Fertigation Frequency for Subsurface Drip-Irrigated Broccoli

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 1 in the irrigation crops has not been well researched. A 3-yr field experiment was water. However, this resulted in N applications 1000 conducted on a sandy loam soil in southern Arizona with subsurface kg N ha 1, 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 1 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. Dur150 and 50 mg N L 1 during vegetative and reproductive ing one of three seasons, fertigation frequency significantly (P 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 1 and ANUE 90 compared applications of all N soil-applied preplant and 81% with 250 and 350 kg N ha 1 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% of the N applied preplant and 60% excessive N losses. applied by fertigation, compared with all N applied preplant on sandy soils in Florida. Dangler and Locascio (1990) found that yield of surface drip-irrigated tomato was higher on a fine sand when 50% of fertilizer N M studies have demonstrated drip-irrigated crop response to N (e.g., Bar-Yosef and Sagiv, was soil-applied before planting, than when all N was applied via fertigation. Cook and Sanders (1991) ex1982; Thompson et al., 2002a). Optimum N rates for many drip-irrigated crops have been published (Hochamined the effect of fertigation frequency (daily to monthly) on subsurface drip-irrigated tomato yields in muth, 1992; Hartz, 1994). Drip irrigation and fertigation with fluid N fertilizer sources offer what is probably two South Carolina soils. Daily or weekly fertigation significantly increased yield compared with monthly ferthe ultimate in flexibility for N fertilizer management. Fertigation events can be scheduled as often as irritigation, but there was no advantage of daily over weekly fertigation on a loamy sand. The same fertigagation, up to several times per day. However, because of system or management constraints very frequent tion frequencies resulted in no differences in yield and quality on a loamy fine sand soil. Locascio and Smajstrla fertigation may not be possible or desirable for some growers. Optimum fertigation interval for drip-irrigated (1995) found that surface drip-irrigated tomato yields with daily fertigation were not increased compared with crops, although important, has not been thoroughly researched (Hartz, 1994). yields with weekly fertigation on a fine sand. Locascio et al. (1997) found that there were no differences in Various authors have recommended very frequent or continuous fertigation for drip-irrigated crops (i.e., Baryield or quality of surface drip-irrigated tomato fertigated either six or 12 times per season. Similarly, yields of surface drip-irrigated pepper (Capsicum annum L.) T.L. Thompson, S.A. White, J. Walworth, and G.S. Sower, 429 Shantz, were not affected by fertigation interval (11 or 22 d) on Dep. of Soil, Water and Environmental Science, University of Aria loamy sand soil (Neary et al., 1995). zona, Tucson, AZ 85721. Received 27 June 2002. *Corresponding author ([email protected]). Abbreviations: ANUE, apparent N use efficiency; NUE, N use efficiency. Published in Soil Sci. Soc. Am. J. 67:910–918 (2003).