The influence of nitrogen application on yield and quality of freshly harvested and stored carrot (daucus carota l. Var. 'nantes') roots.
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Experiments were carried out in two seasons at the Field Station, Kabete Campus, between November, 1988 and May, 1989 to study the effect of nitrogen application rates (0,26,52 and 78kg N/ha) on the yield and quality of fresh and stored carrot roots. Freshly harvested roots were stored at room temperature in perforated and non-perforated polythene bags for six days. Carrot roots were analyzed for splitting, beta and total carotenes, ascorbic acid, dry matter, proximate chemical composition, nitrate accumulation and weight loss. The experimental design used for the field experiment was the randomized complete block design with three replicates while storage experiment was a 4 x 2 factorial experiment (four nitrogen and two storage levels) set out in a randomized complete block design with three replicates. The effect of nitrogen application on root yield and splitting was not significant in both seasons. There were, however, significant differences between seasons in yield. Root yields and splitting were lower in the first season than in the second season. During the first season, nitrogen application significantly (P~ 0.05) increased the contents of beta carotenes in the carrot roots. Total carotene contents were not significantly affected. During the second season, nitrogen application did not affect beta carotene contents in the roots but significantly affected total carotene contents During both seasons, crude protein was not affected by nitrogen top-dressing but crude fat, total ash and fibre contents were. These increased significantly with increasing rates of nitrogen application. Vitamin content, of roots was not affected by nitrogen application in both seasons. During the first season, dry matter contents of roots were not affected by nitrogen application. However, during the second season, the dry matter of roots increased significantly with increasing nitrogen rates. In both seasons, nitrogen application significantly increased nitrate accumulation in the roots. Roots from the second season had accumulated significantly more nitrates than those from the first season. In the first season, there was a net significant increase in weight loss during storage. Roots that had been top dressed with nitrogen had significantly lost more weight than those that had not been top dressed at the end of the storage period. As expected the weight loss was higher in roots stored in perforated polythene bags than in those stored in non-perforated bags for all nitrogen rates in both seasons. The dry matter contents of stored roots was not significantly affected during storage in both seasons. In the first season, roots stored in perforated bags retained more total carotenes than those stored in non-perforated bags. In both storage methods, roots top dressed with nitrogen retained more beta and total carotenes than those that were not top dressed. Vitamin C contents were not affected during storage. Storage significantly decreased contents of nitrates in the roots. Roots in the perforated bags had more nitrates than those stored in non-perforated bags.