Prevention and treatment of magnesium deficiency in Pumpkin with withered leaves

Pumpkin

Main symptoms: magnesium deficiency in pumpkin is easy to occur in the middle and later stage of growth, so it is often mistaken for natural aging. But there is a difference between the two, natural aging leaves yellowing evenly, vein mesophyll synchronous chlorosis, often withered, lack of freshness. On the other hand, the magnesium-deficient leaves remained fresh for a long time, and the veins did not fade. Where there are conditions, the content of available magnesium in soil can be analyzed. Generally, the content of available magnesium (MgO) in soil is less than 100mg / L as the diagnostic index. The diagnostic index of total magnesium in plant leaves is that most vegetables are 0.2% Murray 0.3%. Less than this content is magnesium deficiency.

Causes of magnesium deficiency in pumpkin

Insufficient supply of magnesium in ① soil is the main cause of magnesium deficiency in vegetables. Southeast China is warm and rainy, with strong leaching, which is generally prone to magnesium deficiency, especially in light soil. The main factors affecting soil available magnesium are as follows: first, the degree of soil weathering, different soils due to different soil parent materials and different degrees of weathering, their magnesium content is different, the degree of red soil weathering is high, the mineral decomposition is relatively complete, generally contains very little magnesium, only 0.06% Mui 0.30%, purple soil belongs to the juvenile class, the degree of weathering is low, the content of magnesium can be as high as 3%. In general, the content of total magnesium in soil has a good correlation with available magnesium, and the soil with high total magnesium is also higher in available magnesium. Magnesium deficiency in red soil vegetable bases in the south of the Yangtze River is easy to occur, so it is necessary to pay attention to the application of magnesium fertilizer. Second, the soil texture, soil sand is strong, magnesium is easy to be leached, soil available magnesium is low, often can not meet the needs of crop growth. Generally speaking, the order of available magnesium with different texture from low to high is sand, sandy loam, loam and clayey soil. The coarse magnesium-deficient soils are mainly distributed in river valleys and hilly areas, and their vegetable bases should also be paid more attention to. Third, soil acidity and alkalinity, soil available magnesium is closely related to acidity and basicity, and soil available magnesium decreases with the increase of soil acidity (pH value decreases). Soils with strong acidity tend to lack magnesium supply, mainly due to acid-induced leaching of available magnesium.

The effects of ② climatic conditions on magnesium deficiency are mainly in two aspects, one is rainy, the other is dry early and strong light. Heavy rain leads to the loss of magnesium, and this effect is regional, such as the distribution of magnesium-deficient soils in the south. Magnesium deficiency induced by drought and strong light is a small regional effect. For example, vegetables that are fully exposed to the sun at the corners of the border tend to be more frequent and recurrent than those who are in the shade of each other. Early drying reduces the absorption of magnesium by vegetables, and strong light in summer aggravates magnesium deficiency, which may be due to the destruction of chlorophyll and the acceleration of leaf chlorosis.

Improper application of ③ fertilizer will induce magnesium deficiency when excessive application of potassium fertilizer and ammonium nitrogen fertilizer in vegetables, because excessive potassium and ammonium ions destroy the nutrient balance and inhibit the absorption of magnesium by plants. The widespread application of nitrogen fertilizer in vegetables is also one of the reasons for the lack of magnesium in vegetables.

Prevention and treatment of magnesium deficiency in pumpkin

The application of magnesium fertilizer in ① can supplement magnesium deficiency caused by insufficient supply of magnesium in soil. Magnesium salts such as magnesium sulfate are generally used, and the amount of magnesium fertilizer per mu is about 2Murray 4kg (according to Mg). For some acidic soils, it is best to use magnesium lime (lime fired from dolomite) 50 Mel 100kg, not only to supply magnesium, but also to improve soil acidity. Many chemical fertilizers such as calcium magnesium phosphate fertilizer contain high magnesium, which can be selected according to local soil conditions and fertilization conditions. According to some reports, the combined application of phosphate fertilizer and magnesium fertilizer is helpful to the absorption of magnesium. Magnesium deficiency caused by root absorption disturbance should be corrected by foliar magnesium supplement. Generally, 1% Murray 2% magnesium sulfate solution can be sprayed before the symptoms are serious, spraying once every 5 murmurs every 7 days, and spraying 3 Murray 5 times in a row. Magnesium fertilizer such as magnesium nitrate can also be sprayed.

When the amount of nitrogen and potassium fertilizer is controlled by ②, it is necessary to prevent the effect of excessive nitrogen and potassium fertilizer on magnesium absorption in the soil with the lowest magnesium content. In particular, vegetables in greenhouse often apply too much fertilizer and have no leaching effect, which leads to the accumulation of nutrients in the root layer and inhibits the absorption of magnesium by pumpkins. Therefore, it is best to apply nitrogen and potassium in a small amount of time in the greenhouse.