Water is a finite resource. There is no more fresh water being created or found than now exists on earth. The growing U.S. population eyes the 65–70% of fresh water used in irrigated agriculture today. The demand exceeds the supply. The irrigation industry has vastly improved its water use efficiency from the old flood and furrow method of irrigation to much more effective center pivot and drip irrigation. Even center pivot has increased its efficiency further by low pressure sprinkler heads and other innovations.
Irrigation scheduling by center pivot has been done mostly by guess, watching the first and most easily water stressed parts of the field. Unfortunately, many parts of the field with better water holding capacity were over irrigated and even to the point of harming yield. The maps below show a part of the field that a NDVI map indicated was stressed and predicted a reduction in yield. The cause can be seen in the subsoil layer of an EM map that showed a heavier clay layer at that part of the field. Subsequently, water moved very slowly through the soil profile, denitrifying some nitrogen and inhibiting root growth.
Better irrigation scheduling has been implemented with the use of soil moisture sensors to better analyze soil moisture conditions. Proper placement of the soil moisture probe demands an EM map, a topography map and a yield map to best determine the location of the probe. Then, the above information can also be used for variable rate irrigation. Water rates can be varied in center pivot systems by varying the speed of the pivot. Additionally each section of the center pivot can be varying and finally each nozzle for the entire pivot span. Each step up in precision requires a greater investment in control machinery. MISS collects the data from Crop Metrics used to create the variable rate irrigation map.
