The Journal of Experimental Botany describes irrigation scheduling as "conventionally aimed to achieve an optimum water supply for productivity, with soil water content being maintained close to field capacity. In many ways irrigation scheduling can be regarded as a mature research field which has moved from innovative science into the realms of use, or at most the refinement, of existing practical applications. Nevertheless, in recent years there has been a wide range of proposed novel approaches to irrigation scheduling which have not yet been widely adopted; many of these are based on sensing the plant response to water deficits rather than sensing the soil moisture status directly (Jones, 1990a)."
"Irrigation scheduling is conventionally based either on ‘soil water measurement’, where the soil moisture status (whether in terms of water content or water potential) is measured directly to determine the need for irrigation, or on ‘soil water balance calculations’, where the soil moisture status is estimated by calculation using a water balance approach in which the change in soil moisture (Δθ) over a period is given by the difference between the inputs (irrigation plus precipitation) and the losses (runoff plus drainage plus evapotranspiration). Soil moisture measurement techniques have been the subject of many texts and reviews (Smith and Mullins, 2000; Dane and Topp, 2002)" The former category relying on direct soil moisture measurement is a more reliable method, especially with hourly measurements as current data cancels the need for additional data. Continuous data adapts and reacts to changing weather and other variables that would otherwise make precision irrigation scheduling a guessing game. The Journal of Experimental Botany indicates that the "the water balance approach is not very accurate".
With increasing water restrictions and unpredictable dry-spells irrigation scheduling is fast becoming a crucial tool for sustainable farming. A farmer is able to accurately control their water usage through irrigation scheduling and thereby contribute to sustainable farming practices. Therefore the farmer cannot afford to use inaccurate methods of irrigation scheduling as this would impact on crop yield and soil health.
According to Agriculture and Agricultural Science Procedia "Water is considered as the most critical resource for sustainable agricultural development worldwide. Irrigated areas will increase in forthcoming years, while fresh water supplies will be diverted from agriculture to meet the increasing demand of domestic use and industry. Furthermore, the efficiency of irrigation is very low, since less than 65% of the applied water is actually used by the crops. The sustainable use of irrigation water is a priority for agriculture in arid areas. So, under scarcity conditions and climate change considerable effort has been devoted over time to introduce policies aiming to increase water efficiency based on the assertion that more can be achieved with less water through better management" (Konstantinos Chartzoulakis, 2015).
Precision irrigation scheduling, therefore, would become a critical tool for farmers. Precision engineered equipment (probes, nodes, valve actuators and web-based software) are vital tools of the trade that allows the farmer to essentially "see" in the soil and therefore make informed decisions about watering needs.