Monitoring soil water content for irrigation scheduling in a carambola orchard in a gravelly limestone soil

Rashid Al-Yahyai, Bruce Schaffer, Frederick S. Davies


Multisensor capacitance probes, tensiometers, and a neutron probe were used for assessing soil water content for scheduling irrigation in an 8-year-old carambola (Averrhoa carambola L.) orchard in Krome very gravelly loam soil in south Florida. Four irrigation treatments were applied when soil water content reached four different moisture set points expressed in terms of percentage of field capacity as determined with multisensor capacitance probes. The tensiometers and neutron probe gave a good estimation of absolute soil water content. The use of tensiometers was limited to a maximum soil water tension of 20 cbar due to air entry into the water column of the tensiometer and water column discharge. The use of a neutron probe by growers is not practical because its radioactive source requires health and safety monitoring, and it is also labor intensive. Soil water content determined automatically and continuously with multisensor capacitance probes and computer software designed for irrigation scheduling can be a practical method of irrigation scheduling in gravelly limestone soils. However, capacitance probes are relatively expensive, labor intensive to install and maintain and gave variable readings of absolute water content among sensors in the same treatment. However, the rate of soil water depletion was consistent among probes. Since irrigation scheduling with multisensor capacitance probes is based on the rate of soil water depletion rather than the absolute soil water content, this method may be an effective tool for scheduling irrigation in orchards with Krome very gravelly loam soil. To achieve this, the pre-set soil water depletion rate at which to irrigate must be related to plant vigor, growth and yield.


averrhoa carambola; capacitance probes; neutron probe; tensiometers

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283