Interactive effects of climate and land-use on soil organic carbon, nitrogen, and phosphorous pools in tropical Africa (Zambia, Mozambique)

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Tropical soils contain about 26-30% of global soil organic carbon (SOC) and associated nutrients, of which large parts are usually lost when native open or woody savannah are converted to agricultural fields. We hypothesize that the degree of these losses depends on both climate and management. To test this hypothesis, we will determine SOC, N- and P pools in top- and subsoils of a climosequence (300 to > 1000 mm annual precipitation) under three different land use systems (i) native savannah rangeland ecosystems, preferably in conservation areas, ii) degraded arable lands (arable field, intensively managed for at least 50 years), and iii) adjacent arable lands under traditional farming practice in two tropical countries: Zambia and Mozambique. Soil will be sampled in different depths (0-10, 10-20, 20-30, 30-50cm). Basic soil and nutrient analyses will be measured by the partner universities. In Bonn, we will assess total C, N, and P stocks as well as their distribution into particle-size (< 2 µm, 2-20 µm, 20-250 µm, and > 250 µm) and aggregate fractions (microaggregates < 250 µm; macroaggregates > 250 µm). In addition, we will assess labile to stable P-pools according to the Hedley fractionation scheme, and investigate the origin of C, N and P by biomarker (amino sugars) and 31-P-NMR analyses at selected samples. To elucidate potential effects of temperature rise on the fate of SOC and organically bound N and P, topsoil samples are incubated using the RESPICOND VIII system in the dark, allowing monitoring CO2 release at different temperatures as well as effects of N and P additions. It is a unique trilateral collaboration between Zambia, Mozambique and Germany, that allows method and sample exchange as well as knowledge transfer between the participating countries. A long-term collaboration will be established through the employment of two PhD candidates that already have leading scientific positions at their home scientific institutes.