ISHS Acta Horticulturae 664: IV International Symposium on Irrigation of Horticultural Crops
MONITORING SOIL MOISTURE WITH INEXPENSIVE DIALECTRIC SENSORS (ECHOPROBE) IN A CITRUS ORCHARD UNDER LOW VOLUME IRRIGATION |
| Authors: | N.V. O'Connell, R.L. Snyder |
| Abstract:
A field experiment was established in a 35-year old navel orange orchard near Lindsay, California to measure crop evapotranspiration with the surface renewal method. As part of the experiment, dialectric soil moisture sensors (Echoprobe ®. from Decagon, Inc.) were installed to monitor changes in soil moisture content during the irrigation (April-October) and rainfall (October-April) seasons. The trees were planted at a distance of 6.0 m in the row and 6.4 m between rows for a total of 256 trees per hectare with the orchard floor maintained weed-free by means of herbicides. A low volume irrigation system with one microsprinkler per tree delivering 38 liters per hour was used for irrigation. The sprinkler rows are positioned on the south side of the tree row with heads located at about halfway between the trees and near the drip line. The sprinkler heads have a 360o pattern and throw water with a radius of about 2.5 m. Dielectric (Echo) soil moisture sensors were installed vertically at 0 to 0.3 m and 0.3 to 0.6 m depth at four locations under the tree canopy near the tower supporting the surface renewal monitoring equipment. The sensor locations were (1) within 0.5 m of the sprinkler head, (2) halfway between the sprinkler head and the tree trunk, (3) near the tree trunk, which is about 2.5 m from the head and (4) in the drip line on the opposite side of the tree row. The measurements were recorded with a battery powered data logger. When the sensors worked properly, they showed extraction patterns well and the soil water depletion was related to crop evapotranspiration. However, data were only collected down to 0.6 m and deeper measurements may be needed. Because of the large variation in sprinkler throw pattern, it was difficult to determine the absolute water usage by the trees. However, by monitoring the change in soil water content near the sprinkler head, the sensors could be used to help time irrigation. | |
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