Influence of nitrogen rates and storage conditions on quality and shelf-life of French beans (Phaseolus vulgaris L.)
Two experiments were conducted at the field station of. the Faculty of Agriculture, University of Nairobi, between July 1988 and April 1989 to show the effects of N application on plant growth, yields, quality and shelf-life of pods of French beans (Phaseolus vulgaris L.). The bean plants of Monel variety were topdressed with N at 0, 26, 52 and 78kg/ha and data on dry matter accumulation in leaves, stems and nodules, days to 50% flowering, total and marketable yield, quality and shelf-life of the pods were collected. Freshly harvested pods were analysed for crude protein, total ash, crude fibre, nitrates, ascorbic acid and chlorophyll. For storage study, freshly harvested pods were separated into fine and extra fine grades and stored in 1kg lots in fibre board. cartons at 40C and at room temperatures (23 ± 10C and 25 ± 10C in the first and second experiments respectively). During storage the pods were analysed for weight loss, withering, percent retention of ascorbic acid, and chlorophyll contents and chilling injury for those stored at 40C. Nitrogen application significantly increased the dry matter of the leaves sampled at the bloom and pod stages in the first experiment (first season). Application of 26kgN/ha effected the greatest increase on the dry matter content of the leaves sampled at bloom stage while at pod stage, 52kg/ha effected the greatest increase. The latter rate also had the greatest increase on the accumulation of dry matter - xiii - in the stems. The dry matter yield in the nodules was significantly lowered by N top-dressing. Days to 50% flowering were not significantly affected by N application. Nitrogen application had no significant effect on the total and marketable pod yields but, in the second season, the topdressed plants yielded significantly more reject grade pods than those that were not. The effects of N on crude protein, total ash, crude fibre and nitrate contents were not significant although N tended to increase the crude protein and nitrates and to decrease the total ash and fibre contents. Weight loss, withering and retentions of ascorbic acid and chlorophyll during storage were not significantly affected by nitrogen application. Judged from the extent of withering the extrafine and fine grade pods had a shelf life of two and three days respectively at room temperatures, while judged by the extent of chilling injury the shelf-life of the two grades was also limited to two and three days respectively at 40C. Storage conditions had a significant effect on losses of ascorbic acid and chlorophyll. The losses were generally higher from pods stored at room temperatures than from pods stored at 40C.