Cattle Manure Impacts on Organic Wheat Production in the Northern Great Plains

Project Director: Patrick Carr, Montana State University

Project Overview

The Northwest and Plains regions are home to much of the United States’ organic wheat production, but farmers face challenges when supplying adequate nitrogen (N) and phosphorus (P) to the crop, and they must also contend with low and inconsistent precipitation. These fertility and precipitation challenges can lead to reductions in wheat yield and quality. Legume green manures (LGM) are one option for maintaining soil fertility in organic grain crop rotations, but in years with limited precipitation, wheat yields can suffer if there is not enough time for soil water to recharge between the LGM and wheat crop. Animal manure applications may provide an alternative to LGMs, while also providing soil health benefits including increased soil organic matter.

This study, conducted in a certified organic field at the Montana State University Central Agricultural Research Center, evaluated the impact of a one-time beef cattle manure application at different rates, with or without the inclusion of an LGM or summer fallow, on wheat yield and quality over a four year period.

Farmer Takeaways

A one-time heavy application of beef cattle manure at a rate of 50 Mg/ha can increase organic wheat grain yield, but this yield benefit is most likely to be seen as a legacy effect several years after application, particularly if there is persistent drought.
The use of sweetclover as a legume green manure (LGM) prior to wheat reduced wheat grain yield in some years, but not in others. The amount and timing of precipitation can make it difficult to predict the impact of LGM on wheat grain yield. Future research with different LGM species may be needed.
Wheat grain protein concentration was improved following one-time beef cattle manure application at rates >25 Mg/ha.

Project Objectives and Approach

To evaluate the impacts of cattle manure application rate on organic wheat yield and grain quality over time

Field experiments were conducted on certified organic land over four years (starting in 2021) at the Montana State University Central Agricultural Research Center.
Treatments were implemented using a randomized complete block design with split plots. Fertilizer application rate was the main plot treatment, and included one-time beef cattle manure application at rates of 0, 12, 25, and 50 Mg/ha, in addition to a urea fertilizer treatment.
Manure was applied approximately 10 days before wheat planting in 2021 using a manure spreader and incorporated with a tandem disk.
Wheat grain was harvested using a small-plot combine from the center of each subplot when wheat reached maturity (Zadoks stage 92) and analyzed for yield and protein concentration.

To evaluate the impacts of crop phase (i.e., wheat after a legume green manure (LGM) or wheat after summer fallow (SF)) on wheat yield and grain quality on manure-amended soils

Crop phase was the subplot treatment, and included: 1) wheat after summer fallow, 2) wheat after legume green manure, 3) summer fallow (SF), and 4) legume green manure (LGM; yellow sweetclover).
Yellow sweetclover (Melilotus officinalis (L.) Lam.) was drill-seeded into wheat each spring and terminated by disc the following late June/early July. Disking was repeated approximately 14 days after LGM termination to help control any volunteer clover. Weeds were controlled using a sweep blade when necessary until wheat was planted in the fall.
Plots in the summer fallow treatment were disked in the spring, and weeds controlled as needed until wheat planting.

Key Findings

Applying beef cattle manure one time at a rate of 50 Mg/ha increased wheat yields in Years 3 and 4 of the study, but not in Years 1 or 2. No wheat yield differences were detected at manure application rates ≤ 25 Mg/ha.

Wheat yields were similar across all fertilizer treatments in the first two years, but in Years 3 and 4, the treatment with the highest manure application rate (50 Mg/ha) experienced a significant grain yield benefit. This suggests that a one-time, heavy application of cattle manure may enhance wheat yields and provide soil health benefits several years after application.
In the first two years of the study, drought conditions were present, likely affecting nutrient availability.

Wheat grain yield was more variable when preceded by a sweetclover legume green manure (LGM) than when preceded by summer fallow (SF), and this variability was influenced by precipitation.

Wheat yields for the wheat-after-LGM treatment were 60% lower than yields for the wheat-after-SF treatment in two of four years of the study. The researchers postulate that these yield reductions were the result of decreased soil water availability due to the sweetclover LGM; in other words, insufficient amounts of water re-accumulated between LGM termination and the wheat crop.
Terminating the LGM earlier could solve this issue of soil water recharge, but could come with tradeoffs of reduced soil fertility benefits.

Wheat grain protein concentration increased with the higher manure application rates but was mostly unaffected by crop phase.

Previous research has shown that organically-grown wheat can have low grain protein concentration. In this study, one-time manure applications at a rate ≥25 Mg/ha increased grain protein concentration.

Resources

Carr, P.M., Volkman, M.M., Fordyce, S.I., Crookston, B.S., Yost, M.A., & Reeve, J.R. (2025). Cattle manure impacts on organic wheat production in the northern Great Plains. Canadian Journal of Plant Science, 105, 1-13.

Atoloye, I. A., Cappellazzi, S. B., Creech, J. E., Yost, M., Zhang, W., Jacobson, A. R., & Reeve, J. R. (2024). Soil health benefits of compost persist two decades after single application to winter wheat. Agronomy Journal, 116, 2719–2734.

Rodgers, H., Norton, J., Norton, U., & van Diepen, L. T. A. (2024). Sustaining vulnerable agroecosystems with compost: Lasting benefits to soil health and carbon storage in semiarid winter wheat (Triticum aestivum, L.). Applied Soil Ecology : A Section of Agriculture, Ecosystems & Environment, 204, 105716.

Atoloye, I. A., Jacobson, A. R., Creech, J. E., & Reeve, J. R. (2022). Soil organic carbon pools and soil quality indicators 3 and 24 years after a one-time compost application in organic dryland wheat systems. Soil and Tillage Research, 224, 105503.

Location

Montana

Collaborators

McKenna Volkman, Montana State University

Simon Fordyce, Montana State University

Bradley Crookston, Utah State University

Matt Yost, Utah State University

Jennifer Reeve, Utah State University

Region

Northwest, Plains

Topic

Crop Nutrient Management, Cropping Systems

Year Published

2025