In arid regions of the U.S., high rates of water and N input are commonly used for cauliflower production. Production of cauliflower (Brassica olearacea L. var. botrytis L.) High rates of water and N input, and rapid rates of in the southwestern U.S. is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. Subsurface drip nitrification typical of thermic and hyperthermic soils, irrigation offers what is likely the ultimate in control of the plant can contribute to increased production costs and losses root zone for crop production. However, the water and N-response of water and N. Therefore, accurate guidelines for water characteristics of subsurface drip-irrigated cauliflower have not preand N management for drip-irrigated cauliflower are viously been reported. Three field experiments were conducted in needed. However, management practices that increase southern Arizona in 1993-1996. The objectives were to determine: water and N-use efficiency must also be economically (i) an optimum range of soil water tension for subsurface drip-irrigated feasible. cauliflower, (ii) the effects and interactions of water and N fertilizer Total N uptake by cauliflower ranges from 70 to 260 on crop yield and quality, and (iii) seasonal and daily N uptake for kg ha Ϫ1 in whole plants and 40 to 125 kg ha Ϫ1 in the high-yielding cauliflower. The experiments were randomized comharvested portion of plants (Stivers et al., 1993). In Ariplete block factorial with three irrigation regimes (low, medium, high), four N rates (60-600 kg N ha Ϫ1), and four replications. Irrigation was zona, growers generally apply 224 to 370 kg N ha Ϫ1 (U.S. applied daily to maintain target soil water tensions and all N was Department of Agriculture, 1991), although recomapplied by fertigation. With respect to marketable yield, curd weight, mended amounts are somewhat lower (Doerge et al., and curd diameter, the optimum soil water tension was approximately 1991). Cauliflower is an initially slow-growing crop that 10 to 12 kPa in this sandy loam soil during the 3 years. Marketable takes up little N in its first 60 d of growth; 90% or more yields across all treatments ranged from Ͻ5 to Ͼ30 Mg ha Ϫ1. Yields of its total N accumulation may occur during the final and quality were generally more responsive to N rate than to irrigation 50 to 60 d preceding harvest (Welch et al., 1987). Cauliand showed significant irrigation by N rate interactions during 2 of the flower is highly responsive to N fertilizer inputs and is 3 years. At equivalent N rates, excessive irrigation generally resulted in rarely negatively affected by excessive N applications lower yields and quality. Cauliflower accumulated up to 250 kg N (Stivers et al., 1993). ha Ϫ1 in the aboveground biomass and N-uptake fluxes were as high as 5 kg N ha Ϫ1 d Ϫ1 at the 12-leaf to folding growth stage.
BMPs (Arizona Legislature, 1987). Best management practices are designed to maintain or enhance yields Water ϫ N rate experiments were conducted on subsurface dripand profitability, and to minimize future additions of N irrigated cauliflower (Brassica olearacea L. var. botrytis L.) during three winter growing seasons in southern Arizona. A range of water to groundwater. The use of subsurface drip irrigation and N rates were selected to permit the calculation of appropriate offers the potential for increased water-and N fertilizerwater ϫ N production functions. The objectives were to (i) determine use efficiency and is increasing in the desert Southwest the effects and interactions of irrigation water and N inputs on crop and California. Currently 3600 ha in Arizona and N uptake, residual soil NO 3-N, N-use efficiency, and unaccounted 22 300 ha in California are irrigated with subsurface drip fertilizer N, and (ii) evaluate agronomic, economic, and environmental systems (Anonymous, 1994; Anonymous, 1998). Several production criteria during three growing seasons. Spatial analysis was recent studies have illustrated the efficient nature of used to identify overlap of acceptable zones of marketable yield, net subsurface drip irrigation for delivery of water and nutrireturn, and unaccounted fertilizer N within each growing season. ents (Pier and Doerge, 1995b; Thompson and Doerge, Acceptable yields and net return were defined as Ն95% of the maximum predicted response within the range of the treatments; acceptable 1996b). unaccounted fertilizer N was defined as Յ40 kg ha Ϫ1. Net returns and Evaluation of any crop production system should adaboveground plant biomass N were significantly affected (P Ͻ 0.01) dress agronomic, economic, and environmental outby N rate and in 2 yr by irrigation. There were also significant irrigation comes. Drip irrigation allows great flexibility in both treatment ϫ N rate interactions for net returns and biomass N. Residwater and N management. Water and N are the two ual soil NO 3-N concentrations increased with N rate and decreased inputs to irrigated cropping systems that have the most with soil water tension (SWT). Average amounts of residual soil impact on agronomic, economic, and environmental NO 3-N (0-0.9 m) for the highest N rate during the three seasons were outcomes (Letey et al., 1977). These three criteria have 317, 296, and 180 kg ha Ϫ1 for the low, medium, and high irrigation only recently been evaluated simultaneously for driptreatments, respectively. Unaccounted fertilizer N was significantly affected (P Ͻ 0.05) by irrigation treatment, N rate, and irrigation irrigated crops. The interactive effects of water and N treatment ϫ N rate interactions each year. Overlap of acceptable zones management on yields are reported for drip-irrigated of marketable yields, net returns, and unaccounted N was achieved in corn (Zea mays L.) (Phene and Beale, 1976; Yanuka et one of the three years. The single combination of SWT and N rate al., 1982), tomato (Lycopersicum esculentum L.) (Barthat...
Subsurface drip irrigation offers potential for increased water and N fertilizer use efficiency, and decreased groundwater NO3 pollution. Replicated factorial experiments consisting of four rates of N fertilizer application (60–500 kg ha−1) and three target soil water tensions (SWT) (low, medium, and high) were conducted on subsurface drip‐irrigated broccoli (Brassica olearacea L. Italica) during three winter growing seasons in southern Arizona. Objectives were to (i) determine effects and interactions of irrigation water and N inputs on net economic return, residual soil NO3‐N, and unaccounted fertilizer N, and (ii) use abstract spatial analysis techniques to simultaneously evaluate agronomic, economic, and environmental production functions during three growing seasons. Spatial analysis was used to identify overlap of acceptable zones of marketable yield, net return, and unaccounted fertilizer N. Acceptable yields and net return were defined as ≥95% of maximum predicted response within the range of the treatments, and acceptable unaccounted fertilizer N was defined as ≤40 kg ha−1 During this study, >95% of maximum net return encompassed N rates of 300 to 500 kg ha−1, and SWTs of 7 to 25 kPa. There was little accumulation of NO3 in the top 0.9 m of soil when ≤350 kg N ha−1 were applied. Unaccounted N increased with excessive N and water inputs, and accounted for as much as 46% of N applied. Overlap of acceptable zones of agronomic, economic, and environmental production criteria was achieved in each year. Areas of overlap were bounded by 300 to 325 kg N ha−1 and 8.5 to 12 kPa in 1993–1994, 350 to 500 kg N ha−1 and 11 to 14 kPa in 1994–1995, and 340 to 410 kg N ha−1 and 11 to 24 kPa in 1995–1996.
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