What are the technical key points for fertilizing the seedbed for dry-raised rice seedlings?
The main advantages of the dry-raised rice seedling technique are a short seedling age, strong seedlings, and convenient management. It can be used for machine transplanting and manual hand transplanting, with high work efficiency and good quality. It is suitable for adoption under different production systems.So what are the technical key points for fertilizing the seedbed for dry-raised rice seedlings?
According to experimental research and production practice, all regions generally adopt the three-stage (three-phase) fertilizing method, namely autumn fertilizing (or pre-winter fertilizing), spring fertilizing, and pre-sowing fertilizing. This is relatively ideal for improving the physical and chemical properties of the seedbed soil, especially for improving the soil's physical properties.
(1) Autumn fertilizing: mainly apply organic fertilizer, fertilize throughout the entire layer, and mix evenly. At the same time, apply quick-acting nitrogen in combination, and add a cover material to keep warm and moist and promote decomposition. In production practice, the whole-layer fertilizing method of dry plowing, dry leveling, and dry application should be promoted. Generally, the required application rate is 2 to 3 kg of organic fertilizer per 1 sq m, plus an appropriate amount of quick-acting phosphorus and potassium fertilizer. Organic fertilizer should be applied in layers, and quick-acting chemical fertilizers should be applied early and in split applications, with tillage depth going from deep to shallow. The operation process is: turn and harrow organic fertilizer and farmyard manure into the 0 to 20 cm soil layer in three applications to accelerate decomposition.
(2) Spring fertilizing: fully decomposed organic fertilizer must be applied, and the principle is that it can fully decompose before sowing. When applying it, it is still better to apply early rather than late, and the earlier the better. It is also necessary to insist on turning and harrowing thin slices into the soil and mixing evenly with the seedbed soil. When turning and harrowing the seedbed soil, if large clumps of undecomposed organic fertilizer are found, they must be removed immediately.
(3) Pre-sowing fertilizing: mainly apply quick-acting nitrogen, phosphorus, and potassium to rapidly increase the fertilizer supply intensity. Three points must be noted when applying: First, the fertilizing time must be controlled to more than 15 days before sowing. This is because different parts of the seedlings have different abilities to absorb and assimilate different forms of nitrogen. The root system cannot assimilate ammonium nitrogen. When the root system absorbs too much ammonium nitrogen and it accumulates in the root system, it is very easy to form ammonia toxicity, leading to fertilizer damage, root burning, and seedling death.
Therefore, ammonium nitrogen must be converted into nitrate nitrogen before sowing. Ammonium nitrogen such as urea applied to the seedbed must gradually convert into nitrate nitrogen under the action of oxygen and nitrifying bacteria. This conversion is a process and requires a certain amount of time. In addition, phosphorus fertilizer sold on the market often contains some impurities harmful to seedling growth and development, so phosphorus and potassium fertilizers are best applied early together with nitrogen fertilizer. Second, it is suitable to increase the amount of phosphorus and potassium fertilizer, which can promote root growth and improve seedling stress resistance. Pay attention to balanced application of nitrogen, phosphorus, and potassium. Third, pre-sowing fertilizing generally applies 30 to 50 g of urea, 100 to 150 g of superphosphate, and 40 to 50 g of potassium chloride per 1 sq m, mixed and broadcast onto the seedbed in three applications. After each broadcast application, it must be fully harrowed so that the fertilizer is evenly mixed into the 0 to 10 cm soil layer. Ultimately, the available nitrogen, phosphorus, and potassium content of the seedbed soil should reach fertility levels of 150 mg/kg, 20 to 30 mg/kg, and 120 to 150 mg/kg respectively. At present, in pre-sowing fertilizing, many places choose special strong-seedling nutrient agents, which can omit many operational steps, save labor and effort, and are safe, reliable, and effective. They are worth vigorously promoting and applying.