Relative chlorophyll index and nitrogen status of fertigated coffee plants during the crop season

The chlorophyll meter (SPAD-502, Minolta) is a portable device that measures the relative chlorophyll index (RCI) in a simple, fast and non-destructive way in the field. This index is correlated with leaf N concentration in several crops, and allows the correction of N deficiency, optimizing fertigation. The objective of this study was to test RCI as an indicator of the nitrogen status in coffee trees to adjust fertigation during the development cycle. The experiment was carried out in Botucatu, state of Sao Paulo, Brazil, in an area with two-year old coffee plants of cultivar "Red Catuai", spaced at 2.5 x 0. 8 m, under drip irrigation. The experiment had a randomized block design with four replications and five treatments: control treatment under irrigation and without fertilization, and four N rates using fertigation with 33, 66, 100, and 133 % of the recommended annual N rate (52.8, 105.6, 160. 0 and 212.7 kg ha(-1), respectively). The fertilizer treatments were split in weakly applications. The RCI increased linearly with the N rates and the yield was significantly correlated with RCI, from flowering to harvest. However, there was no correlation between beans yield with the leaf N concentration. The RCIs of high yielding coffee plants were 81.5-83.2 (flowering and beginning of fruit filling), 76.2-78.3 (fruit expansion) 68.3 - 69.8 (beginning of grain formation), 64.0-65.9 (during grain formation) and 61.7-62.7 SPAD units (grain maturation). The chlorophyll meter can be used throughout the coffee development cycle to define the likelihood of N response in coffee trees.