The soil nutrient speed measuring instrument is also called soil fertilizer nutrient speed measuring instrument and soil chemical fertilizer speed measuring instrument. The instrument is mainly used to test the content of nitrogen, phosphorus, potassium in soil, such as water, salt, pH, total nitrogen, ammonium nitrogen, alkali nitrogen, available phosphorus, available potassium, calcium, magnesium and boron. It has greatly eased the demand for soil testing and fertilization by farmers all over the country. It also provides a reliable basis for the professional, systematic, information and dataization of fertilizer production enterprises. It is the first choice for soil testing and fertilization in the agricultural sector. Widely used in agricultural testing centers at all levels, agricultural research institutions, fertilizer production, agricultural resources management, agricultural technology services, planting bases and other fields.
test methods
Sample collection and processing
In order to make the measured sample represent the nutrient status of the field, it is required to mix and sample more than one place. It is forbidden to sample at the edge of the field, at the side of the road, at the edge of the ditch, next to the pile of manure or where the fertilizer is placed. The sampling method may be a diagonal method, a five-point sampling method, a checkerboard sampling method, or the like. Generally, at least five samples should be taken for each plot. When the plot is large, more samples can be taken. The sampling depth is generally based on the plough layer (0-20cm). The samples taken at multiple points should be mixed thoroughly and discarded according to the quadruple method. Remove the excess part, keep about half a catty, and pick up the litter, the residual root, the stone and other impurities. If there is a clod, it should be ground and crushed as the sample to be tested for analysis. The rapid determination of soil nutrients is preferably carried out with fresh soil samples.
Water content determination
1, weighing method
Soil water content not only affects the growth and development of crops, but also requires the use of water content for nutrient content calculation during soil nutrient determination.
The operation steps are as follows:
1 Wipe the aluminum box and weigh it on the balance and record it as W.
2 Put about 5 grams of fresh soil sample to remove impurities into an aluminum box, and weigh it together with the aluminum box, and record it as W.
3 Use a straw to absorb 5-10ml of burning alcohol (take the high temperature of the wet soil sample) into the aluminum box, stir it with the soil and ignite it. After the flame is extinguished, add 5ml of alcohol to ignite. After the flame is extinguished, it will be on the balance. Weigh and record as W.
4 result calculation:
Soil water content (%) = (WW) / (W3 - W) × 100%
2, moisture sensor method (for D-type instruments) see the moisture test instructions.
Determination of soil pH
1. Preparation of soil samples:
Remove the large particles from the soil sample (do not need to air dry), weigh 25g into a small beaker, depending on the soil moisture content, add 1:1 times the weight of the air-dried soil (2:1 times the acid soil) plus distilled water, stir the soil The granules were well dispersed and allowed to stand for half an hour.
2. pH test paper measurement method
Immerse it in the soil sample clear liquid with a pH 5~9 precision test paper, take it out after half a minute, and observe the color of the test paper and the color plate.
pH7.0 is neutral, pH 6.5~7.0 is slightly acidic, pH 6.0~6.5 is weakly acidic, pH 5.5~6.0 is acidic, pH<5.5 is strong acid; pH7.0~7.5 is slightly alkaline, pH 7.5~8.0 is weakly alkaline, pH 8.0~8.5 is alkaline, and pH 8.5 is strong alkaline.
3. pH electrode measurement method
1 calibration
A, pre-test calibration:
Press the "Temperature / PH" button to switch the function number to 5, rinse the pH electrode probe with distilled water and blot the water with filter paper, then put it into the standard buffer solution of PH4.01, press the "Adjust +" button, wait until " After E" is erased and the displayed value (not necessarily 4.01, which is temperature dependent) is stabilized, the calibration (which has to be performed before each measurement) is completed.
B. Regular calibration:
After calibrating the electrode at pH 4.01, rinse the probe with distilled water and blot the water with filter paper, then put it into the standard buffer solution of PH9.18, press the "Adjust -" button, wait until the "E" is erased, and the value is displayed. (Not necessarily 9.18, which is temperature dependent) After the stabilization, the calibration (can be calibrated once a week) is completed.
2 determination
The calibrated PH electrode, rinse the pH electrode probe with distilled water and blot the water with filter paper, then put it into the deep liquid to be tested, wait for 2-3 minutes, after the display value is stable, the displayed value is the solution to be tested. PH value.
Note: Each time the PH electrode is used, the probe part should be rinsed with distilled water and blotted with filter paper, then immersed in saturated potassium chloride solution, and the electrode interface is installed with 50Ω terminator to prevent static interference.
4. Determination of salt content
The soil sample preparation is the same as above. For the method of using the salt meter (measurement range 0-1000ml/l), see the salt meter specification; if the salt content of the sample to be tested exceeds the range, please dilute the sample to be tested. The test value is multiplied by the dilution ratio. The liquid content test value of the liquid.
Determination of nitrate nitrogen
principle
Under acidic conditions, the zinc released from the nitric acid test powder and the hydrogen released from the citric acid crop reduce NO3- to NO2-, and these NO2- together with the original small amount of NO2- in the soil react with p-aminobenzenesulfonic acid to form a diazo compound. The diazonium compound is further reacted with α-naphthylamine to form a red azo dye. The shade of red is proportional to the content of nitrate nitrogen in a certain range.
method
(1) absorbing 1, 2, and 4 drops of mixed standard solution containing nitrate nitrogen 2 and 16 ppm, respectively, in a white porcelain reaction tray;
(2) supplemented with distilled water to all 4 drops;
(3) 4 drops of soil leachate in the white porcelain reaction tray;
(4) Add 4 drops of 60% acetic acid each, stir well;
(5) Add one spoonful of sodium nitrate powder (mung bean size), stir well, and colorimetric within 5-20 minutes.
Calculation
Soil nitrate nitrogen content (ppm) = reading (ppm) * 5
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