Quantitative analysis of soil water content in young drip-irrigated olive orchards

Abstract

The present work was carried out in northern Tunisia (36°40’ N, 10°16’ E) during a single growing season in order to examine how water is distributed within young drip-irrigated olive orchards on the basis of distance to trunk and depth. Soil water content was measured by using a time domain reflectometer (TDR) and a neutron probe calibrated by concurrently measuring soil water content gravimetrically. Measurements were made below the canopies, along the line of drippers and out of the projected canopy area, at distances of 1.4 m, 2.2 m, 2.8 m and 4.2 m from trunks (Compartments G1, G2, G3 and G4), taking into account the heterogeneous distribution of roots. Results showed significant and positive correlations between the series of data collected simultaneously with the PVC and aluminum access tubes and those collected using the different methods and apparatus, demonstrating that any device may be employed, depending only on their availability. Results showed significant changes in soil water contents and stocks according to the season, depth and distance to trunk. During the rainy period, the stocks of water increased homogeneously within all soil compartments, but varied consistently during the dry season with lower values recorded within the upper soil layers. The area situated at 4.2 m from trunks was the driest in summer but it was the wettest during the rainy period. No roots were found at this distance while maximum root densities were observed at 0.4 m from trunk within the upper layers. The lack of water recorded after June affected tree height and fruit growth rates, although irrigation application was sufficient to meet the seasonal crop water needs.