Roca fosfórica acidulada como fuente de fósforo en un suelo ácido con o sin encalado

abstract partial acidulation of the phosphate rock (pr) with sulfuric acid (sa) has been successfully used to improve its solubility and increment the agronomic effectiveness of this p source. to prove the efficiency of pr acidulated with sa and/or ammonium thiosulfate (ats), two greenhouse experiments were conducted with potted cowpea plants grown on non-limed (ph 3,3) and limed soils (ph 5,4), low in p. the p sources evaluated were pr without acidulation, pr acidulated with 30 % ats and 70 % sa (r30t), rf acidulated with ats alone (r100t), pr acidulated with sa alone (ra), and diammonium phosphate (dap), along with a non treated control. in each soil, the treatments were tested in a completely randomized design with three repetitions. after 35 d of crop growth the plants were harvested and the dry matter (dm), p and ca uptake, and soil residual p and ca were determined. the effectiveness of the p sources in terms of increasing dm and p uptake followed the order of dap>r30t=ra>pr=r100t, in both soils. the treatments r30t and ra presented same effectiveness, and since in previous experiences similar results were found in gramineous plants, it is concluded that r30t represents an alternative of partially acidulated phosphate rock suitable for a wide range of annual crops.