Two of the most common problems with farm irrigation systems have to do with irrigation scheduling. Irrigation scheduling is simply answering the questions of “When do I water?” and “How long do I water?”. Starting an irrigation cycle too early and/or running an irrigation cycle too long is considered over watering. At the very least this practice wastes water and money. However, overwatering can cause crop damage if done on a prolonged basis. Likewise, starting an irrigation cycle too late or not running the system for a long enough period of time is considered under watering and can cause reduced yields and poor crop quality which can affect price. Looking at these problems in depth is the key to minimizing their financial and practical impact on crops.
The two most common methods for dealing with these problems are ET based control systems and soil moisture based control systems. Evapotranspiration (ET) is the combined process through which soil moisture is lost directly to the atmosphere through evaporation and plants taking water out of the soil and transpiring it to the atmosphere. ET is typically a calculated value that takes into account factors such as recent rainfall, relative humidity, solar radiation, and a crop coefficient that accounts for the plant size and stage of growth. The calculated ET will give the grower an estimate as to how much water the soil is losing due to ET. Once he knows how much soil moisture he is losing he can determine how long he needs to irrigation to replace the lost soil moisture.
Soil moisture based control systems use soil moisture sensors to measure the actual soil moisture. This method is typically more accurate the ET calculations because it is actually measuring the moisture level in the soil instead of calculating what should be there. Soil moisture control systems tell the grower when to begin an irrigation cycle and also tell him when the soil moisture level reaches field capacity.
Occasionally ET based control systems are used with some type of soil moisture sensor such as a tensiometer to provide some feedback as to the accuracy of the ET calculations. Whichever method you use, ET or soil moisture based controls provide a much more consistent and reliable method of controlling your irrigation system than the “It looks kind of dry, so I guess I’ll water” method.Soil moisture based control systems use soil moisture sensors such as a tensiometer to provide some feedback as to the accuracy of the ET calculations. Whichever method you use, ET or soil moisture based controls provide a much more consistent and reliable method of controlling your irrigation system than the “It looks kind of dry, so I guess I’ll water” method.to
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