Relations between soil and tree stem water content and bulk electrical conductivity under salinizing irrigation
2004
Nadler, A.
In a semiarid region in a grapefruit (Nucellar 'Marsh seedless, Citrus paradise Macf.) orchard irrigated with salinized waters, the water content (theta) and bulk electrical conductivity (sigma(a)) of the trees' stems and the root-zone soil was monitored by time domain reflectometry (TDR) and electrical conductivity meter for a year. For the purpose of irrigation scheduling the objective was to verify correlations between (i) stem and soil theta and (ii) stem and soil sigma. Measured theta(soil) and sigma(a, soil) were in good agreement with the irrigation treatments, peaking in summer and decreasing during autumn. Only a weak correlation between stem's sigma(a) and 0 and the soil's parameters was found and attributed to time after installation of probes in the stem; the higher sigma(a, stem) (5-10 x 10(-1) dS m(-1)), measured up to three months after installation, were accredited to the salt content of ruptured stem cells. After curing of the installation wound the insulating effect of the cells' membranes may explain the lower sigma(a, stem) (2-5 x 10(-2) dS m(-1)) measured 3 to 12 mo after installation. Periods of theta(soil) increase (day of year [DOY] = 80-200, and 200-280) observed by the soil probes indicated surplus irrigation. Presently the rate, intensity, and variability of the grapefruit stem reaction to soil water status and salinity leaves the soil parameters as better indicators for accurate irrigation scheduling.
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