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The large scale conversion of extensive swidden agriculture to intensive market oriented production of maize in upland areas of South East Asia is a cause of environmental concern. This study investigates how intensive maize cultivation affects soil quality in an upland area of Northern Thailand by comparing commonly used indicators of soil quality in soils from maize fields used at various intensities. Relations between these indicators and concentration of permanganate oxidizable carbon (Pox-C) – a low cost proxy for soil quality – are also examined. The extent, type and drivers of land use changes between 2002 and 2012 are investigated by classification of high resolution satellite images, interviews, participatory mapping and questionnaires. We document a widespread change from traditional swidden agriculture to intensive cultivation of maize that is mainly brought about by economcic and political drivers. We show that the concentration of Pox-C in the top soil of the maize fields is closely related to common indicators of soil quality and to farmers' perceptions of soil quality. Most of the other soil quality indicators are negatively – albeit not significantly – related to intensity of maize cultivation. There is a strong negative correlation between intensity of maize cultivation and concentration of Pox-C in the upper 5 cm of the soil where the Pox-C concentration declines with a rate of 40 mg year under maize−1. We conclude that Pox-C is a sensitive indicator of effects of land use intensity on the soil and a useful integrative measure of soil quality. Copyright © 2016 John Wiley & Sons, Ltd.

A considerable growth in the maize (Zea mays L.) sector in Southeast Asia has resulted in a rapid expansion and intensification of maize monoculture on sloping uplands. This practice entailed the heavy use of fertilisers, leading to environmental degradation and farmers' indebtedness. Intercropping of legumes with maize could complement or replace fertiliser inputs; however legume adoption by smallholder maize farmers remains low. This study investigates the constraints and potentials to integrate legumes in maize-based cropping systems in such environments. A comparative study between maize monocropping and maize/legume relay cropping was carried out in two villages of Thailand, using surveys, participatory rural appraisal (PRA) tools and interviews. The results demonstrated that both cropping systems were equally profitable, although the maize yield in maize/legume relay cropping was lower than that in monocropping. Low selling price was the most cited reason by the non-adopters for not introducing legumes. Selling price of legume grains, ease of harvesting, marketability and ease of growing were the four main criteria that determined the adopters' choice of legume species. Among the cultivated legumes, ricebean (Vigna umbellata L.) best fulfilled the criteria for the choice of legume species. Establishing maize/legume relay cropping as an alternative to maize monocropping under rainfed conditions can decrease risks, due to reduced expenses for farm inputs and similar economic returns. This study generated useful information for agricultural policy makers and development practitioners in identifying the barriers and facilitating factors that influence farmers' decision to adopt legumes and the conditions that shape the farmers' decision-making environment. Copyright © 2016 John Wiley & Sons, Ltd.

State-of-the-art predictive models of soil organic carbon (SOC) dynamics associated with land use changes are unable to reflect the diversity of tropical soil types as the knowledge of contrasting site-specific factors in mediating the response of the SOC pool is sparse. This paper examines the influence of soil type and management on SOC dynamics following the conversion of forests to annual cropping in Ghana. Soil from primary forests and from areas with short (2–7 years) and long (20 years) histories of maize cultivation was sampled from a Vertisol dominated by smectite and Ultisol dominated by kaolinite. Wet sieving was used to separate soil fractions below and above 250 µm. SOC concentrations and δ13C signatures of SOC in soil fractions and bulk soil were determined. SOC stocks were calculated by the commonly used fixed depth approach and by the equivalent soil mass approach. After 20 years of cultivation of the Vertisol, the total SOC content was 40 per cent lower than under forest, and about 95 per cent of the forest-derived SOC had been lost. After 20 years of cultivation of the Ultisol, total SOC content was only about 20 per cent lower than under forest and merely 30 per cent of the forest-derived SOC had been lost. Both soil types were managed as they would typically be in small scale farming systems, thus the higher SOC losses and the substantial loss of forest-derived SOC from the Vertisol question the conventional concept of smectite having a higher SOC-stabilizing potential than kaolinite under field conditions. Copyright © 2013 John Wiley & Sons, Ltd.