A low cost soil monitoring system which can measure soil moisture, soil temperature, atmospheric temperature and relative humidity has been developed. the system is modular and consists of different units like sensing unit, energy harvesting and management unit, and data management unit. the advantage of this modularity is that the same instrumentation can be used with any sensor by making output of the sensor in a compatible range with the instrumentation unit. the developed system can be deployed in agricultural farms and polyhouses for controlled irrigation and precision farming, which will result in a significantly improved yield. soil moisture sensor in this system works based on capacitive based measurement using variation of the permittivity (or dielectric constant) of the material with the moisture. we have adopted two approaches for this purpose. in the first approach, soil is a part of the measurement system, of which the permittivity naturally varies with the moisture. the permittivity is then converted to the frequency using an oscillator and the frequency of oscillation is measured and mapped to the volumetric moisture content. in the second approach a moisture sensitive polymer is embedded between the two parallel plates of a micro-fabricated capacitor. the dielectric constant of the polymer changes with the density of water molecules and this change is converted to an automatically measurable voltage. similar polymer based capacitive sensor is used for determining ambient humidity by the system. rtd (resistance temperature detector) is used for the soil temperature measurement and ic lm 35a is used for ambient temperature measurement. the system is equipped with a rechargeable li-ion battery, which can be recharged using solar energy. the system can continuously work for 3 days without recharging. soil moisture sensor systems need calibration. to have a complete solution, we have also developed a relatively low cost system with higher accuracy based on time domain reflectometry (tdr) principle. tdr system generates periodic pulses with sharp rising edges and sends them along the probes in the form of electromagnetic waves. probes act as transmission line, which are first inserted into the soil during calibration only. transmitted wave reflects back from the open end of the probes. traveling time of the wave along the probes depends upon the dielectric constant of the medium, which is a function of the moisture content. this system is independent of the soil type and can be used to calibrate different types of soil moisture sensors. the developed tdr can be also used as a standalone tool for the laboratory and civil engineering applications where accurate measurement of soil moisture is necessary. the developed system has been prototyped in two models as explained below. handheld model – this model of the system is made for farmers who have relatively small holding. the system provides visual indication about the soil moisture content using a coloured led array. using this indication, the farmer can take decision about the irrigation. wireless sensor node model - the measured parameters are processed and the results are transferred wirelessly to a mobile/base station (in the same filed or anywhere else) where decision making for irrigation cycle can be automatically or manually made. this decision making is based on a database, stored on a computer, based on the type of soil and the crop. to add further smartness to the system, and to predict the crop water requirement in advance, we are model the evapotranspiration rate for the crop based on the fao (food and agriculture organization) penman monteith equation. this equation has been universally accepted across the world by the agricultural scientists to estimate the crop water requirement with minimum error. the evapotranspiration rate depends on the soil moisture, ambient humidity, solar radiation (soil temperature and ambient temperature), velocity of the wind and geographical location.