Das Projekt "Nutrient Use and Dynamics in Conservation Agriculture Including Legumes in the Midwest of the Malagasy Highlands" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Agrarwissenschaften, Pflanzenernährung durchgeführt. 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.