Tools to help with irrigation scheduling
By Dan Woolley
By Dan Woolley
Irrigation scheduling can be a very useful tool to enhance production
and to avoid the adverse effects of over-watering, according to Scott
Anderson, Agriculture and Agri-Food Canada’s regional agro-climate
specialist in Atlantic Canada.
Irrigation scheduling can be a very useful tool to enhance production and to avoid the adverse effects of over-watering, according to Scott Anderson, Agriculture and Agri-Food Canada’s regional agro-climate specialist in Atlantic Canada.
Anderson’s Agri-Environmental Services Branch has been co-operating with the provincial departments of agriculture on soil moisture monitoring projects. “What we are trying to do is measure the amount of water in the void spaces between soil particles.”
The branch’s field researchers are looking at field capacity – the ability of soil in a field to hold moisture – and trying to maintain it between 35 to 40 per cent, Anderson explained, adding that a field capacity of 10 per cent is too dry.
“In the past three or four years, we have been looking at differences within the region of relative dryness by evaluating solar evaporation and precipitation (evaporation and transpiration),” he said.
As soil dries out, the soil moisture tension increases, Anderson explained. Once it increases to 45 kilopascals in carrots, for example, anything higher than that indicates dry conditions. In potatoes, an opportune time to irrigate would be at 50 kilopascals, he said, adding that he uses a tensiometer to measure soil tension.
“It is cheap and easy to use.”
But it can give misleading results, Anderson warned, especially if the ceramic tip on the probe touches a rock or sand.
Another tool the climate specialist uses is a Hydrosense moisture probe, which measures the volumetric water in the soil by measuring the soil’s electro-conductivity.
“It is very accurate and costs about $1,600.”
An evapotranspiration weather station costs about $2,000 and can measure the rate of evapotranspiration from soils and plants within the field it is installed in. It is very easy to use and displays the current soil moisture conditions, said Anderson, noting that whether the crop rows are directed north-south or east-west will result in totally different readings.
Another tool Anderson uses is the Watermark sensor probe. It is sunk to varying depths of six, 12, or 18 inches to measure rainfall and irrigation events.
“At 18 inches, there are very few roots but it can tell you if you are over watering,” he said.
Once the probes are installed in the field, the field weather station can download data from them. Anderson said he uses the Hydrosense and Watermark sensors because they are accurate, reliable and less prone to soil compaction related errors.
“(They) also produce better graphical results,” he said.
The monitoring technology they are now using in the field can be used as a water conservation tool. “In some cases we are now telling producers to use more water,” said Anderson. “The grower interest is very high. They are getting more comfortable with the concept of irrigation scheduling.”
A number of growers are interested in connecting field probes and weather stations to their farm office computers and researchers are also looking at using cell phones to report on conditions from field weather stations, he said.
Web-based GIS is another option being pursued in the western provinces, he added.