NO3-, K+, and chlorophyll index in fertigated grapevines in the semi-arid region of Brazil.

Evaluating the effects of N and K supply on grapevines (Vitis vinifera L.) and the techniques for nutritional diagnosis is of great importance for fertigation management of this crop. This study evaluated the effects of N and K fertigation on the soluble concentrations of NO3 ? and K+ in the petiole sap and on the leaf chlorophyll index in drip irrigated ?Syrah? grapevine (from 17 June 2013 to 25 Nov 2014). The treatments consisted of five levels of N (0, 15, 30, 60 and 120 kg ha?1) and K2O (0, 15, 30, 60 and 120 kg ha?1), combined in an incomplete 52 factorial scheme in 13 combinations and arranged in randomized blocks with four replications. We determined NO3 ? and K+ concentrations in petiole sap, leaf chlorophyll index, grapevine cluster mass and number per plant, mean grapevine cluster mass, and phenolic composition. High NO3 ? concentrations contributed positively to grapevine yield; however, increased K+ concentrations caused a negative response of sap. For 120 kg N ha?1 rate, NO3 ? in the sap and chlorophyll index showed higher values at the flowering stage, while high values for K+ were observed during the grape-ripening stage.