Monitoring stored grain: an overview of connected solutions
Only 10% of farm storage facilities in France are equipped with thermometers (Arvalis, 2018) and grain monitoring during storage is generally limited to grain temperature. In this article, we will review the risks and parameters that are important for proper grain storage. We will then present the latest connected monitoring solutions.
Why monitor grain?
Grain monitoring is necessary to anticipate and prevent losses associated with several storage risks:
Insects are the primary threat to grain after harvest, causing an average loss of 14% of production (source: FAO).
Mold and mycotoxins are also a major problem, especially in hot and humid countries. They are responsible for 25% of post-harvest losses (source: WHO 2018). You can find more information in our article on this topic.
Loss of germination capacity, which can decrease rapidly when grain is not stored under the right conditions (this is also a precursor to the proliferation of insects or mycotoxins).
Important parameters for grain storage
Temperature, grain moisture content, and storage duration are the most important parameters to monitor during storage. They affect insect and mold development and germination.
Temperature
Temperature is a key factor in insect development. Below and above certain thresholds (which depend on the type of insect but are on average 15°C and 45°C), insect development is not possible. However, to eliminate them by thermal shock, more extreme temperatures must be reached: freezing and heating above 70°C.
Water content
The moisture content of grain is a reference parameter in grain storage and a marketing criterion. The moisture content of grain is correlated with the water activity of the grain (noted as aw), the value of which determines the development of mold. Below a certain threshold (aw = 0.7), mold growth is not possible. This threshold corresponds to different moisture contents of grain depending on the species at a given temperature.
There are various methods for determining the water content of grain. The standard laboratory method involves taking a sample of grain and evaporating the water contained in the grain in an oven. The water content (expressed as a percentage) is then:
Water content in % = 100% x (initial mass - mass after drying in the oven) / mass after drying in the oven
The water content of the grain can also be determined from the electrical characteristics of the grain: capacitance and conductance (technology commonly used in portable moisture meters).
Finally, the relative humidity (at equilibrium) of the air around the grains and the temperature can be used, based on a mathematical relationship, to determine the water content of the grains (several similar formulas exist).
Loss of dry matter
Grain deterioration is linked to the respiration of the grain and associated organisms. Respiration is the process of oxidizing carbohydrates, which produces carbon dioxide, water vapor, and energy. As a result, respiration consumes the dry matter in the grain! Grain can lose 0.5 to 1% of its dry matter while heating up, which promotes insect development (Kaleta and Grnicki 2013).
Acoustics
When insects move or feed, they emit characteristic sounds at certain frequencies, providing an indication of their presence. Ambient noise does not interfere with acoustic detection in surveys carried out in grain masses such as trucks, silos, etc. The grain mass being surveyed must be stable. The detection threshold of the acoustic solution is one insect (hidden or visible) per 10 kg, bearing in mind that for one visible insect, there are between 6 and 8 hidden forms (larvae).
Smell and color
During manual inspections and with experience, it is possible to distinguish possible deterioration in the volume of the grain by the smell and color of the grain on the surface of the stock. However, this simple method remains unreliable. Research is underway to design electronic noses to detect the characteristic odors of grain deterioration (heating, mold development, etc...).
Duration
The duration of storage is obviously an important factor. Insect development is exponential over time (if the conditions for development are right) (Robert H. Driscoll model). For this reason, it is advisable to clean facilities thoroughly before storing new grain harvests.
Existing solutions for silo storage
Traditional thermometric solutions
A fairly common practice used since the 1950s involves placing cables equipped with temperature sensors (thermocouples or thermistors) at regular intervals in the grain (stored in silos or concrete granaries). These cables are attached to the top of the structure before it is filled with grain. This solution may be offered as part of the storage system by the manufacturer. Examples include:
Multi-sensor systems
Some companies offer connected systems that measure humidity as well as temperature in the silo and send the information to user interfaces (web page, smartphone app).
Examples include:
Some players offer even more advanced solutions. These devices include precise CO2 measurement to detect the presence of insects or mold growth, as offered by Amber Agriculture. Others, such as AgroLog and Eye-Grain, offer fire detection.
Interface GrainX
Connected traps
Insect traps are "plastic tubes" that are inserted on top of the grain to capture insects in order to monitor their development and identify the species present. Pheromones are sometimes used to attract insects, which allows for more targeted pest control.
However, traditional traps must be inspected regularly, which can lead to accidents in silos. Connected traps are now available, which count the insects that fall into the trap. Some traps can even identify the type of species based on the size of the insects, such as the Insector from OPI Systems Inc.
Insector de OPI systems Inc.
Electromagnetic imaging
Electromagnetic imaging is already widely used in the medical field to detect differences in the dielectric properties of materials. When applied to a silo, this technology can determine the water content of grain throughout the entire volume of the silo. The technology is effective but complex to implement and expensive. An American startup, GrainViz, offers this turnkey solution.
Visualisation GrainViz
Acoustic insect detection
French company SYSTELIA Technologies sells various acoustic sensors for different uses (long-term storage, truck reception/shipping, farm storage, flat storage, etc.). Acoustic detection allows insects to be detected more than 20 weeks earlier than with sample/sieve detection.
Sonde et routeur Javelot
Monitoring for automation
French company Javelot offers a connected thermometry solution that controls ventilation based on temperature fluctuations. This solution allows ventilation at the most opportune times and avoids unnecessary movement by storage operators.
When storage isn't in a silo...
Most of the existing solutions we have listed in this article are more suited to silo storage (or concrete granaries). Some companies are starting to offer solutions adapted to other storage formats.
TeleSense sells independent wireless multi-sensor devices that can be inserted into the grain to measure temperature and humidity. The data is analyzed and displayed on an online interface. The user can be alerted when certain threshold values are exceeded.
Centaur Analytics offers the same type of generic sensor that can be adapted to different storage formats. The device can measure temperature, humidity, carbon dioxide levels, and phosphine concentration for fumigation. The company also offers to analyze the data collected from the sensors to determine the effectiveness of fumigation. An online graphical interface is available to view historical data.
Storage in silobags (cylindrical airtight bags several hundred meters long in open fields) is very common in Latin American countries. Some companies offer probes that can be planted at regular intervals in the silobag to automatically measure the parameters inside the silobag. Some of these devices also alert in case of vandalism (detection of silobag opening). Examples in this category include SensDRB GmbH, LESS Industries, Smartium, and DekaGB.
Storage in a silo bag in Argentina
Remote grain monitoring is gradually becoming part of the global agricultural landscape. There are numerous commercial solutions available worldwide, at varying stages of development. Some are limited to simple detection, while others go further and offer centralized data analysis. The objectives are varied: task automation, quality prediction, resource optimization, etc.
It is clear that agricultural storage data is a largely untapped resource worldwide. The emergence of connected crop monitoring is slow and goes hand in hand with the installation and renewal of agricultural infrastructure. Finally, it is likely that in the coming years, new challenges will arise concerning the storage and use of this data, linked to producers' growing digital awareness.