Agronomic efficiency of partially acidulated and granulated Arraias phosphate rock

ABSTRACT Natural phosphate rocks (PR) are characterized by low phosphorus (P) solubility in water. Acidulation is the normal method to raise P solubility of these materials, however, it increases the cost and causes operational issues. The aim of this study was to evaluate the agronomic efficiency of partially acidulated and micro-granulated Arraias phosphate rock, which has a lower P content (6.88 %) than normal apatite concentrates. Two experiments were carried out in a greenhouse at the University of Rio Verde, Goiás State, in which corn was grown in pots with two kg of red clayey Oxisol (Latossolo). Treatments for the first experiment were the natural Arraias phosphate rock; triple superphosphate (TSP); and three partially acidulated phosphate rock (PAPR) with 5, 10 and 15 % of H 2 SO 4 relative to PR mass. Phosphorus diffusion from each fertilizer source was evaluated using Petri dishes filled with soil, with diffusion assessed at 1, 7, 14, 30, and 60 days after preparation. For the second experiment, treatments were 15 % PAPR granulated to average sizes of 0.25, 0.75, 1.50, and 2.4 mm. The agronomic efficiency of all variations of the PR was lower than the TSP. The 15 % PAPR treatment resulted in the highest corn dry mass yield among partially acidulated PR. The phosphorus diffusion radius was greatest with TSP, while diffusion from unacidulated Arraias rock phosphate was undetectable. Diffusion from acidified phosphate rocks increased with higher acidification rates. Granule size affected P absorption and, consequently, the agronomic efficiency of PAPR, but did not significantly influence its overall efficiency. Under the conditions of this study, partially acidulated and granulated phosphate rock was not an effective alternative to TSP.