Prof. Zhu Haizhou Talks about Some Problems in Soil Testing

In the 20 years of reform and opening up, the state invested heavily in the introduction of geotechnical instruments and technologies, which played a significant role in scientific research and teaching work. Rapid testing of the production line and guidance of scientific fertilization techniques are still lagging behind. National ministries and commissions have started since the “6th Five-Year Plan”. Support for the development of various types of soil multifunction instruments and portable small digital photoelectric colorimeter can only be popularized in individual township laboratories. The practice of soil fertilizer test technology promotion in more than ten years has proved that there are two major contradictions: the first instrument is more expensive and the average farmer cannot bear it. Second, the cumbersome chemical operation and complicated calculations can be mastered by non-short-term training and must also have the test. The basic conditions can be carried out. For this reason, in recent years, the development of small, intelligent, low-cost optoelectronic meters for AC and DC has become a hot spot for manufacturers. At the same time, there is an urgent need to improve the simplification of the chemical operation of the soil-photovoltaic colorimetric method and the matching of optoelectronics, so that farmers who do not have chemical knowledge can do so. Do it yourself in the field (or indoors) to perform soil testing and formula fertilization, and send the practical techniques of “precision agriculture” to farmers. The feature of this method is to use the chemical reagents and methods of “Ruilong Brand” soil testing box, and to increase the simple pre-processing of the fertilizer sample with a small digital intelligent photoelectric meter to achieve the effect of rapid testing. The advantages of this combination are:

There is no need to establish laboratories, and glass instruments and medicines are purchased separately so that farmers without knowledge of chemistry can start testing soil.
The low prices of instruments for medicines are suitable for rural and farming households to measure soil in the field or measure fertilizer in the room;
Chemical methods and reagents are the conventional method of microshrinking, and the amount of reagents is small, and the long period of validity is convenient for a few soil samples to be used at any time. However, for a few soil samples, a certain amount of reagents (a small amount is not required) is required for conventional methods, and the remaining reagents will fail in a short period of time. It is only suitable for planned large-scale sample tests. Farmers can send samples at any time and it is difficult to make instant measurements.
The results of the test can be used to formulate fertilization, and conditional intelligence can also be used to perform precise results calculations and fertilizers.
Several issues that should be discussed:

1 test accuracy and practicality:

Compared with the conventional indoor method, the sample is weighed with a scoop instead of a balance, and the reagent is replaced with a drip quantity instead of a glass measuring pipette. This is the main reason that affects the test accuracy. The coloration is the relative volume change with the standard instead of the absolute volume value of the conventional volumetric flask. It is helpful to eliminate the sensory error of human beings, and with the digital concentration direct reading photometer results no longer use the standard curve method, but also avoids the error caused by the influence of different environmental conditions on the color rendering when making the standard curve and when testing. In short the largest error is the sample is not weighing. A large number of comparative experiments have proved that the accuracy of the rapid method is lower than that of the conventional method, and its advantages are simple and practical. It can be taken out of the laboratory immediately. Just like the spring that people carry with them when shopping, it is not as accurate as a legal fair scale, but it can not be arbitrated but can be solved on the spot. problem.

2 Determination of test items: (taking nitrogen as an example)

For a long time, China's soil testing and formula fertilization habits use soil alkali-hydrolyzed nitrogen as an indicator of soil nitrogen supply, which is the sum of available nitrogen and some easily-mineralized organic nitrogen. The mineralization of organic nitrogen is affected by many conditions not all in the current season crop, extending to the total nitrogen in the soil takes longer to fully function, and in terms of effectiveness, total nitrogen is also effective. Is an important indicator to evaluate the overall fertility of the soil. However, the requirement for rapid soil testing in the season should be the level of available nitrogen, especially in the case of large-scale application of chemical fertilizers in modern times. The amount of fertilizer applied to a crop soil test fertilizer is calculated according to the utilization rate of the current season. The aftereffect of the second crop is not counted, and only the soil available nutrients can be re-calculated. Refer to the United States. The agrochemical service center and the experience of soil testing and fertilization in various countries in Europe aim at measuring the fertilization technology of farmers in our country. It is simple and easy to measure only the available nitrogen. In the conditional intensive farms, it is better to use routine indoor methods to regularly guide the whole project to guide fertilization. In addition, the form of other available nitrogen, nitrate-nitrogen and water movement in the soil at any time, usually a sampling of the tillage layer can not measure the relative amount of time, but also does not consider the loss of access to groundwater, according to foreign studies to prove the mobility of ammonium nitrogen Small is mainly concentrated on the relationship between the plough layer and crop growth. Therefore, measuring only ammonium nitrogen still has some effect in the popularization of simple soil testing techniques.

3 Test Error Sources and Optoelectronics Quality Evaluation Method:

The whole process of testing in various industries is mainly divided into two major steps. The first step for the preparation of test liquids is the main technology for professional analysis and the main source of error. The quantitative analysis of a certain element in the second-step test liquid is a universal basic chemical analysis. Technology, a test solution using different analytical methods (such as the weight method, volumetric titration, volumetric colorimetry, spectroscopy) its test results are not much difference, the difference is only different accuracy, such as: the test error of available phosphorus is mainly due to Because of the influence of osmotic intensity and ambient temperature during extraction, it is difficult to replicate in a laboratory without constant temperature leaching conditions. Also, it is difficult to have good reproducibility in the case of repetitive operations in a laboratory without constant temperature leaching conditions. The quantitative measurement method requires a large difference in the amount of extraction, so it cannot be said which quantitative method is accurate. When the results are reported, the extractant used and the method used for quantification must be indicated for the use of results and technical exchanges. If the ammonium acetate leaching (national standard method) of the test solution is directly measured by flame photometry potassium and ammonium removal and then using tetraphenyl boron turbidimetry or potassium electrode potassium law results consistent. Under the premise of understanding the above error sources, we discuss how to evaluate the quality of the photoelectric colorimeter. The photoelectric colorimeter is only used in the final colorimetric phase when the colorimetric method is used for the quantitative determination of elements in the samples to be measured in various industries. It is more accurate than using the human eye to compare with the standard color scale. In the past 20 years, many kinds of electrometers have been widely used in the practice of promoting various electrometers to evaluate the quality of optoelectronic instruments, which is equivalent to the analysis error of the whole process. This is unfair. Even the error of the final colorimetric measurement is not entirely caused by the colorimeter. The color of the measured element after the chemical coloration is relatively stable within a certain period of time. The colorimetric operation must be completed within the specified time. In other words, the color of the tested nutrient solution is constantly changing, which is also the superiority of the digital concentration direct reading instrument compared to the standard curve of the old instrument. Therefore, the stability and sensitivity of the instrument cannot be tested after the color is developed with the standard solution. The chemists determined the constant ionic color as an international common method for testing instrument performance. That is, three (blue, blue) solutions with different concentrations of (color) (yellow) (red) test colorimeter The performance of this is the only objective method to compare the performance of different models of instruments is also a standard method for the quality inspection department to test the colorimetric product quality.

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