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

Abstract

This study, spanning 2 yr at two different sites, compared the effects of nitrogen fertilization on broccoli yield and quality in relation to the influence of site and production season. This research also evaluated the potential use of measuring nitrate in petiole extracts to determine broccoli nitrogen requirements when making a second fertilizer application 5 wk after transplant. 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 fertilization 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 application. Hollow stem incidence showed the same trend as yield, and was greatest when high levels of nitrogen were applied 5 wk after transplant. Interactions between the 5-wk nitrogen application and production year, as well as growing site were significant. The nitrate content of the sap was measured immediately before the 5-wk nitrogen application and 2 wk later. The nitrate concentration measured at 5 wk increased with transplant nitrogen, as did the concentration measured at 7 wk. Nitrate concentration at 7 wk increased curvilinearly with the 5-wk fertilizer application rates. Sap analysis provided clear evidence of the effect of nitrogen application rates, but Environment precluded determination of an absolute threshold of nitrate sufficiency in the sap. Key words: Brassica oleracea L. var. Italica, split application, quality, environment