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Managing our Environment

Land Information Help

Irrigation Management

What is Evapotranspiration?

Evapotranspiration (ET) is the combined loss and use of water measured in millimeters(mms) by a crop or pasture including evaporation of surface moisture from the crop environment and transpiration of water by the plants. Knowledge of the current ET is useful for all farming and horticultural systems particularly when managing irrigation.

ET results from the combined effects of solar radiation, air temperature, the movement of air past the plants and crop surfaces, and the humidity of that air.

When plenty of water is present in the soil, then ET is highest on sunny, windy days, during the warmest months of the year, and often exceeds 5-6 mm per day in Otago. ET is typically less than 1 mm per day in mid winter, when the solar angle is low and air temperatures are cool.

Dairy shed effluent management - Southwest Otago

Soil moisture content and dairy shed effluent application

To apply dairy shed effluent safely to land without resulting in contamination to waterways the soil moisture content must be well below field capacity.

An aquaflex unit installed on "Lonehill" on Pannetts Rd near Clydevale records soil moisture and temperature daily. This information is displayed in graphical form to demonstrate when the soil moisture content is suitable for applying dairy shed effluent to land.

Soil cracking and lower soil moisture conditions

Soil cracking will gradually show up when soil moisture conditions reach lower levels during prolonged drier periods. Effluent applications will need to be carried out with extreme care during these periods and may include delaying effluent application until there is a recovery in soil moisture conditions with the onset of wetter conditions.

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