Effect of abandonment of olive orchards on soil organic carbon sequestration in Mediterranean Lebanon.
The abandonment of agricultural lands is one of the main forces driving the Mediterranean landscape (Cerda et al. 2012). In western Mediterranean countries, rural exodus started after the Second World War, leading to early land abandonment (Vaccari et al. 2012). In Lebanon, the low profitability of the land and the 30-year war have significantly contributed to emptying of rural areas. The combination of rural exodus and urban expansion caused a significant deforestation between the early 1960s and the late 1990s. The loss reached 32% of the forest cover and 31% of the olive area (Masri et al. 2002). This reduction in land cover is exacerbated by the annual emission of greenhouse gases, essentially through mobile and stationary combustion. For Lebanon, some 3704 x [10.sup.3] Mg C is estimated to be emitted annually (Anonymous 2006), the equivalent of 1.28 Mg C per capita, according to estimates of the World Bank (http://data. worldbank.org/indicator/EN.ATM.C02E.PC). Therefore, there is a need to compensate for this emitted carbon by promoting its sequestration.
Soil organic matter (SOM) is the repository for approximately 60% of the global terrestrial carbon pool (West and Post 2002). One of the principal indicators of soil quality, soil organic carbon (SOC) is an important determinant of soil function (Van Camp et al. 2004) and soil resilience to drought (Food and Agriculture Organization of the United Nations 2005). As a very reactive component (Ding et al. 2006), a managerial change moves SOC towards an equilibrium that is characteristic of the soil type, prevailing land use and climate (Bhogal et al. 2008). Under Mediterranean conditions, the succession of dry summers and wet winters increases the emission of carbon dioxide by promoting the decomposition of SOC (Jarvis et al. 2007). Ploughing is considered to cause a rapid loss of SOC (Owens 2004), with Spanish Mediterranean forests converted to cereals reported to have lost approximately one-third of their C stocks (Romanya et al. 2007). Beyond Mediterranean conditions, a meta-analysis showed a decrease in C stocks (-42%) upon a change from native forests to crops (Guo and Gifford 2002).
Inversely, changes in land use through abandonment or reforestation lead to the build up of SOM. In northern Iran, C stocks increased 21 years after afforestation (Kooch et al. 2012), whereas in Spain reforested land had 25% higher SOC than old fields (Cuesta et al. 2012). Abandoned agricultural lands showed an intermediate carbon content between cultivated fields and native woodlands (Dunjo et al. 2003; Zomoza et al. 2009; Cerda et al. 2012). This C storage could be due to a peak of species richness during the first decade of abandonment (Bonet 2004) and to increased incorporation of litter facilitating the development of soil fungi (Zomoza et al. 2009). Abandoned fields were an active carbon sink even in the sandy soils of the Italian island of Pianosa (Vaccari et al. 2012). To identify the SOM acting as a C sink over the short term, a physicochemical separation into five fractions (light fraction, 500 pm particulate organic matter (POM), 53 pm POM, mobile humic acid and calcium-bound humic acid) was attempted (Cao et al. 2011). In a more conceptual approach, models were suggested to describe the dynamics of the SOC. One of these models provided the following measurable SOC pools: unprotected, silt-and-clay protected, microaggregate protected and biochemically protected. The first pool was most sensitive to changes in management practices (Six et al. 2002).
In Lebanon, changes in land use by abandonment concern olives orchards in particular, because these mostly occur on stony and marginal landscapes (Abou Zeid 2007). One of the extensive production systems, olive orchards represent 43% of the land under permanent agriculture (Ministry of Agriculture 2012). The carbon dynamics associated with this change in land use are unknown; hence, the present study investigated the ability of abandoned land to store C. Specifically, the present study focused on the sequestration of organic carbon following abandonment of olive orchards in sub-humid Mediterranean Lebanon.
Materials and methods
Twenty-five abandoned olive orchards were sampled between spring 2010 and autumn 2011. 'Abandonment' was defined as the cessation of ploughing and fertilisation, but not of occasional grazing by herds of goats. The orchards were distributed in Lebanon, from 33[degrees]26'N to 34[degrees]25'N, between 219 and 828 m above sea level. Twenty-five abandoned and 25 actively managed orchards were sampled. Control plots (i.e. actively managed plots) were selected from the immediate proximity of the abandoned fields, taking into consideration the exposure of the fields, their stoniness and the soil properties (colour, calcium carbonate and texture). Two series or chronosequences were found by selecting, within the same location, two fields abandoned for different durations. In another two sites, more than one actively managed plot was selected for the same abandoned plot. The pairing of actively managed and abandoned fields resulted in a final number of 30 pairs (Fig. 1). The climatic conditions are subhumid Mediterranean, with rainfall from 790 to 930 mm and a mean annual temperature between 16.2[degrees]C and 19.6[degrees]C. Olive orchards are, on average, ploughed three times a year before the first rain (October), when the rain stops and the soil becomes workable (November) and in June (Abou Zeid 2007).
The duration of abandonment (years) was obtained through interviews with the landowners or neighbouring farmers. This information was checked against the vegetation colonising the fields. Five plots were characterised by the presence of perennial herbaceous species, whereas shrubs, such as Spartium junceum, Calicotome villosa and Ricinus sp., were found in 12 plots. In plots abandoned for over two decades, small trees (e.g. Pistachio palaestina) had developed (eight plots). The field surface, the number of trees and the canopy cover were obtained using Ikonos Images (Ikonos 2005; resolution: 1 m) and Google Earth Images (https://earth.google.com/, accessed 22 March 2010).
Soil sampling and bulk density
The studied fields belonged to seven soil classes, namely Cambisols (13 pairs), Regosols (six pairs), Luvisols (five pairs), Fluvisols (two pairs), Vertisol, Anthrosol, Calcisol and Arenosol (one pair each). From each field, three subsamples were collected from two positions: (1) a tree area or crown area; and (2) between trees (Fig. 2). In addition, samples were collected at two depths (0-10 cm and 10-30 cm). The number of subsamples was based on the European Union recommendation for soil sampling, where the number of soil samples should be three if the plot area is smaller than 5 ha (Stolbovoy et al. 2007). Soil bulk density was established with the soil pit (or excavation) method. To this end, one pit (20 x 20 x 20 cm), selected in the between-tree area, was dug in each field. All contents of the pit were collected and its volume was determined by inserting a plastic bag in the pit and determining the volume of water needed to fill it. The excavated contents of the pit were separated manually into coarse (>2 mm) and fine earth. The mass of the fine soil was recorded after oven drying samples at 105[degrees]C. The hybrid bulk density (hybridBD) was calculated as the dry mass of the fine fraction divided by pit volume (Throop et al. 2012).
Soil particle size and calcium carbonate
Soil texture was determined using the pipette method in order to obtain five fractions. In samples containing >1.16% of organic carbon (Metay 2006), the organic matter was destroyed by repeated treatments with hydrogen peroxide (30%). Prior to the dispersion of particles, the sample was soaked overnight with sodium hexametaphosphate (50 g [L.sup.-1]) for moderately calcareous soils or with sodium hexametaphosphate (40 g [L.sup.-1]) plus sodium carbonate (10 g [L.sup.-1]) for strongly calcareous soils (Ryan et al. 2001). After dispersion, aliquots were removed with the pipette after 5 min (fine silt and clay) and 4h (clay). Fine and coarse sands were separated by sieving. The predominant textural class was clay (22 pairs), followed by clay loam (three pairs), sandy clay, silty clay loam (two pairs each), silty loam and loam (one pair each). The soil calcium carbonate (CaC[O.sub.3]) content was determined by titrimetry with HC1 (Ryan et al. 2001). Fifteen pairs were strongly calcareous (CaC[O.sub.3] 25%-50%), seven pairs were moderately calcareous (CaC[O.sub.3] 5%-25%), five pairs were non-calcareous (CaC[O.sub.3] <5%) and three pairs highly calcareous (CaC[O.sub.3] >50%).
Soil organic carbon
For analysis of SOC, a soil subsample was fully ground to pass through a 0.5-mm mesh. The soil was treated with a mixture of concentrated sulfuric acid (15 mL) and potassium dichromate (10mL), heated to 150[degrees]C for 30min (Tiessen and Moir 1993). After cooling, 50 mL of water and 5mL of phosphoric acid were added to the mixture. Excess dichromate was titrated with ferrous ammonium sulfate in the presence of o-phenanthroline as an indicator. The SOC densities were classified in four classes instead of the three classes used for south Australian soils (Baldock and Skjemstad 1999). To the low (<12.2 g [kg.sup.-1]), moderate (12.2-19.7g [kg.sup.-1]) and high (19.7-30g [kg.sup.-1]) classes, a very high class (>30g [kg.sup.-1]) was added. Stocks of SOC (Mg [ha.sup.-1]) were calculated as follows:
Stock = OC (Mg C per Mg soil) x hybridBD (Mg [m.sup.-3]) x soil depth (m)
where OC is organic carbon. The absolute stock changes were calculated as the difference between each pair of plots:
[DELTA]Stock (Mg [ha.sup.-1]) = [Stock.sub.abandoned] - [Stock.sub.control]
Particulate organic matter
In addition to SOC density in bulk soil, the SOC content in the silt and clay fractions was determined in the between-trees samples. First, soil samples (14 pairs) from the 0-0.3 m depth were suspended in water (20 g in 100 mL), then dispersed using an ultrasound disperser (Cole Palmer ultrasonic process) at 25 J [s.sup.-1] for 4 min. Second, samples (10 pairs) from the 0-0.1 m depth were dispersed in sodium hexametaphosphate (5 g [L.sup.-1]) by shaking for 16 h on a reciprocal shaker at 250 r.p.m. (Cao et al. 2011). Dispersed samples were passed through a 50-pin sieve to quantitatively separate the sand particles from the silt and clay (Cambardella and Elliot 1992). After drying at 60[degrees]C, the extracts were weighed and then thoroughly mixed in a mortar. Samples with a mass recovery of 100 [+ or -] 5% were considered acceptable. The [OC.sub.silt+clay] (< 50 [micro]m) content was determined using the same method as for bulk soil.
Carbon contents were compared by analysis of variance (ANOVA), using SigmaStat 3.5 for Windows 2006 (Systat Software Inc., San Jose, CA, USA). The effects of depth and management were tested first using two-way ANOVA. Then, the effect of field position (crown area vs between trees) was evaluated by one-way ANOVA. Mean values of stocks were compared for significant differences using confidence intervals.
Abandonment may be caused by the small size of the fields, thereby promoting their neglect. This hypothesis was rejected because the average size of the abandoned plot (1564 [m.sup.2]) was slightly larger than that of the control plot (1345 [m.sup.2]). Therefore, abandonment was not related to the marginal position and size of the terraced fields, but could be due to the rural exodus following the war and to the low profitability of olive production. The number of trees and the crown area were also determined, as a further expression of field status. The mean number of trees was significantly greater in the control compared with abandoned fields (Table 1) because of the rejuvenation of the orchards. However, there was no significant difference in the canopy area (% of field area) between the control and abandoned plots, so the decrease in the number of trees in the abandoned plots was compensated for by larger individual trees.
Land management can significantly affect some soil physical properties. In north-east Spain, SOM bulk density decreased with an increase in the duration of land abandonment (Dunjo et al. 2003). In the present study, mean ([+ or -] s.d.) hybridBD was 1.04 [+ or -] 0.19 g [cm.sup.-3] in the abandoned fields, compared with and 1.05 [+ or -] 0.22 g [cm.sup.-3] in the control plots. This physical variable was not affected by site history, as demonstrated by similar slopes for the regression lines (Fig. 3). As stoniness increased, the hybridBD decreased in both plots.
Soil organic carbon
SOC content was determined separately in two field positions (crown area and between trees) and for two depths. Values of SOC were high, ranging between 19.7 and 30g [kg.sup.-1] soil. Within each field position (crown area/between tree area), the upper soil (0-0.1 m) had a higher SOC than the deeper soil layer (0.1-0.3 m) (Table 2). Significantly higher carbon content was found in the crown area (27.31 g [kg.sup.-1] soil) than in the open space between trees (22.59 g [kg.sup.-1] soil). This spatial variability could be linked to the small tree coverage (<28% of the field surface) in these orchards. In contrast, in lower Saxony (Germany), a 55-year-old pine stand with 76% cover exhibited low spatial variation in needle litterfall and C stocks (Penne et al. 2010).
The abandonment had a positive effect on SOC in the upper soil (Fig. 4), which suggests pedoturbation in the actively managed plots. In order to check whether the fine soil fractions affected carbon content, SOC was plotted against the clay and the fine silt plus clay (< 20 [micro]m) content. The slopes of the linear regressions for clay ranged from 11% ([Control.sub.0-0.1m]) to 22% ([Abandoned.sub.0-0.1m]), whereas only the latter had a significant correlation coefficient (Table 3). In addition, to test the effect of abandonment on SOC, the mineral-associated OC (< 50 [micro]m) was separated from the POM (50-2000 [micro]m). Linear relationships were found between the SOC in the bulk soil (< 2000 [micro]m) and that in the silt and clay fractions (Table 3). Slopes were close to 80% in three of the lines, but decreased to 70% in the abandoned plots, suggesting that 30% of the SOC was as POM.
Spatial variability of C stocks
SOC stocks were calculated separately in the crown area and in the between-tree area. When the whole field was considered, the variability in C stocks, expressed by CV, was close between the control and abandoned plots (CV 30% and 28%, respectively). However, within the crown area, C stocks represented 23.4% (CV 55%) in the abandoned plots and 27.6% (CV 37%) in the control plots. The greater variability in the abandoned fields was a reflection of their heterogeneity, caused essentially by an absence of soil disturbance for different periods of time. The C stocks of two neighbouring plots, abandoned for the same duration, had a CV of 11.5%, compared with 4.5% for two neighbouring control plots. Therefore, a minimum variability of 5% could be expected between two actively managed plots, against some 11% in the case of two abandoned plots.
Sampling and analysing the crown area and between-tree area separately is a lengthy procedure. It could be more practical to aim for the most representative sampling strategy. This was tested by plotting the stocks on a per field basis (crown area and between-tree area) against those between-tree areas. Linear relationships, with slopes close to 1, were found in both treatments (Fig. 5). The high slopes (close to 1) and regression coefficients suggest that between-tree SOC would be sufficient to determine field C stocks. Sampling between trees excludes the need to have the area occupied by the crown area and reduces the number of soil samples analysed by half.
Dynamics of C stocks
As a result of abandonment, the C [stock.sub.0-0.3m] increased in 24 of 30 pairs (Fig. 6), with a [DELTA]Stock of + 18.6 Mg C [ha.sup.-1]. Comparing stocks in the abandoned fields against those in the actively managed plots gave a linear relationship (Fig. 7), with an intercept of 15 Mg C [ha.sup.-1], close to the above [DELTA]Stock.
Inversely, C stocks decreased in six of 30 pairs ([DELTA]Stock = -27.3 Mg C [ha.sup.-1]). This agrees with results reported in Catalonia (Spain), where one of six abandoned plots had smaller SOC than the cultivated field (Garcia et al. 2007). The stock decrease could be explained in three of six pairs (Fig. 7) by an excessively high C stock (>90 Mg C [ha.sup.-1]) in the control plots. This points to an abundant input of organic amendments leading to a significant build up of SOC, nearing C saturation.
The duration of abandonment affected C storage, because it reached 6.22 Mg C [ha.sup.-1] in the 0-0.1 m soil after 6-12 years and increased to 9.46 Mg C [ha.sup.-1] beyond two decades of abandonment. The increase in C storage was not linear because the build up increased by 52% as the time of abandonment doubled. The dynamic of SOC was further evaluated in two chronosequences with different soil classes and calcium carbonate content (Table 4). In Sequence 1, C accumulation ended with the first decade of abandonment (Table 4). After nearly three decades, the absolute stock increase was +12 Mg [ha.sup.-1] in the Vertisol and +28 Mg [ha.sup.-1] in the Cambisol. This corresponds to the results illustrated in Fig. 7, where the stock in the abandoned fields was linked to C levels in the actively managed fields. The relative stock increase was 39% in both sequences. When all 24 pairs were considered, the mean relative increase was 26% for plots abandoned for 6-12 years and 38% for those abandoned for over two decades.
SOC and land abandonment
In Lebanon, olive orchards are found on a variety of soil classes (Darwish 2006) reflecting the tolerance of olive trees to calcareous soils (Abou Zeid 2007). The high SOC (19.7-30 g [kg.sup.-1] soil) contents found in the present study agree with values found in six of nine soil type units occupied by olive trees described in Lebanon (Darwish 2006). However, no link could be established between the soil class of the fields and their SOC. This could be due to the small number of plots belonging to each class (e.g. five pairs of Luvisols) and to the considerable variability of Lebanese soils within each class because of the complex geomorphology and diversified microclimate (Darwish et al. 2009).
Land abandonment had a positive effect on the SOC in the upper soil, similar to results reported for the top 0.05-m of abandoned olive orchards in Catalonia, Spain (Garcia et al. 2007). A similar stratification was found in non-tilled annual crops and a rotation of annual and pasture crops in Uruguay (Salvo et al. 2010) and Spain (Alvaro-Fuentes et al. 2008; Castro et al. 2008), which confirms the mixing of the soil contents through ploughing in actively managed plots. Still, no soil physical or chemical properties were capable of explaining the difference between agriculturally active and abandoned fields in south-east Spain (Zomoza et al. 2009). In the present study, at best 22% of the changes in the SOC could be related to the clay content. In fact, at the decadal level, the clay content did not affect the SOC of arable lands converted to pastures in western Minnesota (McLauchlan 2006). Elsewhere, in Canada and China, the silt and clay of agricultural fields receiving manure, on a long-term basis, were not saturated with C (Feng et al. 2014). A recent interpretation was provided from New Zealand soils, where the surface area of mineral particles rather than their mass proportion was closely correlated with SOC (Beare et al. 2014).
Silt and clay content could affect the mineral-associated C pool but not POM. The light SOM fraction and the POM (>250 [micro]m), considered as unprotected SOM (Six et al. 2002), respond most to changes in land management. In Pianosa Island in Italy, SOC was restored after 10 years of abandonment but, because of its labile and intermediate properties, 40 years of recultivation would bring about a decrease in C (Vaccari et al. 2012). Two years of compost addition in a cereal-lentil succession were sufficient to increase the light fraction and the 53-500 [micro]m POM (Abdelrahman et al. 2012). After 21 years of afforestation, C content was negatively correlated with the clay fraction and positively correlated with the sand fraction (Kooch et al. 2012), suggesting that most of the acquired C was as POM.
Stocks of SOC
Stocks of SOC are more informative than absolute quantities for evaluating the potential of terrestrial ecosystems to offset a portion of the C[O.sub.2] emissions from human activities (Tan et al. 2007). Stocks could not be studied without the evaluation of soil bulk density (hybridBD). No significant change was found in hybridBD as a consequence of the abandonment in the present study. It was essentially the stoniness of the land that affected hybridBD, regardless of land management practices. The SOC was studied separately for the crown area and between-tree area. In contrast, as a result of abandonment, an increase in C stocks in the 0-0.3 m depth was found in 80% of studied pairs. The absolute changes depended closely on the C stock in the actively managed plots, similar to an analysis of experiments involving no-tillage or enhanced crop rotation, where a linear relationship was found between the initial and accumulated C (West and Post 2002).
Next to initial C stock, the duration of abandonment had an effect on stock levels. The increase in C stocks in the 0-0.2 m depth was 102.3 g C [m.sup.-2] [year.sup.-1] for the first decade of abandonment and 159.3 g C [m.sup.-2] [year.sup.-1] for two decades. Both values fell within the range of C increases under notillage experiments (West and Post 2002) but remained well below the C storage of 281.7 g C [m.sup.-2] [year.sup.-1] in Pianosa Island (Vaccari et al. 2012). Beyond 15-20 years of land use change, a C saturation may be reached and consequently the build up would cease (Six et al. 2002).
The rate of C sequestration, as a result of reforestation, is much slower than the rate of C loss after deforestation (Kirschbaum et al. 2013). The build up of SOC in terrestrial ecosystems seems well known, especially as a consequence of the abandonment of agricultural lands. Still, of all European regions, the Mediterranean is considered the most vulnerable to climate change (time period 1990-2080), with a particular negative effect of water shortage and increased forest fires (Schroter et al. 2005). Under these conditions, C sequestration through increased cover vegetation and sustainable practices should be even more of a priority.
Significantly higher carbon contents were found in the tree area than in the between-tree zones. Soil depth also had an effect on C content, with greater values on the surface. These results justify the sampling strategy adopted by separating each field into two zones and two depths. Still, sampling between trees could be highly representative (>90%) of the long-term field C status. Abandoned olive orchards showed higher SOC in the upper soil compared with actively managed plots. A significant vertical stratification ([SOC.sub.0-0.1m] > [SOC.sub.0.1.-0.3m]) was found in the abandoned plots only. Most of the pairs studied (24/30 pairs) showed an increase in C stocks, with a mean build up of 18.6 Mg Cha [ha.sup.-1]. The C storage was directly dependant on the initial C level in the control plots. By introducing sustainable practices, such as conservation agriculture, and assuming that 80% of the Lebanese olive orchards would be able to store C, this would, in the medium term, add up to 40 000 Mg C [year.sup.-1]. This could provide significant compensation for the C emitted through fires, energy production and transportation.
This work was funded by the Lebanese National Council for Scientific Research (CNRS). Engineer Roger Francis provided field assistance throughout the study.
Abdelrahman HM, Olk DC, Cocozza C, Ventrella D, Montemurro F, Miano T (2012) An integrated physical-chemical procedure to monitor soil organic carbon in short-term studies. In 14th International Congress of the European Confederation of Soil Sciences Societies, EUROSOIL 2012'. July 2012, Bari, Italy, p. 1619 [poster].
Abou Zeid M (2007) Baseline study for apples and olives in Lebanon. FAO and Italian Cooperation, Regional Integrated Pest Management Program in the Middle East, GTFS/REM/070/ITA.
Alvaro-Fuentes J, Lopez MV, Cantero-Martinez C, Arrue JL (2008) Tillage effects on soil organic carbon fractions in Mediterranean dryland agroecosystems. Soil Science Society of America Journal 72, 541-547. doi : 10.2136/sssaj2007.0164
Anonymous (2006) Draft GHG inventory report: energy. Lebanon's Second National Communication to the UN Framework Convention on Climate Change. Ministry of Environment, Beirut, Lebanon.
Baldock JA, Skjemstad JO (1999) Soil organic carbon/soil organic matter. In 'Soil analysis: an interpretation manual'. (Eds KL Peverill, LA Sparrow, DJ Reuter) pp. 159-170. (CSIRO Publishing: Melbourne)
Beare MH, McNeill SJ, Curtin D, Parfitt RL, Jones HS, Dodd MB, Sharp J (2014) Estimating the organic carbon stabilization capacity and saturation deficit of soils: a New Zealand case study. Biogeochemistry 120, 71-87. doi : 10.1007/s 10533-014-9982-1
Bhogal A, Chambers BJ, Whitmore AP, Powlson DS (2008) The effects of reduced tillage practices and other material additions on the carbon content of arable soils. Summary report for Delia, project SP0561. (Dept, for Environment, Food and Rural Affairs: UK)
Bonet A (2004) Secondary succession of semi-arid Mediterranean old-fields in south-eastern Spain: insights for conservation and restoration of degraded lands. Journal of Arid Environments 56, 213-233. doi : 10.1016/SO140-1963(03)00048-X
Cambardella CA, Elliot ET (1992) Particulate soil organic matter changes across a grassland cultivation sequence. Soil Science Society of America Journal 56, 777-783. doi: 10.2136/sssaj 1992.036159950056000300 17x
Cao X, Oik DC, Chappell M, Cambardella CA, Miller LF, Mao J (2011) Solid-state NMR analysis of soil organic matter fractions from integrated physical-chemical extraction. Soil Science Society of America Journal 75, 1374-1384. doi:10.2136/sssaj2010.0382
Castro J, Fernandez-Ondono E, Rodriguez C, Lallena AM, Sierra M, Aguilar J (2008) Effects of different olive-grove management systems on the organic carbon and nitrogen content of the soil in Jaen (Spain). Soil & Tillage Research 98, 56-67. doi: 10.1016/j.still.2007.10.002
Cerda A, Gonzalez Penaloza F, Santin C, Doerr SH (2012) Land abandonment, fire recurrence and soil carbon content in the Macizo del Caroig, Eastern Spain. Geophysical Research Abstracts 14, EGU2012-14331.
Cuesta B, Rey Benayas JM, Gallardo A, Villar-Salvador P, Gonzalez-Espinosa M (2012) Soil chemical properties in abandoned Mediterranean cropland after succession and oak reforestation. Acta Oecologica 38, 58-65. doi:10.1016/j.actao.2011.09.004
Darwish T (2006) 'Soil map of Lebanon 1 :50000.' Monograph series no. 4. (Lebanese National Council for Scientific Research: Beirut)
Daiwish T, AbouDaher M, Jomaa I, Atallah T (2009) Soil organic carbon stock estimation in Lebanese territories. In 10th International Meeting on Soils with Mediterranean Type of Climate'. 23-26 June 2009, Beirut, Lebanon. Abstract, pp. 112-117.
Ding G, Liu X, Herbert S, Novak J, Amarasiriwardena D, Xing B (2006) Effect of cover crop management on soil organic matter. Geoderma 130, 229-239. doi: 10.1016/j.geoderma.2005.01.019
Dunjo G, Pardini G, Gispert M (2003) Land use change effects on abandoned terraced soils in a Mediterranean catchment, NE Spain. Catena 52, 23-37. doi: 10.1016/S0341-8162(02)00148-0
Feng W, Xu M, Fan M, Malhi SS, Schoenau JJ, Six J, Plante AF (2014) Testing for soil carbon saturation behavior in agricultural soils receiving long-term manure amendments. Canadian Journal of Soil Science 94, 281 -294. doi: 10.4141 /cjss2013-012
Food and Agriculture Organization of the United Nations (FAO) (2005) 'Drought resistant soils: optimization of soil moisture for sustainable plant production.' (FAO: Rome)
Garcia H, Tarrason D, Mayol M, Male-Bascompte N, Riba M (2007) Patterns of variability in soil properties and vegetation cover following abandonment of olive groves in Catalonia (NE Spain). Acta Oecologica 31, 316-324. doi:10.1016/j.actao.2007.01.001
Guo LB, Gifford RM (2002) Soil carbon stocks and land use change: a meta analysis. Global Change Biology 8, 345-360. doi: 10.1046/j. 1354-1013. 2002.00486.x
Ikonos (2005) Images of June 2005, 8m pan sharp. Ministry of Administrative Reforms. Lebanon.
Jarvis P, Rey A, Petsikos C, Wingate L, Rayment M, Pereira J, Banza J, David J, Miglietta F, Borghetti M, Manca G, Valentini R (2007) Drying and wetting of Mediterranean soils stimulates decomposition and carbon dioxide emission: the 'Birch effect'. Tree Physiology 27, 929-940. doi: 10.1093/treephys/27.7.929
Kirschbaum MUF, Saggar S, Tate KR, Thakur KP, Giltrap DL (2013) Quantifying the climate-change consequences of shifting land use between forest and agriculture. The Science of the Total Environment 465, 314-324. doi:10.1016/j.scitotenv.2013.01.026
Kooch Y, Hosseini SM, Zaccone C, Jalilvand H, Hojjati SM (2012) Soil organic carbon sequestration as affected by afforestation: the Darab Kola forest (north of Iran) case study. Journal of Environmental Monitoring 14, 2438-2446. doi:10.l039/c2em30410d
Masri T, Khawlie M, Faour G (2002) Land change cover over the last 40 years in Lebanon. Lebanese Science Journal 3, 17-28.
McLauchlan KK (2006) Effects of soil texture on soil carbon and nitrogen dynamics after cessation of agriculture. Geoderma 136, 289-299. doi: 10.1016/j.geoderma.2006.03.053
Metay A (2006) Carbon sequestration and greenhouse effect gases fluxes: comparison between no-tillage system and conventional system in the Brasilian Cerrados. PhD Thesis, Institut National Agronomique Paris-Grignon, France.
Ministry of Agriculture (2012) Resultats globaux du module de base du recensement de l'agriculture 2010. Draft final--February 2012. Ministry of Agriculture, Lebanon.
Owens LB (2004) To plow or not to plow? Balancing slug populations with environmental concerns and soil health. USDA-ARS Online Magazine 52. Available at: http://agresearchmag.ars.usda.gov/2004/oct/plow/(accessed 14 August 2015)
Penne C, Ahrends B, Deurer M, Bottcher J (2010) The impact of canopy structure on the spatial variability in forest floor carbon stocks. Geoderma 158, 282-297. doi:10.1016/j.geoderma.2010.05.007
Romanya J, Rovira P, Duguy B, Vallejo R, Rubio A (2007) C sequestration issues in the Mediterranean soils. Greenhouse-gas budget of soils under changing climate and land use (BumOut). Cost 639. 2006-2010. pp. 15-22. www.Bfw.ac.at/010/pdf/Act_639/J_ROMANYA.pdf
Ryan J, Estefan G, Rashid A (2001) 'Soil and plant analysis laboratory manual.' 2nd edn. (ICARDA: Aleppo, Syria)
Salvo L, Hernandez J, Ernst O (2010) Distribution of soil organic carbon in different size fractions, under pasture and crop rotations with conventional tillage and no-till systems. Soil & Tillage Research 109, 116-122. doi: 10.1016/j.still,2010.05.008
Schroter D, Cramer W, Leemans R, Prentice C, Araujo M, Arnell N, Bondeau A, Bugmann H, Carter TR, Gracia CA, de la Vega-Leinert AC, Erhard M, Ewert F, Glendining M, House JI, Kankaapaa S, Klein R, Lavorel S, Lindner M, Metzger MJ, Meyer J, Mitchell TD, Reginster I, Rounsevell M, Sabate S, Sitch S, Smith B, Smith J, Smith P, Sykes MT, Thonicke K, Thuiller W, Tuck G, Zaehle S, Zierl B (2005) Ecosystem service supply and vulnerability to global change in Europe. Science 310, 1333-1337. doi:10.1126/science.1115233
Six J, Conant RT, Paul EA, Paustian K (2002) Stabilization mechanisms of soil organic matter: implications for C-saturation of soils. Plant and Soil 241, 155-176. doi: 10.1023/A: 1016125726789
Stolbovoy V, Montanarella L, Filippi N, Jones A, Gallego J, Grassi G (2007) 'Soil sampling protocol to certify the changes of organic carbon stock in mineral soils of the European Union.' EUR 21576 EN/2. (Office for Official Publications of the European Communities: Luxembourg)
Tan Z, Liu S, Li Z, Loveland TR (2007) Simulated response of soil organic carbon stock to tillage management scenarios in the Northwest Great Plains. Carbon Balance and Management 2, 7. doi: 10.1186/1750-0680-2-7
Throop HL, Archer SR, Monger HC, Waltman S (2012) When bulk density methods matter: implications for estimating soil organic carbon pools in rocky soils. Journal of Arid Environments 77, 66-71. doi: 10.1016/j.jaridenv.2011.08.020
Tiessen H, Moir JO (1993) Total and organic carbon. In 'Soil sampling and methods of analysis'. (Ed. MR Carter) pp. 187-200. (Lewis Publishers and CRC Press)
Vaccari FP, Lugato E, Gioli B, D'Acqui L, Genesio L, Toscano P, Matese A, Miglietta F (2012) Land use change and soil organic carbon dynamics in Mediterranean agro-ecosystems: the case study of Pianosa Island. Geoderma 175-176, 29-36. doi:10.1016/j.geoderma.2012.01.021
Van Camp L, Bujjarabal B, Gentile AR, Jones RJA, Montanarella L, Olazabal C, Selvaradjou SK (2004) 'Reports of the technical working groups established under the thematic strategy for soil protection.' EUR 21319 EN/1. (Office for Official Publications of the European Communities: Luxemburg)
West TO, Post WM (2002) Soil organic carbon sequestration by tillage and crop rotation: a global data analysis. Soil Science Society of America Journal 66, 1930-1946. doi:10.2136/sssaj2002.1930
Zornoza R, Guerrero C, Mataix-Solera J, Scow KM, Arcenegui V, Mataix-Beneyto J (2009) Changes in soil microbial community structure following the abandonment of agricultural terraces in mountainous areas of Eastern Spain. Applied Soil Ecology 42, 315-323. doi: 10.1016/j.apsoil.2009.05.011
T. Atallah (A,C), K. Sitt (A), E. El Asmar (A), S. Bitar (A), L. Ibrahim (A), M. N. Khatib (A), T. Darwish (B)
(A) Faculty of Agricultural Sciences, Lebanese University, Ras-Dekwaneh, Lebanon.
(B) Center for Remote Sensing, Lebanese National Council for Scientific Research, Mansourieh, Lebanon.
(C) Corresponding author. Email: email@example.com
Table 1. Number of trees, canopy area and the between-trees area in abandoned plots and their nested controls Data show the mean [+ or -] confidence intervals. Within columns, values followed by different letters differ significantly (P<0.05) Treatment No. trees Canopy area (1000 [m.sup.-2]) ([m.sup.2] [tree.sup.-1]) Control 41.11 [+ or -]3.05a 5.45 [+ or -]0.71 Abandoned 27.97[+ or -]5.15b 8.65 [+ or -]2.92 Treatment Between-tree areas (% field area) Control 74.0 [+ or -]7.34 Abandoned 78.7 [+ or -]4.79 Table 2. Concentrations of soil organic carbon according to two soil depths (0-0.1 and 0.1-0.3 m) and two field positions Data are the mean [+ or -] s.d. Within columns, values followed by different lowercase letters differ significantly (P<0.05). Within rows, values followed by different uppercase letters differ significantly (P<0.05). The interaction depth x position was not significant Soil organic carbon (g kg Mean depth Canopy area Between tree area (m) Depth (m) 0-0.1 29.08 [+ or -] 9.40a 24.24 [+ or -] 6.67a 26.66a 0.1-0.3 25.54 [+ or -] 8.71b 20.93 [+ or -] 6.98b 23.24b Mean position 27.31 A 22.59B Table 3. Stocks of organic carbon in the soil (0-0.3 m) of two chronosequences or series formed by three plots each, abandoned for different periods of time Sequence and Soil Stock treatment (Mg C Class Clay CaC[0.sub.3] [ha.sup.-1]) (g (g [kg.sup.-1]) [kg.sup.-1]) Sequence 1 Control 70.74 Abandoned <10 years Calcaric 581 427 98.89 25 years Cambisol 99.00 Sequence 2 Control 31.39 Abandoned <10 years Luvic 676 103 37.63 30 years Vertisol 42.96 Table 4. Relationships between organic carbon (OC) in the silt + clay fractions (<50[micro]m; [OC.sub.sm+clay]) and bulk soils (<2000 [micro]m; [OC.sub.Bulk]), as well as between OC and fine particles (clay or clay + fine silt) in abandoned fields and the controls sampled between trees Correlation coefficients (r) in bold are significant at the 5% level Depth (m) 0-0.3 0-0.1 No. pairs 14 10 Treatment: Control [OC.sub.Silt+clay] = [OC.sub.silt+clay] = 0.804 x [OC.sub.Bulk], 0.807 X [OC.sub.Bulk], r=0.904# r=0.890# Abandoned [OC.sub.Silt+clay] = [OC.sub.silt+clay] = 0.811 X [OC.sub.Bulk], 0.700 X [OC.sub.Bulk], r=0.913# r=0.771# Depth (m) 0-0.1 No. pairs 24 27 Treatment: Control OC (g [kg.sup.-1]) = OC (g [kg.sup.-1]) = 0.11 x Clay (g [kg.sup.-1]) 0.15 (Clay + fine + 16.43, r=0.205 silt; g [kg.sup.-1]) + 11.7, r=0.295 Abandoned OC (g [kg.sup.-1]) = OC (g [kg.sup.-1]) = 0.22 x Clay (g [kg.sup.-1]) 0.21 (Clay + fine + 14.30, r=0.392# silt; g [kg.sup.-1]) + 11.2, r=0.378 Note: bold indicated with#.
|Printer friendly Cite/link Email Feedback|
|Author:||Atallah, T.; Sitt, K.; Asmar, E. El; Bitar, S.; Ibrahim, L.; Khatib, M.N.; Darwish, T.|
|Date:||Oct 1, 2015|
|Previous Article:||Assessment of the accuracy of profile available water and potential rooting depth estimates held within New Zealand's fundamental soil layers...|
|Next Article:||Assessment of the surface chemistry of wood-derived biochars using wet chemistry, Fourier transform infrared spectroscopy and X-ray photoelectron...|