NO 3 – , 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 NO 3– 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 K 2 O (0, 15, 30, 60 and 120 kg ha –1 ), combined in an incomplete 5 2 factorial scheme in 13 combinations and arranged in randomized blocks with four replications. We determined NO 3– and K + concentrations in petiole sap, leaf chlorophyll index, grapevine cluster mass and number per plant, mean grapevine cluster mass, and phenolic composition. High NO 3– concentrations contributed positively to grapevine yield; however, increased K+ concentrations caused a negative response of sap. For 120 kg N ha –1 rate, NO 3 – 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.