Soil-Ecological Monitoring of Pasture in Semiarid Mountains


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Soil-Ecological Monitoring of Pasture in Semiarid Mountains

Vladychenskiy A.S.

Faculty of Soil Science Moscow State Lomonosov University, Moscow, Russia

Abstract

The distinctive property of mountain ecosystems, notably arid and semiarid ones, is their low stability. On the other hand, just arid and semiarid mountains have the most intensive pressure of grazing among whole diversity of mountain systems. One of the main forms of land use in mountain ecosystems, especially in upper part of mountain regions, is pasturing. The most part of mountain pastures is overgrazed to a variable degree. To prevent degradation processes is possible during the early stages, when degradation is reversible. Before the destruction of plant and soil covers there are several phenomena which seriously change plant and soil status but don't destroy them yet. For sustainable land use it is necessary to control the state of soil and plant cover to prevent their irreversible degradation by special monitoring system. The main objects of monitoring are the consequences of the negative processes in ecosystem, connected with plant and soil covers.

Introduction

One of the main forms of land use in mountain ecosystems, especially in upper part of mountain regions, is pasturing. The most part of mountain pastures is overgrazed to a variable degree. To prevent degradation processes is possible during the early stages, when degradation is reversible. Before the destruction of plant and soil covers there are several phenomena which seriously change plant and soil status but don't destroy them yet. The general peculiarity of agriculture, including pasturage, in mountain ecosystems is a prevalence of extensive forms of land use. This is the reason that great quantities of natural resources including land ones are involved into agriculture sphere. Limited natures of land resources in the mountains cause the high level of anthropogenic pressure. Unsystematic mountain pasture use leads to their degradation. On measure of the pressure increasing following three stages are consecutively changed:

Depending on intensities of the pasture pressure and length of its influence pasture digression can stop on one or another stage. On the first pasture digression stage floristic composition of plant communities is changed and the biomass stock decrease. The productivity reduction or full disappearance of grass cover as a result of grazing leads to soil erosion development. Subsequent development of soil erosion processes can lead to full removing of soil cover; after that subsoil and rocks can be destroyed. Soil, as the most conservative component of mountain ecosystem is the base of their stability. Plant cover is much less stable. Under intensive grazing influence it can be changed for 4 - 5 years (Shikhotov, 1974). Comparatively quickly proceeds its reconstruction - anyway, in contrast with topsoil. Pasture productivity under their rational use can be restored for 5 years (Mamytov, 1985; Zotov, Sinikovskiy, Shvan-Guriyskiy, 1987). The stability of soils is a necessary condition of such reconstruction; their destruction does impossible a plant community restoration. For soil cover restoration absolutely other periods are required - a hundreds of the years i.e. in real scale of time destroyed erosion soils is possible to consider lost forever. So soil stability is a necessary condition of ecosystem stability as a whole and, on the contrary, its destruction excludes the possibility of ecosystem reconstruction.

The Grazing Influence on Plant Cover
The plant cover is the most sensitive to grazing component of ecosystem. Perennial unsystematic use of mountain pastures leads to their serious degradation. Grazing changes the main features of plant communities: biomass stock and its structure, floristic composition etc. that decreases pasture productivity and reduce stability of soil cover. Different intensity grazing on West Caucasus sub alpine meadows was the cause of important changes in state of their plant communities. Parallel with general biomass stock reduction its overground stock strongly decreases. The underground biomass also decreases, but in smaller degree; this is the cause of biomass structure changing. Floristic composition of plant communities is strongly changed. The share of cereals sharply decreases. If subalpine meadow, not touched by grazing, has an absolute prevalence of cereal on the other species, under moderate grazing influence herbs becomes the most representative; under intensive grazing influence share of cereals decreases much more. This greatly reduces stability of soils because sod becomes thinner and less durable. As pasture use mainly herbal ecosystems - meadows, steppes, semideserts. Much more rarely grazing take place in the woods.

The Grazing Influence on Physical Properties of Soil
The physical characteristics of soil strongly change under the influence of grazing. The essential effect of grazing is its compaction, occurring under animal hoof influence. Sometimes, the compaction is accompanied by displacement of soil mass, which particularly powerfully reveals itself during pasturage on moistened soil, in particular, early spring time. The hoof pressure reaches 1,5 - 2,0 kg/cm2, when animals stand, and 4 kg/cm2 when walking that exceeds the pressure of tractor wheels (Docenko, 1960). During pasture season animals several times (before 10) pass on one and same place (Rabotnov, 1984). The significant value of the hoof pressure is sent on depth 8-12 cm. On compaction of soil sod has a great influence; she prevents deformation of soil and bulk density is changed not so vastly. The compaction of ground depends on intensity and length of grazing, way of its undertaking and characteristic of soil. For year of grazing with pressure 10, 15, 19 and 22 sheep per 1 ha bulk density of loamy soil increased from 0,89 g/cm3 to 0,94 - 1,05 g/cm3 (Willat, Pullar, 1984). Perennial unsystematic grazing with high pressure was the cause of compaction of light kashtanozems (Kirghiz Mountain ridge in Tyan-Shan) from 0,9 to 1,3 g/cm3. Controlled grazing compact soil in a lower degree. On compaction greatly affect the characteristic of soil, and in the first place - a contents of humus. Reach humus soils are packed down to a lesser extent.

The compaction of soil is connected with reduction of porosity. First of all decreases no capillary porosity, increases the share of the capillary pores. This worsens the air regime of soil and reduces its water permeability. The double reduction of noncapillary porosity leads to the reduction of water permeability also in two times. Increase of the pressure progressive reduces both these indices. Grazing within one year with pressure 10, 15, 19 and 22 sheep per hectare was responsible for the reduction of loamy soils water permeability from 19 mm/min to accordingly 13,5, 10,8, 6,0, 3,6 mm/min (Willat, Pullar, 1984). Soils with high content of humus are more stable to such impact. Grazing greatly influences upon structure of soil. On early stage pasture digression or under moderate pressure occurs not as much destruction of soil aggregates as their repacking in consequence of which falls open grain porosity. The Study of kashtanozems of the Kirghiz ridge north slope has pointed that moderate grazing allows to save the quality of the structure. The content of aggregates with size 0,25 - 10 mm in humus horizon forms 66 % on moderate grazing area against 60% on the area without grazing. Intensive unsystematic grazing often leads to formation of blocky structure or to full its destruction.

The Grazing Influence on Chemical Properties of Soil
The most important change in chemical characteristic of soil as a result of grazing is the reduction of humus contents. The humus loss is due to two reasons. The first of them is that grazing greatly changes the character of the biological cycle; the significant share of the overground biomass, eaten animals, is excluded from sphere of humification that breaks the humus balance aside decreasing of its content. A quantity of organic material enters to soil with excrements, but this amount of organic matter can not compensate the appearing deficit of plant remains required for forming humus. Besides, organic material of excrements is extremely unevenly distributed on area of pastures. The second reason of the humus loss is soil erosion, destroying upper part of the soil profile. The study of kashtanozems humus state on Tyan-Shan mountain pasture has shown, humus loss take place here very distinctly. The content of humus reduces in dark kashtanozem under moderate grazing influence in two, but intensive - in four times. Not so sharply, but wholly distinctly humus loss reveals itself in light kashtanozems. In humus reach black-brown soils relative losses of humus are not so significant (Karabaev et al., 1987). In the soils of the more humid mountain systems humus loss under grazing influence is not so large that is connected with smaller ecological stability of soils in the arid and semiarid mountain systems (Table 1). The humus composition, being more conservative in contrast with the total its contents, is changed under grazing in vastly smaller degree.

Soil Cover Degradation on the Pastures
One of the most important consequences of grazing is formation of secondary spatial heterogeneity of plant and soil covers. As a result of uneven animal influence fragments of different degree of degradation appear on pasture. Usually it is possible to allocate the following elements of heterogeneity:

Described spatial heterogeneity of the plant cover is connected with process of pasture degradation under influence of grazing. The stock and structure of the biomass greatly differ between chosen elements of heterogeneity, decreasing from no destroyed area to path. On the path part of cereals and partly of leguminous is more in contrast with no destroyed fragments. The secondary spatial heterogeneity of soil cover, in the same way as plant one, is rather great. The fluctuations of some features between different fragments often exceed the differences between various pastures. So all conclusions about changing of soil and plant cover characteristic under grazing is expediently to do taking into account this circumstance. It is necessary to compare not simply different pastures, but different fragments of heterogeneity within each of them. (Table 2).

Soil-Ecological Monitoring of Mountain Pasture
The important problem is a checking and forecasting of mountain pastures state. At present does not exist the elaborated system of their monitoring, including soil-ecological one. It should be stressed that monitoring of mountain pasture ecosystem has a row of specific particularities. One of them is that usually it is very difficult to take into account the true pressure to the pastures. Besides, the pressure is greatly differentiated on element of the relief (different kinds of slopes, different their steepness etc.). Finally, pasture digression, as it was noted, could run differently in different mountain system and separate their parts. This requires the differentiated approach to performance of soil-ecological monitoring of mountain pasture. As it was noted, one of the main consequences of grazing is formation of secondary spatial heterogeneity of plant and soil covers. Such secondary spatial heterogeneity is a principle particularity of the pasture digression. It should be taken into account by pursuance of soil-ecological monitoring pasture. Otherwise it leads to wrong conclusion. The set of such monitoring indices could be approximately following.

All indices are necessary to define in terms of secondary spatial heterogeneity of plant and soil covers. Majority of these indices is uncomplicated in determination, many of them can be determined right in field. Their checking needs to do once in 3 - 5 years, in some cases more often. In the absence of existing structures of soil-ecological monitoring their indices is possible to determine during agricultural chemistry examination of the territory. The humus composition needs to check more rare, once in 5 - 10 years, also agreeing the time with periodicity of the agricultural chemistry examination.

References

. Docenko, L.S., 1960. The Influence of grazing on physical conditions in soil under perennial grasses. In "Proceedings on agronomic physics", N 8, pp.92-102.
. Zotov, A.A., Sinikovskiy, L.P., Shvan-Guriyskiy, I.P., 1987. The Mountain pasture and hayfields. Agropromizdat, Moscow, 253 p.
. Karabaev, N.A., Dzhunushbaev, A.D., Koychiev, M.K., Alasheva, A.A., Umetalieva, A.S., Kurmanaliev, M.K., 1987. The soil erosion processes in nut-fruit forests of South Kirgiziya at period of the use their as pasture. Proceedings of Kirgiz Institute of soil sience, V. 18. Frunze, pp. 152-166.
. Mamytov, A.M., 1985. Some ecological aspects of agriculture intensification and connected with them problems of environment in Kirgiziya. In "Ecological aspects of mountains environment". Ilim, Frunze, pp. 3-10.
. Rabotnov, T.A., 1984. Lugovedenie. Mosc. Univ., Moscow, 319 p.
. Shikhotov, V.M., 1974. The Mountain pasture, their use and improvement. Kyrgyzstan, Frunze, 131 p.
. Willat, S.T., Pullar, D.M., 1984. Changes in soil physical properties under grazed pastures. Austral. J. Soil Res., v. 22, N 3, pp. 343-348.

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