A Nitrogen and Water Response Surface for Sprinkler‐Irrigated Broccoli¹

Abstract

Abstract Farmers typically apply large amounts of both N and water in commercial vegetable production. As costs of both inputs increase, and with mounting concern over nitrate leaching and non‐point source water pollution, the need for information on optimal management of both resources grows. We investigated the combined effects of five N application rates (0, 87, 190, 255, and 331 kg ha −1 ) and a continuous irrigation variable (1.14 to 32.9 cm of water, or 0.05 to 1.52 times net pan evaporation) applied by a line‐source sprinkler system on broccoli ( Brassica oleracea L., Botrytis group) growth rates and yield. Growth rates generally increased with both water and N treatments, although some interactions emerged. Harvested fresh weights continued to increase throughout the range of treatments, applied, with maximum yields in excess of 20 Mg ha −1 . Yield (Mg ha −1 ) responded to N (kg ha −1 ) and water applied following seedling establishment (cm) according to the equation Y −1.03 + 0.0498 N − 8.73 × 10 −5 N 2 + 1.23 × l0 −3 NW + 0.272 W − 8.20 × 10 −3 W 2 , where Y is yield, N is nitrogen, and W is water applied after seedling establishment. Analysis of the resulting response surface indicated that under these conditions of frequent sprinkler irrigation (approximately twice weekly), relatively low N rates (140 kg ha −1 ) provided the lowest combined N and water cost for 10 Mg ha −1 ) yield. Further, yields increased with higher N and water rates, although quality must also be considered