Influence of nitrogen fertilization on yield, hollow stem incidence and sap nitrate concentration in broccoli

This study, spanning 2 yr at two different sites, compared the effects of n itrogen fertilization on broccoli yield and quality in relation to the infl uence of site and production season. This research also evaluated the poten tial use of measuring nitrate in petiole extracts to determine broccoli nit rogen requirements when making a second fertilizer application 5 wk after t ransplant. Treatments consisted of factorial combinations of three nitrogen fertilization rates at transplant (N-min, 50-N-min and 100-N-min kg N ha(- 1), where N-min was the soil nitrate concentration) and four nitrogen ferti lization rates 5 wk after transplant (0, 50, 100 and 150 kg N ha(-1)). The marketable yield of broccoli increased with the rate of nitrogen applicatio n. Hollow stem incidence showed the same trend as yield, and was greatest w hen high levels of nitrogen were applied 5 wk after transplant. Interaction s between the 5-wk nitrogen application and production year, as wen as grow ing site were significant. The nitrate content of the sap was measured imme diately before the 5-wk nitrogen application and 2 wk later. The nitrate co ncentration measured at 5 wk increased with transplant nitrogen, as did the concentration measured at 7 wk. Nitrate concentration at 7 wk increased cu rvilinearly with the 5-wk fertilizer application rates. Sap analysis provid ed clear evidence of the effect of nitrogen application rates, but Environm ent precluded determination of an absolute threshold of nitrate sufficiency in the sap.