Subsurface drip irrigation and fertigation of broccoli: I. Yield, quality, and nitrogen uptake

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 similar to10 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 X 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 X 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]).