EFFECTS OF NITROGEN-FERTILIZATION ON GROWTH AND SOIL-NITROGEN DEPLETION IN CAULIFLOWER

To examine the possibilities of reducing fertilizer levels and losses of nitrogen, we studied the effects of amount and timing of nitrogen f ertilization on growth parameters and on soil nitrogen depletion in ca uliflower. A higher nitrogen supply, calculated as the sum of fertiliz er nitrogen and mineral nitrogen at transplanting, resulted in a clear increase in nitrogen uptake by the crop and in a higher crop fresh we ight. However, curd fresh or dry weight and looseness of the curd were not affected. Therefore we conclude that total nitrogen supply can be reduced to approximately 250 kg ha(-1) without negative effects on yi eld. An increase in nitrogen supply of 100 kg ha(-1) resulted in 17 kg ha(-1) more residual soil nitrogen, 52 kg ha(-1) more nitrogen in cro p residues, 37 kg ha(-1) more mineralizable N and 15 kg ha(-1) more ni trogen in harvested curds. Changing the timing of nitrogen application , by reducing the application at planting and increasing the second ap plication instead, resulted in a higher curd biomass, a larger amount of nitrogen in the curd and less residual soil nitrogen after harvest. Thus, the efficiency of nitrogen use was increased when more nitrogen was supplied at the time of a higher absolute growth and nitrogen dem and.