Kevin Shelley, Jamie Patton, Univ of Wisc-Madison, Nutrient and Pest Management Program
Even with local market prices for new crop winter wheat currently around $8 per bushel, per acre net returns for wheat grain may be marginal given high production costs. Sale or use of the straw can boost wheat enterprise margins significantly. However, due to current high fertilizer costs and increased attention towards building soil organic matter, some farmers are asking if removing and selling wheat straw from a field is worth the extra income.
Published research-based values for macronutrient contents of wheat straw vary, but average around 13 lbs N, 4 lbs P2O5 and 25 lbs K2O per ton of dry matter (TDM). In most areas of Wisconsin, we can expect straw yields between 1 and 3 tons per-acre. Given current prices for fertilizers, a straw yield of 2 tons per acre would remove about $67 per acre in N, P2O5 and K2O (Table 1). However, the release and availability of nitrogen from the straw to a following crop or cover crop is largely unpredictable due to the straw’s high carbon to nitrogen (C:N) ratio. The C:N ratio of wheat straw is approximately 80:1, well above the 20:1 ratio where nitrogen mineralization begins to occur rapidly. Therefore, nitrogen availability to a cover crop immediately following wheat grain harvest may be increased if the straw is removed from the field, as nitrogen immobilization (tie-up) is reduced. Therefore, arguably, the $41 per acre associated with the straw’s P2O5 and K2O may be the more relevant value/cost to consider when evaluating harvest options.
Table 1. Estimated Nutrient Replacement Costs Associated with Wheat Straw Harvest
|Macronutrients||Lbs. removed per TDM straw||Approximate replacement cost ($/lb)||Straw Removal Cost
($ per-acre, 2 TDM straw yield)
|Total est. nutrient value = $66.60 per acre|
If straw is sold in the cash market, nutrient removal costs, as well as costs incurred for bailing, transportation, and additional field operations, should be covered in the total price. If retained on the farm, the fertilizer replacement value of the straw should be considered when comparing potential uses.
The value associated with the organic carbon in the straw is more difficult to quantify. Straw contains about 40 percent carbon, with the amount of carbon ultimately retained in the soil varying with straw composition, environmental conditions, and soil properties. It is estimated after one year, approximately a quarter of the straw-derived carbon may remain in the soil1. Therefore, 2 tons of straw would add approximately 400 pounds of organic carbon back to the soil. By comparison, a soil with 3 percent organic matter will contain about 30,000 pounds of organic carbon to a 6-inch depth (assuming an acre of soil to 6” depth weighs 2 million pounds and soil organic matter is 50% carbon).
Thus, while not insignificant, a single year of removing wheat straw likely has limited impact on soil health and productivity relative to its value in the cash market or its potential utility in a livestock enterprise. Long-term research in western Canada found straw removal had little impact on soil organic matter, with authors’ attributing soil carbon maintenance to root carbon contributions and reduced need for straw incorporation in the conventionally managed system. Even with straw removal, efforts to increase soil organic carbon contents may be enhanced with post-straw harvest manure applications and/or timely planting and good management of a cover crop.
Even when considering the cost of baling straw (tedding, raking, baling), estimated between $75 and $120 per-acre,3 a current market price around $200 per ton4 would suggest straw harvest is a profitable decision. Costs and returns will vary based on actual straw yield, quality and harvest, transportation, and other labor and equipment costs. Due to variability in straw composition, consider sales based on actual weights and lab analysis for moisture and nutrient content.
1 Gao H, Chen X, Wei J, Zhang Y, Zhang L, Chang J, Thompson ML. Decomposition Dynamics and Changes in Chemical Composition of Wheat Straw Residue under Anaerobic and Aerobic Conditions. PLoS One. 2016 Jul 5;11(7):e0158172. doi: 10.1371/journal.pone.0158172
2 C.A. Campbell, G.P. Lafond, R.P. Zentner, V.O. Biederbeck. Influence of fertilizer and straw baling on soil organic matter in a thin black chernozem in western Canada. Soil Biology and Biochemistry. 1991, 23(5): 443-446. ISSN 0038-0717,https://doi.org/10.1016/0038-0717(91)90007-7
3 Wisconsin Custom Rate Guide 2020. https://www.nass.usda.gov/Statistics_by_State/Wisconsin/Publications/WI-CRate20.pdf.
4 Hay market demand and price report for the upper Midwest – for June 13, 2022. https://cropsandsoils.extension.wisc.edu/hay-market-demand-and-price-report-for-the-upper-midwest-for-june-13-2022/.