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SOIL EROSION AND CONSERVATION AS AFFECTED BY LAND USE AND LAND TENURE, EL PITAL WATERSHED, NICARAGUA Matilde de los Angeles Somaniba-Chang,' Thomas Lee Thurow,' and Amy Purvis Thurow ' 'National Agriculture University Managua, Nicaragua 'Department of Rangeland Ecology and Management Texas A&M University College Station, Texas 11843-2126 USA This work was, in part, made possible through support provided by the Global Bureau, US Agency for International Development, under the terms of Grant No. LAG-G-OO-91-OOO2-OO The opinions expressed herein are those of the authors and do not necessarily reflect the views of the U.S. Agency for International Development Soil and water conservation research in Nicaragua has benefitted from the expertise and friendship extended by numerous colleagues with shared interests. Recognition is given to colleagues at the National Agriculture University (UNA) for their assistance during the field work and in procurement of published data. We also thank directors and technical personnel of the El Pita! Agroforestry Project, the Nicaraguan Agricultural Technology Institute (lNTA) of the Masatepe headquarters, the National Union of Farmers and Cattle Ranchers (UNAG) in Masaya and Granada, the Union of Nicaraguan Coffee Producers (UNlCAFE) of the Masatepe headquarters and the European Economic Community CEE-ALA project in Region IV. We also express our sincere thanks to the 135 fiumen who kindly participated in the interviews that were part of this study. For more copies of this technical bulletin or further information about the CRSP research program, please contact Dr. Tony Juo, Texas A&M University, Department of Soil and Crop Sciences, College Station, TX 11843-2474. As of August, 1999, Tom is Head of the Department of Renewable Resources. University of Wyoming. Amy and Tom Thurow can be reached at 1071 Dum Drive, Laramie, WY 82012 or <[email protected]>. UNITED STATES AGENCY FOR INTERNATIONAL DEVELOPMENT SOIL MANAGEMENT COLLABORATIVE RESEARCH SUPPORT PROGRAM TEXAS A&M UNIVERSITY TECHNICAL BULLETIN Number 99-3 December, 1999 SOIL EROSION AND CONSERVATION AS AFFECTED BY LAND USE AND LAND TENURE, EL PIT AL WATERSHED, NICARAGUA INTRODUCTION produetion (e.g., beans, maize) than previously. Second, the portion of a f.um devoted to annual Throughout the tropics, water induced soil crop produetion is in~' rdated to f.um size. erosion threatens sustainable agricultural produc­ Farm fragmentation associated with tion on steeplands. Nicaragua is the largest agrarian reform and inheritance customs bas country in Central America, with the region' s contributed to the increase in small farms, hcuce highest annual population growth rate, 3.40/0, and there bas been an associated increase in its lowest average per-capita annual income level, cultivation of annual crops, leading to an increase US $420 (The Economist Intelligence Unit 1999). in erosion hazard. Soil consemltion progr.uns Agriculture is the largest sector in the targeted at agrarian reform COJIlDIImities ha\'C Nicaraguan economy. An estimated 7.7 million been successful in proliloong the use of hectares in Nicaragua have been degraded by conservation practices, thus reducing erosion water erosion (IRENA-ECOT-PAF 1994). hazard. Use of geographic information S}'S1anS Farrners with small land holdings make a (GIS), which enable simultaneous anal}'Sis of substantial contribution to the agrieuIturaJ biophysical and land tenure paaems, can aid in economy; many of these small fanns are located targeting where soil consc:n"ation efforts ",ill on steeplands with slopes from 10% to 40%. 1be likely }ield the greatest reIum on in............ ". EI pita] watershed is typical of the many steepland regions in Nicaragua where deleterious effects of Watersbed-scale analysis erosion are increasingly evident. AnaJysis of soil erosion pre- 5 over Overview time at a watershed scale takes into accounI the interrelated biophysical, socioe<:onomi<:, and This study applied Geographic institutional factors which influence natura1 Information Systems (GIS) tools to a combination resource management decisions and OIrtcomes of n:mote-sensed mapping data (1968 and 1981) (Thurow and Juo 1995). Traditional anaJysis of and interview data (1996) to estimate how public and printe in\1:Slmeiits in soil estimated annual soil losses from erosion have conservation ernphasi2es how erosion ad\useI}' changed in the EI pita! watershed over a 28-}"ear affects farmers, through declining crop ~"icIds and period. Changes in land tenure, and associated losses in soil produetivity over time. changes in land use, were the main factors driving A watershed approach also takes into increases in estimated erosion hazard from 1968 account the off-site effects of soil erosion. to 1996. Some observations concerning patterns including drainage disruption, gull)ing of roads, of adoption of soil conservation practices in the EI eutrophication of \Wfer\\."3~'S, siltation ofdams and pita] watershed were profiled, based on interview'S channels, loss of reservoir stcnge capacity, with \35 farmers in 1996. increased flooding risk. loss of wildlife habitat, Evidence from this study supports two damage to public health. and increased water over-arching conclusions. First, erosion hazard treatmer1t costs (PimertteI ct al. 1995). Vl<ithin the El pita] watershed is increasing at an Since the watershed approach iob.ifics increasing rate. 1be primary reason erosion off-site and downstream parties who bcDcfit from hazard is increasing is that much more of the reduetion or prevention of soil erosion on watershed is being cultivated for annual crop steeplands, it changes public debate CODCerlIing how much investment in soil conservation CHARACTERISTICS practices is appropriate and who should pay for OF THE EL PITAL WATERSHED soil conservation. In the aftermath of Hurricane Mitch (October, 1998), these public policy issues The EI Pital watershed is located in the are particularly germane because strategic Pacific region of Nicaragua between II '42'48" investments in soil conservation might have and II '54'47"N; 85'55'12" and 86'09'12"W in prevented a share of the losses which occurred the southern part of the Department of Masaya, both on agricultural lands and downstream. 100 kilometers southeast of Managua (Figure I). In Nicaragua more than 3,000 people The EI Pital watershed borders the northwestern were killed by the hurricane, and the agricultural shore of Lake Nicaragua. The 165 km' watershed sector lost an estimated US $239 million. is comprised of two sub-basins, Mombacho and Smallholders, in particular farmers on steep lands, Diriomo. suffered the most serious losses in proportion to their assets (The Economist Intelligence Unit 1999). The research results reported here have a Honduras role to play in guiding the selection among future soil conservation investment options, in order to mitigate against risks associated with extreme climatic events. Nicaragua Land-use planning using GIS tools ~KE MANAGUA MANAGUA-rJ,-/ STUCY_.~\ To take action at a watershed scale AREA requires land use planning, the systematic PACIFIC OCEAN assessment of land and water potential, alternatives for land use, and socioeconomic Costa Rica conditions, in order to identify land use options. The aim of land use planning is to select land use patterns to best meet the needs of people today Figure 1. Location ofthe EI Pital watershed while also safeguarding natural resources for the future. The discharge area for the Mombacho In considering complex land-use options, sub-basin is 77 km'. Its drainage pattern is sub­ Geographic Information System (GIS) tools are dendritric with four ephemeral streams; the water powerful in (I) generating efficient and effective in these streams usually infiltrates into the views of databases that describe land records, (2) pyroclastic depositions of Mombacho volcano. integrating the land data in ways that foster The Mombacho sub-basin experiences runoff only understanding of relationships, and (3) handling during extreme flood events. The Diriomo sub­ transactional updating of land data to maintain basin is 88 km' and its drainage involves seven current information (Dangermond 1989). ephemeral streams (MARENA 1993). Furthermore, maps generated using GIS tools Seventeen percent of the watershed has slopes allow for comparison and analysis of spatial and greater than 10%, and five percent has slopes temporal patterns (Selman 1991; Brown et a1. greater than 20%. 1994). The ability to consider several data sets The 1994 population of the EI Pital simultaneously, and to display numerous complex watershed was 58,505; its population density was relationships on a single map, makes GIS analysis 148 people per km'. Approximately 62% of El a powerful aid for policy discussions. Pital residents live in small communities, the remaining 38% live on their farms in rural areas. 2 The four IDIIDicipalities in the Masaya Depanmeut were beneficiaries of agrarian moon (BAR) v.iIo are Catarina, Niquinohomo, San Juan de Oriente, lived on 60 farm coopea ativcs. In 1996 farm and San Jose de Masatepe. The four cooperatives controlled 6,457 hectares. municipalities in the Granada Department are approximately 33% of the land in agriculture in Oiriomo, Diria, Granada, and Nandaime. the El Pita! "Watershed. Large Q ilUlacial farms in Latin America Climate which support only a few pcopIe dewte a n:latively small proportion of tbcir land farmed to As cbaracterized by the Koeppen Climatic subsistence annuaJ crops, such as com aDd beans. Classification, the watershed has a humid and dry Annual crops do not prolCd the soil from c:rosicn tropical climate (MARENA 1993). Annual as well as pemmial crops. pasture aDd forest. precipitation averages approximately I ,500 mm.