Morozov A.N.

Lecture 3. Soil substrate is skeleton for soil - what it is itself.

If ones knowledge has not been brought in order, then, the more he (or she) knows, the more muddiness of mind has he (or she).

GERBERT SPENSER.

 

Soil - is living organizm.

We walk in fields and often even don't think - what from consist the soil. Certainly, we can rather easily to distinguish sandy, loamy or stony soil. Anybody of us can describe at once which kind of surface has a field (topography, leveling quality, slopes, and quality of tillage. It is more difficult to define if the soils are waterlogged or salinized. Special knowledge and practice are needed for these purposes.

The question, how to cultivate soil to reach heavy crop is very interested us. We cultivate soil, bring weeds under control, introduce fertilizers, apply leaching to remove extra mineralization. When we till our land, very often we don't begin to think if we generate value to land or worked harm. We believe in case records of previous generations, we apply methods of our neighbors and sometimes we only repeat their actions. We read books, mannuals, papers, listen in, watch TV, we string along with competent managers, agronomists, and we get some mixture of concepts. And that is understandable, because scientists sometimes polemize on how to till land correctly, as far as many efficient methods and ways of land tillage in one natural condition are completely cannot be used in another ones.

Hot-shot farmers, very often not realizing, act on a hunch and apply one or another till methods. And sometimes they cannot even explain why they did it this way rather than another. They gained some knowledge during long farm holding and which is transferred from fathers and grandfathers to children and grandchildren.

But...!!!

The conditions are not remaining the same during ages (even during decades!). Rates of steams flow, water quality are changed; water reservoirs and power plants are constructed there. Degree of land utilization is growing (so called ratio of land utilization - RLU is growing together with development of irrigated farming). Drainage, new canals and water reservoirs are constructed. Crop patterns are changed; new varieties of crop are appeared. All of that impact upon soil, then affect to conditions of its water and salt regimes forming and that accordingly have an effect upon yield. If we take into account the fact that about half of irrigated lands in Uzbekistan conditions is subject to soil salinization, then we can understand the reason of interest either from scientists or farmers side to leaching of salinized soils issue and ways of maintaining of salt regime of soils.

How to be guided in such conditions of quick changes? Where can be taken experience and knowledge, which usually is piled during several peasant generations? How to be adapted to new changed conditions? What should do that people, that took land for renting not far ago, and that have no experience in land cultivation and have no agricultural education?

There is only one way there - get understanding of soil. Investigate its properties, find out the ways of cultivation which are efficient at neighbors, and they could be useful for your soil, and which of them could not be used completely. Learn and understand processes that take place in the soils, read books and think about soil as on living body, say, as about small baby.

D. Karnegie, well known specialist on psychology and management recommended half in jest: "if you are going for fishing then choose something for bait which likes the fish but not you". The same can be told on land till: "If you are going to improve soil fertility, then till it in a way that is useful to it, but not as you like!"

These lectures were developed to help people that have wishing autonomously study out principles on water and salt regimes management. We were trying to present in simple and clear manner all that knowledge and conceptions which will help you and your neighbors on Water Users Associations (WUA) to handle over complicated issues of salinized soils melioration, and as far as possible to learn simple and available methods of management over soils humidity and salinization. But before passing on these not simple issues, let us talk a little on issues supposedly known, but not fully…

Soil environment.
Almost all the plants in nature "live" on soil, and only in condition of wet tropical forest many of plants adapted for living without soil, by abutting on other plants, or parasitize on them. These kind of parasite plants are also available in our climate conditions.
What is soil substrate is? (Substrate is Latin word and means base, chair plate). And what is the difference of it from soil?
As a rule, soil substrates are developed on sedimentary rocks. The "sedimentary" word has already guiding suggestion about its origination.
All the compositions rised as a result of sedimentation of rock debris or plants or animals remain during their movement by water or by air are called sedimentary rocks.
Monolith rocks, as affected by summer hot and winter cold seasons, gradually crackle and fall into pieces of different size which start their movement in mountains together with frost mass and compacted snow - glaciers (see Pict. 3.1) or roll down over mountain rocks and form rockslides.

Picture 3.1. Glacier named after Fedchenko where Vakhsh River starts. Debris, which forms so-called moraines - ledges shifted by the glacier
Stones at rockslides (see Picture 3.2) are moving down by gravity, they rub and strike each other, and gradually they break into smaller pieces.

Picture 3.2. Rockslides to the right of mountain river formed from rock debris are clearly seen at the picture (Chatkal River, it is tributary of Chirchik River in Uzbekistan).
Force of gravity, rains and snow contribute to their replacement to bottom of washes, flows and rivers. Unruly streams aroar pass over them when snowmelts and rainfalls take place in spring season. Stones are picked up by these flows and deliver them to big rivers. The stones moved by water continue with breaking down of mutual collisions and forming smaller pieces of rock.
Intermediate size of stones are gradually reduced in river valleys from head reach to lower coarse as far as river slopes and its velocities are reduced, because water velocity depends on slope mainly, and capability to move deposits in form of stones, sand and clay particles depends on water velocity
Simultaneously, together with stones breaking down into smaller pieces during their transferring in river channel, change of their shape are in process - shapeless stone pieces with sharp edges are pelletized and turn into rather smooth and get rounded shape
At Picture 3.3 we can see stones of big size which were delivered by small flows in mountain, and at Picture 2.4 we can watch significantly smaller sizes of stones in flood plain of the river at site of its coming out from mountains

Picture 3.3. Slightly rounded by water stones could be seen along channel of mountain flow.

Picture 3.4. Typical view of Angren river valley at its exit to piedmont. The river is divided into several channels (river branches) at its flood plain. All the flood plain is filled with water only during flood period. Water flow capability here is enough to transfer only small and mainly rounded stones.
As rates of stream flow are changed along seasons of a year, then capability of rock debris transferring depends very much of that. Rivers are capable to transfer more coarse waste during flood (period of sharp increase of water discharges which take place as a result of glaciers and snow cover melting or rains), but during low water season (period of low water in river -is in autumn and winter), rivers are fed mainly only with groundwater - and they are capable to transfer only smallest, clay particles.

These processes are repeated every year.
The farther rivers are from mountains, the fewer slopes they have and fewer velocity of water in the rivers we watch. Slope is relationship of elevations difference between the two sites divided into distance between the sites, or in other words - changing of height per unit of length (of river, furrow, road etc.). Transferring capacity of water is reduced accordingly because capacity to entrain and transfer particles of different size depends on water velocity. Coarse grains at first, then smaller particles begin to deposit on bottom. The smallest particles - particles of clay, are deposited at lakes and old channels which were separated from main river channel during high water period.

Several million years' history has our Mother Earth. Lots of mountains were ruined down to rock bottom and turned into sand, fine and clay; more young mountains are arisen and ruined beneath our eyes. Rivers deliver debris from mountains to valleys night and day. Climate was changed repeatedly at some parts of our Planet during this period. After periods of high water, dry time came. Rivers appeared and disappeared. Hurricanes and dust storms sorted and moved huge amount of river deposits that was moved to plains during high water periods.

Look at the map (Picture 3.5), and you will see two main rivers of Central Asia - Amudarya and Syrdarya, which were inflowing in Aral Sea not far ago, they delivered huge amount of debris during millenniums of their existence and formed two well-known deserts there - Kara-Kum and Kizil-Kum, and number of steppes closer to mountains.

Picture 3.5. Fragment of Central Asian Region.

Aral Sea as of approximately 1993. From mountains down to Aral Sea enormous areas of steppes and deserts were filled with debris by the two great rivers. (White color - glaciers, brown - mountains, grey-yellow -steppes and deserts, rivers and canals - were shown by blue lines).

Wind plays not insignificant role in movement of soil materials. Sediments delivered for distance of hundred and thousands kilometers to steppes and deserts by powerful flows of water during flood periods, and after the floods decline and drying, the sediments are subject to strong winds, that can have velocity at open flat areas comparable with express train. From spring to autumn strong dust storms take place close to deserts, and then sky is getting of yellow-brown color due to dust.

Satellite photograph at Picture 3.6 shows cyclone over China, which carries huge amount of dust having common to loess soils fawn color. Loess is sort of sediment that consists of silt particles mainly which were transferred by wind.
Wind is doing a kind of "separating plant" of sediments. Stones, gravel and coarse sand can not be shifted even by very powerful wind, and they are left more or less at the same site where they were transferred by water. Sand can move "on all fours" and fill massive barchans (dunes) that were shown at Picture 3.7. But small particles of dust picked up by wind are transferred to huge distances, and after wind velocity reduction, the particles start deposit on surface. As a result of that, so called loess massifs appeared at piedmont areas where wind velocities blowing from deserts are reduced because mountains are obstacle for them .

Picture 3.6. View of huge cyclone over territory of China. Tremendous dust mass of specific color of loess transferred to huge distances are clearly seen at the satellite image.

Picture 3.7. Wind storm shifted overlarge barchan (sand dune) which blocked road.

Loess massifs are also common to other sites, where wind velocities are reduced for some other reasons and dust particles are deposited above ground.
Loess deposits in piedmont area of Tashkent oblast were shown at Picture 2.8
Please, pay attention to uniform structure of soil profile in depth and the wash slopes are vertical and that is one of attributes of loess

Picture 3.8. Loess deposits near Tashkent that cut by water flows

Thickness of Loess deposits can reach several decades of meters. Could you imagine how long it took for formation of such thickness of loess, if dust layer deposited during one year in usual conditions is not more 1-2 mm per year!

Loess like a jacket covers piedmont area and extends along mountain massifs. Its properties, irrespective of location are very similar and practically indistinguishable (in China, Central Asia or in Europe), possibly because of their sources are rather far from deposited sites, and material was well-mixed in air while it transfered by wind for thousands kilometers
One of loess characteristics is its high uniformity in depth, high porosity (total volume of all the pores expressed in % to soil volume), fine wicking properties (capability to lift moisture by means of adhesive power with soil particles), very good water holding properties, stability in dry condition and capability of quick erosion by water.

So, we remind you, how crushes of rock are delivered to flat lands by water flows and how they are sorted in accordance with their fragmentation size. Then these sediments are sorted again, but by wind power, and they partly are returned back to mountain sideward, forming loesslike soil substrate in piedmont areas.
But it is not finish for silt formed the loess massifs. The massifs are "suppliers" of sedimentary materials, which are eroded and transferred by water flows during snow melting, spring rainfalls, or as a result of unskillful irrigation at irrigated fields. Even small water discharges needless to say about flows of high capacity can easily erode loess (see Picture 2.8) and they transfer it again from piedmont areas towards steppes and deserts.
Sometimes they form massifs of re-deposited loess massifs when they are deposited at flat lands (for instance, geologists believe, that soils at Golodnaya Steppe in Uzbekistan mainly formed with such rocks).
Re-deposited loess differs from genuine loess by specific stratification common to all sedimentary strata that formed by water flows, but many of their initial properties they keep also after that.
Usually, re-deposited sedimentary strata are very stratified, especially if they were formed on the basis of older sedimentary strata, and thus availability of high or low water permeability layers can have impact on moisture regime of root zone.

We described in brief on typical processes of soil substrate forming by the example of Central Asia. Glaciers and lakes with swamplands took part in these processes at other places during long Earth history, but anywhere main operators were water and wind.
But it is worth to say, that soils can be formed with any of rocks, including crystallinoclastic rocks, sandstones, limestone, lake and sea deposits.
In the next articles of this website section we shall continue telling on how and where climatic conditions and topography form different soils on the basis of variety of substrates.

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