Rotational Cropping Systems for Nitrogen Management and Weed Control in Dryland Organic Wheat Production
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Diversification of cropping systems with legumes is a common practice used to overcome soil fertility and weed control challenges in organic farming systems. The current study assessed different legume-intensive cropping systems with the potential to minimize management risks for dryland, organic wheat growers in the Inland Pacific Northwest region of the United States. Several cropping systems ranged from cereal-intensive cash crops to legume-intensive green manure and forage, and were grown for the three-year transition period prior to organic certification. The goal was to identify systems that would produce high quality, certified organic wheat. All cropping systems that included a legume for at least one year during the transition phase improved soil inorganic nitrogen (N) levels, but systems that included legumes for the duration of the transition also reduced weeds as a result of repeated mowing. Weed control is as great of a concern as soil N for producing organic wheat and in this study, reduced weed pressure improved wheat yield and protein levels throughout the transition and into organic production. Intercropping a legume cover crop with wheat was used as an additional method to improve soil inorganic N. Competition for soil moisture stress was not a concern, and although N from the legumes was not immediately available to the growing wheat crop, intercropped legume and wheat systems could be grown in rotation with other crops for soil management and weed control. Mechanical removal of the intercrop with a precision inter-row cultivator was a useful crop control method and offered opportunities for further research on cover crop and weed management. Using competitive cultivars and crop-types was also necessary. Intensive management of legumes as intercrops, cover crops, and forage demonstrated the potential to greatly improve organic winter wheat production. However, supplemental soil nutrient sources would need to be added in addition to legumes in order to sustain organic wheat production over time. Organic production of dryland wheat is possible but complex management strategies must be consistent and focus on weed control as much as soil fertility.