1. Determination of Soil Hygroscopicity Soil hygroscopicity refers to the adsorption of moisture in the air on the surface of soil particles under the action of molecular gravity, which is different from the concept of soil moisture content. Soil moisture refers to all the water contained in the soil, including soil moisture, as well as membrane water, capillary water, and gravity water. Soil moisture mainly comes from irrigation water and atmospheric precipitation, and the content of soil moisture is determined by the relative humidity of air, soil texture, and organic matter content in soil. The method of determination is the same as the method for determining the moisture content described above, except that the soil sample is not naturally wet soil but dried soil. Scrub Sheet,Adult Disposable Underpad,Disposable Medical Underpad,Incontinence Bed Pad Shaoxing Lifecare International Trading Co., Ltd , https://www.sx-lifecare.com
2. Determination of the maximum amount of water absorbed by the soil Under the condition that the air humidity is close to saturation, the gaseous water that can be absorbed by the dry sham soil is called the maximum moisture absorption of the soil.
Measuring instruments and reagents: balance (sensitivity 0.01 and 0.001), weighing bottle (Φ5cm, height 3cm), desiccator, oven, soil moisture monitoring system, saturated potassium sulfate (or 10% sulfuric acid) constitute the air with relative humidity close to saturation .
Measurement procedure: 1 Weigh 5 to 20 g of air-dried soil samples passed through the 1 mm mesh (5 to 10 g for soil containing more soil and organic matter), 10 to 15 g for soil containing less soil and organic matter, sand and organic matter content. Very few soils (15 to 20g) are placed in a weighing bottle of known quality and laid flat on the bottom of the weighing bottle. 2 Place the weighing bottle on the perforated porcelain plate in the desiccator. Open the bottle cap so that it does not touch the wall. The lower part of the desiccator contains saturated potassium sulfate solution (about 3 ml of saturated potassium sulfate solution per 1 g of soil sample). After the dryer is covered, place it in a place where the temperature is stable or keep it at a constant temperature of 20°C. 3 About a week after the soil begins to absorb moisture, cap the weighing bottle out of the desiccator, immediately weigh it on the balance, and then put it back into the desiccator to continue to absorb water. Press every 2 to 3 days thereafter. The former method weighs once until the constant weight is reached or the difference between the previous and the next weighing does not exceed 0.005 g, and the maximum number can be calculated. 4 Put the maximum hygroscopic water into a constant weight taxi sample, place it in a 105C oven and dry it to a constant weight. Calculate the maximum moisture absorption of the soil according to the method of calculating the soil moisture content.
Maximum moisture content = (M wet - M dry) / M dry × 100%
M dry--dry soil weight g, M wet--wet soil weight when the humidity is close to saturation g
3. Measurement of Soil Moisture Moisture The soil withered water content (withering coefficient) is the soil moisture content at which the plant begins to wither, and it is the lower limit of the soil that the plant can use.
Soil withered water content can be calculated according to the maximum hygroscopic water content Withered water content (%) = maximum hygroscopic water (%) × 1.5 (between 1.3 and 25)
Withered water content can also be measured according to the biological method. Plants are cultivated in the container until the plants begin to wither permanently due to lack of water. The water content of the soil is measured to obtain the wilting coefficient.
4. Determination of several moisture constants in the soil The soil samples taken from the field using a ring knife are treated as follows:
After removing the upper and lower covers of the ring knife and replacing the bottom cover with a mesh hole with a filter paper, measure the quality of the ring knife humidified soil.
Remove the ring cutter with wet soil, remove the cover with a net and place a filter paper on it, and place it in the porcelain plate (or flat bottom basin). Fill and maintain the height of the water layer in the porcelain plate to the ring. When the blade is on the edge, it can absorb water for 12 hours (the soil sample can be placed in a slightly longer time). At this time, all non-capillary pores and capillary pores in the soil of the ring knife are full of moisture, cover the lid, and remove it horizontally. Immediately invert, and perform weighing (A) to calculate the maximum water holding capacity.
The weighed ring cutter was set to have the end with the mesh hole and the filter paper placed down in the flat pan with dry sand for 12 hours. At this time, the water in the pores of the soil in the ring cutter had all flowed out. However, the capillary of the soil in the ring knife is still filled with water. Immediately weigh (B) to calculate the capillary water holding capacity.
Then, the ring knives after weighing (B) above are placed in a flat pan with dry sand and kept for a certain period of time (a day and night in sandy soil, 2 to 3 days in loam, and 4 to 5 days in clay). The moisture in the soil is capillary water and the amount of water in the field can be calculated immediately by weighing (C).
A soil sample (approximately 20 g), representative soil samples, of the soil in the ring knife after the weighing (C) was placed in an aluminum box and the soil moisture content was measured. Using this soil moisture content, wet weights in a ring knife were converted to dry soil weight, and various soil moisture constants were calculated.
Calculation of results:
The maximum water capacity%=(AW)/(WW ring)×100%
Capillary water capacity%=(BW)/(WW ring)×100%
Field water capacity%=(CW)/(WW ring)×100%
In the formula: A infiltration 12 hours after the knife + wet weight g
B is placed on dry sand for 12 hours after ring knife + wet weight g
C placed on the dry sand after a day and night ring knife + wet weight g
Dry soil weight in the W ring cutter
W ring knife weight g
The lowest moisture content% = field capacity (%) × 0.7
Drainage capacity = maximum water holding capacity and minimum water holding capacity (field capacity)