Cattle manure impacts on organic wheat production in the northern Great Plains
- Carr, Patrick M. [ Montana State University: Research Centers ]
- Volkman, McKenna M. [ Montana State University: Research Centers ]
- Fordyce, Simon I. [ Montana State University: Research Centers ]
- Crookston, Bradley S.
- Yost, Matt A.
- Reeve, Jennifer R.
Supplying adequate N when growing wheat (Triticum spp.) organically can be challenging. The impact of a one-time application of beef cattle manure (manure) at 0, 12, 25, and 50 Mg ha(-1) on grain yield and quality in wheat/summerfallow (SF) and wheat/legume green manure (LGM) systems was determined from 2021 through 2024. Treatments were arranged in a RCB as a split plot with manure rates comprising main plots and crop phases (wheat after SF, wheat after LGM, SF, and LGM) comprising subplots. An additional main plot consisted of a urea fertilizer check. Wheat yields were greater following a manure application of 50 Mg ha(-1) compared to low rates (<= 12 Mg ha(-1)) and the urea treatment in 2023 and 2024 (P < 0.05). Persistent drought confounded wheat yield response in 2021 and 2022. Grain yield was lower when wheat followed LGM than SF in 2022 and 2023. Grain protein concentrations were comparable or higher at heavier (>= 25 Mg ha(-1)) versus lighter (<= 12 Mg ha(-1)) manure rates, and in later years when urea was applied versus manure at any rate due to yield-induced protein dilution. However, at manure rates >= 25 Mg ha(-1), grain protein concentration generally remained above the 121 g kg(-1) threshold of N deficiency. Impacts of preceding wheat with LGM compared to SF on grain protein concentration were inconsistent, as were manure and urea fertilizer effects on wheat grain test weight. A positive legacy effect can result when manure is applied at 50 Mg ha(-1).