Effects of Cover Crops and Compost on Phosphorus Cycling in Calcareous Soils.

Producers of dryland winter wheat (Triticum aestivum L.) in the High Plains region of the western United Stated (US) are challenged by low crop available moisture and calcareous soils. Attempts to reduce wind erosion and increase yields are a balancing act of maintaining profitability while improving soil health. In 2016-2017, greenhouse and incubation studies were conducted to evaluate a one-time high rate compost application followed by cover crop treatments on subsequent winter wheat biomass and phosphorus (P) availability. Selected cover crop species included forage radish (Raphanus raphanistrum L.), buckwheat (Fagopyrum esculentum Moench), faba bean (Vicia faba L.) and oat (Avena sativa L.). Soil was analyzed for available, reserve, fixed, and organic P. Microbial parameters included enzyme assays for acid phosphatase as well as carbon and nitrogen cycling enzymes. Incorporated faba and radish residues led to greater wheat biomass, available P, and reserve P, while soil with faba residue had significantly more activity of every enzyme measured as well as more organic P concentration compared to soil mixed with residue from any other species. While compost addition increased the fixed P fraction in the soil, it also had greater wheat biomass compared with biomass in the un-amended soil. The effect of compost addition on available P was most significant following initial application. When any cover crop treatment was substituted for fallow, wheat biomass and available P increased. These findings emphasize the importance of timing to integrating cover crops into a non-irrigated system, and identify the benefits of implementing cover crops in a calcareous soil.