Crop residue

Crop residue- and chaff- are the by-products of harvesting annual grain crops. The economic value of retaining or removing crop residues depends on many variables. The value of straw and chaff differs greatly from area to area because of this.

A plant (by weight) is about 10-20% roots, 5-10% , 30-40% stems, 5-10% non-grain head parts, and 25-35% grain.

So how much straw and chaff are produced from a particular crop? As crop yield increases due to high moisture and fertility, the amount of straw increases relative to the grain.

A crop in the dark brown zone will produce an average of 35 lbs of straw per bushel of grain and 5-10 lbs of chaff per bushel of grain. A HRS wheat crop in the dark brown soil zone will produce about 65 lbs of straw per bushel of grain and 20-25 lbs of chaff per bushel of grain. A canola crop in the dark brown will produce about 50 lbs of straw per bushel of grain and 15-20 lbs of chaff per bushel of grain. You can see the range of different crops.

If you are considering straw removal, first evaluate your soil erosion risk. Our soil erosion risk in Vulcan County is very high because of our and hurricane like winds. Bare soils are especially vulnerable to erosion. Crop residues reduce wind speeds at the soil surface, and standing stubble anchors the soil. Residue also helps cushion the impact of raindrops so soil particles are not as easily detached, as well as slowing water to allow more infiltration and reduce runoff.

Plant matter is the major source of material that builds soil organic matter. The addition of plant materials or other organic substances is essential to build or maintain soil organic matter. Our soils in the area tend to the side of low organic matter.

Organic matter is a critical component of soil. It contributes to soil structure, binds with nutrients and herbicides, holds moisture, provides food for soil microbes, buffers against changes in acidity and stores carbon, among other tasks.

Crop residue is also vital for moisture conservation.

Nutrients in crop residue are not immediately available for crop use, and their release (mineralization) occurs over a number of years. Roughly, about 10-15% of the nutrients are released from straw by the next year, and about 35% from pea residue. Different crop residues have different nutrient components.

Crop residues are occasionally a detriment. Heavy residue can physically interfere with seeding operations. When residue is not adequately spread, many problems can occur. The chaff row can tie up nutrients, it can contain volunteer and weed seed, disease carryover, and encourage insects.

Every person will be place a different value on crop residue. Producers with low organic matter should place a higher value on straw.

Shilo Andrews, August 26, 2005