Using Sensor Networks for Precision Irrigation and Nutrient Management in the Nursery and Greenhouse Industry

The nursery and greenhouse industry ranks 5th in US farm gate receipts and is in the top five commodities produced in 26 states. Over 75% of nursery crops in 17 states are grown in containers and since lightweight soilless substrates are used, daily irrigations are usually needed.  Precision irrigation scheduling is the key to effective nutrient management, by limiting water applications and hence the leaching of nutrients from containers.  Precision irrigation is difficult, because of the large number of species grown and most growers irrigate with timed applications, on a block-by-block basis.  Gravimetric, tensiometric and ETo methods have been adapted for use in these operations, but most growers still rely upon subjective methods to schedule irrigations, since technology has been imprecise and/or difficult to implement or manage.  We are using wireless sensor networks connected to a variety of capacitance and electrical conductivity sensors, to provide us with real-time data on soil and substrate moisture status, at the micro-scale level.  These sensors provide us with precise substrate moisture readings, and by using substrate-specific calibrations, with accurate matric potential and electrical conductivity measurements in the root zone.  The data is transmitted wirelessly from the field to a computer in the office, where it can be viewed graphically by a user with minimal computer experience, to better schedule irrigation events.  We have also developed an independent irrigation scheduling “micro-pulse” control capability, whereby individual nodes in the field use 4-8 local sensors to automatically operate a solenoid in short 2-second intervals, based upon matric potential readings that are monitored every minute by that node.  This automatic control capability is essential for greenhouse operations that may require irrigation scheduling up to twenty times per day (e.g. cucumber production), to minimize leaching fractions.   We have been able to reduce water applications for four different woody perennial species to between 10% and 20% of best management cyclic scheduling techniques, thereby minimizing leaching fractions and nutrient loss.  We are working toward improving sensor performance through our precision calibration techniques, by incorporating more advanced node designs with longer-range radio cards and power optimization features, and by developing more advanced graphical and statistical software for monitoring and control purposes.