Effect of sources and rates of phosphorus associated with filter cake on sugarcane nutrition and yield
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The application of filter cake associated with phosphorous can prevent the adsorption of this nutrient by soil colloids. The objective of this work was to evaluate the effect of sources and rates of phosphorous on the soil P content and in the nutritional status and yield of sugarcane cultivated in Kandiudalf and Haplustox soils in the presence and absence of filter cake. Experiments were carried out in the 2012/2013 cropping season in the state of São Paulo, Brazil. The experimental design was a randomized block in a 3x4x2 factorial arrangement with three sources of phosphorus (Phosphate of Araxá, Gafsa phosphate and triple superphosphate) and four rates of P [zero (control); 90; 180 and 360 kg ha<sup>-1</sup> of P<inf>2</inf>O<inf>5</inf>] in the presence and absence of 7.5 t ha<sup>-1</sup> of filter cake (dry basis), with three replicates. Treatments were applied in the planting furrows. Parameters evaluated were availability of P in the soil, nutritional status of P in the leaves, yield of straw and stalks and phosphorous buildup by the plants. The application of phosphorous in the soil promoted increases in the levels of P-resin in the top layer (0 - 20 cm) of 53 and 807% and in the sub surface layer (20 - 40 cm) of 839 and 432%, regardless of the phosphorous source in Kandiudalf and Haplustox without the use of filter cake, respectively. The increase of phosphorous availability in the soil increased the absorption of this nutrient with the application of P-fertilizer with filter cake. The use of Gafsa phosphorous source in Kandiudalf increased stalk production compared to the other sources tested, reaching 214 t ha<sup>-1</sup> with the rate of 209 kg ha<sup>-1</sup> of P<inf>2</inf>O<inf>5</inf>, while triple superphosphate yielded 190 t ha<sup>-1</sup> with the highest rate (360 kg ha<sup>-1</sup> of P<inf>2</inf>O<inf>5</inf>), regardless of the presence or absence of filter cake. In the Haplustox, stalk yield increased with P-fertilization (360 kg ha<sup>-1</sup> of P<inf>2</inf>O<inf>5</inf>) with filter cake yielding 188.2 t ha<sup>-1</sup>; 19.6% higher than without filter cake.