The effect of nitrogen rates and sources on leaf production, nitrate accumulation. and thiocyanate content in kale and collard (Brassica Oleracea var. Acephala, D.C.) leaves

Abstract

Two experiments were conducted between August 1986 and March 1987 at the Field Station of Faculty of Agriculture, Kabete Campus, University of Nairobi, to study the effect of rates and sources of nitrogen (N) on leaf production, thiocyanate content and nitrate accumulation in leaves of 'Thouand- headed ' kale and 'Georgia' colIards (both Brassica oleracea var. acephala D.C.). Four N rates (0, l0, 20 and 40 grams (g) per plant) and two sources (calcium ammonium nitrate-CAN and sulphate of ammonia- SA) were used. Leaf yield was assessed by both cumulative 2 leaf weight per 10 m and leaf number per plant. The leaf yield jncreased as rates of N increased. Plants top-dressed with higher rates of N than 10 g per plant did n~t show significant increase in leaf weight. Nitrogen sources had no significant effect on leaf yield. However, varietal effect on lear production was significant. 'Georgia' collards gave significantly higher leaf yield than 'Thousandheaded' kale did. Interactions between N rates and varieties on leaf weight and N sources and varieties on leaf number were significant during the second experiment. Interaction between N rates, sources during the second experiment. Nitrate-nitrogen (N03-N) in the leaves increased with increasing rates of N fertilizer application. Leaves from plants top-dressed with CAN accumulated more N0 -N than those top-dressed with SA. Leaves of 'Thousand-headed' kale accumulated significantly higher N03-N than those of 'Georgia' collards. Interaction between rates and sources of N on N03-N accumulation in leaves was significant during the first harvest of second experiment. The results also show that there was a positive correlation between N03-N in the soil and N03-N in leaves at harvest time and that petioles accumulated more.N~3-N than laminae. Nitrogen rates had no significant effect on thiocyanate ion (SCN-) content in leaves. However, the effect of N sources on SCN content was significant. Leaves from plants top-dressed with SA yielded significantly higher SCN than those top-dressed with CAN. Leaves of 'Thousand-headed' kale yielded significantly higher SCN than did those of 'Georgia' collards. Interaction between rates and sources of N on SCN content in leaves was significant. 1n t c raction between N sources and varieties 011 SCN con tent in leaves was significant during second harvest 011 both experiments.