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Criteria to nitrogen management on common bean crop using portable chlorophyll meter

Abstract

The chlorophyll meter is a device which allows obtain a relative chlorophyll index (RCI) which correlated with the chlorophyll and leaf nitrogen (N) content, therefore, determination of RCI by chlorophyll meter can be an alternative used to predict to necessity N by common bean, however, there are questions about which leaf and N sufficiency index (NSI) are most appropriate to define need for N by the crop. Thus, the aim of this study is establish the leaf diagnosis and value N sufficiency index most appropriated to define N necessity of common bean, through chlorophyll indirect readings through the use of portable chlorophyll meter. For both will be realize a research work consists of two steps: in the first will be conducted two field experiments, one with each cultivar (Pérola and IPR Eldorado) during "rainy" season in the year 2011, with purpose of establishing witch the best leaf diagnostic (first trifoliolate leaf, second and third fully expanded trifoliolate leaf from the top). To define the necessity N of common bean, using the chlorophyll meter (Minolta SPAD-502). The experimental design is a randomized block with five N rates (0, 50, 100, 150 and 200 kg ha-1) and four replications. In the second stage will be conducted four experiments, two with each cultivar (Pérola and IPR Eldorado), in "rainy" and "dry" season in 2012, to define NSI in relation to reference treatment (without N deficiency), more suitable to indicate the necessity N in the crop. The chlorophyll meter readings will be held on the leaf that present higher values of correlations between the RCI, N content and grain yield determined in the first step. In all experiments of the second step, the experimental design is a randomized block with six N managements (M1: 40 kg ha-1 N at sowing + 80 kg at 10 DAE + 80 kg at 20 DAE (reference); M2: 20 kg ha-1 N at sowing + 40 kg at 10 DAE + 40 kg at 20 DAE (recommended rate); M3: 20 kg ha-1 N at sowing + 30 kg when chlorophyll meter readings indicated NSI < 96%; M4: 20 kg ha-1 N at sowing + 30 kg when chlorophyll meter readings indicated NSI < 93%; M5: 20 kg ha-1 at sowing + 30 kg when chlorophyll meter readings indicated NSI < 90% and, M6: control (without nitrogen)) and four replication. The first step will be evaluated: RCI in the first, second and third fully expanded trifoliolate leaf, N Total and N soil inorganic, persistence and release of N from straw, shoot dry weight, N leaf content and N shoot dry matter content, cumulative amount of N in shoot, yield components (final plants population, number pods per plant, number grains per pod and 100- grain weight, and grains yield. In the second step will be evaluated: CRI, NSI, N total and N soil inorganic, amount of straw in area and N straw content, shoot dry weight, N leaf content and N shoot dry matter content, cumulative amount of N in shoot, yield components, grains yield, relative yield and N use efficiency. (AU)

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