Cover Crop Development Related to Nitrate Uptake and Cumulative Temperature

Cover crops have been shown to deplete soil nitrate and reduce nitrate leaching in Mediterranean climates. Cover crop canopy development, N uptake, and root system development were studied during three rainy seasons in Yolo silt loam and Rincon silty clay loam soils, with two cover crops with contrasting root systems and N acquisition strategies: triticale (x Triticosecale), a monocot wheat (Triticum aestivum L.)-rye (Secale cereale L.) hybrid with a fibrous root system, and bell bean (Vicia faba L.), a tap-rooted legume that fixes N. Weed growth was substantial in bell bean plots. Triticale consistently developed a uniform stand and produced a deeper and denser root system with a faster root penetration rate than the bell bean-weed mixture. Growth and N uptake were strongly correlated with accumulated temperature for triticale but not bell bean. Therefore, triticale growth models based on weather data (1982-2014) were used to study the effect of planting and termination dates on N uptake in Davis, CA. Planting before mid-October would enable N extraction from the soil prior to the heaviest winter rains, whereas delaying sowing until mid-November would delay significant N uptake until early spring. Following the current cover crop management approach of sowing triticale before the first significant rain and terminating by the end of February, N uptake from the soil would exceed 45 kg N ha(-1) similar to 56% of the time. Generally, a temperature-based growth model is useful for managing soil nitrate levels with some monocot cover crops during the winter rainy season.