Key Field Management Techniques for Rice During the Heading and Grain-Filling Stage

The heading and grain-filling stage of rice refers to the period from heading to grain maturity. Generally, early-maturing varieties require about 25-30 days, medium-maturing varieties require 30-35 days, and late-maturing varieties require about 40-45 days. The growth characteristics and appearance during the heading and grain-filling stage:

1. Growth characteristics

During this period, leaf growth stops, all parts of the spikelets have completed development, and stem elongation reaches its maximum after heading. The growth center shifts from spike differentiation in the previous stage to grain growth. Physiological metabolism is dominated by carbon metabolism, and 2/3 of the dry matter accumulated in the grains comes from the photosynthetic products of green leaves after flowering. This period is the key stage that determines the number of filled grains and grain weight. The main direction of field management is to protect the panicles, promote grain filling, and increase grain weight.

2. Growth and appearance indicators

The late-stage appearance of high-yielding rice is to maintain a suitable leaf area index and a corresponding number of green leaves per stem. It is required that within 20 days after flowering, each effective tiller can still maintain 3-4 green leaves, with a leaf area index of 4-5. At the full-ripening stage, japonica rice is required to maintain 2 leaves, while indica rice is required to maintain 1-2 leaves or for the flag leaf and second leaf from the top not to be completely yellow, with a leaf area index of about 2, until maturity.

The heading and grain-filling stage of rice is the final stage for grain filling to form yield, improve quality, and maintain long-term favorable conditions in autumn. The time runs from full heading to harvest. The central task in this period should focus on foliar fertilization, intermittent irrigation, control of rice grasshoppers, and maintaining stalk vitality for maturity without lodging. The specific measures and operations are as follows:

1) Spraying foliar fertilizer

The purpose of spraying foliar fertilizer is to plump the grains and improve maturity and fullness. From the perspective of improving quality, it is not advisable to broadcast long-acting nitrogen fertilizers such as urea again. Instead, for fields whose leaf color has turned yellow, it is better to spray foliar fertilizer after full heading. Generally, 2-2.5 kg of potassium dihydrogen phosphate and 4-5 kg of urea are applied per hectare, sprayed with 400 kg of water. Spraying at the flowering stage gives good results. Alternatively, biological potassium, Jinmanli, Huimanfeng, and plant growth regulators can be used in combination. This is not only very effective for plumping grains and increasing yield, but also plays a very important role in prolonging root activity, maintaining stalk vitality for maturity, preventing lodging, and improving quality.

If the leaf color turns yellow 10 days after heading and the degree of yellowing is more severe than the “yellowing at the booting stage,” then grain fertilizer should be used. If grain fertilizer is not applied at this time, the plants will lose vigor, which will accelerate the decomposition of chlorophyll, reduce maturity, and lead to yield reduction. The amount of grain fertilizer is generally 3-5 kg of ammonium sulfate per mu. When applying fertilizer, shallow water should be kept in the field, and after fertilization no water should be irrigated, allowing it to dry naturally.

Topdressing according to seedling condition. After rice heading and flowering, maintaining an appropriate nitrogen level in the rice plants is highly beneficial for improving leaf photosynthetic efficiency and prolonging leaf functional period. At this time, for fields where the mid-stage panicle fertilizer was insufficient or not applied, nitrogen grain fertilizer should be topdressed at the early heading stage, combined with phosphorus and potassium fertilizers. Broadcast 1.5-2.5 kg of urea per mu; for foliar fertilization, use 100-250 g of potassium dihydrogen phosphate per mu each time, or use 0.5-1.0 kg of urea, first dissolved in 20-30 kg of water, soaked for 24 hours, then filtered to remove residue, and then add 50 kg of water for spraying. Foliar fertilization can not only solve the problem of weak root absorption capacity in the late growth stage of rice, but also has high and rapid fertilizer efficiency.

For foliar fertilization, on sunny days it should be done in the evening or from 3-4 p.m., so that the fertilizer solution adheres to the leaf surface for a long time and is absorbed thoroughly. On cloudy days, it can be sprayed throughout the day. During the flowering stage of rice, the period from 9-12 a.m. should be avoided to prevent affecting flowering and pollination.

2) Intermittent irrigation

When rice enters the grain-filling stage after heading and flowering, intermittent irrigation is adopted, which means irrigating once and then irrigating again after the water dries, with the previous water not visible when the next water comes. When the current water infiltrates down, then the next water is irrigated. This can increase soil aeration, achieve root aeration through this method, protect leaves through roots, and protect yield through leaves, making rice roots deep and leaves vigorous, ensuring the three functional leaves in the late growth stage of rice remain green and do not senesce early, improving leaf photosynthesis, increasing dry matter accumulation in grains, accelerating the grain-filling rate, promoting grain maturity, improving maturity, increasing 1000-grain weight, and achieving high yield.

After rice heading, leaf transpiration decreases, and in the late growth stage the effect of water temperature on rice is less than that of air temperature. The basic principle of water management from heading to maturity is: within 20 days after heading, adopt intermittent irrigation to keep the soil in a saturated state, that is, splash irrigation, with each irrigation depth of 3-5 cm; from 20-35 days after heading, adopt the “horse-racing water” measure to maintain a moisture state of 80% of maximum capacity. After that, decide the time to stop irrigation and drain water according to maturity. For poorly drained clay soil or low-lying land, stop irrigation and dry the field at about 25 days after heading; for leaky fields, appropriately extend the irrigation time, and for rice fields with low groundwater level and good drainage, stop irrigation and dry the field at about 35 days after heading. Prevent lodging or reduction of green leaf area caused by too early soil water shortage.

3) Timely control of diseases and insect pests

After rice heading, leaf blight, sheath blight, rice neck blast, and pests such as rice planthopper and armyworm may still occur. Inspections should be made frequently, and once disease or pest damage is found, control should be carried out promptly.

For rice brown spot, akagare disease, and rice blast, early prevention should be carried out. Use double-effect microelement fertilizer diluted 800 times for uniform spraying. If rain occurs within 6 hours after spraying, respray. It has good preventive and control effects on the above several diseases, and can increase rice yield by about 15%. During this period, it is necessary to promptly carry out coordinated control of rice grasshoppers at field edges and corners to ensure that functional leaves are not damaged, so as to achieve increased yield, increased income, and improved quality.

4) Eliminate late-stage weeds

Promptly control floating azolla and algae and other weeds, and remove large weeds in the field and weeds on field ridges, channels, and field edges, so as to avoid shading that affects the rise of water temperature, and also reduce weed infestation in the next year and lower sources of disease and pest infection.

5) Prevent lodging

The main causes of lodging in production are: first, improper fertilization, excessive nitrogen application, excessive early heavy fertilizer promoting overly vigorous growth, and later nutrient deficiency causing starvation and early senescence, withered stems and leaves, improper irrigation, damage from diseases and pests, and the effects of wind and rain, etc., causing lodging and flattened plants. To fundamentally control lodging and flattened plants, we should start from changing unscientific fertilization and ensuring the selection of excellent varieties, sparse sowing and sparse transplanting, frequent shallow irrigation, timely field drying, and comprehensively improve all aspects of cultivation management.