Soil Erodibility Characteristics Under Modified Land-Use Systems as Against Shifting Cultivation in...

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Soil Erodibility Characteristics Under Modified Land-Use Systems asAgainst Shifting Cultivation in Hilly Ecosystems of Meghalaya, IndiaR. Sahaa; V. K. Mishrab; S. K. Khanc

a Indian Institute of Soil Science, Nabibagh, Bhopal, Madhya Pradesh, India b CSSRI Regional Center,Lucknow, Uttar Pradesh, India c Palli Siksha Bhavan, Visva Bharati, Sriniketan, West Bengal, India

Online publication date: 24 May 2011

To cite this Article Saha, R. , Mishra, V. K. and Khan, S. K.(2011) 'Soil Erodibility Characteristics Under Modified Land-UseSystems as Against Shifting Cultivation in Hilly Ecosystems of Meghalaya, India', Journal of Sustainable Forestry, 30: 4,301 — 312To link to this Article: DOI: 10.1080/10549811.2011.531992URL: http://dx.doi.org/10.1080/10549811.2011.531992

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Journal of Sustainable Forestry, 30:301–312, 2011Copyright © Taylor & Francis Group, LLCISSN: 1054-9811 print/1540-756X onlineDOI: 10.1080/10549811.2011.531992

Soil Erodibility Characteristics Under ModifiedLand-Use Systems as Against Shifting

Cultivation in Hilly Ecosystemsof Meghalaya, India

R. SAHA1, V. K. MISHRA2, and S. K. KHAN3

1Indian Institute of Soil Science, Nabibagh, Bhopal, Madhya Pradesh, India2CSSRI Regional Center, Lucknow, Uttar Pradesh, India

3Palli Siksha Bhavan, Visva Bharati, Sriniketan, West Bengal, India

A study was conducted to compare soil erodibility characteris-tics under modified land-use systems such as agriculture, agri-horti-silvi-pastoral, natural forest, livestock-based land use, nat-ural fallow, and the locally most prevalent shifting cultivationsystem at the Indian Council of Agricultural Research Complexfor Northeastern Hill Region, Umiam, Meghalaya, India. Surface(0 to 15 cm) soil samples were analyzed for various soil propertiesand different erodibility indices [i.e., Dispersion ratio = Suspensionpercentage/silt and clay under dispersed condition; Erosion ratio= Dispersion ratio/(clay/moisture equivalent ratio); Erosion index= Disperion ratio/(clay/half of the water holding capacity)] wereworked out from the basic soil properties—mainly textural compo-nents, soil moisture at field capacity, etc., following the standardprocedures. The experimental site had an acidic soil reaction (pH4.33–5.12), clay loam texture, and medium to high organic car-bon content (1.24–3.25%). Shifting cultivation showed the highesterosion ratio (12.46), followed by agriculture (10.42), indicatingthe need to adopt tree-based land-use systems for resource con-servation. Soil loss was significantly higher in shifting cultivation(30.2–170.2 t ha−1 yr−1), agriculture (5.10–68.20 t ha−1 yr−1),and the livestock-based land-use systems (0.88–14.28 t ha−1 yr−1)as compared to other modified land-use systems. Among the modi-fied land-use systems, the agri-horti-silvi-pastoral system performed

Address correspondence to R. Saha, Indian Institute of Soil Science, Nabibagh, BerasiaRoad, Bhopal, Madhya Pradesh 462038, India. E-mail: [email protected]

301

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302 R. Saha et al.

the best, confirming its superiority over shifting cultivation—e-specially under the high rainfall, moderate to steep slopes, andshallow soil depth conditions of Meghalaya. The erosion ratio, dis-persion ratio, and erosion index were also significantly correlatedwith soil physicochemical properties, indicating their suitability forassessing erodibility under such conditions of soil and climate.

KEYWORDS erodibility indices, hilly ecosystems, shifting cultiva-tion, soil erosion

INTRODUCTION

Soil erosion, an important social and economic problem and an essentialfactor in assessing ecosystem health and function, largely depends on theerosivity of rainfall and erodibility of soil. Soil erosion is a function of soilphysical characteristics, climate, and land-use practice (Hudson, 1995). Largedifferences in soil loss are brought about by differences in soil propertieswhen other factors such as rainfall, topography, and vegetation are keptconstant (Kaur, Singh, & Gurang, 2003). Another factor which influenceserodibility, given similar soil characteristics and climate, is the land use.Undisturbed forests and dense grass provide the best soil protection fromsoil loss and runoff. It has been recognized worldwide that soil loss could beminimized by increasing the soil cover with agroforestry-related land uses(Tiwari, Sharma, Tiwari, & Bhatt, 2000).

Northeastern India, comprising the states of Arunachal Pradesh, Assam,Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, and Tripura lies between21◦50′ and 29◦34′ N latitude and 85◦34′ and 97◦50′ E longitude. The regionis known for its inaccessible terrain, fragility, excessive sloping land withrolling topography, rich forest cover, and biotic and abiotic diversity.Morphologically, the region is marked by the development of series of ridgesand valleys, terraces, scraps, and several geomorphologic surfaces at differ-ent elevations (50 to 5,000 m and above). The altitudinal differences coupledwith varied physiographic features give rise to distinct and varied types ofclimate, ranging from near tropical to temperate to alpine, having very highrainfall throughout the year. Due to the undulating topography and highmountains, the net sown area in the region is only 2.82% that of the country.

Shifting cultivation or jhum—the dominant land-use practice of thisregion—in its more traditional and cultural integrated form is an ecologicaland economically viable system of agriculture as long as population densi-ties are low and jhum cycles are long enough to maintain soil fertility (AssamAgricultural University, 1992). The shifting cultivation system became unsus-tainable primarily due to the increase in population, which led to an increasein food demand and resulted in a decline of land cover with great impactson soil, water, energy balance, and ultimately on soil erosion. The jhuming


Soil Erodibility Characteristics 303

cycle in the same land, which extended to 20–30 yr in olden days, hasnow been reduced to 3–6 yr (Borthakur, 1992). Presently, it is estimated thatthe number of people practicing shifting cultivation are around 367,000 tribalfamilies and the area affected by this practice is 385,400 ha annually (Patiram& Verma, 2001). On an average, an area of 3,869 km2 is put under shiftingcultivation every year. Excessive deforestation (net loss of 1,577 km2 for-est cover between 1999 and 2001, Government of India, 2001) coupled withshifting cultivation practices have resulted in tremendous soil loss (200 t ha−1

yr−1; Prasad, 1987), poor soil physical health, and an uncountable loss ofbiodiversity. Studies about the soil fertility status under different jhum cyclesat various elevations suggest that plots with short jhum cycles (5 yr) gen-erally have lower fertility than those with longer cycles (10 or more years;Ramakrishnan & Toky, 1981; Mishra & Ramakrishnan, 1983).

The assessment of soil erodibility—which depends on soil physicalcharacteristics such as the nature and amount of soil aggregates, organicmatter content and particle size distribution, and its relationship with varioussoil physical properties—will help in designing land-management practicesto check the menace of soil erosion in this region. Although there are manyreports on changes in fertility status under shifting cultivation practices, verylittle information is available on the erodibility characteristics of this area,particularly under different land uses. The present study was, therefore, con-ducted to evaluate various soil erodibility indices in relation to soil physicalproperties under different land-use systems of hill agriculture.

MATERIALS AND METHODS

The present study was carried out in different land-use systems that wereinitiated in 1983 at the Indian Council of Agricultural Research Complexfor Northeastern Hill Region, Umiam, which is located in the east KhasiHills of Meghalaya, India (25◦41′ N; 91◦63′ E; 980 m above mean sea level).A map of the region showing the study area is presented in Figure 1. Theregion receives an average annual rainfall of 2,439 mm with a high degree oftemporal and spatial variation; 80% of the rainfall is received between Aprilto October, which is when the land is most prone to erosion hazards. Theexperiment was laid out in a completely randomized block design with sixtreatments replicated 3 times. Six land-use systems—i.e., agriculture, agri-horti-silvi-pastoral, natural forest, livestock-based land use, natural fallow,and shifting cultivation (Jhum)—were considered as treatments, having anet plot size of 0.64, 2.94, 1.03, 1.39, 1.13, and 1.65 ha, respectively. Generaldescriptions of the land-use systems are given in Table 1.

The modified land-use systems were developed for the proper eval-uation of integrated systems so as to evolve an alternative system forsustainable food production in areas with shifting cultivation. Agriculture is


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304



TABLE 1 General Descriptions of the Land-Use Systems

Land-use systemsMajor land capability

classes Soil textureAverage slope

(percent) Area (ha)

Agriculture V IIe cl 32.4 0.64Agri-horti-silvi-pastoral V IIe cl 32.2 2.94Natural forest V IIe cl 45.9 1.03Livestock-based system V IIe cl 32.0 1.39Natural fallow V IIe cl 52.2 1.13Shifting cultivation V IIe cl 38.2 1.65

Note. cl = clay loam.

being practiced with crops like maize (Zea mays), soybean (Glycine max),paddy (Oryza sativa), tapioca (Manihot esculenta), colocasia (Colocasiaesculenta), peas (Pisum sativum), mustard (Brassica juncea), etc. Theagri-horti-silvi-pastoral system is comprised of agricultural crops, horticul-tural crops (pineapple, Ananus squennssa; citrus, Citrus sp.), alder treesspecies (Alnus nepalensis), and fodder grasses. The fodder species in theagri-horti-silvi-pastoral system and livestock-based land-use systems werestylo (Stylosanthes guyanensis), guinea (Panicum maxicum), setaria (Setariasphacelata), and a local grass (Imperata cylindrica). The natural forest sys-tem is largely dominated by trees such as makari-sal (Schima wallichii),bangali-babool (Acacia auriculiformis), queen’s flower/jarul (Lagerstroemiaspeciosa), and bamboo (Bambusa pallida); and there was no agriculturalactivity as such rather trees were grown under natural conditions. Thenatural fallow system is mainly dominated by local grasses, particularlybroom grass (Thysanolaena agrotis), without any agricultural/horticulturalcrop. Ginger (Zingiber officinalis), turmeric (Curcuma longa), colocasia(Colocasia esculenta), maize (Zea mays), and paddy (Oryza sativa) werethe common crops cultivated under shifting cultivation. Ginger/turmeric wascultivated during the 1st yr and upland paddy/maize was grown during 2ndyr in shifting cultivation. Thereafter, the plots were kept fallow for 3 yr andthis cycle was repeated on the same land.

The soil of the study site is acidic in nature and is classified as a TypicHapludalf. The soils are clay loam in texture, acidic in reaction, with amedium to high organic carbon content. According to the land capabil-ity classification (Table 1), the soils of the study area were categorizedunder class VIIe; i.e., highly prone to soil erosion. Surface (0–15 cm) soilsamples were collected periodically from different blocks under all the land-use systems. Soil samples were brought to the laboratory, air-dried at roomtemperature, and passed through a 2-mm sieve for analysis of various soilphysicochemical properties. The soil pH and organic C were measured fol-lowing the standard method (Jackson, 1973); particle size distribution of soilsamples was determined by the international pipette method (Black, 1965);water stable aggregates were estimated using Yoder’s (1936) wet sieving


306 R. Saha et al.

TABLE 2 Various Soil Erodibility Indices and Their Calculation

Sl. no. Erodibility indices Calculation

1. Suspension percentage: Bryan(1968)

Percent silt + clay under undispersedcondition after 5 minutes shaking

2. Dispersion ratio: Suspension percentage(Silt + Clay) under dispersed condition

3. Clay ratio: Bouyoucos (1935) % (Silt + Clay)% Clay

4. Clay/moisture equivalent ratio: % Clay% (Moisture at 0.03 MPa)

5. Erosion ratio: Middleton (1930) Dispersion ratioClay/Moisture equivalent ratio

6. Erosion index: Middleton (1930) Dispersion ratioClay/half of the water holding capacity

technique; field capacity was estimated using a pressure plate membraneapparatus (Black, 1965); bulk density was measured on the basis of undis-turbed core samples collected from respective treatments (Black, 1965); andannual soil loss under various land-use systems was measured using themulti-slot divisor. Using these characteristics, various soil erodibility indiceswere worked out as given in Table 2.

All the data were statistically analyzed using analysis of variance(ANOVA) as applicable to complete randomized block design and thetreatment differences were tested for significance.

RESULTS AND DISCUSSION

Physicochemical Properties of Soil

Soils of the study area are acidic in nature with pH ranging from 4.33 to 5.12under various land-use systems (Table 3), having silty clay loam to clay loamin texture. Mean sand, silt, and clay contents were almost identical for all theland-use systems evaluated. However, the organic carbon content exhibitedprofound variations and it was highest in natural fallow (3.05%) followed bynatural forest (2.95%), the agri-horti-silvi-pastoral system (2.78%), livestock-based system, and agriculture (2.41% each); and least in the shiftingcultivation plots (1.92%). High organic C in the natural fallow system may beascribed to the presence of broom grass, which accumulates organic C in thesoil (Biswas & Mukherjee, 1994; Das, Singh, & Khan, 1997). Soil bulk densityvaried from 0.89 to 1.25 Mg m−3 among all the land-use systems. However,the mean value was highest under shifting cultivation plots (1.19 Mg m−3)and the lowest in the natural forest system (0.98 Mg m−3). Conversely, waterstable aggregates (> 0.25 mm) were highest in the natural forest system(54.47%), which was similar to that of the agri-horti-silvi-pastoral system(54.19%), and were lowest for the shifting cultivation plots (18.17%). The



ability of soil to withstand erosion is directly linked to the relative abun-dance of water stable aggregates and its highest proportion in the forestand agri-horti-silvi-pastoral plots may be attributed to better canopy cover-age and biomass production in these land-use systems. This is consistentwith the observations of Chakrabarti (1969). There was marginal variation inthe field capacity values (38.0–42.8%) among the modified land-use systems,whereas shifting cultivation plots contributed only 31.5%.

Erodibility Indices

The suspension percentage varied from 1.96 to 5.20 and was highest in thejhum plots (Table 4). This may be explained by the silt and clay propor-tion under the undispersed conditions and organic C content of these soils.A similar trend was observed in the case of the dispersion ratio. It variedfrom 1.6 (natural forest) to 12.1 (shifting cultivation), which indicates thatsoils under modified land-use systems and natural forest are less suscepti-ble to erosion compared to shifting cultivation. The clay ratio was minimalunder the natural fallow system and highest under the shifting cultivationand agriculture systems. The clay/moisture equivalent ratio (MER), an effec-tive and relevant index of soil susceptibility to erosion, did not vary amongthe modified land-use systems except in shifting cultivated areas, whereit was much higher (0.97). Among the different erosion indices, the erosionratio and erosion index have been widely accepted as a reliable index of soilerodibility (Bryan, 1968). Shifting cultivation registered the highest erosionratio and erosion index values (12.46 and 6.68, respectively), followed by theagriculture system (10.42 and 5.75, respectively). Natural forest soil showedthe lowest erosion ratio and erosion index values (3.97 and 1.09, respec-tively). Similar findings were also reported by Singh and Prakash (1985). Thelower degree of these erodibility indices in forest plots could be attributedto higher organic C content and greater soil root binding characteristics,which in turn improves soil aggregation. However, considering the valueof 10 as the significant boundary between erodible and non-erodible soils(Middleton, 1930), the soils under shifting cultivation and the agriculture sys-tem are vulnerable to erosion hazards due to their low organic C content andpoor aggregation. Fullen (1991) reported that even a small reduction in theorganic matter content of soil markedly increased soil erodibility. Therefore,the soils on the small hillocks are highly susceptible to erosion and thehazards are aggravated owing to their undulating topography.

Annual Soil Loss

The annual soil loss and percent of rainfall retained under various land-use systems are depicted in Table 5. The rainfall retained under differentland-use systems was very high, ranging from 77.08 to 99.99%. There was


TAB

LE3

Phys

icoch

emic

alPro

per

ties

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ious

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s

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pro

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ties

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stat

istic

sA

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Shiftin

gcu

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tion

LSD

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.05)

pH

(1:2

.5)

Ran

ge4.

90–5

.12

4.39

–5.0

24.

36–4

.80

4.45

–4.7

04.

33–4

.92

4.58

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30.

24M

ean

5.03

a4.

92b

4.41

c4.

65c

4.59

c4.

81b

SD(±

)0.

130.

210.

260.

290.

250.

34O

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96–2

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2.78

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7.24

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49.0

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88(p

erce

nt)

Mea

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29.5

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565.

115.

405.

506.

116.

12Cla

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39.8

025

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42.4

022

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40.1

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38.6

027

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43.2

019

.80–

37.6

03.

66(p

erce

nt)

Mea

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33.2

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.70b

31.8

0b34

.60b

30.6

0b

SD(±

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015.

105.

334.

865.

034.

71B

ulk

den

sity

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0.94

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70.

89–1

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61.

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1.11

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50.

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gm

−3)

Mea

n1.

04b

1.02

b0.

98b

1.03

b1.

04b

1.19

a

SD(±

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110.

120.

100.

080.

100.

22W

ater

stab

leRan

ge15

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26.0

246

.50–

57.3

352

.23–

56.3

243

.51–

53.5

444

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52.7

416

.97–

20.1

13.

50ag

greg

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Mea

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54.1

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343.

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083.

983.

114.

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pac

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ean

38.0

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41.5

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992.

682.

152.

524.

232.

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308


TAB

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Soil

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Soil

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gcu

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tion

LSD

(p<

.05)

Susp

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on

Ran

ge2.

60–8

.30

1.34

–6.6

81.

96–5

.60

2.54

–7.3

21.

82–5

.34

3.46

–10.

301.

82per

centa

geM

ean

3.12

b2.

15c

2.02

c2.

75b

1.96

c5.

20a

SD(±

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881.

141.

021.

551.

112.

42D

isper

sion

Ran

ge4.

87–1

6.54

2.30

–10.

140.

92–6

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2.63

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551.

15–8

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8.52

–23.

572.

25ra

tioM

ean

8.60

b5.

70b

1.60

c6.

80b

3.20

c12

.10a

SD(±

)3.

162.

391.

772.

572.

225.

52Cla

yRan

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58–6

.82

1.30

–4.2

21.

15–3

.85

1.54

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26–3

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1.68

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31.

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1.91

b1.

89b

1.79

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1.74

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90b

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711.

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111.

930.

982.

06Cla

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78–0

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0.81

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90.

80–0

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0.79

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76–0

.85

0.92

–1.0

30.

19M

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0.83

c0.

85c

0.81

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82c

0.81

c0.

97b

SD(±

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260.

240.

220.

230.

240.

35Ero

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2.59

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3.07

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1.18

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652.

30M

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10.4

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73b

3.97

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30b

3.96

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792.

301.

443.

532.

295.

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sion

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1.72

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1.86

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40.

97–8

.37

6.07

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371.

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dex

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3.81

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4.70

b2.

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6.68

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411.

651.

412.

282.

213.

13

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scriptar

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cantly

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alen

tra

tio,L

SD=

leas

tsi

gnifi

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rence

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=st

andar

ddev

iatio

n.

309


310 R. Saha et al.

TABLE 5 Annual Soil Loss and Rainfall Retained Under Various Land-UseSystems

Land-use systemsPercent of annual rainfall

(mm) retained Soil loss (t ha−1 yr−1)

Agriculture 80.74–99.79 5.10–68.20Agri-horti-silvi-pastoral 98.27–99.99 0.38–1.22Natural forest 97.55–99.98 0.04–0.52Livestock-based system 77.08–99.66 0.88–14.28Natural fallow 96.18–99.75 0.37–1.83Shifting cultivation 92.79–98.27 30.20–170.20

no significant variation observed among the various land-use systems. Theannual soil loss values varied significantly within and among the variousland-use systems. The possible reason for the large variation within a sys-tem might be due to spatial variation in soil properties, as well as thedifferences in slope under a particular system. The maximum soil loss of30.2–170.2 t ha−1 yr−1 was recorded under shifting cultivation plots and theminimum of 0.04–0.52 t ha−1 yr−1 under the natural forest system. This find-ing is significantly correlated with the soil erodibility indices. The agriculturesystem, which generally had rainfed crops and kept almost fallow the rest ofthe year, ultimately resulted in soil loss (5.10–68.20 t ha−1 yr−1). This fact hasalso been reflected in the soil dispersion ratio value (12.10), the erosion ratio(12.46), and the erosion index (6.68) under the agriculture system. A similartrend was observed under the livestock-based land-use system, although theextent of soil loss was much lower (0.88–14.28 t ha−1 yr−1) compared to theshifting cultivation and agriculture systems. These soils need to be rejuve-nated through planting with perennial tree and grass species, and throughsuitable soil conservation measures such as contour bunds and trenching.Among the modified land-use systems, the agri-horti-silvi-pastoral system(0.38–1.22 t ha−1 yr−1) was found to be the best next to natural forest. Thismight be due to the soil’s complete coverage with vegetation throughout theyear. The soil loss under the agri-horti-silvi-pastoral system was observed tobe almost on par with that of the natural fallow system. This can be ascribedto the higher soil binding capacity with dense root system of grasses thatprevailed under the natural fallow system.

Correlation of Erodibility Indices with Soil Properties

Among all the erodibility indices, the erosion ratio was positively correlatedwith sand, silt, and bulk density; and negatively correlated with the clay,organic C content, and water stable aggregates (WSA; > 0.25 mm) in all land-use systems (Table 6). A highly significant (at 5% level) relationship with theerosion ratio has been observed with all the soil properties, indicating itssuitability for this soil erodibility study. The dispersion ratio showed signifi-cant negative correlations with clay (r = −.66), organic carbon (r = −.87),



TABLE 6 Correlation Coefficient (r) Values Between Soil Properties and Erodibility Indices

Erodibility indices

Soil propertiesSuspensionpercentage

Dispersionratio Clay ratio Clay/MER

Erosionratio

Erosionindex

Organic C −0.79∗ −0.87∗ −0.72 −0.78∗ −0.84∗ −0.79∗Sand 0.77∗ 0.72∗ 0.66 0.46 0.73∗ 0.77∗Silt 0.86∗ 0.86∗ 0.71 −0.47 0.77∗ 0.82∗Clay −0.66∗ −0.66∗ −0.52∗ −0.33 −0.60∗ −0.64∗Bulk density 0.63 0.77∗ 0.47 0.87∗ 0.72∗ 0.67WSA (>0.25 mm) −0.23 −0.46∗ −0.11 −0.47∗ −0.38∗ −0.34∗

Note. ∗Significant at 5% level. MER = moisture equivalent ratio, WSA = water stable aggregates.

and water stable aggregates (r = −.46); and significant positive correlationswith sand (r = .72), silt (r = .86), and bulk density (r = .77). Similarly, theerosion index has a very significant relationship with all of the soil propertiesexcept bulk density. Therefore, these indices can also be used in conjunc-tion with the erosion ratio for assessing the erodibility of soils in this region.

CONCLUSION

The study, aimed at assessing the relationships among soil properties, land-use systems, and erodibility reveals that the soils under shifting cultivation inthis region are prone to erosion owing to their low content of organic mattercoupled with poor soil structure. Soils under the agriculture land-use systemwere identified as the next sensitive category as revealed by different ero-sion indices. Although the present status is not so alarming due to the highorganic carbon content in the soil, the time has come to think about alter-native farming systems with sustainable management practices for resourceconservation. The natural forest ecosystem is the most suitable for mitigatingsoil losses due to their root binding mechanisms and high organic mattercontent. However, the soils under the agri-horti-silvi-pastoral land-use sys-tem have been found to be resistant with respect to the erosion hazard, withtheir higher organic carbon content and better surface soil binding ability.

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