Detailed Explanation of Precision Quantitative Cultivation Techniques for Rice

(1) Determination of Sowing Date:
The photosynthetic production and accumulation capacity of the population during the heading-to-maturity stage determines rice yield. The heading-to-maturity stage must be arranged under the optimal climatic conditions, known as the optimal heading and grain-filling period. When rice completes flowering during the optimal heading and grain-filling period, the highest seed-setting rate and 1000-grain weight can be achieved. Observations in Jiangsu show that the seed-setting rate is highest when the daily average temperature at the heading stage of japonica rice is around 25°C. The 1000-grain weight is highest when the daily average temperature during the grain-filling-to-maturity stage is around 21°C (the two temperature indicators for indica rice are generally 2°C higher than those for japonica rice). The dates when these two temperature indicators occur in a normal year can be designated as the local optimal heading and grain-filling period. Then, the appropriate sowing date is determined based on the number of days from sowing to the optimal heading period for the variety. Once the sowing date is determined, the seedling age determines the transplanting date. For example, for varieties with 5 elongated internodes, the suitable seedling age for manual transplanting is best controlled within 6 leaves (5 leaves and 1 heart leaf). If the seedling age must be extended (7 leaves and 1 heart leaf), sparse sowing to cultivate multi-tiller strong seedlings and dense fertilizer techniques for large-seedling transplanting should be applied.
(2) Determination of Reasonable Basic Seedling Number: A reasonable basic seedling number is the starting point of a reasonable population. It is necessary not only to increase the tiller-to-panicle rate to 80-90% but also to achieve sufficient panicles. Therefore, determination of a reasonable basic seedling number must be the starting point. The formula for calculating the reasonable basic seedling number is:
X (reasonable basic seedling number (in ten thousand)) = y (suitable panicle number per mu (in ten thousand)) × ES (reliable panicle number per plant)
As the level of fertilization increases, excessively small row spacing causes rice to close the canopy after the jointing stage, seriously affecting the photosynthetic productivity of the population during the panicle elongation stage and the flowering and grain-filling stage, thus restricting yield improvement. Widening row spacing and controlling the peak tiller number and canopy closure timing (booting stage) have become key measures for achieving high yield.
Practical experience in high-yield cultivation has proven that, on the basis of ensuring sufficient panicles, one important measure for achieving large panicles is to reduce basal and tiller fertilizer and increase the application rate of panicle fertilizer. Widening row spacing creates the necessary conditions for increasing the amount of nitrogen panicle fertilizer. Enhancing the assimilation capacity of rice plants for nitrogen panicle fertilizer and balancing sugar-nitrogen metabolism bring a series of benefits: increasing the tiller-to-panicle rate, enhancing the developmental capacity of spikelet differentiation to form large panicles; inhibiting stem and leaf elongation, increasing stem strength and lodging resistance; reducing disease; promoting root growth in the mid-to-late stages (especially upper-layer roots), delaying the senescence of middle and lower leaves during the grain-filling stage, and improving photosynthetic production and accumulation capacity during the grain-filling stage, with significant effects on increasing seed-setting rate, grain weight, and improving grain quality and eating quality; widening row spacing can also increase water temperature during the tillering stage, promoting tillering of rice in cold regions.
(3) Precision Quantification of Fertilization: The precision quantification of fertilization must first address two issues: the reasonable application ratio of N, P, K and the precision quantification of nitrogen fertilizer. The reasonable application ratio of N, P, K can be clarified through soil testing and formula fertilization experiments.
The precision quantification of nitrogen fertilizer requires resolving the reasonable total nitrogen application rate and the ratio of stem-tiller fertilizer to panicle fertilizer. The total nitrogen application rate is calculated using the Stanford difference method, with the basic formula:
Total nitrogen application rate (kg/mu) = Target yield nitrogen requirement (kg) - Soil nitrogen supply (kg) / Nitrogen fertilizer current-season utilization rate (%)
Target yield nitrogen requirement = Target yield × N requirement per 100 kg of rice grain / 100. For existing conventional medium-to-late maturing japonica rice in Jiangsu with a yield of 500-750 kg per mu, the nitrogen requirement per 100 kg of rice grain is generally: 1.85 kg at 500 kg per mu, 2.0 kg at 600 kg, and about 2.1 kg at 700 kg or above. For indica hybrid rice, the nitrogen requirement per 100 kg of rice grain measured in Jiangsu is 0.2 kg lower than that of japonica rice at the same yield level.
The soil nitrogen supply is calculated directly using the rice grain yield of the zero-N plot (basic yield) and its nitrogen requirement per 100 kg of rice grain. The obtained nitrogen uptake by rice reflects the comprehensive soil nitrogen supply. When the basic yield is 400 kg per mu, the nitrogen requirement per 100 kg of rice grain is 1.7 kg for clay soil and 1.5 kg for sandy soil. Regarding the current-season nitrogen utilization rate, based on previous research results, when the current-season nitrogen utilization rate is 40%, it is the critical index value for achieving high yield and also the index value for efficient nitrogen utilization.
When the total nitrogen is reasonable, the highest yield is obtained when the ratio of basal-tiller fertilizer to panicle fertilizer is 5:5 to 6:4. Within the basal-tiller fertilizer, the ratio of basal fertilizer to tiller fertilizer is 7:3. The panicle fertilizer is applied as flower-promoting fertilizer and flower-preserving fertilizer, with a ratio of 6:4. The flower-promoting fertilizer is applied when the 4th leaf from the top emerges, and the flower-preserving fertilizer is applied when the 2nd leaf from the top emerges.
(4) Quantitative Regulation of Water
In the quantitative regulation of water, the early stage focuses on effectively controlling the occurrence of ineffective tillers to increase the tiller-to-panicle rate, while the mid-to-late stage aims to comprehensively improve population quality and enhance the photosynthetic productivity of the grain-filling population.
1. Seedling establishment and tillering stage: During the seedling establishment and tillering stage, irrigation is mainly maintained with a shallow water layer (2-3 cm).
(1) For medium and large seedling transplanting, the seedlings are larger and require water layer management after being transplanted into the field to meet the physiological and ecological water requirements, which helps regulate suitable temperature and humidity in the field, maintain water balance, prevent wilting, reduce transplanting injury, and promote root development and seedling establishment. During the tillering stage, seedling nitrogen uptake is mainly ammonium nitrogen, and the water layer can promote soil ammonification and rice seedling tillering. Therefore, from transplanting to the tillering stage, from both physiological and ecological perspectives, shallow water irrigation should be the main approach, combined with short-term drainage and aeration between irrigations.
(2) For machine-transplanted small seedlings, the seedlings are small, leaf transpiration is not high, and since they are transplanted with some soil around the roots, maintaining soil moisture after transplanting into the field is sufficient to meet physiological water requirements. The main purpose is to maintain soil aeration and promote rapid root development of seedlings. On cloudy days, no water layer is maintained; on sunny days, a thin water layer is applied, drained after 1-2 days, and then a thin water layer is applied again. After the seedlings grow one leaf age and become established, water is cut off and the field is exposed, maintaining a moist state to further promote root development. When the second leaf emerges after transplanting, the seedlings have grown larger. At this point, combined with the application of tiller fertilizer, a shallow water layer is established and maintained throughout the entire effective tillering period.
2. Early field drying. At the N-n-1 leaf age stage (N represents the total leaf number of the main stem, n represents the number of elongated internodes), when the total tiller number of the population reaches about 80% (70-90%) of the target panicle number, drainage and field drying begin. The field drying effect occurs at the N-n leaf age stage, and what is controlled is the ineffective tillers that occur from the N-n+1 leaf age stage onward.
3. From jointing to maturity, implement moist irrigation, alternately dry and wet. Maintaining soil moisture and firmness to meet the physiological water requirements of rice, enhance root activity, and improve the photosynthetic production and accumulation capacity of the population in the mid-to-late stages is one of the key techniques for increasing seed-setting rate and grain weight.