CN105823864A - Method for detecting inherent water suction of soil - Google Patents
Method for detecting inherent water suction of soil Download PDFInfo
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- CN105823864A CN105823864A CN201610125465.9A CN201610125465A CN105823864A CN 105823864 A CN105823864 A CN 105823864A CN 201610125465 A CN201610125465 A CN 201610125465A CN 105823864 A CN105823864 A CN 105823864A
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- soil
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- pedotheque
- potential
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
- G01N33/246—Earth materials for water content
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
- G01N2033/245—Earth materials for agricultural purposes
Abstract
The invention discloses a method for detecting the inherent water suction of soil, and belongs to the field of agricultural water and soil conservation and agricultural engineering. The method comprises the following steps: deducing a relational expression between soil water potential phiS and the water content P based on the Gibbs function of the chemical potential of a mixed substance, determining the soil water potential phiS of soil to be detected and the water content P at a corresponding time to establish a mathematic model between the soil water potential phiS and the water content P and determine parameters in the model, substituting the water content P = 0 into the mathematic model between the soil water potential phiS and the water content P in order to obtain the soil water potential when the water content of soil is 0, and defining the absolute value of the soil water potential under the soil water content of 0 as the inherent water suction of the soil to be detected. The method provides scientific data for evaluating the soil water conservation and irrigating crops.
Description
Technical field
The invention belongs to agricultural water and soil conservation and agricultural engineering field, be specifically related to a kind of method detecting the intrinsic water suction force of soil.
Background technology
Soil moisture content is the key factor affecting plant growth, because the height of soil moisture content directly decides the size of soil water potential.In process of crop growth, soil water potential plays an important role.Soil water suction is the important indicator of reflection soil water sorption ability, not only affects the plant absorption to moisture, also can affect the crop utilization to nutrient simultaneously.
At present, the monitoring method of soil moisture content has TDR method, NEUTRON METHOD, gamma-rays method, weighting method after dried, electric resistance of soil method etc.；The main tensioned meter of detecting instrument, vacuum meter and the dew point water potential meter of soil water potential.The detection method of soil moisture content is a lot, and precision has reached the highest level, but the detection method of soil water potential relatively want single a lot.Tonometer is made up of three parts, porous ceramic cup, piezometer and ceramic cup and manometric connecting tube；Tonometer is to measure the main method of matric potential, and soil water potential is that matric potential is one of soil numerous soil water potential origin cause of formation, has limitation, and tonometer measurement range is the least by coefficient results such as solute potential, matric potential, pressure potentials；Gong Zhen equality (Gong Zhenping, Shao Xiaohou, Zhang Fucang, Deng. agrology and geoponics [M]. Beijing: Chinese Water Conservancy water power publishing house, in " agrology and geoponics " book, 2009:82-84.) point out that the measurement range of tonometer is usually-0.8～0Mpa, it is impossible to soil water potential when detection soil moisture content is low；In addition, the method for embedding of tonometer also can produce impact to measurement result, so degree of accuracy is relatively low.Vacuum meter principle and tonometer are identical, so precision is the lowest.
Dew point water potential meter is the instrument being measured the flow of water by thermocouple sensor specially, automatically maintains the sensing of thermocouple junction constant temperature and control circuit under dew point temperature, and degree of accuracy is the highest, and stable；In recent years, much research about soil water potential is all using dew point water potential meter as observation instrument；According to dew point water potential meter principle, soil to be measured just can must detect containing moisture, i.e. cannot accurately detect water content extremely low time soil water potential.
Summary of the invention
For the deficiencies in the prior art, the invention provides a kind of method detecting the intrinsic water suction force of soil, not only construct the relational model between soil water potential and water content, and the water potential value of soil when different soils water content is 0 can be obtained；By the intrinsic water suction force of soil, the character of soil can be analyzed, understand the ability of adsorption by soil water, provide technical support for understanding soil property in depth.
The present invention realizes above-mentioned technical purpose by techniques below means.
A kind of method detecting the intrinsic water suction force of soil, including step:
Step 1), take the appropriate pedotheque to be measured in field or field, be placed in the most smooth table top and make thinner, remove impurity removing after air-drying, and pedotheque is pulverized；
Step 2), with the field capacity of core cutter method detection pedotheque, it is designated as C；
Step 3), take after above-mentioned pulverizing etc. the pedotheque two parts of quality, and be labeled as pedotheque A and B, add water in pedotheque so that it is water content reaches the field capacity of pedotheque, uniform mixing, load identical container；
Step 4), by pedotheque A and B, it is placed under same environment so that it is dehydration continuously simultaneously；
Step 5), measure soil water potential ψ of different dehydration moment pedotheque A respectivelySAnd water content P of corresponding moment pedotheque B, according to soil water potential ψ of pedotheque ASSituation of change measure 10～15 groups of data continuously；
Step 6), according to step 5) data that record, construct soil water potential ψ to be measuredSMathematical model (1+P) ψ with water content PS=y0+ kln (1+P), y0It is model parameter with k；
Step 7), according to soil water potential ψ to be measuredSWith the mathematical model of water content P, obtain the intrinsic water suction force of pedotheque to be measured.
Further, described step 3) in add water in pedotheque, soil is 1:C with the mass ratio of water.
Further, described step 6) in y0It is by soil water potential ψ with the value of kSMathematical model (1+P) ψ with water content PS=y0+ kln (1+P) matching determines.
Further, described step 6) in y0It is water potential value when 0 for soil moisture content, y0Absolute value ψS0Represent, ψS0=| y0|, then ψS0Represent the intrinsic water suction force measuring soil.
The invention has the beneficial effects as follows:
1. the intrinsic water suction force information of the soil obtained by the present invention is that soil to be measured is intrinsic, is not limited by the weathers such as the temperature measured, humidity and ecological factor, and the result of mensuration has comparability.
2. the intrinsic water suction force information of the soil that the present invention obtains can be used to compare the absorption moisture ability of different soils.
3. the soil water potential formula that the model of the present invention is derived based on being based on the Gibbs function of compounding substances chemical potential, it is the model having mechanism background, there is reliability.The soil water potential that the moisture content range of applying this model to measure is big, the soil water content of 0-100% can measure its flow of water according to the present invention；General water potential meter can be measured and be difficult to the soil water potential of the extremely low water content (water content less than 2%) measured because of the restriction of accuracy and sensitivity.
4. the assay method of intrinsic water suction force, step and the calculating of the soil of the present invention are simple, time-consuming few, are beneficial to universal.
Accompanying drawing explanation
Fig. 1 be two kinds of soil soil water potential and water content between the scatterplot of relation.
In figure :-soil sample 1 measured data, ●-soil sample 2 measured data.
Detailed description of the invention
Below in conjunction with the accompanying drawings and specific embodiment the present invention is further illustrated, but protection scope of the present invention is not limited to that.
The present invention is the loam from Zhengjiang City's Binjiang wetland collection and two kinds of soil samples of loamy texture clay are measured.
Step 1), take two kinds of pedotheque 20kg to be measured at Binjiang wetland, one is that loam is designated as soil sample 1, and another kind is that loamy texture clay is designated as soil sample 2, is placed in the most smooth table top and makes thinner, and removes impurity removing, and pulverized by pedotheque after air-drying.
Step 2), with core cutter method detection soil sample 1 and the field capacity of soil sample 2, respectively C1=23.8% and C2=35.4%.
Step 3), take 1 two parts of each 5kg of the soil sample after pulverizing, and be labeled as pedotheque A1, B1, in A1, B1, add 1.19kg water respectively so that it is reach the field capacity of soil sample 1, uniform mixing, load identical container；Soil sample 2 processes in the same way, and the sample of two parts of 5kg of soil sample 2 is labeled as pedotheque A2, B2, adds 1.77kg water respectively so that it is reach the field capacity of soil sample 2 in A2, B2.
Step 4), pedotheque A1, A2, B1, B2 are placed under same environment simultaneously so that it is dehydration continuously.
Step 5), measure soil water potential ψ of different dehydration moment pedotheque A1, A2 respectivelySAnd water content P of corresponding moment pedotheque B1, B2, according to soil water potential ψ of pedotheque A1, A2SSituation of change measure 15 groups of data continuously；
Soil water potential ψSAssay method be: by two soil water potentials probe inserting steps 2 respectively of dew point water potential meter) in load the internal 8～10cm depths of pedotheque A1, A2 of container and be measured；Soil moisture content P is to be obtained by the quality measuring corresponding moment pedotheque B1, B2.
Step 6), according to soil water potential ψ of above-mentioned pedotheque A1, A2 recordedSAnd water content P of corresponding moment pedotheque B1 and B2, build soil water potential ψ to be measuredSWith the mathematical model of water content P, concrete building process is:
By the Gibbs function u=△ G of material chemical potential0+ RT lnX, substance A, chemical potential u of BA,uBIt is expressed as:
uA=GA+RTlnXA(1)
uB=GB+RTlnXB(2)
In above-mentioned (1), (2) formula, GA、GBIt is the standard Gibbs free energy of substance A and substance B respectively, XA、XBBeing the molar concentration of substance A and substance B respectively, R is gas constant, and T is ambient temperature.
Therefore, after mixing, Gibbs free energy G of system can be expressed as by chemical potential:
G=uAXA+uBXB(3)
Namely Gibbs free energy G of system is after mixing:
G=(GA+RTlnXA)XA+(GB+RTlnXB)XB(4)
Aqueous soil can regard soil and the hybrid system of two kinds of materials of water as, and soil water potential is the chemical potential of this system, and soil regards substance A as, and water regards substance B as, and therefore (3) formula is represented by:
ψS=uSXS+uWXW(5)
In formula, ψSFor soil water potential, uSFor the chemical potential of soil, uWFor the chemical potential of water, XSAnd XWSoil and the concentration of water respectively.
Because (5) u in formulaW=0, therefore (5) formula can be simplified to:
ψS=uSXS(6)
By chemical potential u of soilS=dG0+RT·lnXSAnd the concentration of soilExpression formula substitute into (6) formula, can obtain:
(7) formula can be transformed into:
(1+P)ψS=MdG0+MRTlnM-RTMln(1+P)(8)
In formula, ψSFor soil water potential to be measured, unit is MPa；P is soil moisture content to be measured, and unit is %, dG0Standard free energy for soil；M is molar concentration conversion coefficient.
Make y0=MdG0+ MRTlnM, k=-RTM, then (8) formula becomes:
(1+P)ψS=y0+kln(1+P)(9)
By (1+P) ψ in (9) formulaSReplacing with f (x), ln (1+P) represents with x, then (9) formula can be write as:
F (x)=y0+kx(10)
Mathematical model f (x)=y by f (x) He x0+ kx matching determines y0Value with k.
By Sigmaplot12.5 soil water potential ψ to two kinds of soil samplesSMap with the relation of water content P, as shown in Figure 1；Being fitted the relation of f (x) He x by Excel, fitting effect and equation are as shown in table 1.
Fitting effect between 1 two kinds of soil sample soil water potentials of table and water content and equation
Step 7), parameter y that above-mentioned matching is determined0Substitute into formula (9), as P=0, ψS=y0；I.e. y0Represent when soil moisture content is 0, the size of soil water potential value；The absolute value of this value | y0| represent the intrinsic water suction force ψ of soilS0, reflect the absorbability to water that soil is intrinsic.
As it can be seen from table 1 the y of two kinds of soil0Value is different, the intrinsic water suction force of soil sample 1 and soil sample 2 is respectively 3.683MPa and 4.485MPa, the soil sample 1 absorbability soil sample to be less than 2 to moisture is described, namely the intrinsic water suction force of loam is less than the intrinsic water suction force of loamy texture clay, when this is identical with moisture, it is consistent the fact that clay water suction is more than the water suction force of loam.
Above a kind of method detecting the intrinsic water suction force of soil provided by the present invention is described in detail, apply specific case herein principle and the embodiment of the present invention are set forth, to be described is, the foregoing is only presently preferred embodiments of the present invention, not in order to limit the present invention.All any amendment, equivalent and improvement etc. made within the spirit and principles in the present invention, should be included within the scope of the present invention.
Claims (4)
1. the method detecting the intrinsic water suction force of soil, it is characterised in that comprise the following steps:
Step 1), take the appropriate pedotheque to be measured in field or field, be placed in the most smooth table top and make thinner, remove impurity removing after air-drying, and pedotheque is pulverized；
Step 2), with the field capacity of core cutter method detection pedotheque, it is designated as C；
Step 3), take after above-mentioned pulverizing etc. the pedotheque two parts of quality, and be labeled as pedotheque A and B, add water in pedotheque so that it is water content reaches the field capacity of pedotheque, uniform mixing, load identical container；
Step 4), by pedotheque A and B, it is placed under same environment so that it is dehydration continuously simultaneously；
Step 5), measure soil water potential ψ of different dehydration moment pedotheque A respectivelySAnd water content P of corresponding moment pedotheque B, according to soil water potential ψ of pedotheque ASSituation of change measure 10～15 groups of data continuously；
Step 6), according to step 5) data that record, construct soil water potential ψ to be measuredSMathematical model (1+P) ψ with water content PS=y0+ kln (1+P), y0It is model parameter with k；
Step 7), according to soil water potential ψ to be measuredSWith the mathematical model of water content P, obtain the intrinsic water suction force of pedotheque to be measured.
A kind of method detecting the intrinsic water suction force of soil the most as claimed in claim 1, it is characterised in that described step 3) in add water in pedotheque, the mass ratio of soil and water is 1:C.
A kind of method detecting the intrinsic water suction force of soil the most as claimed in claim 1, it is characterised in that described step 6) in y0It is by soil water potential ψ with the value of kSMathematical model (1+P) ψ with water content PS=y0+ kln (1+P) matching determines.
A kind of method detecting the intrinsic water suction force of soil the most as claimed in claim 1, it is characterised in that described step 6) in y0It is water potential value when 0 for soil moisture content, y0Absolute value ψS0Represent, i.e. ψS0=| y0|, then ψS0Represent the intrinsic water suction force measuring soil.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112034138A (en) * | 2020-08-25 | 2020-12-04 | 塔里木大学 | Calculation method and classification method of soil physical property comprehensive character parameters |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112034138A (en) * | 2020-08-25 | 2020-12-04 | 塔里木大学 | Calculation method and classification method of soil physical property comprehensive character parameters |
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