Rainfed crop energy balance of different farming systems and crop rotations in a semi-arid environment: Results of a long-term trial

Abstract

This study was conducted to determine how energy balances of crop production are affected by three farming systems (conventional, conservation with no tillage, and organic) and four barley-based crop rotations (barley followed by fallow [B–F], barley in rotation with vetch [B–V] or sunflower [B–S], and barley monoculture [B–B]), under the semi-arid conditions of central Spain over a 15-year period (1993/94–2007/08). As inputs, the factors supplied and controlled by farmers were considered. The energy balance variables considered were net energy produced (energy output minus energy input), the energy output/input ratio, and energy productivity (crop yield per unit energy input). The total energy inputs were 3.0–3.5 times greater in the conservation (10.4 GJ ha⁻¹ year⁻¹) and conventional (11.7 GJ ha⁻¹ year⁻¹) systems than in the organic system (3.41 GJ ha⁻¹ year⁻¹). With respect to the crop rotations, the total energy inputs varied from 6.19 GJ ha⁻¹ year⁻¹ for B–F to 11.7 GJ ha⁻¹ year⁻¹ for B–B. The lowest energy use corresponded to B–F in the organic system (2.56 GJ ha⁻¹ year⁻¹), and the highest to B–B in the conventional and conservation systems (16.3 and 14.9 GJ ha⁻¹ year⁻¹, respectively). Energy output was lowest in the organic system (17.9 GJ ha⁻¹ year⁻¹), a consequence of the lower barley grain and vetch hay yields. With respect to the crop rotation, the order followed B–B (19.1 GJ ha⁻¹ year⁻¹) ≈ B–F < B–S < B–V (29.3 GJ ha⁻¹ year⁻¹, 53% higher). All the energy efficiency variables analysed had the highest values for the organic system (net energy of 14.5 GJ ha⁻¹ year⁻¹, output/input ratio of 5.36 and energy productivity of 400 kg GJ⁻¹). No differences were recorded between the conventional and conservation managements. This indicates that, in terms of energy efficiency, the viability of organic systems (low-input practices) under semi-arid conditions, compared to farming systems requiring agrochemicals (conventional and conservation), would appear more recommendable. Cereal monoculture (B–B), independent of the crop management employed, is an energetically unfavourable practice, especially in the driest seasons. However, crop rotations, especially those including a leguminous plant, increase energy efficiency.

Introduction

Energy balances for agricultural systems have been studied since the 1970s (Pimentel et al., 1973, Berardi, 1978). Researchers have performed detailed energy balances for different crops and farm management systems all over the world in attempts to assess the efficiency and environmental impact of production systems (Campliglia et al., 2007, Akpinar et al., 2009). Energy balances provide an important view of the agriculture as a user and producer of energy (Risoud, 2000).

In the economic sense, the aim of any agricultural practice is to achieve maximum profit. However, the viability of a production system does not depend solely on crop yield, but also on its efficiency in the use of available resources. In developed countries, the economic profitability of different productive systems is currently obfuscated by the granting of subsidies of diverse origin that affect both production factors (or inputs) and the final product (or output). Leaving such external aid aside, energy balances should reveal the most efficient, and therefore the most advisable, form of management for each agroclimatic region. In this context, conducting energy balances can lead to more efficient and environment-friendly production systems (Gündoğmuş, 2006).

In recent years the relationship between agriculture and the environment has changed, and concerns regarding the sustainability of agricultural production systems have come to the fore. This has led to tension between “production vs. conservation”. Conservation systems are understood as sustainable production systems, while production first oriented practices imply production should take place, without considering the environmental and energetic effects. Conservation practices, however, balance environmental and energetic effects with production. As a consequence, farmers are now continuously requested to increase crop yields while at the same time preserving the environment by reducing the dependency of agriculture on external, non-renewable fossil energy and reducing the emission of greenhouse gases (Bailey et al., 2003, Bechini and Castoldi, 2009). To achieve these goals, solutions such as developing integrated arable farming systems, conservation tillage practices, and low-input or organic farming have been proposed (Edwards, 1987, Hernanz et al., 1995, Vereijken, 1997, Pervanchon et al., 2002). In general, integrated farming systems involve lower inputs of fertilizer and pesticides, and fewer tillage operations (Edwards, 1987). Conservation agriculture promotes minimal disturbance of the soil (minimum or no tillage), the balanced application of chemical inputs, and the careful management of residues and wastes (Dumanski et al., 2006). This type of system, however, often requires increased pesticide use. Organic or ecological farming is based on the banning of synthetic biocides and fertilizers (Helander and Delin, 2004, Jørgensen et al., 2005), and promotes the use of renewable resources in production and processing systems to prevent pollution and avoid waste (IFOAM, 2002).

In Spain, the energetic and environmental aims for the agricultural sector of the country's Action Plan for Saving Energy and Energy Efficiency 2008–2012 are to save 1634 ktep¹ of primary energy (oil 47.6%, coal 14.4%, nuclear fuel 9.7%, natural gas 21.8%, renewable resources 6.5%) and to achieve a 5112 ktep reduction in CO₂ emissions (the latter representing a €92 million profit). This Action Plan recognizes energy saving and energy efficiency as an instrument of economic growth and social well-being, and promulgates the importance of these concepts in all associated National Strategies, especially in those relative to climate change (IDAE, 2007).

Energy inputs and outputs are important factors affecting the energy efficiency and environmental impact of crop production. The magnitude of these factors, and consequently the energy efficiency of an agrarian system, varies considerably depending on farm location (weather, soil type), crop rotations, the use of fertilizers, etc. (Bonny, 1993, Rathke et al., 2007). This shows the importance of determining energy balances for all pedo-climatic conditions (Pacini et al., 2003).

The efficiency of energy use can be increased by reducing inputs such as fertilizer and tillage operations, or by increasing outputs such as crop yields (Swanton et al., 1996). In some cases, a reduction in energy inputs entails a proportional reduction in crop yield. In such cases energy efficiency is not significantly affected (Risoud, 2000, Bailey et al., 2003). In some modern, high-input farming systems, crop yields have improved continuously as a result of increasing inputs of agrochemicals (inputs of fossil energy) and the growth of more productive cultivars (Hülsbergen et al., 2001). Other studies report reductions in energy efficiency due to energy inputs increasing faster than energy outputs, the result of a growing dependency on inorganic, non-renewable resources (Weseen and Lindenbach, 1998, Gündoğmuş, 2006, Gündoğmuş and Bayramoğlu, 2006).

This study has attempted to achieve greater sustainability of agricultural systems, whatever the production system employed, and to get sustainable and profitable production for the farmer with a minimal energy and environmental damage over time. Under this general assumption, the aim of the present work was to assess the effects of conventional, conservation and organic systems and different barley-based crop rotations (barley monoculture and in rotation with vetch, sunflower and fallow) on the energy balance of crop production under the semi-arid conditions over a 15-year period (1993/94–2007/08). As proposed by Rathke et al. (2007), these production systems were compared under the same site conditions and using the same methods for calculating the energy balance values, which permits a valid comparison among treatments.