Sensor Development and Positioning for Efficient Irrigation in the Inherently Variable Agricultural Field.

The agricultural field and conditions are characterized by high spatial and temporal variability. This variability comprises of soil moisture distribution: due to non-uniform rain or irrigation rate, water uptake, level of ground water; soil properties and content: type, structure, depth, organic matter, salinity; cultivation history: wheel vs. plow tracks (i.e compaction), spray and fertilizer application history; climate: Northern vs. Southern slopes, winds, local topography, shade, daily and seasonal climate; crop: genetically born variability, stand, seeding variations, growth stage. As a result the field’s physical, chemical and biological characteristics (micro-organisms and roots) are local and difficult to measure and describe. Moreover, any single sampling is not representative enough of the field. Therefore, a large number of sensors to measure soil / plant / climate parameters is required to describe the entire field. Another complication in agricultural practice is the fact that the roots which are “our real customer” are hidden, which increase farther uncertainty in inputs application and inefficiency.

Because of all the above mentioned obstacles the efficiency of agricultural inputs is low even where precision agriculture methods which are based on models and sensors are applied. For example, Irrigation efficiency is 30-60% (even drip irrigation efficiency is less than 70%), fertilizer efficiency is 30-40%, and pesticide efficiency is similar.

Mini nuclei of artificial media which is a superb and preferable for root growth that are introduced into the root zone of the entire agricultural field, can serve as “root trap” and as a standard medium to measure root status and to respond in real time to the plant needs. An application for drip irrigation is presented where the effect of sensor location in a spatially varied field on water application is determined showing minimum variability and maximum irrigation efficiency where the sensor is located immediate to the dripper. A practical solution was developed where bands of geotextile that surround subsurface drippers and serve principally at tensiometers to measure the root water potential.  Results of many crops, soil types, seasons and climate show a decrease of about 30 percent in water use and 20 percent yield increase when compared with best current practices.

The use of the standard dripper–geotextile sensor decreased the inherent natural variability and produced an instant response to changing climatic boundary conditions.