Tillage and residue management effects on soil aggregation, organic carbon dynamics and yield attribute in rice–wheat cropping system under reclaimed sodic soil

Soil & Tillage Research 136 (2014) 76–83

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Tillage and residue management effects on soil aggregation, organic carbon dynamics and yield attribute in rice–wheat cropping system under reclaimed sodic soil Shreyasi Gupta Choudhury a,*, Sonal Srivastava b, Ranbir Singh a, S.K. Chaudhari a, D.K. Sharma a, S.K. Singh c, Dipak Sarkar d a

Central Soil Salinity Research Institute, Karnal, Haryana 132001, India Veer Bahadur Singh Purbanchal University, Jaunpur, U.P. 222001, India c National Bureau of Soil Survey and Land Use Planning, Regional Centre, Kolkata 700091, India d National Bureau of Soil Survey and Land Use Planning, Amravati Road, Nagpur 440033, India b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 20 February 2013 Received in revised form 11 September 2013 Accepted 12 October 2013

Conservation tillage and residue management are the options for enhancing soil organic carbon stabilization by improving soil aggregation in tropical soils. We studied the influence of different combinations of tillage and residue management on carbon stabilization in different sized soil aggregates and also on crop yield after 5 years of continuous rice–wheat cropping system on a sandy loam reclaimed sodic soil of north India. Compared to conventional tillage, water stable macroaggregates in conservation tillage (reduced and zero-tillage) in wheat coupled with direct seeded rice (DSR) was increased by 50.13% and water stable microaggregates of the later decreased by 10.1% in surface soil. Residue incorporation caused a significant increment of 15.65% in total water stable aggregates in surface soil (0–15 cm) and 7.53% in sub-surface soil (15–30 cm). In surface soil, the maximum (19.2%) and minimum (8.9%) proportion of total aggregated carbon was retained with >2 mm and 0.1–0.05 mm size fractions, respectively. DSR combined with zero tillage in wheat along with residue retention (T6) had the highest capability to hold the organic carbon in surface (11.57 g kg1 soil aggregates) with the highest stratification ratio of SOC (1.5). Moreover, it could show the highest carbon preservation capacity (CPC) of coarse macro and mesoaggregates. A considerable proportion of the total SOC was found to be captured by the macroaggregates (>2–0.25 mm) under both surface (67.1%) and sub-surface layers (66.7%) leaving rest amount in microaggregates and ‘silt + clay’ sized particles. From our study, it has been proved that DSR with zero tillage in wheat (with residue) treatment (T6) has the highest potential to secure sustainable yield increment (8.3%) and good soil health by improving soil aggregation (53.8%) and SOC sequestration (33.6%) with respect to the conventional tillage with transplanted rice (T1) after five years of continuous rice–wheat cropping in sandy loam reclaimed sodic soil of hot semi-arid Indian subcontinent. ß 2013 Elsevier B.V. All rights reserved.

Keywords: Residue management Conservation tillage Aggregate associated carbon Reclaimed sodic soil Rice–wheat cropping system

1. Introduction Soil aggregation is an imperative mechanism contributing to soil fertility by reducing soil erosion and mediating air

permeability, water infiltration, and nutrient cycling (Spohn and Giani, 2011; Zhang et al., 2012). Soil aggregates are important agents of soil organic carbon (SOC) retention (Haile et al., 2008) and protection against decomposition (Six et al.,

Abbreviations: AR, aggregate ratio; AS, aggregate stability; CPC, carbon preservation capacity; CMacA, coarse macroaggregate; CMacAC, coarse macroaggregated carbon; CMicA, coarse microaggregate; CMicAC, coarse microaggregated carbon; CT, conventional tillage; DSR, direct seeded rice; EWY, equivalent wheat yield; FMicA, fine microaggregate; FMicAC, fine microaggregated carbon; GMD, geometric mean diameter; MWD, mean weight diameter; MesoA, mesoaggregate; MesoAC, mesoaggregated carbon; OC, oxidizable organic carbon; RT, reduced tillage; SOM, soil organic matter; TC, total soil carbon; TIC, total soil inorganic carbon; SOC, total soil organic carbon; TPR, transplanted rice; WSA, water stable aggregates; WSMacA, water stable macroaggregates; WSMicA, water stable microaggregates; ZT, zero tillage. * Corresponding author at: Regional Centre, Kolkata, National Bureau of Soil Survey and Land Use Planning, D.K. Block, Sector-2, Salt Lake City, Kolkata 700091, India. Tel.: +91 033 2359 0727x49/033 23586926; fax: +91 033 23215491; mobile: +91 9804976987. E-mail address: [email protected] (S. Gupta Choudhury). 0167-1987/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.still.2013.10.001

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Table 1 Tillage and residue management treatments. Treatments

Rice (Kharif)

Wheat (Rabi)

T1 T2 T3 T4 T5 T6 T7 T8

Conventional rice transplanting (TPR) Conventional rice transplanting after wheat residue incorporation (TPR + WRI) Direct seeded rice in reduced tillage (DSR + RT) Direct seeded rice after wheat residue incorporation (DSR + RT + WRI) Direct seeded rice in zero tillage (DSR + ZT) Direct seeded rice in zero tillage with wheat residue retention (DSR + ZT + WRR) Direct seeded rice in zero tillage + Sesbania brown manuring (DSR + ZT + BM) Conventional rice transplanting after Sesbania green manuring (TPR + GM)

Conventional wheat sowing (CWS) Wheat sowing after rice residue incorporation (CWS + RRI) Wheat in reduced tillage (WRT) Wheat in reduced tillage after rice residue incorporation (WRT + RRI) Wheat in zero tillage (WZT) Wheat in zero tillage with rice residue retention (WZT + RRR) Wheat sowing in zero tillage (WZT) Wheat sowing in zero tillage (WZT)

2000a). Quantity and quality of SOC fractions have an impact on soil aggregation (Lal, 2000) that in turn physically protect the carbon (C) from degradation by increasing the mean residence time of C (Bajracharya et al., 1997). Soil management through the use of different tillage systems affects soil aggregation directly by physical disruption of the macroaggregates, and indirectly through alteration of biological and chemical factors (Barto et al., 2010). Conventional tillage (CT) generally abrades the network of mycelium by mechanical breakdown of macroaggregates (Borie et al., 2006), and decreases the content of soil organic C (SOC), microbial biomass and faunal activities (Mikha and Rice, 2004; Sainju et al., 2009; Curaqueo et al., 2011). Conservation tillage practices with minimal soil disturbance and residue retention are becoming economically and ecologically more viable option as they save energy and provide more favourable soil conditions (Husnjak et al., 2002) for sustainable crop production and SOC sequestration for future posterity. Rice–wheat cropping rotation has been spread over an area of about 10 Mha in Indo-Gangetic Plains (IGP) of India (Kumar et al., 1998) and together contributes 85% to India’s cereal production (Timsina and Connor, 2001). Intensive tillage, residue removal and burning practised during the whole crop season accelerate soil erosion, environmental pollution, soil degradation (Montgomery, 2007) and affects ecosystem functions (Srinivasan et al., 2012). Therefore, adoption of the rational cropping practices, such as crop residue recycling (Aoyama et al., 1999; Blair et al., 2006), manure application (Hao et al., 2003; Rudrappa et al., 2006), conservation tillage (Gale and Cambardella, 2000; Six et al., 2000a), and farmland fallow (Nair et al., 2009), would be a century need for improving the soil quality and ecosystem function. Available database on on-station farm trials across the Indo-Gangetic Plains in India, divulges the wheat yield increment under conservation tillage ranging from 1% to 12% with an average of 240 kg ha1 across the area of study (Erestein and Laxmi, 2008). Thus, the cultivation of rice (transplanted/direct seeded) and wheat crops grown rotationally with different tillage and residue management practices has been advocated to evaluate its long-term effect on yield attributes, aggregation and C stabilization in different size aggregates in reclaimed sodic soil of north Indian sub-continent. We hypothesize that direct seeded rice under reduced/zero tillage along with crop residue retention could lead to improved soil aggregation and C sequestration and sustainable yield increment for future posterity of the rice–wheat cropping systems. 2. Materials and methods 2.1. The experimental site A long-term field experiment was established in the year 2006 at Central Soil Salinity Research Institute, Karnal, (298430 N 768580 E, 245 m above mean sea level), Haryana, India, with rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system. The mean minimum and maximum temperatures of the site are

18.8 8C and 29.2 8C, respectively. Annual rainfall ranges between 700 and 800 mm and more than 70% of it occurs during the monsoon months of July to September. The experimental plot had a sandy loam reclaimed sodic (pH – 7.72 and EC – 0.32 dS m1) soil (before reclamation classified as Typic Natrustalf; US Taxonomy) having 59.0% sand, 18.0% silt and 23.0% clay with 8 tillage and residue management treatments aimed at developing resource conservation technologies in a strip plot design replicated four times. The treatments included combinations of tillage practices (both conventional and conservation) and residue (with or without) management coupled with system of rice cultivation (transplanted rice; TPR/direct seeded rice; DSR) and also application of brown/green manuring to rice crop (Table 1). Rice seeds (var. CSR 30 in the year 2006, 2007 and Pusa 44 in the year 2008, 2009 and 2010) were sown both in plots (for DSR) and nursery bed (for TPR) in the first week of June. Later, one-month-old seedlings were transplanted in the first week of July with standard package of practices. Each of the treatment was fertilized with 150 kg ha1 N, 60 kg ha1 P2O5 and 6.3 kg ha1 Zn. Nitrogen, phosphorus and zinc were supplied through urea, di-ammonium phosphate (DAP) and zinc sulphate heptahydrate fertilizers. One third of recommended N and full of phosphorus and zinc were applied at the time of transplanting and direct sowing. Remaining nitrogen was applied in two equal splits after 30 days and 60 days of sowing. Dhaincha (Sesbania aculeate) was sown in the first week of June for brown and green manuring in T7 and T8 treatments, respectively. For DSR, Pendimethalin (3 L ha1) was applied before rice sowing as pre-emergence herbicide. Seeds were sown through seed drill. For brown manuring in DSR (T7), Sesbania seeds @ 20 kg ha1 were broadcasted three days after rice sowing and allowed to grow for 30 days and then were dried and killed by spraying 2,4D ethyl ester. After killing, the colour of the Sesbania residue became brown and it was allowed to lie and decompose in situ on field. Wheat straw (33.0% of the total stalk biomass) was incorporated in the soil under T2, T4 and T6 treatments. During the early 20 days of establishment, water was allowed to stand for soil submergence in the transplanted rice. In the later stage, 7.5 cm irrigation was scheduled at one day after disappearance of ponded water. In DSR, 7.5 cm irrigation was scheduled at four days after disappearance of ponded water. The rice crop was harvested in the last week of October. Rice straw (33.0% of the total stalk biomass) was incorporated in the relevant plots in the top 10 cm soil with disc harrow before 3 weeks of wheat sowing. In the plots without rice straw incorporation, the straw was removed from the field. Before seeding of wheat the field was disked four and two times under conventional and reduced tillage treatments, respectively, at the field capacity moisture. Wheat (variety DBW 17) was sown @ 110 kg ha1 in the second week of November and harvested manually in the third week of April each year. A basal dose of 60 kg P2O5 and 30 kg K2O ha1 was applied to wheat each year. Wheat was irrigated with groundwater on phenological stages with 7.5 cm water.

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2.2. Soil sampling and analysis Soil samples were collected after 5 years of rice–wheat cropping in April 2011 (after wheat harvest) from four replications of each treatment. Soil samples were taken from 0 to 15 and 15 to 30 cm depth with a soil auger. Composite samples were made air-dried under shade. One portion of the sample was ground and the whole amount was passed through a 0.15 mm sieve. This sample was used for determining total inorganic carbon (TIC), oxidizable organic carbon (OC) and total carbon (TC) in whole soil. Total carbon (TC) was analyzed by using CHN Elemental analyzer (model Vario EL III); TIC and OC were estimated following the methods of Jackson (1973) and Walkley and Black (1934), respectively. The total soil organic carbon (SOC) was derived by subtracting TIC from TC. The other part of the air dried ungrounded samples were passed through 5-mm sieve and were used for estimating aggregate size distribution by wet sieving method (Yoder, 1936) by using a nest of sieves having pore diameter 2.0, 1.0, 0.5, 0.25, 0.12 and 0.05 mm for the separation of four aggregate size classes namely coarse macroaggregate (>2.0 mm), mesoaggregate (2.0– 0.25 mm), microaggregate (0.25–0.05 mm) and ‘silt + clay’ sized fractions (<0.05 mm). One sample was kept for determination of water stable aggregates, whereas, other was used for estimating primary particles after dispersion with 0.5% (w/v) sodium hexametaphosphate in 1:3 (soil:solution) ratio by mechanically stirring the suspension for 15 min before the vertical oscillation of the apparatus for 30 min at a frequency of 50 cycles per min2 with taking care that the samples on the top sieve remain immersed throughout the full stroke. Before starting the oscillation, soil was left for slaking in water for 2 min. Sieves were then taken out and kept 5 min to drain out the water. The water stable aggregates (without dispersion) and the primary particles (with dispersion) of different sizes were collected from the respective sieves separately and weighed after oven drying at 50 8C for 24 h. Dry soil aggregates were passed through 0.15 mm sieve. Carbon in the aggregates and the whole soil was determined by CHN Elemental analyzer (model Vario EL III). Parameters expressing the status of aggregation were determined as follows: 1. Water stable macro and microaggregates: The macroaggregates were determined by adding the aggregates retained over 0.25– 2.0 mm sieves while the microaggregates referred to aggregates retained on 0.05–0.25-mm sieves. WSA% ¼

½ðweight of soil þ sandÞi  ðweight of sandÞi  weight of sample

AS ¼

ðPercent soil particles > 0:25 mm  Percent primary particle > 0:25 mmÞ ðPercent primary particle < 0:25 mmÞ

4. The aggregate ratio (AR) of soils was computed as: Aggregate ratio ¼

½Percent of water stable macroaggregates ½Percent of water stable microaggregates

2.2.1. Carbon preservation capacity of soil aggregates (CPC) The capacity of the different sized soil aggregates to preserve/ capture C per unit of the specified size of water stable aggregates are called carbon preservation capacity (CPC) of that particular size fraction and it is calculated as:

ðaggregate associated carbonÞi  ðWater stable aggregatesÞi CPC ðg=kgÞ ¼ 100 where i denotes the size of the sieve. 2.2.2. Equivalent wheat yield (EWY) Total crop productivity of each treatment of the system (rice– wheat) was calculated through equivalent wheat yield (EWY) for each year considering the actual grain yield of the crops and their respective minimum support price (MSP) fixed by the Government for unit quantity of the respective grains during the corresponding harvesting seasons.

EWY ðt=haÞ ¼

ðRice yield  MSP of riceÞ þ Wheat yield MSP of wheat

2.2.3. Statistical analysis Statistical analysis was performed by windows based SPSS programme (ver. 16.0, SPSS Inc. 1996) to determine the statistical significance of treatment effects. Duncan’s Multiple Range Test (DMRT) was used to compare means through least significant difference (LSD). The 5.0% probability level is regarded as statistically significant. 3. Results

where i denotes the size of the sieve. The percentage of water stable macroaggregates (WSMacA) and water stable microaggregates (WSMicA) is the summation of soil aggregate size fractions of >0.25 mm and <0.25 mm, respectively. These two were summed up to estimate the total water stable aggregates. 2. The mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates were calculated as: Pn X i Wi ; (i) MWD ðmmÞ ¼ Pi¼1 n i¼1 Wi Pn  i¼1 Wi log X i GMD ðmmÞ ¼ exp Pn i¼1 Wi

class (0.175, 0.375, 0.75, 1.5 and 2.0 mm) and Wi is the weight of soil (g) retained on each sieve. 3. The aggregate stability (AS) of soils was computed as:

(ii)

where n is the number of fractions (0.1–0.25, 0.25–0.5, 0.5–1.0, 1.0–2.0, >2.0 mm), Xi is the mean diameter (mm) of the sieve size

3.1. Different forms of soil carbon Resource conservation practices significantly influenced the total soil carbon (TC), total soil organic carbon (SOC) and oxidizable organic carbon (OC) content of the surface (0–15 cm) soil (Table 2). Zero tillage with (T6) or without residue management (T5) showed significantly higher TC, SOC content of 12.33 and 11.98 g kg1, respectively in T6 and 11.73 and 11.38 g kg1, respectively in T5 (Table 2) as compared to the other treatments. Irrespective of residue incorporation/retention, zero tillage with DSR enhanced 30.7%, 34.1% and 23.8% of TC, SOC and OC, respectively, in surface soil as compared to conventional tillage with transplanted rice cultivation. Simultaneously, residue incorporation caused an increment of 6.4%, 7.4% and 10.6% in TC, SOC and OC, respectively over the treatments with no residue management. There was no significant effect of conservation practices on different forms of carbon under sub-surface (15–30 cm) soil (Table 2).

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Table 2 Effect of tillage and residue management practices on distribution of different forms of carbon in soil. Treatments

TPR/CWS (T1) TPR + WRI/CWS + RRI (T2) DSR + RT/WRT (T3) DSR + RT + WRI/WRT +RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT + RRR (T6) DSR + ZT + BM/W ZT (T7) TPR + GM/WZT (T8)

TC (g kg1)

TIC (g kg1)

SOC (g kg1)

OC (g kg1)

0–15 cm

15–30 cm

0–15 cm

15–30 cm

0–15 cm

15–30 cm

0–15 cm

15–30 cm

8.39f  0.01 9.42ef  0.01 9.95de  0.01 10.49cd  0.04 11.98ab  0.03 12.33a  0.05 11.03bc  0.10 9.24ef  0.11

9.22cd  0.07 9.10cd  0.02 9.91ab0.05 10.40a  0.01 8.81d  0.01 8.12e  0.06 10.24a  0.01 9.57bc  0.01

0.60abc  0.06 0.75ab  0.08 0.90a  0.09 0.60abc  0.06 0.60abc  0.06 0.60abc  0.06 0.30c  0.03 0.45bc  0.05

0.60b  0.06 0.60b  0.06 0.60b  0.06 0.90a  0.09 0.45bc  0.05 0.45bc  0.05 0.30c  0.03 0.30c  0.03

7.79e  0.02 8.67de  0.02 9.05cd  0.01 9.89bc  0.01 11.38a  0.06 11.73a  0.02 10.73ab  0.10 8.79de  0.09

8.62c  0.04 8.50c  0.02 9.31ab  0.02 9.50ab  0.01 8.36c  0.02 7.67d  0.08 9.94a  0.01 9.27b  0.01

6.61e  0.01 7.43de  0.03 7.77bcd  0.01 8.56abc  0.04 8.59abc  0.08 9.41a  0.07 8.78ab  0.03 7.58cde  0.10

7.51cd  0.09 7.47cd  0.01 8.00bc  0.01 8.37b  0.03 7.32d  0.01 6.24e  0.01 9.38a  0.04 7.58cd  0.03

Different small letters within the same column show the significant difference at P = 0.05 according to Duncan Multiple Range Test for separation of mean.

3.2. Conservation management and wheat yield equivalent In the initial two years of experimentation with Basmati rice variety (CSR 30), the transplanted rice with conventional wheat sowing (T1) had significantly higher equivalent wheat yield (EWY) than DSR with wheat in ZT under residue management treatment (T6). With the inclusion of high yielding rice variety (Pusa 44), the total equivalent yield, irrespective of all the treatments abruptly increased by 53.9%, 41.0% and 55.5% (on average) in the year 2008– 2009, 2009–2010 and 2010–2011, respectively, over the initial year (2006–2007) of experimentation (Fig. 1). Residue management (retention/incorporation) could lead to an increased equivalent yield (EWY) by 7.7% and 11.2% in the last two consecutive years, respectively, over the their corresponding non-residue treatments. Among all the treatments, T8 had significantly highest EWY followed by T2 and T6 treatments in the last three years of study. Simultaneously, these three treatments showed a significant and consistent yield increment with passage of time during the period of experimentation. 3.3. Distribution of water stable aggregates and aggregate indices The distribution of soil mass among the size classes of water stable aggregates was strongly influenced by tillage and residue management practices in both the soil depths (0–15 cm and 15– 30 cm). Total water stable aggregates were found to be 2.31% higher in surface soil than in sub-surface soil (Table 3). In both the depths, T6 treatment had the highest water stable aggregates as

compared to the other treatments studied. Compared to conventional tillage, conservation tillage (RT and ZT) coupled with DSR increased 50.13% water stable macroaggregates and decreased 10.1% water stable microaggregates in surface soil. Among all the treatments, T6 had significantly higher (52.8%) proportion of water stable macroaggregates than the other treatments compared. This treatment also showed the highest MWD, GMD, AR and AS in surface soil. In T5, T6, T7 and T8 treatments, the percent macroaggregates were found to be 3.8, 4.9, 4.1 and 3.1 times higher than their corresponding microaggregates. Irrespective of tillage practices (conventional and conservation), residue incorporation/retention resulted in 18.6% and 16.7% higher water stable macroaggregates as compared to the non-residue treatments in surface and sub-surface soil, respectively. 3.4. Soil organic carbon in aggregate size fractions As compared to the conventional tillage treatments, reduced and zero tillage treatments had significantly higher amount of total aggregate associated carbon within all the aggregate size classes in surface soil depth. In sub-surface soil layer (Table 3), conventional tillage with transplanted rice treatments (T1 and T2) resulted in 12.2% higher total soil aggregated carbon as compared to the direct seeded rice (DSR) with wheat in zero tillage treatments (T5 and T6). In surface soil, the maximum (19.2%) and minimum (8.9%) proportion of total aggregated carbon was retained with >2 mm and 0.1–0.05 mm size fractions, respectively. Similarly, in the subsurface layer, >2 mm size particles occluded highest proportion

Fig. 1. Equivalent wheat yield as influenced by conservation technologies.

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Table 3 Effect of tillage and residue management practices on distribution of different aggregate indices. Treatments

Total WSA (%)

WSMacA (%)

WSMicA (%)

MWD (mm)

GMD (mm)

AR

AS

0–0.15 m depth TPR/CWS (T1) TPR + WRI/CWS + RRI(T2) DSR + RT/WRT (T3) DSR + RT+ WRI/WRT +RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT +RRR (T6) DSR + ZT + BM/W ZT (T7) TPR +GM/WZT (T8)

37.07e  1.23 44.85d  0.83 43.71d  1.77 52.96c  3.16 55.11bc  1.71 59.35a  0.05 56.11b  0.49 43.91d  1.85

24.35g  1.51 28.65e  0.35 26.48f  0.6 33.66d  1.32 46.21c  0.41 52.79a  0.25 48.65b  1.15 34.16d  0.14

12.72c  0.28 16.20b  0.48 17.23b  1.17 19.3a  1.84 8.9de  1.3 6.56f  0.2 7.46ef  0.66 9.75d  1.81

0.63ef  0.00 0.70de  0.01 0.58f  0.10 0.77d  0.02 1.14b  0.06 1.24a  0.01 1.20ab  0.04 1.03c  0.04

0.69d  0.01 0.72d  0.00 0.77cd  0.11 1.03ab  0.31 0.98ab  0.10 1.07a  0.01 0.94abc  0.01 0.84bcd  0.02

1.92e  0.16 1.77e  0.03 1.54e  0.07 1.75e  0.10 5.30c  0.73 8.06a  0.28 6.59b  0.74 3.63d  0.67

0.26g  0.02 0.29f  0.08 0.28f  0.01 0.35e  0.01 0.48c  0.00 0.59a  0.01 0.53b  0.00 0.37d  0.00

Mean

49.13

36.87

12.27

0.91

0.88

3.82

0.39

0.15–0.30 m depth TPR/CWS (T1) TPR + WRI/CWS RRI (T2) DSR + RT/WRT (T3) DSR+ RT + WRI/WRT +RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT +RRR (T6) DSR + ZT + BM/W ZT (T7) TPR +GM/WZT (T8)

42.86cd  0.9 45.84bc  1.2 48.03b  1.75 54.29a  0.35 52.07a  3.61 53.6a  0.44 47.56b  0.9 39.94d  5.7

27.79d  0.15 29.39d  0.29 31.96c  0.9 38.80a  0.54 28.61d  3.15 34.94b  0.74 34.45b  0.77 24.71e  1.41

15.07cd  1.05 16.45bc  1.49 16.07bcd  0.85 15.49bcd  0.19 23.46a  0.46 18.66b  1.18 13.11d  1.67 15.23cd  4.29

0.64cd  0.01 0.65bcd  0.05 0.67bcd  0.03 0.71b  0.00 0.62d  0.02 0.61d  0.04 0.86a  0.01 0.70bc  0.05

0.70c  0.01 0.70c  0.02 0.71c  0.01 0.74b  0.00 0.67d  0.01 0.70c  0.01 0.78a  0.01 0.70c  0.03

1.85b  0.14 1.80b  0.18 1.99b  0.05 2.51a  0.07 1.22c  0.11 1.88b  0.16 2.68a  0.40 1.73b  0.40

0.29ef  0.00 0.31de  0.01 0.33c  0.01 0.40a  0.00 0.32cd  0.03 0.37b  0.01 0.36b  0.00 0.27f  0.02

Mean

48.02

31.11

16.69

0.68

0.71

1.96

0.33

Different small letters within the same column show the significant difference at P = 0.05 according to Duncan Multiple Range Test for separation of mean.

Aggregate associated C ( g kg-1 soil aggregate)

(19.0%) of total aggregated carbon followed by 2.0–1.0 mm, 1.0– 0.5 mm, 0.5–0.25 mm, 0.25–0.1 mm, <0.05 mm and 0.1–0.05 mm containing 16.73%, 16.10%, 14.83%, 10.93%, 13.03% and 9.37%, respectively. Conservation tillage (both reduced and zero tillage) caused 21.2%, 9.5%, 28.4%, 13.6%, 15.3%, 2.9% and 24.7% higher accumulation of SOC in >2 mm, 2.1–1.0 mm, 1.0–0.5 mm, 0.5– 0.25 mm, 0.25–0.1 mm, 0.1–0.05 mm and <0.05 mm sized particles, respectively, than conventional tillage (T1 and T2) treatments. Direct seeded rice combined with zero tillage and residue retention (T6) had the highest capability to hold the organic carbon in surface (11.57 g kg1 soil aggregates) and retained least amount of SOC in sub-surface (9.05 g kg1 soil aggregates) soil. In comparison with transplanted rice (TPR), direct seeded rice (DSR) enhanced 16.8%, 7.8%, 17.9%, 12.9%, 14.6%, 7.9% and 17.5% SOC in >2 mm, 2.1– 1.0 mm, 1.0–0.5 mm, 0.5–0.25 mm, 0.25–0.1 mm, 0.1–0.05 mm and <0.05 mm sized particles, respectively (Fig. 2). For easy interpretation of the results, the total aggregate associated carbon was pooled together in four size classes i.e. coarse macroaggregated carbon (CMacAC, >2 mm), mesoaggregated carbon (MesoAC, 2.0– 0.25 mm), coarse microaggregated carbon (CMicAC, 0.25–0.1 mm) and fine microaggregated carbon (FMicAC, 0.25–0.05 mm) as 18 16

TPR

DSR

14 12 10 8 6 4 2 0

>2

2.0-1.0

1.0-0.5

0.5-0.25

0.25-0.1

0.1-0.05

< 0.05

Soil aggregate size class (mm) Fig. 2. Effect of system of rice cultivation on soil aggregate associated carbon.

reported by Gupta Choudhury et al. (2010). A higher proportion of the total SOC was found to be captured by the macroaggregates under both surface (67.1%) and sub-surface layers (66.7%) leaving rest amount in microaggregates and ‘silt + clay’ sized particles (Table 4). Thus, the carbon preservation capacity of different size aggregates varied with treatment imposed. Under conventional and reduced tillage treatments, coarse microaggregates had the higher capacity to capture carbon followed by meso and coarse macroaggregates. The scenario diverted under zero tillage treatments (T5 and T6) and also with brown (T7)/green (T8) manure application (Fig. 3), where, the coarse macro aggregates were found to be 2.5, 3.8 and 12.7 times higher in T5; 3.2, 5.7 and 13.6 times higher in T6; 2.4,4.1 and 10.5 times higher in T7 and 1.7, 2.1, 25.3 times higher in T8 treatments than their corresponding meso, coarse micro and fine micro aggregates, respectively (Fig. 3). 4. Discussion 4.1. Effect of residue and tillage management on soil aggregation and yield equivalent The management of previous crop residues is the key to soil structural development and stability since organic matter is an important factor in soil aggregation (Verhulst et al., 2011). Residue incorporation or retention caused a significant increment of 15.65% in total water stable aggregates in surface soil (0–15 cm) and 7.53% in sub-surface soil (15–30 cm), which depicted that residue management could improve 2.1-fold higher water stable aggregates as compared to the other treatments without residue incorporation/retention (Fig. 4). Application of organics in the form of residue combined with either conventional or conservation tillage improved the formation of water stable aggregates resulting the preponderance of macroaggregates compared to microaggregates. Release of polysaccharides and organic acids during the decomposition of organic material plays a major role in stabilization of macroaggregates (Cheshire, 1979). These polysaccharides and organic acids do not spread far from the site of production and the freshly added residues function as nucleation sites for the growth of fungi and other soil microbes (Puget et al., 1995; Jastrow, 1996). As a result, the residues and soil particulates are getting bound into macroaggregates in higher proportion in

S. Gupta Choudhury et al. / Soil & Tillage Research 136 (2014) 76–83

81

Table 4 Aggregate associated carbon influenced by different treatments. Aggregate associated carbon (g kg1 soil aggregate)

Treatments (0–15 cm)

CMacAC

MesoAC

CMicAC

FMicAC

(Silt + clay)AC

>2 (mm)

2.0–1.0 (mm)

1.0–0.5 (mm)

0.5–0.25 (mm)

0.25–0.1 (mm)

0.1–0.05 (mm)

<0.05 (mm)

11.54c  0.11 14.48ab  0.12 16.17a  2.19 16.03a  2.31 15.25a  0.11 15.61a  0.35 12.64bc  0.23 11.76c  0.58

11.26b  0.11 11.93b  1.50 12.21b  0.35 13.91a  0.81 12.01b  0.23 12.64ab  0.23 11.65b  0.07 11.33b  0.73

10.21d  0.17 10.09d  0.23 11.65c  0.35 12.21c  0.35 13.84b  0.34 14.62a  0.23 13.34b  0.62 12.05c  0.58

9.86b  0.11 9.81b  0.23 10.80a  0.58 10.80a  0.35 11.59a  0.11 11.51a  0.23 10.80a  1.43 9.34b  0.01

8.67cd  0.06 8.68cd  0.92 10.23ab  0.58 9.81ab  0.01 9.34bc  0.11 10.66a  0.23 9.39bc  1.08 7.98d  0.17

6.78b  0.11 6.84b  0.12 6.84b  0.12 6.70b  0.01 7.65a  0.11 6.84b  0.35 6.28b  1.04 5.34c  0.70

7.35cd  0.49 7.50cd  0.12 8.55abcd  0.24 8.85abc  0.37 9.15ab  1.10 10.5a  0.86 9.00ab  0.73 7.95bcd  0.12

Mean

14.18

12.12

12.25

10.56

Treatments (15–30 cm)

Aggregate associated carbon (g kg1 soil aggregate)

TPR/CWS (T1) TPR +WRI/CWS + RRI (T2) DSR + RT/WRT (T3) DSR + RT + WRI/WRT + RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT +RRR (T6) DSR + ZT + BM/W ZT (T7) TPR +GM/WZT (T8)

CMacAC

MesoAC

9.34

6.66

8.61

CMicAC

FMicAC

(Silt + clay)AC

>2 (mm)

2.0–1.0 (mm)

1.0–0.5 (mm)

0.5–0.25 (mm)

0.25–0.1 (mm)

0.1–0.05 (mm)

<0.05 (mm)

TPR/CWS (T1) TPR + WRI/CWS + RRI (T2) DSR + RT/WRT (T3) DSR + RT + WRI/WRT +RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT +RRR (T6) DSR + ZT + BM/W ZT (T7) TPR +GM/WZT (T8)

14.90ab  0.80 13.35abc  0.35 12.50bc  0.12 15.32a  1.04 14.26abc  1.84 11.65c  0.12 14.48ab  2.32 12.62bc  0.35

11.54cde  1.03 12.07bcd  0.23 13.91a  0.81 11.79bcde  0.00 10.33e  0.23 10.66de  0.00 13.34ab  0.58 12.48abc  0.47

10.42c  0.57 11.79b  0.23 12.07b  0.23 12.21b  0.12 10.04c  0.23 10.23c  0.12 13.91a  0.58 11.76b  0.58

9.86bc  0.80 11.08a  0.12 11.65a  0.35 10.80ab  0.12 9.90bc  0.11 9.39c  0.12 11.37a  1.16 11.19a  0.12

10.00ab  0.46 9.95ab  0.12 10.38a  0.23 10.09ab  0.23 8.64c  0.23 7.69d  0.35 9.53b  0.58 8.62c  0.12

7.20abc  0.00 7.41ab 0.35 7.41ab  0.12 7.69a  0.12 6.10de  0.23 6.56bcd  1.04 6.28cd 0.46 5.19de  0.58

7.13c  0.55 7.65bc  0.12 8.55ab  0.37 7.50c  0.01 7.80bc  0.73 7.20c  0.07 7.95bc  0.2 9.00a  0.24

Mean

13.63

12.01

11.56

10.65

6.73

7.85

9.36

Different small letters within the same column show the significant difference at P = 0.05 according to Duncan Multiple Range Test for separation of mean.

surface than sub-surface soil layer (Benbi and Senapati, 2010). The tillage management had a prominent impact on soil aggregation as compared to residue management. Application of ZT with or without residue resulted in 46.5% higher water stable macroaggregates in surface as compared to CT. The decline in the size of macroaggregates in CT could be credited to the disruption of macroaggregates, which may have exposed previously protected SOM against oxidation. Silva and Ribeiro (1992), Oyedele et al. (1999) and Franzluebbers et al. (1999) working on varying soil types in different conditions concluded that the soil mechanical disturbance reduces soil structural stability. Our results indicate that, ZT promotes macroaggregation as compared to CT. The macroaggregates are highly susceptible to oxidation, but, simultaneously, they are rich conserver of SOC. Its presence in higher proportion ensures more carbon sequestration and nutrient availability by regulating proper aeration and water infiltration within the root zone (Gupta Choudhury et al., 2010). The

preservation of macroaggregates with the adoption of RT and ZT, may confirm a better soil-crop environment for the long-term sustenance. The consistently higher EWY under T4 and T6 treatments proved the idea of getting sustainable yield increment with higher SOC sequestration under long-term rice–wheat cropping with conservation tillage and residue management. Monitoring of six sets of farmers’ field over eight years showed the similar trend of yield increment under ZT in north Indian state, Haryana, as reported by Yadav et al. (2005). 4.2. Tillage effects on soil organic carbon and its distribution in different size aggregates Conservation tillage practice have been found to result in enhanced stabilization of SOC within temperate and (sub) tropical soils (Six et al., 2002a;West and Post, 2002) and have been related to the stabilization of aggregates (Six et al., 2002b). Many studies 54.0

4

MacAC

MesoAC

4

CMicAC

FMicAC

52.0

% water stable aggregates

Carbon preservation capacity (g kg-1) soil aggregate

5

3 3 2 2 1 1 0 T1

T2

T3

T4

T5

T6

T7

T8

-1 -1

% WSA (0-15 cm)

Fig. 3. Influence of treatments on carbon preservation capacity of different soil aggregates.

a

% WSA (15-30 cm) 50.0

b

48.0 46.0

b

44.0 42.0 40.0

Without residue Treatments

a

Residue

Residue management Fig. 4. Effect of residue management on water stable aggregates in surface (0– 15 cm) and sub-surface (15–30 cm) soil layers.

82

S. Gupta Choudhury et al. / Soil & Tillage Research 136 (2014) 76–83

Table 5 Effect of tillage and residue management practices on stratification ratios of different forms of carbon in soil. Treatments

SOC

MacAC

Meso AC

MicAC

Silt + clay

TPR/CWS (T1) TPR + WRI/CWS + RRI (T2) DSR + RT/WRT (T3) DSR + RT + WRI/WRT +RRI (T4) DSR + ZT/WZT (T5) DSR + ZT + WRR/WZT +RRR (T6) DSR + ZT + BM/W ZT (T7) TPR +GM/WZT (T8)

0.9  0.01 1.0  0.01 1.0  0.03 1.0  0.02 1.4  0.03 1.5  0.11 0.9  0.09 1.0  0.07

0.8  0.03 1.1  0.04 1.3  0.16 1.0  0.22 1.1  0.13 1.3  0.04 0.8  0.11 1.1  0.07

0.4  0.09 0.9  0.06 0.9  0.07 1.1  0.02 1.2  0.01 1.3  0.01 0.4  0.10 0.9  0.01

0.6  0.03 0.9  0.07 1.0  0.05 0.9  0.01 1.2  0.05 1.2  0.16 0.6  0.07 0.9  0.01

1.0  0.15 1.0  0.01 1.0  0.01 1.1  0.05 1.0  0.05 1.3  0.12 1.0  0.02 1.0  0.01

have reported lower SOC and water-stable aggregates content in conventional tillage when compared to zero tillage (Beare et al., 1994; Six et al., 1999). Zero tillage combined with or without crop residues increases SOC, limits soil disturbance, and enhances soil aggregation. The disruptive effect of tillage results in a loss of SOC through increased soil microbial respiration (Balesdent et al., 2000; Six et al., 2000b). In our study, the significant increment of bulk SOC and the macroaggregated carbon in surface soil under RT and ZT treatments as compared to CT may probably due to the incorporation of crop residues (shallow roots and stubbles) coupled with no-disturbance of the soil surface where the residues could be mineralized and stabilized as soil organic matter (Angers et al., 1997; Lorenz et al., 2005). The aggregated C concentration of coarse macroaggregates were higher (both under CT, RT and ZT) to those of the mesoaggregates and microaggregates. The macroaggregates were generally formed by soil particles held together by organic residues (Tisdall and Oades, 1982). This result resembles to the general trend of getting low content of SOC with fine particles < 2 mm (Six et al., 2000b; Mikha and Rice, 2004). Aggregates of >2.0–0.25 mm in diameter was found to be the main carrier of organic carbon (Zhang et al., 2001; Li et al., 2007). In the present study, the organic free-light fractions were not removed from each aggregate class, which can greatly increase C concentrations in 1.0–0.5 mm and 0.5–0.25 mm aggregates (Razafimbelo et al, 2008). The subsequent increase in C content in ’silt + clay’ sized fraction (11.7% of the total aggregate associated carbon) than the fine microaggregates (9.0% of the total aggregate associated carbon) in surface soil under the respective treatments could be explained due to the presence of numerous reactive sites for having high specific area, where SOM can be sorbed by strong ligand exchange and polyvalent cationic bridges (Sposito et al., 1999; Bandyopadhyay et al., 2010). 4.3. Stratification ratio of soil organic carbon and aggregated carbon Soil organic carbon was relatively uniformly distributed within the surface and sub-surface soil after five years of conventional tillage with transplanted rice (Table 5). In contrast, zero tillage management with DSR resulted in a higher stratification ratio (1.5) of SOC, which depicted the presence of higher SOC in the surface soil than the sub-surface. Apart from bulk SOC, the stratification ratios of different sized aggregate associated carbon were also evaluated. Zero tillage with DSR along with residue management (T6) had the highest stratification ratio of aggregated carbon within all size fractions except CMicAC. Such accumulation of higher SOC at the soil surface was a result of surface placement of crop residues and lack of soil disturbance that kept residues isolated from the lower depth (Franzluebbers, 2002). Decomposition of surface-placed residues is often slower than when incorporated in the soil profile (Brown and Dickey, 1970; Ghidey and Alberts, 1993), primarily because of less optimal moisture conditions (Franzluebbers and Arshad, 1996). The transformation of organic C from plant-derived residues into SOC may be more effective under ZT than under CT (Franzluebbers et al., 1998) because of the less

than optimal decomposition environment in undisturbed soil at the surface compared with disturbance and incorporation with tillage. 4.4. Carbon preservation capacity of different size aggregates Resource conservation influenced the carbon preservation capacity (CPC) of the various size aggregates. Coarse microaggregates (CMicA) had the higher C capturing ability followed by mesoaggregates (MesoA), coarse macroaggregates (CMacA) and fine microaggregates (FMicA) under both conventional (CT) and reduced (RT) tillage treatments; whereas, zero tillage (T5 and T6) and brown (T7)/green (T8) manuring encouraged higher CPC in CMacA. Higher C density under ZT in macroaggregates (both CMacA and MesoA) suggested its role in C sequestration in soil. Greater C accumulation in macroaggregates could be due to the lower decomposable SOM associated with these aggregates. The stability of macroaggregates against slaking could be attributed to the direct contribution of SOM for C enrichment in these size fractions (Puget et al., 1995). Our results (Fig. 3) showed that with reducing soil disturbance and increasing residue derived organic C input (T4, T5, T6, T7 and T8), there was a preferential accumulation of C in macroaggregates due to the fact that organic matter first enters the soil mainly in particulate form. During decomposition this is progressively incorporated into mineral associated pool with a consequent positive effect on stabilization of macroaggregates resulted its high CPC (Aoyama et al., 1999). 5. Conclusion Our study corroborates that DSR and wheat in zero tillage coupled with residue retention is a suitable management practice for enhancing soil C sequestration and sustainable yield increment even in reclaimed sodic soil of hot semi-arid zone of Indian subcontinent. This has a potential to increase total SOC content by 33.6%, equivalent wheat yield by 8.3%, water stable macroaggregates by 53.8% and macroaggregate associated C by 20.8% over conventional tillage with transplanted rice after five years of continuous rice–wheat cropping. The higher stratification ratio of total SOC and different aggregated C under this treatment ensured the greater SOC sequestration in surface than in sub-surface soil layer. Addition of crop residues along with no-disturbance favoured a higher amount of C to be preferentially stabilized in coarse macro and mesoaggregates by physical protection. The high SOC stabilized within the ‘silt + clay’ sized particles was manoeuvred by its chemical recalcitrance nature and may act as a stable soil carbon pool encouraging long-term SOC sequestration. References Angers, D.A., Bolinder, M.A., Carter, M.R., Gregorich, E.G., Drury, C.F., Liang, B.C., Vovoney, R.P., Simard, R.R., Donald, R.G., Beyaert, R.P., Martel, J., 1997. Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada. Soil Tillage Res. 41, 191–201.

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