Effect of Nitrogen Sources and Rates on Yield and Hollow Stem Development in Broccoli

The objective of this study was to determine the effects of N sources and rates on growth, yield and hollow stem development of broccoli (Brassica oleracea L. spp. Italica Plenck ’Green Valiant’). Four N fertilizers [NH4NO3, Ca(NO3)2, (NH4)2SO4 or CO(NH2)2] were side-dressed in a factorial arrangement with rates of 75, 150 or 225 kg N ha−1. Increasing N rate resulted in greater vegetative growth but also in more hollow stem development, as estimated for the first time by a measure of hole volume. In a dry and warm year, however, with a near optimal soil pH, hollow stem development increased more with N rate than did marketable yield. In these conditions, it may therefore be advisable to reduce N applications. Nitrate-containing sources increased yield by 4% but induced 13% more hollow stem so that no N source could be identified that would produce high broccoli yield with minimum hollow stem. The effect of N source was neither function of year nor of N rate; it would therefore be irrelevant to modify N rate according to the source used.Key words: Brassica oleracea L. spp. Italica Plenck, broccoli, calcium nitrate, ammonium nitrate, urea, ammonium sulphate