Adubação com torta de filtro “in natura” e compostada no desenvolvimento inicial da cana-de-açúcar (Saccharum officinarum L.)
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The agricultural use of by-products of the agroindustry, such as filter cake, reduces the production costs of sugarcane and contributes to the mitigation of environmental impacts, since it reduces the use of mineral fertilizers as alternative sources of nutrients. Filter cake is an important alternative source of phosphorus (P), a primary macro-element with limited availability in weathered tropical soils, typical of sugarcane production environments. The objective of this study was to evaluate the initial development of the sugarcane plants, using fertilizers with different types (in natura and composted) and doses (calculated and practiced) of filter cake as a source of P. Pre-sprouted seedlings from the RB855536 variety of sugarcane were transplanted into 40 dm3 pots, filled with soil samples from the topsoil horizon of a dystrophic Oxisol. The experiment was carried out in a greenhouse, with a completely randomized block design, composed of six treatments with five replications: T0 - control; T1 - conventional chemical fertilization; T2 - filter cake “in natura” at the calculated dose (35 t / ha); T3 - “in natura” filter cake in sub-dose (20 t / ha); T4 - filter cake composted at the calculated dose (25 t / ha) and; T5 - filter cake composted in subdose (15 t / ha). At 120 days after transplanting, biometric assessments were performed to collect information about height, diameter, and number of internodes per stem, fresh and dry mass of stems, and chemical analysis of the soil and plant tissue. The results were subjected to analysis of variance and, when significant by the F test, were evaluated by the Tukey test (p<0.05). The use of 20-35 t ha-1 of “in natura” filter cake or 15-25 t ha-1 of composted filter cake had an effect similar or superior to conventional mineral fertilization on biometric parameters, but reduced leaf contents of potassium (K), magnesium (Mg), sulfur (S), boron (B), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn), when compared to conventional fertilization treatment. Leaf nitrogen (N) and calcium (Ca) contents were not altered by the use of filter cake. With the application of 15-25 t ha-1 of composted filter cake, significant increases were observed in the cation exchange capacity and in the contents of K, Ca, sum of bases (SB) and, mainly, of P from the soil. Contrary to expectations, the use of filter cake did not cause significant increases in the soil's organic matter. However, the application of 20-35 t ha-1 of “in natura” filter cake increased the potential acidity and decreased the soil pH. Regardless of the type and dose, the filter cake completely replaced the phosphate fertilizer and ensured adequate P leaf levels in sugarcane plants in the early stage of development. The application of filter cake was an efficient alternative to supply P and, therefore, can reduce costs with phosphate mineral fertilizers.
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