Relationship between phosphorus status and nitrogen fixation by common beans ( Phaseolus vulgaris   L.) under drip irrigation

The current study aims to examine, the response of contrasted recombinant inbred lines of common bean to the application of phosphorus, to identify the bean recombinant inbred lines which were efficient in phosphorus utilization when dependent on nitrogen fixation as a source of nitrogen. The experiment was conducted at the experimental farm of Agricultural Research Station of the Nubaria district, Behera, Egypt, during the winter seasons of 2008-2009. Three levels of mineral phosphorus fertilizers were applied (0, 45 and 90 kg ha^-1 phosphorus pentoxide). Nodulation, plant growth parameters, leaf area, soil Olsen phosphorus, pH, and phosphorus and nitrogen of shoots, nodules and seeds were measured. The results have shown that the recombinant inbred lines responded positively to P application levels. The best values were observed in recombinant inbred lines 75, 83 and 34. Vegetative growth parameters were significantly enhanced by increasing levels of phosphorus. The highest level of phosphorus, i.e., 90 kg ha^-1 phosphorus pentoxide gave the optimal values of growth parameters for all common bean recombinant inbred lines while control plants obtained the lowest values. An increase of Olsen-P and a decrease of soil pH were also observed with increases in phosphorus. These results led to the conclusions that phosphorus applied to Nubaria soil: (1) improved the soil fertility; (2) enhanced the ability of root nodules of common bean recombinant inbred lines to fix atmospheric nitrogen; and (3) increased the release of hydrogen by roots, thus decreasing soil pH and reducing the immobilization of phosphorus in the soil solution and transforming it into available form for the plant.

Keywords
Drip irrigation; Nitrogen fixation; Phosphorus; Phaseolus vulgaris; Recombinant inbred lines; Sandy soil