EFFECT OF NITROGEN-SOURCES AND STORAGE ON THIOCYANATE CONTENT OF KALE(BRASSICA-OLERACEA VAR ACEPHALA) LEAVES

Thiocyanate content of kale leaves reduces its nutritional value and p oses a risk to human health. In order to study this phenomena two expe riments were conducted at Kabete field station, University of Nairobi. The experiments considered the effect of nitrogen sources and leaf st orage conditions on thiocyanate ion content in leaves of thousand-head ed kale (Brassica oleracea var. Acephala D.C.). Two nitrogen sources: calcium ammonium nitrate (CAN) and sulphate of ammonia (SA) at the rat e of 20g N per plant were used. Leaves were harvested and stored under three different conditions: shelf storage; storage with petioles imme rsed in water; and refrigeration at 6+/-2-degrees-C. Leaves were analy sed for thiocyanate at harvest and after storage of two, four and six days. Leaves from plants top-dressed with sulphate of ammonia had sign ificantly higher thiocyanate content than those from plants top-dresse d with calcium ammonium nitrate. Leaves stored on the shelf contained lower levels of thiocyanate than those stored in the refrigerator. Thi ocyanate content of leaves decreases with increasing storage time, the decrease being greatest in leaves stored on the shelf and smallest in those stored in the refrigerator. Top-dressing with calcium ammonium nitrate and storing leaves on the shelf for six days decreased thiocya nate content in the leaves.