Nitrogen and Water Inputs for Trickle-Irrigated Winter Vegetables
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AbstractAn experiment was conducted during 1992-93 at the University of Ariwna Maricopa Agricultural Center to investigate the effects of nitrogen (N) and water management on yield, midrib nitrate-N, and N and water use efficiency of subsurface trickle-irrigated leaf lettuce, collard, and spinach. The experiment was a randomized complete block factorial with three water levels (deficient, optimum, excessive), four N fertilizer levels (deficient, suboptimal, supraoptimal, excessive) and four replications. Trickle tubing was placed in the center of the beds at 15 cm depth. Irrigation was applied daily as needed to maintain the appropriate target soil water tension and N fertilizer (urea ammonium nitrate solution) was applied in 4 to 5 split applications. Midrib samples were collected for nitrate -N analysis at 4 growth stages, and portions of the plots were harvested when plants were marketable size. The 1992-93 growing season was excessively wet, therefore optimum yields were achieved in the deficient irrigation treatment. The wet conditions apparently led to excessive N losses, therefore high rates of N fertilizer were needed for optimum yields. Nitrogen and water use efficiencies were maximized at low rates of water and fertilizer input. Midrib nitrate-N concentrations were responsive to N fertilizer treatments.