Nitrogen and Water Interactions in Subsurface Drip‐Irrigated Cauliflower I. Plant Response

Production of cauliflower (Brassica olearacea L. var. botrytis L.) in the southwestern U.S. is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. Subsurface drip irrigation offers what is likely the ultimate in control of the plant root zone for crop production. However, the water and N‐response characteristics of subsurface drip‐irrigated cauliflower have not previously been reported. Three field experiments were conducted in southern Arizona in 1993–1996. The objectives were to determine: (i) an optimum range of soil water tension for subsurface drip‐irrigated cauliflower, (ii) the effects and interactions of water and N fertilizer on crop yield and quality, and (iii) seasonal and daily N uptake for high‐yielding cauliflower. The experiments were randomized complete block factorial with three irrigation regimes (low, medium, high), four N rates (60–600 kg N ha−1), and four replications. Irrigation was applied daily to maintain target soil water tensions and all N was applied by fertigation. With respect to marketable yield, curd weight, and curd diameter, the optimum soil water tension was approximately 10 to 12 kPa in this sandy loam soil during the 3 years. Marketable yields across all treatments ranged from 30 Mg ha−1 Yields and quality were generally more responsive to N rate than to irrigation and showed significant irrigation by N rate interactions during 2 of the 3 years. At equivalent N rates, excessive irrigation generally resulted in lower yields and quality. Cauliflower accumulated up to 250 kg N ha−1 in the aboveground biomass and N‐uptake fluxes were as high as 5 kg N ha−1 d−1 at the 12‐leaf to folding growth stage.