How to collect soil samples for testing by farmers

The subsidy project of soil testing formula fertilization has entered the stage of popularizing formula fertilizer according to regional large formula since it was launched in 2005. In order to implement the soil testing formula technology in farmland orchards and make "small adjustments" according to local conditions, accurate collection of soil samples and accumulation of soil "physical examination" big data is the premise. In recent years, with the acceleration of moderate scale operation of land, new operators such as large growers, family farms, farmers' professional cooperatives and agricultural socialized service organizations continue to develop. Compared with traditional farmers, they have new changes in farming methods and new requirements for scientific fertilization and improving quality and efficiency. It can be said that the new agricultural management main body will be the main body of implementing soil testing formula fertilization technology. Today, this edition specially invites experts from the Agricultural Technology extension Service Center of Meixian County, Shaanxi Province to popularize relevant professional knowledge, laying a good foundation for farmers to use soil testing formula technology to increase production and income.

To apply fertilizer scientifically and improve the utilization rate of fertilizer, we must first understand the status of soil nutrients, so it is necessary to collect soil samples. The collection of soil samples is an important link to determine the reliability of soil test results. Because of the great difference in nutrients of soil, especially cultivated soil, the error of sampling is several times larger than that of analysis. The sampling standard is that the collected soil samples can represent the average nutrient status of the sampled fields. therefore, collecting representative soil samples is the basis and premise of soil testing and formula fertilization. In the case of lack of professional and technical personnel of soil and fertilizer, allowing agricultural producers to collect soil samples by themselves is an effective measure to speed up the application of soil testing formula fertilization technology. Therefore, teaching them the method of collecting soil samples is particularly important for popularizing the technology of soil testing and formula fertilization and improving farmers' awareness of scientific fertilization.

1 determination of sampling unit

There are great differences in local soil nutrients due to people's production practices, such as uneven fertilization, strip or hole fertilizer application, ridge planting, soil deep ploughing, planting crops and so on. Therefore, according to the difference of soil nutrients, the soil is divided into several sampling areas, which are called sampling units. The soil nutrients of each sampling unit are the same as possible. Each sampling unit can be divided into several small units according to the size of the area. the smaller the area represented by each small unit, the more reliable the representativeness of the soil sample. However, the smaller the area is, the greater the sampling workload is and the greater the analytical workload is. So, what area does a mixed sample represent that is more reliable and economical? In addition to different soil types must be distinguished from sampling, generally a sampling unit can range from a few mu to dozens of mu.

2 determination of sampling time

The content of available nutrients in soil varies greatly with the change of season, soil temperature and moisture, such as the increase of available phosphorus and potassium in winter. Therefore, the analytical results of soil samples collected at the same time can be compared with each other. The determination of sampling time should be different according to different kinds of crops and different purposes of fertilization. For ⑴ food crops such as wheat, rice, corn, etc., soil samples are generally collected before and after the previous crop harvest, and can also be sampled before sowing. ⑵ vegetable cash crops such as tomatoes, cauliflower, small green vegetables, etc., generally collect soil samples before sowing. ⑶ fruit tree cash crops such as apple, pear, kiwifruit and other orchard soil, the purpose of fertilization is different, the soil time is different. If topdressing during the fruit expansion period, soil samples should be collected in mid-late May. If the annual fertilization scheme for fruit trees is determined, the soil should be collected from late September to the first and middle of October, that is, soil samples should be collected for analysis and testing before and after fruit harvest.

3 selection of sampling tools

There are three kinds of professional tools commonly used for sampling: small soil shovel, tubular soil drill and ordinary soil drill (see figure 1). Farmers usually choose shovels or small shovels to take soil samples themselves. No matter using professional sampling tools or farmers sampling with shovels, special attention should be paid to the consistency of upper and lower soil sampling, especially to prevent topsoil from falling off, otherwise, it will have a great impact on the analysis results.

4 collection of mixed samples

Because of the non-uniformity of soil, several points are randomly selected according to a certain route in a sampling unit, and the soil samples collected from each point are mixed to form a mixed sample. The mixed sample is actually equivalent to an average, which is used to reduce soil differences and improve the representativeness of the sample. Generally speaking, according to the area of the sampling unit, a mixed sample consists of 5 to 15 sampling points. Mixed sample collection method:

1. The collection of mixed samples requires that the depth of soil samples collected at each point should be the same, and the upper and lower soil should be the same. Each point is randomly selected, that is, all points in a sampling unit have an equal chance of being picked up. In order to avoid systematic errors, the general sampling routes include diagonal sampling, chessboard sampling, serpentine or "S" sampling (see figure 2).

two。 Depth and location of sampling points ⑴ grain crops and vegetable cash crops are generally taken as a sampling unit, and soil is sampled at 15 points evenly in a sampling unit, with a depth of 020 cm, that is, 0 cm 20 cm soil samples are taken vertically from the surface. The excavation location should be 3-5 meters away from the outer edge of the field block. In the field of cash crops of fruit trees in ⑵, the sampling unit is generally 2 to 20 mu, and 5 to 15 points are selected evenly in each sampling unit. The soil should be collected at 3 points from the projection of the canopy of fruit trees, with a depth of 0 cm to 30 cm (see figure 3). Similarly, the soil sampling position should be 3 meters away from the outer edge of the field.

3. The weight of the mixed sample generally needs about 1 kilogram to send to the laboratory. If the weight of the collected sample exceeds more, you can put the collected soil sample on a plastic sheet or wooden plate, crush the soil with your hand, remove stones, grass roots and litter, mix all the soil samples, and then divide the soil sample into a sample bag (such as plastic bag or paper bag) using the "dichotomy" (see figure 4). Put the soil sample label in the bag, and write clearly on the soil sample label the farmer's name, sampling place, field location, sampling depth, sampling date, sampler, planting crop, variety, and if it is a fruit tree indicating tree age and perennial yield, perennial fertilization management and other farmer cultivation and management measures information. The sample label should be clearly written in pencil.

The collected soil samples are sent to the soil fertilizer laboratory and analyzed by the laboratory technicians. according to the soil sample test results, combined with the perennial fertilizer efficiency test results of the soil fertilizer station, the crop fertilization plan can be formulated to guide farmers to apply fertilizer.