The yield and flux of nitrous oxide (N 2 O) emitted from continuous cereals (with and without urea), legumes ⁄ cereal in rotation and cereal ⁄ legume in rotation all with or without organic manure was moni-

The least-cost economic theory of photosynthesis shows that water and nitrogen are mutually substitutable resources to achieve a given carbon gain. However, vegetation in the Sahel has to cope with the dual challenge imposed by drought and nutrient-poor soils.We addressed how variation in leaf nitrogen per area (N area ) modulates leaf oxygen and carbon isotopic composition (δ 18 O, δ 13 C), as proxies of stomatal conductance and water-use efficiency, across 34 Sahelian woody species.Dryland species exhibited diverging leaf δ 18 O and δ 13 C values, indicating large interspecific variation in time-integrated stomatal conductance and water-use efficiency. Structural equation modeling revealed that leaf N area is a pivotal trait linked to multiple water-use traits. Leaf N area was positively linked to both δ 18 O and δ 13 C, suggesting higher carboxylation capacity and tighter stomatal regulation of transpiration in N-rich species, which allows them to achieve higher water-use efficiency and more conservative water use.These adaptations represent a key physiological advantage of N-rich species, such as legumes, that could contribute to their dominance across many dryland regions. This is the first report of a robust mechanistic link between leaf N area and δ 18 O in dryland vegetation that is consistent with core principles of plant physiology.

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L.,

In the Sahel zone, there is an increasing interest of farmers in conserving and enriching tree diversity on their farms as a source of food and income. Ziziphus mauritiana Lam. is one of the tree species farmers maintain on their farms. Even though the local variety of Ziziphus mauritiana Lam. was ranked as one of the most preferred species, it produces small fruit whereas farmers are interested in varieties producing bigger and tasty ones. A factorial experiment in a split split-plot design was carried out to assess the performance of three introduced cultivars of Indian jujube in Burkina Faso. Investigated factors were irrigation (irrigated with 30 l plant À1 week À1 , non-irrigated), rock phosphate containing 25% P 2 O 5 (0 and 150 g P plant À1 ) and cultivar (Gola, Seb, Umran, and local variety as control). Eighteen months after planting, Umran responded positively to irrigation and rock phosphate treatments by displaying the tallest height (313 cm) and the biggest collar diameter (6.4 cm). Gola gave the largest crown diameter (316 cm) at 18 months and the highest fruit production at the first (15.3 kg tree À1 ) and second (71.6 kg tree À1 ) fruiting seasons in the irrigated and fertilized treatment. The local variety was less productive compared to the introduced cultivars. In terms of income generation irrigated and fertilized Gola and irrigated Umran showed the highest potential after two fruiting seasons with net revenues of F CFA 2,526,915 and F CFA 1,930,546 per hectare respectively. Therefore, Umran and Gola may be recommended in intensive subSaharan peri-urban systems while Seb needs further investigation to improve its water and nutrient use efficiency through either better timing of water and fertilizer application or symbiotic association with arbuscular mycorrhizal fungi.

The impacts of fallow on soil fertility, crop production and climate-forcing gas emissions were determined in two contrasting legumes, Gliricidia sepium and Acacia colei, in comparison with traditional unamended fallow and continuous cultivation systems. After 2 years, the amount of foliar material produced did not differ between the two improved fallow species; however, grain yield was significantly elevated by 55% in the first and second cropping season after G. sepium compared with traditional fallow. By contrast, relative to the unamended fallow, a drop in grain yield was observed in the first cropping season after A. colei, followed by no improvement in the second. G. sepium had higher foliar N, K and Mg, while A. colei had lower foliar N but higher lignin and polyphenols. In the third year after fallow improvement, a simulated rainfall experiment was performed on soils to compare efflux of N 2 O and CO 2. Improved fallow effects on soil nutrient composition and microbial activity were demonstrated through elevated N 2 O and CO 2 efflux from soils in G. sepium fallows compared with other treatments. N 2 O emissions were around six times higher from this nitrogen-fixing soil treatment, evolving 69.9 ngN 2 ON g −1 soil h −1 after a simulated rainfall event, compared with only 8.5 and 4.8 ngN 2 ON g −1 soil h −1 from soil under traditional fallow and continuous cultivation, respectively. The findings indicate that selection of improved fallows for short-term fertility enhancement has implications for regional N 2 O emissions for dry land regions.