How to Prevent and Treat Yellowing of Rice Seedlings? A Detailed Guide to Practical Methods

During rice seedling raising, yellowing of seedlings is very likely to occur, with slow tillering and weak growth, which is not conducive to cultivating strong seedlings and has a serious impact on the seedlings used for field production and even on the improvement of rice yield.

I. Yellowing caused by insufficient base fertilizer

Before the three-leaf stage, seedling growth mainly depends on the endosperm; after the three-leaf stage, it mainly depends on nutrients absorbed from the soil by the root system. However, many people believe that rice seedlings are small during the seedling-raising period and do not need much fertilizer, so insufficient base fertilizer is applied, and nitrogen deficiency becomes the main cause of seedling yellowing.

Countermeasure: Apply 60-75 kg of urea per hectare of seedling field and spread it evenly over the seedbed surface; a 1% urea solution can also be used for foliar spraying in the morning or afternoon, spraying 800 kg of solution per hectare.

II. Yellowing caused by uneven fertilizer application

The seedling field area is small, which is not conducive to repeated harrowing and leveling operations. Chemical fertilizers are mostly broadcast, and uneven application easily forms "bald patches." When the seedlings have just germinated, the leaf color is basically uniform. After the three-leaf stage, differentiation begins: some turn yellow, some stay green, and the yellow and green become clearly distinct. As the seedlings age, the yellowing becomes more serious, the plants do not tiller or tiller little, the leaves are narrow and short, the plants are thin and small, and the leaves dry up from the tip upward from the bottom.

Countermeasure: Use a quick-acting compound fertilizer containing nitrogen, phosphorus, and potassium, 150-225 kg per hectare, and broadcast it around the root zone. The principle is to apply it wherever there is yellowing. At the same time, spray the yellowed seedlings with a 1% urea solution.

III. Yellowing caused by high pH

Soil acidity and alkalinity have a direct impact on rice growth. Acidity and alkalinity greatly affect the transformation of soil nutrients, especially the availability of phosphorus and trace elements. The ⑦ soil acidity and alkalinity suitable for rice growth is close to neutral. Seedlings prefer slightly acidic soil. High pH affects the seedlings' absorption of nutrients, causing the seedlings to yellow due to nutritional deficiency.

Countermeasure: For soil with high pH, reduce the pH by acid adjustment. Apply 10-15 g of zinc sulfate or ferrous sulfate per square meter, adjusting the pH to 4.5-5.0, so as to inhibit mold activity, alleviate the shortage of trace elements in the soil, and promote the formation of chlorophyll.

IV. Yellowing caused by shallow seed covering soil

At sowing, if the seeds are covered with too little soil, some grains are exposed. After the field surface dries slightly, the soil particles dry out, the root system cannot penetrate downward, and nutrients and water cannot be absorbed, resulting in yellow seedlings.

Countermeasure: First, use sieved decomposed organic fertilizer, 1500-2000 kg per hectare, and gently scatter it over the seedbed surface; second, use a loosening shovel about 1.5-2 cm wide to lightly scratch between the seedlings so that the loosened soil particles bury the seeds and root crowns; third, every 1-2 days, use a sprayer or similar device to spray water into the seedling field to keep the field surface moist, accelerate root growth, and promote weak seedlings to become strong as soon as possible.

V. Yellowing caused by a sudden drop in temperature ⟧17⟧ Early spring weather is changeable. At the three-leaf stage, the sugar content in the seedlings is low and their cold resistance is weak. After a sudden drop in temperature, the cell membranes of the root cells of the seedlings are damaged, permeability increases, and the exudation of amino acids and other contents increases. This causes Pythium to multiply rapidly in the root zone and invade the roots, weakening the absorption function of the root system and leading to seedling yellowing.

Early spring weather is changeable, and rice seedlings at the three-leaf stage have low sugar content in their tissues and weak cold resistance. After a sudden drop in temperature, the cell membranes of the root cells of the seedlings are damaged, their permeability increases, and more contents such as amino acids leak out. This causes Pythium in the rhizosphere to multiply rapidly and attack the roots, weakening the root absorption function and leading to yellowing of the seedlings.

Countermeasure: Cultivate strong seedlings and increase the sugar content in the seedlings at the three-leaf stage; Dexon has a special effect on Pythium and also promotes the development of the seedling root system, so it has a good rescue effect on yellowed seedlings. When the seedlings have one leaf and one heart, spray with a 700-fold Dexon solution; for rescue, spray with a 300-500-fold solution, and do not water for 3 days after spraying.