Rhoden, E.G., P. David, and T. Small. 1993. Effect of nitrogen nutrition on roselle. p. 583-584. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.
In many parts of the world, the leaves are consumed as a green vegetable and the stem is a possible source of pulp for the paper industry. According to Adamson et al. (1975), roselle is the only new crop introduced in the southern United States as a pulp source that shows a high level of resistance to nematodes. Roselle is propagated from seeds and cuttings. Seeds planted for the production of fleshy calyxes are drilled in 1 m ' 1 m rows. However, if grown for fiber and pulp, a spacing of 30 to 46 cm ' 30 to 46 cm is used to reduce branching. Harvesting fruits may cause latent buds to develop thereby extending the growth period of the plant. This enhanced growth period coupled with higher applications of nitrogen could further increase the dry matter production of the plant, a desirable improvement. However, little information is available on the commercial production of roselle as a pulp crop.
Most crops grown in the southern United States require high rates of nitrogenous fertilizer for optimum yields, but the nutritional requirements of roselle are unknown (Adamson et al. 1979; Panchoo and Rhoden 1990). When roselle is grown for its calyxes, only half the recommended amounts of fertilizer for vegetables is applied. Excessive ammonia encourages vegetative growth and reduces fruit production. Therefore, increasing the rate of nitrogen application coupled with higher planting densities could be a method of utilizing the roselle plant as a pulp and fiber crop. Small and Rhoden (1991) obtained increased dry matter production with increased applications of ammonium nitrate. The objective of this study was to determine the response of roselle to early applications of nitrogenous fertilizer.
Starting at emergence, each pot was supplied with a base solution of 750 ml containing 3.4 g of 20N-8.6P-16.6K fertilizer/liter each week. At six weeks after emergence, all plants continued receiving the base amount of N-P-K fertilizer, while one-third received 250 ml of 20 g ammonium nitrate and another one-third received 250 ml of 40 g/liter solution. Plants showing any visible signs of water stress were supplied with added amounts of deionized distilled water.
Plant height and stem diameter were determined weekly. Each week, plants were harvested and then separated into roots and stems. Plants were oven-dried at 70°C for 72 h to determine dry matter production. The regular macro-Kjeldahl method was used form determining organic nitrogen (AOAC 1984).
Nitrogen application affected root to shoot ratio. Initially, plants receiving only the base amount of nitrogen had root to shoot ratio of 6:1. However, as plants receiving the base amount of nutrients matured, there was a decrease in the ratio to 2.5:1. The shoot to root ratio for plants receiving added levels of ammonium nitrate increased from a low of 4:1, one week after initial application, to a high of 6:1 four weeks after additional ammonium nitrate. Nitrogen accumulation increased with increasing amounts of applied nitrogen (Fig 2). Percent nitrogen accumulation decreased with maturity probably due to the dilution effects of increasing dry matter content. This study indicates that roselle responds to nitrogen at the early stages of development. Further studies are needed to quantify nutrient interactions.