Lecture 19 Seed Storage
Seed Storage Overview
In the context of agricultural production, seed storage is the final stage of the process, significantly influencing the viability and longevity of seeds. Current storage systems predominantly utilize racking systems, as illustrated by a small example observed at the PBG store, which comprises 8,000 square meters of space with the capability to store 5,000 tons of seed. The top racks reach a height of 11 meters, necessitating the use of forklifts operated under video surveillance for safe and efficient access.
Historical Context of Seed Storage
Traditionally, seeds were stored in a less efficient manner, involved stacking pellets atop each other. This method posed considerable logistical challenges, particularly in locating specific seeds when required. An example provided is from South Pacific Seeds, where boxes each containing approximately 250 kilograms of seed are prepared for export.
Objectives of Seed Storage
Protection: The primary goal of seed storage is to protect and preserve seeds while ensuring profitability. Key aspects of protection include:
Viability: Ensuring seeds can germinate upon planting.
Germination: Referenced as end-of-fight germination for grass seeds.
Genetic Integrity: It is critical to prevent genetic mixing between different seeds during storage.
Pest Prevention: It is vital to keep seeds safe from insect pests and damage.
Factors Influencing Seed Storage Quality
The quality of seeds upon entering storage is paramount and is influenced by various pre-storage conditions:
Field Weathering: Exposure to different weather conditions, including moisture.
Thresher Damage: Seeds should not be overthreshed, as this can damage them.
Proper Drying: Improper drying can lead to deteriorated seed quality.
Storage Duration Before Cleaning: Delayed cleaning can adversely impact seed viability.
Once seeds are stored, their quality can only be maintained; it will not improve. High-quality seeds can withstand adverse storage conditions, whereas deteriorated seeds will fail to store effectively even in optimal environments.
Classification of Seeds by Storage Quality
Excellent Storage: Carbohydrate-based seeds (e.g., cereals such as maize, rice, wheat, grass seeds) are identified as excellent storers due to their high carbohydrate content.
Intermediate Storage: Legume seeds, such as beans and peas, which are protein-rich, rank as intermediate in storage efficiency.
Poor Storage: Oily seeds (e.g., soybean, peanuts, parsnip, onion, lettuce) do not store well and require special handling.
Storage Conditions Considerations
When determining storage conditions, several critical questions must be considered:
Quality of Seed: Assess how well the seed can be stored based on pre-storage history.
Humidity and Temperature Requirements: It is essential to determine what temperature and humidity levels are required for the seed type during storage.
Proper Pre-storage Treatment: Verify whether the seeds were appropriately dried before storage.
Management of Pests and Fungi: Effective strategies should be in place to manage insects, mites, and storage fungi.
Environmental Influences on Seed Longevity
Two pivotal environmental parameters significantly influence seed storage outcomes:
Relative Humidity: Has the most substantial impact on seed viability.
Seeds are hygroscopic, meaning they can absorb or lose moisture based on environmental humidity.
The ideal practice is to select storage areas with low relative humidity.
Regions like Canterbury in New Zealand are favored due to their naturally low humidity.
Temperature: Lowering temperature contributes to extended seed life, generally measured against relative humidity levels.
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Key Relationships for Seed Longevity
Doubling Seed Life:
For every 1% decrease in seed moisture content, the lifespan of the seed approximately doubles.
For every 5-degree Celsius drop in temperature, the lifespan also doubles.
By combining both strategies—lowering moisture by 1% and temperature by 5 degrees—the life of the seed can quadruple.
Example Case Study
If onion seed is stored at a remarkably high temperature of 50 degrees Celsius with a moisture content of 15%, its longevity could be just two days. If modified to 25 degrees Celsius and reduced to 13% moisture, longevity extends to four years; further cooling to 5 degrees Celsius and dropping to 6% moisture can push lifespan to eighteen years.
Table of Safe Storage Conditions
Brassicas: require 8% moisture for a one-year lifespan with conditions of 65-70% relative humidity.
Maize: requires 14% moisture with similar humidity conditions.
Design Elements of Storage Systems
Essential design elements for effective seed storage include:
Prevent Water Ingress: Water must be kept out to maintain seed quality.
Pest Control: Storage must be secure against rodents and insects.
Dust Control: Structures should keep dust accumulation minimal, preventing dust mites.
Temperature Moderation: Adequate ventilation to mitigate heat build-up from the sun.
Design Strategies
Moisture Exclusion: Design should prevent humidity accumulation.
Ventilation: Engage passive ventilation strategies to mitigate heat build-up.
Building Orientation: The long axis of storage buildings should be aligned north-south to minimize sun exposure, contrary to traditional house designs aimed at maximizing sun.
Color of Structure: A light-colored shed (preferably white) minimizes heat absorption, in contrast to dark surfaces, which can significantly raise temperatures.
Types of Storage Systems
Open Storage: Lacks any environmental control.
Controlled Storage Systems: Features manipulated relative humidity and temperature settings. This includes conditioned storage and cold storage options.
Monitoring and Management
Effective management of seed storage includes monitoring humidity and temperature, primarily through data loggers, which track conditions over time and assist in quality management. A typical data logger may hold up to 8,000 data points and offer insight over several months if tracked at 15-minute intervals.
Implications of Storage Conditions
Investment Cost: Conditioned storage is typically more expensive and reserved for high-grade seeds with considerable value.
Durability Needs: Seeds may need specific conditions based on their storage intended duration—ranging from long-term storage in preservation efforts at germplasm centers to commercial short-term needs.
Advanced Storage Techniques
Cold Storage: Noted that cold air is inherently moist, which can lead to complications. Successful cold storage requires controlling humidity alongside temperature.
Deep Freeze Options: Seeds can withstand deep freezing conditions if pre-dried to specific moisture contents before storage.
Liquid Nitrogen Storage: This technology provides an advanced method of seed preservation at sub-zero temperatures (e.g., -196 degrees Celsius), extending seed life potentially to several centuries if properly dried.
Packaging Options for Seed Storage
Effective seed packaging is essential in seed storage:
Moisture-proof containers: This can include plastics, metal tins, and specialized plastic bags able to withstand low temperatures.
Heavy-duty plastics: Around 80 microns thickness is recommended for temperate environments, with even thicker options suitable for tropical locations.
Calcium Chloride Crystals: Used as moisture absorbers within storage containers. They change color when saturated, indicating the need for drying and reuse.
Aluminium Foil Pouches: Common in packaging seeds to keep moisture at bay. These pouches are often employed in commercially packaged seeds.
Importance of Long-Term Storage Strategies
In discussing long-term storage, optimal moisture levels must be controlled: 6-8% for starchy seeds and slightly lower values for oily seeds and various examples provided show the correlation between seed moisture, temperature, and preservation duration.