Changes in Tropical Soil Properties as Affected by Surface-Applied Sugar Cane Ash.

Sugar cane ash, a waste material derived after burning the sugar cane bagasse, is often used as a soil fertilizer in Brazil. The country is the world leader in sugar cane production and that has increased rapidly due to the raise in the global biofuel demand. Environmental concerns come along with the increased production because for each ton of harvested cane about 17Kg of ash is produced and that can be applied to the soil surface. This novel study focused on determining the harmful or beneficial effects of the surface-applied sugar cane ash on soil properties. Specifically we were interested on the fate of metals in the soil after ash application and how that would affect metal concentrations in the soil and leached water. Samples of the A-horizon of an oxisol from the Brazilian Savannah were packed in columns and subjected to three treatments (ash alone; compost – 1/3ash plus 2/3decomposed sugar cane bagasse; control). Four simulated rainfall events (60mm/h with 48-hours time interval between events) were performed on the columns. Leached solution was collected from the columns every 15 minutes during the rainfalls and the soil of the columns was collected after the last rain. The leached solution was weighed and analyzed, together with HNO₃ digested soil samples, for metals (Ca,Mg,K,Mn,Cu,Cr) by atomic absorption. Results showed the concentrations of metals increased in the soil after the rainfalls for the ash and compost treatments. In contrast, the application of ash or compost did not affect the chemistry of the leached water and the water flux into the soil. We concluded that surface-applied ash or compost increases the concentration of metals in the soil however, it does not affect water quality or soil drainage in the short time frame studied here.