Leaf analysis, as the premise of fruit tree nutrition diagnosis method, is that the concentration of various main nutrient elements in leaf tissue is closely related to the reflection of fruit trees. Its basic principle is Justus von Liebig's "Minimum Nutrition Law", that is, the physiological functions of various nutrient elements in plants cannot be substituted for each other. When a certain nutrient element is deficient, it must be supplemented in time to restore the normal growth of plants; The more serious the shortage of nutrients, the greater the potential effect of increasing supply.
Messi (1936) put forward the concept of "critical percentage of nutrient elements" based on dry matter of leaves. He believes that every nutrient element in crops has a fixed "critical percentage". If the concentration of this element in plants exceeds this percentage, it means luxury absorption; if it is lower than this percentage, it means nutrient deficiency. This critical percentage is a conceptual value, which can be said to be a range value, because it will change when it is comprehensively affected by other factors. But for each crop, it is possible to reflect its approximate scope. Accordingly, he divided the correlation curve between plant response and nutrient concentration into several regions or parts.
(1) Minimum percentage area
The concentration of a nutrient element in plants has little change, but the reaction of plants, such as growth, yield and quality, has greatly increased or decreased.
(2) areas with poor supervision
When the concentration of an element in plants increases, the reaction of plants will also increase.
(3) Luxury absorption area
The concentration of an element in plants increases, while the reaction of plants remains unchanged.
Lundegardh( 195 1) thinks that the physiological basis of leaf analysis is mainly two aspects: one is the absorption and distribution of nutrient elements; The second is the relationship between the absorption of nutrient elements and the growth of fruit trees. The curve of figure 5- 1 can show the relationship between the supply level of nutrient elements in trees and the growth or yield of fruit trees. As can be seen from the figure, when the concentration of an element in the tree is very low, such as AB line, the growth and yield of fruit trees are very low. At this time, the appearance of fruit trees presents typical symptoms of element deficiency. Within this line segment, the growth or yield will fluctuate with the profit and loss of nutrient concentration of the tree, and the fluctuation is very steep. When the nutrient elements are in BC segment, the growth or yield of the tree will increase, and the appearance will not show typical symptoms, but there will be a "potential deficiency" period in nutrition physiology. At point C, the nutrient concentration of the tree is the most suitable, and the growth or yield is also the highest. This concentration is the "optimal critical point". In fact, the highest peak of this curve has become an asymptote, and the optimal critical point has become an abstract point. Beyond this point, a range is often defined, which is called "optimal range". On-line CD, the nutrient concentration continued to increase, but the yield changed little, indicating that there was "luxury absorption" of nutrients. In DE line, the concentration of nutrient elements in trees is too high, which leads to toxicity, damage or reduction of growth or yield. The relationship between them can be further illustrated in Table 5- 1.
Fig. 5- 1 Relationship between Nutrient Concentration and Fruit Tree Yield or Growth
Table 5- 1 Nutritional status of trees and reaction of fruit trees
According to the above principle, the task of leaf analysis is to find out all kinds of critical concentrations (nutritional diagnostic indicators) and find out what kind of nutrient element concentrations of the tested fruit trees belong to. In particular, in many orchards, the lack of potential elements is often overlooked. Therefore, in nutritional diagnosis, we should pay special attention to distinguish the potential deficiency of various elements, so as to correct it through appropriate soil testing and formula fertilization measures.
Chapman and Luther divided the indicators of nutrition diagnosis into five grades: lack, small quantity, medium quantity, large quantity and excessive quantity. Leaf analysis can be compared with these indicators, and the technical measures of orchard management can be inspected in detail, thus guiding fertilization. However, Bar Akiva believes that as long as the three grades-deficiency, normal and surplus-are closer to the normal situation of trees, deficiency and surplus are often accompanied by visible symptoms, and their boundary range can be clearly defined on the leaf analysis curve.
In the nutritional diagnosis of fruit trees, we must also pay attention to the proper proportion of various nutritional elements in the tree. If the proportion is out of balance, a nutrient will break or lose its physiological balance, and will soon show the external symptoms of profit and loss, affecting growth or yield. Dumenil( 196 1) used multivariate curve regression to determine the critical levels of various nutrient elements in leaves and their equilibrium relationships. He pointed out that the critical concentration of nitrogen or phosphorus is not a point, but a range, which is determined by the concentration of nitrogen or phosphorus itself and the level of other nutrients in leaves. At the highest yield (or near the highest yield), it is the critical point of nitrogen and phosphorus balance. If the concentration of one nutrient element becomes lower, the critical point of physiological equilibrium of other elements will also decrease. Shear et al. (1946) believe that the growth of plants is a function of the strength of various nutrient elements in leaves and their balance. The so-called nutritional intensity refers to the total molar concentration of all nutrient elements with physiological functions in leaves. Under different nutrient intensities, there will be complex proportions between elements, but only under the optimal concentration and balance conditions can the highest growth or yield be obtained. When the concentration of any one element changes, higher or lower than the optimum intensity, the concentration of other elements also changes, so that various nutrient elements reach a new balance. At this time, a new level of maximum output can be obtained. If the correct sampling method (sampling time and leaf position) is adopted and various factors affecting the accumulation of nutrients in leaves are considered, then the composition of nutrients in leaves is the only effective index to indicate the nutritional status of plants.
Bofil (197 1) put forward a comprehensive method of diagnostic fertilization from the perspective of plant nutrition balance, which is called DRIS method for short. This legal system uses leaf analysis and diagnosis technology to study the relationship between soil, plants and environmental conditions, as well as their relationship with yield or quality, and considers the balance between nutrient elements and various factors affecting crop yield. On the basis of a large number of leaf analysis, the yield results and various parameters that may affect the yield or quality are recorded, so as to determine the diagnostic standard of DRIS method.
Leaf analysis shows that many factors will affect the nutritional level of trees, not only the age, branch type and leaf position, but also the mineral composition of leaves, such as tree species, varieties, combination of rootstock and scion, site conditions, cultivation management, year and fruiting status. Therefore, the influence of these factors must be considered when interpreting the leaf results or applying leaf analysis to guide soil testing and formula fertilization.