Utilization of phosphorus substrates by contrasting common bean genotypes

Phosphorus deficiency limits common bean (Phaseolus vulgaris L.) production in tropical soils, where p may be bound to recalcitrant organic matter, or with aluminum or iron oxides. In a previous study, we showed that P-efficient genotypes perform well in contrasting soils, suggesting that interactions with specific soil constituents did not account for genetic variation. To confirm this finding, a study was done to determine if contrasting bean genotypes differ in their ability to recover P from different P compounds. Six genotypes were planted in pots of silica sand in which P was supplied at four levels as KH₂PO₄, CaHPO₄, inositol hexaphosphoric acid (IP₆), FePO₄, or AlPO₄. Most results could be explained as a function of relative aqueous solubilities of the P sources. KH₂PO₄ gave the greatest uptake and growth and FePO₄ the least. No differences were observed in the ability of the six genotypes to acquire P from the Al, Fe, or IP₆ sources. Andean genotypes, especially the Peruvian landrace G19833, extracted more P from CaHPO₄ than Mesoamerican genotypes. G19833 was capable of acidifying the rhizosphere more than other genotypes. We conclude that (i) differential ability to mobilize P from Fe, Al, and organic ligands does not account for genetic variation in P efficiency, and (ii) Andean germplasm has superior ability to mobilize P from Ca sources, which may be useful in utilizing phosphate rock fertilizers.