Look at the soil
Most of the necessary nutrients for crops come from the soil, that is, the nutrient status of crops has a direct relationship with the status of soil nutrients. Therefore, diagnosis of nutrient status of crops must take into account the diagnosis of soil nutrient status.
1. The extraction of soil available nutrients and indicators The soil nutrients exist in different forms, of which only a part can be directly absorbed and utilized by crops. Due to the differences in soil properties and the nature of various nutrients, to understand the abundance of soil available nutrients, we must carry out soil nutrient analysis. For details, please refer to Soil Nutrient Indicators in Nutrient Analysis.
2. The effectiveness of soil nutrients in the diagnosis of soil nutrients is constrained by many factors. Therefore, the total amount of nutrients contained in the soil does not explain the abundance of crop nutrients. Because of the physical and chemical properties of the soil and the environmental conditions, they all affect the form of their nutrients. At the same time, there are obvious differences in the ability of different crop types and even different varieties to absorb and utilize nutrients in different forms. Therefore, other conditions must be considered in order to make a correct comparison of soil nutrient status. Such as soil pH, temperature, groundwater level, bacteria and other factors affect the crop's absorption and utilization of soil nutrients and normal growth and development.
The effect of soil pH on soil nutrient availability is obvious. One effect is the adaptability of crop characteristics to acidity and alkalinity. For example, if a plant grown in acidophilic conditions is planted in alkaline soils with high pH, ​​it may grow abnormally despite good nutrient conditions. Another effect is the effect of pH on the nutrient presence and the effect on microbial activity. When the pH of the soil is alkaline and gradually increases, the availability of phosphorus, iron, manganese, zinc, boron, and copper decreases, while the availability of molybdenum increases. In acidic conditions, micronutrients, in addition to molybdenum, manganese, zinc, The effectiveness of copper and boron increases, but the pH is too low, and iron, manganese, and aluminum may be poisoned. The effectiveness of phosphorus is also reduced due to fixation by iron and aluminum.
Temperature often affects the absorption of soil nutrients by crop roots. At low temperature, the degree of absorption of some nutrients in the crop roots was reduced by phosphorus> nitrogen> sulfur> magnesium> calcium. It can be seen that low temperature has the most significant effect on phosphorus nutrients. Sometimes it is found that the phosphorus concentration in the plant tissues affected by low temperature is low, but the actual soil phosphorus nutrients are not low.
The groundwater level directly affects the soil moisture status, and the water condition affects the ventilation conditions. When the groundwater level is high or the ground is low, it often results in water accumulation in the soil, resulting in strong reduction conditions. Ferrous iron and sulfides may accumulate, which is harmful to crop roots and absorption of nutrients, resulting in abnormal growth.
Second look at the plants
1), look for the site of symptoms
If the symptoms first appear on the old leaves, it shows that nitrogen, phosphorus, magnesium and zinc are lacking. If the symptoms first appear in the newborn site, the lack of calcium, iron, boron, sulfur and so on.
2) To see whether the old leaves have lesions or if symptoms appear in the new leaves, there are no lesions, which may be phosphorus deficiency or nitrogen: if there is a lesion, it may be potassium deficiency or zinc deficiency. If the symptoms start from the new leaves, if the items easily die, it may be boron or calcium deficiency; when the terminal buds are not easy to die, they may lack iron, sulfur, manganese, molybdenum, and copper.
3) Determine the lack of elements based on specific conditions
1. Nitrogen: When a plant is deficient in nitrogen, it starts yellowing from the lower leaves and gradually expands to the upper part. The roots of crops are whiter and slender than the roots that grow normally, and the amount of roots is reduced.
2. Phosphorus: When plants lack phosphorus, cell division is blocked, growth is stagnant, roots are stunted, leaf stenosis, leaf color is dark green, and turns to purple when severe.
3. Potassium: When a plant lacks potassium, it begins to yellow from the discontinuity and edge of the old leaf, and gradually withers, with small spots on the leaf surface, which then dry up or scorch. Finally, the leaf between the veins of the leaf is dry and leaves in the leaf. Small spots or plaques appear on the face.
4. Calcium: When the plant lacks calcium, the plants are short, the roots are stunted, and the meristem of the stems and leaves and root tips are damaged. When calcium deficiency is severe, the young leaves of the plants are curled, the new leaves are difficult to pull out, and the adhesion phenomenon occurs between the tip of the leaves. The tips and edges of the leaves are yellow or burnt and dead. The root tip cells rot and die.
5. Magnesium: When the plant lacks magnesium, the symptoms first appear in the old leaves. At the beginning, the breaks in the leaves and the tip of the leaf edges fade in color, from light green to yellow and then purple, and then to the leaf base and the center, but The veins remain green, forming a clear network of veins on the leaves, and the leaves are seriously withered and shed.
6. Sulfur: The symptoms of plant sulfur deficiency are similar to those of nitrogen deficiency. In general, the plants are short and small, the leaves are small, the leaves curl upwards, become hard and fragile, fall off earlier, and flowering is late with little results.
7. Iron: When the plant is deficient in iron, the upper young leaves become chlorotic, appear pale yellow and even white, usually appear first among the veins, and the photosynthesis is blocked.
8. Manganese: When the plants are deficient in manganese, the new leaves lose their chlorotic greenness and appear necrotic spots. The leaves have white curls. The fruit trees have chlorotic malformations. The branches are curved, and the tumors are long and hard. The fruit is not brittle.
9, copper: When the plant lacks copper, the new leaves lose green and yellow, appear necrotic spots, curly white hair among the leaves, fruit trees are deformed, branches bent, long nodules, the fruit is hard but not brittle.
10. Zinc: When the plants are deficient in zinc, the leaves are chlorotic and yellow, brown spots appear, and tissue necrosis occurs. The fruit trees have “lobular diseaseâ€.