Yosef and Sagiv, 1982; Stark et al., 1983; Burt et al., 1995). However, very few studies have shown a benefit Subsurface-drip irrigation and fertigation with fluid N fertilizer of frequent or continuous fertigation compared with sources offers substantial flexibility for N fertilizer management. Fertiless frequent fertigation. Bar-Yosef and Sagiv (1982) gation events can be scheduled as often as irrigation, up to several times per day. However, because of system or management constraints practiced continuous fertigation of surface drip-irrivery frequent fertigation may not be possible or desirable for some gated tomato (Lycopersicum esculentum L.) with congrowers. Optimum fertigation interval for subsurface drip-irrigated centrations of 100 to 200 mg N L Ϫ1 in the irrigation crops has not been well researched. A 3-yr field experiment was water. However, this resulted in N applications Ͼ1000 conducted on a sandy loam soil in southern Arizona with subsurface kg N ha Ϫ1 , far greater than N uptake by the plants; drip-irrigated broccoli (Brassica olearacea L. Italica) to i) determine consequently N use efficiency (NUE) was as low as the effects of N rate and fertigation frequency on crop yield, quality, 30%. Stark et al. (1983) determined that 75 mg N L Ϫ1 and crop N status, and ii) estimate a N balance. Broccoli was planted was the optimum concentration for continuous fertigain two rows per raised bed 1.02 m apart, with one drip line buried tion of tomato with surface-drip irrigation. Bhella and 0.15 to 0.20 m deep within each bed. The experiment included factorial Wilcox (1985) advocated continuous fertigation of surcombinations of two N rates and four fertigation frequencies (intervals of 1, 7, 14, and 28 d). Broccoli marketable yield and quality were face drip-irrigated cantaloupe (Cucumis melo L.) with responsive to N rate, but not to increased fertigation frequency. Dur-150 and 50 mg N L Ϫ1 during vegetative and reproductive ing one of three seasons, fertigation frequency significantly (P Յ 0.05) stages, respectively. affected crop N uptake, but there was no trend of increasing N uptake Few studies are reported in which the effects of differwith increasing fertigation frequency. Unaccounted fertilizer N and ent drip-fertigation frequencies on yield and quality of apparent N use efficiency (ANUE) were calculated for two seasons. annual crops are compared. Several researchers have Unaccounted fertilizer N averaged 20 and 75 kg ha Ϫ1 and ANUE 90 compared applications of all N soil-applied preplant and 81% with 250 and 350 kg N ha Ϫ1 applied, respectively. Neither with a combination of preplant soil-applied and in-seawas significantly affected by fertigation frequency. We conclude, son fertigated N on tomato. Locascio et al. (1985, 1989) therefore, that for broccoli production with subsurface-drip irrigation found that surface drip-irrigated tomato yields were on sandy loam or finer soils, fertigation can be applied as infrequently as monthly, without compromising crop yield or quality, or causing higher with 40% o...

Adequate Zn nutrition is critical for commercial pecan production. Providing suffi cient Zn through soil application is particularly problematic in high pH desert soils, due to the low solubility of Zn in alkaline conditions, and also the complexation of soil Zn by carbonate minerals (Lindsay, 1979). Foliar Zn applications are more effective than soil applications and can provide adequate Zn for maximum growth and production (Malstrom et al., 1984).

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