Influence of nitrogen fertilization and plant age on yield, quality and storability of kale and collard (brassica oleracea var-acephala D.C) leaves

Abstract

Two experiments were conducted between June 1988 and July 1989 at the Faculty of Agriculture Field Station, Kabete Campus, University of Nairobi, to study the influence. of nitrogen (N) application rates (0, 5, 10 and 15 gN per plant) on yield quality and storage olpracea ability of kale and collard (Brassica var. aceDhala D.C.) leaves. Calcium ammonium nitrate (CAN) was used as the N source. Leaves were harvested at intervals of 10 days for a period of upto 140 days after transplanting. Leaf yield at each harvest was determined and leaf samples stored on the shelf for 3 days and in a refrigetor for 21 days. Leaves were analysed for crude p,"otein, crude fibre, crude lipid, total ash, calcium, ascorbic acid and beta-carotene, after every other harvest. During storage, ascorbic acid retention was determined initially and at intervals of 2 days of storage for shelf and 7, 14, 21 days of storage for refrigeration_ Increasing N application significantly increased leaf yield. Applying more than 109 of N per plant, however, did not significantly increase yields. yield actually decreased. The results showed Leaf that leaf yield increased with plant age upto 60 days after transplanting, then remained almost constant upto 120 days after transplanting beyond which there was a drop of about 65%. per consecutive harvest. Application of N significantly increased crude protein, crude lipid, total ash and Beta-carotene but decreased ascorbic acid and crude fibre. Calcium remained constant. Crude protein, ascorbic acid and Beta-carotene significantly decreased whereas crude fibre tended to increase with plant age. Crude lipid tended to increase with plant age upto 60 days after transplanting then significantly decreased for the rest of the harvest period. Total ash and calcium did not change significantly with plant age. Ascorbic acid in stored leaves significantly decreased with increasing storage time. Highest decrease of about 72% being in leaves stored on the shelf and lowest of about 25% in the under refrigeration were observed. leaves stored