Soil is the basis for agricultural management, and water is of vital importance to plants, not only as a building material, but as a transport medium of nutrients to the plant. But plants are not the best at utilizing water, only 1% of water that is taken up is converted into biomass. Therefore, it’s important for soil to maintain the functionality of water storage and supply for optimal plant growth.
Soils are natural drainage systems, which ensure aeration and adequate supply of oxygen and other nutrients to plant roots and soil biodiversity. When exposed to excess water, these drainage systems work to move water through the soil levels to the groundwater table – while undergoing periods of drought, plants will have to survive on water reserves built up in wet periods. This is why monitoring soil moisture is so important, not only for plant health but for soil viability as a resource for agricultural management.
Soil is the variable
There are multiple activities which influence a soils’ water holding capacity and can therefor influence the moisture values derived from monitoring tools. Key factors influencing soil moisture are:
- Terrain accents, like higher areas, lower areas, sloping, shade etc.
- Crop type (root depth)
- Soil type (and differences in soil type across fields or projects)
- Organic matter content
- The underground (hard pans, underground water flows, etc.)
- If irrigated: the number of irrigation zones, valves, lines
Soil moisture levels can change drastically within very short distances. This is largely due to the reasons listed above, which is why measuring soil moisture needs to be done at multiple points across a field. Soil isn’t homogeneous, and (hyper)local soil moisture measurements are needed to get a good picture of soil moisture levels across a field, which is the key reason why Sensoterra sensors have a low Total Cost of Ownership (TCO).
It’s our belief that in order to have a complete picture of water behavior within a soil, more datapoints are necessary across a field, rather than just one centralized location.
How many sensors do we need on our farm or project?
Unfortunately, there is no ‘golden rule for the number of sensors per hectare’, but from practical experience we know that a good total picture can be derived from some cleverly placed sensors.
Based on the above factors and years of experience in field, we have developed a couple or rules-of-thumb:
- Terrain accents: if there are altitude difference in fields and/or landscaping projects, it can be assumed that the higher parts are drier, and the lower parts are more wet. This simple physics (gravity), and higher parts are often more exposed to wind and solar radiation. If a field has a higher part and a lower part, we advise at least 2 sensors – one for each scenario. Additional insights can be provided by one or more sensors in the ‘middle’.
- Crop type: if different crops are grown, with different characteristics like for example root depth, leaves, canopy density, and moisture preference, we advise to place at least one sensor per crop type.
- Soil type: different soil types show different moisture behavior. Sandy soils behave completely different than clay soils. If both soils are present in a field or landscaping project, both should be measured.
- Organic Matter: The presence of soil organic matter is relevant as water molecules will bind to organic matter and remain present longer in soils with organic matter than those without or with minimal levels.
- Compaction: Infiltration rates are influenced by soil compaction, where high levels of compaction reduce the water holding capacity, as well as increase topsoil erosion from water and nutrient runoff.
- The underground: this can be a tough one, because we can’t ‘look into the soil’. For example a hard pan can prevent water to infiltrate into lower levels, leading to wet patches. Often, soil moisture sensors are an ‘early warning’ system, giving an indication that a certain area needs to be examined further.
- Irrigation system: for irrigated land/projects, one could choose to put one sensor in every irrigation zone. Of course, this can also be aggregated to 1 sensor per X irrigation zones. Furthermore, with drip irrigation systems or in an orchard, it can be insightful to put multiple sensors along an irrigation line.
Of course, in very large areas It might not be economical to place one sensor per hectare or even one per 2 hectare. In these cases, we advise to split up the terrain or project in ‘zones’ with similar characteristics. A good way to identify these areas is by integrating moisture data from satellites.
By the way, it is often thought that satellite data competes with sensors. We think satellite data is extremely useful and should be used, but it does not provide the insights of real time measurements in the root zone of the plants. Hence the data should be combined, to get the best insights to support decisions.
For more information, visit www.sensoterra.com