domain: sde sdv.sa shs

text:
Elise Audouin
email: elise.audouin@laposte.net

Mariana Odru

Gualbert Dominique Masse

Séraphin Dorégo

Valérie Delaunay

Philippe Lecomte

Jonathan Vayssières

A methodology based on territorial metabolism analysis to assess the multi-criteria sustainability of African village terroirs with contrasted crop-livestock systems

Keywords: territorial metabolism, nutrient cycling, village terroir, agro-sylvo-pastoral systems, livestock fattening, Senegal

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In West Africa, improving living standards and food security are still key issues [START_REF] Lahmar | Tailoring conservation agriculture technologies to West Africa semi-arid zones: Building on traditional local practices for soil restoration[END_REF]. In sub-Saharan Africa in 2012, poverty still affected more than half the population, with 40.3% of the inhabitants earning less than US$2.15 per day, especially in rural areas, which account for 63% of the total population) (The World Bank, 2012a, 2012b). The sustainability of agricultural systems is a major concern since most of the population is rural.

Integrated agro-sylvo-pastoral systems have traditionally predominated in West Africa [START_REF] Dugue | L'intensification écologique : réflexions pour la mise en pratique de ce concept dans les zones de savane d'Afrique de l'Ouest[END_REF][START_REF] Jouve | Jachères et systèmes agraires en Afrique subsaharienne[END_REF]. These systems are based on the complementarity between ruminant herds, cereal crops, and wooded parklands [START_REF] Jouve | Jachères et systèmes agraires en Afrique subsaharienne[END_REF] and their sustainability depends to a large extent on fertility transfers from rangelands to cropped lands, through herd mobility and night corralling [START_REF] Dugue | L'utilisation des résidus de récolte dans un système agro-pastoral sahélosoudanien au Yatenga (Burkina Faso)[END_REF][START_REF] Freschet | Long-term changes in organic matter and microbial properties resulting from manuring practices in an arid cultivated soil in Burkina Faso[END_REF]. The high population growth rate (above +2.4% per year in sub-Saharan Africa since 1961) led to a rapid change in agricultural systems [START_REF] Dongmo | Designing a process of comanagement of crop residues for forage and soil conservation in Sudano-Sahel[END_REF]The World Bank, 2023), when rural populations started to crop rangelands [START_REF] Courtin | Un siècle de peuplement en Afrique de l'Ouest[END_REF][START_REF] Faye | L'embouche bovine paysanne dans le centre-nord du bassin arachidier au Sénégal[END_REF]) and reduce fallow [START_REF] Andrieu | From farm scale synergies to village scale trade-offs: Cereal crop residues use in an agro-pastoral system of the Sudanian zone of Burkina Faso[END_REF][START_REF] Serpantie | Fertilité et jachères en Afrique de l'Ouest[END_REF] to meet their food needs, thereby decreasing fodder resources while increasing pressure on wooded parkland. Wooded parklands have been overused during droughts, resulting in their decline [START_REF] Courtin | Un siècle de peuplement en Afrique de l'Ouest[END_REF]FAO 2003).

As a consequence, herds have become smaller and livestock is fed with crop residues [START_REF] Andrieu | From farm scale synergies to village scale trade-offs: Cereal crop residues use in an agro-pastoral system of the Sudanian zone of Burkina Faso[END_REF]. Farmers progressively have appropriated crop residues for sale or stored them to feed their livestock in the dry season [START_REF] Dugue | L'utilisation des résidus de récolte dans un système agro-pastoral sahélosoudanien au Yatenga (Burkina Faso)[END_REF]Schlecht et al., 2004). This shift in behavior reflects the transition from a collective management system to an individual management system and stresses tensions surrounding biomass resources [START_REF] Courtin | Un siècle de peuplement en Afrique de l'Ouest[END_REF][START_REF] Jouve | Jachères et systèmes agraires en Afrique subsaharienne[END_REF]. Finally, export of the biomass produced in the fields (the main crop products plus the crop residues) combined with continuous cropping has led to soil fertility depletion since nutrient exports are no longer offset by an equivalent supply of livestock manure (Andrieu et al., 2015;[START_REF] Buldgen | Les techniques d'embouche de moutons en région soudano-sahélienne sénégalaise[END_REF]. This phenomenon led to a reduction in crop yields because soils in West Africa are inherently poor in nitrogen and organic matter (Schlecht et al., 2004). Some studies have shown that the intensification of livestock farming combined with crop-livestock integration can address these issues. This strategy can increase farm scale sustainability from both an environmental [START_REF] Alvarez | Whole-farm nitrogen cycling and intensification of crop-livestock systems in the highlands of Madagascar: An application of network analysis[END_REF][START_REF] Bénagabou | L'intégration agriculture-élevage améliore-t-elle l'efficience, le recyclage et l'autonomie énergétique brute des exploitations familiales mixtes au Burkina Faso ?[END_REF] and an economic perspective [START_REF] De Ridder | Milk: the new white gold? Milk production options for smallholder farmers in Southern Mali[END_REF]Duncan et al., 2013). The vast majority of studies focused on the farm level, and few analyzed this livestock-based strategy at plot, farm (here the household) and landscape (here the village) levels simultaneously.

Landscape is the level of analysis at which all the interactions between ecosystem components (livestock, crops and trees) can be taken into account, since in sub-Saharan Africa, herds move around in the landscape thereby creating spatial and horizontal biomass and nutrient flows [START_REF] Bisson | West African mixed farming systems as meta-ecosystems: A sourcesink modelling approach[END_REF][START_REF] Manlay | Organic matter dynamics in mixed-farming systems of the West African savanna. A village case study from South Senegal. T. hèse doctorale[END_REF]. The agricultural landscape in sub-Saharan Africa is organized in village terroirs. The Africanist concept of terroir has been defined as the « area cropped and exploited by a village community » [START_REF] Rabot | Transfert de fertilité et gestion des terroirs, Quelques points de vue[END_REF]. A terroir is also defined as a space with social and geographical features that contains the community's resources and associated rights to satisfy their needs [START_REF] Bernard | What can climate-smart agricultural landscapes learn from the gestion de terroirs approach?[END_REF]. In West Africa, village landscapes are traditionally structured in four concentric rings corresponding to land units [START_REF] Manlay | Spatial carbon, nitrogen and phosphorus budget in a village of the West African savanna-II. Element flows and functioning of a mixed-farming system[END_REF].

Starting from the center and moving toward the periphery, they comprise: (i) the dwelling, i.e. the homestead; (ii) "home fields", i.e. those closest to the homestead, where organic matter is concentrated in order to insure food security through the production of staple foods; (iii) "bush fields", where cash crops are usually grown and where fallow land is used for livestock corralling and grazing during the cropping season; (iv) "rangelands", which form the outermost ring of the village land, and are often less fertile.

In many West African ethnic groups, family members are gathered together in a 'holding'.

Each holding is a dwelling unit grouping several household. Whereas historically, most of the decisions were made at the scale of the holding, today, due to individualization, the household is the usual decision-making unit concerning agricultural resources (herd, land, machinery, etc.) [START_REF] Adjamagbo | Comment les ménages d'une zone rurale du Sénégal gèrent-ils leurs ressources ? Etud[END_REF]. Distinguishing types of households with different strategies and practices makes it possible to account for interactions (e.g. biomass flows) between households and to better explain village-level performance [START_REF] Andrieu | From farm scale synergies to village scale trade-offs: Cereal crop residues use in an agro-pastoral system of the Sudanian zone of Burkina Faso[END_REF]. For instance, agreements between households can improve biomass management and nutrient transfers in village terroirs [START_REF] Diarisso | Biomass transfers and nutrient budgets of the agro-pastoral systems in a village territory in south-western Burkina Faso[END_REF].

Finally, the plot represents the crop management unit, i.e. the level where crop management practices are implemented. For instance, night-corralling means a herd is parked in a particular plot for a specified length of time leading to biomass and nutrient livestockdriven flows between plots (Grillot et al., 2018a). Conventionally, the plot is the level considered to assess the sustainability of cropping systems. For instance, yields and fertility balances are assessed at plot level (Schlecht and Hiernaux, 2004).

In this study, we implemented a multi-level (plot, household, village) biomass and nutrient flow analysis to calculate multiple indicators and to compare two neighboring village terroirs located in the groundnut basin of Senegal. The groundnut basin of Senegal is widely known for its agricultural intensification dynamics. The groundnut basin has undergone spectacular demographic growth [START_REF] Delaunay | Profile: The Niakhar Health and Demographic Surveillance System[END_REF]; in the 1960s, the region already seemed saturated [START_REF] Lericollais | Paysans sereer. Dynamiques agraires et mobilités au Sénégal[END_REF], nevertheless between 1963 and 2009, the population of the region doubled [START_REF] Delaunay | Culture de la pastèque, du sanio et pratique de l'embouche bovine dans la zone d'étude de Niakhar[END_REF]. The strategies used by the villages to adapt to this land pressure have been contrasted. In order to keep livestock in the terroirs, some of the village communities kept common fallow and free-grazing systems, whereas other communities developed livestock fattening systems based on the purchase of feed concentrate [START_REF] Audouin | Réintroduire l'élevage pour accroître la durabilité des terroirs villageois d'Afrique de l'Ouest Le cas du bassin arachidier au Sénégal[END_REF]. The Senegalese groundnut basin is representative of the intensification dynamics that are predicted for the next two to four decades in West Africa [START_REF] Vayssières | The risk of declines in soil fertility and crop productivity due to decreased livestock presence in agropastoral zones of West Africa[END_REF].

This study assesses the consequences of livestock intensification for the functioning and sustainability of two neighboring village terroirs with similar soil and climate conditions, but characterized by contrasted livestock systems: free grazing versus livestock fattening systems.

To this end, a multi-criteria assessment of the two village terroirs' sustainability was undertaken based on environmental (nitrogen balance and nitrogen use efficiency), technical (crop and livestock productivity), social (dependency) and economic (agricultural income and gross margin) indicators.

Description of the study area, methods, and techniques

Study area and the village terroirs

This study focused on two village terroirs located 8 km apart in the former groundnut basin: Diohine (14°30'15.682N; 16°30'8.763W) and Barry (14°34'29.905N; 16°29'18.364W).

Both form part of Niakhar health, demography and environment observatory, one of the oldest observatories in sub-Saharan Africa [START_REF] Delaunay | Profile: The Niakhar Health and Demographic Surveillance System[END_REF]. Most inhabitants belong to the Serer ethnic group (95.2% in Diohine; 88.5% in Barry). Islam is the main religion (47.7% in Diohine; 98.1% in Barry) followed by Christianity [START_REF] Delaunay | Profile: The Niakhar Health and Demographic Surveillance System[END_REF].

The main types of soil are luvic Arenosols and ferric Luvisols [START_REF] Tschakert | Carbon for farmers: assessing the potential for soil carbon sequestration in the old peanut basin of Senegal[END_REF]. Local stakeholders differentiate two main soil types: "dior" and "deck" soils. "Dior" soils account for 70% of the area, they are mainly composed of sand (> 95%), have low organic matter content (< 0.2%) and low nitrogen content (< 0.1‰). "Deck" soils are slightly hydromorphic with high sand content (85-90%), 3-8% clay, 2% silt, 0.5-0.8% organic matter content, and 0.2-0.4‰ nitrogen content [START_REF] Badiane | Région de Diourbel: Gestion des sols[END_REF].

The climate is semi-arid, Sahelian-Sudanese, with 566-mm year -1 average rainfall (mean rainfall measured at Fatick weather station from 2000 to 2012), a short wet season from June to September and a long dry season divided into two seasons: a cool dry season from October to January and a hot dry season from February to May.

Both the agricultural systems are rainfed and the main crop grown is millet (Pennisetum glaucum) and groundnut (Arachis hypogaea) using animal traction [START_REF] Badiane | Région de Diourbel: Gestion des sols[END_REF].

Secondary crops are sorghum and cowpea [START_REF] Tschakert | Carbon for farmers: assessing the potential for soil carbon sequestration in the old peanut basin of Senegal[END_REF]. The main livestock species are cattle (zebu gobra), small ruminants (sheep and goats), and horses and donkeys (used as draught animals) [START_REF] Lericollais | Paysans sereer. Dynamiques agraires et mobilités au Sénégal[END_REF]. The main feature of the village of Diohine is its traditional agricultural system based on collectively managed fallows, free grazing and night corralling in crop fields. The main features of the village of Barry are continuous cropping and livestock fattening in barns based on purchased feed concentrate and harvested crop residues. Figure 1 shows that livestock fattening is practiced by the large majority of households in the village of Barry but rarely practiced in Diohine.

Figure 1 about here

The conceptual model of the socio-agro-ecosystem studied

Metabolism is a key concept in industrial ecology. The analysis of industrial metabolism [START_REF] Wassenaar | Reconsidering Industrial Metabolism: From Analogy to Denoting Actuality[END_REF], or territorial metabolism [START_REF] Barles | L'écologie territoriale et les enjeux de la dématérialisation des sociétés : l'apport de l'analyse des flux de matières[END_REF], is largely based on the quantification of material flows to describe the functioning of existing territories and to design more sustainable territories. This approach has already been used to analyze rural territories [START_REF] Bonaudo | Analyser une transition agro-alimentaire par les flux d'azote : Aussois un cas d'étude du découplage progressif de la production et de la consommation[END_REF]. The analysis of biomass flows is particularly useful to understand how complex agricultural systems function and to assess their sustainability [START_REF] Vayssières | GAMEDE: a Global Activity Model for Evaluating the sustainability of Dairy Enterprises. Part I -Whole-farm dynamic model[END_REF].

Integrated landscape analysis distinguishes multiple levels [START_REF] Minang | Enhancing multifunctionality through system improvement and landscape democracy processes: a synthesis[END_REF]. The present study of village terroirs is based on a stock-flow conceptual model structured around three interlocked systems: the plot, the household, and the village terroir (Figure 2). The village is composed of several households, and each household can be divided into four subsystems: the family, crops and trees, livestock, and organic waste (Figure 2). Livestock usually comprises several herds.

Figure 2 about here

The systems are crossed by biomass flows corresponding to the main types of organic matter circulating within and between farming systems, i.e. crop products (grain, residues, etc.), livestock (dung, meat, milk, etc.), trees (forage, wood, etc.), as well as household purchases (human food, feed concentrate, mineral fertilizers, etc.). Three types of biomass flows are distinguished: inputs, outputs and internal flows. Some outflows at one level (e.g. the plot) are internal flows at a higher level (e.g. the household; Figure 2).

Data collection and processing

Household sampling and survey

Data were collected during household surveys conducted from June to August 2013 and concerned the 2012 cropping season (from June 2012 to May 2013). The exhaustive list of the households in each village and the population data were extracted from the Niakhar observatory data base [START_REF] Delaunay | Profile: The Niakhar Health and Demographic Surveillance System[END_REF]. The surveys in Barry were exhaustive (73 households) but were conducted on a sample of 44 households, corresponding to the Sassem district. In Diohine which is a large village containing 354 households, the districts are regulated by notables who are responsible for the management of the natural resources (e.g. the common fallow). Sassem district is representative of Diohine's agricultural activities, practices and access to resources.

Consequently, the observations and analysis of this district presented in this paper can be considered as representative of the whole village of Diohine.

The aim of household surveys is to describe the structure and agricultural practices of each household and to quantify all household biomass flows, i.e. flows of inputs and outputs to and from all households, plus flows of inputs and outputs to and from the four subsystems (family, crops and trees, livestock, organic waste) of each household (Figure 2).

Computing biomass flows

Biomass flows can be human driven or herd driven (ingestion during grazing and excretion during grazing and night-corralling). Human driven flows were directly quantified with farmers during surveys using local units of measure (cart, bundle, etc.). These flows were then converted into standard units (kgDM). Conversion factors were defined by weightings made during the study or based on data in the literature (Vandermeersch et al., 2013, Appendix 1).

Herd-driven flows were derived from information concerning herd feeding practices and the time spent between the four land units within the boundaries of the village terroir (dwelling, home fields, bush fields, rangelands) collected during the surveys. Herd-driven flows were calculated (in kgDM season -1 ) for each practical season (wet season, cool dry season, hot dry season) defined in section 2.1 above. Free-grazing animals ingest the biomass available in plots: crop residues in cultivated fields after harvest and grass growing on common fallow land and rangelands all year round. Part of the biomass is returned to the soil via animal excreta.

Both ingestion and excreta flows were calculated based on coefficients derived from local observations [START_REF] Wade | Impact of livestock intensification and improved manure management on nitrogen use efficiency in mixed crop-livestock systems in central Senegal[END_REF] or on data available in the literature on West Africa (Appendix 2 and 3).

Between-household livestock-driven plant biomass flows were described for each household by calculating the free-grazing plant biomass balance (ΔFG) corresponding to the difference between (i) inflows by means of intakes by the household herd on external plots (AII) and (ii) outflows by means of intakes by external herds on household plots (AIO).

ΔFG= AII-AIO

(1) AII and AIO were both calculated according to the fodder biomass available for each household the deposition rate (in kgDM TLU -1 hour -1 ). Al is the area of the household's landscape unit l considered. TAl is the total area of the landscape unit l in the village terroir considered. The same two equations (equ. 5 and 6) are applied for urine and dung with their corresponding deposition rates DR (Appendix 3). Deposition rates and nitrogen content vary with the season (Appendixes 3 and 4).

Household typology

To build the household typology, a set of 42 parameters was collected from the 117 households These parameters were grouped in three categories: parameters that concern the farming features that inform the intensity of crop and livestock activities, i.e., total cultivated area (TCA), farm equipment, livestock stocking rate, fattened livestock fattening stocking rate, groundnut and fallow TCA rate inflows and outflows); parameters that concern the family (e.g. number of household members, age of the household head, number of spouses); the impacts of farming practices (i.e. nitrogen and nitrogen use efficiency livestock balances ( § 2.4), free-grazing biomass and excreta balances, night corralling balances).

Household types were determined by cluster analysis and included the following steps: (i) a

principal component analysis was performed on the set of variables, (ii) a hierarchical cluster analysis was conducted using Ward's method.

The principal component analysis procedure (step i) sought uncorrelated linear combinations (components) of the original variables. Then, meaningful variables were identified from the loadings that measured the contribution of each original variable to the variance of the principal component.

The hierarchical partitioning (step ii) sought to build clusters using Ward's minimum variance criterion that minimizes total within-cluster variance.

The final typology represents diverse resource endowments and crop and livestock practices.

All the households differ in size and in their crop and livestock activities, and the intensity of the practices varies according to the type of household. Five types of households were defined:

Low Resource Endowment-Small Herd (LRE-SH), Medium Resource Endowment-Small Herd (MRE-SH), Medium Resource Endowment-Medium Herd (MRE-MH), High Resource Endowment-Medium Herd (HRE-MH), High Resource Endowment-Large Herd (HRE-LH).

Sustainability indicators

Nitrogen is a major limiting factor for agricultural productivity in sub-Saharan Africa, [START_REF] Rufino | Analysing integration and diversity in agroecosystems by using indicators of network analysis[END_REF][START_REF] Schlecht | A critical analysis of challenges and opportunities for soil fertility restoration in Sudano-Sahelian West Africa[END_REF]. Biomass flows (in kgDM year -1 ) were converted into nitrogen flows (in kgN year -1 ) using conversion factors in the literature (Appendix 5). This study assessed three N-based sustainability indicators: productivity, balance, efficiency at three levels (plot, household, village terroir).

Household food security is a major concern on the entire African continent (FAO 2015).

The productivity of the agricultural systems is assessed for livestock in kgLW ha -1 year -1 and for crops in kgDM ha -1 year -1 . The productivity indicator is also expressed in kgN ha -1 year -1 and kgN capita -1 year -1 because sufficient protein availability in the human diet a major problem in Africa (Duncan et al., 2013;FAO 2015).

The nitrogen balance (NB) is a relevant sustainability indicator for soil fertility [START_REF] Manlay | Spatial carbon, nitrogen and phosphorus budget in a village of the West African savanna-II. Element flows and functioning of a mixed-farming system[END_REF][START_REF] Roy | Évaluation du bilan en éléments nutritifs du sol. Approches et méthodologies[END_REF][START_REF] Thornton | Integrated crop-livestock simulation models for scenario analysis and impact assessment[END_REF]. System-gate nitrogen balances were calculated as follows:

NB = (ΣIN-ΣON) ⁄ TCA (8)
where IN and ON are, respectively, total nitrogen inputs and nitrogen outputs in the system considered (plot, household or village terroir, see section 2.2.). The calculated balances are partial balances, i.e. they only include horizontal (i.e. apparent) flows and not vertical flows of N (gaseous emissions, symbiotic fixation, atmospheric deposition, lixiviation and run-off).

Nitrogen use efficiency (NUE, dimensionless, Dmnl) assesses the "return on investment" since for each nitrogen unit supplied to the system, it indicates how many nitrogen units are produced [START_REF] Vayssières | Modélisation participative et intégration des pratiques décisionnelles d'éleveurs dans un modèle global d'exploitation. Thèse doctorale[END_REF].

NUE = ΣON / ΣIN (9)
Agro-sylvo-pastoral systems in sub-Saharan Africa are traditionally low-input systems based on the use of natural resources [START_REF] Vigne | Pluri-energy analysis of livestock systems -A comparison of dairy systems indifferent territories[END_REF]. Agricultural intensification is often based on inputs that considerably modify the system's dependency on external systems.

Dependency corresponds to imports into the system (in kgN capita -1 year -1 , [START_REF] Rufino | Analysing integration and diversity in agroecosystems by using indicators of network analysis[END_REF].

This indicator represents household self-sufficiency (SS) in terms of herd feeding (SSFeed), and in terms of crop fertilization (SSFert). SSFeed (dmnl) is the fraction of the N feed in the herd feed ration produced on the farm. SSFert (dmnl) is the fraction of the plot IN fertilizers originating from organic fertilizers produced on-farm [START_REF] Vayssières | Integrated participatory modelling of actual farms to support policy making on sustainable intensification[END_REF]. A second indicator, dependency (D), only calculated at the village terroir level is the ratio of total nitrogen inputs (IN) to the total system throughflow (TST). Total System Throughflow is calculated as the difference between the sum of a household's IN flows and village terroir IN:

D=IN/TST TST=ΣINh-INt (10) (11)
Household livelihoods are expressed by two economic indicators: gross margin yield and agricultural income. The gross margin yield (GMY in € year -1 ha -1 ) is calculated as the gross margin (GM) per area unit, considering the HH TCA (in ha), as follows:

GMY=GM/TCA GM= (MPcb*MPrcb)-(MS cb*MPrcb)] (12) (13)
where MP cb and MS cb are, respectively, the amount of biomass purchased and the amount of biomass sold per category of biomass cb. MPr cb is the price of each category of biomass. The price of each input (mineral fertilizers, pesticides, seeds, human food, fuel, fodder, feed concentrate, number of animals) and outputs (wood, fodder, main crop products, milk, number of animals sold or given away) was collected during the surveys. The price obtained for an animal depends on its physical condition: fattened animals from in-barn herds fetch higher prices than animals from free-grazing herds (Appendix 6).

The agricultural income (AI in € year -1 ) also includes additional fixed costs:

AI= GM-[Nbe x (MCe+DCe)] (14)
where MCe and DCe are maintenance costs and depreciation, respectively. These cost are listed for each type of farm equipment e (Appendix 7).

At plot level, non-parametric statistic tests were performed on village terroir independent samples. Student's t test, Fisher's F test were performed to see if the results differed significantly. The Mood test was used to compare medians of k independent samples. This test makes no assumptions concerning the distribution of the measurements-and can be considered as a special case of the Pearson Khi² test.

Results

Organization of the two village terroirs

Spatial organization

Diohine is an old village whose dwellings are concentrated and organized in districts.

The dwellings in Barry are fragmented and dispersed as a result of multiple waves of population arrivals. Diohine is consequently governed by a "district hierarchy" while Barry is characterized by a strong "holding hierarchy".

Diohine's terroir is surrounded by 67 ha of lowlands that represent 24% of the total area of the village terroir) and have traditionally been used as rangelands that insure the free-grazing herds do not need to leave the village terroir. Conversely, Barry terroir has no lowlands, ponds or wooded savannah within its traditional boundaries (Figure 3).

Figure 3 about here

Humans, livestock and land use

Human population pressure is lower (180 capita km -2 ) in Diohine than in Barry (320 capita km -2 ) as is the livestock stocking rate (0.96 TLU year ha -1 in Diohine compared with 2.31 TLU year ha -1 in Barry). In Diohine, an extensive livestock system still exists. Based on traditional rules, each year, 20% of the TCA is kept as fallow for grazing in the wet season.

Barry has only a few isolated fallow plots resulting from decisions made by individual households following failed cropping.

Millet is still the main crop in both village terroirs, where it represents 53% of the TCA in Diohine and 55% in Barry. Groundnuts represent only 7% of the TCA in Diohine whereas in Barry they represents 30%.

Household diversity

Households in both villages were classified in five types. The main discriminant variables were the ratio of livestock to cropping activities (i.e., the livestock stocking rate)

and the relative importance of subsistence and cash crop and livestock activities (Table 1).

Table 1 about here

Two of the household types use extensive and subsistence oriented systems: the "Medium Resources Endowment-Small Herd" (MRE-SH, type 2) and the "High Resources Endowment-Medium Herd" (HRE-MH, type 4). Both household types have large fallow land and large freegrazing herds; only a small percentage of the herd is fattened (on average 15% of the herd in type 2 and 3% in type 4). These two types of household depend on their terroir's communal resources (crop residues, fallows and rangeland fodder, and wooded parkland). Type 4 is only represented in Diohine, and more type 2 are found in Diohine than in Barry.

Two of the household types are semi-intensive and cash oriented systems: the "Medium Resource Endowment-Medium Herd" (MRE-MH, type 3) and the "High Resource Endowment-Large Herd" (HRE-LH, type 5). Both focus on commercial production (groundnut and livestock fattening) and both types are only represented in Barry. The proportion of livestock fattening activity is higher in type 5. Type 5 also supports the highest human population density (6.3 capita.ha -1 ; Table 1).

The "Low Resource Endowment-Small Herd" (LRE-SH, type 1) comprises households with limited TCA (average: 3.8 ha) and few livestock. Type 1 is involved in intensification, and trying to invest in groundnuts and/or livestock fattening. This type is the second most common type, and is more frequent in Barry where household individualization is more dynamic (Table 1).

Two household types are particularly involved in livestock rearing: type 4 in Diohine and type 5 in Barry. The average livestock stocking rate is 3.6 TLU ha -1 under type 4 and 3.7 TLU ha -1 under type 5. HRE-MH (type 4) fatten almost none of their livestock (3% of total TLU) and mostly practice free grazing. Conversely, HRE-LH (type 5) fatten 59% of their herd. The animals are kept in barns and are stall-fed with feed concentrate and harvested crop residues.

Analysis of household biomass flows showed that the majority of crop residues produced on-farm are grazed (type 4) or harvested (type 5) to feed the herds. The ΔFG of HRE-MH (type 4) was positive (3451 kgDM ha -1 year -1 ), showing that household herds consume forage in plots belonging to other households, particularly plots belonging to MRE-SH (type 2)

who have a low livestock stocking rate and a negative ΔFG (-225 kgDM ha -1 year -1 ). HRE-MH (type 4) thus benefits from these biomass transfers with the highest dung inputs taking place during night corralling (+758 kgDM ha -1 ). Similarly, type 5 buys crop residues (mainly groundnut hay) from types MRE-SH (type 2) or LRE-SH (type 1), meaning types 4 and 5 extract nutrients from plots belonging to other households that are deposited on their own plots thanks to night corralling (type 4) or through the spreading of solid manure (type 5). HRE-MH (type 4) also provides night corralling to other households with limited manuring capacity (e.g. type 1). According to traditional rules, this agreement gives type 4 the opportunity to borrow external lands the following year [START_REF] Odru | Flux de biomasse et renouvellement de la fertilité des sols à l'échelle du terroir[END_REF].

Farming systems

Crop-livestock coordination across seasons

Livestock farming and cropping practices in the two villages can be described based on their seasonal practices (Figure 4). in Barry versus 0.01 TLU ha -1 in Diohine;). This livestock system reduces direct interactions between livestock and cropping since the livestock are kept in barns within the holding and a large proportion of the feed ration is supplied in the form of harvested crop residues and feed concentrate (e.g. complete concentrates, millet bran, rice bran) purchased outside the village terroir.

During the second part of the cool dry season and in the hot dry season, as the main crop products have been harvested, livestock can move freely throughout the whole village terroir.

Free-grazing ruminants start to consume crop residues left in the fields and at night, are corralled on selected plots. In Diohine, during the cool dry season, free-grazing herds graze crop residues on plots in home fields, where the residues are more abundant. During the first part of the hot dry season, herds free-graze crop residues in bush fields and fodder resources in the lowlands. During the second part of the hot dry season, herds consume crop residues stored for the purpose by the farmers, who prune trees, mainly Faidherbia albida, for fodder [START_REF] Odru | Flux de biomasse et renouvellement de la fertilité des sols à l'échelle du terroir[END_REF].

The ovine fattening period targets Muslim religious events such as Tabaski, when the demand for live sheep for sacrificial purposes is massive. Bovine fattening is spread out over the entire dry season to produce off-season meat, which requires off-season labor and allows farmers to take advantage of fluctuations in market prices. Diohine opted for "finishing" bovine livestock fattening, i.e., some animals are extracted from the transhumance herds to be fattened, whereas Barry opted for "purchase-resale" livestock fattening.

Fertilization of cropland

Herds' excreta (during free grazing or night corralling), solid manure and mineral fertilizer inflows represent the three main N inputs to the plots. They total 83% of N input flows (IN) at plot level in Diohine and 79% in Barry, the remainder being household waste, seeds and feed refusals by livestock. 1).

During the wet season, the common fallow practiced in Diohine results in a negative average nitrogen balance in livestock-driven flows at plot level: -8.32 kgN ha -1 (Table 2). Nevertheless, the higher livestock stocking rate in Diohine than in Barry in the wet season, results in a higher proportion of TCA benefitting from wet season night corralling (Table 2). The deposition of excreta in the wet season is also more intensive in Diohine (Table 2). Conversely, in the dry season, night corralling accounts for higher proportion of TCA in Barry and is more intensive (Table 2).

Application of solid manure

Solid manure represents 14% of the total plot level IN in Diohine and 12% in Barry (Table 2). The average rate of solid manure application is higher in Barry (482 kgDM ha -1 ) than in Diohine (337 kgDM ha -1 ) (Table 2). Furthermore, the households in Barry terroir are better equipped with horse and donkey carts (86% of households in Barry own a cart versus only 48% in Diohine). The higher equipment rate combined with higher solid manure availability results in better spatial distribution of solid manure, since a larger proportion of the TCA is manured;

31% of the TCA is manured each year in Barry versus 22% in Diohine (Table 2).

Application of mineral fertilizers

Application of mineral fertilizer accounts for most of the plot inputs in Barry (27% of IN in Barry versus 8% Diohine) (Table 2). Mineral fertilizers are applied to a bigger proportion of the land in Barry (26% of the TCA) and fertilization is also more intensive, the average application rate in Barry is more than five times higher than in Diohine (Table 2).

Sustainability of the two village terroirs

This section presents the main differences in the sustainability indicators at the level of the village terroir. Indicators are sometimes also provided at household level to make the differences between the villages more explicit.

Productivity

The yields of the main crops are significantly higher for cereals (millet and sorghum) in Barry whereas groundnut yields are similar in the two villages (Table 3). With the exception of legume hay, total yields of straw are substantially higher in Barry (Table 3). Farmers in Barry harvest a bigger proportion of crop residues to stall-feed their own livestock (Table 3).

Table 3 about here

Meat production is 720% higher (252 kgLW ha -1 year) in Barry than in Diohine (35 kgLW ha -1 year -1 ). Total livestock sales and sales of crop-related products are much higher in Barry (13 kgN capita -1 in Barry versus 1 kgN capita -1 in Diohine).

Dependency

Diohine inhabitants tend toward on-farm consumption and recycling of local biomass resources (crop residues, dung and wooded parkland) while the inhabitants of Barry favor exports-imports based on the use of inputs. Considering that the purchase of human food is similar in the two villages (1.66 kgN capita -1 in Barry and 1.62 kgN capita -1 in Diohine), the main difference in IN is due to the purchase of feed concentrate and mineral fertilizer, with significantly higher inflows of this type in Barry (Table 4). Consequently, self-sufficiency rates for feed and fertilizers are higher in Diohine (see SSFeed and SSFert in Table 4) resulting in a lower dependence (D is 2.03 in Diohine versus 12.66 in Barry; Table 4). 4).

Household practices and household functioning lead to higher nitrogen balance at village terroir level (25 kgN ha -1 for Barry and 9 kgN ha -1 for Diohine) and to a higher average at household level in Barry (24 kgN ha -1 ) than in Diohine (13 kgN ha -1 ). Households with livestock-oriented farming system seem to have higher nitrogen balance at household level. For instance, MRE-SH households (type 2) and HRE-LH households (type 5) have respectively the lowest and the highest stocking rates (Table 1) and nitrogen balance at household level (-0.2 kgN ha -1 and 151.0 kgN ha -1 respectively).

At plot level, the average and median nitrogen balance at plot level do not differ significantly between the two village terroirs (average nitrogen balances at plot level are -23 kgN.ha -1 in Barry and -20 kgN.ha -1 in Diohine).

Flows in Barry are more intense with 7 times higher inflows (IN) and 35 times higher outflows (ON; Table 4). Consequently, the NUE in Barry is 4 times higher than in Diohine at the level of the village terroir (Table 4).

Profitability

The average household agricultural income (AI) is positive in both villages but is 19% higher in Barry (2 292 € year -1 ) than in Diohine (1 850 € year -1 ). Households with limited resources and small herds have the lowest agricultural income (1 028 € year -1 ), while the highest income is obtained by households with ample resources and large herds (3 795 € year -1 ; Figure 5).

Figure 5 about here

Considering the gross margin yields, the average results are negative (-214€ year -1 ha - 1 ). In contrast to AI, this calculation includes the purchase of human food. Different patterns are observed depending on the type of household. Like AI, household with small herds have the lowest gross margin yield (-415€ year -1 ha -1 ) while households with large herds and sufficient resource endowment have the best results (-91€ year -1 ha -1 ; Figure 6).

Traditional extensive systems face a number of limitations

The results of this study are consistent with those of other studies on nutrient cycling in sub-Saharan Africa. The nitrogen balance at plot level is generally negative: -23 kgN ha -1 for Barry and -20 kgN ha -1 for Diohine, and -15 kgN ha -1 on average for West Africa (Schlecht and Hiernaux, 2004), range: -37 kgN ha -1 [START_REF] Stoorvogel | Assessment of Soil Nutrient Depletion in Sub-Saharan Africa: 1983-2000[END_REF]) to 3 kgN ha -1 [START_REF] Krogh | Field and village nutrient balances in millet cultivation in northern Burkina Faso: a village case study[END_REF], indicating that crop production depends to a large extent on mining the soil organic nitrogen reserve [START_REF] Smaling | Soil fertility in Africa is at stake[END_REF][START_REF] Waneukem | Relations entre les formes d'azote organique du sol et l'azote absorbé par la plante dans un sol ferrallitique du Sénégal[END_REF]. In the traditional extensive system, nutrient exports were traditionally counterbalanced by livestock-based nutrient transfers from rangelands and fallows to croplands [START_REF] Bisson | West African mixed farming systems as meta-ecosystems: A sourcesink modelling approach[END_REF]. But the negative nitrogen balances indicate that these systems are no longer sustainable. When the uncultivated area (fallows and rangelands) is too small, the nitrogen transfers generated by the free grazing ruminants do not compensate for the export of crop biomass. This is the case in Diohine where the livestock-driven nitrogen balance in common fallows is negative ( § 3.2.2.1).

From a social point of view, interviews indicated that the traditional system is likely to disappear since the collective fallow system is very demanding in terms of social organization and is called into question by different dynamics including household individualization ( § 1.). This is consistent with the dynamics observed in other sub-Saharan contexts, for example, the appropriation of the organic matter resource [START_REF] Andrieu | From farm scale synergies to village scale trade-offs: Cereal crop residues use in an agro-pastoral system of the Sudanian zone of Burkina Faso[END_REF]. In the new semi-intensive systems (Barry), nutrient mining is offset by external inputs, mainly in the form of feed concentrate in the livestock fattening system, which reintroduces nutrients in the households and in the village terroirs.

Livestock intensification seems to be a sustainable intensification pathway

The main indicators of terroir sustainability are shown in a radial diagram (Figure 7) in which the traditional system (Diohine) is the reference system. The sustainability of each village terroir corresponds to the surface area delineated by the lines linking each indicator's value. The semi-intensive system (Barry) is more sustainable, as the majority of indicators (7 out of 9) are higher for this village terroir.

The system based on livestock fattening is more efficient: nitrogen use efficiency (NUE) is 4 times higher in Barry) and the nitrogen balance in Barry is positive and higher (+16.37 kgN ha -1 year -1 at the terroir level; Table 4). The livestock fattening-based system produces higher average millet yields, millet being the main crop in both villages (Figure 7), i.e. an additional +101 kgDM ha -1 of ears and +595 kgDM ha -1 of millet straw ( § 3.3.1).

Figure 7 about here

Gains in yields of crop residues and additional imported concentrate feeds (+20.3 kgN ha -1 year - by +217 kgLW ha -1 . Meat sales produce an additional cash flow that is used for both crop and household inputs (i.e. mineral fertilizer and human food purchase respectively, Table 4). All in all, this system provides an additional +58.7 kgN ha -1 year -1 of inputs at village terroir level, which is a major advantage, because the soils in sub-Saharan Africa are poor in nutrients and most systems are soil mining systems.

In both Diohine and Barry villages, gross margin yields are negative ( § 3.3.5), leading to the assumption that some household expenditures are covered by off-farm activities, as reported in other studies conducted by the Niakhar observatory [START_REF] Maffray | Etude des relations de genre intégrée dans l'évaluation des performances des unités d'exploitation : cas de la société Sereer dans l'ancien bassin arachidier au Sénégal[END_REF][START_REF] Reiff | Analyse diagnostic du système agraire des pays serères au coeur du "bassin arachidier[END_REF].

Nevertheless, agricultural income (AI) is 24% higher in Barry. Higher incomes and higher meat and crop yields make it possible to maintain a 78% higher population density in Barry than in Diohine ( § 3.1.2). These results confirm the hypothesis proposed by Duncan et al. ( 2013):

livestock fattening-based systems could be way to reduce rural exodus.

Semi-intensive livestock production (fattening or off-season milk production) has already been identified as a relevant option to offset declining cash crop markets in a range of different contexts in sub-Saharan Africa (e.g. Mali, Burkina Faso, Madagascar) (de [START_REF] De Ridder | Milk: the new white gold? Milk production options for smallholder farmers in Southern Mali[END_REF]. In the groundnut basin in Senegal, the incentives for groundnut cultivation declined drastically in the 1970s leading to the rapid reduction in the cultivation of this cash crop and in the use of mineral fertilizers [START_REF] Lericollais | Paysans sereer. Dynamiques agraires et mobilités au Sénégal[END_REF]. Livestock fattening favors the cultivation of cash crops, since the economic gains from livestock rearing are partially invested in inputs like seeds and fertilizers ( § 3.1.2). In the present study, the livestock fattening system appears to be a promising option for agricultural intensification. The expected increase in the demand for meat and milk in sub-Saharan Africa represents an opportunity to increase the attractiveness and sustainability of rural areas if livestock intensification is developed.

Better manure management practices would increase the benefits of higher nutrient inputs in the semi-intensive system

This study confirmed that solid manure is a key resource for the sustainable intensification of agricultural systems in sub-Saharan Africa [START_REF] Rufino | Competing use of organic resources, village-level interactions between farm types and climate variability in a communal area of NE Zimbabwe[END_REF] as the use of mineral fertilizers is still limited in the Senegalese villages studied here (1.09 kgN ha -1 in Diohine and 6.28 kgN ha -1 in Barry). Section 3.3.3 underlined gaps in the nitrogen balance depending on the level of analysis ( § 3.3.3). Indeed, the nitrogen balance is generally negative at plot level and positive at household and village terroir levels. This result is consistent with those of other studies in sub-Saharan Africa [START_REF] Diarisso | Biomass transfers and nutrient budgets of the agro-pastoral systems in a village territory in south-western Burkina Faso[END_REF]. Our in-depth analysis of N flows in farming systems (at the household level) in the two study village terroirs explains these differences in the nitrogen balance by inefficient use of organic fertilizers produced by livestock: urine and solid manure. In both villages, some of the N produced on-farm accumulates in the holdings and is not applied to the plots. Differences between N balances at plot and village terroir levels are even bigger in Barry ( § 3.3.3) where solid manure recycling is less efficient. Our analysis of N flows at household level indicates that recycling of solid manure depends to a great extent on the type of household ( § 3.1.3). Paradoxically, the more solid manure that is available, the less is applied per TLU. What is more, the efficient use of solid manure depends to a great extent on the orientation of the household's farming activities.

For instance, in Barry, households that focus on the livestock trade (the HRE-LH, type 5), do not pay much attention to cropping and nor efficiently recycle solid manure, as they use the income they obtain by fattening livestock to buy a large part of their human food. In contrast, households that focus on both trading livestock and growing cash crops such as MRE-MH, type 3, recycle solid manure more efficiently. These results are consistent with those of other studies conducted in sub-Saharan Africa [START_REF] Dugue | Les transferts de fertilité dus à l'élevage en zone de savane[END_REF][START_REF] Rufino | Analysing integration and diversity in agroecosystems by using indicators of network analysis[END_REF][START_REF] Schlecht | A critical analysis of challenges and opportunities for soil fertility restoration in Sudano-Sahelian West Africa[END_REF].

The transition from the extensive system, (i.e., that used in Diohine village) where excreta is directly deposited on fields by livestock, to the semi-intensive system (i.e., that used in Barry village) where solid manure is collected, stored, matured and spread on the fields by humans, calls for new knowledge and means of production to enable more efficient use of solid manure. Indeed, opportunities to improve crop-livestock integration and soil fertility were identified with local stakeholders during participatory workshops [START_REF] Audouin | Identification de voies d'amélioration de la fertilité des sols par atelier participatif[END_REF]. [START_REF] Audouin | Réintroduire l'élevage pour accroître la durabilité des terroirs villageois d'Afrique de l'Ouest Le cas du bassin arachidier au Sénégal[END_REF], the environmental, technical and economic impacts of the most promising option were evaluated for both villages: improvement of solid manure recycling by increasing solid manure transport capacity (i.e. more horse drawn carts) and the creation of manure pits like those experimented in Burkina Faso [START_REF] Blanchard | Comment évaluer un processus innovant ? Cas de l'amélioration quantitative et qualitative de la fumure organique au champ[END_REF].

Appendix 8

This evaluation revealed more opportunities for improvement in households with higher livestock stocking rates and where livestock-fattening activities predominate (Appendix 8).

Use of feed concentrate increases system dependency but also improves its resilience in the face of local climate variability

However, livestock fattening-based systems still require large amounts of imported feed to maintain a high livestock stocking rate (2.31 UBT ha -1 ). All the farmers in Barry import a total of 411 * 10 3 kgDM of feed concentrate annually ( § 3.3.2.) thereby increasing the dependence of village terroir on external inputs, which is 6.7 times higher in Barry than in Diohine.

The use of feed concentrate is questionable. While it reduces household autonomy and exposes the households to fluctuations in the price of cereals and industrial by-products, it also reduces the pressure created by the production system on local natural resources (e.g. soil and trees) and renders them less sensitive to local climate hazard (Grillot et al., 2018b). Indeed, in a traditional system (such as Diohine) the wooded parkland is subject to high pressure to feed livestock in dry years to counterbalance the shortage of crop residues ( § 3.2.1.). The sustainability of traditional systems is thus called into question during long periods of drought.

This was the case during the droughts in the 1970s and 1980s that led to the decline of Faidherbia albida parklands [START_REF] Ndiaye | Analyse par télédétection de la dynamique d'occupation du sol dans trois terroirs villageois du vieux bassin arachidier au Sénégal sur la période 1968-2016[END_REF]. In a livestock fattening-based system (such as that in Barry), the lack of fodder in dry years has less impact since feed concentrates account for most of livestock's feed ration. In a context of rapid climate change and marked climate uncertainty [START_REF] Roudier | The impact of future climate change on West African crop yields : What does the recent literature say ?[END_REF] as well as ongoing land saturation [START_REF] Dongmo | Designing a process of comanagement of crop residues for forage and soil conservation in Sudano-Sahel[END_REF], livestock fattening is attractive because the animals are kept in barns and stall-fed using feed resources most of which are imported from outside the villages.

Conclusion

This article reports the results of comparative analysis of two existing village terroirs that use contrasted agricultural systems based on different livestock activities. The system used in the village of Diohine is close to the Serer's traditional agro-sylvo-pastoral system organized around grazing livestock and common fallow. The system used in the second village, Barry, is organized around stall-fed livestock fattening.

Diohine is an old village terroir where the intergenerational social hierarchy plays a predominant role in the collective management of local resources. Rangelands and common fallow play a key role in supporting the mobile livestock that drive biomass and nutrient transfers in the landscape. But limited extent of rangelands result in insufficient nutrient transfers from rangelands to croplands that no longer compensate for the export of nutrients in the form of grains and residues from crop fields. This calls the sustainability of this traditional system into question.

Barry village terroir is more recent. It has evolved toward a more individual and intensive resource management system, in which the use of feed concentrate and mineral fertilizer plays an important role. Feed concentrate for livestock fattening represent a major household N inflow. The livestock fattening system enables higher sustainability in terms of productivity, profitability, and soil fertility (i.e. the nitrogen balance). Indeed, this systems enables a higher livestock stocking rate, which, in turn, makes organic matter more available, leading to higher crop and livestock N productivity (+39 % for crop main products, +45 % for crop by-products, +720% for meat). Additional cash flows (+24%) make it possible to increase crop and household inputs (mineral fertilizers and human food) resulting in a 2.93 times higher village terroir N balance and a 78% higher population density.

This study reinforces the hypothesis that livestock fattening is a promising pathway for the sustainable intensification of agricultural systems in rural areas in sub-Saharan Africa, and hence to reduce rural exodus. However, the increased quantities of solid manure that would then become available need be used more efficiently, by increasing its return and its benefits to crops, and by reinforcing crop-livestock integration. The main limitation of the system based on livestock fattening is that imports of feed concentrates increase the dependency of households and villages on external inputs and hence their sensitivity to fluctuating market prices; on the other hand, livestock fattening reduces the pressure on local natural resources and reduces sensitivity to local climate variability.

columns, color

columns, color

columns, color

columns, color

( 2 )

 2 AFB) as follows: AFB= ((FPp,c -FHp,c)*Cc) -FNb (If AFB = 0 then AII = 0 and AIO = 0 (3) If AFB > 0 then AII = 0 and AIO = AFB (4) If AFB < 0 then AII = -AFB and AIO = 0 (5) where FPp and FHp are respectively the fodder produced and the fodder harvested per plot p defined by the household's practices. Cc is a consumption coefficient per type of crop c since crop residues are not completely consumed by the livestock. FNb is the quantity of crop residues needed for each batch b of animals belonging to the household. The quantity of crop residues required is calculated based on the size of the batch, the feeding practices of each batch and the standard forage intake per TLU (Appendix 2). Excretion flows between households are described for each household as (i) the amount of excretion by the household herd on external plots (AEO in kgDM season -1 ) and (ii) amount of excretion by the external herd on plots belonging to the household in kgDM season -1 ). They are calculated as follows: AEO= (LUb,l*ATb,l*DR)*(TAl -Al)ATb,l are respectively the size of the batch of animals b (in TLU) and the length of time (in hours) spent by each batch of animals b in the landscape concerned, unit l. DR is

Figure 4

 4 Figure 4 about hereDuring the cropping season, i.e. the wet season and the beginning of the cool dry season, livestock can damage crops. Consequently, some of the ruminants (bovine, ovine, goats) are removed from the village terroir for transhumance to sylvo-pastoral regions of Senegal, for example, the Saloum and Ferlo regions. The remaining livestock are kept away from crops in the lowlands and common fallows in Diohine (Figure3). As a result, Diohine supports a bigger free-grazing herd during the wet season than Barry (0.56 TLU ha -1 in Diohine versus 0.35 TLU ha -1 in Barry). On the other hand, Barry strongly invests in livestock fattening (0.57 TLU ha -1

Figure

  Figure 6 about here

FiguresFigure 1 .

 1 Figures

Figure 2 .

 2 Figure 2. Conceptual stock-flow model of the system studied with three interlocking systems: plot, household and village terroir

Figure 3 .

 3 Figure 3. Agro-ecological zoning of Diohine (left) and Barry (right) during the 2012-2013 cropping season.

Figure 4 .

 4 Figure 4. Livestock farming and cropping practices intensity described as a function of the seasons in the Niakhar region in the former groundnut basin of Senegal

Figure 6 :Figure 7 :

 67 Figure 6: Average gross margin yield according to the type of household in the 2012-2013 cropping season

Figure 1 .

 1 Figure 1. Portion of holdings that practice livestock fattening in 2012 in the 30 village terroirs of the Niakhar demographic and heath observatory (Delaunay et Lalou, 2012).

Figure

  Figure

Figure 2 .

 2 Figure 2. Conceptual stock-flow model of the system studied with three interlocking systems: plot, household and village terroir

Figure 3 .

 3 Figure 3. Agro-ecological zoning of Diohine (left) and Barry (right) during the 2012-2013 cropping season.

Figure 4 .Figure 6 :Figure 7 :

 467 Figure 4. Livestock farming and cropping practices intensity described as a function of the seasons in the Niakhar region in the former groundnut basin of Senegal 2 columns

Table 2 about here 3.2.2.1. Direct deposition of excreta during free grazing and night corralling

 2 The deposition of livestock excreta during free-grazing (excluding night corralling) represents 46% of the total plot IN in Diohine versus 25% in Barry (Table2). In the dry season, in Diohine, a large proportion of by-products is left for free-grazing herds. In terms of N flows, biomass extraction (crop residues or grass) is barely returned via feces and urine (the balance of livestock-driven flows at plot level is on average +0.55 kgN ha -1 Table2). In contrast, in Barry, the free grazing practice results in a positive balance of livestock-driven flows (on average +5.04 kg N ha -1 Table2) since the livestock stocking rate is high and livestock feed is supplemented with feed concentrate. Feed concentrates represent on average, 30% of the feed ration in terms of N in Barry. Indeed, cash oriented households (MRE-MH and HRE-LH), two types of households only represented in Barry, harvest most crop by-products on their fields and supplement their animals' rations with feed concentrate, resulting in the highest free-

grazing and night corralling balance (+8.43 and +9.93 kgN ha -1 for MRE-MH and HRE-LH respectively, Table

Table 4

 4

	about here

Table 2 )

 2 . As the livestock systems differ markedly in the two villages, flows linked to free grazing (free-ranging deposition of excreta and plant withdrawal, deposition during night corralling) are highest in Diohine (TST>IN, Table4), while inflows and outflows linked to livestock related (livestock, fodders, concentrate feeds) are highest in Barry (TST<IN) (Table

Table 1 .

 1 Main features of the five types of household in Diohine and Barry

	846	Appendix 1: Conversion factors from local to standard units
		Category Indicator	Unit	Value	Origin or reference
		Seeds
		bag of cabbage seeds	kgFM		0.3 survey
		bag of chili seeds	kgFM		0.3 survey
		bag of eggplant seeds	kgFM		0.3 survey
		bag of tomato seeds	kgFM		0.3 survey
		basin of bissap seeds (Hibiscus	kgFM		6.0 estimated
		sabdariffa)
		basin of groundnut seeds	kgFM		30.0 survey
		cup of onion seeds	kg FM		0.1 survey
		handful of bissap	kgFM		0.1 calculated
		handful of cowpea	kgFM		0.2 calculated
		handful of groundnut	kgFM		0.2 calculated
		handful of okra	kgFM		0.1 survey
		heap of cassava seeds	kgFM		0.5 survey
		pot of onion seeds	kgFM		0.1 survey
		seed drill of groundnut	kgFM		5.0 survey
		seed drill of sorghum	kgFM		2.0 survey
		1L of bissap seeds	kgFM		0.9 weighed
		1.5L bottle of cowpea seeds	kgFM		1.5 weighed
		10L container of sorghum grains	kgFM		10.0 survey
		20L container of cowpea seeds	kgFM		20.0 weighed
		1kg tomato pot of bissap seeds	kgFM		0.9 weighed
		1kg pineapple pot of bissap seeds	kgFM		0.4 weighed
		50kg bag of groundnut seeds	kgFM		55.0 survey
		Organic matter
		basin of solid manure	kgFM		5.6 survey
		basin of leftover feed	kgFM		17.0 estimated
		basin of waste	kgFM		7.0 weighed
		bucket of waste	kgFM		3.5 weighed
		horse cart of solid manure	kgFM	280.0 survey
		donkey cart of solid manure	kgFM	186.7 survey
		cart of leftover feed	kgFM	180.0 estimated
		cart of solid manure free of leftover feed kgFM	315.0 calculated

Table 2 .

 2 Main indicators of crop fertilization at plot level, average results for the total cultivated area (TCA) in Diohine and Barry for the 2012-2013 cropping season

	Indicator

Table 4 .

 4 N flows entering, leaving, and circulating within village terroirs and corresponding N-flowbased indicators at village terroir level for Diohine and Barry for the 2012-2013 cropping season

	Units	Diohine	Barry

Table 1 .

 1 Main features of the five types of household in Diohine and BarryTable(Editable version)

	Number given to type		1	2	3	4	5
	Code name of type		LRE-SH MRE-SH MRE-MH HRE-MH HRE-LH
	Livestock stocking rate	TLU ha -1	1.3	1.3	3.1	3.6	3.7
	Importance of livestock fattening % of total TLU 23	15	32	03	59
	Population density	capita ha -1	4.5	2.8	4.2	3.1	6.3
	Total cultivated area	ha	3.8	5.5	5.2	5.3	4.9
	Importance of groundnut	% of TCA	26	19	32	8	20
	Importance of fallow	% of TCA	2	11	2	19	0
	Free-grazing plant biomass	kgDM ha -1	-225	-61	-2	3451	-566
	balance (ΔFG)	year -1
	Manure inputs during night	kgDM ha -1	113	25	218	758	323
	corralling	year -1
	Free-grazing and night corralling	kgN ha -1 year -1 0.15	2.99	8.43	3.69	9.93
	balance
	Availability of solid manure from	TLU.h	24843	19431	49274	12505	95522
	livestock housed in barns
	Solid manure input rate per	kgN TLU.h -1 0.00030 0.00063 0.00040 0.00055 0.00012
	livestock tethered close to the
	homestead
	Nitrogen balance at household	kgN ha -1 year -1 52.6	-0.2	42.4	43.0	151.0
	level
	Percentage of household in	%	11	78	0	11	0
	Diohine
	Percentage of household in Barry %	26	49	19	0	6

in Barry) support a higher livestock stocking rate( § 3.1.2)., which, in turn, results in higher organic matter availability and use in Barry (+145 kgDM ha -1 ). It also increases meat production

barrel

Free grazing of plant biomass outside the boundaries of the village

Free grazing of plant biomass outside the boundaries of the village

Acknowledgements

The authors thank the 117 surveyed farmers for their availability and their interest in the study. They also thank Ibrahima Thiaw and Mamadou Lamine Ndiaye, cartography students at Dakar Cheikh Anta Diop University (UCAD), who performed parts of plot georeferencing and produced the maps used in this article. This research was supported by the European Union [grant number FP7-KBBE-2010 AnimalChange project]; and the French national research agency [grant number ANR-13-Agro-002 Cerao project].