Review of indices for precision irrigation decision-making

According to the theory of soil-plant-atmosphere continuum,there are three types of indices for precision irrigation decision-making,including soil moisture,plant water status and weather conditions. This paper reviews the researches and developments in these regards. The technologies for soil water monitoring and measurement have lately made great progress,such as time domain reflectometry,microwave,near infra-red radiation,etc. The plant water status,indicated by the leaf ture,shrinking or swelling of stems or fruits,the capacitance or resistance of crop stem,etc,has been used as indicators for irrigation decision-making. And the temperature difference between canopy and its ambience,including the sap flow of plant, will be a better method to study the crop water status from the literature reviews. The crop reference evapotranspiration,estimated from meteorological data with methods such as the Penman-Monteith method recommended by FAO,is useful for precision irrigation decision-making. And it is concluded that the combination of the applied multi-indices can be used for irrigation management. In this paper,the development of precision irrigation control,as an important part of precision agriculture,is also discussed. The factors,which should be considered for irrigation application at the "proper time" and "adequate quantity" for these purposes,are crop,soil moisture and weather conditions.