Gaseous irrigation control system: descriptions and phisical tests for performance assessment

Abstract

Irrigas is a water tension measuring system made out of a porous cup (sensor), connected to a gas pressurizing/measuring device by a flexible tube. Water tension (T) is obtained from the equation T=Td-p or T=Ts-p, where Td is the sensor desorption critical water tension (bubbling beginning), Ts is the sensor sorption critical water tension (bubbling ceasing) and p is the applied gas pressure. Differently from conventional tensiometers, the irrigas porous cup cavity is filled with air. This characteristics makes the irrigas system nearly maintenance free and also eliminates the need of making hydrostatic pressure corrections for sensor depth. The system was tested both in the desorption and sorption modes. In the first case the Richards pressure chamber was used to adjus)t the soil water tension which makes the porous cup air permeable. The water tension thus obtained was always practically equal to the Td values measured by the bubbling method, observation that is a physical validation of the barrel immersion technique for irrigas usage for irrigation management. Important for instrument dimensioning, porous cup water loss as a function of water tension measured from zero to Td was diminutive, increased with the soil water tension and was smaller in higher Td porous cups. In the sorption mode, functioning as a gaseous tensiometer, driven by a steady air-flow source, irrigas sensors yielded, directly, water tension readings ranging from zero to Ts. For irrigation scheduling purposes, commercial irrigas water tension systems can be selected according to crop critical water tension requirements.

Soil Water Tension, a Powerful Measurement for Productivity and Stewardship

“…The IBP of a specific porous ceramic can be used to estimate whether a soil has reached the specific SWP used as an irrigation criterion. The National Center for Horticultural Research of EMBRAPA, Brazil, used IBP to develop IrrigasÒ to measure SWT (Calbo, 2004;Calbo and Silva, 2006;Marouelli and Calbo, 2009;Paschold and Mohammed, 2003). Irrigas is a pneumatic system to read soil water tension as a difference between the bubbling pressure of a porous cup and the smallest pressure needed to force air out of the cup.…”