Wheat Straw

Straw is what remains of the stem and leaf once the plant has senesced and the grain has been taken from it. By harvest the plant has moved what it could into the ear, and the stem left behind is largely structural material — cellulose, hemicellulose, and lignin — which is precisely why straw behaves as it does. It is strong, bulky, slow to break down, and absorbent, and those properties, rather than any nutritional content, are what its uses are built on.

How much straw a crop leaves, and in what condition, is not fixed. Variety and growing season set the height and stem strength of the crop; the cutting height set on the combine decides how much of the stem is gathered rather than left standing as stubble; and the weather between threshing and baling determines whether the swath is dry enough to bale well. Straw that has been rained on repeatedly in the windrow is a poorer material than straw baled promptly.

Straw is a genuinely useful material with established markets, and none of its uses treat it as something to be got rid of. What they have in common is that they draw on its bulk, its structure, and its absorbency rather than on its feeding value.

• Animal bedding — the largest outlet in many regions, using straw’s absorbency and its bulk to keep housed stock dry and comfortable
• Roughage feed — fed to ruminants as a source of bulk and fibre, generally alongside more nutritious feeds rather than in place of them
• Mushroom substrate — composted and used as the growing medium for cultivated mushrooms, an outlet that depends on straw being clean
• Board and fibre — a raw material for particleboard and other panel and fibre products
• Fuel — burned or otherwise converted for heat and power, drawing on its bulk as a biomass feedstock

The feeding value deserves to be stated honestly rather than talked up. Straw is a poor feed: it is low in protein and its energy is locked in fibre that ruminants digest slowly and incompletely, and non-ruminants scarcely at all. It is fed because it supplies bulk and physical fibre cheaply, not because it is nourishing, and rations built on it depend on what is fed alongside. Treatments exist that improve its digestibility, but they change the economics and do not turn straw into a nutritious feed.

Straw that is not baled is chopped and spread by the combine and incorporated into the soil. This is not disposal — it is a use, and it is the alternative against which every sale of straw is measured. Incorporated straw returns organic matter to the soil, and the nutrients the stem still holds go back with it rather than leaving the field on a trailer. Organic matter contributes to soil structure, to the soil’s capacity to hold water, and to the biological activity within it, and the material that maintains it has to come from somewhere.

So removing straw for sale has a soil cost, and that is the honest way to put it. The bale earns money and the straw goes to a real use elsewhere; what leaves with it is organic matter and nutrients that will not be returned to that field. Incorporation has its own costs and complications in turn — straw is slow to break down, it must be dealt with by the following cultivations, and it can interfere with establishing the next crop.

Straw is baled from the windrow and handled, stacked, and hauled as bales. It is bulky and light for its volume, which dominates its economics: straw is expensive to move relative to what it is worth, so it tends to be used near where it was grown, and bale density is a real commercial variable rather than a technical detail. Baling depends on the swath being dry, which ties the whole operation to the weather in the days after harvest.

In store, moisture is the thing that matters. Straw baled damp or stored wet will heat and mould — a spoilage problem for a bedding or feed material, a health problem for the stock it is used for, and, where bales heat substantially, a recognised fire risk in stacks. Straw is therefore baled dry and kept dry, under cover or sheeted, and stacks are built so that air can move around them.