Subscribe Now Subscribe Today
Research Article
 

Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia



N. Brahim, T. Gallali and M. Bernoux
 
Facebook Twitter Digg Reddit Linkedin StumbleUpon E-mail
ABSTRACT

Sub-humid and semi-arid zones comprise a land area of about approximately 1/3 of Tunisia, good agricultural soils and major organic carbon storage are situated in this region. The objective of this study is to investigate the organic carbon distribution and stocks in soils of this region under different land uses by using different investigations: (1) The conversion from natural forest to agricultural land caused significant loss of Soil Organic Carbon (SOC) stock, it induces a decrease of SOC stock with 19.33 t C ha-1, (2) however, restoring forestry after conversion from agricultural ecosystems to forest, we found an increase of SOC stock with 0.42 t C/ha/year, (3) soil carbon sinks increase most rapidly under practice of no-tillage compared with conventional tillage, no-tillage treatment was found to increase the storage of OC in the surface layer 0-20 cm compared to conventional tillage and (4) irrigation with saline water stock higher than irrigation with freshwater only at superficial layer. Although, under this depth, irrigation with freshwater and at total profile stock higher than saline water. SOC stock is 148.5 t ha-1 in the freshwaters irrigated soils against 139.6 t ha-1 in saline water irrigated soil.

Services
Related Articles in ASCI
Search in Google Scholar
View Citation
Report Citation

 
  How to cite this article:

N. Brahim, T. Gallali and M. Bernoux, 2009. Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia. Asian Journal of Agricultural Research, 3: 55-66.

DOI: 10.3923/ajar.2009.55.66

URL: https://scialert.net/abstract/?doi=ajar.2009.55.66
 

INTRODUCTION

Soil Organic Carbon (SOC) comprises a major stock in the world, comprised between 1500 and 2000 Pg C in the upper 100 cm (Eswaran et al., 1993; Batjes, 1996; IPCC, 2001) equivalent to almost three times the quantity stored in terrestrial biomass and twice the amount stored in the atmosphere, it plays an important role of the global carbon cycle and in regulating the atmospheric greenhouse gases concentration (Houghton, 2003; Smith et al., 2008). Globally, SOC level is dependent on vegetation (Jenny, 1980), which is principally controlled by climate. Arid lands cover 40% of the global terrestrial surface of the earth, but stock only 16% in the upper 100 cm from the global stock. As a result, changes in soil use and management can lead to changes in OC stocks (Lal, 1997; Six et al., 2002) and increases of greenhouse gas emissions in the atmosphere (Bernoux et al., 2001; IPCC, 2007). A good estimation and knowledge of carbon stocks in the soils has been suggested as a means to help mitigate the atmospheric CO2 increase and through which an anticipated change in climate (Kimble et al., 1990; Batjes and Sombroek, 1997; Batjes, 1999; Lal et al., 1998, 2000). Climate change has an appreciable influence on predicted global net irrigation water requirements: an increase of 409 Gm3 by 2080 (Fischer et al., 2006). The impact of climate change will however differ for different parts of the world. In the Mediterranean regions, the combination of low rainfall and high temperature could lead to high evapotranspiration losses and exacerbate water stress for crops. The reduction in availability of good quality water for irrigation would increase the use of saline water, thereby accentuating salinity problems in the region (Vlek et al., 2008). Extensive research has been undertaken on the physicochemical properties of saline and sodic soils and their amelioration, particularly with regard to soil structure and vegetation health (Gallali, 1980; Bramely et al., 2003; Gardner, 2004; Valzano et al., 2001). However, the effects of salinity and sodicity on carbon dynamics, with respect to carbon accumulation from soils, are not as well documented or understood. Incorporation of OM notably in the form of crop residues has been shown to improve soil aggregation and increase SOC stocks (Lal et al., 1999). In sodic or saline soils, gypsum (CaSO4.2H2O) is the most commonly used ameliorant to maintain soil electrolyte levels for improving soil physical and hydraulic properties (Keren, 1996).

The elaboration of map of SOC density in Tunisia, by Brahim et al. (2009), shows that soils have different influences on the OC distribution, depending of the geographical localization and land use. SOC is very spatially variable at the scale of the map. This could have been easily anticipated, given the large spatial heterogeneity of climate and geology, which determine the storage of organic carbon in soils. In order to appreciate the geographical distribution of SOC densities and its pattern, we study in this paper OC sequestration by major land use in Tunisia. Changes in carbon stocks were investigated by measuring the soil carbon stocks in 4 sites with different land-use: (1) the site of Tabarka with a conversion from natural forest to agricultural ecosystems, (2) the site of Siliana a conversion from agricultural ecosystems to forest, (3) the site of Le Kef where we examine the soil organic carbon stock under conventional tillage and no-tillage practices and (4) in the site of alluvial plain of the Medjerda Valley we study the effect of salinity and saline soils.

The objective of this study is to assess and give consistent values of carbon stocks under diverse land-use and the effect of salinity in existing saline soils from carbon sequestration in Tunisia.

MATERIALS AND METHODS

Study Area and Site Descriptions
Tunisia (164.000 km2) situated in North Africa and south of Mediterranean Sea. The study area included regions of northern Tunisia. The area is located between the latitudes of approximately 32 and 34°N and between longitudes approximately 8 and 12°E (Fig. 1). The region is bordered on the north and east by the sea, on the west by Algeria and on the south by the Dorsale Mountain. The Medjerda River represents the major water stream running through the agricultural plains of the region. The region is further characterized by a Mediterranean climate which has a rapidly increasing north to south aridity gradient and two distinct climatic zones: (1) extreme northern region is humid, the annual rainfall is usually between 1200 mm and average temperatures is 17.1°C, natural forests in this region are mainly dominated by three species Quercus suber, Quercus faginea and Pinus pinaster, (2) Northern region is semi-arid, the annual rainfall is usually comprised between 380 and 600 mm and average temperatures is 18.7°C natural forests in this region are largely dominated by Olea europea and Pistacia lentiscus.


Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 1: Map of location of Tunisia and studies sites. 1: Tabarka, 2: Siliana, 3: Le Kef and 4: Alluvial plain of the Medjerda Valley

This Research Was Carried out in Four Experimental Sites

The site of Tabarka is located at humid zone; first, the effect of conversion from natural forest to agricultural ecosystems from carbon stock at experimental field adjacent at forest was studied. The conversion from forest was started from 1960. The site is characterized by a humid climate with a mean annual precipitation of 1000 mm (mainly during the winter) and an average temperature of 18°C. Soil with CPCS classification is called Sol brun lessivé à mull and with FAO-UNESCO (1974) classification Podzoluvisol, with a pH = 6.8 and sandy texture (clay = 20%; silt = 20%; sand = 60%). Tabarka designed at this study T where, T1 (15 ha) is the field plot situated at the forest and T2 (15 ha) is the field plot under agricultural parcel. A toposequence method was used as described by Manlay et al. (2002) for all the sites included in the current study. It is worth noting that the material transfer in the toposequence semi-arid soil is insignificant (Gallali, 1980, 2004)
The site of Siliana is located at semi-arid zone in an artificial park started from 1980. This site is characterized by a semi-arid climate with a mean annual precipitation of 650 mm (mainly during the winter) and an average temperature of 22°C. Soil with CPCS classification is called Sol brun calcaire and with FAO-UNESCO (1974) classification Cambisol, with pH = 7.6 and a loamy-sandy texture (clay = 21%; silt = 36%; sand = 43%). Siliana designed at this study S where, S1 (15 ha) is the field plot under agricultural parcel and S2 (15 ha) is the field plot situated at forest
The field experiment from Le Kef was started from 2000. This site is characterized by a semi-arid climate with a mean annual precipitation of 500 mm (mainly during the winter) and an average temperature of 22°C. According to the CPCS classification this soil is called Sol brun calcaire and with FAO (1974) classification is Cambisol, it is developed from alluvial sediments with a clayey-loamy texture (clay = 35.25%; silt = 32.75%; sand = 24%). Le Kef designed at this study K where, K1 (1 ha) is the field plot situated at the parcel with no-tillage (NT) practice and K2 (1 ha) is the field plot situated at parcel with conventional tillage (CT) practice
The site from the alluvial plain of the Medjerda Valley is located at semi-arid zone. The field experiment was started from 1985 in the experimental site of the Tunisian Ministry of Agriculture in Cherfech from the Medjerda Valley (20 km northwest of Tunis City). This site is characterized by a semi-arid climate with a mean annual precipitation of 500 mm (mainly during the winter) and an average temperature of 17.3°C. The field plot covered a total surface area of 12 ha. According to the CPCS classification this soil is called Sol peu évolué d’apport alluvial peu humifère and with FAO-UNESCO (1974) classification is Gleysols, it is developed from alluvial sediments with a clayey-loamy texture (clay = 37%; silt = 34%; sand = 28%, pH = 8.5 and CaCO3 = 63%). Cherfech designed at this study C where, C1 (5 ha) is the field plot irrigated with ordinary water (freshwater) (water A) and C2 (5 ha) is the field plot irrigated with saline water (water B)

Field Sampling and Laboratory Analysis
Samples were taken from 0-10, 10-20, 20-30 and 30-50 cm depths in each of the soil profiles from sites T, S and K. From site C, samples were taken from 0-20, 20-40, 40-80, 80-120 and 120-150 cm depths. The depths are different between the sites since data was collected from two different data bases (from Tunisian Ministry of Agriculture data base for C and from the data base of CORUS-2 project for T, S and K). Soils were sampled with a shovel from a soil pit at each depth interval. Soil pH was determined in water (1:1) soil-water extract. Organic Carbon (OC) of the soil fraction <2 mm by Walkley-Black method; clay content (particle 0-2 μm); silt (fine and coarse silt) content (2-50 μm); sand (fine and coarse sand) content (50-2000 μm); soil bulk density in weight per volume (Cylinder method) (Mg m-3), it was determined from oven dried cores at 105°C for 24 h; Electrical Conductivity (EC) (dS m-1) (Table 1); Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) are calculated with Eq. 1 and 2 below, respectively:

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
(1)

where, Na+, Ca2+ and Mg2+ are in meq L-1.

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
(2)

Table 1: Laboratory analysis
Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia

where, Naexch+, Caexch2+, Mgexch2+ and Kexch+ are the totals of exchangeable Na+, Ca2+, Mg2+ and K+ in meq/100 g soil.

Procedure for Determining the Individual SOC Stocks
The way of calculating SOC stocks for a given depth consists of summing SOC Stocks by layer determined as a product of Db, OC concentration and layer thickness (Eswaran et al., 1993; Batjes 1996; Bernoux et al., 2002). For an individual profile with n layers, we estimate the organic carbon stock by the following Eq. 3:

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
(3)

where, SOCs is the soil organic carbon stocks (kg C m-2), Dbi is the bulk density (g cm-3) of layer i, Ci is the proportion of organic carbon (g C g-1) in layer i, Di is the thickness of this layer (cm).

RESULTS AND DISCUSSION

SOC Stock after Conversion from Natural Forest to Agricultural Ecosystems
Land transformation causes reductions in organic carbon and other nutrients and the microbial properties. Thus a decrease in microbial biomass in soil may be expected (Cleveland et al., 2003). The conversion of forest into other land-uses resulted in a decrease in plant biomass (Srivastava and Singh, 1991). Conversion from forest to agricultural land strongly impacts soil nutrients and microbial biomass depending on the type of land-use change and the post conversion land management (Sharma et al., 2004). Decomposition of SOM is especially increased by physical disturbance with tillage, which disrupts macroaggregates and exposes previously protected soil to microbial processes (Cambardella and Elliott, 1992). The land-use change from forest to other usage has been conspicuous over the past two decades (Rai et al., 1994). The conversion of natural forest into open cropped area in north-western Tunisia has been effected since 1960. The SOC stock decline in the 0-30 cm for soil under forest to soil (T1) under agricultural systems (T2), 65.52 and 46.19 t C ha-1, respectively (Fig. 2). The conversion resulted in a decrease of SOC stock with 19.33 t C ha-1. This decrease is caused by annual tillage. The results suggest that conversion of forest land to agricultural systems affects soil organic matter. SOC stock may decline immediately following conversion; at this site we examine a decrease of ~30% of stock after ≈50 years.

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 2: Evolution of SOC stock after conversion from natural forest to agricultural ecosystems at Tabarka site (T)

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 3: Evolution of SOC stock after conversion from agricultural ecosystems to forest at Siliana site (S)

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 4: Soil organic carbon stock distribution after 7 years under no-tillage (K1) and conventional tillage (K2) treatments

SOC Stock after Conversion from Agricultural Ecosystems to Forest
From Siliana site we study the effect of conversion from agricultural systems to forest of Pinus halepensus, the conversion has been introduced since 1985. Compared with agricultural system soil (S1: 17.85 t C ha-1) at 0-30 cm depth SOC stock increases under forest soil (S2: 26.38 t C ha-1) (Fig. 3). The conversion resulted an increase of SOC stock with 0.42 t C ha/year. In this site an increase of 32% of stock after 20 years was detected. SOC stocks found in the present study as those found by Arrouays and Pelissier (1994).

SOC Stock under Conventional Tillage and No-tillage Practices
At conventional tillage (CT) treatment, soil was tilled with a disk. No tillage treatment (NT), with successive cover crops (generally cereals/maize). Crop residues are modest on the soil surface, additionally to the cover crops. We compare in this study in two sites, effect of two tillage treatments: conventional tillage (CT) site K2 and no tillage (NT) K1 on adjacent plots. By comparing the distribution of rates of soil OC in both K1 and K2 practices, we see very clearly that the level of OC at the K1 plot is higher than in K2 plot at 0-10 cm and for 10-20 cm portions. However, from 20 cm depth and up to 50 cm, the rate of soil C in the plot under K2 is higher than the plot with K1 (Fig. 4). Generally, when the two tillage treatments were compared at the end of the 7 years period, the amount of SOC in the 0-10 and 10-20 cm intervals was greater in NT than in CT. Accordingly, in the portion 0-10 cm, the plot K1 stores 18.06 t C ha-1, although the plot K2 stores 11.70 t C ha-1. After 7 years we calculated an increase in SOC stock at K1 plot with 6.46 t C ha-1 compared to K2 plot, so a rise of almost 35% from conventional tillage to no-till were an average of 0.90 t C ha/year. An increase of OC in the topsoil (0-10 cm) appropriate to this conservative farming technique has frequently been observed elsewhere, Franzluebbers et al. (1994), observed a significant increase in soil organic carbon under no-tillage compared with conventional tillage, only in the surface soil layers.

Table 2: Soil physicochemical properties at Cherfech site
Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
*Results in %, †Results in me/100 g of soil

Generally, Organic C was higher in NT than in CT. Hunt et al. (1996) and conventional tillage resulted in a significant reduction in organic matter in surface layer of soils (Ding et al., 2002).

SOC Stocks of Saline Soil
Soil salinity refers to a situation in which the presence of salts renders the soil sterile, whereas sodicity or alkalinity is caused by the specific effect of sodium ions adsorbed on clay particles. This leads to deflocculation of soil colloids and reduction of soil porosity (Gallali, 1980). Soil salinity results from natural and artificial causes; (1) the natural causes could be due to the influence of climate, morphology and geology, (2) whereas anthropogenic causes include saltwater intrusion, application of fertilizers and soil amendments and irrigation.

Soil Properties
Soil properties of the sample from Cherfech site are shown in Table 2. Soil has a fine texture; clayey-loamy. Soil bulk density (Db) values under the superficial layer (20 cm) were high and did not show a clear pattern with depth. The CaCO3 (total and active) was highest at the surface and showed a very little decrease at the deeper horizons. Gypsum (CaSO4.2H2O) concentrations at the superficial layer (0-20 cm) are 0%, but at deep horizons when upper limit >20 cm are comprised between 0.4 and 0.7%.

One other important measure of irrigation water quality is the sodium adsorption ratio (SAR), defined at Eq. 1. SAR is an indication of the activity of Na+ in exchange reactions. High alkalinity of irrigation water it manifested at pH greater than 8.5 indicates the predominance of sodium in the solution and the potential for soil sodicity. The SAR of the Cherfech soil was lowest at the surface and showed a general increase with depth (Fig. 5a).

In the surface layer 0-20 and 20-40 cm electrical conductivity (EC) is significantly low than depth layer and showed a general increase with total profile (Fig. 5b).

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 5: SAR, EC and ESP of the Cherfech site

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 6: Characteristics of water A and B used at Cherfech (C) experimental site

Generally, irrigation water with EC below 0.7 dS m-1 poses virtually no danger to crops, whereas values above 2 dS m-1 (Hao and Chang, 2003; Zheng et al., 2009) may markedly restrict crop growth.

The exchangeable sodium percentage (ESP) was lowest at 0-20 cm, it increase at 20-40 and showed a general decrease with depth (Fig. 5c).

Salt-affected soils classified as saline, sodic, or saline-sodic (Vlek et al., 2008). Saline when EC > 4 and ESP <15; sodic when EC < 4 and ESP > 15 and saline-sodic when EC > 4 and ESP > 15. Soil from Cherfech (C) is grouped in two types with depth; (1) from 0-40 cm the EC < 4 and ESP > 15% therefore soil is sodic; (2) from deep horizons when upper limit > 40 cm, EC > 4 et ESP > 15% thus soil is saline-sodic (Fig. 5c).

Water Characteristics
The quality of water applied during irrigation affects soil salinity and sodicity, acidity, nutrient availability, soil structure and crop yields. The salinity of irrigation water is the sum total of inorganic ions and molecules, the major components being Ca2+, Mg2+, Na+, Cl¯, SO42¯ and HCO3¯. From Cherfech site, C1 is the field plot irrigated with freshwater (water A) and C2 is the field plot irrigated with saline water (water B). At Fig. 6 we reported the quality of water A and B used at experimental plots C1 and C2, respectively.

Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
Fig. 7: Impact of irrigation with water from organic carbon content at C1 and C2

Table 3: Soil organic carbon stock under treatment with freshwater A (C1) and saline water B (C2)
Image for - Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia

Soil Organic Carbon
The results show that the organic carbon has different repartitions with depth under C1 and C2. This difference is caused by the irrigation water. Globally, organic carbon under two treatments have an identical allure and show a general decrease with depth (Fig. 7). At 0-50 cm the C2 field plot irrigated with saline water (B) has an organic carbon content higher than C1 irrigated with freshwater. However, after this depth (>50 cm) the organic carbon at C2 plot was lower than C1. Because soil organic carbon content is a function of the decomposition of soil organic matter and root respiration, low rates of respiration and degradation were found in the C2 soil.

Generally, results indicated an increase of organic carbon and nitrogen at surface layer from soil C2 irrigated with saline water (water B). But at the interior layer soil C1, irrigated with freshwater (water A), we find a bigger carbon content than those in C2 irrigated with water B.

Stocks
Irrigation with saline water stock higher than irrigation with freshwater only at superficial layer (20 to 40 cm). Although, under this depth, irrigation with freshwater stock higher than saline water. After twenty five years experiments, the organic matter balance carried out on 1.5 m soil depths is established as follows, organic carbon: 148.5 t ha-1 in the freshwaters irrigated soils against 139.6 t ha-1 in saline water irrigated soil (Table 3).

CONCLUSIONS

In Tunisia, globally and in the long run, SOC level is dependent on vegetation, which is largely controlled by climate. Soil carbon sequestration is a process under the control of human management. Generally, land-use change was found to have a larger net effect on SOC storage. Result of experiments showed that converting forest to agricultural systems caused significant loss of SOC stock (site T), whereas restoring forestry have an increase of SOC stock (site S). Soil carbon sinks increase most rapidly under practice of no-tillage compared with conventional tillage (site K). Experiments from site K, S and T showed that from superficial layer or total profile forest and no-tillage have an increase in SOC stocks. From site C, irrigation with saline water stock higher than irrigation with freshwater only at superficial layer. Although, under this depth, irrigation with freshwater and at total profile stock higher than saline water.

ACKNOWLEDGMENTS

This research was supported by CORUS-2 N°6112 Project: Séquestration du carbone et biodiversité dans les sols africains méditerranéens et leurs vulnérabilités aux changements climatiques.

REFERENCES

1:  Arrouays, D. and P. Pelissier, 1994. Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France. Plant Soil, 160: 215-223.
CrossRef  |  

2:  Batjes, N.H., 1996. Total carbon and nitrogen in the soils of the world. Eur. J. Soil Sci., 47: 151-163.
CrossRef  |  Direct Link  |  

3:  Batjes, N.H. and W.G. Sombroek, 1997. Possibilities for carbon sequestration in tropical and subtropical soils. Global Change Biol., 3: 161-173.
CrossRef  |  Direct Link  |  

4:  Batjes, N.H., 1999. Management options for reducing CO2 concentrations in the atmosphere by increasing carbon sequestration in the soil. NRP Report No. 410-200-031, Dutch National Research Programme on Global Air Pollution and Climate Change and Technical Paper 30, International Soil Reference and Information Centre, Wageningen, The Netherlands, pp: 1-114.

5:  Bernoux, M., M.C.S. Carvalho, B. Volkoff and C.C. Cerri, 2001. CO2 emission from mineral soils following land-cover change in Brazil. Global Change Biol., 7: 779-787.
CrossRef  |  

6:  Bernoux, M., M.D.S. Carvalho, B. Volkoff and C.C. Cerri, 2002. Brazils soil carbon stocks. Soil Sci. Soc. Am. J., 66: 888-896.

7:  Brahim, N., T. Gallali, D. Blavet and M. Bernoux, 2009. Soil organic carbon stocks at Tunisia scale for different soil types. Proceedings of the 10th International Meeting on Soils with Mediterranean Type of Climate, June 22-26, Beyrout-Liban, pp: 107-111

8:  Bramely, H., J. Hutson and S.D. Tyerman, 2003. Floodwater infiltration through root channels on sodic clay floodplain and the influence on a local tree species Eucaluptus largiflorens. Plant Soil, 253: 275-286.
CrossRef  |  

9:  Cleveland, C.C., A.R. Townsend, S.K. Schmidt and B.C. Constance, 2003. Soil microbial dynamics and biogeochemistry in tropical forests and pastures, Southwestern Costa Rica. Ecol. Appl., 13: 314-326.
CrossRef  |  

10:  Cambardella, C.A. and E.T. Elliott, 1992. Particulate organic matter changes across a grassland cultivation sequence. Soil Sci. Soc. Am. J., 56: 777-783.

11:  Ding, G., J.M. Novak, D. Amarasiriwardena, P.G. Hunt and B. Xing, 2002. Soil organic matter characteristics as affected by tillage management. Soil Sci. Soc. Am. J., 66: 421-429.

12:  Eswaran, H., E. van den Berg and P. Reich, 1993. Organic carbon in soils of the world. Soil Sci. Soc. Am. J., 57: 192-194.
Direct Link  |  

13:  FAO, 1974. Soil Map of the World 1: 5,000,000. Vol. 1, FAO, Unesco, Paris, pp: 59

14:  FAO, 1985. Water Quality for Agriculture. Food and Agriculture Organization, Rome, Italy

15:  Fischer, G., F.N. Tubiello, H. Van Velthuizen and D.A. Wiberg, 2006. Climate change impacts on irrigation water requirements: Effects of mitigation, 1990-2080. Technol. Forecast Social Change, 74: 1083-1107.
CrossRef  |  

16:  Franzluebbers, A.J., F.M. Hons and Z.A. Zuberer, 1994. Long-term changes in soil carbon and nitrogen pools in wheat management systems. Soil Sci. Soc. Am. J., 58: 1639-1645.

17:  Gallali, T., 1980. Transfert sels-matiere organique en zones arides mediterraneennes. These d'Etat INPL.

18:  Gallali, T., 2004. Cles du Sol. Centre de Publication Universitaire, USA., pp:366

19:  Gardner, W.K., 2004. Changes in soil irrigated with saline groundwater containing excess bicarbonate. Aust. J. Soil Res., 42: 825-831.

20:  Hao, X. and C. Chang, 2003. Does long-term heavy cattle manure applications increase salinity of a clay loam soil in semi-arid Southern Alberta? Agric. Ecosyst. Environ., 94: 89-103.
Direct Link  |  

21:  Houghton, R.A., 2003. Why are estimates of the terrestrial carbon balance so different. Glob. Change Biol., 9: 500-509.
CrossRef  |  

22:  Hunt, P.G., D.L. Karlen, T.A. Matheny and V.L. Quisenberry, 1996. Changes in carbon content of a Norfolk loamy sand after 14 years of conservation or conventional tillage. J. Soil Water Conserv., 51: 255-258.

23:  IPCC, 2001. Good practice guidance and uncertainty management in national greenhouse gas inventories. Institute for Global Environmental Strategies (IGES) for the IPCC, Hayama (JP).

24:  IPCC., 2007. Summary for policymakers. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.

25:  Jenny, H., 1980. The Soil Resource: Origin and Behaviour. Springer-Verlag, New York, pp: 377

26:  Kimble, J.M., H. Eswaran and T. Cook, 1990. Organic carbon on a volume basis in tropical and temperate soils. Tran. Int. Congr. Soil Sci., 5: 248-253.

27:  Keren, R., 1996. Reclamation of Sodic-Affected Soils. In: Soil Erosion, Conservation and Rehabilitation, Agassi, M. (Ed.). Marcel Dekker, New York, pp: 353-374

28:  Lal, R., 1997. Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2-enrichment. Soil Till. Res., 43: 81-107.
CrossRef  |  

29:  Lal, R., J.M. Kimble, R.F. Follett and C.V. Cole, 1998. The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect. Ann Arbor Press, Chelsea, MI, USA., pp: 128

30:  Lal, R., R.F. Follet, J. Kimble and C.V. Cole, 1999. Managing U.S. cropland to sequester carbon in soil. J. Soil Water Conserv., 54: 374-381.

31:  Lal, R., M. Ahmadi and R.M. Bajracharya, 2000. Erosional impacts on soil properties and corn yield on Alfisols in central Ohio. Land Degrad. Dev., 11: 575-585.
CrossRef  |  

32:  Manlay, R.J., M. Kaire, D. Masse, J.L. Chotte, G. Ciornei and C. Floret, 2002. Carbon, nitrogen and phosphorus allocation in agro-ecosystems of a West African savanna: I. The plant component under semi-permanent cultivation. Agric. Ecosyst. Environ., 88: 215-232.
CrossRef  |  Direct Link  |  

33:  Rai, S.C., E. Sharma and R.C. Sundriyal, 1994. Conservation in Sikkim Himalaya: Traditional knowledge and land-use of the Mamlay watershed. Environ. Conserv., 21: 30-34.
CrossRef  |  

34:  Sharma, P., S.C. Rai, R. Sharma and E. Sharma, 2004. Effects of land-use change on soil microbial C, N and P in a Himalayan watershed. Pedobiologia, 48: 83-92.
CrossRef  |  

35:  Six, J., C. Feller, K. Denef, S.M. Ogle, J.C. de Moraes Sa and A. Albrecht, 2002. Soil organic matter, biota and aggregation in temperate and tropical soils-effects of no-tillage. Agronomie, 22: 755-775.
CrossRef  |  Direct Link  |  

36:  Smith, P., H. Janzen, D. Martino, Z. Zucong and P. Kumar et al., 2008. Greenhouse gas mitigation in agriculture. Philos. Trans. R. Soc., 363: 789-813.
CrossRef  |  

37:  Srivastava, S.C. and J.S. Singh, 1991. Microbial C, N and P in dry tropical forest soils: Effect of alternate land-uses and nutrient flux. Soil Biol. Biochem., 23: 117-124.

38:  Valzano, F.P., R.S.B. Greene, B.W. Murphy, P. Rengasamy and S.D. Jarwal, 2001. Effects of gypsum and stubble retention on the chemical and physical properties of a sodic grey Vertosol in Western Victoria. Aust. J. Soil Res., 39: 1333-1347.
CrossRef  |  

39:  Vlek, P.L.G., D. Hillel and A.K. Braimoh, 2008. Soil Degradation Under Irrigation. In: Land Use and Soil Resources, Braimoh, A.K. and P.L.G. Vlek (Eds.). Springer Science, Dordrecht, pp: 101-119

40:  Zheng, Z., F. Zhang, F. Ma, X. Chai, Z. Zhu, J. Shi and S. Zhang, 2009. Spatiotemporal changes in soil salinity in a drip-irrigated field. Geoderma, 149: 243-248.
CrossRef  |  

©  2021 Science Alert. All Rights Reserved