Straw Study

University of Idaho Extension Educator Grant Loomis has noticed an increasing number of Blaine County farmers have been letting their straw rot in the field after grain harvest rather than baling and selling it.

A recently published UI Extension and U.S. Department of Agriculture cooperative study suggests there may be wisdom in the seemingly counterintuitive management approach.

The paper, “Understanding the Mineral and Nutrient Value of Wheat Residue,” concludes nutrients in straw that growers leave in the field can be worth upwards of two-thirds of the revenue obtained from harvesting that straw and selling the bales. Baled straw is commonly purchased for uses including mushroom cultivation, insulation, making compost and animal bedding. In addition to lending nutrient value, straw left in the field packs several agronomic benefits that are harder for growers to quantify, such as improving soil organic matter, bolstering soil microbial activity, curbing erosion and improving water infiltration into soil.

The straw studies followed up on Loomis’ 2017 master’s thesis project, which was funded by the Idaho Barley Commission and evaluated the efficiency with which plants take up nitrogen when it is tilled into the soil versus broadcast on the surface. Loomis and his colleagues found roughly a quarter to half of nitrogen applied in the study made its way into straw tissue, depending on crop variety and fertilizer application method.

“We saw there was nitrogen in the straw from what I did, and we had the question of what real value does that have to farmers of leaving that straw on the soil, incorporating it into their soil or taking it off and baling it,” Loomis said.

Loomis was still a graduate student when he helped with data collection for straw-study field trials in 2018 and 2019. Other co-authors included Juliet Marshall, Patrick Hatzenbuehler, Biswanath Dari and Olga Walsh with U of I and Curtis Adams, Christopher Rogers and David Tarkalson with USDA’s Agricultural Research Service. Their research was based on replicated trials at the U of I Aberdeen Research and Extension Center and commercial fields in Soda Springs, Rupert, Idaho Falls and Ashton.

Summaries of the key findings were published in the November and December 2024 edition of the American Society of Agronomy’s “Crops & Soils” magazine.

Based on an average yield of 120 bushels per acre of wheat, the researchers estimated the straw contained the equivalent of 38 pounds of nitrogen, 2 pounds of phosphorus and 201 pounds of potassium per acre.

“That was the question that was really unanswered before — it was unknown how much nutrients are in the straw,” Hatzenbuehler said.

During 2023, Hatzenbuehler, an Extension specialist of agricultural economics, made economic calculations for the study, which he presented Feb. 5 during the East Idaho Cereals Conference hosted in Fort Hall. Based on a wheat yield of 120 bushels per acre and using historical average nutrient prices, Hatzenbuehler estimated the value of nutrients in straw left as residue on fields at $77 per acre. Barley straw nutrient values were slightly less, at about $60 per acre.

By comparison, he calculated that farmers could make $122 per acre by selling wheat straw — assuming a straw price of $55 per ton, based on USDA Agricultural Marketing Service reports from January 2025, and an average yield of 2.47 tons of straw per acre from a 100-bushels-per-acre crop. To determine the net profit from such a sale, one would need to account for the costs of baling, hauling, and selling the straw. Grain growers commonly hire contractors to bale and haul their straw, which cuts into profits from selling it.

Hatzenbuehler’s estimates also did not factor in the value of micronutrients contained in straw, such as magnesium and sulfur, or soil-health benefits of leaving straw. USDA has begun research to answer questions about when nutrients from straw become available to crops.

Many farmers in southern Idaho have baled and sold straw for decades, which has depleted their soils of potassium. Some of the region’s farmers have recently resorted to leaving straw on their fields as a means of replenishing their soil potassium.

“This puts the spotlight on a potentially unfavorable long-term economic tradeoff,” Loomis said. “The value of keeping that straw on the farm rather than harvesting and selling it needs to be considered.”

Individual circumstances have a strong bearing on whether keeping or selling straw makes the most economic sense for a farmer. For example, a farmer may need to sell straw to have cash on hand to repay an operating loan. Furthermore, farmers have less certainty regarding how long it may take for nutrients in straw to break down into a plant-available form.

Another potential pitfall of leaving straw in the field is the potential for it to harbor diseases and carry inoculum into the next growing season — a phenomenon plant pathologists describe as a “green bridge.” Diversifying crop rotations is a proven strategy toward avoiding such disease challenges.

Published in Catching Up with CALS