IRRIGATION WATER SALINITY AFFECTS SOIL NUTRIENT DISTRIBUTION, ROOT DENSITY, AND LEAF NUTRIENT LEVELS OF CITRUS UNDER DRIP FERTIGATION

The purpose of this study was to determine the effects of irrigation water salinity on soil nutrient distribution, citrus leaf nutrition and root density. Irrigation water, salinized to an EC of about 0.3, 1.6, or 2.5 dS/m using a 3:1 ratio of NaCl:CaCl2 plus uniform weekly applications of liquid fertilizer, was applied through a drip system. Soil samples were taken at depths of 0-15 and 15-30 cm, both directly under the drippers and 45 cm outward from the drippers, near 8-year old 'Valencia' orange trees on either Carrizo citrange or Sour orange rootstocks growing in a Candler fine sand in lysimeter tanks. In both undisturbed and uniformly mixed soil profiles, soil pH and concentrations of Na, Ca, and P were higher under the dripper than 45 cm outward from the dripper at both depths regardless of salinity level. Soil N and Cl tended to be higher outward from the drippers than near the drippers, except in undisturbed soil at the 0-15 cm depth. Increasing salinity levels in the mixed soil profile not only increased soil EC, Na, Cl, and Ca, but also increased the concentration of P and decreased the concentration of Mg. Root density of both rootstocks were increased by high salinity. Root densities and organic matter percentages were higher in soil sampled under drippers than that sampled outward from drippers. Leaf nutritional values and responses to salinity were dependent on rootstock as trees on sour orange had higher K and Ca, but lower Mg and Cl than trees on Carrizo. Although there were no nutrient deficiencies, K of trees on Carrizo citrange and Mg of trees on sour orange were re-reduced by high salinity. An increase in leaf Ca concentrations when irrigated with salinized irrigation water likely minimized the effects of salt stress.