Compare the advantages and disadvantages of soil nutrition diagnosis and plant nutrition diagnosis.

Plant nutrition diagnosis technology has become an important technical means to guide fertilization. At present, the commonly used diagnostic methods include plant tissue analysis and diagnosis, soil analysis and diagnosis, plant appearance diagnosis, field fertilization test diagnosis, physiological and biochemical analysis and diagnosis, plant tissue fluid analysis and diagnosis, nondestructive testing technology and so on.

Each method has its own advantages and disadvantages. In actual production, several diagnostic methods must be comprehensively applied in combination with specific conditions in order to get correct diagnostic results. The most commonly used nutritional diagnosis methods are: plant appearance diagnosis (morphological diagnosis), soil analysis diagnosis (soil chemical diagnosis) and plant tissue analysis diagnosis (phytochemical diagnosis).

(1) The morphological diagnosis of plant nutrition is to determine the nutritional status of plants according to the appearance and symptoms of plant growth and development. Plant leaves are the most sensitive parts of plant nutrition, and many common element deficiencies can be more accurately concluded by observing the leaves. However, morphological diagnosis also has some limitations, that is, when plants lack more than two nutrient elements at the same time, it is difficult to determine which element is the most lacking or which element is the main and decisive.

(2) Determine the advantages and disadvantages of soil chemical diagnosis, compare the soil nutrient content with the reference standard, and judge the abundance and deficiency. Mineral nutrients needed by crops are basically absorbed from soil, so the yield is determined by the supply capacity of soil nutrients, so soil chemical diagnosis has always been an important means to guide fertilization practice.

According to the relationship between soil nutrient content and crop yield, nutrient levels are usually divided into three levels: high, medium and low. Soil nutrient content is high, fertilization does not increase production; In terms of soil nutrient content, no fertilization may reduce the yield, but the range is not more than 20%? 25%; The soil nutrient content is low, and the yield reduction rate is >10% without fertilization. 25%。

The difference between soil nutrient critical value and plant nutrient critical value is that the latter is rarely affected by region and soil, while the soil critical value is significantly affected by soil pH value and texture. For example, it is more difficult for crops to absorb nutrients from clay than from sand, and the former has a higher critical value. Compared with phytochemical diagnosis, soil chemical diagnosis has its own advantages and disadvantages.

Analysis of cultivated soil; First, it has predictive significance, which can predict what is missing before planting so as to prevent it as soon as possible; Second, as a reason to investigate the malnutrition of crops, it is proved that the soil nutrients are insufficient, or some elements are too much to inhibit the normal growth of crops, and whether there is antagonism between elements.

These are all impossible for plant analysis. Therefore, in general diagnosis, plant analysis and soil analysis are combined to complement each other and confirm each other, so as to improve the accuracy of diagnosis. (3) Advantages and disadvantages of phytochemical diagnosis When crops are malnourished, the contents of some elements in the body are bound to be abnormal. It is one of the basic means of diagnosis to analyze the content of elements in crops and compare them with reference standards to judge whether they are rich or not.

Plant composition analysis can be divided into two categories: total analysis and rapid tissue determination. The former determines the content of elements in crops, while the current analytical technology can determine all the necessary elements and possible elements in plants, with high accuracy and reliable data, which is usually the basic basis for diagnostic conclusions. Full analysis is time-consuming and can only be carried out in the laboratory.

Tissue rapid determination of unabsorbed nutrients in crops is simple and rapid through color reaction and visual grading, and is generally suitable for head diagnosis in the field. Because of its universality, it is usually used as a rough judgment of whether an element is lacking. At present, the test range is limited to several major elements such as nitrogen, phosphorus and potassium. However, the rapid determination of trace elements is difficult to achieve because of its extremely small content and high precision.

① Leaf analysis and diagnosis is a branch of phytochemical diagnosis. Taking leaves as samples, the contents of various nutrients are analyzed and compared with reference standards to judge their abundance and deficiency. Because the results of leaf analysis have achieved great success in guiding fruit tree fertilization and realizing expected yield and quality control, it has been widely valued and developed into a special technology for fruit tree nutrition diagnosis.

Fruit trees are perennial crops, with long leaf life and long stable period of nutrients, which have a good correlation with the nutritional status and yield of trees. The critical value of fruit tree nutrients is little affected by the region. It is found that the lack or toxicity level of certain elements in fruit trees is consistent in different places, especially trace elements.

For example, when the leaf content is less than 30 mg/kg, many fruit trees will be deficient in manganese. Furthermore, the remedial measures taken according to the results of blade analysis and diagnosis can catch up with the time and work of the season. (2) Rapid tissue diagnosis. It is a semi-quantitative analysis to determine the nutrient content of fresh plant tissues by rapid measurement. The measured nutrients are macromolecular nutrients that have not been assimilated or assimilated but are still free, and the results are judged by visual colorimetry.

The biggest feature of this method is its high speed. Generally, a project can be tested in a few minutes or dozens of minutes. Usually, tissue fragments directly react with extractant and chromogenic agent in test tubes for rapid tissue detection. Or drop the tissue fluid on the colorimetric plate or test paper to react with the reagent. This method requires few reagents, which is also called "drop method".

The following aspects should be paid attention to when using tissue rapid detection for diagnosis: (1) The parts that are sensitive to a certain element should be sampled, and the parts that can best reflect the lack (the lowest concentration of nutrients) are suitable parts; Nutrients should be divided into less grades, generally divided into three grades: lack, normal and rich, with less grades and large grade difference, which is conducive to judgment and useless subdivision; In order to reduce the error, fewer samples are used, and the drop test needs more repetition. Attention should be paid to the determination of related elements, such as the diagnosis of phosphorus-deficient crops, nitrogen can be determined at the same time, because the content of nitrate nitrogen in phosphorus-deficient plants is usually high, which is helpful to judge the results; The determination results should be combined with the comprehensive analysis of crop appearance, morphological symptoms, soil conditions, cultivation and fertilization.