Use of Portable Chlorophyll Meter to Determination of Common Bean Cultivars Sidedressing Nitrogen Fertilization.

Management techniques that allow the maximization of N uptake by common bean crop are extremely important, because of high cost of nitrogen fertilizers and N losing. In this sense, estimation N needs of common bean crop by indirect reading of chlorophyll can be a viable alternative. The aims of this study were: determine the correlation between relative chlorophyll index (RCI), obtained by chlorophyll meter reading and leaf nitrogen (N) content of two bean cultivars (IAC Alvorada and Pérola); evaluate the N sufficiency index (NSI) as an indicator of time N application in sidedressing on common bean, and verify that value NSI (90% and 95%) the most appropriate to indicate the moment of fertilization in each cultivar. The experiment was conducted in "rainy" and "dry" season of agricultural year 2009/2010 and a randomized block in split plot scheme, with four replications were used. Plots consisted two bean cultivars (IAC Alvorada and Pérola) and subplots six N managements (M1: 200 kg ha^-1 N; M2: 100 kg ha^-1 N; M3: 50 kg ha^-1 N; M4: 20 kg ha^-1 N at sowing + 30 kg ha^-1 N when chlorophyll meter readings indicated NSI <95%; M5: 20 kg ha^-1 N at sowing + 30 kg N ha^-1 N when chlorophyll meter readings indicated NSI <90% and, M6: control). The results showed that RCI correlated positively with leaf N content from IAC Alvorada and Pérola, in dry and rainy seasons. The NSI 90% based on the measurement of chlorophyll meter allowed to define when to apply N in common bean cultivars, improving N use efficiency (NUE), however, did not provide the same levels yield of reference area. Use of NSI 95% was less efficient than the NSI 90% for the definition when to apply the N sidedressing in common bean cultivars, by provide lower NUE.