Effect of deforestation on selected soil quality attributes in loess-derived landforms of Golestan province, northern Iran

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1 Proceedings of The Fourth International Iran & Russia Conference 546 Effect of deforestation on selected soil quality attributes in loess-derived landforms of Golestan province, northern Iran Farshad Kiani 1, Ahmad Jalalian 2, Abbas Pashaee 3 and Hossein Khademi 4 1. College of Agriculture, Isfahan University of Technology, Isfahan, Iran. kianifarshad@yahoo.com 2. College of Agriculture, Isfahan University of Technology, Isfahan, Iran. Jalalian@cc.iut.ac.ir 3. College of Agriculture, Gorgan University of Agriculture And Natural Resources Sciences, Gorgan. Iran. apashaee@yahoo.com 4.: College of Agriculture, Isfahan University of Technology, Isfahan, Iran. hkhademi@cc.iut.ac.ir Abstract Deforestation and land use change have created serious problems in northern Iran. During the past three decades, forest coverage has decreased from 18 to 12.2 million hectares. To investigate the degree of forest degradation and the effect of land use change on some soil quality attributes in loess land, samples were selected from different land uses including forest, rangeland, degradated rangeland and farmland in Pasang watershed located in the Galikesh area, Province of Golestan, north of Iran (37 16'N, 55 30'E) with annual average temperature of 15 C and a mean annual precipitation around 730 mm.ph, EC, amount of organic matter, CaCO 3 and nutrients (N, P, K) as chemical indicators, hydraulic conductivity, bulk density and porosity as physical indicators and soil respiration as biological indicator were considered. Mean values of different variables were statistically compared by Duncan's method (p 0.05). The results have shown that the amount of organic matter decreased three units when it turns from forest to farmland, and increased two units from farmland to rangeland. The amount of CaCO 3 in surface layer of deforested area was more than the forest soils. The amount of soil N in forest and soil P and K in rangeland were high. Root decomposition and uptake by plants had an important role on distribution of N. Difference in soil P storage may have resulted from changes in biological and geochemical processes. Weathering and leaching have affected soil K. Bulk density and porosity in forest and MWD in rangeland were higher than in other land uses because of decreasing the amount of organic matter and farming activity. Soil respiration in forest was highest as compared to other land uses. Decomposition of organic matter in farmland with no addition of plant residues have caused low respiration rate. So, we can suppose that amount of organic matter, soil N, Bulk density, porosity, MWD and soil respiration are suitable indicators for soil quality evaluation in this area. Understanding and determination of land use change and its effect on soil quality is a priority for researchers and policy makers. Keywords: Deforestation, land use change, soil quality, loess 1. Introduction Floodings in Golestan province are not unexpected events now. Every year this destructive event causes a lot of damage in farmlands and civil constructions. Deforestation and land use change have created serious problems in north of Iran. During the past three decades, the forest coverage has decreased from 18 to 12.2 million hectares. Although deforestation and land use\cover change has often been mentioned as the prime reason for flooding, but tree cutting is not taking the main responsibility. Forest degradation has also negative consequence on soil quality and health. Soil quality, defined by Islam(2000) is the capacity of a soil to function within the ecosystem boundaries and to interact positively with surrounding ecosystems.

2 Proceedings of The Fourth International Iran & Russia Conference 547 Various approaches for soil quality indexing have focused on two important principles associated with soil quality and its assessment. Firstly, soil quality indices are determined by using both inherent and dynamic properties and processes interacting within a living medium. Secondly, the indices are determined holistic consideration of biological, chemical, and physical properties, processes, and interactions within soils (Karlen 2003).The loess derived soils of northern Iran are unique in terms of their characteristics and need special attention. Loess can be defined simply as terrestrial clastic sediment, composed predominantly of silt-size particles, which is formed essentially by the accumulation of wind-blown dust (Kemp 2001). Loess lands, as a useful landscape for agriculture (Catt 2001), are very susceptible to soil erosion. Thus, for land use planning and management in these lands more information about characteristics, properties and reactions are needed. The objectives of this study are to evaluate the soil quality indicators in forest, rangeland and farmland and to determine the effect of deforestation on these indicators. Materials and methods 2.1. Site description The study has been carried out in the Pasang catchment, located in the Galikesh area, Province of Golestan, North of Iran (37 16'N, 55 30'E).(Fig.1). This site is a part of the Goroanrood watershed with annual average temperature of 15 C and a mean annual precipitation around 730 mm. The parent materials are composed of loesses with different ages, and the deep and moderately developed soils of the study area are classified as Alfisols according to Soil Taxonomy. The selected area is about 286 hectares. The whole 286 hectares of study area are covered by farmland, rangeland, degraded rangeland and natural forest with about 50, 15, 15 and 20 percent respectively. The main plant species are Carpinus.sp and Quercus.sp, in forest, Triticum.sp in farmland and Rosaceae.sp in rangeland. The studied rangelands are in fact the former farmlands that were conserved about 30 years ago. Rangeland has been partly grazed recently Soil collection and analysis For each land use, about 20 samples were randomly taken from surface soil (0-10cm), air dried and their chemical properties were measured. Six sites were selected for hydraulic conductivity and infiltration measurements. These measurements were done with six replication in each site. Ten fresh samples were used for soil respiration analysis. Mean values of different variables were statistically compared by Duncan's method (p 0.05). Results and discussion 3.1. Effects of land use on chemical indicators and soil nutrients The ANOVA results are presented in Table1.The ph value of the forest and deforested soils vary significantly.basic ions were leached mainly in forest soils, consequently the acidity of forest area was more than other sites. Cultivation has redistributed the basic leached ions of lower horizons in surface layers of deforested section.the amount of forest soil organic matter, due to addition of tree residues and weak decomposition, was more than the other sites. Although human activity and farming have amplified the decomposition rate in rangeland, but the amount of organic matter compared to farmlands, was increased due to its land cover.grazing

3 Proceedings of The Fourth International Iran & Russia Conference 548 has reduced the amount of organic matter in rangeland but it was not significant when compared with other sites. The amount of CaCO 3 in surface layer of deforested area was more than the forest soils, which was supposed to be due to cultivation. Tillage seems to be responsible for uplifting of lime from underneath calcic horizon. Differences of CEC in all sites were not significant. Although, the difference of organic matter in soils of forest and farmland was high (about 4% against 1.3%), but due to slow rate decomposition of plant residues in forest soils and rapid mineralization of plant residues in farmland, it has not affected CEC in forest soils. Although plants play an important role in regulating the biogeochemistry of ecosystems by fixing the nutrients under disturbance (Xiongwen Chen 2003), but human activities in the forest soils has had great a impact on soil nutrient storage. Soil nutrient had decreased because of (i) residue burning, plowing, and loss of nutrients (ii) tree cutting, moisture loss after tree cutting (iii) species changing. Plant species have different nutrient requirements, and exploit nutrients with varying efficiently, so regulate the soil nutrients with different rates. Different land uses had different effect on soil nutrient circulation. Soil Nitrogen had a high correlation with the amount of organic matter in different sites. and it was completely shown that root decomposition and uptake by plants had an important role on distribution of N. Difference in soil P storage may be resulted from changing of biological and geochemical processes at four land types. Biological controls on P include root growth pattern, amount and quality of detritus inputs, exteracellular enzyme activity, production of organic chelates and micorrizal activity (Xiongwen Chen 2003).In study area, soil P in forest were higher than farmland but lower than rangelands and these differences were not significant. It is supposed that, rangeland plant coverage was more efficient to releasing the P from phosphorous minerals, P up taking and storing in their tissues. However it would be related to other factors other than land use. The amount of soil K was the most in rangeland then in forest, degraded rangeland and farmland respectively. Potassium is reduced by tree cutting because of increasing the leaching processes in degraded forest. High amount of K in rangeland may be resulted from loess weathering and storage by rangeland plants and in farmland, K may be reduced due to leaching Effects of land use on physical indicators Soil texture in study area varied from silty clay to silty clay loam. Soils under cultivation had higher bulk density than forest and rangeland (Table 2) because of having higher amount of organic matter with low weight effect on bulk density. Cultivation has positive affect on soil porosity. So, in forest soils the porosity was less than the other land uses. Organic matter in forest and rangeland soils seems to bridge the loess particles. This action causes to encrustation of organic matter in forest soil surface. Cultivation and plowing in farmland increase the soil infiltration. Because of stable soil structure in forest, it has significantly high hydraulic conductivity rate than the other sites. Difference between value of MWD in farmland and other land use types was significant because of decreasing the amount of organic matter and farming activity Effects of land use on soil microbial respiration In soil quality assessment, the biological indicators play a great role. Biological indicators are most sensitive to change and show the differences better. Enzyme activities, soil respiration and microbial biomass analysis help us to understand health

4 Proceedings of The Fourth International Iran & Russia Conference 549 condition of soils. In this paper soil respiration as a biological soil quality indicator was measured. The difference between lands uses was statistically significant (Table.3).High amount of respiration in forest may be due to high new organic matter (litter) that is annually added to soil surface. Decomposition of organic matter in farmland without adding the new ones seems to have caused low respiration rate. Conclusion Our study showed that deforestation in north of Iran has influenced the soil quality indicators. In many indicators tree cutting decreased the soil quality and resting the farmland and changing to rangeland improved its quality and grazing of this rangeland negatively effect on this improvement. In chemical soil quality indicators, ph and CaCO 3 in forest were low and in contrast organic matter and N were high compared to other land uses. Soil K and P were high in rangeland and CEC did not change significantly. In physical soil quality indicators, bulk density and porosity were in lower and Ksat was in higher level in forest. MWD was increased in rangeland and was decreased by farming. Soil respiration as a biological indicator of soil quality was increased by organic matter and was in highest level in forest. So, we can suppose that amount of organic matter, soil N, Bulk density, porosity, MWD and soil respiration are suitable indicators to evaluation of soil quality in this area. Understanding and determination of land use change and its effect on soil quality is a priority for researchers and policy makers. Acknowledgements We would like to thank the staff laboratory, Soil Science Department, College of Agriculture, Isfahan University of technology. References Catt J ( 2001) The Agricultural importance of loess. Eearth Science Reviews 54: Islam KR, Weil R (2000) Land use effects on soil quality in a tropical forest of Bangladesh. Agriculture Ecosystems &Environment 79:9-16. Karlen DL (2003) Soil quality: why and how. Geoderma 114: Kemp RA(2001) Pedogenic modification of loess: significance for paleoclimatic reconstructions. Earth Science Reviews 54: Xiongwen Chen, Bai-Lian Li(2003) Change in soil carbon and nutrient storage after human disturbance of primary Korean pine forest in Northern China. Forest Ecology and Management 186:

5 Proceedings of The Fourth International Iran & Russia Conference 550 Fig.1. Location map of the study area Table 1.Effect of land use on selected chemical soil quality indicators in Pasang watershed. A, B and C show Duncan grouping at p 0.05 Soil Properties Forest Rangeland Degradated rangeland Farmland ph 7.09 B 7.32 A 7.41 A 7.49 A Organic matter (%) A 3.14 B 2.77 B 1.36 C CaCO 3 (%) C B A 28.7 B N (%) 0.23 A 0.18 B 0.16 B 0.07 C P (ppm) A A A 69.0 A K (ppm) B A B B CEC (meq/100gr) A A A A Table 2.Effect of land use on selected physical soil quality indicators in pasang watershed. A, B and C show Duncan grouping at p 0.05 Soil Properties Forest Rangeland Degradated rangeland Farmland Bulk density (gr/cm3) 1.28 A 1.23 A 1.24 A 1.31 A Porosity (%) B AB AB A Ksat (cm/hr) A 8.32 B 8.66 B 1.46 B MWD (mm) 1.88 A 2.14 A 2.04 A 0.67 B Table 3. Effect of land use on soil respiration (mg co 2 /gr soil.day) in Pasang watershed. A, B and C show Duncan grouping at p 0.05 Forest Rangeland Degradated rangeland Farmland 0.61 A 0.60 AB 0.59 AB 0.51 B