The significance of rapid nutrient measurement

Rapid nutrient measurement is an important method for nutritional diagnosis. The diagnosis includes "diagnosis" and "break". The "diagnosis" is based on the understanding of the content of various nutrients, which is the basis for understanding, and it requires a more sensitive and reliable method. "Off" is based on the analysis of results and other relevant data to determine the abundance of nutrients, is a deep understanding, so there must be indicators. The index is to obtain the correlation between the growth and development of various crops and the nutritional components through field surveys, fertilizer tests, and soil measurements, and find out the corresponding indicators. Therefore, both diagnosis and treatment require analysis as a means. The analysis method can be either routine analysis or rapid measurement. Due to the speed and simplicity of the rapid test method, it can also be used to observe the growth status of crops at the same time in the field, so its production is more targeted.

Of course, the rapid nutrient measurement method is simplified on the basis of routine analysis, and the measured nutrient form and quantity will be different. Some forms of nutrients can not be completely leached, so the number of nutrients detected from rapid tests is generally lower than General analysis. Because the speed measurement method is relatively simple, the accuracy and precision of the speed measurement data are lower than the conventional analysis.

Although there are many shortcomings in the rapid test results, it is still an effective method for diagnosing soil nutrient levels and the nutrient deficiency of plants due to its rapidity and simplicity and certain degree of accuracy. Of course, the diagnosis method is comprehensive. First, we must look at the sky, see the fields, look at the crops, and then combine the chemical rapid measurement of the soil with the rapid test of the crop tissue in order to make a correct diagnosis.

Second, the principle and method of soil nutrient rapid measurement

The chemical principle of soil nutrient rapid measurement is roughly the same as the conventional analysis method. Refer to the “Laboratory” section.

To improve the accuracy of rapid test results, attention must be paid to the accuracy of sampling, leaching, determination methods, and diagnostic indicators.

1, sampling

The soil sample for speed measurement must reflect as much as possible the actual nutrient supply in the field. For this reason, attention should be paid to the sample collection method. Due to the simplicity and low cost of the quick test, the number of samples can be more, and the sampling point should be selected to reflect the level of soil supplying fertilizer sensitively.

The soil samples for the diagnosis of the deficiency are collected near the roots of the diseased plants and treated individually and separately so that they can be compared with the normal soil to understand the status of the soil supply to the local soil.

Soil samples for formula fertilization should not only be sampled before sowing in order to understand the level of soil fertilizer, but also sampled continuously during the crop growing season to understand the dynamic changes of soil nutrients.

For some of the more fluid nutrients, such as nitrate-nitrogen, should also pay attention to the sampling depth, collected samples of the soil layer and the subsoil layer, to understand the nutrient flow within the root range of the crop.

2, leaching

The principle of nutrient extraction is the same as the conventional method, but the type of extractant used, the ratio of soil to liquid, and the extraction time are different.

Nutrient extractants: In order to be simple and convenient, the “universal extractor” is often used for rapid test, that is, one extract can measure multiple nutrients at the same time. Common general extractants include acid salt extractants, such as 3% HOAc - 10% NaAc pH 4.8; neutral salt extracts such as 1 N Na2SO4; alkaline extractants such as 0.5M NaHCO3; chelating and extracting agents , such as DTPA. The choice of extractant should be based on the soil properties and the type of nutrients to be determined. For example, in southern paddy fields, 1N neutral Na2SO4 is used as the leaching agent; in the north, 0.5M NaHCO3+0.5N Na2SO4 is used as the universal immersion agent.

Soil-Liquid Ratio: The sample rate of the rapid test method is generally smaller than that of the conventional analysis, mainly reducing the amount of reagents, reducing the analysis cost, shortening the filtration time, and accelerating the analysis speed. However, if the ratio is too small, filtration is difficult. At present, the proportion of 1:5 is mostly used.

Leaching time: The length of the leach time has an effect on the amount of leaching of certain nutrients. Currently, it usually takes 3 minutes for leaching.

Third, the measurement method

The rapid analysis of nutrients commonly used spot analysis method, that is, only with a drop or a few drops of reagents and extracts, can produce a reaction analysis method. Because color intensity is related to the content of this component, it can be quantitatively quantified by colorimetry.

Colorimetric assay is usually carried out in a drop plate or a small test tube. The number of reagents used for a drop plate is small, and the required equipment is also relatively simple; a small test tube colorimetric method uses more leachate, but the coloration is clearer and often available. High accuracy.

The turbidimetric method is used to determine the components that precipitate with the reagent, such as calcium and potassium. Turbidimetry is based on the visibility of the background. One method is to compare the standard concentration with the same thickness of the liquid layer as the background with unequal thickness or color shades as background. Another method is to adjust the background thickness in the same context until the background is not visible. According to the turbidity method, the liquid layer thickness is inversely proportional to its concentration, and therefore it can be converted to the concentration according to the liquid layer thickness.

Soil nutrient fast-tracking test is usually conducted by visual inspection, its sensitivity is limited, and it is impossible to prepare an ultra-fine standard solution. Therefore, the concentration is usually divided into several levels and the corresponding standard color gradation is produced for comparison.

In recent years, with the development of science and technology, soil nutrient rapid measurement equipment has also developed rapidly, and the most widely used ones are the “Qiansheng” brand soil quick side instrument promoted by the Central Committee of the Communist Youth League and the “YN” series produced by Henan Agricultural University. Earth measuring instruments, these instruments are equipped with now more advanced electronic equipment, the accuracy and efficiency of the measurement have been greatly improved.

Fourth, the results of the application

When the soil nutrient rapid test results are used in diagnosis, the nutrient rating criteria should be determined first. That is to say, the rapid test results are divided into several grades according to their response to plant production, respectively, indicating the degree of abundance. Generally divided into high, medium and low levels. The basis for division is roughly:

High: No high fertilization yield, no significant increase in yield after fertilization, and nutrient levels in the plant are sufficient. This level can also be divided into high and high levels.

Moderate: Low yield without fertilization, yield generally increased after fertilization, and the yield increase rate is less than 25%. The nutrient content in plants can generally maintain normal levels.

Low: The yield of non-fertilizer is very low, the yield after fertilization is significantly increased, the increase rate is greater than 25%, and the nutrient content in the plant is lower than the normal level. This level can be divided into low and very low two levels.

According to the soil nutrient grades classified according to the above principles, the nutrient content range of each grade differs depending on the plant species and soil properties. Therefore, for various crops and all kinds of soils with different properties, according to their supply and demand characteristics of nutrients, they should be graded according to different standards, and fertilizers should be guided according to grades.