Organic transition in dual-purpose wheat systems: Agronomic performance and soil nitrogen dynamics

Authors: HINSON, PHILLIP - Texas A&M University; Adams, Curtis; PINCHAK, BILL - Texas Agrilife Research; RAJAN, NITHYA - Texas A&M University; KIMURA, EMI - Texas Agrilife Extension; SOMENAHALLY, ANIL - Texas Agrilife Research

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2022
Publication Date: 6/2/2022
Citation: Hinson, P.O., Adams, C.B., Pinchak, B., Rajan, N., Kimura, E., Somenahally, A. 2022. Organic transition in dual-purpose wheat systems: Agronomic performance and soil nitrogen dynamics. Agronomy Journal. 114(4):2484-2500. https://doi.org/10.1002/agj2.21093.
DOI: https://doi.org/10.1002/agj2.21093

Interpretive Summary: As a result of its climate, dual-purpose winter wheat cropping systems are dominant in the Southern Great Plains region of the U.S. A dual-purpose wheat system is one in which livestock graze wheat forage, but grain is also produced. Few of these systems are organic, however, representing missed opportunities for producers. Before agricultural land can be certified organic, it must go through a three-year transition period in which only organic management practices are used. But no research had been conducted on organic transition of dual-purpose wheat systems to guide producers. In this project, a multidisciplinary team of scientists directly compared a proof-of-concept organic dual-purpose wheat system during organic transition to a conventional system at field scale (~100 acres). Organic wheat yield was initially lower than conventional due to nitrogen limitation, but there was no yield difference by the third year. Crop rotation with a nitrogen-fixing legume, additional nutrients from application of composted manure, and appropriate wheat variety selection contributed to closing the yield gap. Grain protein of at least 12% is required to sell wheat in the organic food market, but grain protein never reached this level in the organic system. Additional measures will be needed to elevate grain protein, such as in-season application of an available form of nitrogen. Benefits of a cover crop (e.g. additional nitrogen fixation) could not be realized in the organic system, because cover crop establishment was unsuccessful in most years due to limited moisture. This research demonstrated that organic management of dual-purpose wheat systems is feasible and provided a baseline to improve upon.

Technical Abstract: The Southern Great Plains (SGP) region of the U.S. is widely known for its dryland dual-purpose winter wheat cropping systems—integrated systems that provide both livestock grazing and grain production. Few of these systems are organic, however, representing missed opportunities. A large-scale (41-ha) systems study was conducted for three years (2018 to 2021) to directly compare a transitional organic dual-purpose wheat system to a conventional system, with system management components customized to the eco-region. Organic wheat yield was 20% lower than conventional wheat in the first season of organic transition (2018/2019), but there was no yield difference by the third year (2020/2021). The comparable yield of the transitional organic system by the third year may be attributed to N fixation and soil deposition by a legume-based cash crop in the previous winter season (2019/2020), additional nutrients from application of composted manure, and appropriate wheat variety selection. Relying on annual establishment of summer cover crops to deliver fixed N and other ecosystem services to the transition organic system was not feasible in most years due to limited moisture. Grain protein concentration of the transitional organic wheat was below the 120 g kg-1 threshold for a food market organic price premium, ranging from 90.6 to 10.3 g kg-1. In-season application of a more available form of N could be an effective strategy to increase GPC. Organic dual-purpose wheat systems in the SGP can be a viable enterprise, though additional research is needed to address some challenges identified herein.