Soil degradation in tropical agro-ecosystems results in increased food insecurity and in environmental degradation. Conservation agriculture has been proposed to sustainably improve agricultural production in the tropics. This approach combines direct-seeding, permanent mulch cover and a diverse crop rotation. It is being adopted by smallholders of the Midwest in Madagascar to control soil erosion, Striga spp. weeds on cereals and to provide forage for cattle. Little work has been done up to now on nitrogen (N) and phosphate (P) dynamics and their interaction in conservation agriculture as practiced by smallholders in the tropics. Nutrient limitations in these systems indeed might be one of the barriers hindering the adoption of conservation agriculture by smallholders. This project, developed in partnership between the Group of Plant Nutrition of the ETH Zurich, the Laboratory of Radio-Isotopes (LRI) of the University of Antananarivo and the International Research Unit on Sustainable Farming and Rice Cropping Systems (SCRID), aims at understanding how conservation agriculture affects the fluxes and dynamics of N and P in the presence of legumes, and at identifying with farmers strategies that will allow using these resources in the most sustainable way. This information will contribute to the development of tools to evaluate the relevance of conservation agriculture for smallholders. The project will be organized in 4 work packages (WP1-4). In WP1, we will conduct on-farm studies in reference areas of the Midwest where conservation agriculture has been adopted. A survey will evaluate the benefits and constraints to adopt conservation agriculture and locating adoption barriers. We will assess crop performance and nutrient budgets in farmers' fields under conservation and conventional agriculture. In WP2, we will work in a field experiment to disentangle the effect of direct sowing from that of intercropping with the legume Stylosanthes guianensis (thereafter stylo) on maize and rice yields, root growth, and N and P dynamics. In this experiment, we will measure N2 fixation by stylo and N use by rice from different sources. In WP3, we will study the uptake of P derived from different sources by stylo, Cajanus cajan and upland rice and the effect of legume residue application on the dynamics of microbial and organic P in soils. In WP4, we will evaluate the validity and relevance of the results beyond the reference areas studied in WP1. This will be done through an undergraduate students' work in the Midwest and by workshops with stakeholders in the Midwest and in two other ecological zones of Madagascar.
We provide version 1.0 of an open access database created as part of the project “Tropical soil organic carbon dynamics along erosional disturbance gradients in relation to variability in soil geochemistry and land use” (TropSOC). TropSOC v1.0 contains spatial and temporal explicit data on soil, vegetation, environmental properties and land management collected from 136 pristine tropical forest and cropland plots between 2017 and 2020 as part of several monitoring and sampling campaigns in the Eastern Congo Basin and the East African Rift Valley System. The results of several laboratory experiments focussing on soil microbial activity, C cycling and C stabilization in soils complement the dataset to deliver one of the first landscape scale datasets to study the linkages and feedbacks between geology, geomorphology and pedogensis as controls on biogeochemical cycles in a variety of natural and managed systems in the African Tropics.
Sampling procedures are described in each metadata description .pdf file accompanying a specific .csv file that represents a methodologically distinct subset of the database. A general overview of field sampling procedures and design is given in Doetterl et al., (2021, ESSD in review) which describes the dataset as a whole. Analytical procedures are described in each metadata description .pdf file accompanying a specific .csv file that represents a methodologically distinct subset of the database. Data processing and quality control are described in each metadata description .pdf file accompanying a specific .csv file that represents a methodologically distinct subset of the database.