Strategies of conservation planning

Strategies of planning soil conservation measures for certain areas follow three major steps (after Morgan, 2005): erosion risk assessment, land use plan design, and impact assessment.

The complex topography and the heterogeneous soil and land use conditions of the Soyang Lake watershed require special consideration for developing effective conservation plans.

1. Erosion risk assessment

A variety of methods can be used for assessing the erosion risk for a given region using erosivity maps, land classification methods, and erosion surveys with satellite images or detailed field observations (Morgan, 2005).

The agricultural areas within the Soyang Lake watershed are intensively used. Erosion features, such as rills and gullies are removed by tillage, and the cropland top soils are annually replenished with soils from nearby mountain slopes (Park et al., 2010). Instead of surveys, which identify critical areas after erosion occurred, risk assessment can be also performed by using models to predict potential erosion damages, for example with the USLE (Wischmeier and Smith, 1978). Physically based models, such as EROSION 3D (Von Werner, 1995) simulate also the transport pathways and the deposition of the eroded soil (Fig. 2).

Erosion risk assessment by using simulation models requires additional data bases, specifically elevation models, soil maps, land use maps, and recorded rainfall data. If sufficient data is not available, additional surveys and monitoring programs are necessary. Within the Mandae stream watershed, comprehensive soil and land use surveys, and a weather station monitoring program was conducted and used to create and complete existing data bases.

Land use plan example

Site specific control measures should be designed for individual farms and single fields. Soils in the Mandae stream watershed can vary strongly within field sites and the land topography is very complex. Drainage patterns cannot be sufficiently represented by the available soil maps and elevation models, which were used for prior risk assessment. For designing the land use plan, additional field surveys and data collection is necessary for a detailed site characterization, which includes all important erosion controlling factors.

A site specific land use plan can than be developed by using a combination of measures on the basis of the existing farming systems (Fig. 5). If in-field measures are not adequate to sufficiently reduce runoff and sediment transport, additional off-site measures, such as filter strips should be implemented (Wolfe et al., 2002).

3. Impact assessment

Before implementing a new land use plan, the impacts of the proposed conservation measures must be evaluated. Environmental impact assessment can be done by using simulation models (Morgan, 2005). Physically based models can be used to quantify erosion and sediment transport for scenarios of different potential land use plans. Crop production models, such as EPIC (Williams et al., 1984) calculate the long-term farmland productivity for the given site. Model input data for impact assessment requires a higher level of detail than for risk assessment. Data can be obtained from prior field surveys during the land use plan design.

Impact analysis also includes economic assessments at the farmers level, because farmers will only apply the proposed practices, if substantial benefits arise and the investment costs are covered (Morgan, 2005). Therefore, cost-benefit analysis should be made for the different possible management measures and compared to the associated environmental impacts. Conservation plans, which are both, economically efficient and effective in protecting soil and water quality, should be selected for implementation.

ReferencesKim, B., Park, J. H., Hwang, G., Jun, M. S., and K. Choi. 2001. Eutrophication of reservoirs in South Korea. Limnology (2), 223-229

Morgan R. P. C. 2005. Soil erosion and conservation. Third edition. Oxford, UK: Blackwell Publishing

National Resources Conservation Service (NRCS). National conservation practice standards. Available at: http://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/technical/references/?&cid=nrcsdev11_001020. Accessed 14 April 2012

Park, J. H., L. Duan, B. Kim, M. J. Mitchell, and H. Shibata. 2010. Potential effects of climate change and variability on watershed biogeochemical processes and water quality in Northeast Asia. Environ. Intl. (36), 212-225

Toy T. J., Foster G. R., and K. G. Renard. 2002. Soil erosion: processes, prediction, measurement, and control. New York, USA: John Wiley & Sons

Substantial impact on the quantity of erosion and the amount of transported soil and the associated nutrients has the local land management in those regions. The application of best management practices, which reduce erosion to acceptable levels and minimize water pollution is the major goal of conservation planning.

There are various conservation techniques, which can be grouped into agronomic measures, soil management, and mechanical methods (Morgan, 2005), aiming on soil loss reduction within field sites and minimizing the off-site effects of sediment transport. Different standards describing the design and application of those measures are available for example from the NRCS.

The effectiveness of different management practices strongly depends on site specific conditions such as soil, slope, and topography (Wolfe et al., 2002). Furthermore, conservation practices are associated with additional costs, labor, and use restrictions. Therefore, effective conservation planning requires not only individual treatments depending on the local conditions, but must be also socially and economically acceptable to the farmers (Morgan, 2005).

Conclusions

The implementation of a developed land use plan requires the integration of local stakeholders in the decision-making process, instead of simple top-down regulations. A close cooperation between technical experts and farmers is also necessary after successful implementation for maintaining the developed conservation measures.

Soil conservation is a dynamic process and must be capable to adjust to future changes, such as economic pressure to grow certain crops, new technologies or climatic conditions (Morgan, 2005). Conservation plans have to be regularly updated to face new conditions and to optimize the benefits for the farmers. Only long-term-efficient conservation strategies can help to develop a sustainable and environmentally sound agriculture.

2. Land use plan design

After identifying the areas of high erosion risk, a sound land use plan should be designed, based on what the land is best suited for under the present social and economic conditions (Morgan, 2005), which means that the proposed land management is consistent with the requirements of the local communities. Existing farming systems should be analyzed and integrated in conservation plans, which would reduce costs and increase the acceptability of farmers, instead of implementing entirely new techniques from outside (Morgan, 2005).

A. Soil management

Ridging with plastic cover (plastic mulch) is the predominant farmland soil management in the Soyang Lake watershed. Plastic mulch needs special consideration for conservation planning. Control measures that have been effective for conventional crop systems may not apply for plastic mulch (Wolfe et al., 2002). Depending on the farmland topography and the row orientation, plastic covered ridging can even substantially increase soil erosion rates (Fig. 3). High row lengths will increase soil loss compared to conventional crop systems (Wolfe et al., 2002). The orientation of rows in combination with the field topography can play an essential role in erosion control.

B. Crop management

Farmland areas of the Soyang Lake watershed are predominantly cultivated by cash crops. Major crops are cabbage, radish, potato, and bean. High- and long-covering crops (potato and bean) protect the soils from monsoonal rainstorm events. They also provide a large amount of residue after harvest, which stabilizes the soil and reduces the erodibility. Organic crop management additionally protects the inter-row areas from raindrop impact and surface runoff.

C. Land management

Korean mountainous farmland is characterized by a mosaic of small field sites with different crops surrounded by field margins, tracks, channels, forest patches, and riparian areas. Those areas play an important role for protecting streams against eroded sediment from the adjacent field sites (Fig. 4).

Introduction: soil erosion and conservation

Soil erosion by water can generate serious damages in mountainous ecosystems by the irreversible loss of soil productivity and the degradation of surface water quality. Erosion reduces soil depth and can enrich the soil in course particles, which often reduces moisture and nutrient holding capacities (Toy et al., 2002). Eroded sediments from agricultural fields contain adsorbed chemicals that can be major pollutants for downstream water bodies (Toy et al., 2002).

Transported phosphorus associated with eroded agricultural soils is a major cause of eutrophication of reservoirs in South Korea (Kim et al., 2001). Intense monsoonal rainfall during the summer months causes high erosion rates on mountainous farmland. The Soyang Lake, which is the largest reservoir in South Korea, receives high amounts of nutrients from those agricultural fields (Park et al., 2010). Although the watershed is predominantly covered with forests, there are two agricultural hot spot areas with substantial impact on the trophic state of the lake (Park et al., 2010) (Fig. 1).

Strategies to develop and evaluate soil conservatio n measures Strategies to develop and evaluate soil conservatio n measures for complex mountainous farmland in South Koreafor complex mountainous farmland in South KoreaS. Arnhold, E. Stöckler, B. Huwe (Department of Soi l Physics, University of Bayreuth)

EGU General Assembly 2012 EGU General Assembly 2012 -- Vienna (22 Vienna (22 -- 27 April 2012)27 April 2012)

Contact:

Sebastian Arnhold, PhD Student

Dept. of Soil Physics, University of BayreuthUniversitätsstr. 30, 95447 Bayreuth, Germany

Phone: +49 (0) 172 - 84 70 949E-mail: sebastian.arnhold@uni-bayreuth.de

Bayreuth Center of Ecology and Environmental Research

TERRTERRECOECO

Fig. 1. Land use map of the Soyang Lake watershed and location of the two hot spot areas of agricultural pollution (the watersheds of Mandae and Jawoon stream)

Mandae stream watershed

Jawoon stream watershed

University of Bayreuth

Fig. 2. Prediction of erosion, deposition, and sediment transport in the Mandae stream watershed with EROSION 3D

Fig. 3. Soil erosion for plastic mulch, uncovered ridges, and a smooth soil surface as affected by the field topography (on the concave field, ridging produces flow accumulation and ridge breakovers resulting in severe erosion damages)

Fig. 4. Role of land management and landscape structure for sediment retention in the Mandae stream watershed (riparian forests, fallow farmland, and perennial cover crops functioning as buffer areas for eroded soil)

Fig. 5. Possible land use plan for a steep crop field within the Mandae stream watershed (left: current management, right: possible conservation management)

Row direction must prevent flow accumulation with runoff

from the southern field

Riparian forest Fallow land Codonopsis fields

Von Werner, M. 1995. GIS-orientierte Methoden der digitalen Reliefanalyse zur Modellierung von Bodenerosion in kleinen Einzugsgebieten. PhD Thesis. Berlin, Germany: Free University of Berlin, Department of Earth Sciences

Williams J. R., Jones, C. A., and P. T. Dyke. 1984. A modeling approach to determining the relationship between erosion and soil productivity. Trans. ASAE (27), 129-144

Wischmeier, W. H., and D. D. Smith. 1978. Predicting rainfall erosion losses. A guide to conservation planning. Agriculture Handbook 537. Washington, D.C., USA: USDA

Wolfe, M. L., B. B. Ross, J. F. Diem, T. A. Dillaha, and K. A. Flahive. 2002. Protecting water quality: best management practices for row crops grown on plastic mulch in Virginia. Blacksburg, USA: Virginia Cooperative Extension

Ginseng fieldsChannel drains into the streamTrack

Potato fields

Road

Reduced herbicide application to increase inter-row soil cover

If contour farming is not suitable due to complex terrain, rows should drain

runoff to the northern field edge

Maintain rows after harvest