Irrigation is an essential practice on sandy soils, and serves to stabilize yield fluctuations on other soils. In the north central United States, water resources are plentiful and irrigation is a sustainable practice (in contrast to more arid regions). Excessive irrigationwater application, however, leads to leaching of nitrogen and pesticides from the soil and into the ground water.

Additionally, the seasonal demand for electricity to pump irrigation water coincides with that for air conditioning demand, creating large peak power requirements.

The scheduling if irrigation which is based on simple water balances has been adopted by many of the potato and vegtable farmers of Wisconsin, who control the majority of the 300,000 acres of irrigated land in the state. Concern over the spatial representativeness of available evapotranspiration estimates, however, adn the inconvenience of attaining this information in a timely manner, reduces more widespread adoption of such environmentally-based scheduling. A DSS for irrigation scheduling is in common use (The Wisconsin Irrigation Scheduling Program, WISP, U. of Wisconsin Cooperative Extension), but the required daily evaporation estimate input is derived from sparse ground-based observations and is not always available to end users on demand. We propose to link this DSS with spacially-complete data inputs provided by satellites and disseminated by commercial services, assuring immediate access. Reduced ground water contamination and energy usage will be realized at the farm level through wider adoption of scheduling that more closely matches crop needs.

Images of Earth from the Goes-8 Weather Satellite, combined with computer analyses created by our team, can yield values of solar radiation anywhere in the country. We tested the ability of the system to measure solar radiation across Wisconsin. Satellite-derived values of daily insolation were compared to those from ground-based pyranometers that are in the Wisconsin Agricultral Weather Observation Network. The results below demonstrate that the satellite is an adequate replacement for pyranometers on the ground.

[Figure from Diak, Bland, and Mecikalski. 199_. A note on first estimates of surface insolation from GOES-8 satellite data. Agric. Forest Meteorol. (accepted for publication)]

Maps of insolation estimated by satellite can then be used to estimate water use by a well-watered crop. We began producing maps of crop evapotranspiration in Wisconsin in the summer of 1995 as seen below:

Since that time we have added color and have been keeping in shape over the winter by mapping evapotranspiration for irrigated vegtables growing in Florida. Our maps are viewed over the World Wide Web by a horticulturalist in Ohio, who then discusses irrigation needs with field managers on-site in Florida. Recent maps are below (note evaporation over ocean areas is probably not right).