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In Africa, cocoa yields are low, partly due to soil fertility constraints and poor management. While peoples’ knowledge, aspirations, and abilities are key factors explaining their behaviour, little is known about the rationales that underpin soil fertility management practices (SFMPs) of cocoa farmers. To address this gap, we conducted an exploratory survey in two contrasting regions in Cameroon where cocoa is an important crop: the humid forest and the forest-savannah transition zone. Some 30% of farmers in the transition zone as opposed to 13% in the humid forest expressed concerns about soil fertility. The most relevant soil fertility indicators for farmers were high cocoa yield, dark soil colour, ease of tillage, and floral composition. To enhance and maintain soil fertility, farmers used residues from weeding (100%), planting of trees (42%), mineral fertilisers (33%), compost (16%), and manure (13%). More farmers in the transition zone than the humid forest implemented SFMPs. Our findings suggest that soil fertility perceptions, access to inputs, local practices, and experience influence farmers’ use of SFMPs. The limited use of mineral fertilisers was explained by poor access whereas the use of organic fertilisers and tree planting were mostly constrained by lack of labour and knowledge. Farmers prioritised practices to increase yield and viewed SFMPs to be the least important management practices, although they believe high cocoa yield is an important indicator of soil fertility. To foster sustainable cocoa intensification, it is necessary to enhance farmers’ knowledge on SFMPs, increase access to inputs, and ensure returns on investment while considering farmers’ priorities and practices.

International audience; Much effort has been spent on formulating guidelines for inorganic fertilizer use in millet crops in Sub-sahelian farms. However, these guidelines do not take into account the diversity of manuring practices. In this study we analyzed over two years (2016–2017) the use efficiency of an inorganic NPK fertilizer as affected by the two most contrasted categories of organic manure strategies (OMS) found in millet fields of central Senegal. 19 farmers’ fields were selected in a village typical of that region, 11 and 8 of which respectively corresponding to categories OMS1 and OMS2 as follows: OMS1, locally referred to as Homefields, were fields continuously cropped with millet over the last 15 years, having received organic manure regularly in the past, and manured again at the onset of the 2016 rainy season. OMS2 fields locally referred to as Outfields, were not manured in 2016 and were rarely manured in the past. Four of them were continuously cropped with millet and the others had followed a triennial millet-peanut-fallow rotation. In 2017, no manure was applied in any of the OMS1 or OMS2 fields. A pairwise treatments with and without the same inorganic fertilizer dose was applied in each field in both 2016 and 2017 cropping seasons. In 2016, the higher the manure application, the higher the use efficiency of the inorganic fertilizer applied. The use efficiency of the inorganic N was most closely related to soil bulk density and P availability. In 2017, with no new manure amendment, millet yield in OMS1 was about three times higher than in 2016. It was close to the water-limited yield, suggesting that the residual effect of the manure applied in 2016 was high. The use efficiency of the inorganic N was generally low under these conditions. In OMS2, millet yield and use efficiency of inorganic fertilizer remained low in both years. The crop rotation with peanuts did not enrich the soil compared to the millet returning every year, but it reduced Striga hermontica infestation and increased the millet 1000-grain weight. The methodological approach developed here may help in formulating guidelines to deal with the diversity of farming practices in Sub-sahelian villages.

Sustainable alternatives to slash-and-burn shifting cultivation in the (sub)humid tropics rely on the use of external nutrient inputs to address soil fertility decline. The use of organic inputs is widely accepted as a practice to improve soil fertility, in particular soil organic carbon (SOC). On the other hand, its combined use with mineral fertilizer has the potential to maintain or increase crop productivity through positive interactive effects between both resources. Few studies have investigated these effects in the long term. Therefore, the objective of this study was to investigate whether maize productivity and soil SOC can be sustained under permanent cropping with sole and combined use of compost and mineral nitrogen (N) fertilizer. Here, we report results from a long-term experiment carried out in Gagnoa, Ivory Coast, from 1971 to 1990. The experiment followed a randomized block design comprising eight replicates of 12 treatments. The two studied factors were compost (0 or 10 t DM ha−1 yr−1) and mineral N (0, 40, 80, 120, 160 or 200 kg N ha−1 yr−1) additions. Average maize grain yields of the first cropping cycles were significantly lower without compost (5.05 ± 1.57 t ha−1) than with compost addition (6.07 ± 1.31 t ha−1). The annual yield variability as shown by the standard deviation of the mean was reduced by 20% with compost addition. Without compost, 53% of the initial SOC stock in the 0–20 cm soil layer was lost, resulting in a SOC loss rate of − 0.62 t C ha−1 yr−1 compared to 21% with compost (−0.27 t C ha−1 yr−1). Compost addition therefore reduced SOC loss with an apparent SOC storage rate of 0.35 t C ha−1 yr−1. The conversion rate of organic carbon (OC) inputs to SOC was about 12%. The Introductory Carbon Balance Model (ICBM) reproduced well SOC dynamics, especially without compost. Without mineral N and without compost, maize grain yield decreased with decreasing SOC concentration until the introduction of leguminous crops in the second cropping cycle. We conclude that combined application of compost with mineral N fertilizers was effective at maintaining maize productivity but inadequate to prevent the decline of SOC stocks, despite large additions. Leguminous crops in the rotation were key for maize productivity, but probably due to effects non-related to supplementary N supply.

Intraspecific variation in leaf functional traits has gained widespread attention as a means to evaluate, predict, and manage plant responses to environmental conditions, however there are considerable uncertainties regarding the extent and drivers of intraspecific trait variation (ITV) in domesticated plants. In a coffee (Coffea arabica) agroforestry system, we quantified ITV in seven leaf traits [i.e. area (LA), mass per area (LMA), dry matter content (LDMC), thickness (Lth), nitrogen concentrations (LNC), maximum photosynthetic rate on area and mass bases (Asat, Amass, respectively)] across managed gradients of soil fertility and light availability. Leaf physiological traits (Asat, Amass), as well as LA, showed the greatest extent of variation within coffee, while morphological traits (LMA, LDMC, Lth) and leaf N were less variable. All traits differed significantly as a function of light and fertilization treatment, however light was more influential in driving ITV in coffee leaves. Low light availability resulted in greater ITV for physiological leaf traits (Asat and Amass), while high light constrained ITV in most morphological-(LA, LMA, LDMC), physiological-(Asat, Amass) and chemical-(LNC) traits. Fertilization treatments did not induce systematic shifts in the extent of ITV. In addition, shade management treatments explained 9.2% of the variation in multivariate trait syndromes, while nutrient management regimes explained only 2.9%. Our results indicate that highly heterogeneous aboveground resource environments such those created by agroforestry, results in greater ITV for key crop physiological parameters. Based on ecological theory, such patterns indicate that management systems promoting resource heterogeneity should promote higher rates of resource partitioning, and greater resource-use efficiency in agroecosystems.

Oil palm cultivation has environmental impacts, including those associated with nitrogen (N) losses. Improving management practices to optimise yield and N losses is critical. In order to identify the key management and site parameters driving yield and N losses, over a 25-year cycle, we undertook a Morris’s sensitivity analysis of the Agricultural Production Systems sIMulator oil palm model (APSIM-Oil palm), using 3 sites in Papua New Guinea. We selected 12 parameters and 3 outputs: yield, nitrous oxide (N2O) emissions and N leaching. The influence of the 12 parameters on the outputs depended on site characteristics, age of the palms, and climate. The most influential parameters for losses were N mineral fertiliser rate, drainage and fraction of legume in groundcover vegetation. The simulations suggested that APSIM-Oil palm is a useful tool for assessing management options for optimising yield and environmental outcomes in different environments. The results can also guide future measurements needed to improve N loss estimates, and further development of models and risk indicators.

This work showed for the first time that organic nutrient transformation techniques based on locally available materials (manure, green waste and advanced biochar) can increase fertilizing efficiency of the resulting substrate by a factor of three compared with other organic amendments without biochar. We used three different composting methods to investigate the techniques of organic nutrient transformations; i) conventional composting (composting process completed without turning the piles) ii) aerobic composting (composting process with manual turning of piles) and iii) bokashi composting (anaerobic lacto-fermentation). Composting was carried out in the absence (compost alone) and the presence of biochar (co-composted). Biochar was produced locally from an invasive forest shrub ‘Eupatorium adenophorum’. A pot trial with maize grown in silty loam soil was carried out to investigate the agronomic effect produced using three above-mentioned composting methods that were compared with conventional mineral fertilizers (NPK). Significant effects of co-composted bokashi-biochar (60 t ha−1) were observed on maize growth, which increased biomass by 243% compared to mineral NPK, also showing better growth effects than conventional and aerobic composting amendments. Improved soil available nutrients (available P and other exchangeable base cations (K+, Ca2+ and Mg2+)) were probably the cause of the superior growth effect of co-composted bokashi-biochar.

With the depletion of forest reserves, coffee growing based on extensive and shifting cultivation mode is no more reproductive. Thus, soils of different coffee growing areas were studied in order to diagnose the fertility level, their potential for productivity of new varieties of coffee (Coffea canephora Pierre, var. Robusta) and their sustainable managements. In total, 156 soil samples were collected and analyzed in the laboratory using standard methods to determine their physicochemical statutes. The results obtained show a low nitrogen content of less than 0.27% in all soil mapping units, a base saturation percentage lower than 60% for the vast majority of soils and crucial presence of organic matter on distribution of physicochemical properties. Clustering of results identified two main components, which accounted for 88.69% of the variability of the data and the grouping into three communities by similarity of features. In view of these results, a sustainable production of the coffee trees requires a fertilization program for the improvement of soils under coffee trees.

The multifunctional classification of grasslands in the Massif Central aims to characterise the diversity of grasslands and structure our knowledge about their processes and potential. The tool described here provides information to help livestock farmers transition towards more sustainable, grass-based production. The classification system currently covers 60 different grassland types, and the classification key is based on simple criteria such as field characteristics and farming practices. Here, we discuss 6 common and representative grassland types utilised in PDO cheese production in the Massif Central: we compared agronomic productivity (forage quantity and quality), environmental properties (species richness and the occurrence of rare species), and ecosystem services (carbon storage levels and cheese quality). The impact of farming practices was also analysed; the results can help inform discussions with farmers, to help them better match their practices with the production potential of their grasslands.; La richesse et la diversité des prairies du Massif central sont le résultat d’une longue histoire entre facteurs du milieu et pratiques des agriculteurs. La typologie multifonctionnelle des prairies du Massif central permet de caractériser la diversité des prairies et d’organiser les connaissances sur le fonctionnement et les potentiels agro-écologiques de ces surfaces. Cet outil contribue ainsi à accompagner la transition des systèmes d’élevage vers des modes de production plus durables et basés sur la ressource herbe. Les 60 types recensés actuellement sont organisés dans une clé basée sur des critères simples de milieux et de pratiques. Sur la base de 6 types emblématiques des zones AOP du Massif central, nous comparons les performances agronomiques (quantité et qualité de la production) et environnementales (richesse et rareté de la flore) de chacun, ainsi que les services rendus (stockage de carbone et qualité des fromages). L’analyse de l’impact des pratiques au regard des performances et services de chaque type constitue un support de discussion avec les éleveurs pour envisager les adaptations de leurs pratiques aux potentiels de production de leurs prairies.

9 pages; International audience; It has been repeatedly argued that mineral fertiliser application combined with in situ retention of crop residue biomass can sustain long-term productivity of West African soils. Using 20-year experimental data from southern Togo, a biannual rainfall area, we analysed the effect of two rates of mineral NPK fertiliser application to maize–cotton rotation on the long-term dynamics of soil C and nutrient contents, as compared with two control treatments. Mineral fertiliser treatments consisted of application to both maize (first season) and cotton (second season) the research-recommended NPK rates (Fertiliser-RR) and 1.5 times these rates (Fertiliser-1.5 RR). Control treatments consisted of cropping maize and cotton without fertiliser use (No-Fertiliser) and of double annual soil tillage (as done for planted treatments) without planting a crop (Tillage-NoCrop). Maize residue biomass was every year returned to the soil of crops planted treatments, whereas cotton stems were uprooted, piled and burnt on the experimental plots as done locally for phyto-sanitary reasons. Treatment effects were analysed through a long-term change in crop productivity, in soil C and nutrient contents. Our results indicate that productivity of maize and notably of cotton cannot be sustained in this Ferralsol without nutrient inputs. On average, maize yields without fertilisers decreased from 2 t ha−1 after woodland clearing to 0.5 t ha−1 after 10 years of cultivation, while cotton yields decreased from 1.5 to 0.5 t ha−1 only after 5 years. In spite of the need of mineral fertiliser use to sustain productivity of this soil, there was little justification to increase inputs of mineral fertiliser over the research recommended rate. Over 20-year experiment, both maize and cotton while received N, P and K inputs at the research-recommended rates produced virtually the same yields as when these rates were increased by 50%. Although C inputs to soil under RR and 1.5 RR were greater than in the No-Fertiliser control (nil for Tillage-NoCrop), and the N input was more favourable for 1.5RR, the rates in which contents of soil C and N decreased over time did not differ substantially between treatments. Soil available P decreased for all treatments, while exchangeable K concentration increased under RR and 1.5 RR and decreased in unfertilised treatments (No-Fertiliser and Tillage-NoCrop). In fertilised plots and in tillage no-planted plots, soil pH decreased more than in No-Fertiliser plots. A decline of soil pH was associated with a decline of exchangeable Ca and Mg, which were on average 20 and 40% higher in fertilised plots than in No-Fertiliser plots. We conclude that soil C and N decline in this Ferralsol was more determined by a change in soil conditions due to woodland clearance and continuous tillage than by the quantities of C or N inputs added annually.

In Ghana, cocoa has traditionally been grown as a low input crop, which has caused soil fertility deterioration, and thus, the need to integrate fertilizer use into cocoa agricultural practices. However, fertilizers recommended to farmers are general in nature and do not account for specific crop needs and inherent soil fertility conditions. This study evaluates the use of a soil diagnosis model to determine fertilizer recommendations for cocoa based on inherent soil fertility characteristics in the cocoa growing zones of Ghana. The site-specific fertilizer formulations were tested against blanket recommendations (Asaase Wura and Cocofeed) in farmers' settings from 2009 to 2011. The results showed that DS-formulated site-specific fertilizer performed better than all blanket fertilizers in Western soils especially on the Ferralsols which are very acidic and depleted of base cations. On the other soil conditions, the site-specific formulations were comparable to the blanket formulations. Trend analysis of cocoa response to applied fertilizer suggests that P is a major determinant of cocoa productivity and that P205 rates > 120 kg ha- 1 would be required, when justified economically, for optimal cocoa yield, while potassium could be kept at around 45 kg K20 ha- 1. In view of these results, the cocoa fertilizer formulas proposed for western regions of Ghana could be revised according to the DS model recommendations by taking into consideration the optima presented above. For the other cocoa regions, the DS would not be economic and therefore, proposed formulas should keep P20 5 and K20 around the optima above-presented while compensating for nutrients exported by the crop.

Low crop yields in the savannah zones of West Africa are commonly attributed to rainfall deficits and poor soil fertility. In this study, an assessment was made on how the position of fields belonging to different farm types can explain soil variability and related crop yield gaps in two villages in Burkina Faso, Yilou and Koumbia, located, respectively, in the Sudano-Sahelian and Sudanian agro-ecological zones. In each village, four farm types were identified. Soil fertility was generally poor and use of nutrient inputs low in most of the farmer's fields . As a consequence, yields for most crops were low, but differences among farm types were found, which can be linked to their socioeconomic characteristics that influence the amount of inputs used. Application of fertilizers differed also between fields within farms and tended to be greater on the fields near the homesteads in the village of Yilou, especially for organic fertilizers. At both villages, the rates of N and K inputs were insufficient to compensate for their respective output rates, leading to negative partial nutrient balances . The existence of patchworks of soil fertility gives rise to a wide variation in crop responses to fertilizers. Exploitable yield gaps were substantial and to a large extent related to the low fertility status of soils and sub-optimal fertilizer applications.

A expressiva area de plantacoes florestais de arvores de eucalipto de rapido crescimento no Brasil e em outras regioes do mundo encontra-se sob o efeito das mudancas climaticas, do estresse hidrico e da baixa fertilidade do solo, afetando o crescimento volumetrico e a qualidade do seu lenho. O presente trabalho teve como objetivo avaliar o incremento do DAP do tronco de arvores de Eucalyptus grandis por 24 meses, nos tratamentos de reducao da precipitacao pluviometrica e de nutricao potassica e sodica. Os tratamentos foram definidos por 2 regimes hidricos (100 e 66% das chuvas, com reducao artificial com lonas de polietileno) e 3 tipos de nutricao mineral: K (K - 4,5 kmol/ha), Na (Na - 4,5 kmol/ha) e controle (sem aplicacao de K e Na). Foram selecionadas 54 arvores de eucalipto/tratamento e instaladas as faixas dendrometricas no DAP dos troncos. Os resultados indicaram efeito da sazonalidade climatica no incremento do DAP do tronco das arvores de eucalipto, com periodos de maior e de menor taxa de crescimento e o meristema cambial e, desta forma, a mensuracao do diâmetro do tronco com os dendrometros indicam que a resposta a um dado evento climatico se expressa apos o periodo de 15, 30 e de ate 45 dias. As arvores de eucalipto dos tratamentos sem reducao de chuva apresentaram maior valor da taxa de incremento acumulado do tronco, bem como nas arvores do tratamento com aplicacao de K. Os resultados podem ser utilizados na adocao de praticas silviculturais nas arvores de eucalipto nas plantacoes florestais de rapido crescimento em areas afetadas pelo estresse hidrico e na substituicao parcial de K por Na.(Resume d'auteur)

SUMMARYIn the oil palm plantations of Ecuador, two factorial trials (namely CP06 and CP08) were used to assess the effects of N, P and K fertilization on the soil chemical characteristics after 10 years of fertilizer application. The use of ammonia-based fertilizers has resulted in a drop in soil pH, which has reached 1.2 units in one of the two trials. A drop in cation exchange capacity (CEC) was also found, and a loss of exchangeable cations that probably reflected leaching of excess N as nitrates. The use of KCl enriched the soil in K, which contributed to impoverishment in Ca and Mg. In both trials, the highest N and K application rates had no significant effect on yield in comparison with an intermediate fertilization rate; however, their effects on the fertilized soil significantly increased the risk of N and cation leaching towards the deep soil layers. We also compared the effects of the N, P and K factors on soil properties outside the fertilizer application zone. In both trials, the mineral reserves played a major role in meeting the needs of the control palms, which had not been fertilized for 10 years, as no significant yield drop has been observed except in trial CP06 when no KCl was applied. However, uptake of nutrient in the control plots did not lead to significant impoverishment of the soil.

Dans le souci de mettre au point des techniques de valorisation des déchets urbains au Cameroun, les impacts agronomiques, environnementaux et économiques de deux amendements organiques (fumier de poulet et compost d'ordures ménagères) ont été évalués sur la culture de la laitue (Lactuca sativa). Pour y parvenir, un essai au champ a été conduit pendant deux cycles de culture en milieu paysan dans la zone maraîchère de Nkolondom, bas-fond péri-urbain de Yaoundé. Huit fertilisations ont été comparées dans un dispositif à quatre blocs complètement randomisés. Des analyses en laboratoire ont évalué l'évolution de la fertilité du sol maraîcher et les risques environnementaux. Les fertilisations ont amélioré le rendement en laitue de manière très hautement significative pendant les deux cycles de culture. Les rendements ont varié de 1,7-1,2 kg/m2 sur les parcelles témoins à 3,1-4,4 kg/m2, suite à un apport combiné de fumier + NPK. Les amendements organiques donnent de meilleurs résultats lorsqu'ils sont associés aux engrais minéraux complémentaires. L'épandage du fumier ou du compost permet de restaurer la fertilité du sol, notamment en azote, en matière organique, en somme de base échangeable et en CEC. Cependant, il a été observé une baisse de la teneur en phosphate du sol malgré les différentes fertilisations. Contrairement au compost, l'épandage du fumier a amélioré la teneur en potasse des parcelles. La rentabilité économique des amendements organiques est très faible comparativement à celle de l'engrais minéral: le recours au fumier coûte 2 fois plus et celui du compost 20 fois plus que l'emploi de l'engrais minéral. Les compost et fumiers ne présentent pas de danger pour la santé des utilisateurs.

In Côte d'Ivoire, soils in cacao plantations are depleted due to the absence or underuse of fertilisation. A digital map of 130 landunits was created from soil and climatic parameters. A soil diagnosis software was combined with GIS (geographical information system) to convert the current unique fertiliser “Engrais cacao” into a greater number of recommendations more adapted to local conditions, thus more actual. Cacao fertiliser requirements were calculated from soil samples taken in mature cacao plantations in each landunit. The relationships between nutrient requirements and soil chemical parameters enabled building a map of the actual cacao fertiliser recommendations. Soils with identical characteristics were compared regarding their cacao nutritional needs. Highly significant correlations between soil nutrients were found; particularly, Ca and Mg were highly correlated with K, making it possible to calculate the Ca and Mg amounts in fertiliser formulae as function of K (i.e. Ca = 8.5×K and Mg = 3×K). The final map contains 23 N-P-K-Ca-Mg fertiliser formulae. Among them, the currently recommended blanket fertiliser represents 16.5% of the cacao areas. The comparison of our results with a previous study, done 40 years ago, evidenced that the soil nutrients under cacao have significantly decreased over the period, reinforcing the need for fertilizers.

International audience; This study aimed at determining the fate of trace elements (TE) following soil organic waste (OW) application. We used a unique combination of X-ray absorption spectroscopy analyses, to determine TE speciation, with incubation experiments for in situ monitoring of TE availability patterns over a time course with the technique of the diffusive gradients in thin films (DGT). We showed that copper (Cu) and zinc (Zn) availability were both increased in OW-amended soil, but their release was controlled by distinct mechanisms. Zn speciation in OW was found to be dominated by an inorganic species, i.e. Zn sorbed on Fe oxides. Zn desorption from Fe oxides could explain the increase in Zn availability in OW amended soil. Cu speciation in OW was dominated by organic species. Cu release through the mineralization of organic carbon from OW was responsible for the increase in Cu availability. (C) 2016 Elsevier Ltd. All rights reserved.

Recycling empty fruit bunches (EFBs) in mature oil palm stands usually consists in distributing them over a limited area representing 3%–10% of the plot. The impact of this practice on soil quality, including soil biodiversity, is not well known at the plot scale. We analysed soil physical, chemical, and biological variables. Five zones were defined around the palm tree to assess spatial heterogeneity due to plant cover and application of organic and inorganic fertilisers. Each zone was analysed separately. Our study revealed marked variations in mineral contents around the palm tree, ranging from deficiency to excess or nutrient imbalance in adjacent zones, particularly in available P and K, Mg and pH. Similar variations in macrofauna were observed both in the litter and the soil. Our results demonstrate that the changes caused by plant cover and applications of fertiliser are mainly limited in space, but that earthworm communities move as a function of variations in nutrient availability or stress associated with EFB deposition over time. The Amacher index, adapted to the soil nutrient status for oil palm, indicated that average mineral fertility at the plot scale was rather good. The average density of soil macrofauna and nematofauna was low compared to other tropical ecosystems, but reference data from Indonesia are lacking. Application of EFBs on the harvest path mainly improved the homogeneity of soil quality within the elementary plot around the palm. However these data did not show that recycling EFB stimulates soil fauna communities or carbon sequestration at the plot scale.

International audience; Soil acidity is a major constraint for crop production on highly weathered tropical soils characterized by high Al toxicity, low cation exchange capacity and low P availability to plants. To address these constraints, we compared the effects on crop production and soil properties of liming and adding biochar. Experiments were conducted under field conditions in an acidic soil in the Madagascar highlands using a two year rotation of maize intercropped with beans followed by rainfed upland rice over a period of six years. Five different levels of amendment were compared: 10 and 50 t ha−1 of eucalyptus charcoal residues (referred to as biochar), 1 and 3 t ha−1 of dolomite and a control (no amendment). They were combined with two types of soil management (conventional tillage and no tillage) and two fertilization levels. Soil characteristics were measured once after five years. Both biochar and dolomite amendment significantly improved yields of the maize and beans due to an increase in soil pH and a decrease in exchangeable aluminium. However, no significant effect was observed on the yield of upland rice. The incorporation of 50 t ha−1 of biochar was necessary to match the results obtained with 3 t ha−1 of dolomite. Amendment with dolomite was a more practical and cost-efficient option than amendment with biochar in our conditions. Long term trials are now needed to evaluate other types of biochar.

Oil palm is the most rapidly expanding tropical perennial crop. Its cultivation raises environmental concerns, notably related to the use of nitrogen (N) fertilisers and the associated pollution and greenhouse gas emissions. While numerous and diverse models exist to estimate N losses from agriculture, very few are currently available for tropical perennial crops. Moreover, there is a lack of critical analysis of their performance in the specific context of tropical perennial cropping systems. We assessed the capacity of 11 models and 29 sub-models to estimate N losses in a typical oil palm plantation over a 25-year growth cycle, through leaching and runoff, and emissions of NH3, N2, N2O, and NOx. Estimates of total N losses were very variable, ranging from 21 to 139 kg N ha−1 yr−1. On average, 31 % of the losses occurred during the first 3 years of the cycle. Nitrate leaching accounted for about 80 % of the losses. A comprehensive Morris sensitivity analysis showed the most influential variables to be soil clay content, rooting depth, and oil palm N uptake. We also compared model estimates with published field measurements. Many challenges remain in modelling processes related to the peculiarities of perennial tropical crop systems such as oil palm more accurately.

L’intensification de la culture du mais, majoritairement destinee a l’autoconsommation rurale et a l’approvisionnement des villes, est une opportunite pour ameliorer la securite alimentaire des regions septentrionales du Cameroun et limiter la pression fonciere. Pour etudier sa faisabilite, trois niveaux d’intensification ont ete testes en 2013 dans 32 champs de mais a proximite de Garoua dans la region du Nord, 16 consideres comme fertiles par les producteurs et 16 comme degrades : (i) la conduite habituelle par le producteur (CP), (ii) un premier niveau d’intensification (NI1) correspondant aux recommandations actuelles de la vulgarisation agricole et (iii) un second niveau d’intensification (NI2) avec, par rapport a NI1, un renforcement des amendements, un traitement de semences ameliore, de meilleures densite et controle des mauvaises herbes. CP et NI1 ont des rendements proches dans les deux villages : en moyenne 2,3 et 1,3 t.ha–1 , respectivement sur parcelles fertiles et degradees, indiquant que les producteurs suivent assez bien les recommandations de la vulgarisation agricole. Les rendements des parcelles sous NI2 sont significativement superieurs aux autres, en moyenne de 1 t.ha–1 sur le site de Ngong ou la pluviosite est la plus faible et 1,5 t.ha–1 sur le site de Gashiga. Curieusement, le gain de rendement apporte par NI2 est identique sur parcelles fertiles comme degradees, indiquant que la degradation de ces dernieres, averee par leur moindre production, permet neanmoins une reponse a une intensification accrue. Malgre ces resultats, la profitabilite d’une intensification accrue au prix actuel du mais, notamment celui ayant cours au moment de la recolte, n’est pas etablie. Un meilleur prix rendrait profitable l’intensification et la production accrues de la culture du mais dans ces regions, comme le pratiquent deja en partie certaines exploitations dites emergentes, qui maitrisent mieux la commercialisation de leurs productions.

Management practices that simultaneously improve soil properties and yield are crucial to sustain high crop production and minimize detrimental impact on the environment. The objective of this study was to determine the influence of tillage, rice straw mulch and nitrogen fertilization on soil quality and upland rice yield in northern Benin, West Africa. The 2-year (2014-2015) field experiment was conducted with two tillage systems (no-tillage, and manual tillage), two rice straw managements (no rice straw, and rice straw mulch at 3 Mg ha-1) and three nitrogen fertilizer levels (no nitrogen, moderate level of nitrogen: 60 kg ha-1, and high level of nitrogen: 120 kg ha-1). Rice yield was not significantly different as a function of tillage systems. On the contrary, rice yield significantly increased with application of rice straw mulch and nitrogen fertilizer. The highest response of rice yield to nitrogen fertilizer addition was obtained for 60 kg N ha-1 in combination with 3 Mg ha-1 of rice straw for the two tillage systems. Soil moisture and soil microbial carbon were higher under no-tillage, rice straw mulch and nitrogen fertilizer. No-tillage combined with rice straw mulch and 60 kg N ha-1 could be used by smallholder farmers to improve soil quality and achieve higher grain yield in upland rice fields in northern Benin.

Le recyclage des produits résiduaires organiques participe au développement durable des territoires. Il contribue à l'amélioration de la fertilité des sols, notamment via les apports en matière organique, et à une économie circulaire des nutriments (azote, phosphore et potassium principalement) à des échelles très variées. Il faut cependant veiller à la maîtrise des impacts environnementaux, notamment en raison de la difficulté à ajuster les pratiques de fertilisation et de la présence éventuelle de contaminants. L'impact du recyclage est global ; il peut se traduire par une substitution des engrais, préservant ainsi des ressources minières ou les sources d'énergie fossile. Comprendre les processus biogéochimiques impliqués dans le recyclage des produits résiduaires organiques, préciser les usages et proposer des solutions adaptées à différents contextes au Nord comme au Sud ont été les objectifs du travail pluridisciplinaire présenté dans cet ouvrage. Il s'appuie sur les résultats du projet "Intensification des systèmes de production agricole par le recyclage des déchets" (Isard), conduit de 2009 à 2013 avec le soutien financier de l'Agence nationale de la recherche française. Ainsi, de la plaine de Versailles à l'île de la Réunion, en France, et de la péninsule dakaroise, au Sénégal, à la zone périurbaine de Mahajunga, à Madagascar, anthropologues, sociologues, biogéochimistes, modélisateurs, technologues et agronomes se sont associés pour caractériser les déchets organiques et leurs usages, documenter l'intérêt de leur recyclage, mais aussi les risques inhérents à leur emploi. Cet ouvrage est destiné aux professionnels soucieux de pratiques agro-écologiques au Nord comme au Sud. De plus, les études de cas très approfondies intéresseront les scientifiques de diverses disciplines.

International audience; Background and aims. Positive below-ground interactions (facilitation) should be more pronounced when resources limit crop growth, according to the stress-gradient hypothesis. Our aim was to test this hypothesis for intercropped durum wheat and faba bean along a P-fertilizer gradient. Methods. A field experiment was conducted in a long-term P-fertilizer trial with three rates of P-fertilization (No, Low and High P). Microbial biomass was assessed by chloroform fumigation-extraction. Quantitative PCR was applied to evaluate the abundance of relevant microbial groups. Results. Phosphorus availability and microbial biomass systematically increased in the rhizosphere compared to bulk soil. P-fertilization resulted in higher abundance of targeted bacterial phyla, whole bacterial and fungal communities, and depressed mycorrhizal colonization of durum wheat, but not faba bean. Microbial biomass carbon significantly increased in the rhizosphere only in P-fertilized treatments, pointing to P limitation of microbial communities. Intercropping yielded a significant effect on rhizosphere microbial properties only at High P. Microbial biomass P increased in the rhizosphere of intercropped faba bean only at No P level, and was thus the sole finding supporting the stress-gradient hypothesis. Conclusions. P-fertilization was the main driver of microbial communities in this field trial, and P-fertilizer application modulated the species-specific effect in the intercrop. Plant performance did not validate the stress-gradient hypothesis as positive plant-plant interactions occurred regardless of the level of P-fertilization.

Dans les systèmes agropastoraux d'Afrique de l'ouest les résidus de récolte disponibles sur les parcelles récoltées au sein des territoires villageois constituent une source capitale de fertilisants organiques pour l'entretien de la productivité des sols des exploitations agricoles. Leur accès est régi par les règles de vaines pâtures instaurées par les autorités traditionnelles qui autorisent la consommation des résidus de récolte par les troupeaux du village et ceux des troupeaux transhumants. Des contrats de fumure entre producteurs sans troupeaux et producteurs détenteurs de troupeaux permettent ainsi des restitutions de fumure sur les parcelles des premiers en échange de résidus. Ces règles et contrats se traduisent par des flux de biomasses (résidus de récolte et fumure organique) et des transferts de fertilité des sols entre exploitations agricoles au sein du territoire villageois. La croissance démographique rapide observée en Afrique de l'Ouest accompagnée du développement de la traction animale a conduit à une augmentation des surfaces cultivées, des effectifs animaux et à une saturation de l'espace agricole. La disparition associée des contrats de fumure entre les exploitations s'est traduite par une accumulation de fertilité sur les parcelles des producteurs détenteurs de troupeaux au détriment de ceux sans troupeaux. L'objectif de cette thèse est d'explorer différents scénarios de changements de flux de nutriments à l'échelle du territoire villageois sur le fonctionnement des systèmes agropastoraux et la productivité du sol afin de contribuer à l'élaboration de cadres de gestion des ressources agropastorales (résidus de récolte et herbes de pâturage). On a construit quatre types d'exploitation sur la base de leurs capacités de production (nombre d'animaux, main d'oeuvre, équipement, etc.) et des objectifs de production. On a choisi trois exploitations par type (12 exploitations au total par village) pour lesquelles on : i) a quantifié tous les flux de ressources organiques et inorganiques à trois niveaux : l'exploitation, les sous-systèmes de l'exploitation, et les parcelles de l'exploitation ; et ii) évalué l'efficacité de l'utilisation des nutriments et réaliser les bilans en nutriments. Un modèle multi-agents a été développé prenant en compte les transferts de biomasses et des nutriments entre les différentes exploitations agricoles. Les effets de changements climatiques (baisse de 25 % de la pluviométrie par rapport à celle observée dans la zone d'étude) et de l'introduction de 10 % ou 30 % de l'agriculture de conservation sur la production de grain de maïs et la fumure organique chez les exploitations agricoles ont été explorés. Quatre types d'exploitation ont été identifies : producteur d'agriculture de subsistance (SO), producteur intégré au marché (MO), l'agriculteur –éleveur (AE) et l'éleveur – agriculteur (EA). Les deux derniers types d'exploitation collectent au moins 50 % de leurs résidus de récolte qu'ils conservent comme stock fourrager, contre 30 % pour les autres types. Les animaux des types, AE et EA consomment aussi 90 % des résidus restant sur leurs parcelles avant de consommer ceux sur les parcelles des autres types d'exploitation. Le fumier de bovins disponibles dans le village est principalement utilisé pour fertiliser les champs des types d'exploitation, AE et EA. Ces dernières présentent souvent des bilans en nutriments positifs. Les rendements moyens de cultures principales et l'efficience agronomique de l'azote moyen observé étaient beaucoup plus faibles, et de larges écarts ont été révélés entre les types d'exploitations. La conversion de 30 % de superficie cultivable en agriculture de conservation a un résultat négatif sur la production en grain de maïs à l'échelle du territoire villageois mais positif à l'échelle de l'exploitation pour les types SO et MO. Dans le scénario climatique, les types éleveur – agriculteur et agriculteur -éleveur subissent de manière générale les plus grandes baisses de productions en grain et en fumure organique que les autres types. L'amélioration de la gestion interne de nutriments grâce à un meilleur recyclage des biomasses, et l'utilisation plus efficace des engrais disponible est la première option pour les exploitations à faible facultés en ressources de production.

International audience; Cereal residues represent a major resource for livestock feeding during the dry season in southern Africa. When kept on the soil surface instead of feeding them to livestock, crop residues can contribute to increasing soil fertility and maintaining crop productivity in the short- and the long-term. We explored these trade-offs for smallholder cotton–sorghum farming systems in the semi-arid Zambezi Valley, northern Zimbabwe. The analysis was done using simulation models at three scales, the plot, the farm and the territory, to simulate the effects of different sorghum residue allocations to livestock feeding vs. soil mulching, in combination with different application rates of mineral nitrogen fertilizer on crop productivity. The plot-scale simulations suggest that without N fertilization soil mulching has a positive effect on cotton yields only if small quantities of sorghum residues are used as mulch (average cotton yields of 2.24 ± 0.41 kg ha−1 with a mulch of 100 kg ha−1 vs. 1.91 ± 0.29 kg ha−1 without mulch). Greater quantities of mulch have a negative effect on cotton yield without N fertilization due to N immobilization in the soil microbial biomass. With applications of 100 kg N ha−1, quantities of mulch up to 3 t ha−1 have no negative effect on cotton yield. Results at farm-scale highlight the fundamental role of livestock as a source of traction, and the need to feed a greater proportion of sorghum residues to livestock as herd and farm sizes increase. Farmers with no livestock attained maximum crop production when 100% of their sorghum residue remained in the field, as they do not have access to cattle manure. The optimum fraction of crop residue to be retained in the fields for maximum farm crop production varied for farmers with 2 or less heads of cattle (80% retention), with 2–3 heads (60–80%), with 4 or more heads (40–60%). At the scale of the entire territory, total cotton and sorghum production increased with the density of cattle, at the expense of soil mulching with crop residues. The results of our simulations suggest that (i) the optimum level of residue retention depends on the scale at which trade-offs are analyzed; (ii) the retention of all of the crop residue as mulch appears unrealistic and undesirable in farming systems that rely on livestock for traction; and (iii) crop residue mulching could be made more attractive to farmers by paying due attention to balancing C to N ratios in the soil and by promoting small-scale mechanization to replace animal traction.

Erratum paru dans Agroforestry Systems = ISSN 0167-4366. - (2015)vol.89:n°1 p. 95-96. In Sudano-Sahelian agriculture, organic amendments are often limited by resource availability. Small branches (ramial wood, RW) represent an organic resource found in many landscapes but little is known about their effects. This field trial (2007-2009) studied the effects of RW or straw at low application rate (0.69 Mg C ha?1 year?1) on topsoil carbon (C), nitrogen (N) and available phosphorus (P, Pav), termite cast abundance, and sorghum yield. Straw and RW were chopped and either buried (StBu, WoBu) or mulched (StMu, WoMu). Mineral fertilizers were added to straw so that RW- and straw-amended plots received similar applications of C, N, P, and potassium. Another treatment had RW buried with additional N (WoBuN), and there was a control (Ctrl). Branches came from Piliostigma reticulatum, very common in the area. The treatments had little significant effect on topsoil and crop, owing to the low application rate and spatial variability. However, Pav was significantly lower with buried than mulched amendments in 2009, and decreased significantly over time in Ctrl and with buried amendments. Topsoil C also decreased significantly with time in WoMu. Significantly more termite casts were observed with RW. The sorghum yield averaged 0.87 Mg DM ha?1 in 2007 and then decreased. The treatments affected yield significantly in 2008 only: it was higher in WoBuN and StBu than in Ctrl. In 2009, the yield was mainly affected by initial topsoil Pav. These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields.

Chercheur au CIRAD, M. Dugué nous propose une analyse historique des approches de gestion durable des terres en Afrique de l'Ouest. Cet article présente le point de vue d'un agronome sur ce que pourrait être la gestion durable des sols sous cultures pluviales dans la région.

Measurement of recovery of fertilizer N and soil mineral N by maize must be improved in the western semiarid tropics for maximizing crop yield and reducing environmental pollution. The relevant variables for characterizing this N use are the N uptake by the plant from the applied fertilizer (NdfF) and that from the soil (NdfS). The direct measurement of these two variables requires the use of 15 N labeled fertilizer, a difficult and expensive technique. It would therefore be useful to have sensitive indicators for these variables. This study was conducted to measure the variability in the N use from soils. The experiments were carried out with maize at 24 sites in a 3000 ha area of village land with Luvisols located in the central zone of Burkina Faso. Each site had two treatments with two replicates: 0 and 80 kg N ha-' applied as urea labeled with 15 N. Statistical analysis of the results identified three groups of fields differing in soil fertility, each corresponding to a certain distance from the farmstead, and provided a relationship between the variables NdfF, NdfS, and easily measured indicators. The most pertinent indicators (r2 > 0.9) were: (a) for NdfS, the total N in plant without fertilizer (Nplt0) and the apparent crop recovery of N fertilizer (ACR %), and (b) for Nplt0, Nav (available N) as measured by the Waring Bremner test, exchangeable K, and (c) the clay content. The coefficients of determination improved when the regressions were calculated for each soil fertility group. These results have two important applications: (a) the possibility of estimating easily the part of N taken up by maize that comes, respectively, from the soil and the fertilizer; and (b) the identification of two factors limiting soil fertility, that is, the mineral N and exchangeable K + content of the soil before cropping. (Resume d'auteur)

The maintenance of humus balance in cultivated soils is a guarantee of the sustainability of production systems. In West Africa, the advice regarding application of organic manure to fields remains unique and independent of the quality of organic manures available on farms. Some studies show that West African farms produce a diversity of organic manure. Should the advice for organic manure application be reformulated to reflect this diversity of farm-produced organic manure? We propose to analyze the diversity of organic manure produced on certain farms and estimate the optimal amount of organic fertilizer that should be applied to the fields to ensure the renewal of organic matter. The analysis distinguishes a great heterogeneity of farm-produced organic manure. Farm-produced manure with a high amendment value provides a reference for the quality of the manure, but this is also the case for farm-produced manure with an average quality and for farm-produced composts with a high or average amendment value. Depending on the quality of the manure, with these types of organic fertilizer, it would be necessary to apply between 2.4 and 5.1 t·ha-1 per year on sandy soils and 2.1 to 4.4 t·ha-1 per year for clay. Depending on the quality of the compost, it would be necessary to apply between 4.1 and 5.4 t·ha-1 per year for sandy soils and between 3.5 and 4.6 t·ha-1 per year for clay. Taking into account the heterogeneity of the quality of farm-produced organic manure, we can adapt the current technical advice to ensure a renewal of soil organic matter. However, the quantities of organic manure needed are beyond the current capacity of farms. It would be necessary to increase the amount of organic manure produced on farms, to improve its quality and to integrate other modes of soil fertility management at farm level., L’entretien du bilan humique des terres cultivées est un gage de durabilité des systèmes de production. En Afrique de l’Ouest, la recommandation d’application de fumure organique reste unique, quel que soit le type de sol, et indépendante de la qualité des fumures organiques disponibles dans les exploitations. Aujourd’hui, les paysans des savanes d’Afrique de l’Ouest produisent une diversité de types de fumures organiques, ce qui nous amène à caractériser cette diversité et à proposer de nouvelles recommandations pour assurer l’entretien du statut des sols agricoles dans cette région. L’analyse permet de distinguer une grande diversité de fumures organiques paysannes : des fumiers paysans à forte valeur d’amendement correspondant aux fumures organiques de référence, mais également des fumiers de qualité moyenne et des composts de valeur d’amendement forte et moyenne. Avec ces types d’amendement, il serait alors nécessaire d’appliquer, selon la qualité des fumiers, entre 2,4 et 5,1 t·ha-1 paran sur les sols sableux et 2,1 et 4,4 t·ha-1 par an pour les sols argileux et selon la qualité des composts entre 4,1 et 5,4 t·ha-1 par an pour les sols sableux et entre 3,5 et 4,6 t·ha-1 par an pour les sols argileux. Cependant, les quantités de fumure organique nécessaires dépassent les capacités actuelles de production des exploitations agropastorales de la région. Il est donc nécessaire que les producteurs combinent plusieurs voies d’amélioration de la gestion de la matière organique du sol : augmenter les quantités de fumures organiques produites, améliorer leur qualité et intégrer d’autres modes de gestion de la fertilité des sols cultivés à l’échelle des exploitations.

International audience; The maintenance of humus balance in cultivated soils is a guarantee of the sustainability of production systems. In West Africa, the advice regarding application of organic manure to fields remains unique and independent of the quality of organic manures available on farms. Some studies show that West African farms produce a diversity of organic manure. Should the advice for organic manure application be reformulated to reflect this diversity of farm-produced organic manure? We propose to analyze the diversity of organic manure produced on certain farms and estimate the optimal amount of organic fertilizer that should be applied to the fields to ensure the renewal of organic matter. The analysis distinguishes a great heterogeneity of farm-produced organic manure. Farm-produced manure with a high amendment value provides a reference for the quality of the manure, but this is also the case for farm-produced manure with an average quality and for farm-produced composts with a high or average amendment value. Depending on the quality of the manure, with these types of organic fertilizer, it would be necessary to apply between 2.4 and 5.1 t·ha-1 per year on sandy soils and 2.1 to 4.4 t·ha-1 per year for clay. Depending on the quality of the compost, it would be necessary to apply between 4.1 and 5.4 t·ha-1 per year for sandy soils and between 3.5 and 4.6 t·ha-1 per year for clay. Taking into account the heterogeneity of the quality of farm-produced organic manure, we can adapt the current technical advice to ensure a renewal of soil organic matter. However, the quantities of organic manure needed are beyond the current capacity of farms. It would be necessary to increase the amount of organic manure produced on farms, to improve its quality and to integrate other modes of soil fertility management at farm level.; L’entretien du bilan humique des terres cultivées est un gage de durabilité des systèmes de production. En Afrique de l’Ouest, la recommandation d’application de fumure organique reste unique, quel que soit le type de sol, et indépendante de la qualité des fumures organiques disponibles dans les exploitations. Aujourd’hui, les paysans des savanes d’Afrique de l’Ouest produisent une diversité de types de fumures organiques, ce qui nous amène à caractériser cette diversité et à proposer de nouvelles recommandations pour assurer l’entretien du statut des sols agricoles dans cette région. L’analyse permet de distinguer une grande diversité de fumures organiques paysannes : des fumiers paysans à forte valeur d’amendement correspondant aux fumures organiques de référence, mais également des fumiers de qualité moyenne et des composts de valeur d’amendement forte et moyenne. Avec ces types d’amendement, il serait alors nécessaire d’appliquer, selon la qualité des fumiers, entre 2,4 et 5,1 t·ha-1 paran sur les sols sableux et 2,1 et 4,4 t·ha-1 par an pour les sols argileux et selon la qualité des composts entre 4,1 et 5,4 t·ha-1 par an pour les sols sableux et entre 3,5 et 4,6 t·ha-1 par an pour les sols argileux. Cependant, les quantités de fumure organique nécessaires dépassent les capacités actuelles de production des exploitations agropastorales de la région. Il est donc nécessaire que les producteurs combinent plusieurs voies d’amélioration de la gestion de la matière organique du sol : augmenter les quantités de fumures organiques produites, améliorer leur qualité et intégrer d’autres modes de gestion de la fertilité des sols cultivés à l’échelle des exploitations.

In South America, factorial fertilisation trials were set up on oil palm estates managed by Palmeras de los Andes in Ecuador and Indupalma S.A. in Colombia to control fertilisation during the two oil palm crop cycles. These experiments were designed to determine the optimal leaf contents of N, P, K, Mg and Cl, in recent planting materials and to assess the impacts of the first crop cycle on the following cycle. In the two presented trials, nitrogen and chlorine treatments were found to have the greatest impact on production after 10 years of monitoring. The observed leaf N and Cl deficiencies resulted in a significant effect on the average bunch weight, but these differences did not lead to significant differences in yield. However, after 10 years of monitoring, it was found that the yield differences between the highest and the lowest nitrogen rates (N2-N0) and between the highest and the lowest chlorine rates (Cl2-Cl0), increased steadily until reaching a threshold at which some authors consider that supplementary fertilisation is required. In both experiments, soil mineral reserves had not been tapped during the first oil palm crop cycle, which had benefitted from mean rational fertiliser rates of 3 - 5 kg palm-1 yr-1. These reserves were sufficient to limit a yield decline in the non-fertilised treatments. We also noted that it took a long time for the differences in leaf mineral content and yields to become significant, thus confirming that these are long-term effects. Hence, in a suitably fertilised plantation, it is very unlikely that the effects of fertiliser applications during previous years could be reflected by inter-annual yield variations. However, there is no reason to consider that the depressive effect of poor climatic conditions, such as prolonged drought, could be overcome by increasing early fertilisation.

National audience; The benefits of liming permanent grassland are controversial. A long-term trial (carried out on acid soil for 8 years, then on sown cocks foot for 4 years) provided information on the effect of liming (increased production, economic benefits) and on the ecological intensification of this type of grassland. Annual production for non-fertilized unlimed grassland was 1.1 t DM/ha. The positive effect of liming (+ 0,7 t DM/ha) was only true for non-fertilized land. The effect of NPKS fertilization (+ 4,0 t DM/ha) was much higher, which may be attributed to soil phosphorus levels. The effects of liming and fertilization were enhanced for sown cocks foot, where production reached 9 tons. In this case, liming and fertilization are economically beneficial and allow land to be used for intensive farming.; L'intérêt du chaulage dans les prairies permanentes est assez controversé. Un essai de longue durée (prairie permanente sur sol acide semée ensuite en dactyle) procure des informations sur l'effet du chaulage (gain de production, intérêt économique) et pour l'intensification écologique de ces milieux.La réponse au chaulage et à la fertilisation d'une prairie permanente suivie d'une prairie temporaire de dactyle a été étudiée pendant 8 + 4 ans. Laproduction annuelle de la prairie permanente non fertilisée non chaulée (pH 5) est de 1,1 t MS/ha. L'effet du chaulage (+ 0,7 t MS/ha) n'est significatif que sur les parcelles non fertilisées ; l'effet majeur de la fertilisation NPKS (+ 4,0 t MS/ha) est attribué à l'apport de P, limitant dans ce sol. Avec le dactyle (cv. Accord), les effets du chaulage (jusqu'à + 2,7 t MS/ha) et de la fertilisation (jusqu'à + 5,3 t MS/ha) sont supérieurs, la production du traitement fertilisé et chaulé atteignant 9 t MS/ha. Dans ce cas, la fertilisation et le chaulage sont justifiés économiquement et permettent d'utiliser cette parcelle dans un système plus intensif.

Key words: crop production, intensification, extensification, farming systems, tradeoff analysis, maize, legume, manure, fertiliser, southern Africa Soil fertility decline and erratic rainfall are major constraints to crop productivity on smallholder farms in southern Africa. Crop production intensification along with efficient use of chemical fertiliser is required to produce more food per unit area of land, while rebuilding soil fertility. The objective of this thesis was to identify appropriate crop production intensification options that are suitable to the socio-economic and biophysical conditions of selected smallholder maize-based farming systems in southern Africa. Three sites that formed a gradient of intensity of crop and livestock production were selected for the study. Murehwa in Zimbabwe is characterised by the largest intensity followed by Ruaca and lastly Vunduzi both in central Mozambique. In all three sites, maize is a key staple and cash crop.A literature review, field methods based on participatory research, and modelling tools were combined in analysing potential crop production options across an agricultural intensification gradient. A meta-analysis on maize grain yieldunder rain-fed conditions revealed thatconservation agriculture required legume rotations and high nitrogen input use especially in the early years.Reduced tillage without mulch cover leads to lower yields than with conventional agriculture in low rainfall environments. Mulch cover in high rainfall areas leads to smaller yields than conventional tillage due to waterlogging, and improved yields under CA are likely on well drained soils. Crop productivity underconservation agriculture depends on the ability of farmers to achieve correct fertiliser application, timely weeding, and the availability of crop residues for mulching and systematic crop rotations which are currently lacking in southern Africa. Anadditive design of within-row intercropping was compared to a substitutive design with distinct alternating rows of maize and legume (local practice) under no-tillin the Ruaca and Vunduzi communities of central Mozambique. Intercropping increased productivity compared to the corresponding sole crops with land equivalent ratios (LER) of between 1.0 and 2.4. Maize yield loss was only 6-8% in within-row intercropping but 25-50% in the distinct-row option. Relay planting of maize and cowpea intercropping ensured cowpea yield when maize failed thus reduced the negative effects of dry spells. The residual benefits of maize-pigeonpea intercropping were large (5.6 t ha-1) whereas continuous maize (0.7 t ha-1) was severely infested by striga(Striga asiatica). The accumulation of biomass which provided mulch combined with no tillageincreased rainfall infiltration. Intensification through legume intercropping is a feasible option to increase crop productivity and farm income while reducing the risk of crop failureespecially where land limitation. Cattle manure in combination with chemical fertiliser that included N, P, Ca, Zn, Mn were evaluated for their potential to recover degraded soils and to support sustainable high crop productivity in Murehwa, Zimbabwe over nine years. The experiment was established on sandy and clay soils in two field types. Homefields were close to the homestead and relatively more fertile than the outfields due to previous preferential allocation of nutrients. Maize grain yields in sandy soils did not respond to the sole application of fertiliser N (remained less than 1 t ha-1); manure application had immediate and incremental benefits on crop yields in the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 on clay outfield, 7.6 t ha-1 on sandy homefield and 3.4 t ha-1 in the eighth season. Despite the large manure applications of up to 25 t ha-1, crop productivity and soil organic carbon build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. Manure can be used more efficiently if targeted to fields closest to homesteads but this exacerbates land degradation in the outfields and increases soil fertility gradients. The NUANCES-FARMSIM model for simulating crop and animal productivity in mixed crop-livestock farming systems was used to perform trade-off analysis with respect to crop residue management, animal and crop productivity in Murehwa, Zimbabwe. Retaining all maize residues in the field led to severe losses in animal productivity but significant gains in crop productivity in the long-term. Yield increased 4 to 5.6 t farm-1 for RG1, and from 2.8 to 3.5 t farm-1 for RG2. Body weight loss was on average 67 kg per animal per year for RG1 and 93 kg per animal per year for RG2. Retention of all crop residues reduced farm income by US37 and US38 per year for RG1 and RG2 respectively.Farmers who own cattle have no scope of retaining crop residues in the field as it results in significant loss of animal productivity. Non-livestock farmers (60% of the farmers) do not face trade-offs in crop residue allocation but have poor productivity compared to livestock owners and have a greater scope of retaining their crop residues if they invest in more labour to keep their residues during the dry season. This study has revealed that crop production intensification options developed without considering the biophysical conditions as well as socio-economic circumstances of farmers are nuisances. External ideas should be used to stimulate local innovations to push the envelope of crop production without creating new constraints on resource use.

Soil fertility decline is a major constraint to crop productivity on smallholder farms in Africa. The objective of this study was to evaluate the long-term (up to nine years) impacts of nutrient management strategies and their local feasibility on crop productivity, soil fertility status and rainfall infiltration on two contrasting soil types and different prior management regimes in Murehwa, Zimbabwe. The nutrient management strategies employed in the study were: a control with no fertiliser, amendments of 100 kg N ha −1 , 100 kg N + lime, three rates of manure application (5, 15 and 25 t ha −1 ) in combination with 100 kg N ha −1 , and three rates of P fertiliser (10, 30 and 50 kg P ha −1 ) in combination with 100 kg N, 20 kg Ca, 5 kg Zn and 10 kg Mn ha −1 . Maize grain yields in sandy soils did not respond to the sole application of 100 kg N ha −1 ; manure application had immediate and incremental benefits on crop yields on the sandy soils. A combination of 25 t ha −1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha −1 on the homefield clay soils, 6.1 t ha −1 in the clay outfield, 7.6 t ha −1 in the homefield and 3.4 t ha −1 in the eighth season. Yields of the largest manure application on the sandy outfields were comparable to yields with 100 kg N in combination with 30 kg P, 20 kg Ca, 5 kg Zn and 10 kg Mn ha −1 in the homefields suggesting the need to target nutrients differently to different fields. Manure application improved rainfall infiltration in the clay soils from 21 to 31 mm h −1 but on the sandy soils the manure effect on infiltration was not significant. Despite the large manure applications, crop productivity and SOC build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. The major cause of poor crop productivity on the degraded sandy soils despite the large additions of manure could not be ascertained. The current practice of allocating manure and fertiliser to fields closest to homesteads exacerbates land degradation in the sandy outfields and increases soil fertility gradients but results in the most harvest for the farm. On clay soils, manure may be targeted to outfields and mineral fertiliser to homefields to increase total crop productivity. Farmers who owned cattle in the study site can achieve high manure application rates on small plots, and manure application can be rotated according to crop sequences. Consistent application of manure in combination with mineral fertilisers can be an effective option to improve crop yield, SOC and moisture conservation under smallholder farming conditions. Combined manure and mineral fertiliser application can be adapted locally as a feasible entry point for ecological intensification in mixed crop–livestock systems.

[b]Background and Aims[/b][br/]Recent studies showed a positive tree response to Na addition in K-depleted tropical soils. Our study aimed to gain insight into the effects of K and Na fertilizations on leaf area components for a widely planted tree species.[br/][br/][b]Methods[/b][br/]Leaf expansion rates, as well as nutrient, polyol and soluble sugar concentrations, were measured from emergence to abscission of tagged leaves in 1-year-old Eucalyptus grandis plantations. Leaf cell size and water status parameters were compared 1 and 2 months after leaf emergence in plots with KCl application (+K), NaCl application (+Na) and control plots (C).[br/][br/][b]Results[/b][br/]K and Na applications enhanced tree leaf area by increasing both leaf longevity and the mean area of individual leaves. Higher cell turgor in treatments +K and +Na than in the C treatment resulting from higher concentrations of osmotica contributed to increasing both palisade cell diameters and the size of fully expanded leaves.[br/][br/][b]Conclusions[/b][br/]Intermediate total tree leaf area in treatment +Na compared to treatments C and +K might result from the capacity of Na to substitute K in osmoregulatory functions, whereas it seemed unable to accomplish other important K functions that contribute to delaying leaf senescence.

Sur un Acrisol (nomme terre de barre en Republique du Benin), nous avons echantillonne les herbes et le sol (de 0 a 20 cm de profondeur) au debut et a la fin de la periode de culture en 2009 pour mieux connaitre l'interaction entre l'occurrence d'essence a noix et les parametres du sol. Les echantillons furent preleves le long d'une toposequence a la station experimentale du Centre du riz pour l'Afrique en fonction des positions topographiques, du sommet, du haut de versant, de la mi-versant et du bas de versant. Pour chaque position topographique, un quadrat de1m x 1m fut delimite pour etudier l'abondance de Cyperus selon les indices d'abondance 0, 3 et 5. Les especes d'herbes prelevees ont ete identifiees, sechees et pesees. La granulometrie du sol ainsi que les teneurs du sol en C organique, N-total, P disponible, K, Ca, Mg et Fe-extractible ont ete determines. Parmi les trois especes de Cyperus observees, C. rotundus etait le plus frequent sur toute la toposequence alors que C. esculentus et C. sphacelatus se limitaient respectivement au sommet et haut de versant. Les teneurs du sol en sable, Fe et Pa influencaient positivement la presence de Cyperus spp contrairement aux teneurs en C et Mg. Mais seuls ces derniers nutriments faisaient cela de facon continue et significative. Donc, l'apport de matiere organique et d'un engrais riche en Mg pourrait ameliorer le controle des Cyperus. (Resume d'auteur)

L'intérêt du chaulage dans les prairies permanentes est assez controversé. Un essai de longue durée (prairie permanente sur sol acide semée ensuite en dactyle) procure des informations sur l'effet du chaulage (gain de production, intérêt économique) et pour l'intensification écologique de ces milieux.La réponse au chaulage et à la fertilisation d'une prairie permanente suivie d'une prairie temporaire de dactyle a été étudiée pendant 8 + 4 ans. Laproduction annuelle de la prairie permanente non fertilisée non chaulée (pH 5) est de 1,1 t MS/ha. L'effet du chaulage (+ 0,7 t MS/ha) n'est significatif que sur les parcelles non fertilisées ; l'effet majeur de la fertilisation NPKS (+ 4,0 t MS/ha) est attribué à l'apport de P, limitant dans ce sol. Avec le dactyle (cv. Accord), les effets du chaulage (jusqu'à + 2,7 t MS/ha) et de la fertilisation (jusqu'à + 5,3 t MS/ha) sont supérieurs, la production du traitement fertilisé et chaulé atteignant 9 t MS/ha. Dans ce cas, la fertilisation et le chaulage sont justifiés économiquement et permettent d'utiliser cette parcelle dans un système plus intensif., The benefits of liming permanent grassland are controversial. A long-term trial (carried out on acid soil for 8 years, then on sown cocks foot for 4 years) provided information on the effect of liming (increased production, economic benefits) and on the ecological intensification of this type of grassland. Annual production for non-fertilized unlimed grassland was 1.1 t DM/ha. The positive effect of liming (+ 0,7 t DM/ha) was only true for non-fertilized land. The effect of NPKS fertilization (+ 4,0 t DM/ha) was much higher, which may be attributed to soil phosphorus levels. The effects of liming and fertilization were enhanced for sown cocks foot, where production reached 9 tons. In this case, liming and fertilization are economically beneficial and allow land to be used for intensive farming.

Dans un contexte d'accroissement de la pression humaine sur les espaces agricoles, de réduction des pâturages et de divagation des animaux, les paysans sont intéressés par des solutions qui leur permettent d'accroitre la production de biomasses à l'hectare tout en préservant la fertilité de leur sol. Dans la littérature, il est prouvé que les légumineuses jouent un rôle important dans l'amélioration des systèmes de culture. Mais, leur adoption est faible par les agriculteurs dans la zone cotonnière à l'ouest du Burkina Faso. L'objectif de cet article est de déterminer les performances agronomiques et économiques du niébé (Vigna unguiculata L. Walp.) et du mucuna (Mucuna deeringiana [Bort] Merrill) dans le cadre d'une démarche d'expérimentation chez et par les paysans (ECPP). Sur deux campagnes agricoles (2010 et 2011), nous avons utilisés les données sur les caractéristiques de 81 exploitations (45 pour le niébé et 36 pour le mucuna), les données économiques et agronomiques. Les résultats indiquent que le niébé est sensible à l'arrière effet de la précédente fertilisation contrairement au mucuna. Le mucuna qui aurait un réel intérêt pour les agriculteurs engagés dans l'intensification de leur élevage, offre l'opportunité de produire plus de biomasse (plus de 1,5 t ha-1) par unité de surface avec une meilleure qualité. Le niébé pourrait constituer une source de revenu pour les exploitations agricoles du Tuy avec une productivité de travail pouvant atteindre 10 379 FCFA par jour. Mais, dans un contexte de rareté de l'espace agricole, les expérimentations doivent se poursuivre pour tester les associations céréales/légumineuses avec les agriculteurs qui ont un rôle à jouer dans la création de ces cultures associées.

International audience; Mycorrhizal symbiosis is a key component of a sustainable soil-plant system, governing the cycles of major plant nutrients and vegetation cover. The mycorrhizosphere includes plants roots, the mycorrhizal fungi, and a complex microbial compartment. A large number of methods have been used to characterize the genetic and functional diversity of these soil microbial communities. We present here a review of the multivariate data analysis methods that have been used in 16 research articles published in the 2005-2009 period. "Descriptive" multivariate data analysis methods have been priviledged over classical "predictive" methods and univariate statistical tests. Data sets, multivariate data analysis methods, graphical outputs and interpretation results are presented and explained in details on several examples coming from some of the 16 articles. These multivariate and graphical methods are available in the ade4 package for the R statistical software. The discussion underlines the importance of using appropriate statistical methods to obtain a good description of soil microbiological and biochemical indicators and a good evaluation of soil quality.

Soil fertility decline is increasingly leading to reduced food production worldwide. Over 70% of small holder farmers in the central highlands of Kenya are using crop manure, animal wastes and inorganic fertilizers to increase their farms¿ fertility and subsequent productivity. The dilemma with these practices is that less is known on the impact of these resources on the below ground biodiversity particularly the microbial communities which play a key role in determining soil quality. A study was carried out on a 32 year old long-term trial in Kabete, Kenya. These soils were treated with organic (maize stover at 10 t ha-, farmyard manure at 10 t ha-) and inorganic fertilizers (120 kg N, 52.8 kg P plus farmyard manure at 10 t ha-1 (N2P2 + FYM), 120 kg N, 52.8 kg P plus maize stover at 10 t ha-1 (N2P2 + R), 120 kg N, 52.8 kg P (N2P2), and a control (Nil and fallow) for over 30 years. We examined 16S rRNA gene and 28S rRNA gene fingerprints of bacterial and fungal communities, respectively, by PCR amplification and denaturing gradient gel electrophoresis (PCR-DGGE) separation. Bacterial community structure and diversity were negatively affected by N2P2, as evidenced by changes in the PCR-DGGE banding patterns. Bacterial community structure in the N2P2-treated soil was more closely related to the bacterial structure in the untreated soil (fallow and Nil) than that in soils treated with a combination of inorganic and organic or inorganic fertilizers alone. For the fungal community the negative effect of N2P2 alone was not as adverse as for the bacterial community structure since the soils treated with N2P2 were closely related to those treated with N2P2 + FYM and N2P2 + maize stover. However, soils treated with organic inputs clustered away from soils amended with inorganic inputs. Organic inputs had a positive effect on both fungal and bacterial community structures with or without chemical fertilizers. Results from this study suggested that bacterial and fungal community structure was closely related to agro-ecosystem management practices conducted for over the past 30 years.