Complete Center Pivot Automation Using the Temperature-Time Threshold Method of Irrigation Scheduling.

Abstract

It has been shown that the temperature-time threshold (TTT) method of automatic irrigation scheduling is a viable alternative to traditional soil water based irrigation scheduling in the Southern High Plains. The TTT method involves using infrared thermocouples (IRTCs) to remotely examine crop canopy temperatures over the course of a day. If a threshold canopy temperature is exceeded for a predetermined threshold time an irrigation event is scheduled. Applying this method using IRTCs mounted on self propelled irrigation systems such as center pivots or linear moves presents special challenges. First, it necessitates a method of estimating the diurnal canopy temperature dynamics using only a one-time-of-day canopy temperature measurement. Secondly, it requires a method of automatically collecting and analyzing the canopy temperature data and controlling the moving irrigation system based on the data analysis. A method of determining the diurnal canopy temperature curve using a one-time-of-day temperature measurement and a reference temperature curve was developed. The mean absolute error from calculated to observed was approximately 0.5° C from 0800 h to 2200 h. An array of 16 IRTCs were connected to a datalogger and mounted on a three tower center pivot. A separate array of IRTCs was located in stationary positions in the field and also connected to a datalogger. Two different spread spectrum (900 MHz) radios were connected to a desktop computer located nearby that queried both dataloggers, and got pivot status information and send commands to the center pivot control panel. Using scheduled data collection intervals, this computer was able to collect the data, analyze it, determine need for an irrigation event, and issue control commands thus completely automating the center pivot.