The effect of nitrogen sources and storage on nitrate and thiocyanate conttent of Kale (Brassica oleracea var ocephala d.c) leaves
Two experiments were conducted between August 1986 and March 1987 at the Faculty of Agriculture I Field Station, Kabete Campus, University of Nairobi to study the effects of nitrogen sources and leaf storage on the accumulation of nitrate-nitrogen (N03 -N) and thiocyanate ion (SCN ) content in leaves of "Thousand-headed" kale (Brassica oleracea var. acephala D.C.). Two nitrogen sources (Calcium ammonium nitrate CAN and sulphate of ammonia-SA) at the rate of 20 g N/plant and three storage conditions (shelf storage, storage with petioles immersed in water and refrigeration) were used. Leaves were analysed for N03~N and SCN- before storing and after two, four and six days of storage. Leaves from plants top-dressed with CAN accumulated significantly more NO^-N than those top- dressed with SA in the second experiment. The effect of storage conditions on N03~N concentration was not significant. However, the leaves stored with petioles immersed in water had the lowest NO^-N concentration. Nitrate nitrogen concentration in leaves decreased significantly with increasing storage. Interaction between nitrogen sources and storage (xiii) durations for NOg-N concentration was significant. There was a general decrease in NO^-N concentration with storage time but the decrease was more in leaves from plants top-dressed with CAN than those from plants top-dressed with SA. The petioles had significantly higher NO^-N concentration than the laminae . Leaves from plants top-dressed with SA yielded significantly higher SCN than those from plants top-dressed with CAN. Leaves stored on the shelf yielded the lowest SCN while those stored in the refrigerator yielded the highest. Thiocyanate ions in stored leaves decreased with increasing storage time with highest decrease being in leaves stored on the shelf and lowest in those stored in the refrigerator. Unstored leaves yielded significantly hig- r\ ~ her SCN than stored leaves. There was a significant interaction between storage conditions and durations for SCN- content in leaves. Interaction between nitrogen sources, storage conditions and durations for SCN- yield from leaves was significant. Topdressing with CAN and storing the leaves on shelf for six days tremendously decreased SCN content.