Nitrogen and Water Interactions in Subsurface Drip‐Irrigated Cauliflower II. Agronomic, Economic, and Environmental Outcomes

Abstract

Water × N rate experiments were conducted on subsurface drip‐irrigated cauliflower ( Brassica olearacea L. var. botrytis L.) during three winter growing seasons in southern Arizona. A range of water and N rates were selected to permit the calculation of appropriate water × N production functions. The objectives were to (i) determine the effects and interactions of irrigation water and N inputs on crop N uptake, residual soil NO 3 –N, N‐use efficiency, and unaccounted fertilizer N, and (ii) evaluate agronomic, economic, and environmental production criteria during three growing seasons. Spatial analysis was used to identify overlap of acceptable zones of marketable yield, net return, and unaccounted fertilizer N within each growing season. Acceptable yields and net return were defined as ≥95% of the maximum predicted response within the range of the treatments; acceptable unaccounted fertilizer N was defined as ≤40 kg ha −1 Net returns and aboveground plant biomass N were significantly affected ( P < 0.01) by N rate and in 2 yr by irrigation. There were also significant irrigation treatment × N rate interactions for net returns and biomass N. Residual soil NO 3 –N concentrations increased with N rate and decreased with soil water tension (SWT). Average amounts of residual soil NO 3 –N (0–0.9 m) for the highest N rate during the three seasons were 317, 296, and 180 kg ha −1 for the low, medium, and high irrigation treatments, respectively. Unaccounted fertilizer N was significantly affected ( P < 0.05) by irrigation treatment, N rate, and irrigation treatment × N rate interactions each year. Overlap of acceptable zones of marketable yields, net returns, and unaccounted N was achieved in one of the three years. The single combination of SWT and N rate that came closest to producing optimal or near‐optimal agronomic, economic, and environmental outcomes in all three years was 10 to 12 kPa and 350 to 400 kg N ha −1