TR(BR)-16/97-98 : Development of instrument for automation of irrigation scheduling and ground water recharge monitoring using soil moisture measurement

Abstract

Proper characterization of soil water status in the root zone can lead to better predictions of when to irrigate a crop and how much water to apply to a field. This will result in better water conservation practices and prevention of chemical leaching. But, soil moisture in the unsaturated zone is in a dynamic state. Under influence of precipitation, evapotranspiration, etc. the moisture content in a soil profile continuously varies with time.

Effective study and management of the soil-plant-atmosphere continuum will require knowledge bases combining appropriate mathematical models and expert systems, utilizing data from an effective sensor network. However, development of expert systems and complex integrative models for irrigation scheduling, etc. has been limited because of extensive data collection requirements in the field. Numerous sensors need to be monitored on a periodic basis appropriate to the scale associated with water movement in the field. For such applications, rapidly responsive sensor networks would replace labour intensive hand measurements, which are often unreliable. in the field.

The report presents development of a sensor system capable of automated measurement of soil water status, using the four-electrode resistivity (VES) method. in a soil profile. In this method, by changing the separation between two electrodes (metallic rods) placed at the ground surface (without digging any holes), the variation in moisture content in the subsurface soil profile can be monitored. The analysis of the apparent resistivity variations at different electrode spacings make it possible to draw conclusions about the sub surface conditions (e.g. variations in the amount of moisture content in formation). The state-of-art microcontroller based design, with on-board software, makes the instrument suitable for near real-time analysis of the measured data. The data obtained from this instrument can be directly used in various simulation models.