Why does rice exhibit excessive vegetative growth and late maturity?

During rice cultivation, a common phenomenon occurs: even when the rice has reached the stage of yellowing and ripening, it remains green. This occurrence is known as “green‑leaning” or “late maturity.” So, what should be done about green‑leaning and late maturation in rice? What causes it, and how can it be prevented and managed? Let’s take a look!

Characteristics of rice exhibiting excessive vegetative growth and late maturity

1. Leaf color: The most straightforward indicator is to observe the leaf color. Even in the later stages of growth, or when it’s time to harvest, the leaves remain a deep green—while the neighboring plants, which were sown at the same time, look completely out of place in the field.

2. Increase in empty grains: Upon examining the rice panicles, although they have not yet turned yellow, a large number of empty grains are observed; in severe cases, this can exceed 20%, directly impacting yield.

3. Decline in 1,000-grain weight: Under normal conditions, the 1,000-grain weight of rice either remains stable or decreases only slightly. However, in fields with excessive vegetative growth and delayed maturity, the decline is quite pronounced, often falling to less than 80%–90% of the normal weight.

Causes of excessive vegetative growth and late maturity in rice

1. Excessive use of nitrogen fertilizer

Primarily, during rice cultivation, excessive or overly late application of nitrogen fertilizer—such as urea—either as a base fertilizer or as a topdressing can occur. For instance, some farmers, fearing low yields, double the fertilizer rate, believing this will boost production. In reality, this practice disrupts the rice plant’s normal nutrient uptake, creating an imbalance. If this condition persists, nutrients continue to be supplied even in the later growth stages, leading to “green‑leaning” and delayed maturity. As a result, yields not only fail to increase but may actually decline.

2. Illumination

Insufficient light is another major cause of excessive vegetative growth and delayed maturity in rice, as light is a critical factor for photosynthesis. When light is inadequate, photosynthetic activity declines, and the nutrients absorbed cannot be efficiently utilized; excess nutrients remain in the plant, leading to overly vigorous vegetative growth. Additionally, if planting density is too high, the lower and middle leaves may shade one another, further reducing light availability and contributing to the same problem.

3. High temperatures and drought

During its growth cycle, rice can also exhibit excessive vegetative growth and delayed maturity when exposed to prolonged high-temperature and drought conditions. Under drought stress, normal growth is inhibited, development slows, nutrient translocation is impaired, and resource consumption becomes sluggish, ultimately leading to the phenomenon of “excessive greenness.”

Preventive Measures for Late-Maturing, Excessive-Vegetative-Growth Rice

1. Pay attention to planting density.

Planting density should not be too high. Excessively dense planting not only leads to excessive vegetative growth but also exacerbates the incidence of various diseases and pests, resulting in more harm than good. The appropriate planting density depends on whether you’re growing conventional rice or hybrid rice, as well as on soil fertility. To put it simply: for hybrid rice, on well‑fertilized soils, plant 18,000–20,000 hills per mu, with a stand of 60,000–70,000 seedlings; on moderately fertile soils, plant 20,000–22,000 hills per mu, with a stand of 70,000–80,000 seedlings. For conventional (japonica) rice, transplant 25,000–35,000 hills per mu when using early nursery raising, and 40,000–50,000 hills per mu when using wet‑seedling raising.

2. Rational Fertilization

Remember not to overapply nitrogen fertilizer, nor to rely solely on nitrogen. Pay attention to fertilization during the tillering stage, and supplement phosphorus and potassium as needed. In addition, don’t overlook essential micronutrients; foliar applications can help meet these needs.

3. Timely field drying

During the tillering stage, rice fields can be drained and exposed to the sun at an appropriate time to suppress ineffective tillers. When small cracks appear in the soil, apply a shallow irrigation. In fields where excessive nitrogen fertilizer was applied early on and the seedlings are growing vigorously, early and intensive drying is recommended.

4. Pest and Disease Control

Pests and diseases can hinder rice growth and impair normal photosynthesis. For pests such as the rice leafroller, brown planthopper, stem borer, sheath blight, and blast, preventive measures should be taken whenever possible; for those that cannot be prevented in advance, timely chemical control is essential upon detection.