| Two experiments were conducted to investigate the effects of several soluble silicates and supplemental UV-B irradiance on the growth and yield of sugarcane (a complex trispecies hybrid of Saccharum), variety C.P. 63-588, grown in an organic soil.; In the first experiment sugarcane seedlings were allowed to grow inside the greenhouse under enhanced UV-B irradiance provided by fluorescent sun lamps. The UV-B treatments consisted of 2, 3, and 4 sunburn units per hour (S.U./hr) and Mylar S control. Three Si treatments (0, 68, and 136 g Na silicate per 40-liter pot), each replicated 5 times, were imposed within each UV-B treatment in a nested design. Sugarcane seedlings also were allowed to grow inside and outside the greenhouse without exposure to supplemental UV-B irradiance for comparative evaluation. Completely randomized designs were used with 3 Si treatments and 5 replications. Plant and first ratoon crops were studied to investigate effect of treatments on growth and yield of the crop.; Plant height, stem diameter, leaf area, and dry-matter yields of both plant and ratoon crops were significantly increased by Si. Addition of Si also protected plants against stem borer (Diatraea saccharalis (F)). Significant reduction in growth and yield was observed when plants were exposed to UV-B radiation. The 4 S.U./hr UV-B dose reduced dry-matter yield of plant and ratoon crops to 85 and 42% of the control, respectively. However, the plants showed no symptoms of leaf freckling. Plants grown outside the greenhouse without Si experienced severe leaf freckling although they were not exposed to supplemental UV-B irradiance. They also produced more tillers, especially when Si was added. Plants grown inside the greenhouse did not tiller even with the top rate of Si.; The second experiment was conducted in the field to study the response of sugarcane to four rates (5, 10, 15, 20 metric tons per hectare, MT/ha) of three different silicate materials (Fla slag, TVA slag, cement). A factorial experiment was installed in a randomized complete block design within a commercial field using 79.2 m('2) plots. Growth, nutrient concentration in the leaf, cane and sugar yields, and soil composition were studied in both plant and ratoon crops. Growth parameters and soil parameters were measured one time each year while nutrient concentration was studied three times a year.; Application of soluble silicates increased millable stalks, plant height, stalk diameter, chlorophyll content of the leaf, and cane and sugar yields in both plant and ratoon crops. Leaf freckling was greatly reduced in treated plots. Addition of 15 MT material/ha increased sugar yields by 12.6 MT/ha for the two crops. The yield data tend to support the idea of the essentiality of Si, and point to its role in the production of more tillers, more efficient photosynthesis, and correction of leaf freckling. There were no differences in cane and sugar yields among the three materials in spite of their different Si contents. Plant and soil P were enhanced by Fla and TVA slags but were slightly reduced by cement. |
