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Cultivation Intensity in Relation toOrganic Matter and Related Properties ina Vertisol in Southern TurkeyJohn Ryan a , Selim Kapur b , Hayriye Ibrikci b & Murari Singh aa International Center for Agricultural Research in the Dry Areas ,Aleppo, Syriab Faculty of Agriculture , Cukurova University , Adana, TurkeyPublished online: 11 Jul 2011.

To cite this article: John Ryan , Selim Kapur , Hayriye Ibrikci & Murari Singh (2011) CultivationIntensity in Relation to Organic Matter and Related Properties in a Vertisol in Southern Turkey, Journalof Sustainable Agriculture, 35:6, 613-623, DOI: 10.1080/10440046.2011.586577

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Journal of Sustainable Agriculture, 35:613–623, 2011Copyright © Taylor & Francis Group, LLCISSN: 1044-0046 print/1540-7578 onlineDOI: 10.1080/10440046.2011.586577

Cultivation Intensity in Relation to OrganicMatter and Related Properties in a Vertisol

in Southern Turkey

JOHN RYAN,1 SELIM KAPUR,2 HAYRIYE IBRIKCI,2

and MURARI SINGH1

1International Center for Agricultural Research in the Dry Areas. Aleppo, Syria2Faculty of Agriculture, Cukurova University, Adana, Turkey

As most of the organic carbon (C) in the biosphere resides inthe soil in the form of soil organic matter (SOM), tillage prac-tices can potentially increase C losses to the atmosphere as carbondioxide, thus contributing to greenhouse gases that exacerbate cli-mate change. In the past century, conventional tillage, involvingplowing and secondary cultivation, has unwittingly decreased Cstocks in arable soils in North America, Europe, and Australia.The information on the effects of tillage on soil C and relatedproperties in the Mediterranean region is scant, with evidence ofresilience being even rarer. While long-term trials that directlymeasure tillage effects are rare in the Mediterranean, the alter-native is a retrospective based on soil management history. Inthis study of a Vertisol in southern Turkey, we sampled sectionsof a field that had been intensively cultivated for about 20 yearsand 40 years, as well as a section left undisturbed in native veg-etation for 14 years following years of conventional tillage. TheSOM and total nitrogen (N) values were inversely related to cul-tivation intensity or duration, while the highest values were fromthe uncultivated site. Labile biomass C and N values followed thesame trends with cultivation, whereas available P increased withcultivation time; in contrast, the percentage of water-stable aggre-gates decreased with cultivation duration. The study showed thatsuch clay soils show a high degree of resilience and can recoverin a relatively short time period if left uncultivated or in fallow.While preservation or set aside of arable crop land is not a viable

Address correspondence to Hayriye Ibrikci, Faculty of Agriculture, Cukurova University,Adana, 01330, Turkey. E-mail: hibrikci@cu.edu.tr

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option for farmers, reducing tillage intensity is feasible. The studysuggests that minimum tillage or no-till could promote resilienceand mitigate the adverse soil effects of conventional tillage thathave already occurred.

KEYWORDS carbon stocks, labile carbon and nitrogen, biomasscarbon and nitrogen, land use intensity, soil resilience, soilaggregate stability, Vertisols

INTRODUCTION

From the beginning of settled agriculture, crop production was dependenton soil tillage to prepare a favorable seed bed and control weeds. Whilefossil fuel-based intensive conventional tillage systems of the past centuryunderpinned high crop yields, few people realized that such drastic soil dis-turbance could have a negative side-effect, that is, mineralization of soilorganic matter (SOM) and the environmental factors that affect nutrientcycling processes, with attendant effects on nutrient reserves (Baker et al.,2007; Hendrix et al., 1992) and physical properties such as aggregate stabil-ity (Lipiec et al., 2006). Consequently, the subject of SOM and how it canbe influenced by management emerged as a major concern for agriculture(Lorenz and Lal, 2005), ushering in a consideration of sustainable land use(Altieri, 1995). At the global level, the extent to which soils influence climatethrough emission or sequestration of carbon (C), along with food security, isat the forefront of scientific endeavors in the field of agriculture, especiallyagronomy and soil science (Lal, 2007). The direction of change in soil prop-erties related to SOM hinge around tillage and soil and crop management.Some selected multi-year studies serve to illustrate the extent of such tillageand management influences.

In a 12-year trial of dryland systems in North Dakota, as tillage intensitydecreased from conventional till to minimum till to no-till, SOM increased(Halvorson et al., 2002). The fallow rotation reduced soil organic carbon(SOC) compared with other rotations, presumably due to mineralization.Tillage intensity also reduced bulk density. In an earlier related study inMontana (Aase and Pikul, 1998), SOC decreased by 0–4 kg per year withfallow, but the level of SOC was maintained by no-till. Observing a similareffect of tillage systems, Dou and Hons (2006) found that inter-particulateorganic C was proportionally more affected than total SOC. Not only wasreduced tillage shown to decrease C losses, but it also helped to restoresome of the depleted SOC pools (Mishra et al., 2010).

The relative change in SOC with tillage is influenced by several factors,including soil type. Other studies have shown that such trends occurred inresponse to tillage diversity (Al-Kaisi et al., 2005), especially rotations (Sainjiu

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Tillage and Soil Quality in Turkey 615

et al., 2006; West and Post, 2002). A 10-year study in Alabama clearly showedhigher SOC and N in no till systems to an extent influenced by the particularrotation (Wood et al., 1992). The effects of tillage intensity and duration onSOC have had parallel effects on total soil N as both are components of SOM(Campbell et al., 1997; Al-Kaisi et al., 2005). In recent years, studies havefocused on C and N fractions of SOM as possible more sensitive indicatorsof tillage effects than gross measurements of total C and N (Dou et al., 2007),and particular emphasis was given to the labile microbial biomass fraction(Granatstein et al., 1987; Salinas-Garcia et al., 1997).

While most studies in relation to tillage and soil properties emanatefrom the United States and Australia, some research has been done in therelatively harsh semi-arid environmental conditions of the Mediterraneanfocused on the impacts of tillage, notably in Spain, Tunisia, and to alesser extent in Syria. The Spanish studies showed that crop rotations couldsequester C to varying depths in a Vertisol (Lopez-Bellido et al., 2010), that“active” C was a more reliable indicator of tillage change (Meler et al.,2009) as was microbial biomass C (Madejon et al., 2009), and that conven-tional tillage had a negative effect on SOC (Sombrero and de Benito, 2010).However, one study showed that aggregate breakdown was more influencedby the type of tillage implement than tillage intensity (Alvaro-Fuentes et al.,2008). In a study from Tunisia, conventional tillage was shown to have themost serious effect on SOC (Brahim et al., 2009). Ryan et al. (2009a, b)showed that legume-based cereal rotations increased labile and biomass Cand N, though both fractions varied through the season, being influencedby both moisture and temperature.

Given the prevalence of conventional tillage throughout the fragilesemi-arid environment and the virtual absence of conservational tillage atthe farm level, we adopted an alternative approach to assessing SOM inresponse to tillage, using inferences from land area with different cultivationhistories. Thus, we examined soil C and N in plots with varying tillage his-tory on a Vertisol in southern Turkey, and compared its resilience using annon-cropped fallow field that had been set aside for 14 years.

MATERIALS AND METHODS

Experimental Site

The field chosen for this sampling was at the Experimental Farm of theFaculty of Agriculture at Cukurova University in Adana in the southerncoastal region of Turkey (Figure 1). The land area had been compulsorilyacquired from local farmers at the establishment of the University in 1971.Prior to that, it had been in low-input traditional cultivation that involvedplowing and harrowing using animal traction, farmyard manure and minimal

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FIGURE 1 Distribution of Vertisols in Turkey (adapted from Jones et al., 2005).

chemical fertilizer use, and manual weed control. One section of the field(1 ha) had been intensively managed since that time, with rainfed cerealsin the winter season (November to May) and irrigated crops in the sum-mer, mainly corn (Zea mays). An adjacent section (1 ha) has been similarlymanaged, but only for about 20 years. The tillage involved deep plowing(30 cm) followed by secondary tillage for both winter rainfed and summerirrigated crops. These treatments are designated 20 and 40 years, respec-tively. In 1996, another 1 ha section of the field was set aside to assesssoil resilience and botanical changes with time under non-cultivated fallowconditions.

Modal properties of the soil include: 8.0 pH; 30% calcium carbonate,120 cm soil depth, and 60% clay content. Being a typical Vertisol (Arikseries, Typic Haploxerert), the site was generally representative of such soilsdistributed throughout Turkey, constituting about 20% of the country’s totalland surface (Figure 1). The climate of the region is typically Mediterranean(Kassam, 1981), with a moist cool autumn–early summer season. The patternof rainfall and temperature is illustrated (Figure 2), with significant yearlyvariation around the mean of 600 mm. This rainfall is higher than in inlandTurkey and is well above most dryland areas of the Mediterranean region.

The cultivated plots were fertilized according to the local conventionalpractice without using manure. Compound NPK-fertilizers were applied inthe seedbed at rates of 172 kg N ha−1 and 24 kg P ha−1 for wheat and250 kg N ha−1 and 28 kg P ha−1 for maize. No pesticide was used. Themajor crops, wheat (Triticum aestivum L.) and maize were planted onceevery 2 to 3 years. The stubble of the wheat and maize was chopped andmixed with the soil, in contrast to the widespread practice in the regionof burning or clear-grazing by sheep. Thus, the system was conducive toincreasing the SOM content.

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Tillage and Soil Quality in Turkey 617

0

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Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.Months

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FIGURE 2 Rainfall and temperature distribution.

Sampling

Each of the three field sections (about 1 ha each) was sampled with a spadeto a depth of 10 cm. About 30 random sub-samples were taken in a zigzagmanner and mixed in a basin to form a composite sample, from which asub-sample of about 1 kg was taken for analysis following air-drying in thelaboratory. This procedure was repeated to give three composite samples.In addition, each section was sampled with an auger to a depth of 85 cm in20 cm increments with sub-samples from 5–25 cm, 25–45 cm, 45–65 cm, and65–85 cm in order to establish a representative profile of SOM and total N ineach of the field areas. During the actual sampling, the top few centimetersof loose soil with plant debris was removed prior to augering, and thus, theincremental sampling effectively began at about 3–5 cm.

Analysis

The samples were analyzed for organic C using the standard Walkley andBlack procedure using a factor of 1.724 for SOM. Total soil N was mea-sured by the standard Kjeldahl method. Labile forms of C and N weremeasured after 16 h autoclaving (Vance et al., 1987) and biomass C and Nwere measured after fumigating (Brookes et al., 1985). Available P was mea-sured by the standard Olsen procedure. Water-stable aggregates from 2 mmsieved samples were measured by the hydrometer (Leo, 1963). In essence,this procedure involved assessment of particle size analysis (sand, silt, clay)with and without the use of Calgon (sodium hexametaphosphate) as a dis-persant, arriving at a unitless value for aggregate stability. All data wereanalyzed statistically, with treatment differences indicated by least significantdifferences (LSD).

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RESULTS

There were clear differences in soil C, either expressed as SOM or as labile orbiomass C fractions, in relation to cultivation history and intensity of cultiva-tion (Table 1). Thus, all three measurements were highest in the uncultivatedfallow field. With cultivation for 20 years, SOM and biomass C decreasedby about 30% and by 50% for the three C indices. Surprisingly, labile Cafter 20 years of cultivation was somewhat higher, but not significantlydifferent, than that of the uncultivated field that had reverted to regrowthof vegetation (weeds, grasses, legume species) from the soil seed bank.However, labile C values were significantly decreased with the longer tillageduration.

As total N is related to SOM, both parameters followed a similar pattern(Table 2). Total N values were highest under natural conditions and declinedsignificantly with cultivation intensity, with significant differences betweenall three treatments. However, labile N and biomass N only decreased inthe 40-year cultivation treatment. In the 20-year tillage treatment labile Nwas greater than and biomass N was equal to the treatment under naturalconditions.

Reflecting the trends for SOM and its fraction in relation to cultivationhistory, the indices of aggregate stability also showed significant changes

TABLE 1 Soil Organic Matter, and Labile and Biomass Carbon in the Cultivatedand Non-cultivated Areas1

Soil Labile BiomassCultivation organic carbon carbonhistory matter (%)2 (mg kg−1) (mg kg−1)

Non-cultivated (14 years) 3.12 1374.7 74.020 years 2.06 1437.3 48.940 years 1.40 777.3 34.4

1The numbers are the average of 3 replications.2LSD values at the 0.05 probability level are 0.883 for SOM, 360.8 for labile C and 26.2for biomass C.

TABLE 2 Forms of Nitrogen in Soil Samples from the Cultivated and Non-cultivated Areas1

Total Labile BiomassCultivation nitrogen2 nitrogen nitrogenhistory (mg kg−1) (mg kg−1) (mg kg−1)

Non-cultivated (14 years) 1439 147.0 6.820 years 1065 191.0 6.740 years 776 91.8 1.7

1The numbers are the average of 3 replications.2LSD values at the 0.05 probability level are 314.9 for total N, 45.3 for labile N and 5.3for biomass N.

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TABLE 3 Available Phosphorus and Aggregate Stability1

AvailablePhosphorus2 Aggregate

Cultivation history (mg kg−1) Stability3

Non-cultivated (14 years) 3.6 47.020 years 7.2 38.240 years 7.5 28.7

1The numbers are the average of 3 replications.2LSD values at the 0.05 probability level are 3.19 for available P, and8.450 (non-cultivated vs. 20 cm), 9.447 (20 vs. 40 years) and 9.447(non-cultivated vs. 40 years) for aggregate stability.3Non-dimensional index based on Leo (1963).

(Table 3). The uncultivated soil showed higher stability, but the declines inaggregate stability with cultivation were not as pronounced as they were forSOM and total N.

Available P is not a sensitive indicator of the influence of tillage since itis not lost to the atmosphere following mineralization, which occurs in thecase of SOM that is lost as CO2. However, it does reflect to some extent theinfluence of P fertilization that accompanies cultivation. Thus, the cultivatedsites had significantly higher levels of available P than the non-cultivated sitethat had no P input over the past 14 years.

As soil stratification is influenced by pedogenesis and management, theextent to which tillage affected profile distribution of SOM and total N isillustrated in Table 4. Notwithstanding differences in the top 5 to 25 cm, theoverall effect of cultivation was not significant, largely due to similar val-ues in the subsoil of the three profiles. Mean values for SOM in the entireprofile suggest that the two cultivated areas (20 and 40 years, respectively)

TABLE 4 Depthwise Distribution of Soil Organic Matter (SOM) and TotalNitrogen in the Three Experimental Sampling Areas

Non-cultivatedDepth (cm) (14 years) 20-year 40-year Mean

SOM (%)1

5–25 1.75 1.79 1.44 1.66a25–45 1.20 0.96 1.20 1.12b45–65 1.03 0.93 0.96 0.97b65–85 1.03 0.76 0.82 0.87bMean 1.25 1.11 1.11

Total N (mg kg−1)5–25 961 1007 874 947.3a

25–45 692 616 778 695.3b45–65 623 515 613 583.7b65–85 618 491 544 547.7bMean 723.5 654.8 702.2

1LSD values at the 0.05 probability level are 0.225 and 0.259 for the site and depth ofSOM and 120.0 and 138.6 for the site and depth of total N.

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had considerably less than the uncultivated site. While total profile N waslower in the two tillage treatments, differences with the non-cultivated treat-ment were not as accentuated as with SOM. However, overall mean valuesfor SOM and total N decreased with depth, with the top layer being sig-nificantly higher than the lower layers to 85 cm. The discrepancy betweenthe values for surface and profile samples is probably due to the fact thatsurface samples were collected from the 0 to 10 cm layer, while the top fewcm layer was removed prior to the augering.

DISCUSSION

Long-term agronomic trials are the only feasible means for assessing changesin soil management on soil properties (Johnston, 1997). With respect to theassessment of tillage systems, ideally one has to establish the experimentalvariables (tillage vs. non-tillage, or types of tillage) at the beginning ofthe experiment and subsequently monitor the effects of such treatments orthe independent variables, that is, soil properties or crop yields. However,as virtually no agronomic trials meet the definition of “long-term” in theMediterranean region (Ryan et al., 2008b), other approaches have to beadopted to assess tillage systems in relation to soil properties. Given theimportance of SOM for soil quality and the current societal concerns aboutC dynamics in relation to climate change (Lal, 2007), long-term trials thatwould take decades to provide answers to today’s urgent questions wouldbe untenable.

The approach we adopted was a retrospective one, relying on theexamination of adjacent field areas with different cultivation histories. Whileother studies from the region (Ryan et al., 2008a) showed that legume-basedrotation within cereal production systems could increase the SOM contentof the topsoil layer, we are unaware of any studies that deal with “set-aside” formerly cultivated land that has reverted to regrowth of vegetation.The decision to set aside this 1-ha area arose from a recommendation ofthe First International Land Degradation meeting in Adana (Kapur et al.,1996) where the issue of soil resilience (Greenland and Szabolitz, 1994) wasstressed, especially for Mediterranean climatic conditions. While recognizingthe fragility of soils under such environments, Lal (2002) indicated that dry-land areas of West Asia and North Africa with a Mediterranean continentalclimate could potentially sequester considerable amounts of C if managedappropriately.

These considerations let to action by the University to establish the “setaside” area in 1996 in order to subsequently examine soil chemical andbiological changes, as well as botanical composition and plant successionchanges. An earlier survey involving the second author (Ozbek et al., 1974)indicated that the mean soil SOM values were around 1.6%, with noneexceeding 2.0%. Given this information, it is reasonable to expect that prior

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Tillage and Soil Quality in Turkey 621

to the “set aside” in 1996, the baseline SOM values were about 1.6%, a valuethat is close to the present one of 1.4% after 40 years of cultivation.

The data of the study suggest that SOM will continue to decrease withyears of cultivation but at a slower rate. However, restoration to the uncul-tivated native state, involving naturally established vegetation, could restoreSOM levels that may approximate the equilibrium native state prior to culti-vation in the area that resulted in a doubling of SOM within a short periodof 14 years, thus showing considerable resilience. While total N followed thesame trend as SOM, it is unclear why the labile C and N fractions were notsignificantly reduced by cultivation for the shorter period, that is, 20 years.Nevertheless, the effect of the extended period of tillage was evident for allC and N fractions. While the SOM and N data generally followed observa-tions on tillage effects (e.g., Halvorson et al., 2002; Al-Kaisi et al., 2005), thedecreased index of aggregate stability coincided with one of the few studiesin the Mediterranean region that assessed aggregation and tillage (Alvaro-Fuentes et al., 2008). In contrast to such chemical and physical indicesrelated to tillage, available P increased with tillage due to relative P fer-tilization of dryland crops in the region and a gradual buildup of available P(Ryan et al., 2008c).

In conclusion, though the approach for assessing tillage effects on soilquality components in this study was unorthodox, it obviated the need forexpensive time-consuming long-term trials, which are rare in the MiddleEast. Despite the indirect approach adopted, the data presented indicated adecrease in soil quality indicators with tillage duration as well as a recoveryin soil quality after conventional tillage was ceased. Notwithstanding theunconventional approach to assessing soil SOM and its C and N fractions inresponse to cultivation, the data point to a considerable resilience in suchMediterranean environments to recover from man-made degradation. Whilesetting aside agricultural land under cultivation is not a practical option giventhe land-use pressures that exists in the region, it may be feasible to do sofor fragile rangelands that are currently being cultivated for barley (Hordeumvulgare). As tillage intensity, with accompanying soil disturbance, is theprimary cause of soil quality degradation, the data suggest that reducing suchdisturbance through minimum tillage would have positive effects in restoringsoil quality. In addition, rotations with green manures and cover crops thatare compatible with the cereal-based farming system in the Middle East canalso contribute to the maintenance or build up of organic matter in the soil.

REFERENCES

Aase, J.K., and J.L. Pikul, Jr, 1995. Crop and soil response to long-term tillage practicein the Northern Great Plains. Agronomy Journal 87: 652–656.

Altieri, M. 1995. Agroecology: The science of sustainable agriculture. Westview Press,Boulder, CO, USA.

Dow

nloa

ded

by [

Uni

vers

ity o

f C

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ibra

ry]

at 2

3:22

20

Nov

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14

622 J. Ryan et al.

Al-Kaisi, M.M., X. Yin, & A. Licht, 2005. Soil carbon and nitrogen changes asinfluenced by tillage and cropping systems in some Iowa soils. Agriculture,Ecosystems and Environment 105: 635–647.

Alvaro-Fuentes, J., J.L. Arue, C. Cantero-Matinez, and M.V. Lopez, 2008. Aggregatebreakdown during tillage in a Mediterranean loamy soil. Soil and TillageResearch 101: 62–68.

Baker, J.M., T.E. Ochsner, R.T. Venterea, & T.J. Griffis, 2007. Tillage and soil car-bon sequestration—What do we really know? Agriculture, Ecosystems andEnvironment 118: 1–5.

Brahim, N., T. Gallali, & M. Bernoux, 2009. Effects of agronomic practices on thesoil carbon storage potential in Northern Tunisia. Asian Journal of AgriculturalResearch 3: 55–66.

Campbell, C.A., B.G. McConkey, R.P. Zentner, F. Selles, & D. Curtin, 1997. Long-termeffects of tillage and crop rotations on soil organic C and total N in a clay soilin southwestern Saskatchewan. Canadian Journal of Soil Science 97: 395–401.

Dou, F., A.L. Wright, & F.M. Hons, 2008. Sensitivity of labile soil organic carbonto tillage in wheat-based cropping systems. Soil Science Society of America 72:1445–1453.

Granatstein, D.M., D.F. Bezdicek, V.L. Cochran, L.E. Elliott, & J. Hammel, 1987. Long-term tillage and rotation effects on soil microbial biomass, carbon and nitrogen.Biology and Fertility of Soils 5: 265–270.

Greenland, D. and I. Szabolitz, 1994. Soil resilience and sustainable land use. CABInternational, Wallingford, Oxon, UK.

Halvorson, A.D., B.J. Wienhold, & A.L. Black, 2002. Tillage, nitrogen, and croppingsystem effects on soil carbon sequestration. Soil Science Society of America 66:906–912.

Hendrix, P.F., D.C. Coleman, & D.A. Crossley, 1992. Using knowledge of soil nutri-ent cycling processes to design sustainable agriculture. Journal of SustainableAgriculture 2(3): 63–82.

Johnston, A.E. 1997. The value of long-term experiments in agricultural ecologicaland environmental research. Advances in Agronomy 59: 291–333.

Kapur, S., E. Akca, H. Eswaran, G. Kelling, C. Vita-Finizi, A.R. Mermut, & A.D. Ocal,1996. Proceedings of the First International Conference on Land Degredation.10–14 June, 1996. Cukurova University Press, Adana, Turkey.

Kassam, A.H. 1981. Climate, soil and land resources in the West Asia and NorthAfrica Region, Plant and Soil 58: 1–28.

Lal, R. 2002. Carbon sequestration in dryland ecosystems of West Asia and NorthAfrica. Land Degradation Development, 13: 45–59.

Lal, R., R.F. Follett, B.A. Stewart, & J.M. Kimble, 2007. Soil carbon sequestration tomitigate climate change and advance food security. Soil Science 172: 944–956.

Leo, M.W.M. 1963. A rapid method for estimating structural stability of soils. SoilScience 96: 342–346.

Lipiec, J., J. Kus, A. Nosalewicz, & M. Turski, 2006. Tillage system effects on stabilityand sorptivity of soil aggregates. International Agrophysics 20: 189–193.

Lopez-Bellido, R.A., J.M. Fonton, F.J. Lopez-Bellido, & L. Lopez-Bellido. 2010.Carbon sequestration by tillage rotation, and nitrogen fertilization in aMediterranean Vertisol. Agronomy Journal 102: 310–318.

Dow

nloa

ded

by [

Uni

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ity o

f C

hica

go L

ibra

ry]

at 2

3:22

20

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Tillage and Soil Quality in Turkey 623

Lorenz, K., & R. Lal, 2005. The depth distribution of soil organic carbon in relation toland use and management and the potential of carbon sequestration in subsoilhorizons. Advances in Agronomy 88: 35–66.

Madejon, E., J.M. Murillo, F. Moreno, M.V. Lopez, J.L. Arrue, J. Alvaro-Fuentes, &C. Cantero, 2009. Effect of long-term conservation tillage on soil biochemicalproperties in Mediterranean Spanish areas. Soil and Tillage Research 105: 55–62.

Mishra, U., D.A.N. Ussiri, & R. Lal, 2010. Tillage effects on soil organic carbon anddynamics in Corn Belt of Ohio USA. Soil and Tillage Research 107: 88–96.

Özbek, H., U. Dinç, & S. Kapur, 1974. Soils of the University of ÇukurovaCampus Area. University of Çukurova, Faculty of Agriculture Publication 73.The Ankara University Press, Ankara (in Turkish).

Ryan, J., S. Masri, H. Ibrikci, M. Singh, M., Pala, & H.C. Harris, 2008a. Implicationsof cereal-based crop rotations, nitrogen fertilization, and stubble grazing onsoil organic matter in a Mediterranean-type environment. Turkish Journal ofAgriculture and Forestry 32: 289–297.

Ryan, J., M. Singh, and M. Pala, 2008b. Long-term cereal-based rotation trials inthe Mediterranean Region: Implications for cropping sustainability. Advancesin Agronomy 97: 273–319.

Ryan, J., H. Ibrikci, M. Sing, A. Matar, S. Masri, A. Rashid, & M. Pala, 2008c. Responseof residual and currently applied phosphorus in dryland cereal/legume rota-tions in three Syrian Mediterranean agroecosystems. European Journal ofAgronomy 28: 126–137.

Ryan, J., S. Masri, & M. Singh, 2009a. Seasonal changes in soil organic matterand biomass and labile forms of carbon as influenced by crop rotations.Communications in Soil Science and Plant Analysis 40: 188–199.

Ryan, J., S. Masri, M., Pala, & M. Singh, 2009b. Nutrient dynamics in a long-termcereal-based rotation trial in a Mediterranean environment: Nitrogen forms.Communications in Soil Science and Plant Analysis 40: 931–946.

Salinas-Garcia, J.R., F.M. Hons, & J.E. Matocha, 1997. Soil carbon and nitrogendynamics as affected by long-term tillage and nitrogen fertilization. Biologyand Fertility of Soils 25: 182–188.

Sainju, U.M., B.P. Singh, W.F. Whitehead, & S. Wang, 2006. Carbon supply andstorage in tilled and nontilled soils as influenced by cover crops and nitrogen.Journal of Environmental Quality 35: 1507–1517.

Vance, F.D., P.C. Brookes, & D.S. Jenkinson, 1987. An extraction methods formeasuring soil microbial biomass. Soil Biology and Biochemistry 19: 703–707.

West, T.O., and W.M. Post, 2002. Soil organic carbon sequestration rates by tillageand crop rotation. Soil Science Society of America Journal 66: 1930–1946.

Wood, C.W., J.H. Edwards, & C.G. Cummins, 1992. Tillage and crop rotation effectson soil organic matter in a typical Hapludult of Northern Alabama. Journal ofSustainable Agriculture 2(2): 31–41.

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