Dominic Sween BRAE 236 11/02/11 Laboratory 5: Soil/Plant Water Determination In the soils lab, the concept of SMD (Soil Moisture Depletion) was clearly demonstrated both in theory and practice. Also, the class was shown several different devices that are used to compute the relative SMD of a given field. It is important to note that not any one device is 100% correct. Since there are so many variable when measuring SMD, most measuring devices will differ from each other. Since most fields are not completely uniform in their root zone composition, it is impossible to get an accurate representation of the whole field only using one measurement. One device that is used in determining when the soil needs water is the tensiometer. Tensiometers have a limited range that goes from 0 to 80cb. These devices are very sensitive to telling growers when to irrigate, but they do not tell how much to irrigate. Another device that tells when but now how much to irrigate is the resistance meter. Resistance meters usually have a gypsum block on the end that can measure
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