Variation in phosphorus uptake and use efficiencies between pigeonpea genotypes and cowpea

Low bioavailability of soil phosphorus (P) often limits N-2 (nitrogen) fixation and crop production in large parts of the tropics. The efficiency of P acquisition and P use by 21 genotypes of pigeonpea [Cajanus cajan (L.) Millsp.] were studied in a pot experiment using two cowpea [Vigna unguiculata (L.) Waip.] genotypes as controls. The short-duration genotypes produced more dry matter, accumulated more P, and produced more dry matter per unit of absorbed P than the medium-and long-duration genotypes. Dry-matter production correlated positively with the P uptake (r(2) = 0.72) and P-use efficiency (r(2) = 0.86). The P uptake correlated positively with the P-use efficiency (r(2) = 0.36); whereas the P-use efficiency correlated negatively with the P-uptake efficiency (r(2) = 0.50). Root surface did not determine P acquisition of pigeonpea, which absorbed 1.6 mg P cm(-3) from 33 cm(3) soil compared with 0.17 mg P cm(-3) from 387 cm(3) soil for cowpea at 66 d.