Sorghum Development: Insights into Each Growing Phase
I am currently working with sorghum in the field, and I’m documenting its growth stages over time.
Stage 0) Emergence
□ Sowing date: 2023/05/18
□ Emergence: 2023/05/30
As the young sorghum plant pierces the soil’s surface, its initial growth phase is typically gradual. Several factors determine the duration between sowing the seed and its emergence, including the soil’s temperature, the amount and distribution of residue on the soil, its moisture content, the depth at which the seed is planted, and the inherent vigor of the seed.
To optimize growth, it’s essential to calibrate the planting schedule, ensuring that seeds emerge in soils that are warm and have favorable moisture levels. Planting too early can lead to a delay in the emergence due to sub-optimal conditions.
Stage 1) Three-Leaf
Within a span of 10 to 20 days after emergence, the sorghum plant displays three fully matured leaves, each marked by a distinct collar, which is the leaf tissue located where the leaf blade meets the sheath. During this period, the plant’s growing point remains buried beneath the soil’s surface. This positioning offers a level of protection, allowing the plant to endure significant leaf damage, such as that caused by hailstorms, without it being fatal to the plant. This inherent resilience of the sorghum plant is an adaptive trait that enables it to withstand certain adverse conditions in its early growth stages.
Stage 2) Five-Leaf
Approximately 20 to 25 days after emergence, a sorghum plant will have five fully expanded leaves, each displaying a distinguishable collar. At this juncture, the growing point remains buried beneath the soil’s surface. This is a crucial phase as the plant undergoes a spurt in growth, with its root system branching out extensively beneath the ground. Notably, if there’s any loss in leaf area during this period, the plant demonstrates a more robust regrowth compared to when it’s at the three-leaf stage. This resilience is indicative of its adaptive nature and rapid developmental processes.
Regular monitoring for potential threats such as insects, diseases, weeds, and other crop production challenges is essential during this period. The presence of these elements can adversely impact the growth and health of the sorghum. Particularly, warding off weed competition from the moment of planting until this stage of growth is crucial. Weeds can vie for essential resources like nutrients, water, and sunlight, thereby inhibiting the sorghum’s optimal development. Ensuring a weed-free environment allows the sorghum to utilize available resources fully, fostering robust growth and reducing vulnerabilities.
Stage 3) Growing Point Differentiation
Between 30 to 40 days after emergence, the potential number of leaves a sorghum plant can develop becomes established. By this time, the growing point has risen above the soil surface and transitions from a primary focus on leaf generation to head formation. This phase marks the pinnacle of the plant’s growth and its nutrient absorption capacity. After the growing point differentiates itself, the plant enters a period of swift stem elongation complemented by accelerated leaf development. This stage is pivotal in determining the overall productivity and health of the sorghum crop.
Regularly monitoring for the presence of weeds, insects, and potential diseases is essential at this stage. The sorghum plants, having gained strength and size, are now better equipped to compete with invasive weeds, reducing their threat to some extent. However, to truly harness the growth potential of the sorghum, it’s crucial to ensure a consistent supply of necessary nutrients and water. These elements not only boost the plant’s overall growth but also fortify its defenses against pests and diseases, laying the foundation for a healthy crop yield.
Stage 4) Flag Leaf Visible
The ultimate leaf, termed the “flag leaf,” is now discernible within the plant’s whorl. As the head takes shape, there’s a surge in stem elongation coupled with an augmentation in the leaf area. Every leaf, barring the last three or four, has reached its full expansion. The plant is nearly at its zenith in terms of light interception, making the most of photosynthesis. Consequently, the rate of growth and nutrient absorption persists at an accelerated pace, ensuring the plant’s robust health and development.
For optimal growth, it’s imperative that plants have sufficient access to vital nutrients and water. Interestingly, even though the plant has achieved just around 20% of its potential growth at this point, its nutrient absorption rate is disproportionately high. The plant has already assimilated over 40% of its total potassium needs, in excess of 30% of its required nitrogen, and upward of 20% of its phosphorus demand. This early and robust nutrient uptake underscores the plant’s active metabolic processes and preparations for subsequent growth phases, ensuring it’s well-equipped to thrive in later stages.
Stage 5) Boot
At approximately 50 to 60 days post-emergence, the head of the sorghum plant has grown to almost its maximum size, neatly enveloped by the flag-leaf sheath. The upper part of the stalk, commonly referred to as the “peduncle,” starts its elongation process. By this stage, both the potential size of the head and the number of seeds it will bear have been predetermined. Reaching the pinnacle of its leaf development, the plant has maximized its leaf area. To optimize grain filling, it’s crucial to shield and maintain the leaf’s health, ensuring efficient light capture and photosynthetic activity.
During this critical phase, if the plant is subjected to intense moisture deprivation or damage due to herbicides, it could hinder the head from fully emerging out of the flag-leaf sheath. Post this stage, safeguarding the leaf area becomes paramount. It’s essential to shield the leaves from any form of stress or external threats, as they play a crucial role in photosynthesis and overall plant health. Ensuring this protection can help maintain the plant’s vitality and directly impact the yield quality and quantity.
Stage 6) Half-Bloom
During this phase, the head of the plant becomes fully extended, and in a given field, about half of the plants have started blooming. The overall growth of the plant has reached its halfway mark. Analyzing the nutrient content, when measured against what it will be at full maturity, we find that the plant has amassed 60% of its phosphorus requirements, 70% of its nitrogen needs, and over 80% of its potassium quota. This substantial nutrient uptake signifies the plant’s vigorous growth and readiness to progress into the latter stages of its life cycle.
The process of grain formation is set in motion at this juncture. Limitations related to the plant’s size, leaf area, or the number of plants become irreversible at this stage. Nevertheless, with conducive environmental conditions, the sorghum plant possesses the adaptive capacity to adjust both the number of seeds per head and the weight of each seed. For optimal results, it’s crucial to select a hybrid maturity and decide on a planting date in such a way that this critical grain formation stage doesn’t coincide with periods of extreme heat or prolonged dry spells. Making these strategic decisions can ensure a more resilient crop and better yield outcomes.
Stage 7) Soft-Dough
Following the flowering phase, the formation of grains gets underway without delay. This is evident as the grain quickly achieves 50% of its dry weight. During this period, the stem undergoes a weight reduction, which can be attributed to the remobilization process that redirects resources from the stem to support grain development. Given the plant’s prioritization of grain development, it’s imperative to maintain a harmonious balance between the leaves, which act as the primary source of energy, and the grain, which serves as the energy sink. A disruption in this balance could curtail the time span of the grain-filling phase, potentially affecting overall yield and quality.
Experiencing intense stress during this phase might lead to phenomena known as “blasting,” which can cause inadequate head filling, manifesting in grains that are lighter and filled with chaff. Typically, in standard sorghum cultivation practices, the majority of leaves retain their green hue, a characteristic known as “stay green,” right up to the season’s conclusion. Consequently, it’s relatively rare for the sorghum plants to suffer from leaf loss that could potentially reduce the overall yield. This robustness underscores the resilience of sorghum in diverse environmental conditions.
■ Reference
□ Sorghum Growth and Development
