technical report on the semi-detailed soil survey of radhi watershed

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Technical Report on Semi-detailed Soil Survey of Radhi Watershed Soil Survey Unit (SSU) National Soil Services Centre, Semtokha Council for RNR Research of Bhutan…
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Technical Report on Semi-detailed Soil Survey of Radhi Watershed Soil Survey Unit (SSU) National Soil Services Centre, Semtokha Council for RNR Research of Bhutan (CoRRB) Ministry of Agriculture TECHNICAL REPORT ON THE SEMI-DETAILED SOIL SURVEY OF RADHI WATERSHED Report No. SS - 6 December 1999 Last updated: 3/19/2013 Page 1 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed CONTENTS SUMMARY................................................................................................................................ 4 ACKNOWLEDGEMENTS ........................................................................................................ 5 ABBREVIATIONS AND GLOSSARY ...................................................................................... 6 1. 2. INTRODUCTION.............................................................................................................. 9 1.1 Radhi integrated research and extension area ........................................................................9 1.2 Aims of the Radhi semi-detailed soil survey ............................................................................9 SURVEY AREA ............................................................................................................... 10 2.1 Location and extent..................................................................................................................10 2.2 Climate ......................................................................................................................................10 Table 2.1 2.3 Geology and soil parent materials ..........................................................................................13 2.4 Topography and drainage .......................................................................................................14 2.5 Land use and vegetation ..........................................................................................................15 3. PREVIOUS SOILS INFORMATION.......................................................................... 17 3.1 Sinclair Knight (1983)..............................................................................................................17 Table 3.1 3.2 4. Climatic summary for Radhi 1985-1997.................................................................................... 12 Sinclair Knight (1983) soil classes at Radi-Phomi .................................................................... 17 Other studies.............................................................................................................................18 METHODS ...................................................................................................................... 19 4.1 Field ...........................................................................................................................................19 4.2 Mapping ....................................................................................................................................20 4.3 Laboratory ................................................................................................................................20 5. SOIL CLASSIFICATION, CHARACTERISTICS AND CORRELATION ................. 21 5.1 Soil classification ......................................................................................................................21 Table 5.1 5.2 Summary of soil classes in Radhi geog ...................................................................................... 21 Characteristics of soil classes in Radhi geog ..........................................................................22 5.2.1 Grey clay (RGC) ................................................................................................................................. 22 5.2.2 Grey loam (RGL). ............................................................................................................................... 22 5.2.3 Brown loam (RBL). ............................................................................................................................ 23 5.2.4 Brown sand (RBS) .............................................................................................................................. 23 5.2.5 Yellow loam (RYL) ............................................................................................................................ 24 5.2.6 Reddish brown clay (RBC) ................................................................................................................. 24 5.2.7 Humic loam (RHL) ............................................................................................................................. 25 5.2.8 Hillside gleys (RHG) ........................................................................................................................... 25 5.2.9 Analytical characteristics of soil classes ............................................................................................. 25 Table 5.2 Ranges of chemical analyses, by soil classes, Radhi ................................................................. 26 5.3 Soil correlation .........................................................................................................................26 5.3.1 Correlation with Sinclair Knight (1983).............................................................................................. 26 Table 5.3 Correlation with Sinclair Knight (1983) soil classes................................................................. 27 5.3.2 Correlation with soils elsewhere in Bhutan ......................................................................................... 27 Table 5.4 Correlation of Radhi soils with Tethyan phyllite/quartzite Kashi soils ..................................... 27 Table 5.5 Correlation of Radhi soils with Shumar soil profiles at Drametse ............................................ 28 5.3.3 International correlations..................................................................................................................... 28 Table 5.6 International correlations of soil classes at Radhi. ................................................................... 29 5.3.4 Correlation with geotechnical classification of soils ........................................................................... 29 Table 5.7 Geotechnical correlation of Radhi soil classes ............................................................................. 30 Last updated: 3/19/2013 Page 2 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed 6. SOIL DISTRIBUTION AND MAPPING ........................................................................ 31 6.1 Soil distribution ........................................................................................................................31 6.2 Soil mapping units....................................................................................................................31 Figure 6.1 Table 6.1 Table 6.2 7. Soil Map of Radhi ...................................................................................................................... 32 Composition of soil mapping units at Radhi .............................................................................. 33 Areas of soil mapping units, Radhi ............................................................................................ 33 LANDSLIPS AT RADHI ................................................................................................. 34 7.1 Overview of Radhi soils ...........................................................................................................34 7.2 Slope instability in Radhi ........................................................................................................34 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 General ................................................................................................................................................ 34 Natural instability ................................................................................................................................ 34 Anthropogenic factors ......................................................................................................................... 35 Interaction of natural and anthropogenic effects ................................................................................. 36 Implications for intervention ............................................................................................................... 37 REFERENCES ....................................................................................................................... 39 APPENDIX A: Table A.1 APPENDIX B: Table B.I. APPENDIX C: METHODS OF SOIL ANALYSIS USED AT SPAL, SIMTOKHA .......... 42 Summary of current interpretation of SPAL soil analyses ......................................................... 44 SOIL PROFILE DESCRIPTIONS AND ANALYSES ............................. 45 Summary of Radhi soil profiles .................................................................................................. 45 SOIL CORRELATION ............................................................................. 70 C. I Soil classification and correlation in Bhutan. ........................................................................70 C.2 General Criteria .......................................................................................................................70 C.2.1 C.2.2 C.2.3 C.2.4 C. 3 C.3.1 C.3.2 C.3.3 C.3.4 C.3.5 C.3.6 Soil moisture regime ........................................................................................................................... 70 Soil temperature regime ...................................................................................................................... 70 Mineralogy class ................................................................................................................................. 71 Particle size class. ................................................................................................................................ 71 Correlation of Radhi soils .......................................................................................................71 Grey clays and loams (RGC & RGL) ................................................................................................. 71 Brown loams and sands (RBL & RBS) ............................................................................................... 71 Brown clay (RBC)............................................................................................................................... 71 Yellow loam (RYL) ............................................................................................................................ 72 Humic loam (RHL) ............................................................................................................................. 72 Hillside gley (RHG) ............................................................................................................................ 72 APPENDIX D: Table D.1 SSU SOIL SURVEY REPORTS ............................................................... 73 SSU main soil surveys and reports ............................................................................................ 73 Last updated: 3/19/2013 Page 3 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed SUMMARY This is the technical report of semi-detailed soil survey of Radhi geog carried out by the Soil Survey Unit in 1998-1999. Radhi geog has been selected for intensive research and extension activities by Khangma RNRRC because it is highly productive and also because its physical resource base is seriously threatened by recent large-scale landslips. The soil survey was carried out in order to provide colleagues working in the area with a general account of the soil resources. Radhi geog covers about 2450 ha in eastern part of Trashigang dzongkhag, and stretches from about 1200 m to 2700 m asl. The climate is subtropical - warm temperate. Topographically it has a roughly the shape of part of a cone, and radiates out from a narrow zone at the top to broad lower slopes. The lower slopes are extensively used for wetland rice and it is this that makes Radhi an important agricultural production area in Eastern Bhutan. The top of the geog is under broadleaf forest but this has been severely degraded by excessive timber and firewood harvesting, and by overgrazing of cattle from Radhi and the higher lands to the east. The area is mainly underlain by clay-rich marine sedimentary rock, with subordinate quartzite beds. These have been intruded by granitic and basic rocks. The soils are formed from parent materials that are derived from these rocks but many of the materials have been moved and mixed by hillwash and landslips. The distribution of soils is influenced mainly by altitude, rock type, and topography. There is a zone of shallow stony soils on the steep lower slopes close of the river. Above that most of the lower slopes have a mixture of grey clays and loams, which are the main wetland rice soils. They also appear to be the most prone to landslips. The middle slopes have a complex of brown loams and sands, which are the main rainfed cropping soils. These soils stretch down to the lower slopes along the crests of the moderately gentle spurs. The upper slopes have a complex of brown and yellow loams and clays. At the very top of the geog these soils have deep, dark humic topsoils. There are small areas of soils with naturally poor drainage mixed in with all of the main soil types. The landslips are estimated to cover about 150 hectares (360 acres) at present but are still expanding, their possible causes are discussed. The area is naturally prone to this kind of disturbance, and the landscape indicates that similar events have occurred before. The present cycle of landslipping may be inevitable, but it might have been triggered by recent changes in land management, such as expansion of wetlands, over-exploitation of forest resources, and road construction. If the landslips are mainly natural and inevitable, the potential benefits of attempts at stabilisation and soil conservation may be limited, and need to be carefully investigated. SSU anticipate doing further, more detailed surveys of the soils of specific areas at Radhi in the future as the research programme develops. Last updated: 3/19/2013 Page 4 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed ACKNOWLEDGEMENTS The fieldwork for this Soil Survey was done by Tsheten Dorji, Ian Baillie, Kado Tshering, H.B. Tamang and Tshering Dorji. The report and interim map were produced by Pema Wangmo. The final soil map was digitised by Sangita Pradhan. We are particularly grateful to Deputy Forest Ranger Tshering Peljor for his personal hospitality, great logistical assistance, and guidance in the field. We are also grateful to the RNR staff of the Trashigang Dzongkhag and the RNR Centre, Radhi for their assistance on logistics, and to the Gup, Chimi and people of Radhi for their physical assistance and hospitality in the field. The Director and staff of the Khangma RNR-RC, especially Mr J N Pradhan, gave valuable assistance and guidance on the initial organisation, and information on the agricultural and environmental characteristics and problems of the geog. The analyses of the soil samples were done by the Soil and Plant Analytical Laboratory (SPAL), MoA, Semtokha. The supply of meteorological data from the Ministry of Trade and Industry is gratefully acknowledged. We are grateful to the staff of Khangma RNR-RC for discussions on the situation at Radhi and for comments on the draft text and map. Feedback is important, because Radhi is to become a focus of concentrated multidisciplinary research and extension activities. We would like our findings and report to be informative and accessible, so that soils characteristics and distribution receive full consideration in research and extension activities. Last updated: 3/19/2013 Page 5 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed ABBREVIATIONS AND GLOSSARY AAS AHT Alluvial fan AmOAc AP AvP, AP AWC asl BHU BS% SSU C ca CEC Chhu Chhuzing CL Colluvium Complex Consociation CoRRB Creep Danida Dzongkhag EC Exch Extr FAO FC fe FY FYM Geog GIS Gley GPS GSI Gully wash ha HCl ISRIC Last updated: 3/19/2013 Atomic absorption spectrophotometery Agrar - und HydrotechniK, GmbH, (Germany) Poorly stratified and sorted material deposited in side valley Ammonium acetate (extractant for exchangeable cations and for measuring CEC) Arunachal Pradesh Available Phosphate Available water capacity (= MC% FC – MC% WP) Above sea level Basic health unit Base saturation percentage Soil Survey Unit Clay Approximately Cation exchange capacity Stream or river Irrigated agricultural land Clay loam Local hillwash, moved by surface erosion and slow non-glacial creep processes. Soil mapping unit with several co-equal soil classes Soil mapping unit with one soil class dominant but others as minor constituents Council for RNR Research of Bhutan Slow gravitational mass movement of colluvium downslope. Danish International Development Assistance Administrative district Electrical conductivity Exchangeable (for cations) Extractable (for soil nutrients) Food and Agriculture Organisation of United Nations Field capacity (MC% at 0.1 atmospheres suction) fine earth (particle size < 2mm) Financial year (July – June in RGOB) Farmyard manure Block or subdistrict, administrative subdivision of Dzongkhag. Geographical information system Soil that is permanently wet, poorly aerated and has predominantly greyish colours, due to reduction of free iron to ferrous valency state. May have local oxidising conditions giving rust - coloured mottles, especially around root channels. Global positioning system Geological Survey of India Rapid movement of coarse, commonly bouldery, unlayered materials down steep streams. Hectare Hydrochloric acid International Soils Reference & Information Centre, Wageningen, Netherlands Page 6 of 73 Technical Report on Semi-detailed Soil Survey of Radhi Watershed Kamsing, Kamshing Krotovina L LUPP LUSS MC% me me% MLT MoA mS/cm MTI Nd NH4OAc NSSC OC OM Orogeny P PA pH PD PM PPD ppm PSC Puddle Regolith REID RGOB RNR RNR-RC S Saprolite Si Sk SMU SoB SoI Sokshing Solum sp, spp SPAL ST Surface wash Tr Last updated: 3/19/2013 Rainfed agriculture Old faunal burrow filled with dark soil from topsoil Loam Land Use Planning Project, in PPD Land Use and Statistics Section, in PPD Moisture content % (w/w) milliequivalent (unit of exchangeable cations) milliequivalents per 100 g fine earth Miscellaneous Land Type Ministry of Agriculture milliSiemens per centimetre (unit of electrical conductivity) Ministry of Trade and Industry No data Ammonium acetate National Soil Services Centre, REID, Semtokha Organic carbon Organic matter Mountain building by uplift and deformation of the earth’s crust Phosphate Project Agreement Measure of acidity – alkalinity Programme Director Parent material Planning and Policy Division, MoA Parts per million Particle size class (Soil Taxonomy) Intensive cultivation of wet soils before planting wetland rice. Intended to create fine slurry seedbed and to reduce subsoil permeability and water losses Loose material at surface of the Earth. Includes soils and underlying loose materials such as colluvium, alluvium, and landslip, wind and ice deposits Research, Extension and Irrigation Division, of MoA Royal Government of Bhutan Renewable natural resources (includes agriculture, animal husbandry and forestry in RGOB sense) RNR Research Centre Sand Soft weathered rock beneath solum, often reddish Silt Skeletal (hi
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