Irrigation test stations at all levels should regularly measure the structure, texture, and physical and chemical properties of the soil on the test site. The items and methods to be measured should meet the following requirements:
1 The soil bulk density and the proportion of soil particles are determined by stratified soil layering according to the profile level. The soil sample depth should be collected. The dry farmland should not be less than 1m, and the paddy field should not be less than 30cm.
The soil bulk density can be measured by the ring knife method, or it can be measured by the soil compactness tester. If the comparison analysis of the representative sites shows that the results of the two methods are more consistent, other sites can be measured directly with a soil compactness tester. The proportion of soil particles measured by the pycnometer method.
2 Soil porosity and air capacity can be calculated in accordance with B.0.10 of this specification.
3 The mechanical composition (texture) of the soil is measured with a hydrometer or a hydrometer, and the depth of the collected soil is the same as the measured soil bulk density.
4 Soil organic matter and soil nutrients: only plough layer soil was measured. Soil organic matter can be measured using the K2Cr20 volumetric method. Soil nutrient determination items and methods are as follows:
1) Total nitrogen: Kjeldahl method.
2) Hydrolyzable nitrogen; Alkaline solution diffusion method.
3) Ammonium nitrogen: The sample was first prepared by leaching with 2 mol of KCl solution, and one of the samples was selected from the distillation method, colorimetric method, and ammonia electrode method.
4) Nitrate nitrogen: phenol disulfonic acid colorimetric method.
5) Total phosphorus: An acid-soluble molybdenum-antimony colorimetric method or an alkali-soluble molybdenum-antimony colorimetric method.
6) Available Phosphorus: The calcareous soil is leached by molybdenum and antimony anti-colorimetric method using 0.5mol NaHCO3, and acid soil is leached by molybdenum antimony anti-colorimetric method using 0.03mol NH3F-0.025mol HCl.
7) Total Potassium: NaOH melt-flame photometric method.
8) Available potassium: 1mol NH40Ac leaching-flame photometric method, non-flame photometer equipment can be used 1mol NaNO3 leaching a sodium tetraphenylborate colorimetric method.
9) Soil pH: Only plough layer soil was measured. Indoor potentiometric potentiometric method, outdoor colorimetric method used for permanent colorimetry.
The determination of soil nutrients can also be measured with a soil nutrient analyzer and compared with the results of the above method. If the two results are very close, they can be measured directly with a soil nutrient analyzer.
For key test stations that do not have their own measurement conditions, the determination of soil organic matter and soil nutrients can be commissioned by a nationally or locally recognized laboratory.