Effects of Agronomic Practices on the Soil Carbon Storage Potential in Northern Tunisia
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.
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,
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.
||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,
||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
||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 dapport 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
where, Na+, Ca2+ and Mg2+ are in meq L-1.
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
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.
||Evolution of SOC stock after conversion from natural forest
to agricultural ecosystems at Tabarka site (T)
||Evolution of SOC stock after conversion from agricultural
ecosystems to forest at Siliana site (S)
||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.
||Soil physicochemical properties at Cherfech site
|*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 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.
||SAR, EC and ESP of the Cherfech site
||Characteristics of water A and B used at Cherfech (C) experimental
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
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,
||Impact of irrigation with water from organic carbon content
at C1 and C2
||Soil organic carbon stock under treatment with freshwater
A (C1) and saline water B (C2)
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.