(I) Symptoms
When the crop is deficient in nitrogen, the plants are chlorotic. The leaves are pale green or yellow-green. The growth is slow. The plants are small, erect, with few branches, small leaves, and small angles with the diameter; the symptoms expand from the bottom up, serious At the present time, the leaves are yellow and fall early; the roots are small and slender; the lateral buds are dormant, the flowering results are reduced, the ripening is earlier, and the yield is reduced. Rice and wheat have less or no nitrogen deficiency tillers, and fewer grains and spikes; maize leaves are yellowing under nitrogen deficiency, and the tip of the leaves are withered, showing a "V" shape downward; leaves of nitrogen deficiency in leafy vegetables are small and thin, light green Or yellowish green, reduced water content, increased cellulose, loss of tender and juicy features, decreased commercial value; cabbage-leafed nitrogen deficiency leaf ball is not substantial; fruit trees lack of nitrogen shoot thin, small leaves pale, small fruit skin Hard, sugar content is relatively high, but the yield is very low.
Excessive supply of nitrogen for crops shows longevity. Branches and leaves are multiplied, leaves are densely colored, water content is increased, cellulose and lignin are reduced, the organization is tender, resistance to pests and diseases, drought resistance, and lodging resistance are reduced. Grain-filling rate of cereal crops, 1000-grain weight Decrease, poor maturity; tuber potato crops reduce the number of starch, starch rate decreased; melons and fruits falling and fruiting, maturity delayed.
(b) Prone environmental conditions
Crops require large quantities of nitrogen, most of the soil can not meet the needs of crops, if not apply nitrogen fertilizer, the general crops may have symptoms of nitrogen deficiency, the following conditions are more prone to occur: 1 light sand and organic poor soil; 2 poor soil physical and chemical properties Poor drainage, low soil temperature, slow decomposition of organic matter in the soil; 3 the application of a large amount of fresh organic fertilizers, such as green manure and fresh stalks, can easily lead to the proliferation of microorganisms, to seize the effective nitrogen in the soil and cause temporary nitrogen deficiency. Excess nitrogen is generally due to the excessive application of nitrogen fertilizer or an insufficient estimate of the amount of residual fertilizer.
(c) Diagnosis
Form diagnosis
The symptoms of nitrogen deficiency in crops are as above. It is characterized by yellow leaves and short plants, which are usually easy to judge. However, morphological judgment alone, it is inevitable that misdiagnosis, still need to combine the chemical diagnosis of plants and soil.
2. Plant diagnosis
The total nitrogen content of the plant has a high correlation with crop growth and yield. The critical range of nitrogen deficiency for various crops: rice (birth leaves at the tiller stage) is all N 2.4% to 2.8%; wheat, oats (heading stage above ground The Department) is 1.25% to 1.50%, corn (tearing period of ear section leaves) is 2.9% to 3.0%, cotton (bud stage functional leaves) and sorghum (flowering period from top to bottom third leaves) is 2.5% to 3.0% The fruit trees (leaves) ranged from 2.0% to 3.8%. Production was judged as quickly as possible by the time. At the time of diagnosis at the field head, a rapid histochemical method was used: 1 Drought effect nitric acid test method, NO3 in the crop tissue -
N and the test powder, red azo material produced, according to the depth of the red to determine the status of nitrogen. 2With iodine-starch method, the water channel enters the spikelet differentiation stage, and the degree of starch accumulation in the sheath is negatively correlated with the nitrogen level. Sheaths were collected and stained with iodine solution (blue color) for the leaf sheath. The ratio of staining length (A) to leaf sheath length (B) (A/B) was used to judge. This method is limited to determine the need for late panicle fertilizer.