2. Dark chestnut and chestnut soils.

Chestnut soils are a zonal soil type of the arid steppe zone. In Ukrainian arid steppe they are represented by two subtypes (I) dark chestnut and (II) chestnut soils. They differ from the chernozems by a thinner “humusified” layer, smaller content of SOM, brownish or chestnut tint in generally dark grey colour and, more often than not, by a greater extent of salinity and sodicity affection. Soils not affected by sodicity are rarity in the arid steppe of Ukraine. The extent of sodicity generally increases from the north to the south. Below is a typical description of a dark chestnut slightly sodicity affected soil encountered near the village of Bilozirka, Mykolayiv region:

H(e) 0-23 cm: dark-grey with brownish tint, loose, powdery, with gradual transition to the next horizon.

HPi 23-45 cm: transitive illuviated horizon, grayish brown, slightly compacted with nutty structure; transition distinct (along the line of carbonate accumulation).

Pk 45cm and deeper: brownish dull-yellow, clay loam loess with carbonate concretions within the depth of 75-100 cm; crystals of gypsum appear from the depth of 170 cm.

Moderately sodicity affected soils differ from slightly sodicity affected ones by a lighter color of the surface horizon and its more “powdery” structure. Illuvial horizon is more compacted and more dark-colored. The “nuts” of its structure are more distinctly shaped and with colloidal films on the faces of structural aggregares.

Severely sodicity affected soils very much like solonetz soils (alkali soil, sodic soil). Their surface horizon HE is of whitish color (rich in amorphous SiO₂). Illuvial horizon may even be columnar in structure.

Chestnut sodicity affected soils occupy an area of about 0.22 mln ha, of which 0.15 mln ha are a plow-land. They occupy the near-Sivash belt of the Near-the-Black-Sea lowland. They make soil complexes with sodic soils. Below is the description of a virgin soil profile near the village of Chongar, Genichesk, district of Kherson region:

HeI 0-6 cm: a horizon of sod; grey with chestnut tint, moderate clay, cloddy-powdery, slightly platy, loose, with abundant grassroots; transition clear.

H(i) 6-16 cm: a horizon of humus accumulation, very slightly illuviated; chestnut, moderate clay, grainy with clods, compacted, rich in roots; transition gradual.

HPik 16-29 cm: upper transition horizon; effervescent with 10% HCl; dark-brown, moderate clay, cloddy with prisms, spots of colloidal “varnish” on the surface of aggregates; transition gradual.

Phik 29-45 cm: lower transition horizon; brown, light clay, nutty-prismatic, compacted, transition gradual.

PK(h) 45-80 cm: loess with the streaks of humus-containing material. Carbonate concretions below the depth of 50 cm; transition gradual.

Pk/s 80-160 cm: parent material dull yellow loess; moderate clay; soluble salt crystals and veins below the depth of 110cm; gypsum inclusions in the form of roses and spots.

3. Salt-affected soils.

Salt affected soils include saline, alkaline(solonetzic or sodicity affected), and solod (solot) soils. It is generally accepted that water soluble salts, particularly the sodium salts are responsible for the low productivity of salt affected soils. Saline or alkali soils are soils in which the content of salts (or their ions) interferes with the growth of the majority of crops (I. Szabolcs).

In the majority of European countries and the USA, two main groups of these soils are distinguished:

1) soils affected by the natural sodium salts (mainly NaCl and Na₂SO₄).

2) soils affected by sodium salts capable of alkaline hydrolysis (mainly NaHCO₃, Na₂CO₃, Na₂SiO₃).

The development of soil science and soil classification related in the acknowledgement of these two main groups. Soils belonging to the first group have been named saline, and those of the second group, alkali soils.

Very saline soils (solonchaks) are locally spreading in Ukraine along the terraces of the Dnipro, Dnistro, Danube, etc, and on the sea coasts. These soils do not have their typical horizons, though the latter may be preserved as relics of the soils subjected to salting. Solonchaks in Ukraine occupy small areas and are mainly sodium-carbonatic (on the Dnipro terraces) or chloride-sulphatic (on the sea coasts and islands of the Sivash bay). Some such soils may be covered by a crust of salts on the surface. All the horizons may contain salt effervescence veins and nests of soluble salts, or even massive salt crystals. The profiles of saline soils are rather monotonous, from the surface down to the parent material. In a few cases, when saline soils have formed under bog conditions, the top layers are “humous”, their humus content may be lower than 1%. The low contents of N and P₂O₅ are also characteristic of most saline soils. Some saline soils may be converted to normal soils merely by leaching the excess salts from the plant root zone. Plants growing on such soils may appear stunted and have thickened leaves and a dark green color.

Leaching, however, removes the soluble salts more rapidly than it removes exchangeable sodium, which may cause, according to K.K. Gedroiz’s theory¹, conversion to sodic soils. Care should be taken not to allow that to happen by controlling the leaching or irrigation water quality.

Sodic soils present a particularly difficult management problem. Water passes through them only slowly. The pH of sodic soils may be greater than 9 or 9.5, and the clay and organic fractions are dispersed. In some locations, such soils occur in small patches, or slick spots, less than 0.5 ha in extent. Such patches occupy slight micro-relief depressions.

Below is the description of chestnut solonetz soil in loess encountered in Askania-Nova reserve, Kherson region.

HE_d 0-7cm: humuso-eluvial horizon; chestnut-grey, clay loam, powdery with clods, platy, many grass roots; transition clear.

Eh 7-15 cm: elluvial horizon; whitish grey, clay loam, platy, spongy-porous, many roots, transition abrupt.

Ih 15-24 cm: illuvial horizon; dark chestnut, moderate clay, columnar-prismatic; very compacted with thin cracks; scanty grass roots; transition gradual;

PIh/k 24-45 cm: transitive illuviated horizon, chestnut with brownish tint, light clay, nutty prismatic to cloddy prismatic with depth, compacted, calcareous below 40 cm of depth, single roots, transition gradual;

Pk(h) 45-55 cm: slightly “humusified” loess;

Pks 55-170cm: parent material dull yellow loess with carbonate concretions below 60 and to 90 cm of depth and effervescences of soluble salts below 80 cm; roses of gypsum and thick veins of soluble salts below 120 cm.

Solods, according to K.K. Gedroiz, are found under leaching type of water regime from solonetz soils. Exchangeable sodium is gradually substituted by hydrogen ion. Illuvial horizon suffers eluviation in its upper part. A potent eluvial horizon is formed in well developed solods with acid soil reaction. In solod soils the formation of the E horizon is much expressed, and the amount of the so-called KOH-soluble SiO₂ exceeds 1%. In Ukraine, the solods occupy the depressions of micro- and mesorelief in the Forest-Steppe, Steppe, and Arid Steppe zones. In Polissya they may be encountered too.

Speaking about salt affected soils, it is necessary to understand the effects of soluble salts on plants. The main effect is osmotic, since high salt levels make it difficult for the plants to obtain water for growth. Plants growing on saline media can somewhat increase their internal osmotic concentrations by production of organic acids or uptake of salts. This process is called osmotic adjustment. The relative growth of plants in the presence of salinity has been termed their salt tolerance.

Some plants are particularly sensitive to salinity during the germination or seedling stages. Wheat, sorghum, corn, and rice are more sensitive than sugar beet or barley. Field bean is especially sensitive, as well as broad bean. Cabbage, potato, carrot, and lettuce are very sensitive, like most vegetable crops. Spinach is less sensitive and beets (Beta vulgaris) even less. Bermudagrass (Cynodon dactylon) and tall wheatgrass (Agropyron elongatum) are more sensitive than other perennial grasses. Tolerance of various crops to percent of exchangeable sodium in soils is also important. Extremely sensitive (ESP²=2-0) are nuts, citrus, avocado and deciduous fruits; sensitive (ESP=10-20) are beans; moderately tolerant (ESP=20-40) are clover, oats, rise, and tall fescue; tolerant (ESP=40-60) are wheat, cotton, alfalfa, barley, tomatoes, and beets. But even tolerant crops may have stunted growth usually due to adverse physical conditions of soil.