To raise the per-unit yield of double-season rice in Jiangxi, the key lies in changing the "six mores and six lesses" phenomenon

Rice is the most important food crop in Jiangxi, and increasing the per-unit yield of double-season rice is an important way to ensure Jiangxi's position as a major grain-producing region and to ensure that Jiangxi makes a greater contribution to the country's food security. In recent years, although the per-unit yield of double-season rice in Jiangxi has risen steadily, the phenomenon of a relatively low per-unit yield level has still not improved much. Compared with neighbouring Hunan, it is 50-60 kg lower per 667 sq m. Analysis shows that the "six mores and six lesses" phenomenon is the main reason for Jiangxi's low rice per-unit yield.

1. More seeding rate, less seed used. Cultivating strong seedlings and rational close planting are the foundation of high rice yields. In Jiangxi's double-season rice production, transplanting (throwing) of medium or large seedlings is generally adopted, and the quality of the seedlings is particularly important for high yields. Among the many factors affecting seedling quality, seeding rate is the most important. Taking wet seedling raising as an example, according to surveys, the seeding rate of double-season hybrid early rice in Jiangxi is mostly above 15 kg/667 sq m, with the high end exceeding 20 kg/667 sq m; the seeding rate of double-season late rice is generally above 15 kg/667 sq m. The seeding rate is generally 15%-20% higher than that required for cultivating strong seedlings, and the uniformity is poor. At transplanting (throwing), the tillers that emerged during the seedling stage have already died.

An important feature of double-season rice is the short effective tillering period, and ensuring the basic seedlings and basic hills is an important guarantee of high rice yields. For high yields, double-season hybrid early rice should ensure 60,000-70,000 basic seedlings/667 sq m (excluding seedling-field tillers), about 20,000-22,000 basic hills/667 sq m, that is, a seed rate of 1.75-2.0 kg/667 sq m: double-season hybrid late rice should ensure 40,000-50,000 basic seedlings/667 sq m (excluding seedling-field tillers), about 18,000-20,000 basic hills/667 sq m, that is, a seed rate of 1.25-1.4 kg/667 sq m. However, in many places in Jiangxi, the seed rate of double-season hybrid early rice is less than 1 kg/667 sq m, with fewer than 15,000 basic hills/667 sq m; the seed rate of double-season hybrid late rice is less than 0.75 kg/667 sq m, with the lowest only 0.4-0.5 kg/667 sq m, and fewer than 10,000 basic hills/667 sq m.

The phenomenon of a high seeding rate but a low seed rate leads to poor seedling quality, failure to give play to the large-panicle advantage of hybrid rice, and a serious shortage of effective panicles. In many places, without changing other cultivation measures, as long as the seed rate is increased and density is ensured, the per-unit yield can be greatly raised. Therefore, to increase the per-unit yield of double-season rice in Jiangxi, the first thing is to thoroughly change the phenomenon of a high seeding rate but a low seed rate, cultivate strong seedlings, and plant rationally and closely.

2. More nitrogen applied, less potassium applied. "Crops are a flower, all relying on fertilizer as the master." This shows the importance of fertilizer to high crop yields. Nitrogen, phosphorus and potassium fertilizers are the three most important elements for crop growth and development. In Jiangxi's rice production, applying more nitrogen and less potassium is a common phenomenon. For ordinary farmers, the nitrogen application rate (pure nitrogen) for rice can reach 10 kg/667 sq m, with the high end above 15 kg/667 sq m; while the potassium fertilizer application rate (K2O) is often less than 5 kg/667 sq m. Research on high-yield rice cultivation shows that for high-yield rice, the N:K2O ratio is best at 1:0.8-1. The reasons for the phenomenon of more nitrogen and less potassium are, first, that the role of nitrogen fertilizer is relatively the greatest among the three elements; second, that the effect of nitrogen application is easy to see. The consequences of this phenomenon are more weeds and less grain, more pests and diseases, and easy lodging. To change this phenomenon, first, raise rice farmers' awareness of the yield-increasing role of potassium fertilizer, and second, truly implement soil testing and formula fertilization.

3. More nitrogen applied early, less nitrogen applied in the middle and late stages. The "one-shot" nitrogen application method is both traditional and common in Jiangxi's rice production. When basic seedlings and basic hills are insufficient, using this nitrogen management method can play some role in increasing effective panicles, which is also the root reason why this nitrogen management method is commonly used in Jiangxi's rice production. Numerous studies show that the "one-shot" nitrogen application method has low nitrogen use efficiency, many ineffective tillers and severe pests and diseases, and is a nitrogen management method for a low-yield level. For double-season rice to achieve high yields, basal and tillering fertilizer generally accounts for 70%-80% of the total nitrogen application, and panicle-grain fertilizer should account for 20%-30%. Using this nitrogen management method not only gives high nitrogen use efficiency and can play a role in saving costs and increasing efficiency, but also gives a high panicle-forming rate and light pests and diseases, and is a scientific fertilization method with high yield and high efficiency.

4. More ineffective tillers, fewer effective tillers. Large hills but few panicles and a low panicle-forming rate are common phenomena in Jiangxi's rice production. According to surveys, the panicle-forming rate of double-season rice in Jiangxi is generally only 40%-50%. Production practice shows that only a population that evolves from an early-stage early-developing population to a mid-stage high-panicle-forming-rate population and then to a late-stage high-photosynthetic-efficiency population is a high-yield or super-high-yield rice population. And raising the panicle-forming rate is the key to achieving this population evolution. There are many reasons for a low panicle-forming rate, such as applying too much nitrogen too late in the early stage and not draining the field in time. If the panicle-forming rate can be raised from the current 40%-50% to about 70%, the yield of double-season rice in Jiangxi will take a great leap. To change this situation, on the basis of changing "more seeding rate, less seed used; more nitrogen applied, less potassium applied; more ineffective tillers, fewer effective tillers," timely field draining should be carried out.

5. More pesticide used, less water used. In crop production, doing a good job in pest and disease control is the guarantee of obtaining high yields. Pest and disease control includes biological control, agricultural control, physical control and chemical control. Putting prevention first and integrating control is the basic principle for doing a good job in pest and disease control. In recent years, although biological, agricultural and physical control measures such as using ducks to control insects, using water to control stem borers, and using frequency-vibration lamps to trap insects have been widely applied, in rice production the use of pesticides for pest and disease control is still indispensable. Many rice farmers believe that as long as enough pesticide is used, pests and diseases can be well controlled. Under the guidance of this mistaken understanding, many rice farmers use twice the suitable amount of pesticide, while the amount of water used is only 1/3-1/2 of the amount that should be used. This pest and disease control method of more pesticide and less water not only increases the cost of pesticide use, but also fails to achieve the control effect (especially for pests and diseases at the base of rice or inside stems, such as sheath blight, rice planthopper and striped stem borer, the control effect is even worse), and sometimes causes seedling burn due to excessively high pesticide concentration. Therefore, whether from the perspective of high yield or from the perspective of saving costs and developing green agriculture, the phenomenon of more pesticide used and less water used in rice production must be changed, and pest and disease control must be carried out according to the instructions for pesticide control.

6. More irrigation early, less irrigation late. Water can regulate fertilizer, air and temperature. Rice both likes water and fears water, and scientific irrigation is another key to obtaining high rice yields. The irrigation method for high-yield rice is aerobic irrigation, that is, throughout the rice growth period, except for intermittent shallow-water irrigation during water-sensitive periods (booting stage, heading and flowering stage) and when applying pesticide and fertilizer, no water layer or moist irrigation is generally used as the main method, so that the soil is in an oxygen-rich state, promoting root growth and enhancing root activity. Specifically, this means shallow-water transplanting to establish the seedlings, thin exposure to promote rooting and tillering, and when applying tillering fertilizer the field surface is required to be without water, with shallow water applied together with fertilization to achieve the purpose of carrying fertilizer with water: when the number of stems and tillers reaches about 180,000/667 sq m (about 9 stems and tillers per hill), start multiple light field drainings, with the maximum number of seedlings per 667 sq m controlled at about 300,000, and properly heavier field draining for those with excessive vegetative growth. Starting from the leaf age stage of the second leaf from the top (about 15 days before heading), alternate wetting and drying irrigation is adopted, so that the previous water is not seen when the next water comes, in order to coordinate the root system's demand for water and air, until maturity. Practice has proved that adopting aerobic irrigation can increase the soil oxygen content, raise soil temperature, improve the soil environment for rice growth, promote root growth and deep rooting, enhance root activity, improve fertilizer use efficiency, improve the seed-setting rate and filling degree, reduce the amount of field water irrigation and discharge, and can effectively control the pollution of the environment caused by chemical fertilizers and pesticides being discharged with flowing water. However, in Jiangxi's rice production, flood irrigation in the early stage, untimely field draining in the middle stage, and too early water cutoff in the late stage (high yield requires water cutoff 5-7 days before rice panicle formation, while many places begin water cutoff 10-15 days before rice panicle formation, resulting in a low seed-setting rate and poor filling degree), that is, the phenomenon of more irrigation early and less irrigation late, are widespread. To further increase the per-unit yield of rice in Jiangxi, the existing irrigation methods should be changed, and aerobic irrigation should be promoted on a large scale.