East Africa remains one of the most severely affected regions impacted by food insecurity with an increasing number of undernourished people (NEPAD 2013). The sustainable management of agricultural land and water resources is recognized as essential to achieve global food security. Almost 70% of the population of East Africa rely on agriculture (NEPAD 2013), and land degradation combined with declines in soil fertility constitutes a major barrier resulting in poverty and decreases in per-capita food production especially in Ethiopia (Zeleke et al. 2010; Agegnehu et al. 2014). Limited irrigation water resources and the deficiency of irrigation infrastructures have also, until now limited yield production, especially in smallholder farming systems experiencing climatic stress (Barron et al. 2015). Therefore, analyzing soil and water conservation issues should be considered and prioritized in the different countries of East Africa.

The intensification of maize cultivation, mainly for rural consumption and cities supply, is an opportunity to improve food security in the Northern regions of Cameroon, and to face land constraints. To study its feasibility, three levels of intensification have been tested in 2013 in 32 maize fields near Garoua in the Northen Region, of which 16 considered fertile by farmers, and 16 as degraded: (i) the conduct by the producer (CP), (ii) a first level of intensification (NI1) corresponding to the currently recommended agricultural specifications, and (iii) a second level of intensification (NI2), which compared to NI1 benefited of a strengthening in fertilization, improved seed treatment, better density and weeds control. CP and NI1 have close yields in both villages: an average of 2.3 and 1.3 t. ha(-1), respectively on fertile and degraded fields, proving that producers follow pretty much the broadcast technical specifications. Yields on plots under NI2 are significantly superior to others, on average of 1 t. ha(-1) at the Ngong site where rainfall is lower, and 1.5 t. ha(-1) at the Gashiga site. Curiously, the yield gain provided by NI2 is identical on fertile plots as on degraded ones, indicating that the degradation of the recent years, demonstrated by their lower production, nevertheless allows a response to increased intensification. Despite these results, the profitability of an increased intensification at the current price of corn, especially the one at the harvest time, is not established. A better price would allow the profitability of an increased intensification and production of corn in these areas as already partially practiced by some emerging farms, as they are named, which have more control over the marketing of their products.

Soils degradation is the factor that most affects the profitability of crop management on maize cultivation in Northern Cameroon and reduces the interest of their intensification. It is also affected by severe weather conditions but mainly by low valuation of agricultural products. Maize cultivation intensification is only possible with the help of a seasonal credit system to acquire inputs. The use of casual hired labor and an increase in the purchase price of corn are other conditions that will favor its implementation. (Resume d'auteur)

In northern Cameroon the adoption of the Direct seeding Mulch-based Cropping system (DMC) is limited by the sharing of forage crop residues during the dry season between livestock and soil cover. Increasing forage production is therefore required as well as taking the various types of livestock production systems into consideration (sedentary, transhumant, etc.). In the current conditions (poor ground cover, few successive years of DMC), the expected effects of DMC systems are uncertain. However, if the outcome of the extension of the DMC is very limited in this region, it has led to the emergence of farmers' innovations such as forage crops, or regulation of common grazing land, have been observed in some localities. In this context, the design and extension of innovative systems (DMC, forage crops) should involve joint work on the technical and organizational components of innovation, particularly support to rural populations in the definition of management plans and development of village territories.

The global context expects increased food production in the agricultural sector thereby substituting benefits in the petroleum sector and related services i.e. the conservation of biodiversity or carbon sequestration. These objectives are intended to be achieved under the constraint of expected climate change. Progress is particularly hoped for African agriculture, which by its low-intensity practices and low current yields is faced with a substantial margin of progression. The study conducted in two villages (Gashiga and Kawtal) in northern Cameroon during the 2013 farming season aimed to understand the feasibility of maize intensification in the current physical, climatic and economic conditions. Gashiga experienced sporadic rainfall during the 2013 farming season contrary to better rainfall conditions at Kawtal. Two levels of intensification were compared to the peasant practices (NP) consisting of 36 plots of producers with contrasting soil fertility levels, two repetitions conducted per plot. The first level (N1) corresponds to the specifications of the crop currently disseminated. The second level (N2) comprised of more intensive techniques (variety, seed treatments, organo-mineral fertilization and fight against weeds). The test cluster analysis showed increased production for N1 and N2 against NP (respectively 0.8 and 1.9 t.ha-1) of maize grain at Kawtal. Yields for NP and N1 were equivalent at Gashiga and N2 experienced an increase of 1.5 t.ha-1 of maize grain Soil fertility impacted just NP. Factors such as crop density and weed pressure limited the result of intensification. Despite the increased production achieved, both levels of intensification were not profitable. More than climate, economic conditions are a major constraint for crop intensification in North Cameroon. (Resume d'auteur)

Soil respiration is a major component of the global carbon cycle which links ecosystems and the atmosphere. To evaluate the reaction of soil respiration after wetting, during a dry period, soil respiration and associated environmental factors were measured over a 24-h period, during the dry season in North Cameroon after wetting the soil. Over 24-h, soil respiration rates followed a quadratic curve during the day coming close to linear at night, while soil temperature and moisture together explained at least 73 % of the variations during the 24-h observed. These soil respiration rates increased during the morning, peaked between 11h00 and 13h00 and then decreased gradually to the minimum around 06h00. These observations were used to propose a method for estimating mean daytime and nighttime soil respiration after wetting the soil. The method proposed in this study has the advantage of being based on a small number of measurements and is, therefore, easier to implement for monitoring 24-h soil respiration after the first rains following a long dry period.

Chemical weed control and weed management in cotton in north Cameroon. The aim of this study, which was conducted between 2005 and 2007, was to analyse the weed control practices used by farmers in two regions of north Cameroon (Mafa Kilda and Mowo) and to test the different techniques of weed management. The survey included 39 and 49 farms in Mafa Kilda and Mowo, respectively. Experimental blocks were set up across five farms. Four treatments were tested, one with soil tillage and the three others with no tillage (direct sowing) with the application of non-selective and selective herbicides, followed by early weeding. Results show that hand weeding remains widespread, despite the increase in draught cultivation and the adoption of herbicides. The direct sowing treatments plus herbicides help improve weed management at the start of the growing season. The yields observed are significantly higher with these treatments. The advantage of herbicide use is that it saves labour (3 h/ha per application) compared to tillage (14 h/ha). The double application of low rates of glyphosate and paraquat, followed by early mechanical tillage (15-20 days after sowing) seems to be the best technical protocol for integrated weed control.

A study based on survey among farmers and on farm observations was conducted in four selected villages of Northern Cameroon in order to understand how farmers assess the fertility of their land, i.e., the capacity of farm land to produce crops. The result shows that the farmers use four groups of criteria in order to determine the fertility level of the soil: i) the weeds present-, ii) the biophysical state of the soil, which includes the macro fauna present, the texture and the colour of the soil; iii) the productivity of labour; and iv) the productivity of the land, variable from crop to crop on the same land. Once they have collected all this information for a given land, the farmers are able to assess its fertility level and on that basis choose the crops most likely to yield the best results.

A study based on survey among farmers and on farm observations was conducted in four selected villages of Northern Cameroon in order to understand how farmers assess the fertility of their land, i.e., the capacity of farm land to produce crops. The result shows that the farmers use four groups of criteria in order to determine the fertility level of the soil: i) the weeds present; ii) the biophysical state of the soil, which includes the macro fauna present, the texture and the colour of the soil; iii) the productivity of labour; and iv) the productivity of the land, variable from crop to crop on the same land. Once they have collected all this information for a given land, the farmers are able to assess its fertility level and on that basis choose the crops most likely to yield the best results.

Soil Fertility Characterization Based on Present Weed Specie. In order to determine the soil fertility level using weed indicators, a study was conducted in 4 villages in northern Cameroon. It was based on farmers' interviews and fi eld surveys. It appears that the soil fertility status can be determined by using two groups of weeds: "guide" weeds, orienting the diagnosis according to their relative importance; "indicator" weeds, used to discriminate the two soil types (fertile/ degraded). Presence or absence of the identifi ed species allows farmers to determine whether the plot is fertile or degraded. He can then decide to use the fi eld or not.

Résumé — En vu de déterminer le niveau de fertilité des sols à partir d'indicateurs végétaux, une étude a été menée dans quatre terroirs du Nord-Cameroun. L'étude s'est basée sur une enquête menée auprès des paysans et des observations réalisées sur les parcelles. Il apparaît que le niveau de fertilité d'un sol peut s'évaluer par l'identification de deux groupes d'adventices : les herbes guides, non discriminantes mais dont l'importance oriente le diagnostic ; et les herbes indicatrices, dont la présence ou l'absence est discriminante. La présence ou l'absence de ces espèces, permet au paysan de déterminer si les parcelles sont fertiles ou à l'inverse dégradées. A partir de là, il décide d'exploiter ou non le champ. Abstract — Soil fertility characterization based on present weed species. In order to determine the soil fertility level using weed indicators, a study was conducted in 4 villages in Northern Cameroon. It was based on farmers' interviews and field surveys. It appears that the soil fertility status can be determined by using two groups of weeds: "guide" weeds, orienting the diagnosis according to their relative importance; "indicator" weeds, used to discriminate the two soil types (fertile/degraded). Presence or absence of the identified species allows farmers to determine whether the plot is fertile or degraded. He can then decide to use the field or not.