Although, the potential of management induced changes of soil organic matter, soil hydraulic properties (SHPs) and soil physical quality has been studied particularly in relation to tillage, few studies have evaluated combined effect of tillage, crop residue retention and cropping sequence, which are essential components of conservation agriculture (CA), on stratification and storage of soil organic matter, its effect on near-saturated soil hydraulic properties and soil physical quality in intensive cereal based irrigated cropping systems. Hence, the present study critically analyses the effects of CA on organic matter and hydro-physical properties of soil in a long-term CA field trial in NWIGP, India, which is one of the most fragile agro-ecosystems in the world. The objectives were (I) to investigate the stratification of soil organic carbon (SOC), total nitrogen (TN), C/N ratio and evaluate SR as an indicator of storage of SOC and TN and soil quality for different CA practices, (II) to assess the long-term effect of CA practices and short-term effect of crops on near-saturated soil hydraulic conductivity and water transmission properties, and (III) to assess the effect of CA practices on soil physical quality using capacitive and dynamic indicators. There were four treatments: (1) conventionally tilled rice-wheat cropping system (CT-RW), (2) reduced till CA-based rice-wheat-mungbean system (RT-RWMB), (3) no-till CA-based rice-wheat-mungbean system (NT-RWMB), and (4) no-till CA-based maize-wheat-mungbean system (NT-MWMB).
To achieve these objectives, soil bulk density, SOC and TN were measured in an increment of 5 cm up to 30 cm soil depth. Furthermore, the effects of CA were also evaluated in terms of soil hydro-physical properties. Soil physical properties such as bulk density and soil aggregate distribution were evaluated in two cropping seasons along with near saturated hydraulic properties. Steady state infiltration rates were obtained at four pressure heads by hood infiltrometer consecutively over two cropping seasons, i.e. during harvest season of rice/maize (October 2017) and maximum crop growth stage of wheat (February 2018). Data were analysed in terms of soil hydraulic conductivity, k(h), flow weighted mean pore radius (r0), hydraulically active porosity (ε) and threshold pore radius (rbp), a new pore measure indicative of macropore stability derived by substituting soil’s bubble pressure in the capillary equation. Finally, the effects of CA on soil physical quality in terms of both capacitive and dynamic indicators, derived from soil moisture retention curve and field measured hydraulic conductivity, respectively, were assessed and related with crop yield to infer which indicator better represented the soil physical quality and its effect on crop yield under irrigated intensive cereal based cropping systems.
Results showed that CA had profound impacts on distribution of SOC and TN in the soil profile. Significantly higher proportion of both SOC and TN were observed in the top soil in the CA-based treatments as compared with conventional intensive tillage-based treatment. The mean stratification ratio of both SOC and TN were found > 2 in CA-based treatments whereas the same was < 2 in intensive tillage-based treatment. Storage of SOC and TN in the 0-30 cm were found higher in CA-based treatments as compared with the intensive tillage-based treatment. These results on vertical distribution and storage of SOC and TN indicated a relatively better soil carbon sequestration and soil quality in CA-based treatment. The higher concentrations and storage of soil organic matter in CA-based treatments were, however, not translated into significantly (p < 0.05) lower bulk density due to probable compaction effect of no-tillage and harvest machinery and hydraulic pressure exerted by the flooded irrigation water. However, the increased soil organic matter in the top soil in CA-based treatments improved the soil aggregation significantly which helped in enhancing soil structural quality. Improvement in soil structure was reflected in relatively higher near saturated hydraulic conductivity in CA-based treatments. Irrespective of crop seasons, higher k(h) was observed under CA due to formation of macropores with better continuity, greater size and numbers as compared with conventional intensive tillage treatment. Moreover, higher r0 values were observed for a given k(h) for CA treatments suggesting that interaggregate pores are the dominant pathways of infiltration in CA. A relatively smaller temporal variation of rbp was indicative of a more stable macropore system established by rice-based CA as compared with maize-based CA. CA also enhanced hydraulically active macropores as compared with intensive tillage based conventional agriculture. Results also indicated that crops play an important role in relative distribution of the hydraulically active macropores in the root zone. The impact of CA on soil organic matter stratification and soil hydraulic properties were found to be expressed in terms of changes in soil physical quality. Soil moisture retention curves and pore size distributions under different treatments suggested higher soil water storage in structural pores in CA as compared with intensive tillage-based conventional agriculture. The impact of CA on soil physical quality and consequent effect on crop yield was found to be more expressed through dynamic indicators such as hydraulically active porosity rather than capacitive indicators derived from soil moisture retention curve. Overall, this study reveals that conservation agriculture has great potentials to reverse the intensive tillage induced degradation of soil resources in Indo-Gangetic Plains of India by improving the soil hydro-physical properties and soil physical quality.:Table of Contents
Declaration i
Declaration of Conformity ii
Acknowledgements iii
Table of Contents v
List of Figures vii
List of Tables xi
List of Symbols, Abbreviations and Acronyms xiv
Abstract xvii
1 Introduction and Background 1
1.1 General Overview 1
1.2 Statement of the Research Problem 5
1.3 Objectives 6
1.4 Research Flow and Chapter Description 7
2 Materials and Methods 9
2.1 Study Area Description 9
2.1.1 Study site 9
2.1.2 Climate 9
2.1.3 Soil 10
2.1.4 Treatments 10
2.1.5 Field Campaigns and Measurement/Analysis 14
2.2 Methods and Theoretical Considerations 14
2.2.1 Soil Sampling and Analysis 14
2.2.1.1 Calculation of Stratification Ratio 15
2.2.1.2 Calculation of SOC and TN Storage 15
2.2.1.3 Aggregate Size Distribution 16
2.2.2 Infiltration Measurements 16
2.2.3 Soil Moisture Retention Experiments 17
2.2.4 Derivation of Hydraulic Properties from Steady State Infiltration Rates 18
2.2.4.1 Near-Saturated Hydraulic Conductivity 18
2.2.4.2 Flow Weighted Mean Pore Radius 20
2.2.4.3 Equivalent Threshold pore Radius 21
2.2.4.4 Hydraulically Active Porosity 21
2.2.5 Determiation of Soil Moisture Charachtristics and Pore Size Distribution 22
2.2.6 Derivation of Soil Physical Quality Indicators 23
2.3 Statistics 25
3 Results and Discussion 26
3.1 Stratification and Storage of Soil Organic Matter 26
3.1.1 Bulk Density 26
3.1.2 Concenrations of SOC 27
3.1.3 Concentrations of TN 28
3.1.4 C/N Ratio 29
3.1.5 Stratification Ratio of SOC, TN and C/N Ratio 30
3.1.6 Storage of SOC and TN 33
3.1.7 Discussion 34
3.1.8 Summary of Results 39
3.2 Soil Hydro-Physical Properties 40
3.2.1 Soil Physical Properties 40
3.2.2 Near-Saturated Hydraulic Conductivity 43
3.2.3 Soil Pore Characteristics-Conductivity Relationship 47
3.2.4 Hydrailically active Porosity 51
3.2.5 Summary of Results 54
3.3 Soil Physical Quality (SPQ) 56
3.3.1 Soil Moisture Retention Curve (SMRC) 56
3.3.2 Soil Pore Size Distribution (SPSD) 58
3.3.3 Capacitive Indicators 59
3.3.4 Dynamic Indicators 60
3.3.5 Relationship between capacitive indicators of SPQ with dynamic indicators of SPQ and long-term crop yield 60
3.3.6 Relationship between dynamic indicator of SPQ (hydraulically active porosity) and Long-term Crop Yield 62
3.3.7 Summary of Results 64
4 Synthesis and Conclusions 65
5 Implications and Outlook 69
References 71
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:79169 |
| Date | 13 May 2022 |
| Creators | Patra, Sridhar |
| Contributors | Feger, Karl-Heinz, Schwärzel, Kai, Pradhan, Sanatan, Technische Universität Dresden, United Nations University-Institute for Integrated Managment of Material Fluxes and of Resources |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | info:eu-repo/grantAgreement/Indian Council of Agricultural Research New Delhi/Netaji Subhash ICAR- nternational Fellowship/ // / |
Page generated in 0.0137 seconds