R O C Z N IK I G L E B O Z N A W C Z E T. X X V , D O D A T E K , W A R S Z A W A 1974
S A T U R N IN Z A W A D Z K I, W E N A N T Y O L S Z T A
U SE OF S A N D -B O X M E T H O D
FOR TH E C A P IL L A R Y C O N D U C T IV IT Y D E T E R M IN A T IO N
Soil Science Laboratory
of the Institute fo r Land Reclam ation and Grassland Farm ing in Lublin
The question of determining capillary conductivity К in the unsatu rated zone of soil profile is of theoretical and 'practical importance for water economy in soil [5].
A number of the proposed methods of К value determination can be encountered in the literature, e.g., the method o f outflow from a press ure plate, proposed by G a r d n e r [3], lysimetric investigations of F e d d e s [2], the method of w ater infiltration in cylinders proposed by W e s s e l i n g - W i t [6], model and field experiments of C h u r a y e v
[1], etc.
It is to stress that the capillary conductivity investigations are d iffi cult and complicated in view of a constant drying up and saturation of the profile occurring in the nature.
The measurements of both flo w and moisture 'potential, with regard to their variability in time are very troublesome. The control of all the elements simultaneously is possible only at a laboratory well-equipped in necessary implements and apparatus sets.
A t the Soil Science Laboratory of the Institute for Land Reclamations and Grassland Farming in Lublin in 1969 an attempt was made to in vestigate the possibility of the sand-box method application 1 for measur ing soil évapotranspiration value in laboratory condition [9]. These in vestigations constituted an initial fragment of the experiments on moi sture translocation in the unsaturated zone. The measurements were then carried out on the samples of 100 cm3 in volume.
A t the second stage it w as tried to apply the sand-box method for measuring the capillary conductivity value K. The investigations w ere
1 The sand-box method [4, 8] is used fo r determ ining the w ater retention a b ility in soil form ations w ithin the range of the pF value between 0.4 and 2.0.
carried out on soil monoliths with undisturbed structure, taken into the P V C cylinders of 15 cm in dia and 35 cm in length 2. In the cylinders openings were made at the distance of every
10
cm (counting from the bottom), into which the tensiometer ends w ere stuck. The cylinders with soil were placed in a sand-box covered with plastic foil protecting the block surface against evaporation. In the plastic foil openings have been made preliminarily, corresponding closely with the inner diameter of the cylinder. Consequently a direct contact of the monolith foundation in cylinder with the sand-box surface has been secured through the openings in the foil. Upper surface of the monolith is in a direct contact with atmospheric air (Fig. 1).Soil monoliths in cylinders in the state of actual moisture are put up on the surface of saturated blocks to ensure a mutual capillary con tact. Since that moment the monolith with the block is regarded as a wholeness simulating w ater conditions in the soil profile.
The water level in the sand-box is controlled b y means of a levelling vessel connected w ith the box by a transparent plastic pipe. W ater eva porated from the monolith surface is supplemented from the feeding flask according to the principle of connected vessels and its volume is read from the calibration on the bottle. The évapotranspiration intensity can be controlled by means of radiator bulbs and the air flo w changes [
1
].The soil suction at contact of the soil monolith with the sand-box
я
1 — soil m onolith in the P V C cylin der w ith the porous tensiom eter ends stuck in itself, 2 — plastic foil, 3 — silt block connected by a transparent pipe w ith the levelling vessel, 4,5 — calibrated feeding bottle, 6 — m easure fo r setting w a ter level in the sa n d-b o x , Fig. 1. Scheme of a device fo r measuring ca
p illa ry conductivity of soils
7 — manom eters
2 A t initial trials, the results of which are quoted in the further part of the work, monoliths of 48 cm in height w ere applied. For practical reasons how ever the height of 35 cm was recommended in this method.
Use o f sand-box method... 17
surface is determined by the situation of the levelling vessel in relation to the box surface in cm. The soil suction in a soil monolith over the block is measured by manometers (connected with tensiometer drains) in millimeters of the mercury column.
The values of evaporation and flow as welle as of the moisture po tential gradients measured by the device proposed w ere used for calcu lation of the capillary conductivity coefficient K. These coefficients being in agreement with the D arcy’s law, have been calculated from the equation:
where :
К — capillary conductivity coefficient (mm/day), V — flo w velocity (mm/day),
— moisture potential gradient (cm/cm).
a h
The results of the moisture potential investigations have been present ed on soil monoliths of 48 cm in height and 15 cm in dia (Fig. 2).
Fig. 2. M oisture potential course ip in the p rofile of drained soil monolith. Lines are numbered from left to
rigjht 1, 2, 3, 4
Moisture potential yj fin cm of water column)
40 80 120 160
The lines 1 and 2 for V — 1.78 mm/day and V — 2.04 have been
obtained at the vacuum on the lower area of the cylinder foundation
equal to zero (water table on the sand-box surface), the curve 3— for
V = 1.52 at the vacuum of 65 cm and the curve 4— for V = 1.62 at the
vacuum on the sand-box surface amounting to 80 cm of water column.
The gradient and shape of the lines presented in Fig. 2 depend on the
évapotranspiration intensity denoted here with the symbol V.
The évapotranspiration value V in the case of stabilized conditions
of water movement in the monolith (constant soil suction and equal
air moisture saturation deficits — Fig. 2, Table 1 lines 1 and 2) is re
garded as a flow velocity V in the whole monolith. At variable conditions
of water movement in the monolith, however (Fig. 2, Tab. 1, lines 3 and 4), the measured evaporation value corresponds with the flow velo city V only in an upper monolith layer (of about 10 cm). For the remain ing (lower) layers the flo w value has been determined from the pF curve (Fig. 3) while reading from it the moisture contents corresponding with the soil suction changes at a definite time interval.
T a b l e 1 Specification of the data used for calculation of the К coefficient
Ко. of line in Fig. 2 Depth cm cm d Ф - Ü L - 1 dh V mm per day E mm per day dh 1 5 43 1.10 0.10 1.78 17.8 15 32 1.10 0.10 1.78 17.8 25 21 1.10 0.10 1.78 17.8 55 13 1.10 0.10 1.78 17.8 48 0 1.05 0.05 1.78 35.8 2 5 56 1.10 0.10 2.04 20.4 15 45 1.10 0.10 2.04 20.4 25 34 1.10 0.10 2.04 20.4 55 23 1.10 0.10 2.04 20.4 48 0 1.05 0.05 2.04 41.0 3 5 125 4.00 3.00 1.52 0.507 15 100 1.75 0.75 1.07 1.430 25 90 1.10 0.10 0.63 6.300 35 70 1.10 0.10 0.63 6.300 48 65 1.03 0.03 0.63 21.000 4 5 150 5.00 4.00 1.62 0.405 15 118 2.00 1.00 1.30 1.300 25 106 1.30 0.30 0.68 2.266 35 92 1.22 0.22 0.68 3.090 48 73 1.22 0.22 0.68 3.090
A t substitution in the above formula the potential gradients (dyj) calculated from Fig. 2 for the appropriate soil layers (dh), the values of capillary conductivity coefficients К [7] have been obtained (Tab. 1).
It ought to be stressed that in the case o f a shallow 'ground water table only a narrow soil suction range is obtainable in view of steady feeding upper soil layers with moisture (Fig. 2, lines 1 and 2). A t a va cuum of 100 cm (on the sand-box surface), however, the moisture po tential values (soil suction ?/•) up to about 700 cm of water column, were obtained.
in-Use of sand-box method.. 19
vestigation of capillary conductivity of soils, is the preliminary pF curve determination for the monolith investigated.
A t application of the purposed method also the fact must be taken into consideration that the moisture potential value y> (soil suction) at contact of the soil monolith investigated with the sand-box surface depends on physical properties of porous material of the sand-box. In
jiF
Fig. 3. pF curve fo r the soil monolith investigated
g НОН/100 cub. cm of soil
our case the maximal soil suction value yj obtainable in the sand-box is 125 cm of water column, what corresponds with the pF value 2.1 [
8
].Despite the limitations mentioned, the proposed method enables si mulation of actual conditions occurring in the nature, what may constitute an essential advantage of this method.
REFERENCES
[1] C h u r a y e v N.: M odelow e i polow e badania ruchu w ody w wierzchnich warstwach torfu. Wiadomości IM U Z 10, 1972, 3.
[2] F e d d e s R. A.: The use of lysim eter data in the determination of capillary rise, available w ater and actual évapotranspiration on three soil profiles. Trans. 9th luteum. Comgr. Sodl Sei. Adelaide, Australia, 1, 1968, 107-124. [3] G a r d n e r W. R.: Calculation of capillary conductivity from pressure plate
ou tflow data. Soil Sei. Am er. Proc. 20, 1965, 317-320.
[4] H a r s t van de G. G., S t а к т a n W. P.: Soil moisture retention curves. II. Direction fo r the use of the sand-box apparatus range pF 0 to 2.7. ICW , W ageningen 1965.
[5] O s t r o m ę c k i J.: U dział podsiąku z poziomu w ody gruntowej w pokrywaniu niedoborów m iędzy parowaniem a opadem. Rocz. Nauk roi., 77-F-2, 1969. [6] W e s s e l i n g J. and W i t K. E.: A n infiltration method fo r the determ i-
maition o f the capillary conductivity o f undisturbed soil cores. Biuletyn ICW , No. 81, W ageningen 1969.
[7] W i n d G. P.: Capillary conductivity data estimated by a simple method. Biuletyn ICW , No. 80, W ageningen 1969.
[8] Z a w a d z k i S.: Laboratoryjn e oznaczenia zdolności retencyjnych utw orów glebowych. Wiad. IM U Z 11, 1973, 2.
[9] Z a w a d z k i S., O l s z t a W.: The use of the sand-box method fo r the determination of soil évapotranspiration under laboratory conditions. Polish Journal of Soil Sei. 2, 1969, 2.
С. З А В А Д З К И , В. О Л Ь Ш Т А П РИ М Е Н Е Н И Е М Е Т О Д А П Ы Л Е В Ы Х Б Л О К О В Д Л Я О П РЕ Д Е Л Е Н И Я К А П И Л Л Я Р Н О Й П РО В О Д И М О С Т И П О Ч В Ы Лаборатория мелиоративного почвоведения Института мелиораций и луговодства в Лю блине Р е з ю м е В труде рассматривается метод измерения и схема оборудования д ля опре деления коэффициента капиллярной проводимости К . Рассматриваются такж е результаты исследований проведенных на почвен ном монолите отобранном в ненарушенной структуре в пластмассовые ц и ли н дры диаметром 15 см и высотой 48 см. И з-за практических соображений р е комендуется применение цилиндров высотой 35 см. Предлагаемое устройство позволяет контролировать величину испарения с верхней площ ади монолита, а такж е определять изменения потенциала в л а ж ности (сосущей силы ) во всем монолите. Необходимым условием применения пы левого блока д ля исследования ка пиллярной проводимости почвы является предварительное определение кривой pF д ля исследуемого монолита. С ледует такж е подчеркнуть что величины сосущей силы в нижней п л о щади монолита могут достигать не больш е чем 125 см столба воды, что отве чает величине pF = 2,1. S. Z A W A D Z K I , W . O L S Z T A A P P L IC A T IO N DE L A M É TH O D E DU B LO C DE PO U SSIÈ R E À L ’ÈTUD E DE L A C O N D U ITE C A P IL L A IR E DU SO L
Laboratoire de la Pédologie am eliorative
de l ’Institut d’H ydraulique agricole et des Herbages Ä Lublin
R é s u m é
Dans l ’ouvrage on a discuté la méthode du mesurage et le scheme de l ’ensemble servant à exam iner le facteur de la conduite capillaire K.
On a aussi présenté les résultats des recherches faites sur un m onolyte de sol pris dans sa structure intacte aux cylindres de P V C (diam etre 15 cm et hauteur 48 cm). Pour la pratique on a recommandé l ’application des cylindres ayant 35 cm de haut.
Use of sand-box method... 2 1
L ’arrangem ent proposé perm et de contrôler la grandeur de vaporisation dans la surface supérieure du m onolyte et les changements du potentiel d’humidité (force aspirante) dans tout le monolyte.
L a nécessité de déterm iner préalablem ent une counbe pF pour le monolyte exam iné est une condition de l ’application de la méthode du bloc de poussière aux recherches de la conduite capillaire de sols.
It faut aussi souligner que la valeu r de la force aspirante pour la surface inférieu re du m onolyte peu atteindre le m axim um d’environ 125 cm de la colonne d’eau, ce qui correspond à la valeur de pF = 2,1.
S. Z A W A D Z K I , W . O L S Z T A
A N W E N D U N G DER S T A U B B L O C K M E T H O D E F Ü R DIE E R M IT T L U N G DER K A P IL L Ä R E N L E IT F Ä H IG K E IT DES BODENS
Laboratorium für M eliorations-Bodenkunde des Institutes für M eliorationswesen und Grünlandforschung in Lublin
Z u s a m m e n f a s s u n g
In der A rb eit w ird die Messungsmethode und der Satz der Einrichtungen für die Erm ittlung des K oeffizien ten der kapillärer L eitfäh igk eit К beschrieben.
Auch w erden die Ergebnisse der Untersuchungen auf dem m it unversehrter Struktur in die P V C -Z y lin d er von 15 cm Durchmesser und 48 cm Höhe entnom menen Bodenm onolit erörtert. Aus praktischen Gründen w ird die Anwendung von Zylindern m it der Höhe von 35 cm empfohlen.
Die vorgeschlagene Einrichtung erlaubt die Verdunstungsgrösse von der oberen M onolitfläche nachzuprüfen sowie den Potential der Feuchtigkeit (Saugkraft) im ganzen M onolit zu ermitteln.
D ie unerlässliche Anwendungsbedingung der Staubblockmethode fü r die E rm it tlung der kapillären L eitfäh igk eit des Bodens ist vorherige Bestimmung der p F -K u rv e fü r den untersuchten Monolit.
Es ist auch zu bemerken, dass die Saugkraftw erte in der unteren M onolito- berfläche höchstens ca 125 cm Wassersäule, was der pF-Grösse von 2, 1 entspricht, reichen kann.
S. Z A W A D Z K I , W . O L S Z T A
Z A S T O S O W A N IE M E T O D Y B L O K U P Y Ł O W E G O DO B A D A N IA P R Z E W O D N IC T W A K A P IL A R N E G O G L E B Y Pracow nia G leboznawstwa M elioracyjnego IM U Z w Lu blinie
S t r e s z c z e n i e
W pracy omówiono metodę pomiaru oraz schemat zestawu służącego do badań współczynnika przew odnictw a kapilarnego K.
Podano rów nież w yn ik i badań przeprowadzonych na m onolicie glebow ym p o branym w nienaruszonej strukturze do cylindrów z P C V o średnicy 15 i w y s o kości 48 cm. Ze w zględ ów praktycznych zaleca się stosowanie cylindrów o w y sokości 35 cm.
Zaproponowane urządzenie pozwala kontrolować w ielkość parowania z górnej powierzchni m onolitu oraz zm iany potencjału wilgotności (siły ssącej) w całym monolicie.
W arunkiem stosowania metody bloku pyłow ego do badań przew odnictw a ka pilarnego gleb jest konieczność wyznaczenia uprzednio dla badanego m onolitu krzyw ej pF.
N ależy rów nież podkreślić, że uzyskane wartości siły ssącej w dolnej p o w ierzchni m onolitu mogą osiągać maksimum ok. 125 cm słupa wody, co odpowiada wartości pF = 2,1.
Pr o f . d r hab. Sa tur ni n Z a w a d zk i P ra c o w n i a G le b o z n a w s t w a M e l i o r a c y j n e g o I M U Z Lu b l i n , al. P K W N 29
