University of California Water Resources Center

Greenhouse and field experiments were conducted to characterize relationships between fertilizer and water management in irrigated vegetable production in California. Greenhouse trials were conducted both in hydroponic solution culture and in soil culture, with tomatoes and lettuce, to establish functional relationships between nitrogen and water uptake by single plants, and nitrogen recovery efficiency as a function of method and rate of application and placement for a simulated drip irrigation system with one fertilizer material, urea-ammonium nitrate. Over a wide range of solution culture nitrogen concentrations, the relationshp [sic] between nitrogen absorbed and water absorbed by the plant was constant. Slightly more N was taken by plants where emitters delivered it to the soil surface; less than 0.1% of the supplied N was recovered in acid traps as volatilized ammonia. Field trials with drip-irrigated tomatoes and celery, furrow-irrigated broccoli, celery, and corn, and sprinkler-irrigated celery and broccoli established relationships between the quantity of N applied, method of N application (soil-applied soluble or slow release fertilizers, midseason sidedressing, application through irrigation water), quantity of water applied, and crop yield and nitrogen accumulation. Application of fertilizer in the irrigation water was most efficient where no runoff occurred, and where plants grew rapidly. When plants grew slowly due to intermittent drought stress, nitrogen recovery efficiency was lower than where adequate but not excessive quantities of water were applied. Application of fertilizer in the irrigation water must anticipate crop nutrient demand to be effective, and must be placed in the root zone.