Martin Yemefack

Soil Atlas of Africa

of water, nutrients and as a medium for growing. Soil stores, filters, buffers and transforms substances that are introduced into the environment. This capability is crucial in producing and protecting water supplies and for regulating greenhouse gases. Soil is a provider of raw materials. Soil is also an incredible habitat and gene pool. Soil is a fundamental component of our landscape and cultural heritage. The properties of soil vary tremendously from region to region. Soils under tropical rainforests are vulnerable to erosion and nutrient depletion if the vegetation cover is removed. Oasis regions in deserts and the Sahel show how seemingly infertile soils can be cultivated in the presence of water. The wetlands of Congo and other major African systems are stores of soil organic carbon and important wildlife habitats. The black, clay-rich soils of the Nile Valley in Sudan are rich in nutrients but difficult to cultivate when very wet or very dry. Soils with high salt levels are not suitable for the cultivation of crops but may support a unique plant community. AFRICA SOIL ATLAS OF

Phylogeny and nitrogen fixation potential of Bradyrhizobium species isolated from the legume cover crop Pueraria phaseoloides (Roxb.) Benth. in Eastern Cameroon

Abstract Pueraria is an herbaceous, perennial legume crop originating in Asia. Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) is frequently introduced into production systems and is used as green manure, a cover crop and a forage plant, making it important economically. We used P. phaseoloides as a trap crop to study and characterize soil rhizobia in Eastern Cameroon. Bacteria were isolated from fresh nodules collected from field-grown P. phaseoloides roots. The 16S-23S rRNA internal transcribed spacer (ITS) sequences from 30 bacterial isolates were amplified by polymerase chain reaction (PCR) and the reaction products were sequenced. Phylogenetic analysis revealed that all isolates were ascribed to the genus Bradyrhizobium and were grouped into three clusters of Bradyrhizobium sp. strains, one cluster of B. yuanmingense strains, and one cluster of B. elkanii strains. Acetylene reduction assay (ARA) results indicated that the B. yuanmingense strains had significantly higher nitrogen fixation potential and that they could be used as inoculants to enhance nitrogen fixation in Pueraria grown in Eastern Cameroon.

Soil legacy data rescue via GlobalSoilMap and other international and national initiatives

Legacy soil data have been produced over 70 years in nearly all countries of the world. Unfortunately, data, information and knowledge are still currently fragmented and at risk of getting lost if they remain in a paper format. To process this legacy data into consistent, spatially explicit and continuous global soil information, data are being rescued and compiled into databases. Thousands of soil survey reports and maps have been scanned and made available online. The soil profile data reported by these data sources have been captured and compiled into databases. The total number of soil profiles rescued in the selected countries is about 800,000. Currently, data for 117, 000 profiles are compiled and harmonized according to GlobalSoilMap specifications in a world level database (WoSIS). The results presented at the country level are likely to be an underestimate. The majority of soil data is still not rescued and this effort should be pursued. The data have been used to produce soil property maps. We discuss the pro and cons of top-down and bottom-up approaches to produce such maps and we stress their complementarity. We give examples of success stories. The first global soil property maps using rescued data were produced by a top-down approach and were released at a limited resolution of 1km in 2014, followed by an update at a resolution of 250m in 2017. By the end of 2020, we aim to deliver the first worldwide product that fully meets the GlobalSoilMap specifications.

Evaluation of sustainability of mixed food crop fields by monitoring particulate organic matter (POM) status and nutrient concentrations

Particulate organic matter (POM) status is a useful indicator to assess labile soil organic matter (SOM) and to evaluate soil fertility under different agricultural systems, mainly in low-input agriculture as practiced in most of the sub-Saharan region of Africa. Total POM (53–4000 µm), different sized POM fraction characteristics (mass, C and N contents), and nutrient concentrations of soils were evaluated under 2 mixed food crop field types: a preceding forest fallow (forest) and a preceding fallow dominated by Chromolaena odorata (King & Robinson) (Chromolaena spp.) in the 0–0.10 m horizon of Rhodic Kandiudult, Typic Kandiudult, and Typic Kandiudox soils. The mass and C and N contents of total POM were higher in the Typic Kandiudox than in the Typic Kandiudult, while the Rhodic Kandiudult was intermediate. The pH was lower in the Typic Kandiudox (4.67). Forest had higher pH, Ca2+ and Mg2+ concentrations, and effective cation exchange capacity, while Chromolaena had higher C content in medium (2000–250 µm) and fine (250–53 µm) POM fractions and higher N content in coarse POM (4000–2000 µm). Considering nutrient concentrations, forest appears to be more suitable for a mixed-crop field-crop system than Chromolaena; however, the opposite was found when considering POM status.