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Effect of different rice establishment methods on soil physical properties in drought-prone, rainfed lowlands of Bihar, India.

Introduction

Among countries growing rice (Oryza sativa L.), India has the largest area (42.5 Mha) producing 29% of the nation's calorie requirements, making it the most staple food crop of the country (IRRI 2014). Worldwide, rice feeds -50% of the human population and provides 19% of its global caloric intake (IRRI 2014). Therefore, improving and sustaining the production of rice is essential for global food security. In India, rice is mainly grown by manual transplanting in puddled fields. Puddling (wet tillage) is done to reduce water infiltration and to maintain the standing water in the field, which helps in weed management and facilitates easier transplanting (Sharma and De Datta 1986). The impact of puddling on rice productivity varies according to soil characteristics and climate (Kirchhof et al. 2000). Field preparation for transplanting rice is an energy-intensive process and requires a considerable amount of water. Tillage also influences weed emergence because of changes in the mechanical characteristics (bulk density, penetration resistance, aggregate mean-weight diameter and surface roughness) of the seedbed (Carman 1996; Mohanty et al. 2004). In addition, puddled and flooded soils have many benefits such as neutralised soil pH, improved availability of plant nutrients (phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), and iron (Fe)), and accumulation of organic matter (Ponnamperuma 1972; Sahrawat 2005). An indirect increase in the availability of nutrients by puddling is due to a reduction in cation (e.g. [NH.sub.4.sup.+]) leaching (Aggarwal et al. 1995). There is also the potential for biological nitrogen fixation by blue-green algae and Azolla in the puddlcd-transplant system, which can save up to 20-30 kg nitrogen (N) [ha.sup.-1] (Singh and Bisoyi 1989).

There are, however, some problems associated with puddling in rice, such as deterioration of soil structure and creation of a hardpan (Sharma and De Datta 1986; Thierfelder and Wall 2009), increased methane emissions and hydrogen sulfite formation (Ponnamperuma 1972), and increased bulk density and soil compaction (Kirchhof et ai 2000). Moreover, puddling and transplanting require large amounts of scarce water resources as well as labour (Kumar and Ladha 2011). Puddling operations consume -25% of the total water required for rice during the growing season. Extensive field studies on fine-textured soils (clay content varying from 41% to 74%) in the Philippines and Indonesia revealed that puddling was not necessary, and could be omitted without any yield loss (So and Kirchhoff 2000). The destruction of soil aggregates (or soil structure) and formation of a hardpan during puddling have adverse effects on the yield of subsequent non-rice crops in rotation, and these crops also require more energy for field preparation (Fujisaka et al. 1994; Kumar and Ladha 2011). Another consequence is that the soil infiltration rates in the wheat season are less where the land had been puddled for rice than when the soil had been dry-drilled or kept under no-tillage (Singh et al. 2011).

Problems in the Eastern Indo Gangctic Plains (EIGP) include small farms, land fragmentation, inadequate irrigation infrastructure, weak institutions and markets, and poverty (Balasubramanian et al. 2012). Cereal production systems in these less favourable, rainfed and drought-prone areas often result in low yield and low farm income. Often, farmers delay wet tillage (puddling) of rice until after the onset of the monsoon, resulting in low rice yields and consequently low wheat yields due to delayed sowing as a result of the late rice harvest.

Rice can be grown under non-puddled and even no-tilled soil conditions by mechanical transplanting (Kamboj et al. 2013) or direct seeding (Yadav et al 2009; Singh et al. 2011), sometimes even with yield advantages and/or overall increased profits compared with the traditional method of rice cultivation (puddling followed by manual transplanting), provided weeds arc managed properly. Higher grain yields of rice have also been reported when grown with the system of rice intensification (SRI) method than conventional rice culture (Hugar et al. 2009; Thakur et al. 2010; Zhao et al. 2010). Therefore, eonservation agriculture together with best management practices (BMP) used in other parts of the IGP offer potential to be extended to the EIGP. In light of these facts, the present study was undertaken with the aim of evaluating the effect of alternative rice establishment methods on soil physical properties and productivity of the rice-wheat cropping system in rainfed, drought-prone environments.

Materials and methods

Experimental site

Three sets of on-station field experiments were conducted in 2012-13 and 2013-14 at the experimental farm of the Indian Council of Agricultural Research Complex for the Eastern Region in Patna, Bihar, India (25024.912'-25[degrees]25.971'N and 85o03.536,-85[degrees]03.624,E). Drought-tolerant rice varieties were evaluated using different rice-crop establishment methods in drought-prone, rainfed environments of Bihar, followed by notillage wheat (Table 1). The climate of Patna is subtropical humid (Fig. 1), with an average annual rainfall of 1130 mm (85-90% of which is received from June to September), daily minimum temperatures of 7-9[degrees]C in January, daily maximum temperatures of 36-41[degrees]C in May, and relative humidity of 60-90% throughout the year. The rice crop season in the region normally lasts from June to November (kharij), and wheat (rabi) from November to March. However, rice harvest in large areas commonly extends to late December, leading to delayed wheat sowing from mid-Dcccmbcr to early January, and delayed harvest up to April.

The soil physical and chemical properties in different experimental plots were similar because the trial plots of three sets of experiments were adjacent (they belonged to one big field plot). The soil at the experimental site had a loam texture, was of Gangetic alluvial origin, very deep (>2 m), flat (-1% slope) and well drained. Detailed soil characteristics to a profile depth of 30 cm were measured just before laying out the experiment and are presented in Table 2. At the onset of the field experiment, the surface soil (0-15 cm) was mildly alkaline (pH 7.7), non-saline (electrical conductivity 0.08 dS[m.sup.-1]), low in organic carbon (OC, 0.48%), high in available P (0.5 M NaHC[O.sub.3]-extractable P, 24.1 kg [ha.sup.-1]), and medium in K (1n N[H.sub.4]OAc-extractable K, 216 kg [ha.sup.-1]).

Treatments and crop management

The treatments from which soil samples were taken were: (i) puddled, transplanted with BMP (P-BMP); (//) puddled, transplanted with SRI (P-SR1); (in) unpuddlcd, transplanted (UP-TR); and (tv) unpuddled, direct-seeded (UP-DS). Particle density of the soil was 2.645 g [cm.sup.-3], and, sand, silt and clay contents were 42.2%, 35% and 22.8%, respectively. Puddled experimental plots (P-BMP and P-SRI) were dry-ploughed followed by deep harrowing (twice), levelling and proper puddling before rice transplantation. For unpuddlcd plots (UP-TR and UP-DS), only one dry ploughing followed by harrowing and leveling was done before water ponding. No puddling was done and rice seedlings were transplanted into the saturated soil (UP-TR), or the seed was direct-seeded with a seeding machine (UP-DS). Seedlings of rice (21 days old) were transplanted in both puddled and unpuddled plots by using one seedling per hill at a spacing of 25 cm (row to row), with 15 cm between hills. In P-SRI, 12-day-old seedlings were transplanted in the first week of July. In each plot, the designated plant stand was maintained and standard agronomic practices were followed. Chemical and mechanical weed-control methods were employed. During the winter (rabi) season, no-tilled wheat was grown under rainfed conditions across all plots without disturbing the original layout. Recommended rates of fertiliser were uniformly applied in both rice and wheat crops during both years.

Soil sample collection, bulk density and penetration resistance

Composite soil samples from depths of 0-15 and 15-30 cm in each replicated plot were collected at wheat harvest in the second year for determination of aggregate size distribution. For bulk density analysis, undisturbed core samples were collected at wheat harvest. The undisturbed cores were further used for generating soil-water retention functions. For determination of soil chemical properties, triplicate disturbed samples were collected from each treatment after wheat harvest.

Bulk density of the samples (g [cm.sup.-3]) was determined by core method (Blake and Hartge 1986). Fresh soil cores of known volume were processed in the laboratory, weighed and then dried at 105[degrees]C in the oven until they attained constant weight.

Soil penetration resistance was measured using a hand penetrometer (Eijkelkamp Soil & Water, Giesbeek, The Netherlands). It is an instrument for indicative measurement of maximal resistance to penetration. The base area of the cone was 2 cm2. The maximum resistance that can be recorded by the instrument is 1000N. For each depth, the probe attached with the instrument was inserted vertically and maximum reading was recorded. Before taking the second reading, the instrument was set back to zero. The cone resistance was calculated according to Eqn 1:

Cone resistance = manometer reading 5- base area of cone (1) Soil aggregate analyses

Soil samples were prepared in the laboratory by carefully breaking larger clods (field-moist soil) by hand into smaller segments along natural cleavages and then air- dried. Air-dried samples were then passed through an 8-nnn sieve and retained on a 6-mm sieve. The aggregates were then wet-sieved through a collection of six sieves (mesh sizes 4, 2, 0.5, 0.25, 0.12 and 0.0.53 mm), following the procedure described by Yoder (1936). A shaking operation was performed for 20 min with 35cpm.

The aggregates retained on each sieve were transferred to a set of pre-weighed beakers, oven-dried at 60[degrees]C for 48 h and weighed. The mean-weight diameter (MWD) was calculated as an index of aggregation (van Bavel 1950) along with other indices as follows. The line between macro- and microaggregates is commonly drawn at 0.25 mm (Edwards and Bremner 1967; Oades and Waters 1991). Therefore, the macro-aggregates were determined by adding the weight of the aggregates retained in the 4-, 2-, 0.5- and 0.25-mm sieves. Micro-aggregates were calculated by adding the weight of aggregates retained by the 0.12- and 0.053-mm sieves. The MWD and geometric mean diameter (GMD) of aggregates (Kemper and Roseneau 1986) were calculated according to Eqns 2 and 3:

MWD (mm) = [[summation].sup.n.sub.i=1] XiWi/[[summation].sup.n.sub.i=1] Wi (2)

GMD (mm) = exp [[summation].sup.n.sub.i=1] xi log Wi/[[summation].sup.n.sub.i=1]/ [[summation].sup.n.sub.i=1] XiWi/[[summation].sup.n.sub.i=1] (3)

where Wi is the weight of aggregates retained over the particular sieve and Xi is the mean diameter of the size class (mm). The aggregate ratio (AR) of soils was computed according to Eqn 4:

AR = % water-stable macro-aggregates/ /% water-stable micro-aggregates (4)

Water-retention curve and available water capacity

The pressure plate apparatus (Soil Moisture Equipment Corp., Goleta, CA, USA) method was used for obtaining the water-retention curve (Klute 1986). Water retention of undisturbed soil core samples was determined at 33, 50, 75, 100, 350 and 1500 kPa. The pressure plates were saturated overnight and undisturbed soil samples (cores) were placed on the plate in separate rubber rings. Then water was added to saturate the sample for 24 h until complete saturation. Saturated plates with the soil samples were placed in pressure chambers and desired pressures were applied. For attaining equilibrium, they were kept for 48 h at the specified pressure. Then, samples were taken out from the chambers and the weights of the soil core samples were recorded. After passing the highest pressure-step, the soil core samples were oven-dried at 105[degrees]C until constant weight and the dry weights were recorded. The moisture content retained by each sample at a specified potential was then calculated from the moist and dry weight recorded. Water-holding capacity of soil was determined by the Keen box method (Piper 1966).

Measurement of crack parameters

Each experimental plot was divided into four parts, and squares 1 m by 1 m were demarcated in each part. Within each of these squares, total crack length apparent on the soil surface was measured with a flexible twine run along the crack (Dasog and Shashidhara 1993). The average depth and width of cracks were based on measurements made at 0.5-m intervals along the course of the crack. The crack depth was measured with a 2-mmdiameter steel rod inserted until it offered resistance to further penetration, and the width was measured with an adjustable divider at 1 cm below the soil surface (Dasog et al 1988). A depth of 1 cm was chosen to avoid exaggerated widths caused by surface disturbance. For measurement of crack parameters at different water potentials, one tensiometer was installed in each plot. Crack volume measurement was done at -60 kPa soil moisture potential with sand and measuring cylinder. An area of 0.5 m by 0.5 m was selected and sand was poured into the cracks until they were all filled. The measured volume was multiplied by four to express the volume per [m.sup.2] area.

Chemical analyses of soil

Prior to analysis, soil samples were air-dried and passed through a 2-mm sieve. The principal chemical properties of soil were determined by standard methods (Sparks et al. 1996). In particular, the pH and EC was measured for sample--water mixtures of 1 :2.5, and the OC content was determined by dichromate oxidation of the sample and subsequent titration with ferrous ammonium sulfate (Walklcy and Black 1934). The mineralisablc N content was obtained by the Kjcldahl method followed by titration with diluted sulfuric acid (Subbiah and Asija 1956). Available P content was determined by the NaHC03-ascorbic acid method (Watanabc and Olsen 1965), and available K content with the ammonium acetate method using a flame photometer (Hanway and Heidel 1952). Physicochemical properties of the experimental field from the composite soil samples taken from 0-15 and 15-30 cm were also determined at the beginning of experiment (Table 2). The measured available N, P and K were converted to kg [ha.sup.-1] according to Eqn 5;

Available N. P or K (kg [ha.sup.-1]) = Measured value (mg [kg.sup.-1]) x 2.24 (5)

Results

Bulk density

A noticeable difference in bulk density values was recorded for the various rice-crop establishment methods. In the 0-15 cm soil layer, significantly higher bulk density was found under puddled conditions than unpuddled conditions. It was highest in P-BMP (1.631 g [cm.sup.-3]), followed by P-SRI (1.625 g [cm.sup.-3]) and UP-TR (1.590 g [cm.sup.-3]), and lowest bulk density was recorded in UP-DS (1.584 g [cm.sup.-3]) (Fig. 2). A similar trend was observed in the second layer (15-30 cm). However, irrespective of the rice-crop establishment method, all treatments showed higher bulk density in the lower than the upper layer. Bulk density was similar in P-BMP and P-SRI, followed by UP-TR and lowest in UP-DS, which was significantly different from P-SRI. Further down the profile (30--45 cm layer), bulk density was again higher than in the layers above; however, no difference was observed among the various treatments.

Soil penetration resistance

The effect of puddling on soil penetration resistance was clear (Fig. 3). In the surface layer (0-10 cm), penetration resistance was highest in P-SRI (1.50 MPa) followed by P-BMP (1.49 MPa), UP-TR (1.47 MPa) and UP-DS (1.44 MPa). In the second layer (10-20 cm), penetration resistance was always higher than in the layer above. Again the highest resistances were recorded in puddled treatments (1.54 MPa in the P-BMP treatment), with unpuddled treatments recording lower resistances (1.46 MPa in the UP-DS). A similar trend was also observed in the next layer (20-30 cm) but the difference in penetration resistance among various treatments was small. Beyond 30 cm soil depth, no difference in penetration resistance was detected.

Soil aggregate size distribution

The effect of different rice-crop establishment methods on soil aggregate size distribution was prominent. For the surface 0-15 cm soil layer, the highest MWD was recorded in UP-DS (1.16mm), followed by UP-TR (1.01mm), P-SRI (0.94mm) and UP-BMP (0.81mm) (Tabic 3). Water-stable aggregates showed a similar trend. The lowest water-stable aggregate percentage was measured in P-BMP (89.5%), and the highest in UP-DS (94.6%). In the 15-30cm soil layer, UP-DS again recorded the highest water-stable aggregate percentage. Irrespective of rice-crop establishment methods, all treatments except P-SRI showed higher MWD values in the second than in the upper layer. Maximum and minimum MWD values were recorded in UP-DS (1.19 mm) and P-BMP (0.85 mm), respectively.

Soil moisture content and water holding capacity

There were clear differences in soil moisture characteristics between the different rice-crop establishment methods (Table 4). Water-holding capacity, the maximum amount of water that a given soil can retain, is a function of volume and size of pores and was highest in UP-DS (0.346 [cm.sup.3] [cm.sup.-3]), followed by UP-TR (0.331 [cm.sup.3] [cm.sup.-3]) then P-BMP (0.327 [cm.sup.3] [cm.sup.-3]), and lowest in P-SRI (0.305 [cm.sup.3] [cm.sup.-3]). However, a different trend was observed for plant-available water. At low soil moisture potentials (at and close to saturation), soil water content was clearly higher in puddled soils than unpuddlcd soils. But with increasing soil moisture potential, the moisture content decreased faster in puddled soils and the difference between unpuddled and puddled soil diminished (Fig. 4). Therefore, the available water up to 1500 kPa was higher in puddled soils than in unpuddled soils.

Cracking behaviour

The cracking behaviour of soils was highly affected by different rice-crop establishment methods. Deeper and wider cracks were recorded throughout the whole range of soil moisture potential in puddled conditions. Initially (at -10 kPa), crack depth in puddled condition was 5.03 cm and in unpuddled condition 3.87cm (Fig. 5). As the soil moisture potential increased, the difference in depth between puddled and unpuddled soils widened. The range of difference increased from 30% at -10kPa to 78% at -60 kPa. A similar trend was observed for crack width. Crack width was always greater in puddled condition. Crack width varied from 3.73 to 7.37 cm in puddled soils, whereas it ranged between 2.57 and 4.57 cm in unpuddled conditions. Crack length reflected the same trend as crack width and crack depth. Crack volume was more than three times higher in puddled soils. It was estimated at 8.82 and 2.85 L [m.sup.-2] area in puddled and unpuddled soils, respectively.

Nutrient status in soils

The nutrient status of soils mainly depends on the input used, through both organic and inorganic sources, and the cropping system followed. Only small variations in nutrient concentrations were found among the different treatments (Table 5). In the topsoil (0-15 cm), OC concentration was marginally higher in unpuddled soils than in puddled treatments. The highest OC concentration was recorded in UP-DS (4.8 g [kg.sup.-1]) and the lowest value in P-BMP (4.4 g [kg.sup.-1]). A similar trend was observed for the three major nutrients (N, P, K. Unpuddled treatments recorded higher nutrient content than puddled treatments. In the next layer (15-30cm), N and P but not K recorded lower values than in the topsoil. Within the same layer, variations among treatments were not great.

Rice and wheat yield

Yield data of rice and wheat are presented in Fig. 6. In case of rice, highest yield was produced by the P-BMP treatment (3412 kg [ha.sup.-1]), followed by P-SRI (3187kg [ha.sup.-1]), UP-TR (3062 kg [ha.sub.-1]) and UP-DS (2062 kg [ha.sup.-1]). For the wheat crop, highest and lowest yields were recorded in P-SRI (3133 kg [ha.sup.-1]) and P-BMP (2680 kg [ha.sup.-1]), respectively.

Discussion

Soil physical properties

Differences in bulk density values under various rice-crop establishment methods were clearly caused by puddling and non-puddling before transplanting. Puddled conditions under P-BMP and P-SRI showed higher bulk density, which can be attributed to the smearing action of puddling, resulting in the breakdown of aggregates and more compaction of soil aggregates after drying. Sharma and De-Datta (1985) also reported higher bulk density in puddled soils upon drying of the soil after rice harvest. The lower bulk density values in unpuddled conditions were therefore due to better (and maintained) aggregation of soil particles. The higher bulk density in the second soil layer can be explained by eluviation of fine soil particles from the top layer into the layer below due to puddling (Aggarwal et al. 1995; Hobbs and Gupta 2000). In addition, the puddling operation does compress the layer below. No difference in bulk density values among the various treatments could be observed in the 30-45 cm layer, indicating that the tillage and puddling effect was limited to the upper 30 cm.

No data on the critical soil strength at which root growth could be hampered are available for the present soil. However, based on the limited information available in literature, 1.54 MPa (the maximum range of values in P-BMP at 10-20 cm depth) appears not to be a limiting value. In our study, penetration values never exceeded 2 MPa, at which root elongation was also not likely to be restricted. However, root growth can be hampered by reduced gas exchange and oxygen supply to the roots, which affects wheat roots more than rice roots. The higher penetration resistance in puddled conditions than unpuddled conditions will have been caused by the breakdown of soil aggregates, which in turn leads to a more compact arrangement of soil particles. A comparatively hard layer was clearly observable from penetration resistance values in puddled soils (both P-BMP and P-SR1) at 10-20cm depth. Creation of a hardpan and compaction due to puddling were also reported by Sharma and De Datta (1986) and Kirchhof et al. (2000). The difference in penetration resistance between puddled and unpuddled conditions was reduced in the deeper soil layers.

The aggregation index and MWD of aggregates could clearly differentiate the puddled and unpuddled treatments in both 0-15 and 15-30 cm layers. More of the smaller macro-aggregates with an average diameter of 0.053-0.25 mm in puddled soils clearly demonstrated the breakdown of larger macro-aggregates (>0.25 mm) into smaller size fractions. Similarly, Chaudhary and Ghildhyal (1969) and Painuli (1993) reported a decrease in aggregate size due to puddling. Thus, less disturbance of soils without puddling resulted in significantly higher macroaggregates in these unpuddlcd conditions (UP-TR and UP-DS). The results for unpuddled treatments, showing an improvement in soil aggregation, average MWD and water-stable aggregates, proved the interactive effect of the absence of soil disturbance. Similar results were presented by Singh and Malhi (2006), whose data on aggregate-size distribution indicated a larger effect of no-tillage on soil structure. The size distribution of aggregates is intimately linked to soil quality in relation to water stability of aggregates and soil carbon accumulation (Saha et al. 2011, 2014). The positive effect of no puddling in UP-TR and UP-DS was clearly reflected in terms of MWD, proving again that this structural index might be a valuable parameter for soil quality indices.

Higher water-holding capacity in unpuddled conditions will be closely related to better soil aggregation and the presence of more macropores, which can be drained at lower soil water tensions. Therefore, moisture content at field capacity under puddled condition was lower despite higher water-holding capacity. The greater moisture retention at higher potentials indicated the possibility of a greater number of medium-sized pores under unpuddled condition, enabling the soil to retain more moisture, which is available to plants at these potentials. Puddling resulted in breaking down of aggregates and therefore, reduced the number of macropores.

Cracks play an important role in physical processes of soil. The frequency, size and rate of development of cracks influence water, air, solute and heat dynamics in soils, and hence influence crop productivity and the potential for groundwater pollution. Our results indicated that wider, deeper and longer cracks could be attributed to the puddling operation. This finding is in agreement with the study of Flowers and Lai (1999), who reported an increase in the area and volume of cracks with a decrease in the soil-water content. Puddling resulted in breaking down of larger aggregates into smaller aggregates, which in turn helped the crack-development process. Sudhir-Yadav et al. (2011) showed that there was greater cracking on puddled soils than on non-puddled soils during soil drying, and that this was associated with a faster rate of drying in the puddled soil. Mohanty et al. (2006) also found that the surface area of cracks was larger in puddled soils than in non-puddled soils.

Soil nutrient status at the end of the experiment

Minor improvements or no significant differences in the soil nutrient status after a period of only 2 years could well be expected in the present study. However, even the little improvement observed under unpuddled conditions (UP-TR and UP-DS) was encouraging and this could be expected to improve the soil health further in the longer term.

Yield of rice and wheat

The effect of different crop-establishment methods on yield of rice was prominent; however, the carryover impact on the succeeding wheat crop was not yet significant. Significantly lower rice yield in UP-DS than in the P-BMP treatment could be partly attributed to suboptimal management and higher weed infestation. Lower yield in direct-seeded rice, mainly due to greater infestation of weeds, has been reported by many researchers elsewhere (Bhushan et al. 2007; Ladha et al. 2009; Yadav et al. 2009; Singh et al. 2011). Puddling in rice did not bring about any significant adverse effect on the productivity of wheat, although the trends did indicate a negative effect on wheat in the P-BMP treatment. Longer experiments would probably be needed to clarify the effect of slow changes in soil quality. Otherwise, puddling has already been extensively reported to be detrimental not only to soil health but also to nonrice upland crops in rotation (Sharma et al. 2003; Gathala et al. 2011; Laik et al. 2014). Also, there were inconsistent results elsewhere with regard to effect of puddling on the performance of wheat (Kirchhof et at. 2000; Mousavi et al. 2009). This could also indicate that the effect of puddling and its impact on crop growth may vary depending on intensity of puddling, soil type and crop grown, but no meta-study on this topic is currently available.

Conclusions

Cereal production systems in the EIGP arc traditional, with low yield and low farm income, and they have largely missed out on the benefits of the Green Revolution. Traditional systems of rice cultivation use puddling to increase water availability and control weeds in rainfed, stress-prone environments. This practice has a significant impact on soil physical properties. It was found that omission of puddling (UP-TR and UP-DS) quickly improved the physical properties of soil, such as bulk density, penetration resistance, aggregation stability and cracking behaviour. In addition, there was an improvement in soil aggregation, average MWD and water-stable aggregates under non-puddled conditions. Unpuddlcd conditions increased macro-aggregates by 18-33%. Later, a hard layer was noticed in puddled conditions (P-BMP and P-SRI). Wider, longer and deeper cracks developed in the plots that were subjected to puddling, and unpuddlcd treatments recorded slightly higher nutrient contents than puddled treatments. Therefore, the present study clearly showed that puddling deteriorates soil health. Based on the present study, it can be concluded that not puddling can create conditions that are more favourable for soil health, including improvement in bulk density, aggregation stability, pore size distribution and penetration resistance, which in the longer term should improve crop growth. Productivity and profitability of rice-based systems in unpuddlcd, transplanted conditions may become the better options, because these conditions help to improve soil health, reduce the energy required and costs for soil preparation, and require less labour. However, long-term research is needed for better understanding of the impact of such practices on the productivity of rice and succeeding dry-season crops. The results of this study ean form the basis of further long-term experiments in the IGP and in mega-deltas comprising parts of India, Bangladesh and Myanmar.

http://dx.doi.org/10.1071/SR15346

Acknowledgements

We arc most grateful to the International Rice Research Institute in Los Banos, Philippines, and the Bill and Melinda Gates Foundation (BMGF) for rendering the financial assistance through the IRRAS project in Bihar. Authors thank Dr S. Singh, Dr Ashok Yadav, Dr Stephan M. Haefele, Dr S. S. Singh, Dr Bikash Sarkar and two anonymous reviewers for suggesting improvements in the manuscript.

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Surajit Mondal (A,B), Santosh Kumar (A), A. Abdul Haris (A), S. K. Dwivedi (A), B. P. Bhatt (A), and J. S. Mishra (A)

(A) ICAR Research Complex for Eastern Region, Patna, Bihar, India.

(B) Corresponding author. Email: surajit.icar@gmail.com

Table 1. Details of field experiments conducted at ICAR-RECR,
Research Station

SRI, System of rice intensification; CT, conventional transplanting;
BMP, best management practices; NT, no-till

Expt   Experiments

no.

1      Evaluation of drought-tolerant rice genotypes under SRI and CT
         using BMP in puddled condition followed by NT wheat in
         rainfed, drought-prone systems
2      Evaluation of drought-tolerant rice genotypes or lines in
         unpuddled transplanted conditions and NT wheat in rainfed,
         drought-prone systems
3      Evaluation of rice varieties or lines in unpuddled dry direct
         seeding and NT wheat in rainfed, drought-prone systems

Expt         Year              Treatment

no.                        Rice          Wheat

1      2012-13, 2013 14   P-BMP,  P-SRI   NT
2      2012-13, 2013-14   UP-TR           NT
3      2012 13,2013-14    UP-DS           NT

Table 2. Soil physico-chemical properties before start of the
experiment

Soil parameters                            Soil layer (cm)

                                            0-15    15-30

Texture                                    Loam     Loam
Sand (%)                                    42.2     43.2
Silt (%)                                    35.0     29.8
Clay (%)                                    22.8     26.9
pH                                           7.7      7.8
Electrical conductivity (dS [m.sup.-1])      0.08     0.09
Organic C (g [kg.sup.-1])                    4.8      3.2
Avail. N (kg [ha.sup.-1])                  225.8    194.4
Avail. P (kg [ha.sup.-1])                   24.1     17.9
Avail. K (kg [ha.sup.-1])                  216.2    224.5
DTPA Fe ([mciro]g [g.sup.-1])               29.7     31.2
DTPA Mn ([mciro]g [g.sup.-1])               28.1     26.3
DTPA Cu ([mciro]g [g.sup.-1])                3.5      3.07
DTP A Zn ([mciro]g [g.sup.-1])               0.7      0.6

Table 3. Aggregate-size distribution, mean-weight diameter (MWD),
water-stable aggregates (WSA) and geometric mean diameter (GMD) as
affected by different rice-crop establishment methods

Values are means [+ or -] standard error of mean. P, Puddling; BMP,
best management practices; SRI, system of rice intensification; UP,
unpuddled; TR, transplanted; DS, direct-seeded

Treatment          Aggregate-size distribution
                (%) by aggregate size group (mm):

                    8-1                   4-2

0-15 cm

P-BMP       1.17 [+ or -] 0.04    5.55 [+ or -] 0.20
P-SRI       1.38 [+ or -] 0.14    4.74 [+ or -] 0.24
UP-TR       1.32 [+ or -] 0.11    6.87 [+ or -] 0.43
UP-DS       3.51 [+ or -] 0.29    7.59 [+ or -] 0.27

15-30 cm

P-BMP       1.47 [+ or -] 0.08    5.05 [+ or -] 0.13
P-SRI       1.65 [+ or -] 0.16    5.68 [+ or -] 0.48
UP-TR       2.87 [+ or -] 0.24    7.86 [+ or -] 0.88
UP-DS       3.92 [+ or -] 0.38    9.07 [+ or -] 0.76

Treatment          Aggregate-size distribution
                (%) by aggregate size group (mm):

                   2-0.5               0.5-0.25

0-15 cm

P-BMP       16.77 [+ or -] 1.11   26.38 [+ or -] 1.03
P-SRI       28.94 [+ or -] 1.29   26.97 [+ or -] 1.25
UP-TR       29.55 [+ or -] 2.33   28.17 [+ or -] 1.67
UP-DS       28.63 [+ or -] 0.77   28.61 [+ or -] 0.63

15-30 cm

P-BMP       17.25 [+ or -] 0.20   31.07 [+ or -] 1.26
P-SRI       17.63 [+ or -] 1.08   32.85 [+ or -] 0.83
UP-TR       22.63 [+ or -] 1.81   30.56 [+ or -] 1.39
UP-DS       26.21 [+ or -] 0.99   28.41 [+ or -] 0.71

Treatment          Aggregate-size distribution
                (%) by aggregate size group (mm):

                 0.25-0.12            0.12-0.053

0-15 cm

P-BMP       29.74 [+ or -] 1.15    9.85 [+ or -] 0.17
P-SRI       17.17 [+ or -] 0.40   11.35 [+ or -] 0.34
UP-TR       12.01 [+ or -] 0.54   13.40 [+ or -] 0.45
UP-DS       15.68 [+ or -] 0.32   10.55 [+ or -] 0.57

15-30 cm

P-BMP       28.49 [+ or -] 0.56   10.89 [+ or -] 0.42
P-SRI       29.11 [+ or -] 1.42    9.76 [+ or -] 0.40
UP-TR       20.04 [+ or -] 0.80   10.43 [+ or -] 1.02
UP-DS       18.49 [+ or -] 0.71    8.65 [+ or -] 0.45

Treatment     Aggregate-size              MWD
             distribution (%)            (mm)
             by aggregate size
                group (mm):

                  <0.053

0-15 cm

P-BMP       10.54 [+ or -] 1.40   0.81 [+ or -] 0.02
P-SRI        9.44 [+ or -] 1.88   0.94 [+ or -] 0.03
UP-TR        8.69 [+ or -] 2.28   1.01 [+ or -] 0.03
UP-DS        5.42 [+ or -] 1.48   1.16 [+ or -] 0.02

15-30 cm

P-BMP        5.78 [+ or -] 1.88   0.85 [+ or -] 0.01
P-SRI        3.31 [+ or -] 0.63   0.90 [+ or -] 0.02
UP-TR        5.62 [+ or -] 2.19   1.06 [+ or -] 0.01
UP-DS        5.25 [+ or -] 1.34   1.19 [+ or -] 0.01

Treatment           WSA                   GMD
                    (%)                  (mm)

0-15 cm

P-BMP       89.46 [+ or -] 1.40   0.73 [+ or -] 0.01
P-SRI       90.56 [+ or -] 1.88   0.78 [+ or -] 0.02
UP-TR       91.31 [+ or -] 2.28   0.80 [+ or -] 0.03
UP-DS       94.58 [+ or -] 1.48   0.86 [+ or -] 0.02

15-30 cm

P-BMP       94.22 [+ or -] 1.88   0.77 [+ or -] 0.01
P-SRI       96.69 [+ or -] 0.63   0.80 [+ or -] 0.01
UP-TR       94.38 [+ or -] 2.19   0.83 [+ or -] 0.01
UP-DS       97.04 [+ or -] 1.34   0.87 [+ or -] 0.01

Treatment                Aggregates (%)

                   Macro                 Micro

0-15 cm

P-BMP       49.87 [+ or -] 0.27   39.59 [+ or -] 1.19
P-SRI       62.03 [+ or -] 2.45   28.53 [+ or -] 0.67
UP-TR       65.91 [+ or -] 2.56   25.41 [+ or -] 0.50
UP-DS       68.35 [+ or -] 1.21   26.23 [+ or -] 0.71

15-30 cm

P-BMP       54.84 [+ or -] 1.28   39.38 [+ or -] 0.73
P-SRI       57.82 [+ or -] 1.89   38.87 [+ or -] 1.30
UP-TR       63.91 [+ or -] 0.91   30.47 [+ or -] 1.30
UP-DS       67.62 [+ or -] 0.87   27.13 [+ or -] 1.16

Treatment        Aggregate
                   ratio

0-15 cm

P-BMP       1.26 [+ or -] 0.03
P-SRI       2.18 [+ or -] 0.13
UP-TR       2.60 [+ or -] 0.14
UP-DS       2.61 [+ or -] 0.08

15-30 cm

P-BMP       1.39 [+ or -] 0.02
P-SRI       1.49 [+ or -] 0.10
UP-TR       2.10 [+ or -] 0.06
UP-DS       2.50 [+ or -] 0.11

Table 4. Water-holding capacity (WHC), soil moisture retention at
different potential, and available water ([cm.sup.3] [cm.sup.-3])
under different treatments

Values are means [+ or -] standard error of mean. P, Puddling; BMP,
best management practices; SRI, system of rice intensification; UP,
unpuddled; TR, transplanted; DS, direct-seeded

Treatment           WHC               Soil moisture
                                     potential (kPa):

                                            33

P-BMP       0.327 [+ or -] 0.003   0.249 [+ or -] 0.004
P-SRI       0.305 [+ or -] 0.004   0.246 [+ or -] 0.003
UP-TR       0.331 [+ or -] 0.003   0.216 [+ or -] 0.004
UP-DS       0.346 [+ or -] 0.002   0.222 [+ or -] 0.003

Treatment         Soil moisture potential (kPa):

                     50                     75

P-BMP       0.214 [+ or -] 0.003   0.164 [+ or -] 0.004
P-SRI       0.224 [+ or -] 0.004   0.162 [+ or -] 0.003
UP-TR       0.208 [+ or -] 0.004   0.170 [+ or -] 0.004
UP-DS       0.202 [+ or -] 0.003   0.166 [+ or -] 0.005

Treatment         Soil moisture potential (kPa):

                    100                    350

P-BMP       0.122 [+ or -] 0.002   0.073 [+ or -] 0.002
P-SRI       0.110 [+ or -] 0.004   0.068 [+ or -] 0.003
UP-TR       0.129 [+ or -] 0.004   0.073 [+ or -] 0.004
UP-DS       0.147 [+ or -] 0.004   0.083 [+ or -] 0.003

Treatment      Soil moisture            Available
              potential (kPa):
                                          water
                    1500

P-BMP       0.050 [+ or -] 0.001   0.199 [+ or -] 0.005
P-SRI       0.052 [+ or -] 0.003   0.195 [+ or -] 0.006
UP-TR       0.052 [+ or -] 0.003   0.164 [+ or -] 0.006
UP-DS       0.052 [+ or -] 0.001   0.170 [+ or -] 0.004

Table 5. Soil pH and electrical conductivity (EC, dS [m.sup.-1]) and
nutrient status (g [kg.sup.-1]) after wheat harvest in 2014

Values are means [+ or -] standard error of mean. P, Puddling; BMP,
best management practices; SRI, system of rice intensification; UP,
unpuddlcd; TR, transplanted; DS, direct-seeded

Treatment           pH                    EC

0-15 cm

P-BMP       7.82 [+ or -] 0.02    0.10 [+ or -] 0.01
P-SRI       7.76 [+ or -] 0.08    0.09 [+ or -] 0.01
UP-TR       7.75 [+ or -] 0.11    0.11 [+ or -] 0.01
UP-DS       7.82 [+ or -] 0.08    0.11 [+ or -] 0.01

15-30 cm

P-BMP       7.77 [+ or -] 0.07    0.10 [+ or -] 0.01
P-SRI       7.81 [+ or -] 0.11    0.09 [+ or -] 0.01
UP-TR       7.77 [+ or -] 0.11    0.11 [+ or -] 0.01
UP-DS       7.76 [+ or -] 0.06    0.10 [+ or -] 0.01

Treatment       org. carbon            Nitrogen

0-15 cm

P-BMP        4.4 [+ or -] 0.02    203.8 [+ or -] 5.4
P-SRI        4.5 [+ or -] 0.03    209.6 [+ or -] 9.5
UP-TR        4.6 [+ or -] 0.02    213.3 [+ or -] 9.6
UP-DS        4.8 [+ or -] 0.00    221.0 [+ or -] 10.9

15-30 cm

P-BMP        3.5 [+ or -] 0.01    187.9 [+ or -] 2.3
P-SRI        3.8 [+ or -] 0.01    183.1 [+ or -] 9.1
UP-TR        3.8 [+ or -] 0.03    192.8 [+ or -] 21.8
UP-DS        3.6 [+ or -] 0.05    172.5 [+ or -] 5.0

Treatment       Phosphorus             Potassium

0-15 cm

P-BMP       23.9 [+ or -] 1.25    199.0 [+ or -] 9.2
P-SRI       23.0 [+ or -] 2.75    222.5 [+ or -] 6.1
UP-TR       29.7 [+ or -] 4.52    218.4 [+ or -] 15.7
UP-DS       27.5 [+ or -] 3.05    221.3 [+ or -] 24.0

15-30 cm

P-BMP       15.7 [+ or -] 0.92    220.9 [+ or -] 6.5
P-SRI       16.1 [+ or -] 0.86    231.6 [+ or -] 8.5
UP-TR       17.5 [+ or -] 3.76    231.5 [+ or -] 10.2
UP-DS       18.2 [+ or -] 1.61    226.9 [+ or -] 13.8


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Author:Mondal, Surajit; Kumar, Santosh; Haris, A. Abdul; Dwivedi, S.K.; Bhatt, B.P.; Mishra, J.S.
Publication:Soil Research
Article Type:Report
Geographic Code:9INDI
Date:Nov 1, 2016
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