• Energy Research

Soil organic carbon (SOC) management is key for soil fertility and for mitigation and adaptation to climate change, particularly in desertification-prone areas such as Mediterranean croplands. Industrialization and global change processes affect SOC dynamics in multiple, often opposing, ways. Here we present a detailed SOC balance in Spanish cropland from 1900 to 2008, as a model of a Mediterranean, industrialized agriculture. Net Primary Productivity (NPP) and soil C inputs were estimated based on yield and management data. Changes in SOC stocks were modeled using HSOC, a simple model with one inert and two active C pools, which combines RothC model parameters with humification coefficients. Crop yields increased by 227% during the studied period, but total C exported from the agroecosystem only increased by 73%, total NPP by 30%, and soil C inputs by 20%. There was a continued decline in SOC during the 20th century, and cropland SOC levels in 2008 were 17% below their 1933 peak. SOC trends were driven by historical changes in land uses, management practices and climate. Cropland expansion was the main driver of SOC loss until mid-20th century, followed by the decline in soil C inputs during the fast agricultural industrialization starting in the 1950s, which reduced harvest indices and weed biomass production, particularly in woody cropping systems. C inputs started recovering in the 1980s, mainly through increasing crop residue return. The upward trend in SOC mineralization rates was an increasingly important driver of SOC losses, triggered by irrigation expansion, soil cover loss and climate change-driven temperature rise.

Wheat yields are predicted to decrease over the next decades due to climate change (CC). Mediterranean regions are characterized by low soil fertility and stressful conditions that limit the effect of technological improvements on increasing yield gains, while worsening the negative CC impacts. Additionally, organic farming (OF) lacks specifically adapted genetic material. Accordingly, there is a need to search for varieties adapted to these conditions and whose cultivation may help semi-arid agroecosystems sustainability, focusing on specific agronomic and functional traits. To this purpose, wheat landraces and modern wheat varieties were evaluated under Mediterranean rainfed conditions during three growing seasons under contrasting situations: A conventional farm and an organic farm. Results regarding straw production, weed biomass and biodiversity, and grain N concentration suggest that the cultivation of landraces under Mediterranean rainfed conditions can enhance agroecosystem sustainability through positive effects on ecosystem services such as soil quality, functional biodiversity, or grain protein content, without significant reductions in grain yield. Results highlight the relevant role of wheat landraces as genetic resources for the development of cultivars adapted to Mediterranean agroecosystems conditions, especially for organic farming, but also for conventional agriculture.

This paper documents the origin and conceptual ambiguity of the terms Sustainable, Ecological and Agroecological Intensification. It defines the concept of Ecological Intensification from an agroecological perspective, and examines in energy terms whether it may be sustainable. To illustrate the theory, we apply Land Cost of Sustainable Agriculture (LACAS) methodology to Spanish agriculture, which is representative of Mediterranean agroclimatic conditions. As a result, we demonstrate the impossibility of generalizing an extensive Organic Farming (OF) scenario under the techniques currently used by organic farmers. This is due to the fact that it would bring about a reduction of 13% in agricultural production. Which necessarily means that OF has to be intensified under agroecological criteria. This option is also explored in two scenarios. As a result, we show that it is possible to compensate the yield gap between OF and conventional agriculture by implementing low-entropy internal loop strategies which reduce the land cost of generating the necessary nitrogen flows. However, these cannot exceed the limits established by the structure of Spanish territory. That is, agroecological intensification cannot be prolonged indefinitely over time since it is limited by the land available.

For a large extent of historiography, the history of Spanish agriculture during the twentieth century is a story of success. However, this narrative has been built on monetary analysis, and it does not usually take into account the effects on rural society and agroecosystems. The aim of this paper is to analyze what has happened from a biophysical perspective to ascertain whether transformations linked with industrialization of agriculture have also been positive. For this, we have integrated the results—some unpublished and others already published—of a broader research project about different aspects of food production from a biophysical perspective in Spain, applying methodologies pertaining to the Social Metabolism. Our research seeks to provide a new narrative, emerging through the consideration of environmental aspects of the process, providing a more complex vision of the process of industrialization in European agriculture. The results show that the industrialization of Spanish agriculture has brought about profound changes in land uses and in the functionality of the biomass produced, increasing pressure on croplands and, paradoxically, facilitating the abandonment of an important proportion of pasture and croplands. This has led to the subordination of a very significant portion of Spanish agroecosystems to the feed demands of intensive livestock farming. This process has been based on the injection of large quantities of external energy. Agricultural production has undergone significant growth since the 1960s, but this has been insufficient to deal with the growing demand created by the change in the Spanish diet and the increasing trend to focus on livestock farming. The process of globalization has allowed both roles to be reconciled, although in recent decades Spain has accentuated its role as a net importer of biomass from a biophysical perspective, with very significant impacts on third party countries, particularly in Latin America. From a biophysical perspective, the industrialization of Spanish agriculture has entailed negative consequences that threaten the sustainability of Spanish agroecosystems and also negatively affect the sustainability of other territories.

In recent years, the transition to sustainability at a food systems’ scale has drawn major attention both from the scientific and political arenas. Agroecology has become central to such discussions, while impressive efforts have been made to conceptualize the agroecology scaling process. It has thus become necessary to apply the concept of agroecology transitions to the scale of food systems and in different “real-world” contexts. Scaling local agroecology experiences of production, distribution, and consumption, which are often disconnected and/or disorganized, also reveals emergent research gaps. A critical review was performed in order to establish a transdisciplinary dialogue between both political agroecology and the literature on sustainable food systems. The objective was to build insights into how to advance towards Agroecology-based Local Agri-food Systems (ALAS). Our review unveils emergent questions such as: how to overcome the metabolic rift related to segregated activities along the food chain, how to feed cities sustainably, and how they should relate to the surrounding territories, which social subjects should drive such transitions, and which governance arrangements would be needed. The paper argues in favor of the re-construction of food metabolisms, territorial flows, plural subjects and (bottom-up) governance assemblages, placing life at the center of the food system and going beyond the rural–urban divide.

This article is intended as a review of the current situation regarding the impact of olive cultivation in Southern Spain (Andalusia) on soil degradation processes and its progression into yield impacts, due to diminishing soil profile depth and climate change in the sloping areas where it is usually cultivated. Finally, it explores the possible implications in the regional agricultural policy these results might have. It tries to show how the expansion and intensification of olive cultivation in Andalusia, especially since the late 18th century, had as a consequence an acceleration of erosion processes that can be identified by several indicators and techniques. Experimental and model analysis indicates that the rate of soil erosion accelerated since the expansion of mechanization in the late 1950s. In addition, that unsustainable erosion rates have prevailed in the region since the shift to a more intense olive cultivation systems by the end of the 17th Century. Although agroenvironmental measures implemented since the early 2000s have reduced erosion rates, they are still unsustainably high in a large fraction of the olive area in the region. In the case of olive orchards located in steeper areas with soils of lower water-holding capacity (due to coarse texture and stone content), cumulative erosion has already had a high impact on reducing their potential productivity. This is one of the factors that contributes towards increasing the gap between these less intensified orchards in the mountainous areas and those in the hilly areas with more gentle slopes, such as for instance the lower stretches of the Guadalquivir River Valley. In the case of olive orchards in the hilly areas with better soils, easier access to irrigation and lower production costs per unit, the efforts on soil conservation should be oriented towards limiting off-site damage, since the soil water-storage function of these soils may be preserved in the medium term even at the current soil erosion rates. The assessment made in this manuscript should be regarded as an initial approximation, since additional efforts in terms of increasing experimental records (for current or historical erosion) and of improving model analysis, with more comprehensive studies and more robust calibration and validation processes, are required.

Along the last century there has been an unprecedented growth in both global food production and related socioecological impacts. The objective of this paper is to analyse the effects of long-term metabolic patterns of agrarian systems on land use and cover changes (LUCC) (...)