The Effects of Cobalt on Sugarcane Growth and Development in Plant Cane and Two Ratoon Crops

This study was conducted to identify the effect of cobalt (Co) in three successive crops of sugarcane grown in Louisiana, USA. The treatments consisted of an untreated control and four rates of Co (29, 58, 87 and 116 g ha(-1)). In the plant cane and second ratoon crops, the following variables were determined: the number of leaves and tillers, stalk diameter, plant height, stomatal conductance (gs), chlorophyll index (SPAD), cane yield, sugar yield and sugar quality (TRS, purity and fiber). For the first ratoon, it was only possible to determine the number of leaves, tillers and plant height, as well as yield parameters. The plant cane results demonstrate that foliar application of Co at 29 and 59 g ha(-1) increased the number of open stomata, the number of leaves and tillers and the sugar yield. When Co was not applied to the first ratoon crop, the effects on measured parameters were less pronounced, although positive effects on tillers were still observed. Results for the second ratoon crop showed positive benefits on stomatal conductance, the number of leaves and tillers, stalk heights, stalk weight, stalk diameter and sugar yield. Higher rates of Co (85 and 116 g ha(-1)) decreased the growth parameters except the number of internodes and tillers during second ratoon crop. Results from this study demonstrated that foliar application of low levels of Co to sugarcane can increase sugarcane growth and yields. Further research is needed to optimize Co fertilization rates and to elucidate the effects of Co on plant hormone levels.