Long-term effects of different land use and soil management on various organic carbon fractions in an Inceptisol of subtropical India.
The carbon stock in agricultural soils is affected by changes in land use or management practices and converting forests to croplands has contributed to the historical rise in global levels of atmospheric C[O.sub.2] (Wilson 1978; Houghton et al. 1983; Flach et al. 1997). Therefore, the dynamics of C in terrestrial ecosystems have been at the centre of attention and there is much interest in assessing the potential capacity of highly managed agricultural soils to store surplus atmospheric C[O.sub.2].
Land-use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical region, can alter soil C (Chen et al. 2003). Therefore, soil organic C (SOC) concentrations reflect soil and ecosystem processes as well as past management practices for both agricultural and nonagricultural soils (Collins et al.. 2000). However, Murty et al.. (2002) found no significant overall change in SOC due to land-use change from forest to pasture, although changes in soil C at individual sites ranged from -50% to +160%. These findings showed a high variability in soil C stocks in the changed ecosystems and possibly even within one ecosystem. Hence, ecosystems may lose or gain C, depending on soil type, tillage operations, pasture management, plant residue retention or removal, fertiliser applications, organic manures/residues additions, and integrated nutrient management (Fearnside and Barbosa 1998). Although the effects of no tillage on soil organic matter (SOM) have been well documented, the information on land use and soil management effects on SOM is scarce. Sometimes the trend is inconsistent because of many factors such as soil type, cropping systems, residue management, and climate (Reicosky et al.. 1995).
Accumulating evidence suggests that certain fractions of SOC are more important sensitive indicators of management practices (Cambardella and Elliott 1992; Caner et al. 1998; Von Lutzow et al. 2002; Freixo et al. 2002). The SOM fractions that are considered important include microbial biomass C (MBC), particulate organic C (POC), C mineralisation ([C.sub.min]), and microbial metabolic quotient ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) (Rudrappa et al. 2006). Microbial biomass has been found to be more responsive to cultural treatments than changes in total SOM (Powlson and Jenkinson 1981; McGill et al. 1986). Physical protection of POC in soils is thought to be associated with encrustation by clay particles (Tisdall and Oades 1982) and/or entrapment in small pores within soil aggregates that may be inaccessible to microbes (Elliott and Coleman 1988). Physical protection is likely to be less in cultivated than in uncultivated soils because tillage periodically breaks up soil aggregates and exposes previously protected SOM (Balesdent et al. 1990).
Agro-forestry is an important land use practiced on degraded soils in the tropics for improvement in fertility and productivity through storing of additional C. But there is a paucity of information available on the long-term effect of agro-forestry plantations on soil C sequestration in tropical climates. Besides, in peri-urban agriculture around major metropolitan cities in India the use of domestic and industrial effluents for irrigation is inevitable due to over-exploitation of underground water. The farmers are enthusiastic to use sewage effluent for the purpose of irrigation because this is a rich source of organic matter and essential plant nutrients (Rattan et al. 2005). Rice-wheat is also one of the important cropping systems followed by the farmers engaged in peri-urban agriculture in the Inceptisol of Indo-Gangetic alluvial plains. Vegetables are also grown profusely in the periphery of metropolitan cities with and without organic manures in order to fulfill the huge demand of the ever-growing population of the cities. To date, no information is available on the long-term effects of the above land uses and soil managements on different SOC and its different fractions. Nevertheless, most of the C aggradation studies are confined only to the areas under temperate climate. Under tropical conditions the turnover rate of SOM is very rapid (Chander et al. 1997). Only few studies have been conducted on SOM dynamics and soil microbial activities in relation to different fertiliser and manure management practices (Goyal et al. 1993, 1999; Rudrappa et al. 2006).
The hypothesis for the present study was that different contrasting land use and soil management (different cropping systems, cultivation practices, fertiliser and organic matter additions) practices could bring significant changes to various SOC fractions. The objectives of the study were to (i) assess the depth-wise (0-0.05, 0.05-0.10, 0.10-0.20 m) as well as the whole soil layer (0-0.20 m) distribution and accumulation of different organic C fractions, e.g. SOC, POC, MBC, [C.sub.min], microbial quotient, and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], across contrasting land use and soil management practices (agro-forestry plantation, vegetable field, sewage-irrigated rice wheat, tube-well irrigated rice-wheat, and uncultivated soil); (ii) quantitatively assess the changes in different organic C fractions in various land uses and soil managements compared with uncultivated soil in semi-arid subtropical India.
Materials and methods
The study was conducted in soils collected from different land use and management systems present at the Indian Agricultural Research Institute Farm (28[degrees]4'N, 77[degrees]12'E; 228.2m a.s.l.), New Delhi. The climate of Delhi is semi-arid subtropical, with a mean annual temperature of 30[degrees]C and total annual rainfall of approximately 769 mm, mostly occurring during Jul-September.
The important land use and soil management practices chosen for the current investigation comprised agro-forestry plantation (AF), vegetable field (VF), sewage-irrigated rice-wheat (SIRW), tube-well irrigated rice-wheat (TIRW), and uncultivated soils (UC). Agro-forestry (irrigated with tube-well water) comprises mixed plantations of Eucalyptus tereticornis L. and Leuceana leucocephala L. The vegetable field grows Solanum melongena L., Brassica oleracea var. capitata L., Brassica oleracea var. botrytis L., and Lycopersicon esculentum L. up to maturity, mainly with chemical fertilisers (N, [P.sub.2][0.sub.5], and [K.sub.2]O at 80, 40, and 40 kg/ha, respectively), with occasional dressing of farmyard manure applied at 10 t/ha. In the sewage-irrigated rice-wheat cropping system the high-yielding varieties of both the crops (rice, wheat) are grown with chemical fertilisers. A fertiliser dose of 120kgN, 60kg [P.sub.2][0.sub.5], and 60kg [K.sub.2]O/ha is applied to each crop. Both the crops are irrigated with sewage effluents emanating from sewage treatment plants at the Indian Agricultural Research Institute Farm. In tube-well irrigated soils the rice and wheat are cultivated in sequence with the same management practices as that of sewage-irrigated soil except for the source of irrigation, which is met here through tube-well water. In uncultivated soil, grass species of Cynodon dactylon L. and Cyperus rotundus L. grow in patches. All these land uses and soil management practices have been operative at the farm of the Indian Agricultural Research Institute, New Delhi, India, for more than 2 decades.
Each land use had 3 replicated plots. Soil samples from each replicated plot were collected randomly from 5 spots with the help of a core sampler (50 mm i.d., 0.05 and 0.10 m height). The individual soil core was divided into segments of 0-0.05, 0.05-0.10, and 0.10-0.20 m. One composite sample representing each replication was prepared by mixing 5 cores of respective soil depth. The soil samples were obtained after removing plant debris from the surface. Immediately after collections, the soil samples were brought to the laboratory in a cooler. The soil cores were preserved in a refrigerator before measurement of [C.sub.min] and MBC. A subset of soil samples was air dried and passed through a 2-mm sieve for determination of pH, SOC, and POC. Bulk density was determined by using the core method (Veihmeyer and Hendrickson 1948). The DTPA-extractable Zn, Cu, Cd, Pb, and Ni contents in rice-wheat sewage-irrigated soils were 9.5, 4.1, 0.1, 3.8, and 0.4mg/kg, respectively (Lindsay and Norvel 1978). The textural analysis of the soils was done by the hydrometer method (Table 1) (Bouyoucos 1962). The soils are of alluvial origin, clay loam in texture, and belong to the hyperthermic family of Typic Haplustept.
Soil pH was measured in water at a soil-suspension ratio of 1 : 5 (McLean 1982). The content of the beaker was mixed thoroughly with a glass rod, intermittently for 30 rain. The pH of the soil suspension was measured with a pH meter.
A carbon mineralisation study was carried out in the laboratory on soils collected from 0-0.05, 0.05-0.10, and 0.10-0.20m depths. Soil was moistened to field capacity and incubated for 90 days at 28[degrees]C. Incubated soil (100g on an oven-dry basis) was placed in a 500-mL glass jar along with a vial containing 0.1 N NaOH to trap evolved C[O.sub.2] (Zibilske 1994). The alkali was replaced twice during the first 2 weeks, followed by once a week for the rest of the incubation period. The unspent alkali was titrated back with standard HCl to estimate the C[O.sub.2]-C evolved from soil.
Soil C fractionation and measurements
Soil organic C was determined by wet digestion with potassium dichromate along with 3:2 [H.sub.2]S[O.sub.4]: 85% [H.sub.3]P[O.sub.4] digestion mixture in a digestion block set at 120[degrees]C for 2 h (Snyder and Trofymow 1984). A pre-treatment with 3 mL of 1 N HCl/g of soil was used for removal of carbonate and bicarbonate. Particulate organic matter (POM) was separated from 2 mm soil following the method described by Cambardella and Elliott (1992). The C content in POM was determined following the method of Snyder and Trofymow (1984). Soil MBC was determined by the chloroform fumigation extraction method (Horwath and Paul 1994). The C contents in [K.sub.2]S[0.sub.4] extracts of both fumigated and unfumigated soil samples were digested in the presence of potassium persulfate ([K.sub.2][S.sub.2][O.sub.8]) and 0.025 M [H.sub.2]S[O.sub.4] in a digestion block set at 120[degrees]C for 2 h. The amount of C[O.sub.2]-C thus evolved was estimated by the same procedure as described in the case of SOC estimation (Snyder and Trofymow 1984). We used an efficiency of extraction of 0.35 as reported by Voroney et al. (1991). Microbial quotient was measured as the ratio of MBC to SOC. Respiratory quotient ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) was measured as lag C[O.sub.2]-C evolved in the last week of incubation per hour per mg of MBC. The weight of soil in 1 ha (10 000 [m.sup.2]) to an individual depth (0.05 m in the upper 2 depths and 0.1 m in the lowest depth) was determined by using bulk density value. Soil organic C and its fractions, e.g. [C.sub.min], MBC, and POC, were estimated as Mg/ha separately in 3 soil depths and these were added to get C fractions throughout the soil profile (0-0.20 m). The ratios of various organic C fractions in 0-0.05 m to that in 0.10-0.20 m depth were also calculated.
The experiment was conducted using a completely randomised design with Duncan's multiple range test (DMRT) for separation of means. For each soil parameter, the differences among various land uses and soil managements were calculated by DMRT for individual depth with the PC-based SPSS version 10.0 statistical package at a probability of 0.05. The significant difference between various land uses and uncultivated land at 0-0.20 m was statistically analysed by t-test at the 5% level of significance with the PC-based MSTATC program. The hypothesis in this case was that the difference between the experimental land use and uncultivated land is not different from 0.
The uncultivated soil showed significantly higher pH than all other land use and soil management systems (Table 2). Among the cultivated soils, sewage-irrigated rice-wheat showed significantly lower pH, particularly in the 0-0.05 m and 0.10-0.20 m soil layers. But this decline was not so conspicuous at subsurface soil layers. Agro-forestry plantation, vegetable field, and tube-well irrigated rice-wheat soils showed almost similar pH values. Except for the tube-well irrigated rice-wheat, the others had a marginal increase in pH from the surface to the subsurface soil layer.
Irrespective of soil depth, there was a greater relative decrease in bulk density in agro-forestry soil, taking uncultivated soil as the benchmark, which showed the highest bulk density jointly with the vegetable field soil at all depths (Table 2). Even under the same cropping system (rice-wheat), sewage irrigation resulted in lower bulk density than tube-well irrigation. In general, bulk density increased from the surface to the subsurface soil layer. The bulk density at 0-0.20 m was lowest in agro-forestry soil; uncultivated soil jointly with vegetable field soil showed the highest bulk density. Sewage-irrigated rice-wheat soil had lower bulk density than tube-well irrigated rice-wheat soil. The bulk density in soils under various land use and management practices at 0-0.20m increased in the following order: agro-forestry (1.34 Mg/[m.sup.3]) < sewage-irrigated rice-wheat (1.41 Mg/[m.sup.3]) < tube-well rice-wheat (1.43 Mg/[m.sup.3]) < vegetable field (1.49 Mg/[m.sup.3]) = uncultivated soil (1.49 Mg/[m.sup.3]).
Soil organic C
Soil organic C in agro-forestry soil was greater than in other treatments particularly at 0-0.05 and 0.05-0.10m soil depth, whereas at 0.10-0.20m, agro-forestry jointly with sewage-irrigated rice-wheat soil showed highest SOC content (Table 3). Among the arable soils, sewage-irrigated rice-wheat had significantly higher SOC content than tube-well irrigated rice-wheat as well as vegetable field soil at all soil depths. Although the above 2 land uses showed greater SOC than uncultivated soil, the vegetable field and/or tube-well irrigated flee-wheat soils had similar SOC to uncultivated soils. It is quite interesting that the decrease in SOC along soil depth ([SOC.sub.0-0.05 m]/[SOC.sub.0.10-0.20 m]) was significantly higher in agro-forestry than in cultivated soils (except VF) (Table 4).
Soil organic C stock in the 04).20 m soil layer was highest in agro-forestry soil (33.7Mg/ha) (Fig. 1). Under the same rice-wheat cropping system, sewage irrigation showed significantly higher SOC accumulation (28.6 Mg/ha) than tube-well irrigation (21.1Mg/ha). Soil organic C did not differ significantly among soils under tube-well irrigated rice-wheat, vegetable field, and uncultivated land. The absolute change in SOC in various land uses and managements compared with uncultivated soil was maximum in the agro-forestry plantation (12.SMg/ha) followed by sewage-irrigated rice-wheat soil (7.68 Mg/ha) (Fig. 2). This change was significantly negative (-0.51 Mg/ha) in the case of vegetable field soil.
[FIGURES 1-2 OMITTED]
Particulate organic C
Irrespective of soil depth, POC was greater in the agro-forestry plantation (Table 3). There was a greater accumulation of POC in sewage-irrigated rice-wheat compared with vegetable field and tube-well irrigated rice-wheat soils at all soil depths. Particulate organic C content was lowest in uncultivated and tube-well irrigated flee-wheat soils at the 0-0.05 m soil depth, whereas at the other 2 depths these 2 along with vegetable field soils had similar POC contents. The decreases in POC along soil depth ([POC.sub.0-0.05 m]/[POC.sub.0.10-020 m]) were greater in vegetable field, agro-forestry plantation, and sewage-irrigated flee-wheat than in tube-well irrigated rice-wheat and uncultivated soils (Table 4). The % POC of SOC was greater in the agro-forestry plantation (Table 5). At the 0.05-0. l0 m soil depth, sewage-irrigated rice-wheat was similar to agro-forestry plantation soil with respect to % POC of SOC, whereas at 0.10-0.20 m, vegetable field and tube-well irrigated rice-wheat soils were similar to agro-forestry plantation soil.
Particulate organic C stock in the 0-0.20 m soil layer was highest in agro-forestry plantation (3.58 Mg/ha) and lowest in uncultivated soil (jointly with tube-well irrigated rice-wheat soil) (1.76 Mg/ha) (Fig. 1). Sewage-irrigated rice-wheat ranked second with respect to POC stock (2.42 Mg/ha). Vegetable field soil was in between the highest and lowest values for POC stock. The absolute change in POC stock in agro-forestry plantation compared with uncultivated soil was highest (Fig. 2). Sewage irrigated rice-wheat and vegetable field soil showed significantly positive changes with respect to POC stock.
Microbial biomass C
Microbial biomass C content in soils under different land use and management practice showed an almost similar pattern to that of SOC content (Table 3). Irrespective of soil depth, MBC was greatest in agro-forestry soil. Relative contents of MBC in sewage-irrigated rice-wheat and tube-well irrigated rice-wheat soil showed a dissimilar pattern at the 0-0.05 and 0.05-0.10 m soil depths but at 0.104).20 m these 2 systems did not differ. At both 0-0.05 and 0.05-0.10 m soil depths, MBC contents in sewage-irrigated rice-wheat were significantly higher than in tube-well irrigated flee-wheat soil. Uncultivated soil along with vegetable field or tube-well irrigated rice-wheat soil showed lowest MBC depending upon the soil depth. Microbial biomass C decreased down the soil depth. This decrease in MBC along soil depth ([MBC.sub.0-0.05 m]/[MBC.sub.0.10-0.20 m]) was highest in sewage-irrigated rice-wheat and was lowest in tube-well irrigated rice-wheat (jointly with uncultivated soil) soil (Table 4). Agro-forestry and vegetable field soils were in between the above 2 land uses.
Microbial biomass C stock in 0-0.20 m depth was greatest in agro-forestry soil (0.81 Mg/ha) (Fig. 1). Uncultivated soil jointly with tube-well irrigated flee-wheat showed the lowest amount of MBC stock. Sewage-irrigated flee-wheat soil ranked second (0.63 Mg/ha) and vegetable field ranked third with respect to MBC stock (0.54 Mg/ha). The absolute changes in MBC stock in agro-forestry plantation and sewage-irrigated rice-wheat compared with uncultivated soil were significantly positive (Fig. 2).
Cumulative C mineralisation
Total amount of C mineralised over 90 days incubation period was highest in sewage-irrigated rice-wheat at the 0-0.05 m soil depth, whereas at both 0.05-0.10 m and 0.10-).20 m the highest amount of [C.sub.min] was observed in sewage-irrigated flee-wheat soil (Table 3). Irrespective of soil depths, vegetable field soil showed the lowest [C.sub.min]. Soils from the vegetable field showed an almost equal magnitude of [C.sub.min] down the soil profile, whereas the decrease in [C.sub.min] ([C.sub.min 0-0.05 m]/[C.sub.min 0.10-0.20 m]) along the depth was drastic in agro-forestry soil (Table 4).
The total amount of [C.sub.min], in the 0-0.20m soil layer was highest in sewage-irrigated rice-wheat and agro-forestry soils (Fig. 1). The decreasing order of [C.sub.min] was as follows: sewage-irrigated rice wheat (4.92 Mg/ha) = agro-forestry (4.44 Mg/ha) > tube-well irrigated rice wheat (3.54 Mg/ha)= uncultivated soil (3.12 Mg/ha)> vegetable field (1.72 Mg/ha). The absolute change in [C.sub.min] was significantly negative in vegetable field compared with uncultivated soil, whereas agro-forestry plantation and sewage-irrigated rice-wheat soils showed significantly positive changes (Fig. 2).
At 0-0.05 m soil depth the microbial quotient varied from 0.025 to 0.035 and it was greater in sewage-irrigated rice-wheat and vegetable field soil (Table 5). The quotients were lower in soils under agro-forestry plantation, tube-well irrigated rice-wheat, and uncultivated soils. The value drastically reduced from surface (0-0.05 m) to subsurface (0.05-0.10 m) soil, where vegetable field and uncultivated soil exhibited higher quotients than others. At 0.10-0.20m soil depth, the relative pattern of microbial quotients was different from that obtained at 0-0.05 m. The quotients in soils under agro-forestry plantation, tube-well irrigated rice-wheat, vegetable field, and uncultivated soils were almost similar. Interestingly, sewage-irrigated rice-wheat (which showed the highest microbial quotient at 64).05 m) recorded the lowest quotient at this depth.
Microbial metabolic quotient
Microbial metabolic quotient ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) behaved differently from microbial quotient (Table 5). Irrespective of soil depths, the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] values were highest in uncultivated soils, whereas at 0.05-0.10 m, sewage-irrigated rice-wheat soil showed a similar quotient to uncultivated soil. In the 0-0.05 and 0.05-0.10m soil layers, vegetable field and tube-well irrigated rice wheat ranked third with respect to [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], whereas agro-forestry was second highest in this respect. At 0.10-0.20 m, sewage-irrigated rice-wheat and vegetable field soil were second and third highest, respectively, whereas at the same depth the lowest [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was observed in the agro-forestry system (jointly with tube-well irrigated rice-wheat soil), and the highest in uncultivated soil. In general, unlike microbial quotient, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] increased along the soil depth. Such increase was not dramatic in the tube-well irrigated rice-wheat system, which recorded very low metabolic quotients down the profile.
Agro-forestry plantation showed highest SOC, POC, and MBC, followed by sewage-irrigated rice-wheat soil. This corroborated the findings of Vidya et al. (2002) who also reported highest MBC in natural forest soil among different land use systems. The transformation of lmperata grassland to tree-based systems further increased soil fertility and organic C stock resulting from enhanced nutrient cycling (Macandog et al. 1998). The build up of different C fractions in the agro-forestry plantation is mainly due to long-term additions of C through leaf litter. Nevertheless the soils of this plantation are never disturbed by tillage operations that are otherwise very frequently practiced in other cultivated soils of the present study. Thus SOC and its fractions in this land use accumulated more significantly in the surface layer than in the subsurface soil layer. This is further proved from the ratio of [SOC.sub.0-0.05 m]/[SOC.sub.0.10-0.20 m], which was greater in the agro-forestry system than in other cultivated soils (except VF). Compared with other land uses, the vegetable field exhibited the lowest amount of SOC at 0.10-0.20 m and thus increased the ratio of [SOC.sub.0-0.05 m]/[SOC.sub.0.10-0.20 m], which was comparable with the agro-forestry plantation. The vigorous puddling during rice cultivation in both sewage-irrigated rice-wheat and tube-well irrigated rice-wheat soil facilitated uniform mixing of surface soil with subsurface soil. Therefore, the [SOC.sub.0-0.05 m]/[SOC.sub.0.10-0.20 m] ratio was significantly lower in rice-wheat than in agro-forestry soil.
Sewage-irrigated rice-wheat soil supported higher SOC as well as MBC than other cultivated and uncultivated soils probably be due to accumulation of organic materials added through sewage effluents. The reduction of pH in this soil might be due to long-term cumulative additions of acidic material through sewage effluents. In this land use the decrease in MBC down the soil layer ([MBC.sub.0-0.05 m]/[MBC.sub.0.10-0.20 m]) was highest possibly due to proportionately higher accumulation of SOC at 0-0.05 m than at 0.10-0.20 cm depth. Vegetable field, tube-well irrigated rice-wheat, and uncultivated soils showed less SOC and MBC. However, very high values of these parameters have been reported in vegetable and paddy fields from China (Chert et al. 2003).
Uncultivated soil that supported patches of grasses showed lower organic C, POC, as well as MBC. Particulate organic C, a physically protected moderately labile pool, is generally accumulated in such management systems where soil is not disturbed. In this respect, the agro-forestry plantation protected the POC well due to non-disturbance of soil in this system. Nevertheless there is a greater stratification of POC down the soil layer in this system compared with cultivated land where the soils are disturbed frequently through tillage operations. Thus the ratio of [POC.sub.0-0.05 m]/[POC.sub.0.10-0.20 m] was highest in agro-forestry (jointly with VF and SIRW) soil. Particulate organic C as a percentage of SOC (POC/SOC) can be quite high under an agro-forestry plantation. The proportion of POC to SOC in our study varied from 6.37 to 11.6%. A higher proportion of 32% was reported from Minnesota (Huggins et al. 1997) and 39% in a virgin grassland soil in Nebraska, USA (Cambardella and Elliott 1994). It has been observed from our study that the uncultivated soils showed fewer organic C fractions. However, it was reported that the permanent grasslands are capable of accumulating very high SOC (Gardi et al. 2002; Leifeld and Krgel-Knabner 2005). Although sewage irrigation in the rice-wheat system improved both SOC and POC fractions, stratification was less in this system compared with the agro-forestry plantation. This was primarily due to repeated soil disturbance during tillage operations in the cultivated system. As improvement in SOC is inversely associated with reduction in bulk density, a negative association between these 2 parameters was expected and reported elsewhere (Aragon et al. 2000; Deshpande et al. 2000; Rudrappa et al. 2006).
Although agro-forestry soil showed the highest amount of SOC, the relative amount of C mineralised in it was comparatively lower than that in sewage-irrigated rice-wheat and uncultivated soils. This clearly suggests that the agro-forestry plantation could support a more stable pool of SOC. This result indicated that the quality of organic matter, in terms of different SOC pools having different residence times in the soil, ultimately dictated the microbial population and its respiratory activities. Tornquist et al. (1999) reported higher mineralisable C levels from a pasture surface soil, but no differences in mineralisable N were found in soils under pasture and agro-forestry plantation. The ratio of [C.sub.min 0-0.05 m]/[C.sub.min 0.10-0.20 m] was greatest in the agro-forestry soil, suggesting more accumulation of mineralisable C in the surface than in the subsurface soil layer. In other cultivated soils this ratio was lower because of less stratification of mineralisable C due to repeated tillage operations. As the organic C input in uncultivated soil is very low, the SOC accumulation is lower.
The microbial quotients in our study are within the range of reported values of 1-4% (Jenkinson and Ladd 1981; Brookes et al. 1984; Anderson and Domsch 1989). Tube-well irrigated rice-wheat, vegetable field, and uncultivated soils were lower in both SOC and MBC; hence, exhibited lower microbial quotients. The decline in microbial quotient from 0.023 to 0.011 due to a decrease in SOC from 65 to 15 g C/kg, was reported by Haynes and Tregurtha (1999).
Respiratory quotient ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) actually measures the efficiency of an agro-ecosystem to preserve organic C in soil. Agro-forestry soil, being stable in organic C, probably showed a moderate level of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. By contrast, sewage-irrigated rice-wheat soil showed a considerable accumulation of SOC, and the stability of SOC in this soil might be lower, leading to enhanced [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. In this soil, MBC was not adversely affected at the present level of heavy metals added through sewage effluents; thus, it could show moderate to high respiratory quotients. As the vegetable field and tube-well irrigated rice-wheat soils were continuously cultivated without much organic input, these could only retain stable organic C fractions with the loss of the majority of labile C pools over time. Therefore, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was lower in these land use systems. It has been reported previously that the combined application of chemical fertilisers and farmyard manure or wheat straw along with continuous waterlogging can markedly increase SOC, but significantly reduce the paddy labile SOC fractions (Yang et al. 2005). In general the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in the arable land of our study was lower than under the undisturbed site, although the reverse trend was reported by Haynes (1999). The microbial quotient declined with depth, whilst [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. A similar trend was reported by Rudrappa et al. (2006).
Conversion of arable soils into agro-forestry plantations for more than 2 decades could substantially sequester organic C stock in soils of subtropical India. This could be one of the management practices for converting degraded arable land with sequestrations of large amounts of organic C. On arable land, sewage-effluent irrigation benefited the soil more in terms of organic C accumulation than tube-well irrigation. Cultivation of vegetable or rice-wheat with tube-well water did not deplete the organic C fractions compared with uncultivated soil.
Funding provided by the Director, Indian Agricultural Research Institute, New Delhi, to carry out this research work is gratefully acknowledged.
Manuscript received 12 June 2006, accepted 11 December 2006
Anderson JPE, Domsch KH (1989) Ratios of microbial biomass carbon to total organic carbon in arable soils. Soil Biology and Biochemistry 21, 471-479. doi: 10.1016/0038-0717(89)90117-X
Aragon A, Garcia MG, Filgueira RR, Pachepsky YA (2000) Maximum compactibility of Argentine soils from the Proctor test: the relationship with organic carbon and water content. Soil and Tillage Research 56, 197-204. doi: 10.1016/S0167-1987(00)00144-6
Balesdent J, Mariotti A, Boisgontier D (1990) Effect of tillage on soil carbon mineralization estimated from [sup.13]C abundance in maize fields. Journal o['Soil Science 41,587-596. doi: 10.1111/j.1365-2389. 1990.tb00228.x
Bouyoucos GJ (1962) Hydrometer method improved for making particle size analysis of soils. Agronomy Journal 54, 464-465.
Brookes PC, Powlson DS, Jenkinson DS (1984) Phosphorus in soil microbial biomass. Soil Biology and Biochemistry 16, 169-175. doi: 10.1016/0038-0717(84)90108-1
Cambardella CA, Elliott ET (1992) Particulate soil organic matter changes across a grassland cultivation sequence. Soil Science Society of America Journal 56, 777-778.
Cambardella CA, Elliott ET (1994) Carbon and nitrogen dynamics in soil organic matter fractions from cultivated grassland soils. Soil Science Society of America Journal 58, 123-130.
Carter MR, Gregorich EG, Angers DA, Donald RG, Bolinder MA (1998) Organic C and N storage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada. Soil and Tillage Research 47, 253-261. doi: 10.1016/S0167-1987(98)00114-7
Chander K, Goyal S, Mundra MC, Kapoor KK (1997) Organic mater, microbial biomass and enzyme activity of soils under different crop rotations in the tropics. Biology and Fertility of Soils 24, 306-310. doi: 10. 1007/s003740050248
Chert Guo Chao, He Zhen Li, Chen GC, He ZL (2003) Effect of land use on microbial biomass-C, -N and -P in red soils. Journal of Zhejiang University Science 4, 480-484.
Collins HP, Elliot ET, Paustian K, Bundy LG, Dick WA, Huggins DR, Smucker AJM, Paul EA (2000) Soil carbon and fluxes in long-term corn belt agroecosystems. Soil Biology and Biochemistry 32, 157-168. doi: 10.1016/S0038-0717(99)00136-4
Deshpande AN, Pawar RB, Kale SP (2000) Effect of different crop sequences on physical properties of Inceptisols under dryland conditions. Journal of Soils and Crops tO, 46-49.
Elliott ET, Coleman DC (1988) Let the soil work for us. Ecological Bulletin 39, 23-32 [Copenhagen].
Fearnside PM, Barbosa RI (1998) Soil carbon changes from conversion of forest to pasture in Brazilian Amazonia. Forest Ecology and Management 108, 147-166. doi: 10.1016/S0378-1127(98)00222-9
Flach KW, Barnwell TO Jr, Crosson P (1997) Impacts of agriculture on atmospheric carbon dioxide. In 'Soil organic matter in temperature agro-ecosystems: long term experiments in North America'. (Ed. EA Paul) pp. 3-13. (CRC Press: Boca Raton, FL)
Freixo AA, Machado PL, Santos HP (2002) Soil organic carbon and fractions of a Rhodic Ferralsol under the influence of tillage and crop rotation systems in southern Brazil. Soil and Tillage Research 64, 221-230. doi: 10.1016/S0167-1987(01)00262-8
Gardi C, Tomaselli M, Parisi V, Petraglia A, Santini C (2002) Soil quality indicators and biodiversity in northern Italian permanent grasslands. European Journal of Soil Biolology 38, 103-110. doi: 10.1016/S1164-5563(01)01111-6
Goyal S, Chander K, Mundra MC, Kapoor KK (1999) Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions. Biology and Fertility of Soils 29, 196-200. doi: 10.1007/s003740050544
Goyal S, Mishra MM, Dhankar SS, Kapoor KK (1993) Microbial biomass turnover and enzyme activities following the application of farmyard manure to field soil with and without previous long term applications. Biology and Fertility of Soils 15, 60-54. doi: 10.1007/BF00336290
Haynes RJ (1999) Size and activity of the soil microbial biomass under grass and arable management. Biology and Fertility of Soils 30, 210-216. doi: 10.1007/s003740050610
Haynes RJ, Tregurtha R (1999) Effects of increasing periods under intensive arable vegetable production on biological chemical and physical indices of soil quality. Biology and Fertility of Soils 28, 259-266. doi: 10.1007/s003740050491
Horwath WR, Paul EA (1994) Microbial biomass. In 'Methods of soil analysis, Part 2. Microbiological and biochemical properties. SSSA, Book Series No. 5'. (Eds JM Bingham, SH Mickelson) pp. 753-773. (ASA, SSSA: Madison, WI)
Houghton RA, Hobbie JE, Mellilo JM, Moore B, Peterson B J, Shaver GR, Woodwell GM (1983) Changes in the carbon content of terrestrial biota and soils between 1860 and 1980: a net release of CO2 to the atmosphere. Ecological Monographs 53, 235 240. doi: 10.2307/1942531
Huggins DR, Allan DL, Gardner JC, Karlen DL, Bezdicek DF, Rosek M J, Alms MJ, Flock M, Miller BS, Staben ML (1997) Enhancing carbon sequestration in CRP-managed land. In 'Management of carbon sequestration in soil'. (Eds R Lal, JM Kimble, RF Folette, BA Stewart) pp. 323-350. (CRC Press: Boca Raton, FL)
Jenkinson DS, Ladd JN (1981) Microbial biomass in soils; measurement and turnover. In 'Soil biochemsitry, 5'. (Eds EA Paul, JN Ladd) pp. 415-417. (Marcel Dekker: New York)
Leifeld J, Krgel-Knabner 1 (2005) Soil organic matter fractions as early indicators for carbon stock changes under different land-use? Geoderma 124, 143 155. doi: 10.1016/j.geoderma.2004.04.009
Lindsay WL, Norvel WA (1978) Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Science Society of America Journal 42, 421-448.
Von Lutzow M, Leifeld J, Kainz M, Kogel-Knabner I, Munch JC (2002) Indications for soil organic matter quality in soils under different management. Geoderma 105, 243 258. doi: 10.1016/S0016-7061 (01)00106-9
Macandog DBM, Predo CD, Rocamora PM (1998) Environmental and economic impacts of land-use change in tropical Imperata areas. Philippine Journal of Crop Science 23, 20-26.
McGill WB, Cannon KR, Robertson JA, Cook FD (1986) Dynamics of soil microbial biomass and water soluble organic C in Breton L. after 50 years of cropping to two rotations. Canadian Journal of Soil Science 66, 1-9.
McLean EO (1982) Soil pH and lime requirement. In 'Methods of soil analysis, Part 2. Chemical and microbiological properties. SSSA, Book Series No. 9'. (Eds AL Page, RH Miller, DR Keeney) pp. 199-223. (ASA, SSSA: Madison, WI)
Murty D, Kirschbaum MF, McMurtrie RE, McGilvary H (2002) Does conversion of forest to agricultural land change soil carbon and nitrogen? A review of the literature. Global Change Biology 8, 105-123. doi: 10.1046/j. 1354-1013.2001.00459.x
Powlson DS, Jenkinson DS (1981) A comparison of the organic matter, biomass, ATP and mineralizable N contents of ploughed direct drilled soils. Journal of Agricultural Science (Cambridge) 97, 713-721.
Rattan RK, Datta SP, Chhonkar PK, Suribabu K, Singh AK (2005) Long-term impact of irrigation with sewage effluents on heavy metal content in soils, crops and groundwater--a case study. Agriculture, Ecosystems and Environment 109, 310-322. doi: 10.1016/j.agee.2005.02.025
Reicosky DC, Kemper WD, Langdale GW, Douglas CL Jr, Rasmussen PE (1995) Soil organic matter changes resulting from tillage and biomass production. Journal of Soil and Water Conservation 50, 253-261.
Rudrappa L, Purakayastha TJ, Singh Dhyan, Bhadraray S (2006) Long-term manuring and fertilization effects on soil organic carbon pools in a Typic Haplustept of semi-arid sub-tropical India. Soil and Tillage Research 88, 180-192. doi: I 0.1016/j.still.2005.05.008
Snyder JD, Trofymow JA (1984) Rapid accurate wet oxidation diffusion procedure for determining organic and inorganic carbon in plant and soil samples. Communications in Soil Science and Plant Analysis 15, 1587-1597.
Tisdall JM, Oades JM (1982) Organic matter and water-stable aggregates in soils. Journal oJSoil Science 33, 141 163. doi: 10.1111/j.1365-2389.1982.tb01755.x
Tornquist CG, Hons FM, Feagley SE, Haggar J (1999) Agroforestry system effects on soil characteristics of the Sarapiqui region of Costa Rica. Agriculture, Ecosystems and Environment 73, 1928. doi: 10.1016/ S0167-8809(99)00004-3
Veihmeyer FJ, Hendrickson AH (1948) Soil density and root penetration. Soil Science 65, 487-494. doi: 10.1097/00010694-194806000-00006
Vidya KR, Hareesh GR, Rajanna MD, Sringeswara AN, Balakrishna G, Balakrishna AN, Gowda B (2002) Changes in microbial biomass C, N and P as influenced by different land-uses. Myforest 38, 323-328.
Voroney RP, Winter JP, Gregorich EG (1991) Microbe/plant interactions. In 'Carbon isotope'. (Eds DC Coleman, B Fry) pp. 77-99. (Academic Press: New York)
Wilson AT (1978) Pioneer agriculture explosion and C[O.sub.2] levels in the atmosphere. Nature 273, 40-41. doi: 10.1038/273040a0
Yang C, Yang L, Ouyang Z (2005) Organic carbon and its fractions in paddy soil as affected by different nutrient and water regimes. Geoderma 124, 133 142. doi: 10.1016/j.geoderma.2004.04.008
Zibilske LM (1994) Carbon mineralization. In 'Methods of soil analysis, Part 2. Microbiological and biochemical properties. SSSA, Book Series No. 5'. (Eds JM Bingham, SH Mickelson) pp. 853 863. (ASA, SSSA: Madison, WI)
T. J. Purakayastha (A,C), P. K. Chhonkar (A), S. Bhadraray (A), A. K. Patra (A), V. Verma (A), and M. A. Khan (B)
(A) Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi--110 012, India.
(B) Central Potato Research Institute, Modipuram, Meerut--250 110, Uttar Pradesh, India.
(C) Corresponding author. Emails: email@example.com, firstname.lastname@example.org
Table 1. Particle size analysis of soils under various land uses and managements AF, Agro-forestry; VF vegetable field; TIRW tube-well irrigated rice-wheat; SIRW, sewage-irrigated rice-wheat; UC, uncultivated soil Soil depth Silt Textural (m) Sand (%) Clay class AF 0-0.05 26.3 35.3 38.4 Clay loam 0.05-0.10 26.3 35.3 38.4 0.10-0.20 28.3 35.3 36.4 VF 0-0.05 26.3 35.3 38.4 Clay loam 0.05-0.10 24.3 35.3 40.4 0.10-0.20 24.3 29.3 46.4 SIRW 0-0.05 26.3 34.3 39.4 Clay loam 0.05-0.10 28.3 33.3 38.4 0.10-0.20 27.3 35.4 37.3 TIRW 0-0.05 28.3 33.3 38.4 Clay loam 0.05-0.10 26.3 33.3 40.4 0.10-0.20 26.3 35.3 38.4 UC 0-0.05 28.3 33.3 38.4 Clay loam 0.05-0.10 26.3 29.3 44.4 0.10-0.20 26.3 37.3 36.4 Table 2. pH and bulk density (BD) of soils under various land uses and managements AF Agro-forestry; VF vegetable field; TIRW, tube-well irrigated rice--wheat; SIRW, sewage-irrigated rice wheat; UC, uncultivated soil. For the same measurement at a particular soil depth, means followed by the same letter are not significantly different (P=0.05) by Duncan's multiple range test Soil pH Depth (m): 0-0.05 0.05-0.10 0.10-0.20 AF 7.86b 8.03b 8.23b VF 7.63b 7.93b 7.97c SIRW 7.17c 7.47c 7.43d TIRW 7.836 7.50c 7.5d UC 8.26a 8.36a 8.67a BD (Mg/[m.sup.3] Depth (m): 0-0.05 0.05-0.10 0.10-0.20 0-0.20 AF 1.29d 1.35c 1.38d 1.34d VF 1.46ab 1.48a 1.54a 1.49a SIRW 1.37c 1.42b 1.44b 1.41c TIRW 1.43b 1.44b 1.49a 1.45b UC 1.47a 1.48a 1.52ab 1.49a Table 3. Soil organic C (SOC, g/kg), particulate organic C (POC, g/kg), microbial biomass C (MBC, g/kg), and C mineralisation ([C.sub.min] g/kg) in soils under various land uses and managements AF, Agro-forestry; VF, vegetable field; TIRW, tube-well irrigated rice-wheat; SIRW, sewage-irrigated rice-wheat; UC, uncultivated soil. For the same measurement at a particular soil depth, means followed by the same letter are not significantly different (P=0.05) by Duncan's multiple range test SOC Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 20.5a 13.1a 8.5a VF 9.9c 7.9d 4.7c SIRW 13.4b 10.2b 8.4a TIRW 10.1c 8.9c 5.0bc UC 9.9c 7.4d 5.3b POC Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 2.38a 1.30a 0.85a VF 1.06c 0.55c 0.46c SIRW 1.29b 0.98b 0.59b TIRW 0.95d 0.57c 0.45c UC 0.95d 0.56c 0.43c MBC Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 0.57a 0.30a 0.17a VF 0.32d 0.21b 0.09c SIRW 0.46b 0.226 0.11b TIRW 0.26d 0.18c 0.11b UC 0.26d 0.20bc 0.10bc [C.sub.min] Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 3.88a 1.11bc 0.87b VF 0.66d 0.56d 0.54c SIRW 2.36b 1.74a 1.44a TIRW 1.33c 1.246 1.146 UC 1.35c 1.04c 1.10b Table 4. Soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and C mineralisation ([C.sub.min]) ratios of 0-0.05 m to 0.10-0.20 m soil depth in soils under various land uses and managements AF, Agro-forestry; VF, vegetable field; TIRW, tube-well irrigated rice-wheat; SIRW, sewage-irrigated rice--wheat; UC, uncultivated soil. For individual organic C fraction ratios, means followed by the same letter are not significantly different (P = 0.05) by Duncan's multiple range test [SOC.sub.0-0.05m]/ [POC.sub.0-0.05m]/ [SOC.sub.0.10-0.20m] [POC.sub.0.10-0.20m] AF 2.47a 2.21a VF 2.38a 2.33a SIRW 2.09b 2.20a TIRW 2.01b 1.70b UC 1.86b 1.81b [MBC.sub.0-0.05m]/ [C.sub.min 0-0.05m]/ [MBC.sub.0.10-0.20m] [C.sub.min 0.10-0.20m] AF 3.27b 3.07a VF 3.38b 1.23b SIRW 4.09a 1.68b TIRW 2.27c 1.17b UC 2.46c 1.41b Table 5. Microbial quotient (mg MBC/mg SOC), microbial metabolic quotient ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], mg [CO.sub.2]-C/mg MBC.h), and ratio of particulate organic C (POC) to soil organic C (SOC) (%) in soils under various land uses and managements AF, Agro-forestry; VF, vegetable field; TIRW, tube-well irrigated rice-wheat; SIRW, sewage-irrigated rice wheat; UC, uncultivated soil. For the same measurement at a particular soil depth, means followed by the same letter are not significantly different (P = 0.05) by Duncan's multiple range test Microbial quotient Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 0.028b 0.023b 0.020a VF 0.033a 0.027a 0.020a SIRW 0.035a 0.021b 0.013b TIRW 0.025b 0.021b 0.022a UC 0.026b 0.027a 0.020a Microbial metabolic quotient Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 0.0026b 0.0032b 0.0025d VF 0.0013c 0.0018c 0.0053c SIRW 0.0029b 0.0054a 0.00766 TIRW 0.0014c 0.0017c 0.0022d UC 0.0062a 0.0049a 0.093a POC/SOC Depth (m) 0-0.05 0.05-0.10 0.10-0.20 AF 11.6a 9.95a 10.04a VF 10.8b 7.04bc 9.68a SIRW 9.62c 9.65a 6.95c TIRW 9.41c 6.37c 9.02ab UC 9.57c 7.59b 8.09bc
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|Author:||Purakayastha, T.J.; Chhonkar, P.K.; Bhadraray, S.; Patra, A.K.; Verma, V.; Khan, M.A.|
|Publication:||Australian Journal of Soil Research|
|Date:||Feb 1, 2007|
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