Several classes of soils in Brazil have been used for sugarcane cultivation, inclusive soils with low soluble silicon contents. The objectives were to evaluate silicon availability in soils and the relationship between availability and uptake. Therefore, we assessed the dry matter yields of sugarcane cultivated in three soil types, with and without silicon fertilization. The experiment was set up in a completely randomized factorial scheme (4 x 3 x 2) with four silicon rates (0, 185, 370 and 555 kg ha-1 Si) as Ca-Mg silicate and three soils: Quartzipsamment (RQ), Rhodic Hapludox (LV) and Rhodic Acrudox (LVdf), in four repetitions. All plots (100 L) received same Ca and Mg quantities with additions of dolomitic lime and or MgCl2. The LVdf soil showed the higher soluble silicon concentration, followed by LV and RQ. Added Si applied increased the amounts of soluble content in all soils but Si uptake in leaves of sugarcane were just increased to RQ and LV. However, addition of Si to the soils did not promote changes in dry matter yields and Si uptake on stalks of sugarcane.

The hollow stem disorder (HSD) is a common problem in cauliflower caused by B deficiency. Its occurrence is related especially to nitrogen and boron supply. There is only little information about this subject in Brazil. Two experiments were carried out in a randomized complete block design with 4 replications from November 2005 through February 2006. The objective was evaluate rates of nitrogen (100, 150, 200, 250 kg ha-1) and B aplication (0 at planting; 1.5 kg ha-1 planting + 1.5 kg ha-1 at curd initiation; 3 kg ha-1 at planting) on production and HSD incidence in cauliflower “Sharon” cultivated on Kandiustalf (PVA; 0.54 mg kg-1 B) and Rhodic Kandiudox (NVef; 0.84 mg kg-1 B) soils. The curd diameter and total yield were neither influenced by N nor B application in spite of generally low N concentrations in leaves and curds. On NVef soil HSD occurred without affecting commercial yield even with B concentrations in leaves and curds suggesting adequate B status. On PVA soil B application increased commercial yield by reducing the incidence of HSD. There was negative correlation between B concentration in leaves (r=0.66; p < 0.05) and curds (r=0.76; p < 0.05) with hollow stem disorder. Further studies appear necessary to control this B deficiency induced physiological disorder prevailing under tropical conditions.