Dryland fallow vs flex-cropping decisions in inland Pacific Northwest of USA

Abstract

CONTEXTDryland cropping systems in the inland Pacific Northwest (iPNW) of USA are predicted to be more dynamic with greater use of annual fallow under projected climate change. Increased use of fallow can result in soil degradation and greater cropping system uncertainty. In view of that, a regional simulation study was planned to explore for different spring crop options that can fit in place of fallow in rotation with winter wheat. OBJECTIVEThe main goal of the study was to provide spring crop pre-plant yields and available soil water left after harvest of spring crop as forecasts at regional scales to compare fallow versus spring crop choices known here as flex-cropping. METHODSModel simulations were conducted using CropSyst (Cropping System Simulation model) and were based on historic (1981–2010) and historic combined with recent year's weather identified as Dry/Average/Wet. Historic weather was joined with recent weather at different forecast dates (Dec. 1st, Jan. 1st, Feb. 1st, March 1st, and April 1st). Hence, weather until forecast dates consisted of recent and historic later on. To identify a suitable forecast date, regression analysis was conducted to compare yields of spring crops on different forecast dates with corresponding yields obtained on recent weather years. Regional simulations were run on identified forecasting date to forecast yields and available water left in the profile after harvest. RESULTS AND CONCLUSIONSRegression analysis showed high correlation (R2) between yields obtained on forecast dates of Feb/March/April 1st with yields on recent years. Coefficient of variation (CV) was also lower for spring crops yields simulated on forecast dates of Feb/March/April 1st compared to Dec. 1st and Jan. 1st. Feb 1st was considered important to select as forecast date due to much variability in the spring crop planting across the region. Regional forecast maps of spring crop yields, their CV and available water are presented in the study. Spring pea was identified as flex-crop to intensify cropping systems in grain fallow. Spring canola and spring wheat were expected to have negative rotational impact, therefore were better options to diversify the systems in annual crop and annual crop transition areas. Keeping in mind the limitations of simulation models, this study highly recommends for validation field trials at different locations across iPNW. SIGNIFICANCEMaps of predicted spring crop yields, their CVs and predicted available water after fallow will aid in decision making related to intensification and diversification of iPNW.