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In sub-Saharan Africa, long-term maize cropping with low external inputs has been associated with the loss of soil fertility. While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with mineral N on the change of soil organic carbon concentrations (SOC) over time (and SOC stocks in the year 2021) in four ongoing long-term trials in Kenya. These trials were established with identical treatments in moist to dry climates, on coarse to clayey soil textures, and have been managed for at least 16 years. They received organic resources in quantities equivalent to 1.2 and 4 t C ha−1 per year in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality, intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard manure (variable quality, intermediate turnover). Furthermore, the addition or absence of 240 kg N ha−1 per year as mineral N fertilizer was the split-plot treatment. At all sites, a loss of SOC, rather than gain, was predominantly observed due to a recent conversion from permanent vegetation to agriculture. The average reduction of SOC concentration over 19 years in the 0 to 15 cm depth ranged from 42 % to 13 % of the initial SOC concentration for the control and the farmyard manure treatments at 4 t C ha−1 yr−1, respectively. Adding Calliandra or Tithonia at 4 t C ha−1 yr−1 limited the loss of SOC concentrations to about 24 % of initial SOC, while the addition of saw dust, maize stover (in 3 of 4 sites) and sole mineral N addition, showed no significant reduction in SOC loss over the control. Site specific analyses, however, did show, that at the site with the lowest initial SOC concentration (about 6 g kg−1), the addition of 4 t C ha−1 yr−1 farmyard manure or Calliandra plus mineral N led to a gain in SOC concentrations. All other sites lost SOC in all treatments, albeit at site specific rates. While subsoil SOC stocks in 2021 were little affected by organic resource additions (no difference in 3 of 4 sites), the topsoil SOC stocks corroborated the results for SOC concentrations. The relative annual change of SOC concentrations showed a higher site specificity in high-quality organic resource treatments than in the control, suggesting that the drivers of site specificity in SOC buildup (mineralogy, climate) need to be better understood for effective targeting of organic resources. Even though farmyard manure showed the most potential for reducing SOC loss, our results clearly show that maintaining SOC with external inputs only is not possible at organic resource rates that are realistic for small scale farmers. Thus, additional agronomic interventions such as intercropping, crop rotations or strong rooting crops may be necessary to maintain or increase SOC., EGUsphere

Usually grown between two cash crops in an annual rotation, cover crops can increase species diversity and provide a number of ecosystem-services as an efficient tool to support sustainable agricultural production based on the principles of agroecology. Brassicaceae or crucifers cangenerate glucosinolate-related biocidal effects both during the growing period when hydrolysis products such as isothiocynalates are released in the rhizosphere around the growing roots or when tissue disruption occurs following cover crop termination and incorporation. The new paradigm of multi-service cover crop has been proposed by Couedel et al. (2019) to capture these multiple benefits and emphasise the need to refocus cover crop biocontrol research from a largely “pesticide” paradigm, targeting maximum production of bioactive compounds by sole crucifer cover crops, to a multi-service paradigm in which selected crucifer-legume mixtures may offer promise in the quest for the sustainable intensification of agriculture. By taking a wider systems approach, beyond pest management, and then by using a multi-service paradigm, cover crops may enhance the physical, chemical and biological fertility of the soil. Understanding the trade-offs between abiotic and biotic services within a system approach is now key to assess services and disservices provided by cover crop mixtures. Now, the potential provision of multi-services depends on species or mixture of species, the management of the cover crop, the pedo-climatic conditions and the cash crop sequence involved. We showed that the biocontrol services of crucifer sole crops could be largely maintained in crucifer-legume mixtures while improving nutrient services and C sequestration, and reducing potential disservices, such as water and nitrogen pre-emptive negative effects for the following cash crop. However, multi-service cover crop mixtures cannot be seen as a stand-alone solution to manage pests and pathogens, but it is likely that adequate levels of control will require combinations with other pest management tactics.

Multi-service cover crops grown during the fallow period between two main cash crops are a tool to support sustainable crop production. Crucifer-legume mixtures may provide improved multi-ecosystem services compared to sole cover crops, but trade-offs between the known crucifer biocontrol potential and N cycling benefits of legumes are uncertain. We review suppressive effects of crucifers as sole crops and in mixtures with legumes for a wide range of pathogenic and beneficial organisms to compare the services and potential disservices of the strategies. We conclude that biocontrol services of crucifer sole crops could be largely maintained in crucifer-legume mixtures while improving nutrient services, and reducing potential disservices. The lack of comprehensive multi-disciplinary field studies that investigate the multi-service paradigm limit our current understanding of the trade-offs between services, but reveal fruitful research opportunities. We emphasize the need to refocus cover crop biocontrol research from a largely “pesticide” paradigm targeting maximum production of bioactive compounds by sole crucifer cover crops, to a multi-service paradigm in which selected crucifer-legume mixtures may offer promise in the quest for the sustainable intensification of agriculture.

Intensifying production on existing plantation area can help Indonesia to meet palm oil production goals and avoid massive conversion of natural ecosystems. Yield potential is the yield of a well-adapted cultivar when grown without water and nutrient limitations and without incidence of biotic stresses such as weeds, insect pests, and pathogen. The yield gap is defined as the difference between yield potential and current average farmer yield. Smallholder plantations comprise about 44% of the total of 12 million ha of Indonesian oil palm plantation. Estimated average fresh fruit bunch yield (FFB) in large plantations and, especially, smallholder plantations is well below yield reported for top producing oil palm blocks which is close 30 t FFB/ha/y. Indeed, national average yield is ca. 18 t FFB per ha. Hence, there is a large gap between current oil palm yield and the yield potential as determined by climate and soil, which suggests that there is significant room for increasing palm oil production on existing plantation area. However, estimates of yield potential obtained following a consistent, robust protocol that makes use of the best available sources of (weather, soil, and management) data are lacking for major oil palm producing areas in Indonesia. Here we describe a protocol for estimating yield gap in oil palm in mineral soils in Indonesia following the principles of the Global Yield Gap Atlas (www.yieldgap.org). We used a combination of best available sources of weather, soil, and agronomic practices, a recently upgraded oil palm simulation model (PALMSIM), and spatial analysis to estimate average long-term yield potential and yield gaps for oil palm in 22 locations across the archipelago. These site-specific estimates of yield potential and yield gap were subsequently up-scaled from local to regional and national levels. Production potential for different scenarios of crop intensification and land use change are discussed.

Multi-service cover crops (MSCC) grown during fallow period between two cash crops provide various ecosystem services. Among species used as MSCC, crucifers can efficiently prevent nitrate and sulphate leaching by catching residual soil mineral nitrogen (N) and sulphur (S) after the preceding cash crop (N and S catch crop services). Crucifers also have a unique capacity to suppress pathogens due to the biocidal hydrolysis products of endogenous secondary metabolites called glucosinolates (GSL). The aim of our study was to assess the provision of various ecosystem services linked to N, S cycles and biocontrol potential for a wide range of bispecific crucifer-legume mixtures in comparison to sole cover crops of legume and crucifer. We carried out experiments in 2 contrasted sites (Toulouse and Orléans regions, France) during 2 years in order to assess these services and the compatibility of various bi-specific crucifer-legume mixtures. We tested a great diversity of species, such as i) crucifers : rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket, and ii) legumes: Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin. Our study demonstrated that crucifer-legume mixtures can provide and mutualize various ecosystem services by reaching from 2 thirds (GSL production, S and N green manure) to the same level of service (N and S catch crop) than the best sole family of species. GSL profile and concentration did not change in mixtures meaning that cruciferpests interactions were identical. Through a literature review we also illustrated that biocontrol services of crucifers could be largely maintained in crucifer-legume mixtures for a wide range of pathogens and weeds while reducing potential disservices on beneficials and increasing N related services.

Cover crops grown in rotation with cash crops provide ecosystem services by reducing pollution and anthropogenic inputs. Among cover crop families, crucifers can efficiently prevent nitrate and sulphate leaching by catching residual soil mineral nitrogen (N) and sulphur (S) (N and S catch crop services). Crucifers also have a unique capacity to suppress pathogens due to the biocidal hydrolysis products of endogenous secondary metabolites called glucosinolates (GSL). However, compared to legume cover crops, crucifers provide less mineralised N to the subsequent main cash crop (N green manure service). Bispecific crucifer–legume cover crop mixtures can be seen as a potential solution to increase biodiversity and to combine ecosystem services of both species. However there is a lack of information on the impact of plant–plant interaction on levels of ecosystem services linked to the N and S cycles and GSL production compared to sole crops. The aim of our study was to assess production of all these ecosystem services for a wide range of bispecific crucifer-legume mixtures in comparison to sole crops. Experiments were conducted at two sites (near Toulouse and Orléans, France) over two years where few cultivars from eight crucifers (rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket) and nine legumes (Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin) were tested in sole-crop and in 98 bispecific mixtures (substitutive design of 50%-50% sole crops). Crucifer - legume bispecific mixtures provided the same N and S catch crop service (mean soil acquisition of 50 kg N ha-1 and 12 kg S ha-1) and significantly increased the N green manure service (mean mineralisation of 22 kg N ha-1) compared to pure crucifers (mean mineralisation of 8 kg N ha-1). Despite half the density of crucifers, S green manure service was only reduced by 15% in the mixture (mean mineralisation of 5.5 kg S ha-1). Furthermore, crucifers in mixtures have the same GSL types and concentrations as in sole crops while they tend to have more biomass per plant. As a result, despite halving the crucifer density, GSL production on an area basis declined by only 19% in mixtures. On a species basis, despite the high and variable competition for abiotic resources generated by crucifers, no incompatibility of development was observed in mixtures. Overall crucifers and legumes are sufficiently complementary to provide the expected multi-ecosystem services. Our study confirms for a wide range of cover crop species and on 4 sites x years that crucifer-legume mixtures can provide multi-ecosystem services beyond well-known N management services. Therefore it can be recommended to diversify the species included in cover crops in order to provide a high level of multi-ecosystem services and to secure the success of cover cropping.

Ce numéro est constitué d’articles issus du colloque CIMS : Des Cultures Intermédiaires Multi-Services pour une production agroécologique performante, organisé le 4 octobre 2017 à Auzeville.; Cover crops are used to produce ecosystem services, particularly for nitrogen management, such as“nitrate catching” and "green manure" effects. Sowing cover crop mixtures including legumes and nonlegumeshave the advantage of combining the production of both services thanks to phenomena ofniche complementarity and / or facilitation in the capture of abiotic resources. When complementaritiesare optimized, these mixtures can achieve both effects similarly to those produced by the average ofmonospecific cover crops. The best performances are mainly obtained when the availability of mineralnitrogen at sowing is low, which is in agreement with the conclusions from the literature on arable crops.In addition, the complementarity for the access to light thanks to species having different aerialarchitectures and contrasted temporal complementarities enable to obtain effective mixtures producing"relay" services, in particular in the case of long fallow periods. However, in order to achieve the desiredeffects, care should be taken to limit competition between species.; Les cultures intermédiaires sont utilisées pour produire des services écosystémiques, notamment pourla gestion de l’azote par des fonctions « engrais vert » et « piège à nitrate ». Semer des mélanges decultures intermédiaires comprenant des légumineuses et des non-légumineuses permettrait decombiner la production de ces services grâce à des phénomènes de complémentarité de niche et/ou defacilitation dans la capture des ressources abiotiques. Lorsque les complémentarités sont optimisées,ces mélanges peuvent atteindre des performances proches de celles produites par la moyenne descultures monospécifiques. Les meilleures performances sont principalement obtenues lorsque ladisponibilité en azote minéral est faible lors du semis des cultures intermédiaires multi-services, ce quiest en concordance avec les conclusions issues de la littérature sur les cultures de vente. De même, lacomplémentarité pour l’accès à la lumière grâce à des espèces ayant des architectures aériennesdifférentes et des complémentarités temporelles contrastées permet d’obtenir des mélanges efficacespour produire des services en « relais », notamment dans le cas d’intercultures longues. Cependant,pour obtenir les effets escomptés il faut veiller à limiter la compétition entre les espèces.

Ce numéro est constitué d’articles issus du colloque CIMS : Des Cultures Intermédiaires Multi-Services pour une production agroécologique performante, organisé le 4 octobre 2017 à Auzeville.; Crucifers cover crops have a strong potential for pathogen control (fungi, bacterias, nematodes,weeds, …) thanks to the production of secondary metabolites called glucosinolates. These allelopathiceffects can occur during the crop growing period and can be increased at cover crop termination when alarge quantity of glucosinolates is degraded into the soil (biofumigation principle). Beyond theirpathogen control services these molecules could engender negative effects on beneficials fungi andbacterias. It corresponds to disservices that have to be taken into account according to the specificitiesof the considered agroecosystem. A high variability of allelopathic effects efficiency is sometimesobserved among different studies and can be explained by the influence of both environment andagronomic practices on the glucosinolate production and fate in the soil. Furthermore other factorsinherent of the cover crop use as organic matter incorporation, or host/non-host cover crops effects areinvolved on pest management. Causes of pathogen control (allelopathy or not) are still to be determinefor numerous pathosystems in order to consequently adapt species choices and agronomic practices.; Les cultures intermédiaires de crucifères présentent un fort potentiel de gestion des bioagresseurs(champignons, bactéries, nématodes, adventices, …) via la production de métabolites secondaires àeffet biocide, les glucosinolates. Ces effets allélopathiques peuvent avoir lieu lors de la période deculture mais ils sont accentués lors de la destruction des couverts lorsqu’une grande quantité deglucosinolates est dégradée dans le sol (principe de biofumigation). Au-delà des services de régulationdes bioagresseurs ces molécules peuvent engendrer des effets négatifs sur les champignons etbactéries antagonistes, ce qui correspond à des dis-services qu’il convient de prendre en compte enfonction des problématiques du système de culture considéré. Une forte variabilité d’efficacité desprocessus allélopathiques est parfois observée entre les études et s’explique par l’influence nonnégligeable de l’environnement et de la conduite de culture sur la production de glucosinolates et surleur devenir dans le sol. De plus d’autres facteurs inhérents à l’utilisation de cultures intermédiaires sontimpliqués dans la gestion des bioagresseurs comme notamment l’incorporation de matière organique etles effets hôte/non hôte des couverts. Les causes du contrôle des bioagresseurs (allélopathique ounon) restent à déterminer pour de nombreux patho-systèmes dans le but d’adapter en conséquence lechoix des espèces de couverts et les pratiques culturales.

Les cultures intermédiaires de crucifères présentent un fort potentiel de gestion des bioagresseurs (champignons, bactéries, nématodes, adventices, …) via la production de métabolites secondaires à effet biocide, les glucosinolates. Ces effets allélopathiques peuvent avoir lieu lors de la période de culture mais ils sont accentués lors de la destruction des couverts lorsqu’une grande quantité de glucosinolates est dégradée dans le sol (principe de biofumigation). Au-delà des services de régulation des bioagresseurs ces molécules peuvent engendrer des effets négatifs sur les champignons et bactéries antagonistes, ce qui correspond à des dis-services qu’il convient de prendre en compte en fonction des problématiques du système de culture considéré. Une forte variabilité d’efficacité des processus allélopathiques est parfois observée entre les études et s’explique par l’influence non négligeable de l’environnement et de la conduite de culture sur la production de glucosinolates et sur leur devenir dans le sol. De plus d’autres facteurs inhérents à l’utilisation de cultures intermédiaires sont impliqués dans la gestion des bioagresseurs comme notamment l’incorporation de matière organique et les effets hôte/non hôte des couverts. Les causes du contrôle des bioagresseurs (allélopathique ou non) restent à déterminer pour de nombreux patho-systèmes dans le but d’adapter en conséquence le choix des espèces de couverts et les pratiques culturales., Crucifers cover crops have a strong potential for pathogen control (fungi, bacterias, nematodes, weeds, …) thanks to the production of secondary metabolites called glucosinolates. These allelopathic effects can occur during the crop growing period and can be increased at cover crop termination when a large quantity of glucosinolates is degraded into the soil (biofumigation principle). Beyond their pathogen control services these molecules could engender negative effects on beneficials fungi and bacterias. It corresponds to disservices that have to be taken into account according to the specificities of the considered agroecosystem. A high variability of allelopathic effects efficiency is sometimes observed among different studies and can be explained by the influence of both environment and agronomic practices on the glucosinolate production and fate in the soil. Furthermore other factors inherent of the cover crop use as organic matter incorporation, or host/non-host cover crops effects are involved on pest management. Causes of pathogen control (allelopathy or not) are still to be determine for numerous pathosystems in order to consequently adapt species choices and agronomic practices.