This study was conducted at the Experimental Nursery of the Ornamental Horticulture Department, Faculty of Agriculture, Cairo University, during the two successive seasons of 2006 and 2007. The aim of this work was to investigate the response of Plumbago capensis plants, grown in sandy soil, to some soil amendments and chemical fertilization treatments. Clay, composted sewage sludge and taffla were incorporated into the sandy soil at a ratio of 4:1 (sand : soil amendment, v/v). After planting, the plants were fertilized with the commercial slow-release chemical fertilizer "Haiflow" (16 N - 8 P2O5 -16 K2O) at the rates of 21 or 45 g fertilizer/plant/3 months, or with a conventional chemical NPK fertilizer (8 N - 4 P2O5 - 8 K2O) at the rates of 14 or 30 g fertilizer/plant/month. In addition to the soil amendment and chemical fertilization treatments, plants receiving no soil amendment or chemical fertilization treatments were used as the control.
Results showed that clay and composted sewage sludge (as soil amendments) or chemical fertilization treatments increased the values recorded for the different vegetative and flowering parameters, as well as the contents of total chlorophylls, carotenoids, total carbohydrates, N, P and K, compared to the untreated plants. Clay was the most effective soil amendment in promoting vegetative and flowering characteristics (giving the highest mean values for plant height, stem diameter, number of branches/plant, leaf area, root length, fresh and dry weights of leaves, stems and roots/plant, number of inflorescence/plant, fresh and dry weights of inflorescences/plant and inflorescence diameter), as well as the contents of total chlorophylls and carotenoids, total carbohydrates, N, P and K. Raising the fertilization rate of each chemical fertilizer resulted in steady increases in values of all the studied parameters. The conventional NPK fertilizer gave generally higher values for most of the vegetative and flowering characteristics, as well as chemical components, compared to the slow-release fertilizer "Haiflow".
Combining clay with the highest rate of the conventional NPK fertilizer (30 g/plant/month) resulted in the highest values for vegetative and flowering parameters, as well as the contents of total chlorophylls, carotenoids, total carbohydrates, N, P and K.
From the obtained results, it can be recommended that, for the best vegetative and flowering characteristics of Plumbago capensis plants grown in sandy soil, the soil should be amended with clay and the plants should be supplied with 30 g/plant/month of the conventional chemical fertilizer (8% N - 4% P2O5 - 8% K2O).