Conservation Agriculture (CA) was introduced at the lake Alaotra, in Madagascar, in a context of yield drop and silting-up of rice fields in the low lands. Land tenure pressure linked to the attractiveness of the area leads to the colonization of surrounding uplands, very sensitive to erosion. Conservation agriculture deals with a double constraint: i) increase household income ii) preserve natural resources. This study assesses the economic impact of CA systems on the income of modelised representative farm holdings for each area, through a prospective analysis in the midterm, 10 years. The processing of the databases from the diffusion operators has highlighted a light increase of yield according to the age of CA systems. These systems also have a buffering effect on climate hazards. Parts of CA systems diffuse spontaneously within farming systems. Surveyed cropping systems have been deeply modified by the effect of BV-Lac project; the smallholder’s population at the lake has innovative practices. Modeling has highlighted that CA systems improve significantly net farm income at plot scale in the midterm. The results are not as clear at farm scale. Indeed, the higher the farl income generated by irrigated or PWC rice fields is, the lower is the impact of CA systems on farm income. For farm holdings with few irrigated rice fields, CA systems insure the income by stabilizing and improving yields of rain fed crops.

Soil erosion of productive top soils is an obstacle for achieving an increased food production in a more sustainable way. The three principles of Conservation Agriculture (CA) of no tillage, permanent soil cover and crop rotations, are often seen as a promising solution. This study was undertaken within the framework of the CA2AFRICA project which aims at understanding the physical effects of CA and the reasons of its (non)adoption in Africa. A field level modeling approach was chosen to assess the effect of three types of CA cropping systems on soil loss, compared to a traditional cropping system for the region of Lake Alaotra in central Madagascar, using the Revised Universal Soil Loss Equation (RUSLE). The most accurate method for estimating erosivity R was based on daily effective rainfall data, resulting in a value of 8487 (SI units). For erodibility K, the average of five estimation methods was taken, resulting in a value of 0.038 (SI units). Three slope scenario’s were chosen, with LS values ranging from 0.6 to 4. Together, these factors form a potential erosion of about 484 ton·ha-1yr-1. The crop cover C was divided into a crop component estimated with percentage of canopy cover, and a mulch component estimated with the Mulch Factor. C-values were determined at half month time intervals for four cropping systems: 1) ‘Traditional’, a two year rotation of upland rice and maize with an average C of 0.56; 2) ‘Stylo 1’, a three year rotation including Stylosanthes guianensi at test field yielding an average C of 0.04; ‘Stylo 2’ as Stylo 1, but for situation at farmers’ fields, yielding an average C of 0.14 and 3) ‘Dolichos’, a two year rotation including Dolichos lablab with an average C of 0.13. Support practice values P were set at 0.4 and 0.1 for respectively the traditional and the CA cropping systems. Resulting annual soil loss (ton·ha-1yr-1) was about 87 for ‘Traditional’, 2 for ‘Stylo 1’, 5.5 for ‘Stylo 2’ and 9 ton·ha-1yr-1 for ‘Dolichos. Although validation with a Unit Plot is necessary, the estimated parameters give an indication of the effect of CA on soil loss and allow for future scaling up of soil loss quantification.

Madagascar, la Grande Île, is a place on earth with some most peculiar natural features. The current degraded status of its soils is unfortunately less unique. The vulnerable environment suffers from the increasing pressure of the growing population. Cropping on slopes causes erosion. Soil fertility is low, and soil nutrient inputs are needed. The concept of Conservation Agriculture (CA) has been introduced as the way to fight worldwide soil degradation and change soil mining agriculture into a more sustainable system. At this time, the concept is used on 6-7% of the world’s cropland (FAO, 2009). The adoption rate among African smallholders has been very limited. This is the starting point for the EU-project CA2AFRICA. It aims at examining the conditions that determine success or failure of CA (CA2AFRICA, 2009). The project uses three scales to analyze CA: field, farm/village and regional. This research is focused on the scale of farm and village.This research focuses on the highlands in the region of Vakinankaratra. NGO’s and scientists have undertaken activities to introduce CA, but so far the practices have not been implemented on a large scale in the highlands. The research has been carried out from June to September 2010.

The Lake Alaotra basin, surounded by high hills, is one of Madagascar’s primary rice producing regions, with over 100,000 hectares of rice fields. The region, is known as the "Malagasy rice granary". It produces an annual surplus of rice, and plays an important role in inter-regional trade, serving as a critical supplier of rice for the country’s capital Antananarivo, and largest port city, Tamatave. Rice production of the Alaotra was greatly enhanced through the hydro-agricultural schemes managed by SOMALAC (Société Malgache d'Aménagement du Lac Alaotra) in the 1960s and 1970s (Devèze, 2007). For 40 years, the demographics of the region have been marked by the high rates of immigration of farming families attracted to the wealth of the region. High population growth,has tripled the population since 1960 (and is doubling it every 18 years) leading to land tenure saturation and an increasing pressure on natural resources (Durand et Nave, 2007). Land tenure is saturated in low land areas (Irrigated Paddy Fields (IPF), Poor Water Control Paddy Fields (PWCPF) and baiboho). Therefore, when seeking new land for cultivation, farmers tend to expand onto uplands, the tanety (hills), previously under- developed or reserved for grazing herds (Domas et al., 2009). Deforestation, repeated burning, and the exclusion of fallow periods have accelerated natural erosion processes in these degraded and fragile soils,, resulting in an alarming loss of soil fertility, siltation of downstream irrigation canals, and declining yields to fisheries. Today, on 30, 000 hectares of rice fields developed by the SOMALAC, between 10,000 and 15,000 hectares are currently under good water control (Durand and Nave, 2007). In the context of increasing degradation of natural resources, research and development programs (both Malagasy national and French) have set up projects for the extension of agro- ecological techniques, based on the principles of conservation agriculture (CA). Direct mulch cropping (DMC) is one of these techniques, introduced in the Lake Alaotra region in the 1990’s, with the objective of introducing new cropping systems to improve yields while preserving natural resources. Having encountered many problems (constrained access to inputs, technical complexity that is overwhelming for small farms), the adoption of CA grew significantly since 2000 with the launch of the project “Mise en valeur et protection des Bassins Versants du Lac Alaotra » (BVLac). The project, started in 2003 and was conducted in two phases over a period of five years each, from technical advisory at the field scale, to a holistic approach at the farm scale