Photo Courtesy of Curtis Young
Article from https://agcrops.osu.edu/newsletter/corn-newsletter/2024-21/nutrient-value-wheat-straw by Laura Lindsey, Ed Lentz, CCA, Eric Richer, CCA
Before removing straw from the field, it is important for farmers to understand the nutrient value. The nutrient value of wheat straw is influenced by several factors including weather, variety, and cultural practices. Thus, the most accurate values require sending a sample of the straw to an analytical laboratory. However, “book values” can be used to estimate the nutrient value of wheat straw. In previous newsletters, we reported that typically a ton of wheat straw contains approximately 11 pounds of N, 3.7 pounds of P2O5, and 29 pounds of K2O. According to the 2024 Second Quarter Fertilizer Prices Across Ohio bulletin (https://u.osu.edu/ohioagmanager/2024/04/15/2024-second-quarter-fertilizer-prices-across-ohio/) and nutrient removal “book values”, one ton of wheat straw would remove approximately $14.12 of P2O5 & K2O.
In addition to Table 1, you may also download and use this Excel-based spreadsheet: https://stepupsoy.osu.edu/wheat-production/wheat-profitability-calculator to estimate the profitability of wheat production with and without straw removal. In Tab 1 of the spreadsheet, enter your production costs or use our default values. Then, Tab 4 of the spreadsheet will estimate the partial return of wheat production with and without straw removal. Several other cropping scenarios are also available for profitability comparisons.
Although N adds value, we do not give it an economic value in the form of fertilizer (as seen in Table 1). Within straw, N is in an organic form and will not immediately be available for plant uptake. The organic-N will need to be converted by microorganisms to ammonium-N (an inorganic form) before it is available for plant uptake – a process called mineralization. The rate of which mineralization occurs depends on the amount of carbon (C) and N in the straw (C:N ratio). The USDA reports a C:N ratio of 80:1 for wheat straw which means there are 80 units of C for every unit of N. Mineralization rapidly occurs when the C:N ratio is ≤ 20:1. At a C:N ratio of 80:1, mineralization will be much slower. (For comparison, corn stover is reported to have a C:N ratio of 57:1.) Rate of mineralization is also influenced by soil moisture and temperature. Since mineralization is a microbial-driven process, mineralization will be slowed (halted) in the winter when temperatures are cold. Thus, no N credit (i.e., value) is given for wheat straw since it is not known when the N will mineralize and become available to the following crop.
In addition to N, removal of straw does lower soil K levels. If the straw is removed after heavy rainfall, some of the K may have leached out of the straw, lowering the nutrient value. However, a soil test should be done to accurately estimate nutrient availability for future crops. Besides providing nutrients, straw has value as organic matter, but it is difficult to determine the dollar value for it.