Formation ofhumussoils, their morphology and agrochemical properties

Humus soils were formed as a result of cespitose process in the conditions of meadow and steppe and steppe grassy vegetation, having passed long and difficult evolution in the remote past. All image of these soils testifies to wealth their organic substance, a humus. Accumulation of a large number of a humus is considerably caused by features of biological circulation in steppe landscapes.

The natural grassy vegetation of humus steppes annually alienates in a significant amount of organic weight from which 70 — 80% fall to the share of the root remains. Opad of grassy plants differs in the high maintenance of cindery elements (7 — 8%) and nitrogen (1 — 1,4%). Therefore annually to the soil comes with vegetation of 600 — 1400 kg on 1 hectare of nitrogen and cindery elements among which there are a lot of the bases, especially calcium. This quantity of cindery elements and nitrogen much more, than under coniferous (40 — 300) and the broad-leaved (150 — 500) woods located to the north of humus steppes. Therefore, the meadow and steppe and steppe grassy vegetation creates more intensive circulation of substances in system the soil — a plant that makes the first major feature of biological circulation at a humus .

At decomposition of the vegetable remains many bases, especially calcium that promotes preservation of reaction of the top horizons of humus soils, neutral or close to it, are released. It, in turn, favors to development of very plentiful microflora as a part of which bacteria and aktinomitseta prevail; it is much less than mushrooms, than in forest soils. Therefore the process of hymification going at the same time proceeds in the conditions of neutral reaction, excess of calcic salts and saturation of the formed humic substances calcium. Conditions of moistening and temperature in a humus zone also develop very favorably for hymification process. Richness of a vegetable opad of humus steppes nitrogen and calcium, mainly bacterial structure of microflora, neutral reaction, frequency of cycles of a mineralization and hymification cause an orientation of process of hymification as formation of the humic acids connected with calcium, and also their fixing in the soil. Fulvic acids it is formed a little, they are in the form connected with humic acids and their influence on process is small. Such is the second feature of biological circulation of substances under grassy vegetation of humus. It is necessary to add to it that due to migration of calcium in the form of Sa (NSOE) and there is a formation of the carbonate illuvial horizon.

Weak washing of soils and a significant amount of humic gels in the form of humates of calcium and magnesium, and also development of powerful root systems meadow стспной and steppe vegetation promote formation of strong structural units from closely connected organic and mineral substances. Therefore, the essence of genesis of humus is reduced to formation of humic substances, mainly humic acids, their interaction with mineral part of the soil and to accumulation of humates of calcium in the form of organo-mineral connections, as well as migration of water-soluble products down a soil profile.

Humus are characterized by unsharp differentiation of soil thickness on the genetic horizons. In their profile allocate a phaeochrous 35 — 150 cm humic layer, and intensity of coloring with a humus of this layer the non-uniform. Therefore it is usually subdivided into two independent horizons: And — uniformly painted, with granular structure, the power of 25 — 50 cm, and AVATARS — humic, evenly painted, with the general poburenny, or it is non-uniform painted with alternation of humic potek and sites of the horizon In, but with prevalence of humic coloring. Below a layer (A-f AVATARS) the horizon, transitional to breed, with a humus, but with prevalence of brown coloring (VIV some humus this horizon follows (textural, W) or contains carbonates and then is called illuvial . Further breed with accumulation of carbonates , readily soluble salts and plaster follows.

Gradualness of transition of the humic horizon to maternal breed testifies to absence in humus of strong leaching, and consequently, and to richness of these soils nutritious elements, necessary for plants. Only in the and some lixivious humus a little raised maintenance of SiCb in the horizon And and insignificant moving of one-and-a-half oxides to the illuvial horizon is observed.

Thanks to carbonates of calcium, magnesium and other salts in maternal breed, and also a weak rainfall humus soils have a high saturation the bases. In the absorbing complex of humus calcium which contents reaches 80 — 90% of the sum of the exchange bases prevails. Reaction of soil solution of humus mainly neutral, i.e. the best for cultural plants. More rare it happens subacidic or alkalescent. The number of water-soluble connections is in most cases measured in humus by the 100-th shares of percent. The substances drawn by water consist of organic and mineral compounds.

Thanks to wealth a humus and saturations calcium humus have strong granular structure, and in this regard and favorable water, air and thermal properties. The few soils in the nature have the valuable structure which is so made agronomical, as humus.

Humus in comparison with other soils are characterized by higher natural fertility, have the powerful humic horizon, support a humus and the general of nitrogen in the package horizon with gradual decrease them on a profile (tab. 1) much more.

The gross stock of a humus and nitrogen in a layer of 0 — 20 cm makes respectively 60 — 220 and 3 — 15 t on 1 hectare, and in a meter layer — is 3 — 4 times more. The general content of phosphorus (P2O5) fluctuates from 0,1 to 0,3%, and a gross stock of its 2 — 4,5 t on 1 hectare. Reaction of these soils is close to neutral or alkalescent (рН 6 — 8), exchange acidity, as a rule, is absent, hydrolytic acidity fluctuates from 0 to 4 мэкв on 100 g. Humus have the high capacity of absorption and degree of a saturation the bases. At the typical humus the greatest power of the humic horizon, higher maintenance of a humus, the general nitrogen, phosphorus and their gross stocks (respectively 120—220, 7—15 and 3,5 — 4,5 t on 1 hectare), and also absorption capacity. To the North — at the lixivious chernozem and to the South — at ordinary and especially southern chernozems these indicators decrease. Reaction of the soil subacidic at the lixivious chernozem and alkalescent at ordinary and southern at which saturation degree the bases is also higher, and insignificant or at all is absent hydrolytic acidity. At lixivious humus hydrolytic acidity reaches often 3 — 5 on 100 g. All subtypes of humus are rich with potassium, the general contents it is equal 2,5 — 3%, and a gross stock of 45 — 60 t on 1 hectare. Despite high potential fertility of humus, security with their forms of nitrogen and mobile phosphorus, especially old arable and poorly fertilized soils, very often low. Therefore on these soils high efficiency phosphoric is observed, and under more favorable conditions of moistening — and nitric fertilizers. On old arable and humus reserves of the general and exchange potassium therefore on such soils, especially under cultures (sugar beet, potatoes, sunflower, etc.), use of potash fertilizers is effective decrease in comparison with virgin (together with nitric and phosphoric). Mineral fertilizers are more effective in more humidified western regions of the humus zone, in east areas (in parallel with deterioration of conditions of moistening) their efficiency decreases.