B O H D A N D O B R Z A Ń SK I, H EN R Y K CZACHOR
TEMPERATURE EFFECT ON THE HORIZONTAL INFILTRATION PROCESS IN SOIL
In stitu te of A grop h ysics, P o lish A ca d em y of S cien ces, L u b lin
In forecasting of w ater conditions in soil the knowledge of the rention curve as well as of hydraulic conductivity and w ater diffusion coefficients is indispensable. Dependence of the above indices on mechanical composition, porosity and m oisture of soil has been recognized relatively well. The specification of param eters significant for the soil solution tran sport processes should take into consideration also soil tem perature. It is w ell-known from the literatu re th a t the tem perature changes of upper soil layer can reach 30 К per day, surpassing the air tem perature fluctuations.
Most works on tem perature dependences of soil w ater param eters concern the tem perature effect on the soil w ater potential [7, 8, 12, 14]. Only few works deal w ith the soil solution transport processes depending on tem perature [3, 12].
The aim of the present work was to recognize the effect of tem pe ra tu re on coefficients determ ining the horizontal w ater infiltration in soil and the w ater diffusion as well as the possibility of application of the capillary model of soil pore stru ctu re for explanation of the found relationships.
IN V E ST IG A T IO N M ETHODS
Laboratory m easurem ents of horizontal infiltration of w ater in soil put into column, the construction of which is presented in Fig. 1, were carried out. The column consists of two concentrically situated glass cylinders. The space betw een them 2.5 mm) is filled up w ith w ater — 2 and its circulation and tem perature are regulated by the term ostate system. W ater infiltrates into soil — 1 from the M ariotte’s vessel — 3, through a filter w ith wide pores — 2. The soil tem perature is equal to
Fig. 1. W ater d istrib u tio n in th e colum n 1 — so il, 2 — w a ter, 3 M ario tte’s v e sse l
the tem perature of infiltrating w ater. The m easurem ents were carried out at three tem peratures : 12, 26 and 42°C. Soil m oisture was m easured at use of the m ethod of monoenergetic transm ission of a beam of gamma rays (4). The isotopic apparatus rendered possible also the soil density uniform ity estimation. The respective calculations have proved th a t not only the mean soil density standardization, but also ensuring uniform density of soil (and thus of its porosity) in every cross-section of the column, would be indispensable. The incidental filtration coefficient of
K f for a soil sample consisting of two layers w ith the thickness of Xi
and x2 and the filtratio n coefficients of K ± and K2 are (5) :
K f= K t . K 2 (xx+ x 2) / (К, . x 2+ K 2x,) (1) The analysis of the expression (1) and the K ozenny’s [11] dependence prove th a t uniform soil has higher filtration coefficient than stratified soil w ith identical mean porosity. This consideration enabled to define conditions w ith which the soil column prepared for m easurem ents should correspond. It has been ascertained th a t for carrying out the planned experim ents such packing of soil in the column should be ensured, so as the m axim um relative deviation of soil density (porosity) from its
Aq Ae
m ean value in an arbo trarily chosen profile, i.e. — ---- were less
Qsr
th an 2%.
The column was filled up while pouring dry soil in a uniform stream , at sim ultaneous putting column walls into vibration, w hat enabled to get a relatively dense packing of soil particles. The above condition was necessary in view of possible sedim entation of looser soil at its contact w ith w ater.
The control of density (porosity) of soil was carried out by means of the isotopic apparatus. The following dry soil porosity values were o b tained: for arable layer (I) : ei = 0.38 cm3 • cm“ 8, for subarable layer (II): e2= 0.33 cm* cm-3. The measurements were carried out on podzolic
soil developed from weakly loamy sand taken from two layers : arable and subarable one.
In the first approach the dependence of the boundary w etting cycle on tem perature was not taken into consideration and thus the analysis of the equation (3) was carried out at its omission. Both superficial tension and w ater viscosity are decreasing w ith the tem perature, and
I N V E S T I G A T I O N R E S U L T S A N D T H E IR IN T E R P R E T A T IO N
Horizontal infiltration m easurem ents resulted in determ ination of the dependence of volum inal m oisture 0 on the distance from the x column head, the param eters being tim e t and tem perature T, i.e. :
T i 0 = f (x) 7
tx
Owing to a nondestructive character of radiom etric m easurem ents, a great num ber of dependences of this type could be obtained for one filling up column.
Basing on these dependences for the tem peratures investigated, curves of m oistening front kinetics, i.e. :
X. t \ T i
x =l
( x ) e = o were derived, w here : T i —12, 26 and 42°C.A common feature of the graphs obtained in such a way was th a t higher value of m oisture front range corresponded always w ith higher tem perature for the same time.
The results obtained were compared w ith those concluded from the theory of flow of liquid in cylindrical capillaries. It follows from this theory th a t the x menisk range is connected w ith t time in the equation :
(
2)
w here :о — surface tension,
t? — viscosity of the liquid, r — capillary radius,
&g — boundary w etting angle.
For the definite t time the range change accompanying the tem pera tu re change is determ ined by the dependence :
do drj
thus < 0 , -==- < 0 however, since the absolute values
a 1 cil
It follows from the above th a t the results of pedologie experim ents are conformable quantitatively w ith theoretical anticipations concerning cylindrical capillary. To estimate, instead, qualitatively the conformity of the results obtained w ith the theory on the basis of m oisture front kinetics curves, the dependence x = f (y~t~) has been derived.
In the literatu re the following dependence analogic to the equation (2) is used [10] for description of the relationship between the m oisture front range in soil at horizontal infiltration of a and the time of t :
where : P — w ater perm eability of soil.
If to assume th a t the m oisture front translocation rate changes in soil caused by tem perature changes occur in consequence of superficial tension changes and solution viscosity, so the relation
would be for the given soil constant, independent on tem perature. From the graph x = f (\/£~) the perm eability of P (as a tangent of the straigh t line inclination) was determ ined. While assuming on the basis of special m easurem ents th a t soil filtrate features would be representable for the solution, the value of superficial tension and viscosity were m easured.
It appeared th a t values of the expression (5) are not constant and are increasing w ith the tem perature. Relative differences of this value for extrem e tem peratures am ounted: for arable layer — to 5.8%, for subarable layer — to 8.6°/o*. While assuming th a t capillary phenomena would play in this case a decisive role in the solution transp o rt process, divergences between the experim ent and the theory could be explained by boundary w etting angle changes. A decrease of a superficial tension value of the solution at a grow th of its tem perature leads to a decrease of the boundary w etting angle, i.e. to a better w ettabilizy of the soil solid phase. These presum ptions have been confirmed by the results of physico-chemical investigations of Fox and Zisman [1].
x = P t 0-5 (4)
The moisture profiles got from the radiometric measurements constituted also a basis for determination of the soil water diffusion — D (0). For this purpose the method of B r u c e and К 1 u t e [2] was applied. The diffusion coefficient was calculated rom the dependence :
at use of the num erical method. The program worked out enabled the interpolation of experim ental curve preceding the calculation of values cf the equation (6). Calculation results presented in Figs. 2 and 3 constitute mean for eight reDlications.
Fig. 2. W ater diffusion coefficient of the arable layer for three tem peratures
The above graphs prove that the effect of temperature on the diffus ion coefficient value is not equal for the whole moisture range. This effect was estimated quantitatively while calculating the relative change of the D (0) coefficient value corresponding with extreme temperatures falling per 1°C. The results are presented in Fig. 4.
Fig. 3. W aler d iffu sio n c o e ffic ie n t of the su b arab le soil layer for th ree tem p eratu res
*Fig. 4. R e la tiv e ch an ge of th e w a ter d iffu sio n c o e ffic ie n t of the arab le I and su b arab le II la y er of pod zolic soil d ev elo p ed from w e a k ly lo a m y sand, corresp on
d ing w ith a u n it ch an ge of th e tem p eratu re
C O N C L U S IO N S
The investigations of podzolic soil developed from weakly loamy sand have proved as follows :
— changes of the w ater penetration coefficient accompanying the tem perature changes occur in consequence of tem perature relationships between surface tension, viscosity of the solution and boundary angle of the solid phase moistening,
— for the given m oisture higher w ater diffusion coefficient values are correlated w ith higher tem peratures,
— the effect of tem perature on the w ater diffusion coefficient value depends on soil m oisture and is the highest for m oistures approxim ating the saturation state.
REFEREN CES
[1] A d a m s o n A. V. : P h y sic a l ch em istry of su rfaces. In teresci. P u b lish ., N ew Y ork—L ondon— S y d n ey 1967.
[2] B r u c e B. R., К 1 u t e A. : The m easu rem en t of soil m oisture d iffu siv ity . S o il S ei. Soc. A m . Proc. 20, 1956, 4.
[3] С h a g a 1 R. S. : E ffect of tem p era tu re and trapped air on m atric suction. S o il S ei. 100, 1965, 4.
[4] С z a c h o r H. : R ad ioisotop ic ap p aratu s for th e m oistu re m ea su rem en t in soil colum ns. Zesz. probl. P ost. N auk rol. 220, 1979, 2.
[5] C z a c h o r H. : D octor’s th esis, SG G W -A R , W arsaw 1979.
[6] D o b r z a ń s k i В., D o m ż a ł H. : M oisture dynam ics in soil developed from sand. A nn. U M CS 18, s. Ser. E, 1963.
[7] G a r d n e r W. R. : W ater du rin g sorption as a ffected by tem p eratu re. S o il Sei. Soc. A m . Proc. 23, 1959.
[8] H a r i d a s o n M., J e n s e n R. D. : E ffect of tem perature on pressure head w a te r c o n ten t rela tio n sh ip and c o n d u ctiv ity of tw o soils. S o il S ei. Soc. A m . Proc. 36, 1972, 5.
[9] H i d e J. C. : A grap h ic p resen ta tio n of tem p eratu re in the su rfa ce fo o t in com p arison w ith air tem p eratu re. S o il S ei. Soc. A m . Proc. 35, 1942.
[10] J a c k s o n R. D. : T em p eratu re and soil w a ter d iffu siv ity relation sh ip . S oil Sei. Soc. A m . Proc. 27, 1963, 4.
[11] J e l i n e k K. : P a rtic le size a n a ly sis. W iley, N ew Y ork 1974.
[12] K ę d z i o r a A. : D ep en d en ce of the su ction p o w er of so ils on its m oistu re and tem p eratu re. D octor’s th esis, W SR P oznań, 1971.
[13] P e c k A. S. : C hange of m oistu re ten sio n w ith tem p eratu re and air pressu re. S o il S ei. 89, 1960, 6.
[14] R i c h t e r J. : Zur A b h ä n g ig k eit d es B o d en w a sserp o ten tia ls v o n der T em peratur. Z. P fl. u. B odenk. 131, 1972, 3.
[15] S i e r o l a w s k i H.: T h erm ic con d ition s of som e soils of the P u ła w y en viron s. Pam . pul. P race IU NG , 30, 1967.
В. D O BRZAŃSK I, H. CZACHOR
W PŁY W TEM PE R A T U R Y N A PRO CES H O R Y Z O N TA L N E J IN FIL T R A C JI W ODY W G LEBIE
Zakład A g ro fizy k i P A N w L u b lin ie
S t r e s z c z e n i e
Zbadano w p ły w tem p eratu ry na w sp ó łczy n n ik i o k reśla ją ce h oryzon taln ą in filtr a c ję w o d y w g leb ie i d y fu zję w od n ą oraz za sto so w a n o k a p ila rn y m od el b u d o w y p orów g leb o w y ch do w y tłu m a czen ia stw ierd zo n y ch zależności. P rzep ro w a dzono p om iary in filtr a c ji h oryzon taln ej z w y k o r z y sta n ie m m etod y g ra m m a -a b - sorpcji w tem p eratu rach 12, 26, 42°C dla g leb y b ie lic o w e j w y tw o rzo n ej z p ia sk u słabo g lin ia steg o .
P ro /, dr B oh dan D o b r za ń sk i
I n s t y t u t G l e b o z n a w s t w a S G G W - A R W a rsz a u a ul. R a k o w i e c k a 26/32
