How Much Straw Do You Produce?

Chapter 3 – Residue Management, No. 12, Summer 1989

Don Wysocki

Reducing the amount of straw residue in a field to an operable level, but maintaining adequate cover for erosion protection is a key objective of a conservation farming system. In reduced tillage systems it is preferable to have straw residue uniformly distributed, broken into small fragments and mulched into the soil surface. This protects the soil from erosion and minimizes nutrient tie-up and problems with residue plugging machinery, In no-till systems straw distribution is equally important, but must be achieved solely by straw spreading while combining. The amount of straw produced is a factor in choosing and designing tillage and residue handling techniques.

Producers commonly observe considerable seasonal variation in straw production. Some years straw production is very heavy while others it is not. The amount of straw produced by a cereal crop is dependent on several factors. These include timing and amount of precipitation, temperature, stored soil water, soil fertility, soil depth, grain variety and pest problems.

A method of expressing straw production is the straw to grain ratio (S/G), This is simply the weight of straw produced compared to the weight of grain produced, In the past, several STEEP researchers have measured S/G of 1.16 to 2.00 or 70 to 100 pounds straw/bushel of wheat. A frequently used rule of thumb to estimate straw production has been 100 pounds straw/bushel of grain. Lately this has been revised to 80 pounds straw/bushel of wheat.

Variation in Straw Production

STEEP researchers Dale Wilkins, Paul Rasmussen and Harold Collins at the Columbia Plateau Conservation Research Center at Pendleton measured S/G of Stephens wheat at four locations for various crop years (Table 1).

Sites 1,2 and 3 are part of the Integrated Pest Management (IPM) project. These plots are in a winter wheat-pea rotation and are being studied to understand relationships among weeds, insects, root diseases, tillage and and crop residue. Site 4 is the long-term Crop Residue Management (CRM) plots at the Ag Research Center near Pendleton.

Whole plant samples were cut, bushelndled, weighed, threshed and the grain weighed. Straw to grain ratios were calculated by the following equation:

S/G = (bundle weight – grain weight)/(grain weight)

Averaged S/G for the plots are shown in Table 2. As a reference, ratios of 1.33, 1.67 and 2.00 correspond respectively to 80 pounds, 100 pounds and 120 pounds of straw/bushel. The 1PM plots produced less than 80 pounds straw/bushel in 1985 and 1987 and exceeded 120 pounds straw in 1988. The CRM plots produced less than 80 pounds straw/bushel in 1985 and 1986; from 80 to 100 pounds straw/bushel in 1979, 1982 and 1987; from 100 to 120 pounds straw/bushel in 1980 and 1981; and exceeded 120 pounds straw/bushel in 1978, 1983 and 1984. Variation in S/G was.greater from year to year than from site to site. This demonstrates the importance of growing season characteristics such as quantity and distribution of precipitation, heat and wind in determining straw production. Wide S/G can result when conditions are favorable during vegetative growth but poor during reproductive growth, Plants produce much straw but less grain. Conversely, less favorable conditions during vegetative growth followed by improved conditions during reproductive growth can result in more narrow S/G’s. A year short on water but with timely late season rains would be an example.

Table 1. Location, elavation, annual precipitation and soil characteristics of sampling sites and years sampled (Wilkins, Rasmussen and Collins, ARS Pendleton).

Table 2. Average straw to grain ratios for Stephens wheat at the study sites (Wilkins, Rasmussen, Collins ARS, Pendleton).

Conclusions

The relationship between straw and grain yield is varicultural practices also have an effect. Straw yields can be expected to range from 80 to 100 lb/bu of wheat in most years. Estimates of straw yield derived from grain yields is not exact, but are useful as general guidelines. In years of high or low straw production, tillage or other residue management practices should be adjusted to achieve optimum conditions for plant health and erosion control. An additional consideration is the physical behavior of straw during tillage, flailing or other operation. Factors such as water content, chemical composition and cultivar type can influence the ease with which straw can be broken and/or incorporated.