Maintenance and improvement of soil quality is critical to sustaining agricultural productivity and environmental quality. Soil organic carbon (SOC) and Arbuscular Mycorrhizal Fungi (AMF) are among key soil quality and agronomic sustainability indicators. AMF are involved in nutrient transfers and C sequestration, relevant in the global carbon cycle and greenhouse gas abatement. Conventional agriculture adversely affects SOC, AMF and the environment, yet little is known on the impact of alternative options. In this dissertation, I examined the impact some options on selected soil quality indicators in temperate and tropical settings to address some existing research gaps. In Chapter 1, I examined the role of nutrient management and crop diversity on SOC and aggregate stability in a 20 year field study of the Living Field Laboratory (LFL) at KBS-LTER in Michigan. I assessed responses of Integrated Fertilizer and Integrated Compost management on a diversity gradient comprising of monoculture Corn, Corn-soy rotation, Corn-soy-wheat rotation, and Corn-soy-wheat rotation with a cover crop. Management rather than diversity exerted significant influence on SOC and labile carbon (POXC) status across treatments with higher SOC and POXC levels in compost treatments. Crop diversity exerted positive influence on aggregate stability. Diverse rotations had greater aggregate stability than monocultures regardless of nutrient management system. Thus crop diversity can enhance soil structural stability in the long term, and compost management holds promise in ameliorating both poor soil Carbon status and soil structural stability associated with continuous corn monoculture systems. In Chapter 2, I investigated AMF spore diversity using morphological techniques to assess abundance and diversity of AMF in the LFL. Proportions of AMF taxa varied with crop diversity. Surprisingly, nutrient management influenced soil organic matter but not AMF community composition across management systems. In Chapter 3, I report on the influence of land use on soil bio-resources in the tropical landscape of Machinga District in Malawi, a country in Sub-Saharan Africa. I examined communities of AMF in Miombo woodlands and croplands nested within Malosa Forest Reserve. The Shannon- Weiner diversity index (H ́) differed significantly among land use types being higher in agricultural soils than in the natural forest soils reflecting community compositional shifts among communities under study.In Chapter 4, I report on SOC spatial distribution at landscape scale in Machinga district located in sub-Saharan Africa and evaluated SOC prediction accuracy among various interpolation techniques. SOC distribution was greatly influenced by land use type and spatial topographic attributes. Overall, mean SOC content on surface layer soils declined over a period of 2 decades. Ordinary kriging with spherical semivariogram model fitting was found to be the optimal approach for investigating SOC spatial distribution and variability in the complex landscape. The study provides important contributions to the understanding of SOC spatial distribution that can guide land management policy, carbon sequestration and climate change mitigation strategies.
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