Problems of evaluation of soil moisture for water balances on large areas
7. Moisture in ranges FS-FC: humid range
3. Moisture in ranges FC-FDA: semi-humid range.
4. Moisture in ranges PDA- W P : seini-arid range.
5. Moisture in ranges WP-HC: arid range.
6. Moisture less than H C : hyper-arid range.
The variation of the moisture content is characterized by (a) the change of moisture from one range to another in the same layer, (b) the possibility of different duration of the ranges, and (c) the stratification of moisture, by which is meant the difference between the moisture ranges in the topsoil and subsoil.
As the primary factor in the proposed classification system, the author considers the moisture ranges prevailing over a large time interval in the whole profile. Moisture ranges having short duration and the moisture stratification are considered to be secondary factors. The proposed system is therefore based on the following scheme:
1. The class-determined according to the moisture content range of the whole profile for a period equal to or more than 6 months or according to the dominant range.
There are therefore 6 moisture classes designated in the same way as the ranges of moisture, i.e. by numbers I to 6.
Miruslui, Kuiíleli
II. The order-determined according to the moisture range for shorter periods:
A. permanent order with a dominant range duration over 10months and non- B. temporary order with a dominant range diiration over 6 months and one of the C. indifferent order, in which no range has a duration equal to or more than 6 months
dominant range lo less than 2 months;
non-dominant ranges for a time 2-6 months;
and does not contain any marked subsidiary ranges.
III. The suborder-determined according to the season.
IV. The type-classified according to moisture classification in the topsoil and subsoil.
The following types are distinguished:
(u) permanently decreasing;
(6) temporarily decreasing;
(cj fluctuating;
(d) monotonic;
(e) temporarily increasing;
(fj permanently increasing.
The proposed system of ecologic classification of soil moisture is written out in detail in Table 1.
The range of moisture and its duration is determined from the graph of time dependent water storage. To determine the class, the appropriate moisture range for a duration equal to 6 months or more is read off the curve. If the curve shows expressive peaks out- side the range boundary, their duration and their appropriate range is recorded. Moisture ranges of 2-6 months duration, or up to 2 months are decisive for the determination of themoisture order. If out of three moisture ranges none has a duration of at least 6 months, the decisive range for class determination is the central range between two extreme ranges. If any range has a duration of less than 1 month, it is not considered. For example, let us have the following moisture ranges: (2) humid for 4 '/2 months, (3) semi-humid for 31/? months, (4) semi-arid for 4 months, then the class is determined as (3) semi-humid.
Tf 4 moisture ranges, each having a duration longer than 1 month but less than 6 months appear, then the class is determined by that of the two central ranges which, together with one of the extreme ranges has the longer duration. For example w e m a y read from the duration curve of water storage: (2j humid range for 2 months, (3) semi-humid for 31/2 months, (4) semi-arid for 31/2 months, (5) arid for 3 months. The class is determined as (4) semi-arid. These last combinations are however less frequent.
The lower unit, the order, specifies, in which direction the soil moisture develops during the rest of the year. The number in brackets after the basic notation of the order defines, into which ranges the moisture passes for shorter duration. If there are more combinations, the moisture range numbers are arranged according to duration. The previous example of 4 moisture ranges is classified as 4 C(3,5).
The suborder defines verbally the season in which the dominant moisture range exists.
The type distinguishes the moisture stratification and similarly to class and order classification for the whole profile, a classification of the topsoil
V )
and subsoil (S) is made. Types are characterized in the following manner:(a) Permanently decreasing-subsoil class is lower than topsoil class, order of both is ( h ) Tcnlpordriiy decreasing-subsoil class is lower than topsoil class, order of both is A,
A and not even a short inversion takes place.
during a short period up to two months the iuoisture range exhibits inversion.
ProbIerns uf eucrlirntion of soil moislirre for wtricr hnlrrtices oli large arens
TABLE I. Ecological classificatioii of soil moisture Class Order
T. G. Chopmun
(c) Fluctuating, either with marks (h) or (e). Subsoil class is lower or higher than topsoil class but inversion sets in for a time longer than 2 months. The order of one layer is A, of the other B or C. The secondary inark (b) or (e) is determined according to class sequence and is written as an index.
(d) Monotonic, usually with marks (6) or (e). A piirely monotonic type is found in both layers for similar class and order, that is for the same range of the same duration.
The order of both layers is B or C. The secondary mark (h) or (e) is determined accord- ing to class or order sequence and is written as an index. If class is the sanie, then the secondary mark is determined by sequence of the order.
(e) Temporarily increasing-subsoil class is higher than topsoil class, order of both is A and during a short period up to 2 months the moisture range shows the inversion.
(f) Permanently increasing-subsoil class is higher than topsoil class, order of both is A aird no inversion takes place.
If no inversion (&es place and the moisture ranges overlap over a period of less than 2 months, the type is classified as permanently increasing or decreasing regardless of order A, B, or C.
If
no inversion takes place but the moisture ranges overlap over a period of more than 2 months but less than 6 months, the type is classified as temporarily decreds- ing or increasing according to the class sequence. Example of classification: The moisture regime of the topsoil was classified as T4B(5), that one of the subsoil as s 3B(4,5). The type willbe monotonic with marks of the temporarily increasing type: de.REFER ENCES
BELL, J. P. and MCCULLOCH, J. S. G. 11969): The use of neutron moisture gauges in catchmcnt hydrology. Int. Synip. Radiometric Methods and fnstr. for the Deterin. OJ Density und Moistlire of Build. Mut. and Soils, Brno.
KUTiLEK, M. (1966): Vodohospodáfská Pedologie (Soil Science for water Management, in Czech), SNTL Praha.
KUTILEK, M. (1968): Methods of Evaluation the Soil Moisture for World Water Balance Purposes.
Report for W M O . (Unpublished).
LANGEFORS, B. (1966): Theoretical Analysis of Information Systems. Studentenliteratur, Lund.
RODE, A. A. (1956): Vodniy rezhim pochv i yevo tipi (Hydrological regimes of soils and their types, in Russian) Pochvoved. No. 4, 1-23.