Vegetative ash biomass as a potential source of silicon for soils in eucalyptus plantation

In face of the need to broaden the knowledge about the effects of ashes in eucalypt plantations, this study evaluated the use of ashes in two typical Brazilian soils for forest plantations. The experiment was done in a greenhouse, from November 19 to December 19 (2014), in Uberlândia, MG. The ashes were obtained from eucalypt wood and bark, eucalypt twigs and leaves, pine wood and bark and sugar cane bagasse, applied to a sandy soil (experiment 1) or to a clayey one (experiment 2). In each experiment, incubation tests were done in a completely randomized design as 4×2+1 factorial consisting of four ash sources. Vegetative ash biomass from eucalypt wood and bark (EWB), eucalypt twigs and leaves (ETL), pine wood and bark (PWB) and sugar cane bagasse (SCB), two doses (200 and 400 kg ha-1), and a control (with no silicon source), with three replications. Soluble silicon, pH, and exchangeable Ca and Mg were determined after incubating the soils for 30 days. PWB supplied more Si to both soils. The SCB did not increase Ca and Mg to either soil, regardless of the dose. The ashes that most reduced soil acidity in the sandy soil were those of eucalypt, at 400 kg ha-1, while no pH change was observed in the clayey one. The best silicon source evaluated for both soils was pine wood and bark (PWB) at 400 kg ha-1; however, EWB and ETL should be used whenever available.