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Why hybrid rice is empty
In recent years, the promotion of hybrid rice has led to a higher rate of empty pods, primarily due to its inherent physiological weaknesses. Here are the main reasons:
Firstly, hybrid rice exhibits lower photosynthetic efficiency during the later growth stages, which contributes to a higher empty pod rate. Research shows that except for the tillering stage, the photosynthetic efficiency at the young spikelet differentiation, booting, and milk ripening stages is lower compared to conventional rice. While hybrid rice benefits from a strong early photosynthetic advantage, leading to large panicles, this is often followed by a decline in efficiency later on, resulting in insufficient grain filling and a greater number of empty pods than in traditional varieties.
Secondly, hybrid rice has a narrow temperature adaptability, making it vulnerable to both high and low temperature stresses. Most hybrid rice varieties grown in China originate from Southeast Asia and are sensitive to temperature fluctuations. The biological starting temperature for hybrid rice is about 1–2°C higher than that of conventional rice. When daily temperatures fall below 23°C, the earing rate increases significantly, but the necking phenomenon becomes more severe. Conversely, when temperatures exceed 35°C, the shell rate rises, further reducing seed setting.
Thirdly, hybrid rice often has weaker resistance to diseases and pests. Many currently promoted hybrid combinations are susceptible to major pests and diseases, especially because of their lush foliage, dark green leaves, and longer grain-filling period. Additionally, hybrid rice seedlings tend to have 3–4 times more populations per plant under the same density as conventional rice. If pest or disease control is not timely, the damage can be more severe than in traditional rice.
To improve the seed setting rate of hybrid rice, several practical measures are commonly used in farming:
Nursing and growing techniques play a crucial role. The development of different parts of the rice plant requires a specific process, particularly in early and late-season rice. Vegetative growth typically takes up about half to three-quarters of the time spent in the paddy. Proper aging of the plants is key to achieving high yields. The shorter the growth period after transplanting, the more important it is to ensure strong and healthy growth.
Appropriate planting age and reasonable density are also essential. Hybrid rice generally has medium photoperiod sensitivity and moderate basic nutritional growth. Planting at the right age helps prevent seedling aging, maximizes yield potential, and ensures better performance. With large panicles and strong tillering ability, hybrid rice requires less dense planting than conventional rice. However, it's important to maintain a balance—protecting enough healthy seedlings while ensuring sufficient panicle development for optimal grain weight and yield.
Rational fertilization is another key factor. Increasing phosphorus and potassium fertilizer application in the early growth stage, controlling it moderately in the middle, and applying granular fertilizer later can help optimize nutrient uptake and support better grain development.
Proper irrigation practices are also vital. After transplanting, seedlings are usually protected with deep water. During the tillering phase, shallow water irrigation is used, and the field should be drained at the end of the tillering period. It’s not advisable to expose the plants to direct sunlight for long periods; instead, light exposure and periodic dry-wet cycles are recommended. Avoid cutting off water completely during the maturation phase, as this can cause premature aging and reduce grain weight.