Updated: Sep 8, 2020
Monitoring soil water content is essential to help farmers optimize production, conserve water, reduce environmental impacts, and save money. Monitoring soil moisture can help farmers make better irrigation scheduling decisions, such as determining how much water to apply and when to apply it. It can also help farmers match the crop's water requirements with the quantity of irrigation water; and thus avoid excessive water losses to deep percolation, surface runoff or avoid applying an insufficient quantity.
Excess irrigation can increase energy consumption and water costs, increase the movement of fertilizers below the root zone, cause erosion and transport of soil and chemical particles to the drainage channels. Insufficient irrigation can reduce crop production.
Why Monitoring Soil Moisture is Important?
How to Use Soil Moisture Sensors?
Different Techniques for Measuring Soil Moister
Why Monitoring Soil Moisture is Important?
The humidity of the soil makes it possible to preserve the life of the soil fauna and improve the germination and growth of plants. Water in the soil is essential for life. Monitoring soil moisture is therefore decisive in agronomy. Monitoring soil moisture improves irrigation decisions. Providing only the water necessary for the plant at the right time provides increased plant vigor, optimal crop yields, better crop quality, resistance of plants to disease, greater water value and reduced cost of irrigation.
Soil Texture determines its Water Retention Capacity
The capacity of water retention by a soil varies according to its texture and its compaction. The amount of water available for crops differs from one soil to another. Loamy soils can absorb more water, but they also have high drainage rates. The control of irrigation will not be identical in loamy soil or in clay soil.
Several thresholds define soil moisture in agronomy.
Field Capacity is the maximum volume of water that the soil can retain in macro and micro porosities being drained. If we compare the soil to a sponge we can say that this is the moment when the sponge is full, when it no longer drips because all the accessible porosities are full. To know the capacity of the soil in the field, it is necessary to wait two to three days of drying after saturation of the soil by the rains and to make the measurement with a humidity measuring device.
The Wilting Point of the Plant
The wilting point is the level of water at which the plant is no longer able to absorb water from the soil which is retained by soil particles. The plant will wilt. The wilting point of a soil can vary slightly from one species to another.
Soil Water Availability
Soil Water Availability is the amount of water lying between the field capacity and the point of wilting. Irrigation is managed in the plant's hydrological comfort zone. Outside this area, the plant suffers from water stress due to lack of water or lack of air if too much water has been supplied.
How to Measure Soil Moisture?
Soil moisture is measured by soil sampling or using soil moisture sensors fitted in the ground. Capacitive electrodes allow immediate measurement of the water contained in the soil, continuously and at several depths in the root system of plants.
Capacitive probes come in several dimensions and depths which allow them to adapt to all types of perennial crops: apple orchards, plum trees, hazelnut trees, walnut trees, kiwis, nurseries ... up to annual crops: corn, beans, peas, seed beets, wheat, soybeans, ... as well as horticultural crops in field or glasshouse trials.
Capacitive probes have the particularity of having several calibration curves according to the type of soil and in particular its structure which influences its capacity in the field.
There are Different Techniques for Measuring Soil Moister:
This method consists in drying a soil sample and then knowing by second weighing (brought back to the initial weighing) the weight of water contained by the sample.
Reference method, but long, expensive and destructive.
Neutron probe method
This method remains particularly effective but expensive and now much too regulated to be used simply by an operator.
Method by measuring electrical conductivity
This very economical method is unfortunately very imprecise, and remains strongly influenced by the nature of the soil and the salinity of the soil.
An economical electromagnetic method, but with a limited influence volume (1 to 2 cm around the sensor tips) and influenced by the type of soil, temperature and salinity.
Born in the 1980s, the TDR method is an essential method both in terms of the quality and the user-friendliness of its measurements.
The principle of this measurement is based on the determination of the propagation time of an electromagnetic pulse along an electrode introduced into the ground. The propagation time of this pulse depends closely on the humidity of the soil.
Its volume of influence is greater than that of capacitive techniques. The measurement is also weakly influenced by temperature, salinity and type of soil.
This technology allows precise measurements at a price that is now affordable.