The effect of nitrogen application and deflowering on vegetative growth, yield and quality; and postharvest storage stability

Abstract

Two experiments were cond~c~ed between August, 1990 and April, 1991, at the Faculty of Agriculture Field Station, Kabete Campus, Universi~y of Nairobi to study the effects of nitrogen rates (0, :"3, 26 and 52 kgN/ha) and deflowering on vegetative growth, leaf yield and quality of Gynandropsis gynandra L. The experiments were setup in a randomized complete block design with eight factorial treatments and three replications. Quality of the leaves was evaluated by analysing for ascorbic acid, ~-carotene and total phenolics contents. Storage stability of the leaves was evaluated under two storage conditions (shelf and refrigerated) and two packaging methods (perforated and non-perforated polythene bags) by analysing for losses in ascorbic acid and moisture and colour change over time of storage. .s Plants top-dressed with N and deflowered had increased vegetative growth and significantly higher mean weekly and cumulative leaf yields. Nitrogen application also tended to extend the harvest duration. Increasing N rate significantly decreased the content of ascorbic acid in leaves, although the leaves generally had high contents on dry matter basis. Deflowering, and the two-way interactions between N, deflowering and plant age had significant effects on ascorbic acid contents in the leaves during the second experiment. Nitrogen application .ocfo a~d deflowering had no significant effects on ~he contents of B-carotene and total phenolics in the leaves. The contents of ascrobic acid, B-carotene and total phenolics were significantly affected by plant age. The content of ascorbic acid increased with plant age whereas that of total phenolics decreased. The content of B-carotene was highest at the 7th week of growth after which it decreased. The non-perforated polythene bags showed effective control of moisture loss from leaves despite the storage condition, and made the leaves retain ascrobic acid better than the perforated ones. Temperature had a dominant effect on colour deterioration with refrigerator condition having very slow deterioration. Shelf storage could be effective for storage upto 2 days and refrigerator up to 12 days.