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Solid Earth An interactive open-access journal of the European Geosciences Union

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doi:10.5194/se-2016-175
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
10 Jan 2017
Review status
A revision of this discussion paper is under review for the journal Solid Earth (SE).
Development of a composite soil degradation assessment index for cocoa agroforests under tropical conditions of southwest Nigeria
Sunday Adenrele Adeniyi1,2, Willem Petrus de Clercq3, and Adriaan van Niekerk1,4 1Department of Geography and Environmental Studies, Stellenbosch University, South Africa
2Department of Geography, Osun State University, Nigeria
3Department of Soil Science, Stellenbosch University, South Africa
4School of Plant Biology, University of Western Australia, Australia
Abstract. Cocoa agroforestry is a major landuse type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroforests of southwest Nigeria. Plots where natural forests have been converted to cocoa plantations of ages 1–10 years, 11–40 years and 41–80 years, respectively representing young cocoa plantations (YCP), mature cocoa plantations (MCP) and senescent cocoa plantations (SCP) were identified to represent the biological cycle of the cocoa tree. Soil samples were collected at a depth of 0–20 cm in each plot and analysed in terms of their physical, chemical and biological properties. Factor analysis of soil data revealed four major interacting soil degradation processes, decline in soil nutrient, loss of soil organic matter, increase in soil acidity and the breakdown of soil textural characteristics over time. These processes were represented by eight soil properties (extractable zinc, silt, SOM, CEC, available phosphorus, total porosity, pH, and clay). These soil properties were subjected to forward stepwise discriminant analysis (STEPDA), and the result showed that four soil properties (extractable zinc; cation exchange capacity; soil organic matter and clay) have the highest power to separate the studied soils into YCP, MCP and SCP. In this way, we hope to have controlled sufficiently for redundancy in the final selection of soil degradation indicators. Based on these four soil parameters, CSDI was developed and used to classify selected cocoa soils into three (3) different classes of degradation. The results revealed that 65 % of the selected cocoa farms are moderately degraded, while 18 % have a high degradation status. Finally, the value of the CSDI as an objective index of soil degradation under cocoa agroforests was statistically validated.

Citation: Adeniyi, S. A., de Clercq, W. P., and van Niekerk, A.: Development of a composite soil degradation assessment index for cocoa agroforests under tropical conditions of southwest Nigeria, Solid Earth Discuss., doi:10.5194/se-2016-175, in review, 2017.
Sunday Adenrele Adeniyi et al.
Sunday Adenrele Adeniyi et al.
Sunday Adenrele Adeniyi et al.

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