Subsurface Drip Irrigation and Fertigation of Broccoli
2002
Thompson, Thomas L. | Doerge, Thomas A. | Godin, Ronald E.
Production of broccoli (Brassica olearacea L. Italica) in the southwestern USA is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. The water and N-response characteristics of subsurface drip-irrigated broccoli have not previously been reported. Field experiments were conducted in southern Arizona during 1993 through 1996. The objectives were to determine: (i) subsurface drip-irrigated broccoli response to a range of soil water tension (SWT), (ii) effects and interactions of water and N fertilizer inputs on crop yield and quality, and (iii) seasonal and daily N uptake. Experiments consisted of factorial combinations of three irrigation regimes (low, medium, and high) and four N rates (60–500 kg N ha⁻¹). Irrigation was applied daily to maintain target SWT, and all N was applied by fertigation. With respect to marketable yield, the optimum SWT was ∼10 kPa in this sandy loam soil, as indicated by response surface models. Marketable yields across all treatments ranged from <3 to >18 Mg ha⁻¹ Marketable yield was significantly affected by N rate during all three seasons, and by SWT during two of three seasons. There were no significant SWT × N interactions for marketable yield. Quality parameters (head weight and diameter) were much more responsive to N rate than to SWT, and there were few significant SWT × N interactions for broccoli quality. Broccoli accumulated up to 320 kg N ha⁻¹ in the aboveground biomass, and N uptake fluxes were as high as 5 kg N ha⁻¹ d⁻¹ at the first bud growth stage (825–1000 heat units after planting [HUAP]).
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