Soil moisture measurement for better irrigation management

Question

Dear friends, I want to know some user-friendly and cheap solutions for measuring soil moisture at farm level. I am trying to optimise the water use in agriculture for irrigation. If you have used any moisture sensor which provides correct results, please share information with me. Let me tell you that the Tensiometers are not suitable for us as the soil characteristics are different across the field at our project area. Please share your suggestions for measuring soil moisture at farm level.

Gabriel Camhi · Answer

Measuring the soil moisture of soil, without knowing the Retention Curve, is of no use, since the same moisture level in two different soil, have a completely different meaning. We use very precise tensiometres fixing the ranges according with the Retention curve data and have excelent results.

Prem Baboo · Answer

Daer Sam Following ways to measure soil moisture:
Electrical Resistance Blocks —A meter is used to read the electrical resistance of moisture blocks installed in the ground. The blocks come in a variety of configurations but generally incorporate two electrodes imbedded in a gypsum material .The block may be entirely gypsum or covered with a porous material such as sand, fibber glass, or ceramic. Meters are portable and are intended for use in reading a large number of blocks throughout one or more fields. Since the blocks are porous, water moves in and out of the block in equilibrium with the soil moisture. Meter resistance readings change as moisture in the block changes which, in turn, is an indication of changes in the amount of water in the soil. The manufacturer usually provides calibration to convert meter readings to soil tension. Proper installation is important for reliable readings. Good soil contact with the block is essential. Resistance methods are suitable for most soils, and the readings cover most of the soil moisture ranges of concern to irrigation management. The blocks tend to deteriorate over time, and it may be best to use them for only one season. Problems may occur with highly acid or highly saline soils Tensiometers —soil moisture tension tells you how easy it is to extract water from soil. When a soil is saturated, there is plenty of water in the pore spaces and plenty of water coating the soil particles. All this moisture makes it very easy for plant roots to get water and the soil moisture tension is low.This is a sealed, water-filled tube with a vacuum gauge on the upper end and a porous ceramic tip on the lower end. The tensiometer is filled with water and the porous tip is buried in the soil to the desired depth (Figure 3). Tensiometers have been called mechanical roots since they provide an indication of how hard it is for the plant to get water from the soil. Tensiometers measure soil water potential or tension. Water in the tensiometer will come to equilibrium with water in the soil. Readings are an indication of the availability of water in the soil. Readings are in centibars (1/100 of a bar). A reading of 100 is equal to 1 bar of tension. Tensiometers generally are effective only at less than 85 centibars of tension, because the gauge will malfunction when air enters the ceramic tip or the water in the tube separates. The usable range from 0 to 85 centibars, however, is the most important range for irrigation management. Properly installed and maintained, the tensiometer provides an accurate measurement of soil tension. It is not suitable where soil tension routinely exceeds 85 centibars. Even though portable units are available, tensiometers are normally planted or installed at one location for the duration of the irrigation season. Tensiometers do not directly give readings of soil water content. To obtain soil water content, a moisture release curve (water content versus soil tension) is needed. Feel Method —A soil probe is used to sample the soil profile. Soil moisture is evaluated by feeling the soil. Then a chart is used to judge relative moisture levels. It is important to sample numerous locations throughout the field as well as several depths in the soil profile Portable Measuring Devices —Several types are available for estimating soil moisture. Most have electronic meters and use either resistance or capacitance technology. Some use the same principle as a tensiometer. Gravimetric Technique -The classical method of measuring the amount of water in a soil sample is to use the Gravimetric Technique. This method involves taking a volume of soil, accurately weighing it, completely drying it out in an oven, re-weighing the dry sample and calculating soil moisture percentage from the weight loss. This is a time consuming and painstaking procedure Radioactive Technique -A method which uses radioactivity is called the Neutron Probe technique. Because of the radioactive transmissions, these instruments are very expensive and measurements need to be taken by qualified personnel. Usually the services of a Neutron Probe company are employed to take soil moisture percentage readings on a weekly basis. Shafts are permanently installed at the measurement site which the Neutron Probes lowered each time the readings are taken. This method is expensive and inflexible. Measurement sites are not easily changed, and readings are infrequent. Regards Prem Baboo

Rieks Bosch · Answer

contact wageningen agrcultural university or DACOM http://www.dacom.nl/

Dr Johan Aad VAN DIJK · Answer

Please have a look at this one... Hope it helps.

shankar mallipatna · Answer

A conventional age old practice is pan evaporation method. Google pan evaporation to find plenty of information. Alternatively, sensors with remote wireless display unit.

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