Methods for preventing and controlling rice seedling stunting and key technical points

The main causes of rice seedling stunting are three types: phosphorus deficiency stunting, zinc deficiency stunting, and saline-alkali damage stunting. The main prevention and control methods are:

1. Phosphorus deficiency stunting

It generally occurs during the tillering stage after seedling recovery, manifesting as slow growth, short plants, slender and upright leaves, dark green leaf color, neat leaf cluster tips, significantly shortened leaf sheath distance, partial tillering, red leaf tips, and old leaves turning brownish-red or even dying. The main causes are (1) soil lacking available phosphorus; (2) low soil temperature, low water temperature, or soil containing hydrogen sulfide, ferrous iron and other reducing harmful substances, which reduce the root's absorption capacity; (3) excessive nitrogen fertilizer application, causing available nutrients to lose their relative balance.

The prevention and control measure is to determine a reasonable phosphorus application rate based on the available phosphorus content data measured by the "soil testing and fertilizer recommendation method."

2. Zinc deficiency stunting

When rice is mildly deficient in zinc, brown spots appear on the basal leaves; with moderate zinc deficiency, the leaf color is light green, rust disease increases, and the midrib loses green and turns white; with severe zinc deficiency, the leaf sheath distance shortens, growth is inhibited, new leaves become smaller, plants are short, tillering is hindered, black roots are severe, heading is delayed, and yield is severely reduced. The main causes are low available zinc content in the soil, or excessive application of phosphate fertilizer and ammonium fertilizer, causing an imbalance in the ammonium-zinc ratio; in addition, a large amount of organic fertilizer combined with long-term waterlogging can also easily cause zinc deficiency. The main prevention and control measures are: apply 1~1.5 kg of zinc sulfate per 667 sq m (mu), or after seedling recovery, lightly apply a 0.1%~0.2% zinc sulfate aqueous solution when stunting occurs.

3. Saline-alkali damage stunting

This type of stunting is a complication of salinity-alkalinity, phosphorus deficiency, and zinc deficiency. It mostly occurs in coastal rice areas. The main manifestations are leaves rolling longitudinally from top to bottom like sudden wilting, root systems rapidly necrosing, no guttation from leaves, and after the tips of lower leaves roll longitudinally, they begin to lose green from the leaf base and develop upward, until the leaves die. The main causes are: high saline-alkali content in the soil or irrigation water, or high pH of the irrigation water. The main prevention and control measures: in saline-alkali soil rice areas, carry out field soaking and alkali washing. During the rice growth period, according to the salt-alkali tolerance of rice at different growth stages, strictly control the saline-alkali standard of irrigation water, ensure smooth irrigation water flow, and maintain a water level difference of more than 40 cm between the field surface and the drainage ditch water level, so as to lower the pH of the rice field.