In rice seedlings, phosphorus deficiency often manifests during the tillering stage, when growth slows down. Affected plants show stunted growth, thin and erect leaves, dark green coloration, and tightly packed leaf clusters. The angle of the leaves becomes significantly smaller, and some may develop red tips. Older leaves turn brown and eventually die. This condition typically arises from low available phosphorus in the soil, or from environmental factors such as low soil and water temperatures, or the presence of harmful substances like hydrogen sulfide and ferrous compounds, which impair root function. Excessive nitrogen application can also disrupt nutrient balance, leading to reduced phosphorus uptake. To manage this, it's essential to conduct soil testing using the "measured fertilization method" to determine the appropriate phosphorus levels for the crop.
Zinc-deficient rice seedlings display different symptoms depending on the severity. Mild deficiency shows brown spots at the base of the leaves, while moderate deficiency causes yellowing, increased rust, and chlorosis in the middle parts of the leaves. Severe cases result in shortened internodes, stunted growth, smaller new leaves, and weak plants. Roots may become black and the heading process is delayed, leading to significant yield losses. Zinc deficiency is commonly caused by low available zinc in the soil, excessive phosphate or ammonia application, or an imbalance between nitrogen and zinc. Long-term flooding and insufficient organic fertilizer can also contribute. To address this, applying 1 to 1.5 kg of zinc sulfate per 667 square meters, or foliar spraying with a 0.1% to 0.2% zinc sulfate solution after symptom onset, can help restore zinc levels.
Salt-alkali damage in rice is a complex issue involving salinity, alkalinity, phosphorus deficiency, and zinc deficiency, commonly found in coastal rice-growing areas. Symptoms include upward drying of leaves starting from the top, rapid root necrosis, and spitting of water from the leaves. Chlorosis begins at the base of the leaves, causing them to roll vertically and eventually die. High salt or alkali content in the soil or irrigation water, along with high pH levels, are primary causes. To prevent and control this, farmers should implement practices like leaching saline soils with fresh water. During the growing season, irrigation water should be carefully managed according to the plant’s salt tolerance at different stages. Maintaining a water level difference of more than 40 cm between the field surface and drainage helps reduce soil acidity and improve rice health.
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