ROCZNIKI GLEBOZNAWCZE. T. X X X II. NR 3; W ARSZA W A 1981
B O H D A N D O B R Z A Ń SK I, B A R B A R A W ITK O W SK A -W A LC Z A K
WATER PERMEABILITY AS A FACTOR OF THE SOIL STRUCTURE In stitu te of A grop h ysics P o lish A cad em y of S cien ces, L u b lin
The w ater m anagem ent, a basic aim of w hich is to control th e natu ral w ater resources, is closely connected w ith the w ater circulation in the biosphere. One of the most im portant objects in nature responsible for the w ater circulation in the biosphere is soil perform ing the role of a w ater distributor receiving atmospheric precipitations, possibly retaining them and partly translocating them to deeper horizons and feeding subterranean w aters as well as returning a p art of the w ater to atm osphere by means of evaporation and transpiration. Soil jointly w ith the area inclination determ ines also the w ater am ount flowing down over its surface [4, 6, 7, 9]. There are its two properties : capacity and perm eability of w ater, which exert a basic effect on relations between components of the w ater balance of soil. The w ater capacity determines, namely, the possibility of w ater retention by soil, whereas the perm e ability is responsible for its ability to translocate w ater into deeper layers [4, 5].
The aim of the present work was to determ ine the soil stru ctu re effect on the value of the w ater perm eability coefficient. The recognition of this dependence will, namely, enable to execute agronomy measures aim ing at changes of the aggregation of soil from the viewpoint of the content of w ater retention in the soil profile, m ainly in the period of snowmelt in spring and intensive rainfalls in summer. It is of im port ance p articularly in the areas, where a low perm eability of arable layer makes impossible the w ater infiltration into soil and, jointly w ith the area inclination, constitutes a main cause of the soil erosion [1, 2].
IN V E ST IG A T IO N M ETH ODICS
The investigations were carried out on chernozem developed from loess (Werbkowice), distinguishing itself w ith a high aggregation degree
18 В. Dobrzański, В. Witkowska-Walczak
and a considerable waterproofness of soil aggregates. The soil m aterial was taken from the arable layer in the form of horizontal monoliths dried up in the laboratory for the air-d ry state and passed through sieves w ith the mesh diam eter of 0.25, 0.5, 1.0, 3.0, 5.0 and 10.0 mm. W ith the fractions of aggregates : <0.25, 0.25-0.5, 0.5-1, 1.0-3.0, 3.0-5.0 and 5.0-10.0 mm, separated in the way as above, cylinders w ith the capacity of 100 cm3 were filled up at use of a vibrator, to ensure a uniform density. Then the aggregates were subjected to w etting-drying cycles, which resulted in a stabilization of physical properties of samples, necessary for fu rth er investigations. At the same time it is to stress th a t an averabe diam eter of aggregates of each fraction, e.g. 2 mm for the fraction of 1.0-3.0 mm, has been assumed as an independent variable. It resulted from the fact an appropriate mechanical cultivation of soil enables getting the w anted monoaggregation of soil, which, however, can change under the effect of outer factors (precipitations, tem pera ture) ; non the less it constitutes always a definite function of the initial aggregation of soil [10].
Total porosity of aggregated soil samples were determ ined by the Loebell’s porometer, whereas the little, medium and large pores (their percentage in the total volume of sample) was calculated on the basis of w ater retention curves.
Investigations aiming at determ ination of the w ater perm eability coefficient value were carried out at use of the apparatus for the w ater perm eability m easurem ent, constructed by Zawadzki and O l s z t a [И] at the Branch Division of the Institute for Land Reclamation and G ras sland Farm ing in Lublin. The investigations were carried out by the method of m easurem ent at a constant hydraulic pressure, consisting in the m easurem ent of flow and pressure differnce between the w ater level in the w ater container and the cylinders w ith soil. The m easure m ents were carried out in 20 replications for every fraction of aggregates w ithin 12 subsequent days.
IN V E ST IG A T IO N R E SU L T S A N D T H EIR D IS C U S S IO N
Results of the investigations on the w ater perm eability coefficient from differently aggregated soil samples in consecutive days of the m easurem ent have proved th a t the size of aggregates affects the w ater perm eability of soil (Table 1). The highest w ater perm eability coefficients showed soil samples built of large aggregates, i.e. of 5-10 and 3-5 mm in dia, the lowest — those containing sm all-sized aggregates, i.e. less than 0.25 and 0.25-0.5 mm in dia. W ater perm eability coefficient values for aggregates of <0.25 mm in dia corresponded w ith the w ater perm eability of silty sand, for those of 0.25-0.5 mm in dia — w ith the
Water permeability of soils structure 19
T a b l e 1
W ater p e r m e a b ility c o e f f i c i e n t v a lu e s f o r a g g re g a te d s o i l sampler;
I n i t i a l f r a c t i o n nun Day W ater p e r m e a b i l i t y c o e f f i c i e n t к X 1 0 cm • s “ 1 < 0 , 2 5 0 . 2 5 - 0 . 5 0 . 5 - 1 1 - '5 i - 5 5 - 1 0 1 0 ,0 3 0 .23 1.63 3.3!; 16.5 29.3 0 .0 3 0.21 1.6 1 3.08 17.7 27 .5 3 O JO 0 .23 1.53 2.66 19.3 2 6 .7 4 0 .0 0 0.20 1.50 2.75 20.1 25.2 5 0.1 0 0.21 1.55 2.83 19.7 23.5 6 O.Ou 0.21 1.55 2.66 19.7 22.8 7 0.06 0.21 1.56 2.50 19.5 21.8 8 0.03 0.20 1.53 2.75 19.3 21.8 9 0 .0 0 0.21 1.53 2.66 19.3 21.5 10 0 .0 0 0.21 1.50 2.5Ł 19.3 21.7 11 0 .0 0 0.21 1.55 2.66 19.3 21.7 12 0 .0 0 0.21 1.55 2.66 19.3 21.7
w ater perm eability of fine-grained sand, for those of 0.5-1.0 and 1.0-3.0 mm in dia — w ith of m edium - and coarse-grained sand, whereas for those of 3-5 and 5-10 mm in dia — w ith th a t of fine-grained gravel (Fig. 1) [3, 8, 11]. Hence the aggregates of 3-5 and 5-10 mm in dia can be assigned to strongly perm eable formations, those of 0.25-0.5, 0.5-1.0 and 1.0-3.0 mm in dia belong to medium perm eable and those of <0.25 mm in d ia — to weakly perm eable form ations [3].
It follows from the data presented in Table 1 th a t the w ater perm e ability value for aggregates of > 1 mm in dia underw ent changes in the course of the experim ent. The w ater perm eability for aggregates of 1-3 and 5-10 mm in dia decreased accordingly from 3.33X10“ 2 cm • s“ 1, to 2.66X 10“2 cm • s“ 1 and from 29.3X10-2 cm • s_1 to 21.8X10“ 2 cm • s ^ 1, whereas the perm eability of aggregates of 3-5 mm in dia increased from 16.5 X 10~2 cm • s'-1 up to 20.1 X 10“ 2 cm • s1“ and then decreased down to 19.3X102- cm • s“ 1. A fter 6-8 days of investigations a stabilization of the w ater perm eability coefficient value was observed. Such course of the w ater perm eability coefficient value in aggregated samples in the course of investigations can be explained by changes of situation of the finest soil particles caused by w ater movements in the soil sample, which would result in closing and opening of pores of dif ferent size, w hat led consequently in the first phase of the experim ent to changes of their perm eability.
The total porosity and the percentage of little, medium and large pores for different fractions of soil aggregates is put together in Table 2, w hereas in Fig. 2 the relationship between the size of aggregates on
20 В. D obrzański, В. W itk ow sk a-W alczak
Fig. 1. W ater p e r m e a b ility c o e ffic ie n t v a lu e for a g g reg a tes of d iffe r e n t size and ran ges of w a te r p e r m e a b ility c o e ffic ie n t v a lu e s for d iffe r e n t form ation s after
H illel
I — silty sand, 2 — fin e -g ra in ed sand, 3 — m ed iu m - and coarse-grain ed sand, 4 — fin e -g r a in e d g r a v e l
V alu es o f th e w a ter p e r m e a b ility c o e ffic ie n t are m ea n v a lu e s o b ta in ed in th e la st four days of th e m easu rem en t, w h en th e w ater p e r m e a b ility b ccam e sta b ilized
T a b l e 2 T o t a l p o r o s i t y a n d p e r c e n t a g e o f p o r e s o f d i f f e r e n t d i m e t e r i n a g g r e g a t e d s o i l s a m p l e r I n i t i a l f r a c t i o n T o t a l p o r o s i t y i!iu::bcr o f pc o ' . : -mm * LAm 3 - 3 m ^ l i t t I-.; 0 . 2 - 1 8 , 5ä10"4i Er'; d l um > 13.5к10~ит < 0 . 2 5 53.5 14.2 32,1 7.2 0 . 2 5 - 0 . 5 6 2 . 3 11.5 26.5 22.3 0 . 5 - 1 6 5 . 0 10.7 17*7 зс .с 1 - 3 63.0 11.3 14.0 37.7 3 - 5 6 7 . 5 9.9 16.7 40.9 5 - 1 0 6 7 . 0 10.0 15.1 41.9
the one hand and total porosity (P0) and the num ber of large pores (Pd) on the other is presented. The data p u t together in Table 2 prove a low influence of the size of aggregates on the total porosity and the num ber of little pores contained in the soil samples examined. However, they
W ater p erm ea b ility of so ils stru ctu re 21
Fig. 2. R ela tio n sh ip b etw een th e size of a g g reg a tes on th e one hand and th e total p orosity (P 0) and the n u m ber of large pores (Pd) on th e other
lead to the conclusion th a t along w ith an increase of the size of aggre gates decreases the num ber of medium pores (from 32.1% m 8m “ 8 for aggregates of <0.25 rnm in dia down to 15.1% m 3m “ 3 for aggregates of 3-10 mm in dia), at a simultaneous increase of the num ber of large pores. The num ber of large pores am ounted for aggregates of <0.25 mm in dia to 7.2% m 3m -3 and for aggregates of 5-10 mm in dia — to 41.9% m 3m -3. On the basis of the situation of pores (Fig. 2) and of the respect ive calculations it has been proved th a t the relationship between the num ber of large pores and the size of aggregates is of the character of a function, the general shape of which would be :
-p‘i= a у ф where:
Pd — the num ber of large pores (% m 3m “ 3), Ф — diam eter of aggregates (mm),
2 2 В. D obrzański, В. W itk ow sk a-W alczak
In case of the soil under study the above function would assume the shape of
Pd —25.64 j / 0
While comparing the character of the dependence on the w ater perm eability coefficient value on the size of aggregates (Fig. 1) as well as of the num ber of large pores on the size of the grow th of the w ater can be concluded th a t a direct cause of the grow th of the w ater perm eability coefficient value along w ith an increase of the size of aggregates would be the grow th of the num ber of large pores caused by the increased num ber of aggreates contained in soil samples.
The relationship between the w ater perm eability coefficient value and the num ber of large pores in soil samples containing aggregates of different size, is presented in Fig. 3. The course of this relationship
Fig. 3. R elation sh ip b etw een th e w a te r p erm ea b ility c o e ffic ie n t v a lu e and the n u m b er of large pores in soil sam p les of d iffe r e n t size of agg reg a tes illu strates the effect of the num ber of large pores in the soil on the w ater perm eability coefficient value, which can be described on the basis of the situation of points and respective calculations by the function, the general shape of which would be :
Water permeability of soils structure 23 k = a (Pd)n
w here :
к — w ater perm eability coefficient (cm • s“ 1), Pd — num ber of large pores (% m 3m -3), a, n — param eters depending on the soil kind.
In case of the soil under study the above function would assume the shape of
Moreover, it can be stated basing on Fig. 3 th a t there is a boundary num ber of large pores determ ined by the size of aggregates, the excess of which would lead to a rapid grow th of the w ater perm eability of soil. In case of the soil under study it would be the value lying w ithin the interval of 37.7—40.9% m3m “ 3 of the num ber of large pores. This boundary value of the num ber of large pores in a valuable practical index enabling to state th a t the attainm ent ow grow th of the w ater perm eability of soil would be possible only in case of such changes of the size of aggregates, which would resu lt in a grow th of the num ber of large pores over the above value. It means th a t for chernozem such mechanical cultivation should be applied to ensure the possibility of absorption and translocation of w ater from its surface in great amounts, in result of w hich in the arable layer aggregates of the size of 3-10 mm in dia could be formed.
On the basis of the respective investigations and their results it has been found th a t the size of aggregates, of which the arable layer is built, determines, the value of the w ater perm eability coefficient i!n such a w ay th a t along w ith the grow th of the size of aggregates an increase of the w ater perm eability coefficient value would take place. The above relationship is conditioned directly by the effect of th e size of aggregates on the num ber of large pores (of the diam eter exceeding 18.5X10“ ° m), which is the function of the shape of
n /
Pd = a J / Фу whereas the relationship between the w ater perm eability coefficient value and the num ber of large pores assumes the shape of the function of k = a (Pd)n. In case of the soil under study, i.e. of cher nozem developed from loess, the relationship assume the shape of
Moreover, it has been found th a t there is a boundary num ber of large pores conditioned by the size of aggregates, the excess of which
k = 15 . 10 “ 7 (Pd)3
24 В. Dobrzański, В. Witkowska-Walczak
would lead to a rapid grow th of the w ater perm eability coefficient value. Its knowledge is a practical index of the w ay and direction of measures of mechanical cultivation of soil to be carried out, aiming at an increase of the w ater perm eability of soil, and consequently at an increase of the am ount of w ater retained in the soil profile.
REFEREN CES
[1] D o b r z a ń s k i В. : W ater m an agem en t in lo ess soil. A nn. U M CS Sec. B, 2, 1947.
[2] D o b r z a ń s k i В., M a l i c k i A., Z i e m n i c k i S. : S o il erosion in P olan d . PW R iL, 1953.
[3] H i 11 e 1 D. : S o il and w ater. A cad. P ress, N e w Y ork 1971.
[4] K o z ł o w s k i T. T. : W ater d e fic its and p lan t grow th. V. I, II, A cad. Press. N ew Y ork 1968.
[5] L v o v i c h M. I. : V od n yi b alan s i p o ch v en n y i pokrov. P och v. 9, 1966. [6] R о s e C. W. : R ainfall and soil structure. Soil Sei. 91, 1, 1961.
[7] S e b i 11 о 11 e M. : S tru ctu re sta b ility and w a ter b alan ce of soiol. A nn. A gron. 19, 4, 1968.
[8] S m i t h R. M., B r o w n i n g D. R. : Som e suggested laboratory standards of subsoil p erm ea b ility . Proc. S oil Sei. Soc. A m er. 11, 2, 1946.
[9] V i s s e r W. C. : T he aim of m o d e m h ydrology. T echn. B ull. 90, 1974. [10] V/ a 1 с z a к R., W i t к o w s к а - W а 1 с z а к В. : E ffect of w e ttin g -d r y in g c y cle s
on the a ggregation of soil. Rocz. glebozn. 3?., 1981 (in print).
[1 1 ] Z a w a d z k i S., O l s z t a W. : M odified W it’s apparatus for laboratory determ in ation of w a ter p erm ea b ility of soils. W iadom . IM UZ 14, 2 (in print).
B. D O BRZAŃSK I, В. W ITKOW SKA-W ALCZAK
PRZ E PU SZ C Z A LN O ŚĆ W O D N A JA K O F U N K C JA ST R U K T U R Y GLEBY Z akład 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
P rzed sta w io n o w y n ik i badań w p ły w u w ie lk o ś c i ag reg a tó w g leb o w y ch na w sp ó łczy n n ik p rzep u szczaln ości w od n ej w strefie n a sy co n ej. S tw ierd zon o, że w ie l kość agregatów tw o rzą cy ch w a r stw ę orną g leb y d eterm in u je p rzep u szczaln ość w od n ą w taki sposób, że w raz ze w zro stem w ie lk o śc i ag reg a tó w w zra sta w sp ó ł czyn n ik p rzep u szczaln ości, a zależność ta w a ru n k o w a n a jest w p ły w e m w ie lk o śc i agreg a tó w na ilość porów dużych. Z w iązek m ięd zy w ie lk o śc ią w sp ó łczy n n ik a p rze p u szczaln ości w od n ej a ilością porów d u żych ma p ostać fu n k cji k = a (Pd)n- Ponadto stw ierd zon o, że is tn ie je gran iczn a ilość porów d u żych w a ru n k o w a n a w ie lk o śc ią a g regatów , p rzek roczen ie k tórej p o w o d u je g w a łto w n y w zro st p rzep u szczaln ości w od n ej. W przypadku agreg a tó w czarn oziem u w y tw o rzo n eg o z lessu jest to w a r tość zn ajd u jąca się w p rzed ziale 37,7-40,9% (m3m -3 ) ilości porów dużych w ogólnej ob jętości próbki.
Prof. dr B o h d a n 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 r sz a w a , ul. R a k o w i e c k a 26132
