Modos de aplicação e substituição parcial de fosfato solúvel por fosfato natural na cultura da laranjeira Pera Rio

Abstract

The combination of reactive natural phosphates with either fully acidified phosphates or with slow-release phosphates and applied in a piecemeal manner may be a strategy to improve the efficiency of phosphate fertilization in tropical soils with high phosphorus (P) adsorption potential, such as in most of Brazilian soils. The objective of this study was to evaluate whether the partial replacement of conventional soluble superphosphate or slow-release superphosphate by phosphate rock influences the availability of P in soil, nutritional status and the development of young plants of Pera Rio orange [Citrus sinenses (L.) Osbeck]. The experiment was installed in a randomized complete block design, with four replications and three plants per experimental unit, totalizing 132 useful plants. The plants were grown under 150 kg of P2O5 ha-1, using a 5x2+1 factorial combination, involving five different proportions of Arad natural reactive phosphate with conventional triple superphosphate or slow-release superphosphate (in%) (0-100 , 25-75, 50-50, 75-25 and 100-0, respectively), with two modes of application (application of the full dose in the first year and partial application in the pit, 1/3 of the total dose applied in the first year and 1/3 of the total dose applied in the second year) plus one additional treatment without the provision of P. The plants were maintained under these conditions for 36 months. Every 12 months, the availability of P in the soil and the degree of variation in the nutritional and biometric parameters of each plant were evaluated. The proportions of 0:100, 25:75 and 50:50 (% of Arad natural reactive phosphate and % of conventional triple superphosphate) and the proportions of 0:100 and 25:75 (% Arad natural reactive phosphate and % slow-release triple superphosphate) yielded the highest values of P available in the soil in the total application mode. The methods of application and the partial substitution of the conventional triple superphosphate by Arad natural reactive phosphate did not interfere in the nutritional status nor in the growth of the orange trees. The total application mode and the partial substitution of the slow-release triple superphosphate by the Arad natural reactive phosphate in all proportions provided the highest levels of P in the leaf and the highest coverage rate in the canopy on the orange tree planting street.