Abstract

SEQUERA, Omaira  and  RAMIREZ, Ricardo. Phosphate rock acidulated with sulfuric acid and ammonium thiosulfate as sources of phosphorus for cowpea in two soils. Bioagro [online]. 2013, vol.25, n.1, pp.39-46. ISSN 1316-3361.

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·kg^{-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.}

Keywords : Root length; residual phosphorus; residual calcium; Vigna sinensis.

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