Wilting point is one of the critical indicators of vegetation health. If the wilting point of crops is low or crosses the bare minimum, plants are permanently damaged and will die. So, it is important to prevent them from reaching the permanent wilting point. It is feasible with ongoing soil moisture and crop state monitoring, and satellite imagery assists in the remote control.
What Is The Wilting Point?
It is the soil moisture that crops can absorb; otherwise, they will wither. Wilting point is reached when available moisture drops lower than a plant can get. The deficiency may cause either temporary or permanent withering.
Wilting point is a ratio of moisture content to dry earth weight or volume. Its percent expression (of the dry weight) is the wilting coefficient.
Wilting point of soil is not a unique value. It correlates with multiple factors:
- soil type (texture, porosity, compaction, structure);
- air and soil temperature;
- osmotic stress due to soil salinity;
- spreading of plant roots;
- specifics of transpiration;
- moisture throughout the soil profile.
Does Wilting Point Vary For Different Plant Species?
Yes, it depends on the crop type but is typically about -1.5 MPa (-15 atmospheres/bars), which is common for sunflower, wheat, or corn.
Does The Wilting Point Depend On Soil Texture?
It does. Soil moisture volumes at the soil wilting point are approximately 15-20% in clay soils and just 5-10% in sandy ones. Finer soils have better water-retaining capacity. However, wilting point depends on the soil texture and its porosity that predetermines the ease of roots’ growth and their capability to uptake soil moisture. This is why hairy roots in silty sand absorb water better and survive twice longer than coarse root systems in clay loam, even despite moisture present in the soil matrix.
What Happens Once A Plant Reaches A Temporary Wilting Point?
As the term suggests, crops droop at this level but temporarily. It is typical on hot days under a lack of soil moisture. At the temporary wilting point, crops recover once the air temperature falls or after rewetting.
Foliage may droop even under sufficient air humidity and won’t return to its firm condition until the roots can absorb enough water.
What Is The Permanent Wilting Point?
It is the lowest amount of moisture plants require not to wither irrevocably. Unlike in the state of temporary withering, crops can’t return to their normal activity even after soil moisture is replenished. Drooping usually happens because the transportation of water from the roots decreases. When it occurs, plants limit photosynthesis and transpiration due to lessened stomata turgor pressure (stomata are small holes on the leaf surface). If water availability drops below the critical level, it eventually means yield loss.
Why is a permanent wilting point for various species different? Needle-leaved plants like cacti are naturally protected from water evaporation that causes withering. Besides, root systems and osmotic resistance also differ in different crops.
Permanent Wilting Point Signs
Withering crops reveal drooping leaves that later fade and dry out. Vegetation foliage doesn’t droop simultaneously. Withering starts from basal leaves and then shows in apical ones. These two stages are known as the first and ultimate permanent wilting points correspondingly.
Why Can’t Plants Absorb Water At The Permanent Wilting Point?
When plants wither, it doesn’t mean that there’s no water in the ground at all. There is, yet it is not available to crop roots because soil particles hold moisture too strong and its amount is generally small.
What plants can get water under the permanent wilting point? Typically, agricultural crops can’t absorb any moisture if tension drops below -1.5 MPa, which is considered the critical limit. Yet, the creosote bush (Larrea divaricata) gets water in deserts even at -6.0 MPa.
Wilting Point Among Other Causes Of Crop Withering
Lacking moisture in the root zone is the most common cause of withering, and vegetation survival depends on the root system, soil type, and the temporary or permanent limits for the individual crop. If temperatures drop overnight, plants have a chance to recover. Yet, combined with other unfavorable circumstances like dry winds or long droughts, yield losses will be even higher. Also, crops are especially sensitive to water stress at certain development stages. For example, soybeans are the most vulnerable to water stress during the period of flowering to pod filling.
However, foliage drooping does not always mean the crop has approached the soil wilting point. For example, not only water deficiency but overwatering may lead to withering because waterlogged roots are deprived of oxygen and subject to crop diseases like rots. So, it is critical to monitor fields and save plants by managing permanent wilting point signs early or avoiding the problem with properly scheduled irrigation events.
EOSDA Crop Monitoring For Wilting Point Control
The best way to prevent plants from withering is through the ongoing measuring of this parameter considering the crop type and field specifics. However, satellite imagery can be also helpful in wilting plants monitoring, and EOSDA Crop Monitoring provides a lot of useful analytics for farmers. The most valuable features in this regard are:
- monitoring various vegetation indices to identify withering;
- tracking NDMI values to detect water content drops in plants;
- analyzing root zone and surface soil moisture to adjust irrigation to avoid water deficiency in plants.
By comparing vegetation indices and NDMI values, it is possible to understand their correlation. If there is any, the field should be inspected for factors that may cause withering. With no causes detected, it is necessary to measure the wilting point and take proper actions if needed.
Does irrigation increase soil wilting point? It does. Soil moisture must be timely replenished to support proper crop growth. This is why artificially irrigated crops should be never allowed to reach their permanent withering limits.
EOSDA Crop Monitoring To Meet Your Agribusiness Needs
EOSDA Crop Monitoring is an effective management tool for small and large-scale farming. The EOSDA satellite-based platform can also be beneficial for insurance companies, agricultural equipment producers, chemicals and seed suppliers, and other business entities. Integration of satellite analytics into all existing systems will not only help you get more data faster as such but optimize your facilities’ use. Furthermore, the obtained insights will allow well-grounded business decision-making and understanding of relevant customer needs.
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Vasyl Cherlinka has over 30 years of experience in agronomy and pedology (soil science). He is a Doctor of Biosciences with a specialization in soil science.
Dr. Cherlinka attended the engineering college in Ukraine (1989-1993), went on to deepen his expertise in agrochemistry and agronomy in the Chernivtsi National University in the specialty, “Agrochemistry and soil science”.
In 2001, he successfully defended a thesis, “Substantiation of Agroecological Conformity of Models of Soil Fertility and its Factors to the Requirements of Field Cultures” and obtained the degree of Biosciences Candidate with a special emphasis on soil science from the NSC “Institute for Soil Science and Agrochemistry Research named after O.N. Sokolovsky”.
In 2019, Dr. Cherlinka successfully defended a thesis, “Digital Elevation Models in Soil Science: Theoretical and Methodological Foundations and Practical Use” and obtained the PhD in Biosciences with a specialization in soil science.
Vasyl is married, has two children (son and daughter). He has a lifelong passion for sports (he’s a candidate for Master of Sports of Ukraine in powerlifting and has even taken part in Strongman competitions).
Since 2018, Dr. Cherlinka has been advising EOSDA on problems in soil science, agronomy, and agrochemistry.