Water and Nitrogen Interactions in Subsurface Drip Irrigated Broccoli and Cauliflower Production

Abstract

Field experiments were conducted during the 1995-96 winter growing season at The University of Arizona's Maricopa Agricultural Center to determine the response of broccoli and cauliflower to a factorial arrangement of water rates and nitrogen (N) fertilizer rates. Both the broccoli and cauliflower experiments were randomized complete block factorial designs with three water levels (deficient, optimum, and excessive), four N fertilizer levels (deficient, suboptimal, supra optimal, excessive), and four replications. Drip tubing was buried at a depth of eight inches along the midline of each planting bed. Irrigation was applied daily as needed to maintain the predetermined target soil water tension levels and N fertilizer (urea ammonium nitrate solution) was applied in 4 or 5 split applications. Broccoli spears and cauliflower curds were harvested weighed and graded according to prevailing commercial practices. The optimum marketable yield of broccoli of 4.6 tons/acre was achieved with a total application of 18.9 inches of water and 267 lbs. N/acre. The optimum marketable yield of cauliflower of 9.5 tons /acre was achieved with a total application of 18.5 inches of water and 178 lbs. N/acre. For both crops a nitrogen deficiency had a greater negative impact on marketable yield than either deficient or excessive water application. Optimum marketable yields, earliness and head quality for both crops were achieved when the average soil water tension level for the entire season was maintained at about 10 cbars (or 13 cbars uncorrected gauge reading).