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Influence of forest litter onreclamation of semiarid sodic soilsBajrang Singh aa National Botanical Research Institute/CSIR , Rana PratapMarg, P. B. No. 436, Lucknow, 226 001, IndiaPublished online: 09 Jan 2009.

To cite this article: Bajrang Singh (1996) Influence of forest litter on reclamationof semiarid sodic soils, Arid Soil Research and Rehabilitation, 10:3, 201-211, DOI:10.1080/15324989609381435

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Influence of Forest Litter on Reclamation ofSemiarid Sodic Soils

BAJRANG SINGH

National Botanical Research Institute/CSIRLucknow, India

Litter fall and forest floor organic detritus mass were estimated in a 36-year oldrehabilitated forest on sodic soils at Lucknow, north India (26°45' N, 80° 53' E). Of the11.9 ± 1.7 Mg ha-1 yr-1 of litter input, 63% leaf, 22% twig, and 15% flower-fruit weredetermined. Monthly litter fall declined exponentially (from 330 to 25 g m-1) fromspring to autumn. The forest floor was differentiated into L, F, and H organic layers,ranging from 3 to 5 Mg ha-1 in detritus mass. Litter decomposition was from 43% to47% per year. Leaf litter contained the largest quantities of ash, N, and P. Conversely,woody litter contained a higher amount of C. Carbon concentrations decreased fromthe L to the H layer as the trend of ash content increased. Throughputs of C andnutrient contents across the forest floor significantly altered some of the soil proper-ties. Bulk density, EC, and pH were reduced in the forested soil. Additionally, in-creases in C and N contents enriched the fertility of the sodic soil. However, concen-trations of available N and P fractions did not change significantly.

Keywords carbon, humus forms, litter fall, nitrogen, organic detritus, phosphorus,rehabilitated forest, soil amelioration

Sodic or saline alluvial soils in arid and semiarid regions of north India have receivedpriority attention for afforestation during the past few decades (Khan & Yadav, 1962;Yadav, 1975, 1980). Many attempts to establish plantations on such soils have failed.However, one successful site established in the 1950s has shown substantial improvementin microrelief (Khoshoo, 1987). It is well known that trees influence many soil properties(Kittredge, 1948) but their role in the reclamation of sodic soils has been only recentlyaddressed (Singh, 1989; Garg & Jain, 1992; Shukla & Misra, 1993). Because sodic soilsare reclaimed primarily through the input of large amounts of forest litter, the quality andquantity of the litter will affect the degree of soil reclamation in a specified period subjectto its decomposition rate. In a favorable environment, litter is humified within a year afterits deposition. However, microbial decomposition of litter is significantly influenced bythe C:N ratio of the litter as N-rich substrates are mineralized quickly (Coats et al., 1976;Adams & Attiwill, 1982). On degraded sites, trees generally shed N-poor litter due tohigher résorption efficiency (Pugnaire & Chapin, 1993). In addition, a wide range ofmicrobial populations does not exist in such soils. Therefore, litter decays slowly to form

Received 1 June 1995; accepted 8 December 1995.The author is grateful to Dr. P. V. Sane, director, NBRI, Lucknow for providing the necessary

facilities to complete the work. He is also thankful to Dr. P. N. Misra, scientist-in-charge, BanthraResearch Station, for the establishment and management of the forest reserve studied. Technicalsupport rendered by Mr. Gajendra Singh is also acknowledged.

Address correspondence to Dr. Bajrang Singh. National Botanical Research Institute, RanaPratap Marg, P. B. No. 436, Lucknow, 226 001. India.

201

Arid Soil Research and Rehabilitation, 10:201-211, 1996Copyright © 1996 Taylor & Francis

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202 B. Singh

ectoorganic layers of humus on the mineral soil. This, in fact, conserves moisture as wellas nutrients, checks soil erosion, and exerts a profound influence in alteration of soilproperties. In view of the nitrogen scarcity in sodic soils, the forest growth is predomi-nantly sustained by the magnitudes of their recycling. The objective of this study was toassess the inputs of litter types, seasonality, quality, decomposition, and accumulation inorganic layers in a subtropical man-made forest and their implications in the ameliorationof the once sodic soils.

Material and Methods

The study was conducted in a 36-year-old rehabilitated forest of 3 ha on sodic soilsat Banthra, Lucknow (26°45' N, 8O°53' E). The forest is characterized as a dry subtropicalforest of high species diversity. Dominant species of this forest include Acacia auriculi-formis A. cumm. ex. Benth., Albizia procera (Roxb.) Benth., Bauhinia variegata L.,Dalbergia sissoo Roxb. ex. DC, Syzigium cumini (L.) Skeels, and Terminalia arjuna(Roxb. ex. DC.) Wight ex. Arn. Most of these species were of a deciduous nature exceptAcacia.

These species were established in barren sodic soils (pH 10) in 1956 through repeatedrevegetation attempts. Several saplings were planted in the plantation pits each of 1 m3

size and duly refilled with a mixture of compost manure and leafmold. Initial saplingpopulation density was kept around 1000 individuals per hectare. Suitable drainage wasmaintained to avoid water-logging conditions, which are very common on sodic soils. Indue course, other plant species including Ficus, Leucaena, Hibiscus, Pendenus, Putran-jiya, Stribulus, and several herbs have invaded and colonized the area.

Litter was collected monthly during 1991-1993 in 1 m2 porous trays under the canopyof the dominant trees. Fifteen trays were placed randomly under the five deciduousspecies. Each litter collection was separated into leaf, twig, and flower-fruit categories.The forest floor was also sampled quarterly for 3 years. Litter deposits were differentiatedinto intact litter (L), partially decomposed fermentation layer (F), and fully decomposedhumus layer (H). Samples were dried at 70° C to constant weight, ground in a Willey mill(<0.1 mm mesh sieve) and analyzed for nutrient contents. Ash content was determined byigniting 1 g samples in silica crucibles in a muffle furnace at 550-600°C for 4-5 hours.The weight loss on ignition divided by a factor of 2 provided the carbon concentration.Nitrogen was estimated by the Kjeldahl digestion and distillation method (Piper, 1950).Phosphorus was extracted through triacid digestion followed by spectrophotometric mea-surement of the blue molybdophosphoric acid complex (Jackson, 1967).

The surface soil (0-30 cm) under the six tree species and a control from the sur-rounding barren land (six composite replicates) were sampled in 1992. Bulk density wasdetermined with a 100 cm3 volume core cylinder (Wilde et al., 1979). Organic carbon wasestimated by the Walkley and Black rapid titration method (Piper, 1950). Total N in thesoil was analyzed as for litter (Piper, 1950); whereas available N in the same soil wasdetermined by the alkaline permanganate method (Chopra & Kanwar, 1982). Available Pin soil was extracted in sulfuric acid (0.002 N) and measured by spectrophotometry(Jackson, 1967).

A separate core (1000 cm3) was taken monthly to measure fine root biomass in soilat depths of 0-30 cm. There were three replicates each under the six species, split into twoequal depths (3 x 6 x 2 = 36 samples per month). The core soil was washed (<1 mm meshsieve) through a fine jet of water. The remaining roots were allowed to soak overnight inwater and were then re washed. These roots, dried in the oven at 80° C to constant weight,

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Sodic Soil Réclamation 203

were measured as fine root biomass by total soil volume. Fine root mortality was esti-mated by summing up all negative differences of the fine root biomass between the twoconsecutive months in a year.

Results

Most of the species shed the maximum amount of litter (330 g m~2) in April owing to theirdeciduous nature. Average litter fall (5 species, 3 replicates, 3 years) declined exponen-tially from spring to autumn (Figure 1). Leaf, twig, and flower-fruit litter constituted 63%,22%, and 15%, respectively, of the total litter fall (Table 1). Total litter fall among thespecies was lowest for Dalbergia sissoo. The forest floor was differentiated into L, F, andH layers with minor variations between species (Table 2). A 43% reduction in forest floorlitter and organic detritus mass occurred from spring to winter. These constituents re-mained loosely aggregated in the form of a thin layer (7-10 cm) over the mineral soil.Because of the greater thickness of the F and H layers than that of the Ah horizon (2.5 cm)of the soil, the humus form was categorized to the leptomoder order as described by Greenet al. (1993).

Litter decomposition occurred more rapidly in nylon net bags than under original fieldconditions (Van Wesemael, 1993). Thus, we estimated litter decomposition using the

4oo-i

35O

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250

" EO> 2 0 0

w

« 150

_i

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M J J A S O H D J F

Month

M

Figure 1. Annual litter fall in a man-made forest at Banthra, Lucknow. Bars indicate standard error,curve is a logarithmic simulation (In y = 5.38 - OAlx, r = 0.763, P < 0.01).

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204 B. Singh

Table 1Annual litter fall (Mg ha"1) in a 36-yr-old man-made forest developed on sodic

wasteland's at Banthra, Lucknow

Species

Acacia auriculiformisAlbizia proceraBauhinia variegataDalbergia sissooTerminalia arjuna

Mean ± SEPercent of total

Leaf

8.05 ±1.237.57 ± 0.659.15 ±1.425.24 ±0.357.34 ±1.08

7.47 + 0.6463

Component

Twig

1.06 ±0.217.00 ± 0.733.25 ± 0.350.59 ± 0.071.37 ±0.16

2.65 ±1.1722

Flowers andFruits

5.92 + 0.670.07 + 0.020.80 ±0.140.12 ±0.031.99 ±0.37

1.78 ±1.0915

Total

15.014.613.25.8

10.7

11.9100

relationship between the annual litter fall (A) and forest floor litter (F) as AI{A + F), asdescribed by Jenny et al. (1949) and Gosz et al. (1976), where F was considered as thelowest value in an annual cycle. Although this gives a relative estimate of litter disap-pearance from the forest floor, it is meaningful to observe the differential patterns acrossthe species, sites, regions, or zones. The decay constant K for the species under study didnot vary much and indicated that, on average, the forest floor retained about 53% of theannual input remaining to be decomposed in subsequent years (Table 3). These aregenerally characterized as coarse lignified and cellulotic organic residues, which decayslowly. Mean residence time is the reciprocal of K, which entails the longevity of litter toits identity until it is converted into fine humus. The difference between litter fall and itsdecomposition is reduced gradually over a long course of time to maintain the forest floorat a steady state level. Through the present pattern of litter accumulation, the half-life(i = 50%) and time required to reach 95% of steady state levels,of the forest floor wereprojected following Olson's (1963) procedure. This procedure predicts that the forest floorwould likely attain a level of 95% of the steady state after 6 years.

Table 2Forest floor litter of 36-year-old man-made forest (Mg ha""1)

Organic layert I Mean

Species L F H Fe < F,05

Acacia auriculiformis 3.49 4.00 4.72 4.07Albizia procera 3.26 4.30 5.04 4.20Bauhinia variegata 2.31 3.97 4.36 3.55Dalbergia sissoo 2.58 3.53 5.38 3.83Syzygium cumini 3.39 4.71 5.02 4.37Terminalia arjuna 2.91 3.89 5.74 4.18

Mean (LSD05 = 0.52) 2.99 4.07 5.04 4.03

Organic layers are L, undecomposed litter; F, partially decomposed fermentationlayer; and H, fully decomposed humus. LSD, least significant difference; Fo5.

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Sodic Soil Reclamation 205

Table 3Decay constant (K), mean residence time (MRT) of litter on forest floor,and the time required to reach half and 95% steady state level for decay

MRT* / 50%c 195%c

£ (yr) (yr) (yr)Acacia auriculiformis 0.61 1.64 1.14 4.92Albizia procera 0.52 1.92 1.33 5.77Bauhinia variegata 0.54 1.85 1.28 5.55Dalbergia sissoo 0.43 2.33 1.61 6.98Terminalia arjuna 0.53 1.84 1.31 5.66

Mean ± SE 0.53 ±0.03 1.9210.11 1.33 + 0.07 5.77 ±0.33

"Jenny et al. (1949).*Gosz et al. (1976).cOlson (1963).

Different types of litter depicted variable concentrations of ash, C, N, and P. Ingeneral, the foliar litter contained elevated amounts of ash, N, and P (Table 4). Con-versely, woody litter contained elevated amounts of C. These properties of litter play asignificant role in their decomposition and mineralization. Leaf litter decays faster thanwoody components. Large inputs of ash and carbon contents, measured in a proportion of1:5, contribute mainly to restore the soil structure. On the other hand, influx of N and Psustains the forest growth on these low-fertility soils.

Ash and carbon proportions in litter varied during the humification process. A sig-nificant reduction in C and an increase in the ash content were determined during thetransformation from the L to H layer (Table 5). However, changes for N and P concen-trations and C:N and C:P ratios were not significant. These ratios showed an inverselyproportional relation to each other during the transformation from the L to H layer. Theforest floor of the leguminous species had a higher nitrogen content than that of otherspecies. Because decomposition and humification in tropical and subtropical forests pro-ceed faster than in temperate forests, quantities of humus (H) exceeded from the L and Flayers in this forest, and thus the H layer contained an increased amount of elements.However, this pattern was not significant for P content. Incorporation of humus into theunderlying mineral soil and its further mineralization is a relatively slow process. Con-sequently, soil amelioration was observed only in the surface layer at 30 cm. At lower soildepths (100 cm) there was no significant change between the soils of a forest stand andadjacent barren land. The turnover rate and time (ratio of a flux to its pool size andreciprocal) for the input of C, N, and P elements to the forest floor did not vary signif-icantly from 1, indicating its closeness to the homeostatic forest floor.

Soil properties of the forested site changed notably in comparison to the surroundingunforested land. The measured indices herein document the extent of alterations during aparticular period. A marked reduction for pH, EC, and bulk density values in the forestedsoil indicated a good degree of reclamation of the once sodic soil (Table 6). Manifoldincreases in the status of C (12 times) and N (3 times) raised soil fertility, making itsphysical condition suitable for the growth of less tolerant forest species for sodic soils.Most of the nitrogen in the forest soil was associated with organically bound N in soilorganic matter, as the available N between the forested (0.14 mg g"1) and abandoned

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206 B. Singh

Table 4Litter quality and annual input through litter fall in a man-made forest ecosystem at

Banthra, Lucknow

Species

Acaciaauriculiformis

Albiziaprocera

Bauhiniavariegata

Dalbergiasissoo

Terminaliaarjuna

Forestmean ± SE

Component

LeafTwigFlower

and fruitLeafTwigFlower

and fruitLeafTwigLeaf

LeafTwigFlowerand fruit

Ash

%

6.325.334.98

11.214.685.00

8.666.83

12.14

10.068.849.56

kg ha"1

508.756.5

294.8

848.6327.6

3.5

792.4221.9636.1

734.0121.1190.2

947 ±93

Carbon

%

46.847.347.5

44.447.647.5

45.646.543.9

44.945.545.2

5.25

Mg ha"1

3.770.502.42

3.363.340.03

4.181.512.30

3.300.620.90

±0.82

Nitrogen

%

2.591.662.28

2.322.071.86

2.281.971.86

1.661.651.86

kg ha"1

208.517.6

134.9

175.6144.9

1.3

208.662.497.4

121.822.637.0

227 ±44

Phosphorus

%

0.1320.1210.125

0.1410.1340.121

0.2320.1810.176

0.1530.1240.143

18.31

kg ha"1

10.631.287.40

10.679.380.08

21.235.889.22

11.231.702.85

±2.92

desolated soils (0.12 mg g l) was almost similar. Likewise, the concentration of availableP did not vary significantly between these two sites; this may have been because of thehigh quantity of available P in alkali soils (Chhabra et al., 1981). The specific role ofindividual species litter has been inconspicuous in reclamation of these sodic soils owingto the minor variations of the forest floor litter among the species. Some amount of freshlitter is also mixed up by wind storms. Additionally, surface and subsurface drainagewould abate the effects of individual species in a mixed forest.

Discussion

Low fertility of arid soils has been attributed to extremely low organic matter content(Newbould, 1989; Stott & Martin, 1989). Enhancement of organic matter is therefore ofvital importance to biological processes and soil productivity. Reclamation efforts onsodic soils of the Indogangetic plains using chemical treatments for crop production assuggested by Gupta and Abrol ( 1989,1990) do not build up a sufficient amount of organicmatter in soil. Organic mulching with green or compost manure was deemed too costly.Attempts made to reclaim these soils by afforestation rendered better results (Singh, 1989;Singh & Tripathi, 1993). These efforts restore the stability and resilience of degradedecosystems in addition to providing a quality environment. Forest litter contributes muchmore to soil reclamation than other influences. Litter quantity depends on age and treepopulation density of the forest. In the present study, litter fall was estimated to be almost

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Table 5Litter quality and nutrient pool of forest floor in a man-made forest ecosystem at Banthra, Lucknow

Species

Acacia auriculiformis

Albizia procera

Bauhinia variegata

Dalbergia sissoo

Syzygium cumini

Terminalia arjuna

Forest mean ± SE

TotalLSDO5

Littertype

LFHLFHLFHLFHLFHLFHLFH

%

131714142855

42021

72832192334

92531

11 ±2.223 ±1.831 ±5.7

9.2

Ash

Mg ha"1

0.450.680.660.461.202.770.090.790.920.180.991.720.641.081.710.260.971.78

0.35 ±0.080.95 ± 0.071.59 ±0.30

2.890.55

%

434143433628484039463634403833453734

44 ±1.138 ± 0.835 ±2.1

3.7

C

Mg ha"1

1.501.642.031.401.551.411.111.591.701.191.271.831.361.791.661.311.441.95

1.31 ±0.061.55 ±0.071.76 ±0.09

4.620.23

%

2.41.52.51.92.52.92.01.51.81.41.02.21.01.31.21.01.31.0

1.6 ±0.211.5 ±0.211.9 ±0.31

NS

N

kg ha"1

83.760.0

118.061.9

107.5146.046.259.578.436.135.3

118.333.961.260.229.150.557.4

48.5 ± 8.562.3 ±9.896.4 ± 14.8

207.234.3

P

mgg"'

0.990.820.961.271.161.192.001.501.801.240.790.711.191.080.741.371.890.85

1.34 ±0.141.21 ±0.171.04 ±0.16

NS

kg ha'1

3.453.284.534.144.996.006.525.957.853.202.793.824.035.083.713.997.354.88

4.22 ±0.44.90 ±0.75.13 ±0.6

14.25NS

Ratios

C/N

182717231910242722333615402927452834

30 + 4.327 ± 2.221 + 3.5

C/P

434500448338310235240266216371455478336352446328195440

341 ±25346 ± 47370 ±47

Litter type is L, undecomposed litter; F, partially decomposed fermentation layer; and H, fully decomposed humus. LSD, least significant difference; NS, notsignificant.

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208 B. Singh

Table 6Soil characteristics under trees and their relations with surrounding barren site

Species

Acaciaauriculiformis

Albiziaprocera

Bauhiniavariegata

Dalbergiasissoo

Syzygiumcumini

Terminaliaarjuna

Forested meanBarren sitemean

LSDO5

Probability

pH

M 8.06SE 0.06M 7.73SE 0.06M 7.78SE 0.1M 7.64SE 0.04M 7.36SE 0.12M 7.66SE 0.06

7.709.82

0.930.001

EC(mS nT1)

110.7

153

151

120.692

121.6

1236

150.01

BD(g cm"3)

1.280.041.390.051.490.071.450.071.620.051.410.05

1.441.83

0.310.05

MC(%)

10.350.87

11.680.77

10.360.798.771.24

12.120.47

12.040.66

10.888.68

1.650.05

OC(%)

0.990.220.720.120.930.161.030.220.840.210.790.05

0.880.07

0.110.001

N(mgg"1) 1

0.510.050.550.050.500.090.600.020.530.030.440.04

0.520.19

0.080.001

P

:^g g"1)

436

314

518

266

296

416

3741

NS

C/N

19

13

18

16

16

18

174

C/P

230

232

182

396

289

193

23717

BD, bulk density; MC, water content; OC, organic C; M, mean; and SE, standard error of themean.

double with a lesser proportion of leaf than in an 8-year-old stand on sodic soil (Garg,1992). However, the differentiation of organic layers of the forest floor was achievedfaster in a high-density plantation in an arid region of India (Toky & Singh, 1993).Tropical and subtropical forest floor litter acts as a buffer medium in soil conservationefforts to release nutrients slowly. Consequently, soil reclamation takes a longer time thanbuilding of the forest floor, and amelioration will depend on the rate of organic residuebiodégradation.

Litter accumulation and decomposition are known to be influenced by climatic con-ditions, microorganisms populations and diversity, and substrate quality. Decompositionenriches the soil and residual litter, on the other hand, protects the soil from water andwind erosion. Decomposition estimated in our study by direct (decrease in forest floor)as well as indirect (\-K) methods compared fairly well with decomposition on the orderof 43% and 47% per year of the standing crop of litter. This rate was slower than ratesreported for other tropical forests (Olson, 1963; Singh & Singh, 1991). At this rate, meanresidence time of the litter on the forest floor was longer than that of many naturalforests of the tropical and subtropical regions (Vogt et al., 1986). The longer meanresidence time might be expected because of lower microbial populations and diversity insodic soils. Tissue chemistry effects on decomposition played the greatest role in nutrientreplenishment for a favorable substrate quality (Swift et al., 1979; Melillo et al., 1982). Asubstrate quality of a higher nutrient content and a lower lignin content is always preferredby the microorganisms, and therefore, low availability of N and P restrained the Cturnover from the litter (Vitousek et al., 1994; Constantinides & Fownes, 1994). The leaf

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Sodic Soil Reclamation 209

tissues are preferably disintegrated and their nutrients are mineralized faster than thewoody litter owing to a better substrate quality.

Though the pool sizes of C and N in the organic detritus mass (LFH) were only 12%and 9% of the underlying mineral soil (30 cm), respectively, their regular throughputsacross the forest floor had significantly altered many of the soil properties during the 36years. Such changes over short intervals (2-8 years) were monitored in other studies,showing a reduction of pH from 2% to 17% of the initial pH status, and a twofold tosixfold increase for C content (Singh, 1989; Garg & Jain, 1992; Shukla & Misra, 1993).Bioreclamation is generally a very slow process, and therefore, hasty conclusions maylead to ambiguous projections about the reclamation efficiency. Besides litter, tree rootinputs also contribute to some extent to soil reclamation, particularly the fine root mor-tality, which was estimated as 19% of the total litter input in periodic decrease of fine rootbiomass during the annual cycle.

Despite the large variations in N content between the leguminous and nonleguminousspecies litter on the forest floor layers (60-100%), species effect on soil N pool was notdifferentiated. However, species tolerance to sodicity has varied substantially (Singh et al.,1992). Verma et al. (1982) reported that mixed litter from multiple species reclaimed thesodic soils more efficiently in comparison to litter of individual species. Introduction offast growing exotics, such as eucalyptus and poplar in recent rehabilitation programs, hasbeen found to be relatively less effective in soil reclamation (Gill et al., 1987) because ofa lesser mineralization rate of Eucalyptus litter in comparison to the natural Acacia standsstudied elsewhere (Bernhard-Reversat, 1988). Moreover, eucalyptus and poplars requireincreased nutrient levels for growth. Therefore, further stand development may depend ona sustainable nutrient pool on sodic soils during their restoration.

Litter dynamics showed that the building of forest floor had reached an almost steadystate level over 36 years. Soil reclamation was still incomplete due to limited mineral-ization of nutrients from the accumulated litter. Consequently, it could not alter theavailable fraction of the growth-limiting nutrients (N and P) in the soil. However, thecontents of total N and available P in these soils compared closely to that of a dry tropicalnatural forest of India measured as 0.6-0.7 mg N g"1 and 30-32 P (xg g"1 (Singh & Misra,1979). Nevertheless, C and N contents have been reported 4-5 times greater in the soilsof a well-managed plantation forest (sal, teak, eucalyptus, and pine) in the humid tropicsof India (Sharma & Pande, 1989). It is, therefore, concluded that the organic matter andN contents had not been replenished in the soil because the system was so depleted thatthe litter inputs had not yet offset the degraded conditions. Conversion of organic N intothe inorganic forms (NH4

+, NO2~, NO3") was impeded during the reclamation of sodicsoils. Of the N that was mineralized, some was immobilized in microbial biomass, whileanother portion was consumed in plant uptake. This has led to reduced available N contentin the forested soil, whereas the available P has maintained its original status because ofan already high pressure.

References

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