Seed has been vital to human survival since the dawn of civilisation. In prehistoric times, humans collected and preserved seeds for food and propagation.
There is a strong connection between the development of ancient populations and grain production. The ancient Romans even worshipped “Ceres,” the goddess of grain and fertility.
Maize seeds were essential for the survival of native American Indians.
Today, seeds are a crucial source of food, beverages, and medicine for humanity.
Seeds form a living link between parent plants and offspring, and facilitate the spread of various plant species. Sometimes, seeds must survive harsh conditions like extreme cold, fire, flooding, or even animal digestion before the conditions become favourable for germination and growth.
Biologically, seeds are fertilised, mature eggs. Agriculturally, the definition is broader, including various monocot and dicot seeds, which are key to a farmer’s success.
The first step to a maize farmer’s success is germination, followed by seedling growth for rapid and uniform emergence to achieve the recommended plant population per hectare.
To a seed physiologist, germination refers to morphological changes, where the radicle (root) breaks through the seed coat and then extends into the coleoptile. This all happens below the soil surface, out of sight. However, farmers see germination as seedlings emerging above the soil. In truth, the process involves a significant component of seedling growth. The definition, therefore, depends on the perspective.
Modern farmers are equipped with technology and, in a sense, must put on the hat of a seed physiologist during the planting process. Establishing the right plant population is critically important. Therefore, today’s farmer must understand the germination process followed by seedling growth in fine detail. This is the only way the optimal genetic potential of a maize cultivar in a given environment can be exploited. It is also essential for the farmer to understand the influence of environmental factors on germination and seedling growth, and know how to manipulate them effectively.
Technically, germination is the resumption of active growth, involving the breaking of the seed coat and the emergence of the seedling.
Germination includes the following physiological and morphological events:
- Imbibition and absorption of water
- Hydration of seed tissue
- Absorption of oxygen
- Activation of enzymes and digestion of the endosperm
- Transport of hydrolysed molecules to the embryonic axis
- Increase in respiration rate and assimilation
- Activation of cell division and cell elongation
- Emergence and growth of the embryo
Thus, many complex processes occur unseen beneath the ground when a maize kernel germinates. The success of these processes is tested by a seed company under ideal laboratory conditions and indicated as seedling vigour on a seed bag. Germination ends when the radicle appears, and a normal seedling is formed. During this stage, nothing is visible above the ground surface.
After seedling growth occurs, the mesocotyl extends upward, allowing the coleoptile to break through the soil surface, revealing the first maize leaf. This stage is called emergence. However, several factors influence the success of this process. Elements such as soil moisture, soil temperature, seedling diseases, insects, soil crust formation, and even chemical herbicides can affect the outcome. The energy required for seedling growth, which is measured by the speed and uniformity of emergence, is unpredictable and cannot be guaranteed due to many external factors.
Against this backdrop, it is crucial for maize farmers to do everything in their power to create an ideal seedbed and select favourable climate conditions during planting time. The seed company guarantees seeds with reliable germination strength within legal quality specifications.
The following are essential aspects to consider during seedbed preparation:
1. Water
A fine and firm seedbed ensures sufficient contact between the seed and the soil particles. The better the contact, the better the imbibition process occurs. Imbibition of water is the first process where germination begins. This happens in the first 18 hours after a maize kernel is planted. Seed cells need to be hydrated so that seed metabolism can kick in and release energy for seedling development. Both living and dead cells absorb water passively. The amount of water absorption is determined by the chemical composition of the seed. If sufficient soil moisture is available, a maize seed absorbs approximately 35% of the seed mass as water. In soya beans, up to 50% of the seed mass is absorbed as water. Therefore, it is very clear that sufficient soil moisture is crucial for germination. Less than optimal soil moisture conditions lead to partial imbibition, which hinders the hydration process and seed metabolism. In this case, growth and development are initiated but not completed. This is when the seed suffocates and dies in the soil at planting depth.
When repeated rain or irrigation wets the seed and periodically dries it, it is possible that germination is completed, but seedling vigour is severely limited. The number and intensity of the cycles are decisive.
2. Temperature
During germination, several enzyme-controlled processes occur within the seed cells. These processes consist of complex metabolic reactions that are temperature-driven and highly sensitive. The cardinal temperatures (minimum, optimum, and maximum) for the germination of most crops are typically the same as those required for normal vegetative growth. Optimal temperatures refer to the range at which the highest percentage of germination occurs in the shortest time. For maize, the minimum temperature is 8 to 10 °C, the optimum is 23 to 28 °C, and the maximum is 40 to 44 °C.
Temperature can be easily managed by selecting the right planting date and planting at the appropriate depth. At a planting depth of 6 to 8 cm, the soil temperature typically ranges between 23 and 28 °C, which is optimal for germination.
In western production areas, these optimal soil temperatures are usually reached from early November to mid-December. In the eastern regions, rainfall occurs earlier, and the planting season typically begins in October. Farmers should be cautious of cold fronts and low soil temperatures during these early plantings, as they, along with certain herbicides, can have serious negative effects on germination and especially seedling growth.
3. Gases
Germination usually requires high levels of oxygen to drive all the enzymatic reactions for optimal seedling development. Most plant species respond well to gas compositions of 20% oxygen, 0,03% carbon dioxide, and 80% nitrogen. Good seedbed aeration is the best practice to ensure enough oxygen for germination. Large quantities of rain during planting usually create conditions of compaction and oxygen-poor soil, which hinders germination.
In summary, the ideal seedbed conditions for optimal germination can be described as:
- Moist for good imbibition
- Firm for good contact between seeds and soil particles
- Even for uniform planting depth and few waterlogged spots
- Weed-free for no competition
- Optimal temperatures through the right planting date and depth
- Good pore distribution for sufficient oxygen aeration
- Good structure to limit crust formation
These conditions, combined with quality seeds, lead to good germination and seedling growth. Quick and uniform emergence is a critical first step for a successful harvest.
For more information, contact Pioneer at info.rsa@pioneer.com or visit www.pioneer.com/za.
