The potential of organic fertilizers and water management to reduce N2O emissions in Mediterranean climate cropping systems. A review

Abstract

International audienceEnvironmental problems related to the use of synthetic fertilizers and to organic waste management have led to increased interest in the use of organic materials as an alternative source of nutrients for crops, but this is also associated with N2O emissions. There has been an increasing amount of research into the effects of using different types of fertilization on N2O emissions under Mediterranean climatic conditions, but the findings have sometimes been rather contradictory. Available information also suggests that water management could exert a high influence on N2O emissions. In this context, we have reviewed the current scientific knowledge, including an analysis of the effect of fertilizer type and water management on direct N2O emissions. A meta-analysis of compliant reviewed experiments revealed significantly lower N2O emissions for organic as opposed to synthetic fertilizers (23% reduction). When organic materials were segregated in solid and liquid, only solid organic fertilizer emissions were significantly lower than those of synthetic fertilizers (28% reduction in cumulative emissions). The EF is similar to the IPCC factor in conventionally irrigated systems (0.98% N2O-N N applied(-1)), but one order of magnitude lower in rainfed systems (0.08%). Drip irrigation produces intermediate emission levels (0.66%). Differences are driven by Mediterranean agro-climatic characteristics, which include low soil organic matter (SOM) content and a distinctive rainfall and temperature pattern. Interactions between environmental and management factors and the microbial processes involved in N2O emissions are discussed in detail. Indirect emissions have not been fully accounted for, but when organic fertilizers are applied at similar N rates to synthetic fertilizers, they generally make smaller contributions to the leached NO3- pool. The most promising practices for reducing N2O through organic fertilization include: (i) minimizing water applications; (ii) minimizing bare soil; (iii) improving waste management; and (iv) tightening N cycling through N immobilization. The mitigation potential may be limited by: (i) residual effect; (ii) the long-term effects of fertilizers on SOM; (iii) lower yield-scaled performance; and (iv) total N availability from organic sources. Knowledge gaps identified in the review included: (i) insufficient sampling periods; (ii) high background emissions; (iii) the need to provide N2O EF and yield-scaled EF; (iv) the need for more research on specific cropping systems; and (v) the need for full GHG balances. In conclusion, the available information suggests a potential of organic fertilizers and water-saving practices to mitigate N2O emissions under Mediterranean climatic conditions, although further research is needed before it can be regarded as fully proven, understood and developed. (C) 2012 Elsevier B.V. All rights reserved

Greenhouse gas emissions from conventional and organic cropping systems in Spain. II. Fruit tree orchards

“…The type of fertilizer does not seem to represent a driver of the yield gap between organic and conventional production that we found, as other studies under Mediterranean conditions have shown that yields are not affected by fertilizer type and could even be increased by the presence of organic inputs (Palese et al 2013; see also Aguilera et al 2013b). Therefore, there is a need for more research in order to close this yield gap; e.g., in irrigated organic fruits, this gap is mainly due to pest and disease problems, which are not well controlled.…”

“…Reduced fossil energy consumption in organic orchards (Guzmán and Alonso 2008;Alonso and Guzmán 2010) suggests that there may also exist greenhouse gas emissions savings in these systems, taking into account the high importance of energy-related emissions in the carbon footprint of herbaceous Spanish cropping systems . At the soil level, evidence suggests low N 2 O emissions associated to organic fertilizers (Aguilera et al 2013b) and higher soil organic carbon (SOC) stocks in organically managed soils under Mediterranean climate (Aguilera et al 2013a). All these features point to a large mitigation potential of Mediterranean fruit tree orchards and particularly of organic agro-ecosystems, but comprehensive assessments of their global warming potential are very scarce.…”

Carbon management in dryland agricultural systems. A review

“…However, this strategy is only applicable in certain developed areas with nutrient surpluses. Another recent work shows a decrease in N 2 O emissions when using organic fertilizers in comparison with the use of synthetic products in dryland areas (Aguilera et al 2013b).…”

Eco-innovations in the German fertilizer supply chain: Impact on the carbon footprint of fertilizers

“…All emission data were additionally compared with ammonium nitrate (AN) in FG. These data were gathered from a meta study comparing different irrigation systems (drip, furrow, rainfed) in Mediterranean climates (Aguilera et al 2013b). Production of the irrigation equipment and its transportation was not taken into account, because it was assumed that FG only takes place in regions were irrigation is a standard measure in all cultivation systems.…”

“…Irrigation is mostly applied during summer periods when soil temperature, and due to irrigation also the soil moisture conditions for N 2 O production after fertilizer application, are more favourable (Jambert et al 1997, Hao et al 2001, Scheer et al 2008, Aguilera et al 2013b) and therefore a strong stimulation of the N 2 O fluxes might occur. Adapting nitrogen supply closely to crop nitrogen demand during the vegetation period and thereby lowering nitrogen peaks in the soil might be the most important reason for overall lower N 2 O emission via fertigation.…”