Soil Moisture, Soil Electrical Conductivity and Tomato Root Distribution of Automated Drip Irrigation System Controlled by Soil Moisture Sensors.

The use of soil moisture sensor (SMS) and irrigation scheduling techniques has been shown to increase irrigation water use efficiency and reduce the potential N-leaching losses. During the spring of 2006 and 2007, field experiments were conducted to evaluate the use of SMS and subsurface drip irrigation (SDI) on soil moisture and soil electrical conductivity (EC) patterns in the soil profile, in addition, to evaluate the tomato spatial distribution and density of roots as function of soil water availability and soil nitrate movement. SMS control system treatments irrigated depending on the volumetric soil water content readings up to a maximum of 5 irrigation events could occur per day totaling 2 hr, and the amount of application time equivalent to the once a day (TIME) fixed time treatment. Fertigation occurred weekly. Soil moisture content and EC in the soil profile were monitor by capacitance probes. All of the SMS based treatments irrigated for short periods of time and resulted in a relatively small increase in soil moisture, consequently decreasing the volume of percolate. SMS and SDI irrigation treatments showed higher EC values in the 0-25cm compared to TIME, which showed higher EC spikes in depths below 25cm. There was a higher concentration of roots closer to the irrigation and fertigation drip lines independent of the irrigation treatment. At the beginning of reproductive phase about 70-75% of the root system was distributed in 0-15 cm depth layer and about 15-20% of the roots were found in the 15-30 cm depth layer. In the middle of the reproductive phase 68% and 22% of the root system were found at 0-15 and 15-30 cm depth layer, respectively. Higher concentration of roots below 30 cm depth for TIME The root distribution in the soil profile appears to be driven by soil moisture and nutrient availability.