(I) Symptoms
The common symptom of magnesium deficiency is the chlorosis and chlorosis of the lower leaf mesophyll. The morphology is similar, and most of them occur in the later period of fertility, especially after the formation of seed germination. Most of the broad-leaved plants formed clear reticulate leaves after chlorosis. The main veins and veinlets remained green, and some formed "ribs"-like yellow-leafed leaves. The plaques blew green along the sides of the main vein and the leaf margins did not fade. The shape is complete; in some cases, the chlorosis begins from the leaf margin to the middle rib extension, and when severe, the edges become brown and necrotic (similar to potassium deficiency) and dry off. Monocotyledonous plants are mostly yellow-green stripes and mosaics. The residual greenish green spots of the Mai-Mg-deficient veins are linked together as a rosary (especially wheat is typical), which is characteristic of wheat-deficient magnesium; the lower leaves of the rice are yellow-green intertwined leaves, often with yellowish red , There is a slight tendency to lose water, the leaves are slightly inward and unique in leaf body; the lower leaves of rice are striped between yellow and green leaves, the edges are often yellow-red, have a slight tendency to dehydration, the leaves are slightly inward, and the leaves are from Drooping water at the leaf occipital; corn stripe mosaic, sometimes visible rosary green spot, later appeared purplish leaf; soybean magnesium deficiency faded whole leaf veins, veins clear, late pass leaves changed orange or orange Red; deep purple patches appear behind the cotton leaves and even the whole leaves turn red, showing red veins and green veins; macular or purple patches appear on the rape leaves, yellow, orange, purple and other variegated mottled leaves; tomato, radish, etc. Significant macular, uneven distribution; apple leaves were pale green or gray, and later turned yellow-brown, dark brown, necrosis, leaving the top leaves as rosettes; citrus leaves showed large plaques along the midribs yellow, late Turn yellow, early fall off, strong trees Chi Chang retransmission; between old grape leaf veins yellow, brown after red, green veins, color industry particularly clear.
(b) Prone environmental conditions
(1) The acidic soils in rivers and alluvial deposits where the texture is coarse and light in the warm and humid regions, such as the silt soil in the valleys, and the soils with high temperature and weathering leaching, such as the red and yellow soils in the Quaternary clay.
(2) Red sandy soil with red sandstone development.
(3) Excessive application of potassium fertilizer and partial application of ammonia nitrogen fertilizer induced magnesium deficiency.
(4) Sensitive crops are grown. Generally, there are more fruit and vegetable crops than field crops. The common ones are: kidney beans, loofah, soybeans, pepper,
Sunflower, broccoli, rape, and potato; followed by corn, cotton, wheat, rice, etc.; grape, citrus, peach, and apple are also more likely to occur in fruit trees.
(c) Diagnosis
1. Morphological diagnosis
Symptoms are as above. Some crops have specific symptoms of magnesium deficiency. For example, the green leaflets in the leaves of wheat are in the form of glomus; the diseased leaves of the rice leaflets are sagging from the leaf occipital lobe, and drowning surfaces, etc. provide convenience for judgment. However, magnesium deficiency forms many types of mosaics, some are similar to iron deficiency, some are similar to potassium deficiency, and they are easily confused. Attention should be paid to identification. The difference from iron deficiency lies in the location of symptoms. Iron deficiency occurs in the upper leaves and magnesium deficiency occurs in the middle. , the old leaves of the lower position; and the difference between the disease and potassium deficiency due to the same leaf position, the identification is more difficult, but there are the following points for comparison to identify:
(1) Mg deficiency chlorosis often tends to whitening, potassium deficiency is yellowing.
(2) In the late stage of magnesium deficiency, shades such as purple or orange are often present, and potassium deficiency is rare.
(3) Some broad-leaved plants lack obvious magnesium leaf surface wrinkles, veins subsidence, mesophyll convex, and potassium deficiency is not common.
In addition, magnesium deficiency disorders mostly occur in the later period of fertility, and are easily confused with physiological aging. However, the leaves of the aging leaves are uniformly yellow, whereas the magnesium deficiency is yellowish and yellow, and it remains fresh and does not fall off in a relatively long period of time.
2. Plant analysis and diagnosis
The critical value of magnesium deficiency in different crops is 0.1%~0.3%. Wheat, oats and corn plants lack a critical value for magnesium (Mg)
3. Soil diagnosis
Soil exchangeable magnesium is generally used as an index, and the effectiveness of magnesium is also influenced by the ratio of other coexisting ions and total magnesium substitution. When the soil substitute magnesium is greater than 100 mg/kg, the magnesium/potassium ratio is greater than 2 or substituted. When magnesium substitution is more than 10% of total substitution, magnesium is generally not deficient. Soil replacement magnesium (Mg)
(IV) Prevention and control
1. Magnesium fertilizer application
Acidic magnesium-deficient orchard soils, applying magnesium-containing lime (fired from dolomite), both provide magnesium and neutralize the acidity of the soil, and have the most immediate and long-term effects. In general, Daejeon uses magnesium sulfate for more, and hectares use 150 to 225 kg. Emergency correction, suitable for foliar spraying, concentration 1%~2%, continuous 2~3 times. Other magnesium fertilizers such as magnesium chloride, magnesium nitrate, magnesium carbonate, etc. can be applied, but magnesium carbonate is slower and longer, suitable as base fertilizer. Experiments have shown that orange sprayed magnesium with magnesium nitrate is better than magnesium nitrate. Calcium, magnesium phosphate fertilizer, steel slag phosphate fertilizer and smelting slag (magnesium) are also available. The magnesium contained in the slag is soluble in sulphate, which is suitable for acid soil and basal fertilizer. Seawater salt by-products such as bitter brines (crystallized as crude magnesium sulfate) and processed products such as potassium and magnesium can be used, but they all contain more chlorine and should be used with caution.
2. Potassium, magnesium balance
Potassium and magnesium have strong antimony action, excess potassium in the soil, inhibition of magnesium absorption, induced magnesium deficiency, more foreign reports. Domestic use of potassium is still low, but it is still rare. However, it is hard to say that it should be noted.
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