Uniform Cereal Variety Testing Program

The Value of Straw
by Greg Schwab, WSU Soil Fertility Extension Specialist

9/26/01

While traveling through eastern Washington you can’t help but notice there is a lot of straw being baled.  Stacks of straw, like the ones below, are showing up all over the high rainfall region.  I assume that most growers are looking at this as an opportunity to reduce residue without burning or tillage, and are (hopefully) planning to direct-seed these fields next spring.  One of the questions I have been answering recently is what is the fertilizer value of the straw when residue is removed compared to when it is burned?  Table 1 shows the average nutrient content of straw.  When a field is burned, the volatile nutrients, nitrogen and sulfur, are lost (the amount loss depends on burning temperature, but for this example we will assume 100% loss) while the other nutrients are returned to the soil in the ash.  When straw is baled approximately 80% of all nutrients are removed.  Using the data in Table 1, and assuming 4 tons of wheat residue was produced, the value of the nutrients lost when burning is $16.41 per acre while the value of the nutrients lost from baling is $26.37 per acre.  Soils in the Palouse are naturally high in potassium, so one season of harvesting straw will not significantly reduce soil K levels.  With continued straw removal, however, soil K levels will decline especially in eroded soils.  In addition to N, P, K and S loss, micronutrients, especially chloride,  is also removed with residue.  Micronutrient removal has not been studied and could be highly variable depending on the fertility of a given field.  I am currently in the process of sampling some of the straw so we can gain a better understanding of nutrient removal in baled straw. 

There are many other factors to consider.  Carbon sequestration would be higher when baling the residue because approximately 20% of the carbon is left behind, and depending on the end use of the straw the rest of the carbon could be sequestered in the final product (straw board or paper).   If direct-seeding is used, the 20% of straw that remains after baling will protect the soil from erosion and should improve water infiltration and in the long term improve soil quality.  Because future environmental regulation might prevent agricultural burning now is the time to begin  thinking about alternative residue management practices and how it affects total nutrient removal.

Table 1.  Average nutrient contents in straw per ton of straw*

*approximately one ton of straw is produced for each 20 bushel of grain.

** based on fertilizer prices of 30¢/lb N; 31¢/lb P₂O₅; 15¢/lb K₂O; and 18¢/lb S.