Design, implementation, and evaluation of sustainable soil rehabilitation in degraded agricultural lands

Thesis Abstract

Soil degradation from erosion, compaction, and organic matter decline threatens agricultural productivity and food security in semi-arid cropping systems; despite numerous remediation attempts, there is limited evidence on integrated, scalable rehabilitation approaches that combine soil physical restoration, organic matter replenishment, and agroecosystem resilience under real-world constraints. The study aims to design, implement, and evaluate a sustainable soil rehabilitation package for degraded agricultural lands, with specific objectives to (i) quantify baseline soil health and productivity indicators, (ii) implement an integrated intervention comprising targeted mulching, cover crops, reduced tillage, and biochar amendments, (iii) monitor short- and medium-term soil physical, chemical, and biological responses over two growing seasons, (iv) evaluate crop yield, water use efficiency, and ecosystem services, and (v) develop a scalable guideline for policy and practice. Guided by the Sustainable Livelihoods and Soil Health theories, the research adopts a mixed-methods multi-site design to capture biophysical and socio-economic dimensions of rehabilitation. The methodology employs a quasi-experimental design across three degraded fields in the Central Plateau region, with a total experimental area of 15 hectares. A purposive sampling approach identifies fields exhibiting similar baseline degradation indices. Within each field, a randomized block design assigns four treatments (1) conventional management (control), (2) mulching plus cover crops, (3) reduced tillage with compost amendments, and (4) integrated system with mulching, cover crops, reduced tillage, and biochar at 6 t ha-1. The population comprises soil profiles and cropping systems under smallholder-intensive agro-ecosystems. Data collection instruments include standardized soil sampling protocols for bulk density, infiltration rate, soil organic carbon, aggregate stability, pH, cation exchange capacity, microbial biomass carbon, and enzyme activities; crop yield records; water use efficiency metrics; and farmer adoption surveys. Instrument validity is ensured through pilot testing and calibration with independent laboratory analyses. Reliability is guarded by duplicate soil cores per plot and inter-analyst replication for laboratory assays. Data analysis follows a sequential explanatory design. Descriptive statistics summarize baseline and post-implementation soil and yield indicators. Analysis of covariance (ANCOVA) tests treatment effects on soil health indicators and yields, controlling for initial conditions. Repeated-measures ANOVA assesses temporal changes across seasons. Multivariate regression models identify relationships between soil health improvements and crop productivity, while structural equation modeling evaluates mediating pathways among soil physical recovery, organic matter dynamics, and yield outcomes. Thematic analysis of semi-structured interviews with farmers elucidates adoption barriers and enabling factors; triangulation integrates quantitative and qualitative findings. A soil health index is computed using principal component analysis to synthesize key indicators into a single policy-relevant metric. Ethical considerations include informed consent, data privacy, and environmental risk assessment. Expected findings indicate that the integrated rehabilitation package will significantly improve soil physical properties (bulk density reduction by ~0.15 g cm-3, infiltration rate increase by ~40%), soil chemical status (organic carbon increase by 1.5–2.3 g kg-1, pH stabilization within the optimal range for the dominant crops), and biological activity (increased microbial biomass carbon and enzyme activities by 20–35%). These biophysical gains are anticipated to translate into higher crop yields (15–25% lift in maize and legume components) and improved water use efficiency (15–20% reduction in irrigation water per unit yield). The study also expects enhanced soil resilience indicators, such as greater aggregate stability and reduced erosional losses, under the integrated system. Contributions to knowledge include (i) empirical evidence on the effectiveness and scalability of an integrated soil rehabilitation framework in degraded agricultural landscapes, (ii) quantification of synergies between organic amendments, reduced tillage, and biological inputs on soil health and productivity, and (iii) a context-specific guideline for policy-makers and extension services on implementing sustainable rehabilitation at scale. The main conclusion is that a holistic, farmer-centered rehabilitation package can induce substantive and sustained improvements in soil health and productivity, even under resource constraints. Recommendations emphasize staged adoption, farmer training modules, access to biochar and compost inputs, and integration with watershed management plans to maximize long-term sustainability and resilience of degraded agricultural lands.