Seeds form the foundation of global food security and a sustainable future. To feed future generations, seeds must be stored for long periods under appropriate temperature and humidity conditions. High humidity and temperature can negatively impact the germination and growth capacity of seeds, leading to mold and fungal growth. Proper temperature and humidity control can preserve the viability and nutritional value of seeds, ensuring healthy and safe food sources for future generations. Seeds, with their high nutritional value compared to other parts of the plant, form the basis of human and animal nutrition and are also sought after by many living organisms, from diseases and pests to rodents. Seeds primarily consist of a miniature structure that will form the young plant (embryo), endosperm (nutrient tissue) that provides the nutrition and energy needed by the embryo until it can photosynthesize, and testa (seed coat) that protects these structures. The new challenges faced by today's society make the use of phytogenic resources essential to support sustainable development. Therefore, it is necessary to provide the required conditions for the processing and storage of seeds before use.
The viability of seeds can decrease or increase depending on the temperature and humidity data during storage. Seed storage aims to minimize the loss of seed viability and vigor. Orthodox seed storage can be categorized into three main storage periods:
Short-term storage from harvest to the next planting season, lasting 6-8 months,
Medium-term storage for 1-5 years,
Long-term storage for 5-20 years or longer in gene banks protected by law, research and development, or seed testing laboratories.
In all three storage phases, temperature and humidity control are crucial for the sustainable preservation of seeds. This necessity increases with the length of the storage period. For long-term seed storage, particularly orthodox seeds that are tolerant to drying and low temperatures and can be stored for several years under optimal conditions with low moisture content are used.
According to Harrington's rule (Harrington Thumb Rule: 1963), there is a relationship between temperature and seed moisture. Each 1% increase in seed moisture and every 5°C increase in temperature halve the storage life of seeds. This rule applies to seed moisture levels between 5-14% and temperature reference values between 0-50°C. Temperature and humidity directly affect the storage life of seeds. Temperature is a direct determinant of the respiration rate of the product and the life of harmful organisms. When the temperature is lowered to extend the storage life, relative humidity levels inevitably rise due to thermodynamic principles. Increased relative humidity values cause seeds to tend to exceed the safe moisture range, depending on their type and variety, storage purpose, storage duration, storage insulation structure, and packaging method. Particularly seeds with moisture-absorbing properties tend to draw moisture from the environment. The moisture value at which these seeds do not draw moisture from the environment and are in balance with the climatic conditions is called the "equilibrium moisture." Equilibrium moisture is directly related to the chemical and physical structure of the seed. For example, the equilibrium moisture of high-oil seeds is different from that of thick-coated seeds. High seed moisture levels damage storage conditions, while low moisture levels harm the seed's viability.
In short and medium-term seed storage systems, the storage environment should be maintained at 5-10°C and 20-30% relative humidity. Under these temperature and low relative humidity conditions, the use of dehumidifiers for climate conditions in these rooms is inevitable. Since the dew point corresponding to the temperature and relative humidity values falls below zero, mechanical dehumidifiers with condensation should not be used in such operational activities. Instead, the use of industrial-type rotor dehumidifiers, also known as chemical dehumidifiers, yields more accurate results, considering energy costs. In long-term storage (15-20 years), products are preserved by freezing in frozen rooms at -18°C. At this point, proper positioning of dehumidifiers within the room and maintaining temperature stability within the room are crucial. The air should be blown from the evaporator's intake to ensure that the dry and hot air is prepared at the source as dry and cold air and delivered to the room. Otherwise, the mixture created by distributing air from two sources with different temperature and humidity conditions will directly affect the temperature and humidity wave within the room. Especially in storage areas with significant height differences between the floor and ceiling, the dehumidifier should be projected close to the evaporators on the ceiling line. In seed storage, the design of air distribution is also vital. The products should be evenly exposed to dry air until they reach equilibrium moisture and should not be forced to release excess moisture. Otherwise, the product will exceed the equilibrium point and lose viability.
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