Nitrogen Management in Drip Irrigated Leaf Lettuce, Spinach and Green Crops

Preliminary nit s: (N) management experiments with spinach, leaf lemece,romaine collard and mustard were conducted on a Casa Grande el. soil at the Maricopa Agricultural Center in the winter and spring of 1990 -91. The purpose of this N rate experiment was to develop initial Best Management strategies for N fertilizer use for emerging high vahte crops grown in Arizona using subsurface drip irrigation. Three rates of urea,ammonium nitrate were applied to each cultivar to provide deficient (N1), adequate (N2) and supraopti real (N3) levels of N. All cultivars responded dramatically to the application of N. Fresh weight yields in the NI and N2 treatments averaged 45 and 53% of the N3 treatment The average N3 yields recorded in these trials were 23.1, 128 and 21.8 tons of marketable produce per acre for greens, spinach and leaf lettuce /romaine crops, respectively. Preliminary plant tissue test results indicated that for all five crops, whole plant total N (TN) levels and midrib + petiole NOrN and leaf blade TN concentrations in the youngest mature leaf were responsive to differences in soil N supply and show promise as diagnostic N tissue test procedures. The midrib + petiole NOrN test appeared to be the best indicator of plant N status throughout the growing season for all five crops studied Introduction The research base needed to formulate nitrogen (N) fertilizer BMP's for most of the major acreage crops grown in Arizona is adequate. Tissue testing procedures for monitoring the in season nitrogen needs of cotton, small grains, melons, head lettuce and a number of other major vegetables are currently available. However, nitrogen management for virtually all emerging "new crops' is not well documented and needs further study. These are primarily high -value vegetable and specialty crops such as bok choy, greens, leaf lettuce, parsley, rapini, romaine, spinach and squash. The objective of this research was to develop initial Best Management strategies for nitrogen fertilizer usage in emerging high value crops grown in Arizona, specifically leaf lettuce, romaine, spinach, collard and mustard. Materials and Methods Field trials were initiated in the fall of 1990 at the Maricopa Agricultural Center (MAC) to develop nitrogen Best Management Practices (BMP's) for three high value vegetable crops. Leading commercial varieties of leaf lettuce (Waldmann's Green), romaine (Parris Island Cos), spinach (Crystal Savoy and Indian Summer), collard (Vates) and mustard (Southern Giant) were planted on 25 October. The experimental design for each of the five crops was a randomized complete block with four replications. Three rates of N were applied to provide deficient (N1), adequate (N2) and supraoptimum (N3) N as shown in Table 1. The soil type in the experimental area was a Casa Grande sandy loam with a preplant soil test NO3 -N level of 1.2 ppm. This is considered an extremely low value.