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| **Overgrazing Effect on Rangeland Soil Properties**\                  |
| \                                                                     |
| Mudahir Ozgul, Taskin Oztas\                                          |
| \                                                                     |
| Ataturk University, Faculty of Agriculture, Department of Soil        |
| Science, Erzurum, Turkey                                              |
|                                                                       |
| **Abstract**\                                                         |
| \                                                                     |
| Overgrazing is one of the main factors causing range degradation by   |
| leading erosion, reducing biodiversity, and altering soil properties. |
| The objective of this study was to evaluate soil properties of an     |
| overgrazed range site with those of a protected range site. Two study |
| sites had similar grazing history until 1990. But the protected site  |
| has never been grazed since after then. Soils of both sites formed    |
| from calcareous parent material on similar topography. In both sites, |
| morphological description of the soil profiles was defined, and some  |
| physical and chemical properties including particle size              |
| distribution, bulk density, moisture content, aggregate stability,    |
| penetration resistance, soil pH, organic matter content, plant-       |
| available P, and CaCO3 content were determined. Canopy coverage rate  |
| of soil surface was also measured. Results were indicated that the    |
| protected site; had at least four times biomass, higher amounts of    |
| clay content, low penetration resistance and bulk density, higher     |
| moisture and organic matter content, and more water stable aggregates |
| than those of uncontrolled range site.\                               |
| \                                                                     |
| **Introduction**\                                                     |
| \                                                                     |
| Rangelands have special importance in resource management. About 80 % |
| of land under erosion risk in the world consists of rangelands        |
| (Thurow, 1991). Grazing is the most economical way of evaluating      |
| rangeland vegetation. But, overgrazing or uncontrolled grazing always |
| reduces plant cover that protects the soil and finally causes soil    |
| erosion and compaction (Oztas et al. 2000). Overgrazing and its       |
| attendant effect of depletion of plant cover and litter and trampling |
| of the soil is the most important factor contributing to erosion      |
| (Branson et al. 1981), which threats about 85 % of our lands in       |
| Turkey. The grazing lands of Turkey are subject to quite heavy,       |
| uncontrolled grazing pressure and the forage production capacities of |
| these lands are gradually decreasing, therefore, ultimately           |
| reflecting typical examples of land degradation all over Turkey       |
| (Tukel&Hatipoglu, 1996). Overgrazing which led to deterioration of    |
| plant cover on rangelands was initiated in 1950s and has been         |
| continued up until today (Koc et al. 2000). As a result of increasing |
| grazing pressure, Turkey\'s rangelands has lost about 90 % of their   |
| climax vegetation (Genckan et al. 1990). Koc (1995) emphasized that   |
| rangelands in our country were in poor and moderate categories with a |
| canopy cover rate of 20 % on the average, and the degradation was too |
| severe in lower altitudes. The objective of this study was to         |
| evaluate soil properties of an overgrazed range site with those of a  |
| protected range site.\                                                |
| \                                                                     |
| **Material and Methods**\                                             |
| \                                                                     |
| An overgrazed rangeland and a rangeland protected from grazing for    |
| ten years were selected to determine changes in some soil properties  |
| and biomass. The study sites are located in Tuzcu village, which is   |
| about 5 km southwest of Erzurum. Soils of both sites formed from      |
| calcareous parent material on similar topography. Sheep fescue was    |
| the dominant species in both sites. The study sites have never been   |
| cultivated. Average slope gradient in the study sites was about 15 %. |
| Both sites had similar grazing history until 1990. In the region      |
| farmers tend to graze range lands as long as climatic conditions are  |
| favorable for grazing. Grazing starts with the melt of snow in spring |
| and continues until the snowfall in autumn (approximately 9 months).  |
| The study area has a semi-arid moisture regime with a mean annual     |
| precipitation of 446.2 mm and a mean annual temperature of 5.9 oC.    |
| The mean annual evaporation and relative humidity are 1059 mm and 63  |
| % respectively (Anon., 1997).\                                        |
| \                                                                     |
| After searching for typical profiles to represent overgrazed and      |
| protected sites, two soil profiles were dug. The profile I was        |
| located in overgrazed range site, and the profile II in protected     |
| site. There was only 500 m distance between two range sites. The      |
| range sites on which profile II was dug, was surrounded by wire about |
| ten years ago, and it has never been grazed since 1990. Morphological |
| description of the soil profiles was performed according to the Soil  |
| Survey Division Staff (1993) and presented in Tablo1 & 2. Observation |
| on topography of the site, the extent of erosion, and the degree of   |
| drainage and soil moisture status were reported. Disturbed and        |
| undisturbed soil samples were collected from different horizons, and  |
| analyzed for some physical and chemical soil properties including     |
| particle size distribution, bulk density, moisture content, aggregate |
| stability, soil pH, organic matter content, plant- available P, and   |
| CaCO3 content. Penetration resistance of soils was determined using   |
| field-type penetrometer.\                                             |
| \                                                                     |
| **Results and Discussion**\                                           |
| \                                                                     |
| Measured physical and chemical properties of soils are given in Table |
| 3. Clay content of different horizons in Profile I was almost         |
| constant, except the surface horizon which had about 20 % less clay   |
| content than those of the lower horizons. This may due to erosion     |
| losses. Although the profile II had greater amounts of clay content   |
| (around 30 %, except the deepest horizon) than the profile I, there   |
| was no changes in clay contents between the top horizon and the lower |
| horizons. This clearly indicated that erosion losses were minimized   |
| in protected range site by keeping plant cover on soil surface, which |
| reduces raindrop impact and run-off.                                  |
|                                                                       |
| ![](media/image3.png){width="5.104166666666667in"                     |
| height="3.9895833333333335in"}\                                       |
| ![](media/image4.png){width="5.104166666666667in"                     |
| height="2.6666666666666665in"}                                        |
|                                                                       |
| ![](media/image5.png){width="5.104166666666667in"                     |
| height="3.9895833333333335in"}\                                       |
| ![](media/image6.png){width="5.104166666666667in"                     |
| height="2.6458333333333335in"}                                        |
|                                                                       |
| Soil bulk density values of the samples representing the profile I    |
| were higher than those of the profile II. This may be related to soil |
| texture. The profile I had around 50 % sand that may cause high bulk  |
| density values. Although bulk density values were almost constant and |
| changed around 1.04 g cm-3 through the soil profile dug in the        |
| protected site, there was no such situation in the soil profile of    |
| overgrazed range site. High bulk density of the top horizon in the    |
| overgrazed range site may be resulted from soil compaction due to     |
| extreme pressure by heavy grazing.                                    |
|                                                                       |
| ![](media/image7.png){width="5.427083333333333in"                     |
| height="2.7604166666666665in"}                                        |
|                                                                       |
| Soil water percentages at the time of sampling showed significant     |
| differences between two sites. The overgrazed site was drier than the |
| protected site. Soil water percentages were respectively constant     |
| throughout the soil profile at the protected site. However, soil      |
| moisture content decreased down to 2.44 % in the surface horizon of   |
| the profile at the overgrazed site. It could be concluded that soil   |
| water losses from the profile were higher in the overgrazed site      |
| because of lack of plant cover on soil surface. Aggregate stability   |
| of soils, which affects soil\'s resistance against erosive forces,    |
| was higher in samples from the protected site. This means that a      |
| higher amount of aggregates in soil at the protected site was         |
| water-stable as compared to that of soil at the overgrazed site. This |
| may be a result of high amounts of clay and organic matter content in |
| soil at the protected range site. On the other hand, penetration      |
| resistance that also effect water movement into soil as related to    |
| runoff losses was higher in soils at the overgrazed range site. It    |
| was almost twice in overgrazed site than the protected site had.      |
| Organic matter content of soils at the overgrazed site was less than  |
| 3.5 % in the upper two horizons, but it was higher than 4 % at the    |
| protected site soils. This may be directly related to higher surface  |
| cover rate in the protected site.\                                    |
| \                                                                     |
| CaCO3 contents of the range site soils were quite similar in both     |
| sites. It increased with depth and reached the highest value at the   |
| deepest horizon. Low CaCO3 values at the upper horizons were resulted |
| from leaching. Similar to the variation of organic matter content,    |
| plant-available-P content was the highest at the surface horizon of   |
| both sites. There were no significant differences in plant available  |
| P contents of soil between lower horizons. However, surface horizon   |
| at the protected site had significantly higher amount of available P  |
| than that of the overgrazed site soil had. On the other hand, it was  |
| determined that while the rate of canopy coverage at the overgrazed   |
| site was lower than 20 %, it was higher that 80 % at the protected    |
| range site. Results were indicated that the protected site had at     |
| least four times biomass, higher amounts of clay content, low         |
| penetration resistance and bulk density, higher moisture and organic  |
| matter content, higher amounts of plant available P, and more water   |
| stable aggregates than those of the overgrazed range site. In         |
| conclusion, the results of this study support the idea that           |
| overgrazing causes low level of vegetation and poor soil properties.\ |
| \                                                                     |
| **References\                                                         |
| **\                                                                   |
| **.** Anonymous. 1997. Weather Forecasting Sub-Directory Bulletin.    |
| General Directorate of Government Meteorological Works. Ankara (In    |
| Turkish).\                                                            |
| **.** Branson, F.A., Gifford, G.F., Renard, K.G. & Hadley, R.F. 1981. |
| Rangeland hydrology. 2nd ed. E.H. Reid (ed). Soc. Range Manage.       |
| Kendull/Hund Publ. Com. Iowa.\                                        |
| **.** Genckan M.S., Avcıoglu R., Soya H. & Dogan O. 1990. Türkiye     |
| mer\'alarının kullanımı, korunması ve geliştirilmesine ilişkin        |
| sorunlar ve çözüm yolları. Türkiye Ziraat Mühendisliği 3. Teknik      |
| Kongresi, 8-12 Ocak 1990, Ankara s. 53-61.\                           |
| **.** Koc A. 1995. Topografya ile toprak nem ve sıcaklığının mer\'a   |
| bitki örtülerinin bazı özelliklerine etkileri (Doktora Tezi). Atatürk |
| Üniv. Fen Bil. Enst., Tarla Bit. Anabilim Dalı, Erzurum.\             |
| **.** Koc, A., Oztas, T. & Tahtacıoglu, T. 2000. Rangeland-livestock  |
| interaction in our near history: Problems and recommendations p.      |
| 293-298 13-17 June 2000. Konya-Turkey.\                               |
| **.** Oztas, T., Koc, A. & Comakli, B. 2000. Changes in vegetation    |
| and soil properties along a slope. Proceedings of International       |
| Symposium on Desertification, Konya, pp 57-61.\                       |
| **.** Soil Survey Division Staff. 1993. Soil Survey Manual. Soil      |
| Conservation Service. USDA. Handbook 18.\                             |
| **.** Thurow, T.L. 1991. Hydrology and erosion. p. 141-159. In        |
| Grazing management an ecological perspective (Ed) R.K. Heitschmidt &  |
| J.W. Stuth. Timber Press, Inc.,\                                      |
| **.** Tukel, T. & R. Hatipoglu. 1996. Turkish grazing lands; Causes   |
| for misuse and likely measures of preventing degradation. Int.        |
| Conference on Land Degradation. June 10-14, Adana - Turkey p, 53.     |
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