CN109460633B - Quantitative method for days of relieving spring drought in frozen soil spring thawing mode - Google Patents
Quantitative method for days of relieving spring drought in frozen soil spring thawing mode Download PDFInfo
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Abstract
The invention provides a quantitative method for relieving spring drought days by frozen soil spring thawing, belonging to the field of agriculture. Based on the potential energy principle of soil moisture movement, the method for quantitatively calculating the number of days for relieving the spring drought of the crops in the cold region by frozen soil spring thawing is provided through theoretical derivation, the defects of the current qualitative analysis are overcome, and the blank at home and abroad in the field is filled. Therefore, the method can quantify the effect of measures for relieving spring drought in frozen soil areas such as deep scarification after autumn, (deep scarification) autumn irrigation, straw coverage after autumn and the like, provides theoretical basis for formulating economic and reasonable measures for relieving spring drought, improves the spring sowing emergence rate of dry crops such as corn, soybean and the like, and ensures stable and high yield of grains.
Description
Technical Field
The invention provides a method for quantitatively calculating the days of the frozen soil spring-thaw season for alleviating the spring drought of crops in cold areas, and accordingly, the effect of measures for alleviating the spring drought in the frozen soil areas such as deep scarification after autumn, (deep scarification) autumn irrigation, straw coverage after autumn, straw coverage at the early jointing stage of crops and the like can be quantized, and further economic and reasonable measures for alleviating the spring drought are taken.
Background
The black longjiang, jilin, liaoning, inner Mongolia, gansu, xinjiang and other places in cold areas of China are all main food production areas of the country, the annual food yield accounts for about 30 percent of the annual food yield (about 1.2 trillion jin) of the country, famous loose and tender plains, sanjiang plains, river jacket plains and other places in the abdominal region are all important commodity food of the country, and the burden of national food safety and 1000 hundred million jin of food newly added in the country in 2020 is born. In these areas, the water and soil resource allocation is basically balanced in total amount, but in spring, more wind and less rain are often caused, and in nine spring drought in ten years, and in arid areas, the less rain and spring are, so that seedling emergence of dry crops such as corn and soybean is incomplete, seedling growth is hindered, and yield of grains is reduced.
Most farmlands in cold regions are in seasonal frozen soil regions, and the seasonal frozen soil has the characteristics of being frozen in winter and melted in spring: in early winter, the field is gradually frozen from the surface layer to the deep layer at the speed of about 1cm every day and night due to the reduction of the air temperature within 10-11 months according to the difference of regional landforms such as mountainous regions, plains and the like and the height of regional latitude, the moisture in the frozen layer is frozen and stored in the soil, the moisture in the soil at the lower part of the frozen layer is gathered in the upper frozen layer under the action of capillary potential gradient and temperature potential gradient, and the maximum freezing depth of the soil can reach 90-300 cm; in 3-4 months of the next spring, the frozen layer is melted from the ground surface to the bottom and from the deep soil to the top in two directions due to the temperature rise and the ground temperature rise, the melting speed from the ground surface to the bottom is higher than that from the deep soil to the top due to the temperature rise speed being higher than the ground temperature, the melted layer is generally positioned at the position 60-200 cm below the ground, and the melted layer lasts to the first winter when the upper soil begins to freeze again in some areas.
For the dry crops, the frozen soil is frozen in winter and melted in spring, namely the soil moisture is preserved in winter and is released in spring, and the seeding of the crops in spring is facilitated. In spring 4-5 months every year, sowing starts when frozen soil of the soil plough layer melts and the ground temperature of the plough layer rises to more than 10 ℃, the un-melted layer under the melted layer prevents soil moisture from infiltrating downwards, and moisture in the melted layer is gradually transferred to the upper plough layer under the action of capillary potential gradient for supplying crop growth needs and relieving spring drought. In other words, in spring sowing, frozen soil prevents the stored water from seeping down and running off in winter due to the existence of the unmelted layer, and the unmelted layer melts more slowly than non-frozen soil, so that the frozen soil can provide water for crops for a longer time in spring thawing. Then, how long spring drought can be relieved by frozen soil spring thawing? There is no quantitative calculation method so far.
In the production practice of people throughout the year, a series of measures for relieving spring drought based on the characteristics of frozen soil and spring thawing, such as deep loosening after autumn, are summarized: a large amount of rainwater can be accumulated by deeply loosening the plough bottom layer before rainfall after autumn; and (3) irrigating in autumn after deep scarification or directly irrigating in autumn: in spring of the next year, irrigation sometimes causes ground humidity and low ground temperature to delay seeding and seedling emergence, and in autumn, irrigation can avoid the contradiction of water contention in spring of the next year to a certain extent and is beneficial to timely seeding of crops in spring; straw cover after autumn: evaporation can be effectively inhibited, and soil of a plough layer is protected from being eroded by wind and rain; covering the straws at the initial stage of crop jointing: compared with the coverage after autumn, the coverage at the early jointing stage can not cause the damage of top seedlings to the seedling emergence of crops, but can not relieve the drought at the seedling emergence stage. Then how do these spring drought relief measures work, and how reasonably should they be implemented? In order to ensure stable and high yield of grains, research needs to be urgently carried out on the problems.
Disclosure of Invention
The invention provides a method for quantitatively calculating the number of days for relieving spring drought of crops in cold regions by frozen soil and spring thawing based on the potential energy principle of water movement in unsaturated soil and theoretical derivation.
The technical scheme adopted by the invention is that the method comprises the following steps:
(1) A method for calculating the time T (unit is s) for relieving spring drought of frozen soil spring thawing is provided:
known as z r (generally, 0.20 m), theta may be selected 0 、θ a 、θ i 、
(the last four parameters can be obtained by actual measurement), and the parameters are substituted into the formula (10), so that the frozen soil spring thawing (and the deep loosening after autumn, the deep loosening after autumn and the straw after autumn based on the frozen soil winter spring thawing characteristics) are obtained by calculationCoverage, etc. spring drought relief measures) the time T to relieve spring drought in the next year;
(2) Known as z r (generally, 0.20 m), T, θ can be selected a 、θ i 、
(the last four parameters can adopt the average value of the years or the predicted value of the years), the formula (10) is substituted, and the test algorithm is adopted to obtain theta 0 (at this time,. Theta.) 0 When the dry crops are sown in the spring of the next year, the average water content of the soil with the thickness of about 0.40m needs to be reached for relieving the spring drought); then according to the measured average water content theta of the soil with the thickness of about 0.40m before autumn irrigation in the year -0 And the average number of the effective utilization coefficient of the water quantity of the autumn irrigation over the years or the predicted value eta of the effective utilization coefficient of the autumn irrigation; by means of the formula>
And (3) calculating the autumn irrigation water quantity W (unit is m) of the year.
Some basic knowledge of soil and agriculture is briefly described below:
liquid water in the soil can be divided into absorption water, capillary water and gravity water according to the stress characteristics, and the absorption water is mainly subjected to molecular suction on the surface of soil particles and is distributed on the surface of the soil particles; the capillary water is mainly under the surface tension of the interface between water in the soil capillary and the concave meniscus of air and is distributed on the outer layer absorbing the water; the gravity water is mainly under the gravity and is distributed on the outer layer of the capillary water. The absorbed water can be divided into hygroscopic water (also called strong bound water) which cannot be absorbed by the plant root system due to the extremely large molecular attraction of soil particles and film water (also called weak bound water), and part of which can be absorbed by the plant root system. The capillary water can be divided into suspended capillary water and ascending capillary water, the supplementary water source of the former is water infiltrated from the ground surface, and the latter is supplemented by underground water source, both of which can be absorbed by plant root system. The gravity water is easy to seep and run off under the action of gravity, and although the gravity water can be absorbed by plants, the absorption amount is small and is not considered in general calculation.
The volume water content of the soil water content can be used(volume of water/total volume of soil). The moisture content of the soil when the moisture absorption water reaches the maximum is called the moisture absorption coefficient theta w (ii) a When the membrane water reaches the maximum, the maximum molecular water holding rate theta of the soil is called m ，θ m ≈(2.0～4.0)θ w (ii) a The time when the water in the suspended capillary reaches the maximum is called the field water holdup theta c ，θ c The non-frozen soil can be used as the upper limit of the effective water quantity absorbed by the roots of crops; when the rising capillary water reaches the maximum, the water holding rate of the capillary is called as the maximum capillary water holding rate theta r ，θ r The upper limit of the effective water amount which is supplied to the root of the crop by the frozen soil spring energy can be considered; when the gravity water reaches the maximum, the water content is called as the saturated water content theta s 。
The water content of the soil which is not absorbed by the plant and is withered permanently is called as the withering water content theta f ，θ f ≈(1.5～2.0)θ w (ii) a In the production practice, irrigation can not be carried out until crops wither and can not revive to supplement soil moisture, and the soil moisture content when the soil needs irrigation is called as the moisture content required to be irrigated theta i ，θ i ≈(0.6～0.7)θ c 。
The following describes the inventive process and the inventive content:
the research of soil moisture movement generally has two ways, one is a capillary method, and the other is a potential energy principle. The method qualitatively considers soil as a bundle of capillary tubes with uniform or different pipe diameters, simplifies the soil moisture movement into the movement of water in the capillary tubes, and is suitable for analyzing some simple problems; the latter considers that the soil moisture movement is movement from a position with higher potential energy to a position with lower potential energy, and based on the movement, a soil moisture movement equation can be established. The basis of the potential energy principle is Darcy's law, which is firstly applied to the water movement in saturated soil and then is extended to the unsaturated soil, and Darcy finds that the water movement speed in the soil is in direct proportion to the hydraulic gradient (potential energy head difference/seepage length).
Based on the potential energy principle of soil moisture movement, the physical differential equations followed by upward movement of soil moisture when the frozen soil is used for relieving spring drought are formulas (1) to (2), the initial condition is formula (3), and the boundary conditions are formulas (4) to (5):
equation of motion (i.e. darcy's law):
continuous equation (i.e. law of conservation of mass):
initial conditions: non-zero ventilation of theta (z, t) t＝0 ＝θ 0 (3)
Boundary conditions: non-zero ventilation of theta (z, t) z＝0 ＝θ a (4)
θ(z,t)| z→-∞ ＝θ 0 (5)
Wherein t is a time variable and has the unit of s;
z is a position variable, 0 on the earth's surface, positive upward, in m;
v z -the speed of movement of soil moisture in the z direction, i.e. upwards, is a function of z and t and has the unit m/s;
θ (z, t) -volumetric soil water content, as a function of z and t;
k (θ) — the permeability coefficient of the soil,
the unit is m/s. Wherein k is s Theta is equal to theta s Permeability coefficient of time; n is an empirical constant, and is generally 3.5 to 4.0;
θ 0 -initial soil vertical profile average water cut;
θ a -surface soil moisture content.
Substituting the formula (1) into the formula (2) to obtain:
will be provided with
Substituting the formula to obtain:
in view of
Substituting the formula to obtain:
considering that the key factor for relieving the upward movement of soil moisture in spring drought is the change of h along with theta, in order to simplify the calculation, if the change of K along with theta is ignored, the above formula is changed as follows:
order to
(D (θ) is called soil water diffusion degree, and represents the soil water flow rate per unit area under the unit water content gradient, and the unit is m 2 And/s) into the formula:
the above equation is a nonlinear partial differential equation, and is difficult to directly solve, and for simplifying the calculation, the average value of D (theta) is approximated
Instead of D (θ), the above equation is simplified to a constant coefficient linear partial differential equation:
according to dimensional analysis, independent variables z, t and soil characteristics
A dimensionless quantity can be composed: />
Substituting the formula to obtain:
in the same way, will
The formula (3) and the formula (5) are carried out:
θ(ζ＝∞)＝θ 0 (7)
in the same way, will
Carrying out the following step (4):
θ(ζ＝0)＝θ a (8)
in this way, the partial differential equation solution problem (equations (1) to (5)) which is difficult to solve is converted into the ordinary differential equation side value problem (equations (6) to (8)) which is easy to solve, and the following is obtained by solving:
θ(ζ)＝θ 0 +(θ a -θ 0 )[erfc(ζ)]
in the formula
-a complementary error function.
Will be provided with
And (3) carrying out the formula to obtain a distribution function of the soil moisture content along with the position and the time:
in the above formula, if z is the water absorption depth z of the crop root system r Theta (z, t) water ratio required for irrigation theta i Then, the quantitative calculation formula (i.e. the content of the invention) for relieving the spring drought time T (unit is s) of crops in cold areas by freezing soil and spring thawing is as follows:
where erfc -1 (x) As an inverse function of erfc (x).
The effects of measures for relieving spring drought, such as deep scarification after autumn, (deep scarification) irrigation after autumn, straw mulching after autumn and the like, can be quantified by the formula (10), and further guide the reasonable implementation of the measures. Deep-loosening after autumn increases k, which will cause theta if there is rain or irrigation after deep-loosening 0 Increase in T, and thus increase in T; autumn irrigation increases theta 0 And further increase T; after autumn straw cover increases theta a And thus also increases T.
The invention provides a method for quantitatively calculating the number of days for relieving the spring drought of crops in cold areas by frozen soil spring thawing based on the potential energy principle of soil moisture movement through theoretical derivation, overcomes the defects of the existing qualitative analysis, and fills the blank in the field at home and abroad. Therefore, the method can quantify the effect of measures for relieving spring drought in frozen soil areas such as deep scarification after autumn, (deep scarification) autumn irrigation, straw coverage after autumn and the like, provides theoretical basis for formulating economic and reasonable measures for relieving spring drought, improves the spring sowing emergence rate of dry crops such as corn, soybean and the like, and ensures stable and high yield of grains.
Detailed Description
(1) A method for calculating the time T (unit is s) for relieving spring drought of frozen soil spring thawing is provided:
known as z r (generally, it may be 0.20 m), θ 0 、θ a 、θ i 、
(the latter four parameters can be obtained by actual measurement), and substituting into the formula (10), calculating to obtain the time T for relieving spring drought in the coming year by the frozen soil spring thawing (and measures for relieving spring drought such as deep loosening after autumn, irrigation after deep loosening) and straw coverage after autumn based on the characteristics of the frozen soil in winter and the frozen spring thawing);
(2) Known as z r (generally, 0.20 m), T, θ can be selected a 、θ i 、
(the last four parameters can adopt the average value of the years or the predicted value of the years), the formula (10) is substituted, and the test algorithm is adopted to obtain theta 0 (at this time,. Theta.) 0 When the dry crops are sowed in the spring of the next year, the average water content of the soil with the thickness of about 0.40m needs to be reached for relieving spring drought); then according to the measured average water content theta of the soil with the thickness of about 0.40m before autumn irrigation in the year -0 And the average number of years of the effective utilization coefficient of the water quantity of the autumn irrigation or the predicted value eta of the effective utilization coefficient of the autumn irrigation; by means of a formula>
And (3) calculating the autumn irrigation water quantity W (unit is m) of the year.
1) When calculating the time for relieving the spring drought of crops by the frozen soil spring thawing, a known crop characteristic parameter z is required r And theta 0 、θ a 、θ i 、
Four soil characteristic parameters in total.
Spring crop emergence stage z r Generally, 0.20m can be taken; theta.theta. 0 Soil with a melting layer of about 0.40m thick in sowing is generally taken and measured by a drying method; theta a Generally, the surface soil thickness of about 0.05m in sowing is measured by a drying method; theta.theta. i ≈(0.6～0.7)θ c ，θ c Measuring the soil after 2-3 d of saturated irrigation by a drying method;
can be obtained by integral calculation according to the soil moisture characteristic curve (soil negative pressure-water content) actually measured by a pressure film method, and can also be obtained by tests such as an indoor horizontal earth pillar infiltration method and the like, because D (theta) of loam is in theta a ～θ c Change more slowly in between, so>
May be generally at θ a ～θ c Averaged therebetween.
2) To obtain z r 、θ 0 、θ a 、θ i 、
After five parameters are totally obtained, the five parameters are substituted into the formula (10), and the time T for relieving the spring drought of the crops in the frozen soil and the spring thawing is calculated.
The following examples are given to illustrate the practice.
A certain grain base in the southwest of Heilongjiang province is in a semi-arid climate region, the soil category is loam, nine spring dryland in ten years, two groups of comparison experiments are set for testing the capability of relieving spring drought due to frozen soil and spring thawing, the field #1 has no autumn irrigation, and the field #2 has water irrigation of 0.05m in autumn.
Before sowing corn in spring, the average water content theta within 0.40m of the field piece #1 soil melting layer is measured 0 0.27 and the surface soil water content theta a 0.16, field water holdup theta c Is 0.33. Average degree of diffusion of soil moisture
Is 1.52X 10 -7 m 2 /s。
Water absorption depth z of root system in seedling stage of crop r Taking out 0.20m of water content theta to be filled i Take 0.6 theta c =0.20, the formula (10) given in the invention is adopted to calculate the time T for relieving spring drought of frozen soil spring melt of field block #1 1 ：
Before sowing corn in spring, the average water content theta within 0.4m of the field piece #2 soil melting layer is measured 0 0.31 and the surface soil moisture content theta a 0.16, field water holdup theta c 0.33, average soil moisture diffusion degree
Is 1.52X 10 -7 m 2 /s。
Water absorption depth z of root system in seedling stage of crop r Taking out 0.20m of water content theta to be filled i Take 0.6 theta c =0.20, the formula (10) given in the invention is adopted to calculate the time T for relieving spring drought of the frozen soil spring melt of the field block #2 2 ：
Generally, if the soil moisture is proper, when the ground temperature of a plough layer is between 20 and 10 ℃, the seedlings can emerge 5 to 20 days after the corn is sowed; from the above calculation results, the field #2 with the thickness of 0.05m irrigated in autumn in the base relieves spring drought for about 13 days next year, and can provide soil moisture for about 6 days for crops compared with the field #1 without autumn irrigation; therefore, the emergence rate of the field #2 with the thickness of 0.05m in autumn irrigation should be higher than that of the field #1 without the autumn irrigation, which is consistent with the emergence situation observed in practice.
This example study shows that the effect of the spring drought relief measure can be quantified using the formula (10) provided by the present invention. The purpose of quantification is to formulate appropriate measures to alleviate spring drought. In fact, measures for relieving spring drought such as deep scarification after autumn, (deep scarification) autumn irrigation, and straw mulching after autumn are implemented in the first year and autumn, how should these measures be made? This requires solving equation (10) in reverse.
As previously mentioned, equation (10) is known for z r 、θ 0 、θ a 、θ i 、
Solving for T; when solving it backwards, it is generally known as T, z r 、θ a 、θ i 、/>
Finding theta by trial algorithm 0 . At this time, θ 0 When the dry crops are sown in the next spring, the average water content of the soil with the thickness of about 0.40m needs to be reached for relieving spring drought; t is the estimated drought duration of the emergence stage of the dry crops (from the beginning of sowing) in the spring of the next year, and the average of measured values of the past years in the region can be generally taken when no predicted value exists; z is a radical of r Generally, 0.20m is taken; theta a In order to estimate the soil moisture content of the surface soil with the thickness of about 0.05m when the seeds are sowed in the spring of the next year, when the straw covering measures after autumn are not adopted in the current year, the average number of the measured values of the area in the past year can be generally taken when no predicted value is adopted (when the straw covering measures after autumn are adopted, theta is increased a The amount of increase can be determined experimentally); theta i And &>
Typically, the average of the measurements taken over the area during spring sowing over the past year or the predicted value for the next year is taken.
Obtaining theta by trial calculation in reverse according to the formula (10) 0 Then, according to the measured average water content theta of the soil with the thickness of about 0.40m before autumn irrigation in the current year -0 And the average number of years of the effective utilization coefficient of the water quantity of the autumn irrigation or the predicted value eta of the effective utilization coefficient of the autumn irrigation; by the formula
And (3) calculating the autumn irrigation water quantity W (unit is m) of the year. />
Claims (1)
1. A method for quantifying days for relieving spring drought in frozen soil spring thawing is characterized by comprising the following steps:
(1) A method for calculating the time T for relieving spring drought of frozen soil spring thawing is provided:
known as z r Taking 0.20m as the water absorption depth of the root system in the seedling stage of the crop, and actually measuring to obtain theta 0 、θ a 、θ i 、
Substituting the obtained value into a formula (10), and calculating the time T for relieving spring drought in the next year by using the frozen soil spring thawing method, wherein the unit is s; wherein:
θ 0 is the average water content of the initial soil vertical section, theta a Is the surface soil water content, theta i Is the water content of the soil when irrigation is needed,
is the average soil moisture diffusivity;
(2) Known as z r Taking 0.20m, and adopting the average value of the years or the predicted values T and theta of the next year a 、θ i 、
Substituting into formula (10), and adopting trial algorithm to obtain theta 0 ，θ 0 When the dry crops are sown in the spring of the next year, the average water content of 0.40m thick soil is required to be achieved for relieving spring drought; then according to the measured average water content theta of the soil with the thickness of 0.40m before autumn irrigation in the current year -0 And the average number of the effective utilization coefficient of the water quantity of the autumn irrigation over the years or the predicted value eta of the effective utilization coefficient of the autumn irrigation; by means of the formula>
And (4) calculating the autumn irrigation water quantity W of the year in the unit of m. />
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