Superfosfato simples contendo fosfato de ferro de baixa solubilidade aplicado em solos de várzea do Rio Grande do Sul

Abstract

Some rocks used in fertilizer production contain impurities of low solubility in water such as iron aluminum phosphate (Fe- Al- P). The use of these rocks generates simple superphosphate which may contain impurity levels that do not meet the fertilizer legislation in Brazil. One of the possibilities for the use of fertilizers containing high degree of impurities of iron phosphate would be to apply in flooded soils. Thus, the aims of this work were: a) to study the phosphorous behavior originating from the simple superphosphate containing impurities of iron phosphate with low solubility in water, when submitted to flooding conditions in different flooding soils from RS used for the cultivation of the rice; b) to study the efficiency of the use of phosphorus originating from fertilizers containing impurities of insoluble iron phosphates in water when compared to single superphosphates without residues of iron phosphates in rice plants (Oryza sativa). Six lowland soils were collected from different places in the State of Rio Grande do Sul: two soils in Santa Maria (Planossolo and Gleissolo) and the others in Santa Vitória do Palmar (Chernossolo); Uruguaiana (Chernossolo); Cachoeirinha (Gleissolo) and Pelotas (Planossolo). The soils were conditioned in 8 L plastic vases. The treatments were structured in a bifatorial 6x3 (six soils, two P sources, simple superphosphate and simple superpohosphate with (Fe-P) residues without P addition). In treatments with P, 100 mg P Kg-1 was added to the soil. A water layer was maintained at 5 cm of height in vases above the soil and the collection of the soil solution was carried out weekly. pH and redox potential were measured immediately after each collection of the solution and the reading of the amount of P, iron and manganese was done just after that. Forty five days after flooding, eight exemplars of rice cultivar IRGA 422 CL were transplanted to be cultivated for 45 more days. The yield of dry matter from aerial part, the P amount in the tissue and the calculation of the P amount absorbed were determined. The results showed an increase of pH and of the amount of P, iron and manganese as well as a decrease of Eh in all soils. The simple superphophate containing insoluble impurities of iron phosphate in water presented behavior similar to simple superphosphate without impurities when applied in soils of meadow from Rio Grande do Sul, evidencing its potential to be used in these soils Rio Grande do Sul, evidencing its potential to be used in these soils.