Long-run evaluation of fertilization strategies for dryland wheat in Northcentral Oregon: Simulation analysis

Abstract

Farmers commonly apply fixed ‘blind’ quantities of nitrogen fertilizer during the fallow or at seeding in rainfed winter wheat-fallow systems in Northcentral Oregon, an area characterized by high year-to-year variation in growing conditions. Knowing crop response to available N depends on growing conditions; some farmers apply additional N during the crop season in years of good rains. A simulation model was designed to estimate crop response functions for each fallow-crop cycle in a sequence of 59 harvests, based on monthly precipitation and temperature records from 1917 to 1976 at Moro, Oregon. Five strategies, blind fallow applications (BF), blind seeding time applications (BS), calculated crop season applications (CC), and combinations (BF + CC) and (BS + CC), were each evaluated across this long sequence of years under three cost/price scenarios. Calculated applications, adjusted to particular growth and market conditions, resulted in highest average profits with the lowest coefficients of variation.