Fall Rye Reduced Residual Soil Nitrate and Dryland Spring Wheat Grain Yield

Limited information about how cover crop management impacts the agronomic performance of succeeding annual crops in semiarid regions constrains cover crop utilization. Th erefore, over 2 yr we quantifi ed how cover crop species (fall rye [Secale cereale L. 'AC Remington'] or oilseed radish [Raphanus sativus L. 'Tillage radish']) and nutrient source (compost or inorganic fertilizer) aff ected cover crop biomass and N uptake, soil nitrate N (NO3-N) and ammonium N (NH4-N), and the agronomic performance of the succeeding spring wheat (Triticum aestivum L.) test crop. Fall rye reduced pre-plant NO3-N by 2 to 18 times compared with oilseed radish, and reduced spring wheat grain yields by 38 to 58% compared with amended soils with no cover crop and oilseed radish. Inorganically fertilized soils led to 21% greater pre-plant soil NO3-N concentrations than the compost-amended soil in 2013-2014 but nutrient source did not signifi cantly aff ect NO3-N concentrations in 2014-2015. A quadratic function explained 93% of the variability between pre-plant soil NH4-N plus NO3-N (0-7.5-cm depth) and spring wheat grain yield in 2014, indicating that the N supply limited spring wheat grain yield. We conclude that fall rye scavenged residual NO3-N better than oilseed radish during the non-growing season, particularly during the spring period when this perennial species assimilates N, but under semiarid conditions it may decompose and mineralize too slowly to supply N at the right time for the subsequent crop, while oilseed radish tended to boost spring wheat grain yield.