to incorporate the straw into the soil as soon as possible to start the breakdown of the straw back into the soil organic matter pools.
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You can check out the latest Tillage newsletter at Tillage Newsletter - June 2022
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