Genotypic variation in phosphorus utilisation of soybean [Glycine max ( L.) Murr.] grown in various sparingly soluble P sources

This study compared the utilisation of sparingly soluble P among soybean genotypes selected from 3 geographical regions with contrasting soil pH. Plants of 5 genotypes from each region were grown for 72 days in soil columns supplied with hydroxyapetite ( Ca-P), AlPO4 ( Al-P), or FePO4 ( Fe-P) at a rate of 25 mg P/kg soil. NaH2PO4 ( Na-P) was used as control at the same rate. Shoot weights ranged from 2.4 to 5.9 g/plant. On average, the genotypes selected from calcareous soils of north-west China produced the highest shoot biomass whereas those from neutral soils of the north-east region the least. Root biomass and root surface area followed the same trend. In contrast, the root-to-shoot weight ratio was highest in Fe-P and lowest in Na-P while root length in Na-P and Fe-P was greater than in the other P forms. The genotypes from the north-east region had higher P concentration in the shoot than those from the other 2 regions. Total P uptake ranged from 9.0 to 15.9 mg/ plant for Na-P, and from 6.3 to 12.4 for the sparingly soluble P. Average total P uptake was the highest for the genotypes from the north- west region, and was greatest in Na-P and lowest in Fe-P. The genotypes from the north- east region displayed the greatest ability to use sparingly soluble P, and those from the north- west the least relative to Na- P. Total P uptake from the sparingly soluble P correlated highly with plant biomass production, N(2 fi)xation and nodulation, and seed P, while the relative P uptake correlated highly with P concentration in shoots but neither correlated with root carboxylate release nor leachate pH. The results suggest that there is a substantial genotypic variation in utilisation of sparingly soluble P, which is related to early vigour, nodulation, and seed P reserve but not to origin site pH or root exudation.