Hopeful Hill Ranch - Weather Station

Weather Station

Our weather station - all from Davis Instruments:

Model 6163 wireless weather station

Model 6345 wireless leaf and soil moisture/temperature station.

Model 6440 soil moisture sensor

Model 6470 temperature probe

Model 6510USB data logger and WeatherLink software

Pasture Irrigation

We use the data from the weather station to help manage our pasture irrigation.

In addition to the usual temperature, humidity, wind direction, wind speed, and barometric readings, the weather station also measures evapotranspiration. Evapotranspiration (ET) is the loss of water to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues). It is an indicator of how much water your crops, lawn, garden, and trees need for healthy growth and productivity.

We have added a soil moisture probe and a soil temperature probe. These probes are buried at the top of the clay layer in the pasture and connected to a wireless transmitter (the small white box on the side of the weather station post.) The measurements from these probes are also reported by the weather station. Here is a plot of the ET and soil moisture for the period when we harvested our hay.

[Plot of ET and soil moisture June 13 to July 13, 2007]

[Plot of ET and soil moisture June 13 to July 13, 2007]

The vertical bars are the daily ET measurements in inches of water and the line is the soil moisture measurements in centibars (cB). The higher the centibar value, the dryer the soil. For our clay-based soil, the bottom of the chart (0-10 cB) represents about 2.6 inches of water and the top of the chart (51-60 cB) is 1.25 inches of water.

The ET is water loss and usage. The soil moisture is the amount of water still in the soil. We use these two measurements to determine when to water the pasture and how much water to use. Our goal is to maintain a balance between under- and over-watering. Thus, conserving water while we grow grass for hay.

Near the bottom of the chart are notations for when we watered, cut, baled the grass, and watered again. As soon as we stopped watering the pasture in preparation for cutting, the grass started using the residual water in the soil. Resuming the watering replenished the soil water supply almost immediately.

Montana State University has an excellent chart on Conversion Tables for Automatic Soil Moisture Monitors. We use their conversion charts to interpret the ET and soil moisture measurements.

California ranchers and farmers can use the California Irrigation Management Information System (CIMIS) to get evapotransporation data for their region.