Orchard and horticulture systems in Spanish Mediterranean coastal areas: Is there a real possibility to contribute to C sequestration?

Abstract

Agriculture in the Mediterranean basin is currently contributing to greenhouse gas emissions (GHG) and in the future is expected to be strongly affected by climate change. Increasing soil organic carbon (SOC) via soil organic matter (SOM) improvement is widely regarded as a way to both mitigate and adapt to climate change. Using as a case study the Mediterranean coastal area in Spain, which is regarded as one of the most intensively managed areas in Europe for orchards and horticultural cropping, we analyzed the potential for climate change mitigation of introducing different practices that are expected to increase SOC. We selected both as a single Agriculture, Ecosystems & Environment 238 (1): 153-167 (2017) 2 measure and in combination, cover cropping and application to the soil of the available underutilized exogenous organic matter (EOM), treated (e.g. composted or digested) or nontreated. These practices were compared against a baseline scenario that intended to reflect the current practices in the area (e.g. all livestock manure produced in the area is applied to the agricultural soil). We carried out a modelling exercise at the regional scale using the agricultural activity data and current climatic conditions as inputs. Modelling runs were performed coupling a widely used dynamic model of SOC turnover (RothC) with a model to simulate the GHG emissions from EOM processing or storage prior to soil application (SIMSWASTE). Results indicate that the most promising practice, considered as a single measure and with respect to the baseline, was introducing cover crops in woody cropping systems. This practice resulted in an increase of 0.44 Mg C ha-1 yr-1 during the first 20 years (range 0.41-0.52 Mg C ha-1 yr-1) and led to a total SOC accumulation of about 30 Tg C after 100 years. Amendment of all agricultural land with available underutilized EOM resulted in an increase of up to 0.09 Mg C ha-1 yr-1 (range 0.07-0.16 Mg C ha-1 yr-1) as a single measure (urban waste) and 0.13 Mg C ha-1 yr-1 (range 0.11-0.21 Mg C ha-1 yr-1) as a combined measure (urban waste and composted agroindustry by-products), leading to a total SOC accumulation of about 7 Tg C (urban waste) and 10 Tg C (urban waste and composted agroindustry by-products) after 100 years. Manure anaerobic digestion or composting as a single measure did not result in significant SOC changes but, if GHG emissions and savings from manure storage and processing management stages are considered, they could help to reduce about 4.3 (anaerobic digestion) or 1.1 Tg CO2eq yr-1 (composting) in the study area, which represents a significant amount compared with total agricultural emissions in Spain. Production Study area Agricultural availability Biodegradability Gg C yr-1 Gg C yr-1

Soil organic carbon stock on the Majorca Island: Temporal change in agricultural soil over the last 10 years

“…Under Mediterranean conditions, characterised by seasonal dryness due to hot-dry summers and mild-wet winters, several authors have observed lower SOC levels than in temperate areas (Aguilera et al, 2013;Chiti et al, 2012), and have remarked on the difficulty of increasing SOC due to the rapid mineralisation and low humification rates under hyper-thermic conditions (Gervois et al, 2008). Several studies have reported national or regional SOC stocks under these Mediterranean conditions (Álvaro-Fuentes et al, 2008;Doblas-Miranda et al, 2013;Muñoz-Rojas et al, 2012;Rodríguez Martín et al, 2016), with some simulations made about the possible climate change effect on lowering SOC levels (Jebari et al, 2018;Pardo et al, 2016). However, information on the tendencies of these SOC stocks based on real situations through different temporal soil samplings is lacking.…”

Modeling Regional Effects of Climate Change on Soil Organic Carbon in Spain

“…The application of organic amendments to agricultural soils and the use of cover crops are also regarded as effective ways of restoring soil C stocks. Experimental and modeling studies have successfully shown an increase in SOC after application of organic amendments such as pruning residues (Sofo et al, 2005) or compost (Mondini et al, 2012), and using cover crops for both woody (Pardo et al, 2017) and arable (Bleuler et al, 2017) cropping systems.…”

“…In this context, the SOM model RothC (Coleman and Jenkinson, 1996) has been applied to numerous field studies worldwide under various types of agricultural management and agroclimatic regions (Jenkinson et al, 1999; Kaonga and Coleman., 2008; Liu et al, 2009). In Mediterranean Spain, process‐based models (e.g., the Century model: Álvaro‐Fuentes et al, 2012a) have already been used at the plot (Nieto et al, 2010; Álvaro‐Fuentes et al, 2012b; Nieto and Castro, 2013) and regional (Álvaro‐Fuentes et al, 2012a; Pardo et al, 2017) scales. Among these studies, Álvaro‐Fuentes et al (2012a) was the first to investigate the effect of Spanish climate change conditions on SOC changes at the regional level, but they did not use the C model under a spatially explicit environment.…”

Exploring the possibilities of parsimonious nitrogen modelling in different ecosystems

“…Nitrogen inputs to aquatic environments produce their eutrophication stimulating harmful algal blooms (Álvarez et al, 2017;Le Moal et al, 2019), while sediment inputs contribute to their habitat degradation and biota impairment (Collins et al, 2011;Mtibaa et al, 2018). Nevertheless, the use of elevated fertilizer doses (Pardo et al, 2017;Poch-Massegú et al, 2014) to increment crop yield and poor support conservation practices (Panagos et al, 2015) are still a common practice in agricultural areas. Both produce a direct impact on water quality through the nitrogen surplus and soil erosion, but the latter also produces an indirect impact contributing to soil degradation through the removal of the topsoil and finest fraction of soils, where organic matter and nutrients are concentrated (García-Ruiz et al, 2015;Merchán et al, 2018), which usually entails a crop yield decline (García-Ruiz et al, 2015).…”

“…The second approach is developed in an intensive irrigated agricultural watershed under a semiarid climate. These areas are characterized by an elevated use of fertilizers (Pardo et al, 2017;Poch-Massegú et al, 2014), and hence, improving their sustainability is essential. Conversely, the main mineral nitrogen input is not the natural nitrogen mineralization but the fertilization process.…”