Phosphoric rocks of Chile. II. Agronomic efficiency and its use as phosphate fertilizer in volcanic ash soils

Gloria Sepúlveda W.1, Eduardo Besoain M. y Rosa Molina M.

It was realized an experiment of glass house pots of ryegrass fertilizer with phosphoric rocks use as phosphate of direct use in volcanic soils. Since, the response of phosphoric rocks (PR) when being applied as phosphate fertilizer of direct use depends on the soil properties, the plants or crops and the type of phosphoric rocks. It was determined the yield of ryegrass (Lolium perenne) applying as phosphorus (P) sources three chilean phosphoric rocks (PR), la Serena, Bahía Inglesa and Mejillones and the PR Tampa from Florida (USA), used as reference. The rocks were applied in a natural way, grounded (300 mesh), without treatment and partially acidulated with 30 or 50% H2S04, comparing its effect in the yield with the triple superphosphate, normal superphosphate and with acid potassium phosphate, reagent grade. The soil used was the Andisol Vilcún from the south of Chile, with low phosphorus available, < 3 (mg/kg) and acid pH 5.5. The soil was collected to (0-20 cm) of depth in the General lópez area (IX Región). The P sources were incorporated in the soil at rates of 0, 100, 200 and 400 (mg/pot) of P and it was also applied a base fertilization, except P and the nitrogen was added every 15 days. In every treatment it was quantified the yield and it was calculated the P absorption efficience and the relative agronomic effectiveness (RAE) of the dry matter accumulated in the amount of six cuttings, during six months. The RAE was determined by means of response curves at differents rates of phosphorus. The experimental design was of random blocks with three repetitions. Also it was realized the analysis of the available phosphorus and the pH of the soil before and after the experiment.
The behaviour of RFPA is different in comparison with the unfertilized witnesses the RFN from la Serena does not increase the yield, its value is the some to the one ofthe witness, however it improve its EAR when it is acidulated, the some of RF

Keywords: Phosphoric rocks, partíal acidulation, phosphated fertilizers, PR and acid soils, volcanic soils, apatites.
1 Centro Regional de Investigación La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.