Dehesa System Research Articles

Free-range acorn feeding results in negative carbon footprint of Iberian pig production in the dehesa agro-forestry system

Iberian pig production has its own quality regulation, which defines different handling and feeding systems for this breed. These differences influence production costs, market price and environmental impact. The most extensive system of fattening Iberian pigs is based on foraging acorns in a silvopastoral system named dehesa, and consumers usually associate the Iberian pork with this system, although nowadays more intensive systems are dominant due to their productivity and management simplicity. The aim of this study is to assess the Carbon Footprint (CF) of the different Iberian pig production systems using the Life Cycle Assessment (LCA) methodology.This study is based on data collected from 19 Iberian pig farms producing nursery growers (≤25 kg, 2 farms), pre-finished pigs (100–110 kg, 3 farms) and 3 types of finished pigs (150–175 kg), including free-range fattened pigs (17 farms), outdoor intensively fattened pigs (2 farms) and indoor intensively fattened pigs (2 farms). The CF was calculated with a “cradle to farm gate” approach using the kg of live weight (kgLW) as functional unit, and including C sequestration in soils and biomass, which was calculated by field monitoring in a selection of measuring points. The average CFs of the final products were 9.2 ± 2.5 kg CO2eq kgLW−1 for nursery growers, 5.6 ± 2.42 kg CO2eq kgLW−1 for pre-finished pigs, −5.6 ± 6.5 kg CO2eq kgLW−1 for free-range fattened pigs, 3.1 ± 1.5 kg CO2eq kgLW−1 for outdoor intensively fattened pigs and 7.7 ± 0.3 kg CO2eq kgLW−1 for intensively fattened pigs. The main C sinks of the dehesa system (trees and soil) sequestered an average of 3.18 t CO2eq ha−1 year−1. This C sequestration, averaging −10.2 ± 6.7 kg CO2eq kgLW−1 in free-range pig production, offsets 223% of the GHG emissions in those systems, which resulted in a negative CF (net CO2 sequestration). There was a direct relationship between CF and pig stocking rate, leading to strongly negative CF values on those farms with the lowest pig stocking rates.

Subsoiling for planting trees in dehesa system: long-term effects on soil organic carbon

Incorporating trees into agricultural systems, including grasslands, increases the soil organic carbon sequestration and contributes to climate change mitigation. Site preparation for tree establishment is a common practice that can involve a variety of techniques and agricultural implements such as subsoiling. This study aimed to evaluate the long-term effects of subsoiling on soil organic carbon (SOC) concentrations and stocks in a Mediterranean grassland afforested with holm oaks 22 years ago and now converted into a Dehesa agroforestry system. The study was conducted in a dehesa farm in Southwest Spain. Soil samples were taken at six depths under 10 tree canopies within and outside the original subsoiling line. Subsoiling significantly decreased SOC concentration. Mean SOC concentration in the first 20 cm was 30% lower at the subsoiling line. SOC stocks for the first 60 cm were 2660 g m−2 within the subsoiling line and 4320 g m−2 outside the line. There was a clear reduction in SOC concentration and stock with increasing depth. Root abundance and deeper rooting increased with subsoiling but did not translate into sufficient carbon accumulation in the soil, which is moderate even after 22 years. This study reveals that, in the long term, there is a trade-off in CO2 sequestration between tree planting and soil subsoiling, highlighting the need for further research into the potential benefits and detriments of subsoiling.

A Farmer’s Perspective on the Relevance of Grassland-Related Innovations in Mediterranean Dehesa Systems

Grasslands are of key importance for the provision of ecosystem services (ES). Suitable management is essential to guarantee their persistence and functionality. There is a growing interest in innovations such as new technologies aimed at facilitating and improving the management of grasslands while increasing their provision of ES. The uptake of innovations by farmers is a complex process, and relevant socio-economic or technological factors that are crucial to farmers are often overlooked. This information can be useful for increasing the adoption of these innovations through the design of public policies to facilitate them. This paper analyses the relevance of the main innovations that can be applied to the management of the grasslands of Dehesa farms for the farmers and the factors that might affect this relevance. Through questionaries, we gathered information on the relevance that farmers give to the selected innovations and analysed it by cumulative link models. The results show that innovations aimed at increasing the biomass production of grasslands and resilience such as the use of seed mixtures and the use of forage drought-resistant species are considered highly relevant by Dehesa farmers. However, high-tech innovations such as GPS collars were poorly rated which could denote low applicability to the context of Dehesas or the existence of barriers hindering the adoption but also a need for further development and better information on their potential. Characteristics of the farmer and farm such as age, education level, and stocking rate seem to be related to the relevance given to some of the innovations. These results provide insightful information for the implementation and research of relevant grassland-related innovations in the context of Mediterranean Dehesa/Montado systems, as well as for the design of policies supporting them.

Carbon sequestration offsets a large share of GHG emissions in dehesa cattle production

The contribution of cattle production to climate change is increasingly recognized, and there is a need to identify those systems minimizing emissions and maximizing carbon (C) sinks. In the Southwest of the Iberian Peninsula, cattle are produced on dehesa agroforestry systems, where cows and calves graze together until weaning, and calf fattening is based on external feed. The aim of this study was to assess the Carbon footprint (CF) of beef of this extensive production system using Life Cycle Assessment (LCA) methodology.The study collects data from 15 extensive cattle farms, 6 organically (ORG) and 9 conventionally (CONV) managed; 4 farms had their own fattening facilities while most of the farms sold calves to 2 specialised fattening farms also studied. CF calculation includes field monitoring of C sequestration on soils and woody biomass in a selection of well-known points with previous estimations. The limit of the system was “cradle to gate”, and the functional unit was 1 kg LW of calf at slaughtering age. The main C sinks of the dehesa system sequestered an average of 3.3 t CO2eq ha−1 year−1. The average CF of the final product was 6.43 ± 21.46 kg CO2eq kgLW−1, with numerically lower but not statistically different average CF in ORG than in CONV systems. The inclusion of C sequestration, that averaged −13.52 kg CO2eq kgLW−1, offset 95% and 54% on ORG and CONV farms, respectively. In some cases, C sequestration compensated all GHG emissions and resulted in negative CF. There was a direct negative relationship between CF and stocking rate, leading to negative CF values in those farms with lowest stocking rates.

Crop Yields in European Agroforestry Systems: A Meta-Analysis

Agroforestry is the practice of integrating woody vegetation with crops and/or livestock production in order to strengthen ecological services on farmland and achieve a more multi-functional agricultural system. Crop yields determine economic outcomes when trees are young, but information on yields is scattered in the literature and a quantitative overview of crop yields in European agroforestry systems is lacking. We therefore synthesized published information on crop yields in European agroforestry systems, using meta-analysis. A systematic review of the literature was conducted, highlighting quantitative information on yields is available only for traditional Dehesa systems in Spain and Portugal and for modern alley cropping experiments, mostly in northern Europe. Relative cereal crop yields in alley cropping systems (systems with tree rows with interspersed crop strips) were 96% of sole crop yield at tree planting. Crop yields in alley cropping decreased on average with 2.6% per year over the first 21 years of the tree stand, indicating increasing competitive effects of the trees with their age. On the other hand, studies in traditional Dehesa and Montado systems in Southern Europe showed no negative influence of the trees on crop production, indicating that competition between crops and trees plays a less important role in those systems than in alley cropping. Overall, the systematic review showed a need for more experimental data to further substantiate the benefits of agroforestry and elucidate optimal agroforestry practices under European conditions.

The influence of tree and soil management on soil organic carbon stock and pools in dehesa systems

This study evaluated the effect on SOC concentration, stock and fractions in a dehesa divided into two areas of similar soil type but different soil management. The first area was a pastured dehesa (P) with young Holm oaks, planted in 1995 (70 trees ha−1, 12 m × 12 m) and, since 2000, grazed by sheep (3 sheep ha−1) with an average period of grazing of six months a year. Prior to this it was managed in the same way as the second adjacent area. The second area was a cropped dehesa (C) with widely spaced mature Holm oak (14 trees in a 12-ha dehesa), on which a mixture of vetch and oats was cultivated every three years and tilled with a chisel plough. After 22 years both dehesas showed similar SOC stock distribution amongst areas with different soil management, with approximately 40 t ha−1 in the top 100 cm of the soil. The P dehesa only showed higher SOC stock than the C dehesa on the surface 0–2 cm (5.86 ± 0.56 t ha-1vs 3.24 ± 0.37 t ha−1). The influence of the trees, increasing SOC concentration and content when compared to the area outside the canopy projection, was only detected under the mature trees in the C dehesa. In the area outside the tree canopy, both systems showed a similar distribution of soil organic carbon among their different fractions, with the unprotected fraction being the dominant one, followed by the physically and chemically protected fractions. In the C dehesa, the mature trees’ presence significantly modified the distribution of soil organic carbon in their surroundings, increasing the relevance of the unprotected fraction. The distribution of soil organic carbon in the unprotected and physically and chemically protected fractions were strongly correlated to the overall organic carbon concentration in the soil, indicating the rapid response of these three fractions to management, with the biochemically protected fraction showing no correlation, suggesting a high resilience to the changes in carbon budget.

Creating market opportunities in rural areas through the development of a brand that conveys sustainable and environmental values

Abstract The dehesa is the most widespread agroforestry system within the European Union and provides an important set of provisioning, regulating, and cultural ecosystem services. However, these systems have been in decline for a number of years, to a great extent because of their lack of profitability. Among the different options available to add value to agroforestry systems such as the dehesa and make them more profitable, the development of brands that would help consumers identify the products they generate is one of the most promising alternatives. In this way, the value of dehesa products would be enhanced and the revenue obtained from them increased. However, whilst such products are locally appreciated, a challenge exists in so far as neither national nor international consumers are able to identify dehesa products and therefore they are not willing to pay a premium for them. In this context, the creation of an umbrella brand covering the products derived from the dehesa is considered to be useful for boosting revenues in dehesa systems. This piece of research used a qualitative approach combining discussion groups with projective techniques during a series of workshops to identify relevant branding concepts and imagery for dehesa products. The findings showed that the term dehesa is recognised and appreciated by consumers, although it is associated with traditional and expensive products. It was also found that in order to make the brand more attractive to more consumers -especially younger consumers-additional concepts such as “sustainability” and “socially-responsible” production need to be incorporated in the branding. Imagery displaying forests and other environmental motifs were found to be the strongest graphical means of depicting these concepts within the brand design. It is considered that these findings could help enhance the demand and revenues associated with dehesa products and sustain the benefits they provide for the environment and for society.

A qualitative approach to study social perceptions and public policies in dehesa agroforestry systems

Agroforestry systems, which include woodlands, pasturelands and various livestock species, are multifunctional systems that must be productive in order to guarantee their conservation, as well as their provision of services such as the maintenance of the landscape and/or cultural uses.These systems generate commercial and environmental values, which are not always perceived by the society. It is therefore necessary to analyse the value society places in agroforestry systems, with a special focus on the dehesa system as a paradigmatic example.The information has been obtained from 4 focus groups organised in Badajoz and Caceres (Spain) in May/June 2015. The discussions involved 35 people with an even distribution of age and gender being sought for each group.The results of the study revealed a lack of citizen familiarity with the agroforestry system, as well as of the services it supplies, besides those that are purely associated to food production. Other key findings were the low importance given by the consumers to the item “production system” – a key aspect in order to valorize the products derived from these systems – as well as the difficulty perceived by the citizens in finding a compensation for the proprietors of these systems as suppliers of ecosystem-related services.In summary, it has become clear that it is necessary to implement specific policies and complement the existing ones so that system proprietors can be financially remunerated for the services supplied to the society, although citizen awareness must also be reinforced so that they become conscious of the goods they receive from the agrosystems and therefore understand their value.

Scattered trees and livestock grazing as keystones organisms for sustainable use and conservation of Mediterranean dehesas

Mediterranean scattered oak woodlands support relatively high biological diversity, and provide important ecosystem services. However, there is still a lack of knowledge about livestock-tree-grassland relationships, knowledge necessary for effective conservation management in these systems. To address such lacuna, we measured the effects of scattered trees and grazing animals (livestock vs. wild ungulates, mostly deer) on biomass and diversity (and their relationship) of the herbaceous layer (understory) of open holm oak woodland (known as dehesa) in Central Spain, for two years. We located two 1-ha plots within three different grazing management schemes (cattle, sheep and wildlife only). Within each plot, we randomly selected four focal trees from which a subplot was established in two directions and three distances. In each subplot, we measured plant diversity and biomass, along with microclimatic variables across sites. We found rainfall variability affected herbaceous biomass and diversity in the dehesa system, and the effects were nuanced: in a dry year (<300mm annual rainfall) the presence of livestock grazing correlated with higher herbaceous biomass (14%), and in moister year (>600mm annual rainfall) the effect was enhanced, as plots under livestock grazing exhibited even higher herbaceous biomass (42%). In addition, livestock, particularly cattle, generated a more diverse community (52 speciesm−2). Microsites created by trees generated high plant diversity among herbaceous communities, where alpha diversity was higher (20%) in ecotone and inter-tree gaps than under the canopies. In addition, species turnover was higher than 50% in all cases. Biomass was higher (15%) under the canopies only under humid conditions. Legume dry matter was positively related to plant diversity. We concluded that agroforestry management practices such as promoting tree development through silvicultural techniques to create different microsites, and maintaining livestock grazing are needed to preserve these emblematic ecosystems.

A Day in the Life of Vimala Nair

A Day in the Life of Vimala Nair

Grazing, tilling and canopy effects on carbon dioxide fluxes in a Spanish dehesa

There is increasing interest in carbon sequestering capacity of agroforestry systems especially in relation to climate change. Appropriate implementation of silvopastoral practices in dehesa systems may contribute to their sustainability; improve soil carbon (C) and nitrogen (N) storage capacity while reducing the carbon dioxide (CO2) flux from the soil to the atmosphere. The response of soil respiration (Rs) to grazing and tilling practices and trees canopy influence were studied in a dehesa ecosystem in the center of Spain from July 2008 to February 2010. Four different treatments were established: non grazed-non tilled; non grazed-tilled; grazed-non tilled and grazed and tilled. In all the treatments Rs, soil temperature (Ts), soil moisture (Ms), soil C and N stocks were measured. Grazing reduced Rs by 12 % across all experiment. Increments of 3 Mg/ha in C stocks and 0.3 Mg/ha in N stocks in grazing soils were observed. Although, no clear tilling effect on Rs was found, a decrease of 3.5 Mg/ha in soil C stocks and 0.3 Mg/ha in N stocks was detected in tilled soils. Presence of tree canopy induced increases in Rs, soil C and N stocks; while decreases in Ts were observed, but grazing decreased the tree canopy influence on annual C losses by Rs. The Ms constrained the temperature response of Rs during the experiment, and meaningful Q10 values were only obtainable during the wettest time, ranging from 2.5 to 5.7. Grazing and tree canopy had a positive influence in the ability of soils to store soil C and N, while tilling had a negative effect on soil C and N store capacity in this study. Maintaining the beneficial practices and improving tillage management in this area may have important consequences in carbon sequestration capacity in this dehesa system.

Can Organic Amendments Be Useful in Transforming a Mediterranean Shrubland into a Dehesa?

AbstractTransforming a shrubland into a dehesa system may be useful for recovering certain productive and regulatory functions of ecosystems such as grazing potential, soil erosion control, and also for reducing the risk of wildfire. However, the productivity of the herbaceous cover and tree development in the transformed system may be limited by soil fertility, especially after wildfire events. Previous studies have shown that adequate doses of sewage sludge may improve soil fertility and facilitate plant recovery, but few studies have focused on plant biodiversity assessment. Here, we compare the effects of sewage sludge that has undergone different post‐treatments (dewatering, composting, or thermal drying) as a soil amendment used to transform a fire‐affected shrubland into a dehesa, on tree growth and pasture composition (vegetation cover, species richness, and diversity). In the short term, sewage sludge causes changes in both pasture cover and tree growth. Although no major differences in vegetation species richness and composition have been detected, fertilization using sewage sludge was shown to modify the functional diversity of the vegetation community. Rapid replacement of shrubs by herbaceous cover and ruderal plants (e.g. Bromus hordeaceus and Leontodon taraxacoides) and of the three grass species sown (Festuca arundinacea, Lolium perenne, and Dactylis glomerata) was observed, whereas N‐fixing species (leguminous) tended to be more abundant in nonfertilized soils and soils amended with composted sludge. These results indicate that sewage sludge modifies the functionality of vegetation when applied to soils, and that the response varies according to the treatment that the sludge has undergone.

Land use changes and ground dwelling beetle conservation in extensive grazing dehesa systems of north-west Spain

Traditional management practiced over centuries in Mediterranean cultural landscapes has led to singular agrosilvopastoral ecosystems such as dehesas. Recent abandonment of dehesa management has resulted in shrub encroachment, habitat homogenisation and increased fire risk. Mechanical shrub cutting to decrease biomass load creates novel cleared dehesas with yet unknown consequences for the ecosystem function. We investigated the effects of these land use changes on ground dwelling beetles (carabids and staphylinids) as model organisms by comparing traditionally grazed, long-time abandoned and newly cleared dehesas. Land use changes affected beetle species composition by altering habitat structure (e.g., litter layer) and the availability of feeding resources. Grazed dehesas held the highest number of exclusive species and particular functional guilds of carabid seed eaters and staphylinid coprophiles, utilizing food resources related to the presence of grazing livestock (annual herbs and coprophagous insects). Beetle assemblages of abandoned dehesas, resembling those known from surrounding human disturbed oak forests, exhibited the lowest abundance and greatly differed from beetle assemblages of grazed dehesas. Shrub clearance after dehesa abandonment benefited opportunistic beetle predators feeding on decomposers associated with cutting slash left on the ground. The habitat structure and beetle species composition of cleared dehesas slightly approached those of grazed dehesas, therefore suggesting shrub cutting as a first step towards restoration of abandoned dehesas. However, since livestock grazing is an essential driver of ground dwelling beetle composition, it should be promoted after shrub cutting in cleared dehesas to restore the characteristic assemblages, species interactions and ecosystem function of grazed dehesas.

Analysis of Prinobius myardi Mulsant population dynamics in a Mediterranean cork oak stand

The dehesa is a silvopastoral system of a high economic and ecological significance in the Iberian Peninsula that is protected under the EEC/92/43 Habitat Directive. One of the most serious problems the dehesa system is currently facing is oak decline. This tree decay process is largely caused by three xylophagous cerambycids of which Prinobius myardi is the least known. In this study, we used a capture-mark-recapture method to identify the models best fitting the behaviour of this species with a view to estimating basic population parameters such as survival rate (phi), recapture rate (p) and transiency index (T). Prinobius myardi adults were captured by hand following visual detection in the trees of a cork oak (Quercus suber) plot located in the close vicinity of the Doñana National Park (SW Spain). Males exhibited a constant survival rate exceeding 85.4% throughout their flight period, a maximum transiency index of 1.82% and a recapture rate ranging from 42.50% to 76.90%. These results are suggestive of a sedentary behaviour in P. myardi males. By contrast, the small number of females captured precluded calculation of the previous parameters for this gender; in any case, field observations revealed a fleeing, less sedentary behaviour with respect to the males.

Abandonment and management in Spanish dehesa systems: Effects on soil features and plant species richness and composition

Quercus pyrenaica dehesas have been traditionally used as communal extensive grazing systems in the León province (NW Spain). In this region, recent abandonment of rural areas and the subsequent gradual decrease in livestock load have led to the invasion of shrubs in the understory, increasing the risk of fires. Indeed, even if there is no need of creating new pasturelands for livestock breeding, the remaining landowners keep on burning to clear these montane patches. Alternatively, the regional administration encourages shrub cutting as a better way of managing these areas and preserving the pasturelands. Our aim was to determine the effects of the dehesa abandonment and shrub cutting on plant species richness (annual herbs, perennial herbs and woody plants) and species composition, as well as on topsoil properties. For that, we compared three types of dehesas with different management regimes: (1) grazed dehesas (used at the present), (2) abandoned dehesas (more than 20 years without grazing) and (3) dehesas where shrub cutting was applied after abandonment (i.e. cleared dehesas). We selected three replicates or stands per dehesa type. The highest organic matter content (O.M.), total nitrogen (N) and available phosphorus (P) were found in cleared dehesas, while the lowest values corresponded to the grazed ones. Abandoned dehesas were characterized by the highest values for available calcium (Ca 2+). No significant differences were detected regarding the vegetation richness values (S alpha, gamma or beta), although higher mean values of S alpha and gamma were found in grazed dehesas, and lower values in the cleared ones. Concerning the vegetation life forms, grazed dehesas held significantly greater species richness and cover of annual herbs, while abandoned dehesas had significantly higher woody species cover. Both grazed and abandoned dehesas harboured plant species (38 and 13 species, respectively), which were exclusively found in one dehesa type. Contrary to that, cleared dehesas scarcely had “exclusive” species. To conclude, our results indicated that shrub cutting alone (not followed by livestock grazing) may cause loss of plant species richness, suggesting that it is not the most appropriate management method to restore vegetation, except for reducing the risk of fire.

Economic and management characterization of dehesa farms: implications for their sustainability

Dehesa agroforestry systems occupy around 6 million ha in the Iberian Peninsula. Their economic and environmental sustainability depends on the maintenance of the extensive livestock farms which created this typical ecosystem. This work analyzes dehesa farms in the Extremadura region (SW Spain) using technical and economic indicators of 69 randomly selected holdings. Principal component analysis (PCA) allowed us to establish a valid model explaining 65.8% of the variance. The two principal components having most weight were Iberian pig production (explaining 20% of the variance of the model), and which ruminant species were raised on the farm (15% of the variance). A cluster analysis distinguished five types of farms: sheep farms at high and low stocking rates, beef cattle farms, wooded farms with mixed livestock, and farms with a high level of cropping activity. The most profitable farms were those with either high overall livestock density or a high level of Iberian pig production. While high stocking density has historically attracted high levels of subsidy, production of Iberian pigs was profitable because of the high value of the product. In the light of CAP reform, Iberian pig production seems the most readily sustainable type of farming for the dehesa system.

Forest planning and traditional knowledge in collective woodlands of Spain: The dehesa system

Since the middle of the 19th century, the German Forestry School's doctrines gained acceptance in Spain, spreading the idea that it was necessary to maintain some collective property forests under state control. The official recognition of this measure marked the beginning of a technical and economic planning process in the country, with the purpose of replacing the traditional management in communal and municipal woodlands. The main aim of the present work is to show the results of this process in Extremadura, a vast region situated in the south-west of Spain, which has been historically characterized by the preponderance of a type of open oak parkland, known as ‘dehesa’. The natural peculiarities and the traditional multiple-use management of this woodland variety created special conditions which planning had to face in the region. In this process, the central forest administration tried to implement German technical management principles, based on the Central European high forest and a focus on timber and firewood production. Given the particular features of the dehesa, this task had to be reviewed and updated by the foresters to adapt it to the local economic and ecological surroundings. This paper explores the process by which the knowledge gradually accumulated by the forest engineers who were in contact not only with Extremadura but also with other regions of Spanish triggered the development of a new forest economy in the country, based on the recognition of the traditional resources of the Mediterranean woodland.

The effect of grazing abandonment on species composition and functional traits: the case of dehesa grasslands

Summary This study attempts to identify the consequences of grazing abandonment for changes in floristic and functional vegetation composition in dehesa systems. Species cover was quantified in plots on grazed and abandoned dehesas in Central Spain. Using literature and field measurements, we analysed plant attributes linked to dispersal, establishment, and persistence for the 85 most abundant species. A Detrended Correspondence Analysis of the species × plots matrix and the traits × plots matrix was used to describe differences in species composition and functional traits in relation to grazing. The latter matrix was obtained by multiplying the traits × species matrix by the species × plots matrix. Grazed sites had a higher proportion of prostrate species, medium specific leaf area, early flowering, cryptophytes, unassisted seeds and clonal reproduction. Ungrazed sites had a higher proportion of taller plants, heavy leaf dry weight, late flowering species and chamaephytes as well as species with heavy seeds and fruits with adhesive structures.

Plant production and nutritive quality of savannah-like grasslands (dehesas) in semi-arid zones of the province of Salamanca [Spain

A study was made of two savannah-like (dehesa) pastures on which cattle (Morucha cows × Charolais bulls) are raised for beef. The soil of dehesa system A was developed over slate, while that of B was developed over granite. The type of vegetation, dry matter yield (DM), raw protein (RP) content, digestible organic matter (DOM) content and the metabolizable energy (ME) of each system was determined to provide the nutritive value of the two types of pasture. Dietary supplements were assessed in the same way. The DM yields for 1989, 1990 and 1991 were 751, 1900 and 1438 for system A, and 577, 1937 and 1361 kg ha-1 for system B. The RP values for April and December were 17.6 +/- 1.4%, falling to a minimum of 6.7 +/- 0.4% in July-October. Intermediate values were seen for the rest of the year. The ME showed mean values of 9.4 +/- 0.3 and 7.9 +/- 0.2 MJ kg DM-1 for systems A and B respectively, while mean metabolicity was 0.50 +/- 0.2 and 0.44 +/- 0.1 (P &lt; 0.05) and the DOM was 67.5 +/- 4.2% and 44.3 +/- 3.9% respectively. These values were affected by the year and harvest date (P &lt; 0.05) and were always greater (P &lt; 0.05) on soils developed over slates. The greatest pasture ME was achieved in spring and represented some 77-95% of total pasture production, depending on the year. Supplements represented approximately 20% of the total available ME.

Runoff and losses by erosion in soils amended with sewage sludge

AbstractIn order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha−1 of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha−1 of composted sludge, 50 t ha−1 of fresh sludge and 11ċ3 t ha−1 of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 John Wiley &amp; Sons, Ltd.