Case Study Experiment - Mitigating soil erosion in agricultural land
The Spanish Case Study is testing the mulching impact of straw on soil and water losses.
|Straw mulching experiment to prevent soil erosion|
Alicia Morugán-Coronado, Fuensanta García-Orenes, Artemi Cerdà (2015) Changes in soil microbial activity and physiochemical properties in agricultural soils in Eastern Spain. Spanish Journal of Soil Science Vol 5, No. 3 DOI: 10.3232/SJSS.2015.V5.N3.02
Prosdocimi M, Burguet M, Di Prima S, Sofia G, Terol Esparza E, Rodrigo Comino J, Cerdà A, Tarolli P (2017) Rainfall simulation and Structure-from-Motion photogrammetry for the analysis of soil water erosion in Mediterranean vineyards. Published in: Science of the Total Environment, 2017, 574, 204-215 http://www.sciencedirect.com/science/article/pii/S0048969716319532
Prosdocimi, M., Tarolli, P., Cerdà, A (2016) Mulching practices for reducing soil water erosion: A review. Published in: Earth-Science Reviews, 2016, 161: 191–203 http://www.sciencedirect.com/science/article/pii/S0012825216302264
Cerdà, A., González-Pelayo, O., Giménez-Morera, A., Jordán, A., Pereira, P., Novara, A., Brevik, E.C., Prosdocimi, M., Mahmoodabadi, M., Keesstra, S., García Orenes, F., Ritsema, C. (2016) The use of barley straw residues to avoid high erosion and runoff rates on persimmon plantations in Eastern Spain under low frequency – high magnitude simulated rainfall events. Published in: Soil Res, 2016, 54, 2, 154-165 http://www.publish.csiro.au/sr/sr15092
Keesstra, S., P. Pereira, A. Novara, E. C. Brevik, C. Azorin-Molina, L. Parras-Alcántara, A. Jordán, and A. Cerdà (2016) Effects of Soil Management Techniques on Soil Water Erosion in Apricot Orchards. Published in: Science of the Total Environment, 2016. 551-552: 357- 336 http://www.sciencedirect.com/science/article/pii/S0048969716301784
Rodrigo Comino, J., T. Iserloh, T. Lassu, A. Cerdà, S. D. Keesstra, M. Prosdocimi, C. Brings, et al. (2016) Quantitative Comparison of Initial Soil Erosion Processes and Runoff Generation in Spanish and German Vineyards. Published in: Science of the Total Environment, 2016, 565: 1165-1174 http://www.sciencedirect.com/science/article/pii/S0048969716310932
Rodrigo Comino J, Iserloh T, Morvan X, Malam Issa O, Naisse C, Keesstra SD, Cerdà A, Prosdocimi M, Arnáez J, Lasanta T, Ramos MC, Marqués MJ, Ruiz Colmenero M, Bienes R, Ruiz Sinoga JD, Seeger M, Ries JB (2016) Soil Erosion Processes in European Vineyards: A Qualitative Comparison of Rainfall Simulation Measurements in Germany, Spain and France. Published in: Hydrology, 2016, 3 (1), 6; http://www.mdpi.com/2306-5338/3/1/6/htm
The Cànyoles river watershed is located in Eastern Spain. It is representative of the many changes suffered by Northern Mediterranean countries during the last fifty years: land abandonment in the mountainous terrain; population increase and urbanization in the lowland areas of the catchment; soil sealing due to urbanization; increase of chemical use in agriculture; and aquifer overexploitation. The parent material of the Cànyoles river watershed is mainly limestone, with intense agriculture in the bottom of the valleys and almost abandoned slopes, and has a mean annual rainfall > 500 mm.y-1.
The study area has a rugged terrain , which favors intense soil erosion. Mild temperatures characterize the climate in winter and hot summers (16 ºC mean annual temperature) are also characterized by recurrent droughts. The autumn thunderstorms are characterized by intense thunderstorms (< 100 mm.day-1). In the past farmers used terraces to reduce soil losses but more recently with the development of large citrus farms these terraces have been removed and soil erosion has increased due to inappropriate land management practices.
Main soil threat
The Cànyoles river watershed is a typical Mediterranean landscape with rainfed agriculture that has been replaced by traditional irrigation systems (flooding) in the bottom of the valleys and by drip-irrigation systems on the sloping terrain. The traditional irrigation systems are millennia old, but the drip irrigation has only been established recently. The new drip-irrigation systems are triggering high erosion rates and soil degradation due to the lack of vegetation cover, the compaction of the soil and the lack of organic matter in soils due to intensive ploughing, herbicides and intense fertilization
The increases in soil erosion rates due to new citrus orchards on slopes, are being controlled by means of catch crops, but most of the farmers are not aware of the problem. Thus, this represents a social, economical and physical environmental problem. The use of vegetation cover is a positive cost-efficient treatment as farmers can be subsidized, especially those that are registered as organic farmers. There is a need to inform farmers, and to show them that a different land management option is available. This project must improve the exchange of knowledge between farmers and scientists.
One of constraints is the lack of appropriate agricultural machinery to move from ploughing to no-till practices. But the main constraint is to convince farmers that they can be environmental agents. The challenge is to find the funding/subsidies to encourage the farmer to move to more sustainable land management. Farmers, due to a tradition of clean soils (no plants, no stones... bare soil), like to keep the farm weed-free, and are reluctant to take up measures such as no-till. The project aims to improve the information exchange with farmers so that they can utilize effective new strategies to manage their farm (i.e. organic farming). This will require demonstrations and knowledge exchange with the farmers.
Other soil threats
The Cànyoles River watershed is also threatened by soil sealing of otherwise fertile lands due to urban expansion, increase of the number of secondary residences as well as transportation infrastructure. Soil biodiversity is inhibited due to the use of pesticides, herbicides and chemical fertilizers in chemically managed farms. The same agents are also a source of soil, air and water pollution. Soil organic matter is reduced due to tillage, lack of vegetation cover and lack of use of manure and compost that used to be the traditional fertilizers before the arrival of chemical farming. Soil compaction due to heavy farm machinery is becoming more important since farm expansion and mechanization.
Location and Digital Elevation Model (DEM) of the Cànyoles river watershed
Geology & Soils
The Case Study is in the border (fault) of the Iberian System and the Betic System which renders the region very tectonically active as signified by events such as the Earthquake of 1748 that caused damages to Xàtiva and destroyed the Montesa Castle. The large numbers of faults, associated with the main fault of the Montesa corridor, indicate an intense tectonic activity in the region. The tectonic uplift is affecting the integrity and continuity of the lithostratigraphic units and the faults bring in contact different lithostatigraphic units with different hydrogeological characteristics. Dolomicrites and dolomitic marls dominate the Limestones of the Cretaceous. Formations from the Tertiary (Neogen) are characterized by marls, and basins has undergone multidirectional extensional tectonic events which are found in the North and South of the region, with the valley covered with marls in the bottom. Quaternary materials are found covering the Limestone and Marls, and they are Pediment and slope deposits. The fluvial terraces are present but they are small remains due to the intense erosion as a consequence of the Uplift of the area and the incision of the rivers. There is also Gypsum and Keuper Clays from the Triasic that are found where the faults allow deeper material to reach the surface as diapirs. The main geological coverage of the basin includes Dolomites and Limestones (70%), and the Quaternary materials (1%) and Marls and Keuper Clays (29%), and the main soil types are Calcic cambisols and Eutric Fluvisols.
Parent materials (left) and Land Use (right) at the Cànyoles river watershed
A dense forest of Quercus ilex covered the Cànyoles river watershed before the arrival of agriculture and grazing 6 millennia ago. The Iberians (500 BC) already used the land for grazing and agriculture, as the archaeological sites of Castellar de Meca and the La Bastida de Moixent show. Traditional Aleppo pine plantations (Pinus halepensis) were abandoned in the 60’s due to intense immigration. The recovery of the understory and the lack of maintenance resulted in the spread of wildfires and as a consequence the recovery of the Maquia and the removal of the Pinus halepensis.
Nowadays, the main land uses (agriculture, rangelands and urban) have been similar between 1986 (EU agreement) and 2005: around 75% of the land is rangelands, forest or meadows, meanwhile 22% is agricultural land. During this period, urban areas increased from 1.4 to 4.4%, which shows a dramatic increase in soil sealing. At a finer classification there is a clear shift towards cultivation of citrus and fruits and a reduction in olive trees and vineyards. The reduction of olives (from 9 to 4.75%) took place mainly due to the increase of citrus (from 6 to 9%). The main change in forestland took place due to the impact of the land abandonment and wildfires. The reduction of the meadows took place due to the loss of the grazing in the Case Study. This acute change of land use, in combination with grazing abandonment is currently resulting in greening of the mountainous terrain, and as a consequence, in forest fires which trigger intense soil erosion rates.
|Land Uses [ha]||1986||2005||1986-2005||%|
The climate at the Cànyoles River watershed is characterized by typical summer droughts and is classified as dry sub-humid according to UNCED (Paris Convention on Desertification, 1994). The Eastern part of the Iberian Peninsula has a typical Mediterranean dry climate with the rainy season taking place in autumn and spring and summer being the dry period - below. The mean annual rainfall ranges from close to 500 mm y-1 in the Massís del Caroig to 700 mm y-1 in the Xàtiva, which shows the clear control of the distance from the sea over precipitation. There is a general trend of a slight increase in precipitation (1 mm for the last 50 years) but the variability is very high as shown below. The mean annual temperature is also controlled by altitude and the distance from the sea. The Xàtiva meteorological station (103 m a.s.l.) registers 18oC as the mean annual temperature and the Enguera sites (320 m a.s.l.) 14oC.
Temperature ranges from the 15.7 to 25.7oC during summer and from 8.7 to 12.6oC during winter. Mean annual temperature amplitudes from 6 to 14.7oC. The mean annual temperature is increasing which is mainly due to the increase in the mean minimum temperature (temperatures at night), and also the decreasing temperature variability amplitude. This has huge implications for the agricultural management and the change in the crops between the coast and inland.
Limestone is the main parent material and this is the key factor for the hydrology of the Case Study. The infiltration capacity of the soils developed on limestone and the high hydraulic conductivity of the thalwegs results in deep percolation and consecutively in limited surface runoff (Cerdà, 1996). The second key characteristic of the Case Study is the karst developed in the limestone area and the resulting karstic springs that contribute to the traditional flood irrigated agriculture. During the last 50 years, the development and expansion of new citrus plantations and subsequent growth of the irrigated land has resulted in the depletion of the aquifer and the reduction in spring discharge. As shown in Figure 7.4, the Riu dels Sants spring discharge is gradually lost due to the over-exploitation of the aquifer. This loss of flow has ecological, geomorphological, hydrological, as well as socioeconomic consequences, affecting a community of farmers that were using the water as the main resource for a millennium. This quickly sparked land abandonment, urban growth on traditional orchards and changes from flood irrigated to drip irrigated land in the traditional flood irrigated zone of the Cànyoles river watershed.
Drivers and pressures
In Eastern Spain, the increase of the irrigation systems to produce vegetables and fruits at competitive prices is resulting in the depletion of the aquifers. In our research area, the farmers use more than 90% of water resources, being the use by industry minimal. The increase in water demand is maintained year after year as new plantations require irrigation to be viable. New plantations are using water and chemicals intensively, also depleting soil organic matter. As a consequence of soil erosion and pollution, water pollution with nitrates and other chemicals, landscape changes are being accelerated. The main drivers of this change have been the Common Agriculture Policy oriented at investments in new chemically managed farms, as well as investments coming from the construction, industry and tourism sectors. The arrival of new capital to agriculture (powered by the subsidies) contributed to the degradation of traditional rain-fed and flood irrigation systems and the development of new farms: larger, mechanized, and subsidized. The technification of the agriculture resulted in an increase in the production although a net reduction in cultivated area has been registered. This trend is very clear for the vineyard in Cànyoles river basin, where although total area is reducing wine production is increasing - see below.
Although soil erosion is mainly a consequence of agricultural intensity and ultimately caused by forest fire, agriculture has additional environmental impacts. The new land managements and the removal of the old traditional terraces are accelerating soil erosion. The overexploitation of the aquifers for irrigation is triggering a reduction in the water resources resulting in flows inadequate to sustain the traditional spring-supplied irrigation by flooding. This is resulting in a social and economic problem. Moreover, the new drip irrigation systems are reducing the number of ditches and most of the water now flows in pipes; as a consequence the biological diversity has been dramatically reduced. Also, natural groundwater recharge is being reduced by the lack of flooding. The expansion of drip irrigation serves as an alternative to the traditional flood irrigated orchards. As a consequence the traditional ditches are being removed and the flow of water is disappearing which results in the reduction of the flora and fauna diversity. The use of herbicides is also contributing to this loss of biodiversity as it causes the removal of most of the vegetation. It also results in a selection of the plants that tolerate the herbicides. The urbanization of the rural areas as a consequence of the expansion of the drip irrigation (each property needs an equipment storage space) results in a landscape of patchily distributed small low quality structures.
Extent and production of wine in the Cànyoles river watershed during the period of
intensification of the agriculture from 1977 till 2010 due to the Common Agriculture Policy
Soil organic matter in the soils of the study sites. Samples were collected in Summer 2012 at ten representative soils by land-use. Columns represents the average of 20 samples (left); Runoff coefficient (%) (4 plots per column) in the Cànyoles river watershed under rainfall simulation experiments of 1 hour at 66.1 mm h-1 in each plot (right).
The monoculture of the citrus is developing into another problem as year after year they are covering more surfaces. The areas that due to the climate cannot be colonized by the citrus are being abandoned or transformed into vineyards. As the Case Study site of the Cànyoles river watershed is an old path between the coastal land and the central Iberian Peninsula the increase in roads and railway in the last two decades is increasing soil erosion in the construction sites. The expansion of the citrus plantations (irrigated) on traditional rain-fed agriculture areas is depleting the aquifer, and this results in a shortage of water in the old traditional flood irrigated orchards, transforming the irrigation system in a drip irrigated by aquifer pumped water, intensifying the risk of aquifer depletion.
There is also a general decrease in the organic matter of the soils under cultivation due to a lack of manure or compost application - above. Chemical fertilizers are the most important in use and abuse due to the subsidies and the good reputation they have among farmers. Catch crops, mulching and weeds are not used. As a consequence the depletion of the organic matter in the soil is a problem and it is necessary to find new strategies to maintain the soil fertility within the natural cycles.
Status of soil threat
Previous studies show that the problems of soil degradation in the Cànyoles Case Study area is mainly focused on the soil erosion, runoff generation and soil organic matter depletion, which contribute to desertification (Bodí et al., 2013; Cerdà 2007, 2009a, 2009b). Figure below shows characteristic signs of degradation in the Case Study.
View of the Case Study. Upper left: Castellar de Meca archaeological site, where intense use of the land by the Iberians has occurred, as the marks of the wheels show. Upper right: intense soil erosion on new chemically managed citrus plantation. Lower left: soil erosion in vineyards. Lower right: the consequences of the forest fire: a new maquia development and the reduction of the forests
Maps on the current state of land use, soil degradation and soil conservation in the case study area have been produced using the WOCAT (World Overview of Conservation Approaches and Technologies) methodology
The steps of this process are as follows:
1) The area to be mapped is divided into distinctive land use systems (LUS).
2) The team gathers the necessary data on soil degradation and conservation for each LUS using a standardised questionnaire, in close consultation with local land users, and supported where possible by remote sensing or field data.
3) For each LUS, the soil degradation type, extent, degree, impact on ecosystem services, direct and indirect causes of degradation, as well as all soil conservation practices, are determined.
4) Once collected, the data is entered in the on-line WOCAT-QM Mapping Database from which various maps can be generated.
Following the principles of all WOCAT questionnaires, the collected data are largely qualitative, based on expert opinion and consultation of land users. This allows a rapid and broad spatial assessment of soil degradation and conservation/SLM, including information on the causes and impacts of degradation and soil conservation on ecosystem services.
More details about the methodology used to produce these maps and their interpretation can be found here.
Land Use (click on maps to expand)
The degree of degradation reflects the intensity of the degradation process, whilst the rate of degradation indicates the trend of degradation over a recent period of time (approximately 10 years).
The "effectiveness" of conservation is defined in terms of how much it reduces the degree of degradation, or how well it is preventing degradation. The Effectiveness trend indicates whether over time a technology has increased in effectiveness.
Effects of soil threat on soil functions
Table below summarises the effects of abuse and misuse of agriculture soils leading to dramatic reduction of soil functions of the Cànyoles Case Study.
|Functions of soil||Explanation||Effect|
|Biomass production||Losses in the agriculture production due to the depletion of the organic matter, weakening of the soil structure and soil erosion.||H|
|Environmental interactions||Use of concrete walls, asphalt and concrete to protect the agriculture infrastructure, and they results in soil sealing||H|
|Gene reservoir/ Biodiversity pool||Local species are losing their habitat primarily due to the removal of the flood irrigation, the monoculture of citrus, olive and vineyards, and the urbanization of the land.||H|
|Physical medium||Urbanization of the land due to drip irrigation systems based on small houses to install all the equipment||H|
|Source of raw materials||There is a decrease of biomass as the herbicides reduce the weeds in the agriculture fields.||H|
|Carbon pool||Data on C stocks is little due to the fact that the soils are losing organic matter.||H|
|Cultural heritage||The traditional sustainable farming is being removed and new productivity and market oriented strategies are in place.||H|
Administrative and socio-economic setting
Rural migration took place in the western part of the Cànyoles River watershed (La Font de la Figuera) since the 1950’s. Meanwhile the municipalities in the Eastern part of the watershed increased the population as new industries were developed (textile, leather, paper, etc.). Then, the Cànyoles river watershed displayed the contrasted evolution of the population in Spain, which passed from a rural population to an urban population in two decades. The socioeconomic changes that took place during the last century (i.e. industrialization and industrial area expansion and the subsequent financial crisis in textiles, paper and leather) resulted in the construction and the subsequent abandonment of industrial developments on the best agriculture soils. This has led to a direct loss of resources and ultimately land degradation. The intensification of the agriculture in the drip-irrigation areas in the bottom of the Cànyoles basin has resulted in the abandonment of the traditional rain-fed land.
There is a growing concern due to the farmer’s loss of knowledge on traditional agriculture. The industrialization of agriculture is resulting in the lack of knowledge on the natural cycles, and the loss of the diversity in the plants and animals. Furthermore, there is lack of knowledge on the relevance between unsustainable agriculture management practices and water pollution, sediment transport and landscape changes. More importantly, there is little information on strategies against land degradation and little action towards the development of soil care strategies towards sustainable agriculture. This renders the Cànyoles river watershed less shelf-sufficient of agricultural products, although it is an agriculture region.
Within the scope of the RECARE Project, interviews with mayors of the municipalities and the main political leaders of the Cànyoles watershed reveal the key issues related to policy and governance in the area. We found that the professional policy makers take into account the low population political activity. Besides the high participation of citizens in exercising their right to vote every four years, their contribution to the daily policy development program is rare. Therefore, awareness of the citizens about their contribution to improve the land management is absent. Farmers also think that solutions towards a better care of soils should come from policy makers rather than farmers themselves, and that their main tasks are limited to food production.
Population of the Cànyoles River watershed (left) and GDP per capita trends for Spain and the Euro Area (right, Source: EUROSTAT)
Sustainable land management practices include the use of catch crops, mulches, and vegetation barriers (Giménez Morera et al., 2010).
Relevant end-users and local stakeholder groups include;
- Farmers union
The research project will be presented in each community in order to show the aims of the researchers and citizens will be encouraged to be involved in the development of new strategies and management approaches to help reduce land degradation.
This web page is authored by:
A. Cerdà and O. González-Pelayo from University of Valencia
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