How to produce more biomass for direct seeding mulched based cropping system in sub-saharian Africa ? Example in North Cameroun

In North Cameroon, from 2001 to 2006, more than 250 farmers tried direct seeding mulchbased cropping systems (DMC) in their fields. DMC systems were based on farmer traditional rotation i.e. cereal//cotton. Farmers compared on their own field cereals (maize, sorghum, millet) cultivated with conventional techniques and the same cereal conducted with DMC techniques i.e. : i) intercropped with a cover crop (Mucuna pruriens, Brachiaria ruziziensis, Crotalaria retusa, Vigna unguiculata, Dolichos lablab), ii) sowed without ploughing from the first or the second year of experimentation. Associations were made for the following objectives: i) produce aboveground biomass to produce mulch for the following crop (mainly cotton), ii) improve the soil's physical and chemical quality through the contribution of associated plants, iii) produce forage, iv) help to control weed, v) protect the soil surface against erosion and rain impacts, vi) produce grains for human or animals consumption. Each of the 5 cover crops used are different regarding their fulfilments of above objectives and their adaptation to North Cameroon local agro-climatic conditions (rainfall from 700 to 1200 mm). Thus, Brachiaria ruziziensis produces aboveground biomass in quantity (4-5 T of dry matter/ha even when associated with cereal) and quality (persisting of the mulch for over one year after production). Further, it seems to be very efficient in controlling Striga hermonthica and it is a good forage. However, it can impoverish the soil if its biomass is exported several times without any fertiliser or manure input. Crotalaria retusa is a nitrogen fixing legume and thus can improve soil fertility. Furthermore, this plant is non edible for cattle, which is an advantage for farmers who cannot protect their field from grazing during the dry season. C. retusa is also very efficient to fight against other weeds. Six years of experimentation with farmers permits us to produce practical recommendations for intercropping of cereals with cover crops: sowing date, crop type, tolerance to herbicides, limitation of competition with cereals, etc. This experimentation has also allowed us to see what is the behaviour of the 5 cover crops in farmer's conditions. (Résumé d'auteur

Sustainability of conventional agriculture and conservation agriculture in small-scale cotton-based regions in west and central Africa : lessons from northern Cameroon

Sustainability of agricultural practices is a suitable concept to evaluate both agronomic and economic performances of conventional agriculture and conservation agriculture. In this study, the concept of sustainability is analysed through its three main components: economic sustainability also called economic efficiency, dealing with the ability of the farming system to ensure sufficient and competitive output production to fulfil market and population needs; social sustainability or social equity, dealing with agricultural ability to ensure equitable revenue or return to different stakeholders of the agricultural production chain; ecological sustainability, dealing with intergenerational preservation of the environment referring here to the sum of natural resources used to ensure agricultural production such as soil fertility. Ecological sustainability is commonly the only aspect of sustainability taken into account by agronomists. Sustainability of conventional agriculture is addressed in this study in small-scale cottonbased agriculture surveys in northern Cameroon. Economic efficiency of cotton in conventional agriculture is analysed through a multi-year data base of a permanent agricultural survey of SODECOTON (Cotton Development Company), while social equity is addressed based on different production cost distribution within cotton production stakeholders. Ecological sustainability is analysed through agronomic variables such as yield variation over time, and mainly soil fertility evolution. Results of the study revealed that economic efficiency of cotton cultivation in conventional agriculture, after attaining acceptable levels in the early 1990's mainly due to high yields and prices and low inputs cost, is now declining. Fertiliser prices for example varied from 500 US $per ton in 2005 to more than 1000 US$ per ton in 2008. Social equity even if strongly reinforced by an equalizing prices approach and inputs cost determination system, is limited with a high ecological differentiation between ecological areas varying from 600 mm rainfall in the far north to 1200 mm rainfall in the south of the cotton belt, hence affecting different respective yields. As for soil fertility, decreasing yields and increasing expenditures on fertilisers and other water harvesting and soil conservation technologies revealed progressive weak response of soil resource to cropping systems management. Conservation agriculture appears to be a suitable alternative to conventional production systems for small-scale cotton based agriculture to attain the three main objectives of a sustainable agriculture, since it can ensure economic efficiency of the farming system, a better social equity and a better soil resource management. (Résumé d'auteur