How to avoid soil sampling error in soil analysis
Soil analysis is an important means to determine soil nutrients, moisture, fertilizers, etc., then how to conduct soil sampling, how to conduct analysis and analysis, how to apply analysis results, etc. require professional knowledge to explain.
The analysis of soil samples and soil samples is an equally important aspect of ensuring the accuracy of the analysis results. In a sense, the importance of sampling is even greater than that of analytical measurements, because there are certain rules for the analysis and determination of soil. There is no complete and scientific specific provision for sampling so far. Sampling is often based on their own subjective knowledge to select the sampling method, determine the sampling point and the number of samples, it is worth mentioning that the representativeness of such sampling lacks strict verification standards, and it is bound to cause great-probability.
If two samplers enter a piece of cultivated land at the same time, collect the soil sample of the cultivated layer to measure the soil moisture.
The allowable error may be up to several times. Therefore, if the representative sample of the soil sample is not strong, the analysis and measurement method is better, and the accuracy of the analysis result is even higher, it is impossible to correctly reflect the actual nutrient status in the soil, and even to make contradictory results.
Over the years, soil geography, soil surveys, soil research, and agricultural scientists and technicians are sometimes dissatisfied with the analysis results provided by analysts. They feel that actual observations in the field, or the results of the cultivation experiments and the relative analysis data are inconsistent, and the analysis results are difficult to apply. Soil sampling The error cannot be ruled out.
The survey shows that the variation in the nutrient density in the cultivated soil layer of arable land is very significant. In the same wasteland and cultivated land adjacent to the meadow white pulp soil, soil samples were collected and the main nutrient results were analyzed, as shown in Table 1.
From the comparison of the heterogeneity of soil nutrients in wasteland soils and cultivated land, we can see that the heterogeneity of nutrients in the cultivated soil increased. Except that total nitrogen remained basically the same, other analysis items changed, and the heterogeneity of organic matter increased from 0.04 to 0.16. The hydrolysis of nitrogen increased from 0.054 to 0.14, and the available phosphorus increased from 0.11 to 0.37, most prominently. If you do not notice this change, sampling on the soil of the arable land according to the sampling method of the wasteland soil will inevitably lead to the increase of sampling error and loss of sampling representativeness.
In order to further verify the current status of soil nutrient inhomogeneity in cultivated land, sampling has been performed on farmland black soil in general fertility and analyzed.
On the arable land surveyed, 50 soil samples were collected at a single point using the equidistant grid method, and their available phosphorus was analyzed by the method of phase analysis. The analysis results of available 50-sample phosphorus were shown in Table 2. The order in Table 2 is the sampling point. The actual location. The mean value of the 50-point available phosphorus analysis was only 2.349 mg/100 g soil, with a very poor (R) of 4.51, a variance (52) of 1.1, and a non-uniformity (CV) of 0.348.
The highest available phosphorus analysis result for this cultivated land was 4.73 mg/100 g soil, the lowest was 0.42 mg/100 g soil, and the relative difference was 12 times. The relative error of the highest analysis result is 59%, and the relative error of the lowest analysis result is 82%, which is about tens of times larger than the allowable error of soil available phosphorus for the analysis of available phosphorus.
In the second row in the lower right corner of Table 2, there are four adjacent results, which are 3.03, 4.27, and 0. Ling 2.74 mg/100 g soil. If, sampling at any point, the analysis of available phosphorus results will be Does not represent the actual nutrient status of the cultivated land. At the same time, it also proves that the distribution of nutrients in cultivated soil is extremely uneven, and the available nutrients are particularly serious.
Sampling representativeness is a relative concept. In order to increase the representativeness, the number of mixed sampling points will be more. With scientific and practical possibilities, sampling points will eventually be limited. How to determine the sampling quantity according to the experimental and analytical requirements, because this There is not much work done in this area and we still need to continue to explore.
Also take the results of the 50-point available phosphorus analysis in Table 2 as an example and analyze the results at points 5, 10, 15, 20, 25, 30, 35, and 40, respectively. Each random combination 10. This time, it was proved that in this piece of cultivated land, 5, 10, or even 40 points were collected, respectively, and the average probability of reaching the point was closer to the true value (average value). Through the mathematical statistics of the above analysis results, the trends as shown in Table 3 can be preliminary obtained.
In Table 3, the average of the results of the five-point sampling analysis, one hundred statistical analysis results, higher than the average (true value) ten. , 93, lower than the average (true value) of a 1.35. The range (R value) between the 5 and 10 points has a magnitude of 0.42,1. The range (R value) between point and 15 is 0. Ling 5. The range (R value) between 15 and 20 points is 0.44, and the range difference between 20 and 25 (R value) The amplitude is significantly smaller, and the sampling point continues to increase without greater change. Figure 1.
In order to verify the above statistical analysis trends, confirm the frequency distribution analysis of one hundred statistical results.
Since the average is 2.345 mg/100 g soil, it can be considered as an approximate mean range between 2.0 and 2.5 mg/100 g soil. The more frequency in this range, the better the sampling performance. Assuming that only five mixed samples are taken at a time for analysis, only 43 out of a hundred times may be close to the average, with 9 chances not being higher than 3.0 mg/100 g soil, or lower than 1.5 mg/100 g earth.
In the 25-point mixed sample analysis, there will be 85 chances in a hundred times near the average value, ie close to the true value.
When collecting quick-impact soil analysis samples, if the soil is within a larger area, the sampling area should be divided according to the soil type, the status of the cultivation layer, the cultivated crop and growth potential, the physical properties of the water, and the topographic changes. Grid method, single sample mining soil sample, mixed analysis.
Sampling in soil analysis is a very complicated issue. According to the type of soil, the purpose of the analysis is different. Different sampling methods are used. The above introduction has very limited limitations. It is only a preliminary discussion and a comprehensive solution to the sampling problem requires soil workers. work hard.
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