What are the advantages of semi-dry rice cultivation?

Semi-dry cultivation refers to a new rice-growing method in paddy fields where, according to a certain specification, trenches are dug and ridges are raised to form beds, rice is transplanted on the water line on both sides of the ridge top or on the bed surface, water is irrigated in the trenches, and the water level is adjusted according to the different growth stages of rice, implementing infiltrated irrigation. It is a new rice cultivation technique developed through experimental research based on the ecological characteristics of farmland, applying the principle of natural no-tillage and the theory of soil biothermodynamics. It is suitable for winter paddy fields, especially for application in deep-footed fields, cold-waterlogged fields, muddy fields and heavily fertilized fields. Therefore, in recent years, the area has expanded rapidly. In 1987, the promoted area in Sichuan, Guizhou, Hubei, Guangdong, Fujian and other provinces reached 5,129,300 mu, with an average yield increase of 70 kg of grain per mu and a value increase of 55.50 yuan.

Reasons for the yield increase of semi-dry cultivation:

① Accelerating the exchange of matter and energy between soil and the outside. After ridging, the soil temperature is raised, the micro-topography is artificially changed, the mature soil layer for rice growth is thickened, and the total surface area of the field (increased by about more than 1/3) and the air contact area (the soil-air contact surface changes from zero to 410-470 sq m/mu) are expanded, speeding up the exchange of matter and energy between soil and the outside, greatly increasing the area of soil exposed to light and absorbing solar radiation heat, and correspondingly expanding the heat dissipation area of the soil. In addition, the water content in the soil body is less than that of flat fields, the soil heat capacity is reduced, the soil temperature rises easily (2-3°C higher than flat cultivation), and the diurnal temperature difference is also larger. This helps overcome the drawback of cold, shady and muddy fields where seedlings stagnate in early spring due to low temperatures. A large diurnal temperature difference helps reduce the respiratory consumption of rice plants, increase the accumulation of dry matter in the body, and lay a material foundation for rice growth.

② Changing the form of water movement to coordinate the contradiction between water and air. After ridging, the surface water in the field changes from multi-directional turbulent flow in the original flat field to directional flow in the trenches. In the upper soil body of the ridges, gravitational water is basically excluded, forming a movement form dominated by capillary water rise, so that the natural soil structure can be maintained. The soil body will neither dry up and crack nor be dispersed by water (flooding) into a muddy state. It presents a loose and porous layer, and aeration is significantly improved. More air enters the soil body (Eh is 160-180 millivolts higher than in flat-cultivated fields), the contradiction between water and air is more coordinated, the gasification potential is enhanced, and the total amount of reducing substances can be reduced by 75-80%, which helps eliminate the harm of toxic substances to rice roots.

③ Strengthening soil enzyme activity, promoting the activity of aerobic microorganisms, and improving the soil's fertilizer-supplying capacity. Due to the significant improvement of heat conditions and aeration conditions in the soil, aerobic microorganisms in the soil become active, with a total amount 1-5 times greater than in flat-cultivated fields. Hydrogen peroxide (H2O2) enzyme activity is high, reducing the harm of soil reducing substances to rice roots and increasing rice root exudates, thereby improving the enzyme activity of rhizosphere microorganisms. This is beneficial to the mineralization of organic matter in the soil and the transformation of mineral elements. Available nutrients in the soil increase, organic nutrients decompose quickly, organic nitrogen decomposes quickly, nitrogen metabolism is strong, the soil's nitrogen-supplying capacity is improved, and transport is also more convenient. According to measurements, total available nitrogen and nitrate nitrogen have increased somewhat, while ammonium nitrogen has decreased somewhat. Because nitrate nitrogen is easily leached and denitrified, ridge cultivation cannot reduce the amount of nitrogen fertilizer; in particular, surface fertilizer should be applied heavily and tillering fertilizer should be applied early. In addition, because the soil water content is low, the pH value rises, the soil available zinc content increases, and available phosphorus decreases somewhat, so attention should be paid to increasing phosphorus fertilizer application.