Response of Common Bean (Phaseolus vulgaris L.) to Rhizobium Inoculation and Nitrogen Fertilization.

Common bean (Phaseolus vulgaris L.) producers need greater N use efficiency to decrease production costs. The goal of this research was to identify bean lines that are better adapted to low N soils. Three field experiments were conducted at the Isabela Substation in northwestern Puerto Rico on an acidic clay soil (Oxisol, Coto series). Ninety-six bean lines were evaluated in field trials planted in February 2007. RCB experimental designs with 6 replications were used. Fertilization was 50 kg/ha of N-P₂O₅-K₂O. Rhizobium leguminosarum biovar phaseoli strain was applied at planting at a rate of 3.33 g of inoculant per 3.8 L of water. Nodulation scores were determined using the CIAT 1-9 scale where 1 = > 80 nodules and 9 = < 10 nodules/plant. The lines with the best nodulation scores and seed yield were: VAX 3 (3.5 and 1,859 kg/ha), Cardenal (4.0 and 1,509 kg/ha) and RAB 655 (4.5 and 1,723 kg/ha). A second experiment was planted in June 2007. A split plot arrangement of a RCB design with 5 replications was used. Whole plots were two N levels (0 and 25 kg/ha) and sub-plots were the best 40 bean lines selected from the previous experiments based on their performance. Lines with the best nodulation scores were: Salagnac 90A (2.7), Arroyo Loro Negro (2.8) and PR0427-7 (3.5). The best nodulation scores were observed in the low N plots (0 kg/ha). A third field experiment was planted under low N conditions in January 2008 using a RCB design with 5 replications. The lines with the best nodulation were: OAC Rico and PR0427-7 with scores of 1.7 and 4.7, respectively. PR0340-3-3-1, PR0443-151, VAX 3, and A 774 produced the greatest seed yields in the second and third experiments at the 25 kg/ha of N level.