ROCA FOSF 3RICA ACIDULADA CON \uc1CIDO SULF aRICO Y TIOSULFATO DE AMONIO COMO FUENTE DE F 3SFORO PARA FRIJOL EN DOS TIPOS DE SUELO

La deficiencia de f\uf3sforo en los suelos tropicales es com\ufan. Una fuente natural de este nutriente es la roca fosf\uf3rica acidulada (RFA) con \ue1cido sulf\ufarico (AS), aunque una alternativa m\ue1s econ\uf3mica es la acidulaci\uf3n sustituyendo el 30 % del AS por tiosulfato de amonio (R30T). Para probar la eficiencia de esta \ufaltima forma se trabaj\uf3 con dos experimentos usando un suelo \ue1cido y otro neutro. Se aplic\uf3 P en forma de superfosfato triple (SFT), RFA y R30T en dosis de 0, 70, 140 y 210 mg\ub7kg-1. Se us\uf3 un dise\uf1o completamente aleatorizado con cuatro repeticiones, y se sembr\uf3 frijol (Vigna sinensis) el cual se cosech\uf3 a los 35 d\uedas para determinar materia seca (MS), longitud radical (LR), P absorbido, y Ca y P residual en el suelo. La MS y el P absorbido en promedio fueron parecidos donde se aplic\uf3 SFT, RFA y R30T. La MS dependi\uf3 altamente de la concentraci\uf3n de P y Ca en ambos suelos, as\ued como de la concentraci\uf3n del P en la planta. La LR mostr\uf3 un mayor crecimiento con el incremento del P disponible en el suelo \ue1cido, no as\ued en el suelo neutro. Se concluye que la acidulaci\uf3n parcial de la roca fosf\uf3rica con tiosulfato de amonio y \ue1cido sulf\ufarico permite producir un fertilizante tan eficiente como la RFA para el crecimiento del sistema radical tanto en suelo \ue1cido como neutro, y se ratific\uf3 su eficiencia en la producci\uf3n de materia seca y absorci\uf3n de f\uf3sforo por la planta. ABSTRACT Phosphate rock acidulated with sulfuric acid and ammonium thiosulfate as sources of phosphorus for cowpea in two soils Phosphorus deficiency in tropical soils is a common constrain. Acidulated phosphate rock with sulfuric acid (RFA) is a natural source of P, but a cheaper alternative is the acidification of phosphate rock by replacing 30% of sulfuric acid with ammonium thiosulfate (R30T). To test the efficiency of those fertilizers and superphosphate two experiments were conducted using an acidic soil and a neutral one. The doses of P applied were 0, 70, 140 and 210 mg\ub7kg-1. A completely randomized design was used with four replications, and cowpea plants were grown. Plants were harvested at 35 days old and dry matter (DM), P uptake, residual P and Ca in soil, and root length (RL) were determined. When RFA was applied, DM and P uptake were similar to those in R30T and SFT. DM was highly related to soil P and Ca contents as well as to P concentration in the plant. RL increased as available P was higher in the acidic soil, but not in neutral soil. It is concluded that partial acidulation of phosphate rock with ammonium thiosulfate and sulfuric acid produces a fertilizer as efficient as the RFA for growth of the root system in both acid and neutral soil, and confirmed its efficiency in the production of dry matter and phosphorus uptake by the plant