Straw incorporation review

Abstract

The traditional uses of straw as animal bedding or feed are nowadays being supplemented by new markets for straw as a bioenergy crop or renewable material. Farmers are also becoming more aware that incorporating straw not only provides a valuable source of plant nutrients, but can also help to maintain or build soil organic matter (SOM) levels. The decision on whether to remove and sell straw or to incorporate it into the soil is farm specific and depends on a number of factors. The aim of this review was to examine the environmental, economic and practical impacts of wheat and oilseed rape (OSR) straw incorporation versus removal, to facilitate the decision making process for farmers and to provide information for policy makers.

Soils. Long-term studies have indicated that straw incorporation can increase soil total nitrogen (N) reserves by c.7% over the long term (8+ years), although this has not been shown to have a significant effect on crop N fertiliser requirements. Straw incorporation also returns significant amounts of potash, and some phosphate, magnesium and sulphur. Based on 2013 prices, the nutrient value of wheat straw was around £3/ha for phosphate and £17/ha for potash (plus £15/ha for magnesium). Whilst the phosphate and potash value will be realised on soils at Index 2 or less (except for potash-releasing clay soils), the Mg value will only normally be realised on deficient soils (Index 1 or below).

Whilst a number of studies have shown modest improvements in SOM and soil physical properties following medium to long-term straw incorporation (i.e. >8-10 years), there was little evidence of short-term impacts on soil quality, workability or yield. Whilst it was not possible to ascribe an economic value to these changes, the importance of maintaining or building SOM levels is recognised. Where SOM levels are low (<5% organic matter), it is more effective to build levels by the addition of bulky organic materials such as solid livestock manures, compost or biosolids.

Agronomy. In most situations, straw incorporation has little impact on weed, pest and disease control. However, where slug populations are high, straw incorporation could increase costs by c.£20/ha, and where oilseed rape disease (i.e. light leaf spot, verticillium wilt and sclerotinia) pressure is high by c.£30-100/ha.

Operational issues. The operational impacts of straw removal or incorporation (such as delays to cultivation and subsequent crop establishment) should be considered on an individual farm and field basis. In principle, straw removal could reduce fuel and machinery wear costs by around £5/ha (by not chopping straw), although importantly, the risk of soil compaction during straw removal can be substantial on medium/heavy soils in wet years, costing up to £55/ha to remedy.

A decision support tree has been developed to guide growers through the factors they need to consider when deciding whether to remove and sell their straw or to incorporate it into the soil.

Abstract

The traditional uses of straw as animal bedding or feed are nowadays being supplemented by new markets for straw as a bioenergy crop or renewable material. Farmers are also becoming more aware that incorporating straw not only provides a valuable source of plant nutrients, but can also help to maintain or build soil organic matter (SOM) levels. The decision on whether to remove and sell straw or to incorporate it into the soil is farm specific and depends on a number of factors. The aim of this review was to examine the environmental, economic and practical impacts of wheat and oilseed rape (OSR) straw incorporation versus removal, to facilitate the decision making process for farmers and to provide information for policy makers.

Soils. Long-term studies have indicated that straw incorporation can increase soil total nitrogen (N) reserves by c.7% over the long term (8+ years), although this has not been shown to have a significant effect on crop N fertiliser requirements. Straw incorporation also returns significant amounts of potash, and some phosphate, magnesium and sulphur. Based on 2013 prices, the nutrient value of wheat straw was around £3/ha for phosphate and £17/ha for potash (plus £15/ha for magnesium). Whilst the phosphate and potash value will be realised on soils at Index 2 or less (except for potash-releasing clay soils), the Mg value will only normally be realised on deficient soils (Index 1 or below).

Whilst a number of studies have shown modest improvements in SOM and soil physical properties following medium to long-term straw incorporation (i.e. >8-10 years), there was little evidence of short-term impacts on soil quality, workability or yield. Whilst it was not possible to ascribe an economic value to these changes, the importance of maintaining or building SOM levels is recognised. Where SOM levels are low (<5% organic matter), it is more effective to build levels by the addition of bulky organic materials such as solid livestock manures, compost or biosolids.

Agronomy. In most situations, straw incorporation has little impact on weed, pest and disease control. However, where slug populations are high, straw incorporation could increase costs by c.£20/ha, and where oilseed rape disease (i.e. light leaf spot, verticillium wilt and sclerotinia) pressure is high by c.£30-100/ha.

Operational issues. The operational impacts of straw removal or incorporation (such as delays to cultivation and subsequent crop establishment) should be considered on an individual farm and field basis. In principle, straw removal could reduce fuel and machinery wear costs by around £5/ha (by not chopping straw), although importantly, the risk of soil compaction during straw removal can be substantial on medium/heavy soils in wet years, costing up to £55/ha to remedy.

A decision support tree has been developed to guide growers through the factors they need to consider when deciding whether to remove and sell their straw or to incorporate it into the soil.