Ramírez-Madera, Axel O.

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    Response of the common bean (Phaseolus vulgaris L.) to Rhizobium inoculation and nitrogen fertilization
    (2009) Ramírez-Madera, Axel O.; Beaver, James S.; College of Agricultural Sciences; Sotomayor-Ramírez, David; Estévez de Jensen, Consuelo; Muñoz-Muñoz, Miguel A.; Department of Crops and Agro-Environmental Sciences; Borges, Sonia
    Common bean (Phaseolus vulgaris L.) producers need to use bean lines with improved nitrogen (N) use efficiency to decrease production costs. The goal of this thesis was to identify bean lines adapted to soils with low N availability. Four field experiments were conducted at the Isabela Substation in northwestern Puerto Rico on an Oxisol of the Coto series (very-fine Kaolinitic Isohyperthermic Typic Eutrustox). In the first experiment ninety-six bean lines were evaluated for yield and nodulation score in February 2007. Randomized Complete Block (RCB) experimental designs with 6 replications were used. Fertilization was 50 kg ha-1 as N, P2O5, and K2O. Inoculation of 2.5 kg ha-1 of Rhizobium leguminosarum biovar phaseoli inoculant was applied at planting at a rate of 3 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-1. Small red and black bean lines had the best nodulation scores and seed yields. The second and third field experiments were planted in June and October 2007. A split plot arrangement in a RCB design with 5 replications was used for both experiments. Whole plots were two N levels (0 and 25 kg ha-1) and sub-plots were the best 38 bean lines selected from previous experiments. Lines with the best nodulation scores in the June 2007 field experiment were: Salagnac 90A (2.7), Arroyo Loro Negro (2.8) and PR 0427-7 (3.5). In general, the best nodulation scores were observed in the low N plots (0 kg ha-1). There was a significant (p<0.05) and positive correlation (r=0.38) between the June 2007 nodulation scores and plant vigor scores from the October 2007 field experiment, which had a severe amount of root rot. A fourth field experiment was planted under low N conditions in January 2008 using a RCB design with 5 replications. The lines with the best nodulation scores at 67 days after planting were: OAC Rico and PR 0427-7 with scores of 1.7 and 4.7, respectively. Lines PR 0340-3-3-1, PR 0443-151, and VAX 3, produced the greatest seed yields in the second and fourth field experiments.