Eric Justes

How to implement biodiversity-based agriculture to enhance ecosystem services: a review

Intensive agriculture has led to several drawbacks such as biodiversity loss, climate change, erosion, and pollution of air and water. A potential solution is to implement management practices that increase the level of provision of ecosystem services such as soil fertility and biological regulation. There is a lot of literature on the principles of agroecology. However, there is a gap of knowledge between agroecological principles and practical applications. Therefore, we review here agroecological and management sciences to identify two facts that explain the lack of practical applications: (1) the occurrence of high uncertainties about relations between agricultural practices, ecological processes, and ecosystem services, and (2) the site-specific character of agroecological practices required to deliver expected ecosystem services. We also show that an adaptive-management approach, focusing on planning and monitoring, can serve as a framework for developing and implementing learning tools tailored for biodiversity-based agriculture. Among the current learning tools developed by researchers, we identify two main types of emergent support tools likely to help design diversified farming systems and landscapes: (1) knowledge bases containing scientific supports and experiential knowledge and (2) model-based games. These tools have to be coupled with well-tailored field or management indicators that allow monitoring effects of practices on biodiversity and ecosystem services. Finally, we propose a research agenda that requires bringing together contributions from agricultural, ecological, management, and knowledge management sciences, and asserts that researchers have to take the position of “integration and implementation sciences.”

Phosphorus availability and microbial community in the rhizosphere of intercropped cereal and legume along a P-fertilizer gradient

Background and aimsPositive 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.MethodsA 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.ResultsPhosphorus 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.ConclusionsP-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.

Peaks of in situ N2O emissions are influenced by N2O producing and reducing microbial communities across arable soils

Agriculture is the main source of terrestrial N2 O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2 O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2 O-reducers (nosZII) was related to the potential capacity of the soil to act as a N2 O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N2 O-producers and N2 O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2 O emissions. The abundance of both ammonia-oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as inxa0situ N2 O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the inxa0situ N2 O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N2 O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of inxa0situ N2 O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2 O-reducing bacteria to agricultural practices and how it may ultimately affect N2 O emissions.

A new plug-in under RECORD to link biophysical and decision models for crop management

Developing sustainable crop systems is a major challenge. Presently, management practices are simulated using either biophysical models or simple farmer decision models. As a result, there is a lack of generic models integrating both biophysical parameters and farmer decision parameters. Here, we developed an original graphical plug-in to sketch and implement decision-making models and to link them with biophysical models. For that, we used the RECORD platform, standing for REnovation and COORDination of agro-ecosystem modeling. Different pop-up windows allow to create the model using a decision formalism then to implement the model under the RECORD platform. The sequence of technical operations is formally modeled as a direct multi-graph without retroaction. The plug-in allows defining activities, relation between activities, and decision rules to trigger the different activities. The resulting model is independent of any biophysical model and can then be linked with different crop models. An example is given on an innovative cropping systems part of the MicMac-Design project. The decision-making model is then linked with the STICS crop model.

Eco-functional Intensification by Cereal-Grain Legume Intercropping in Organic Farming Systems for Increased Yields, Reduced Weeds and Improved Grain Protein Concentration

Intercropping, i.e., simultaneously growing two (or more) species in the same field for a significant period of time but without necessarily concomitant sowing or harvest, is a practice aimed at eco-functional intensification.

Behaviour of S-metolachlor and its oxanilic and ethanesulfonic acids metabolites under fresh vs. partially decomposed cover crop mulches: A laboratory study

At the time of spring pre-emergent herbicide application, the soil surface in conservation agriculture is most of the time covered by cover crops (CC) mulches. The state of these mulches depends on their destruction date and on the selected species. Sorption and degradation of 14C-S-metolachlor on and within 8 decaying CC-covered (2 speciesu202f×u202f4 initial decomposition state) soils corresponding to conservation agriculture were compared to its fate in bare soil (BS) corresponding to conventional agriculture. 14C-S-metolachlor and its metabolites distribution between mineralized, extractable and non-extractable (NER) fractions was determined at 5 dates during a 20u202f°C/84-d period. Herbicide mineralization was weak (<2%) for both CC and BS. Extractability of 14C in BS was intermediate between CC that were decomposed 28 or 56u202fdays and 0 or 6u202fdays before application. Degradates consisted in up to 43% of total radioactivity, with specificities according to the CC or soil compartment. NER formation was equivalent in BS and in the much decomposed CC-amended microcosms, and was stronger in less decomposed CC. S-metolachlor DT50 was 23-d in BS, and 9, 15, 39 and 25-d for CC ordered by increased decomposition state at the time of application. These results were attributed to the proportion of 14C intercepted by CC, and to higher levels of organic matter and microbial activity in less decomposed CC as compared with more decomposed ones. Then the state of decomposition level of CC residues determines the behaviour of SMOC (S-metolachlor) sprayed on the mulch in the conditions of conservation agriculture.

Crucifer-legume cover crop mixtures provide effective sulphate catch crop and sulphur green manure services

Background and aimsCrucifers grown as cover crops are known to reduce sulphate leaching (S catch-crop service) and release large amounts of mineral sulphate for the subsequent cash crop once incorporated into the soil (S green-manure service). Crucifer-legume cover crop mixtures are effective to obtain high nitrogen related services, but few data exist on their performances for S-related services. Our study aimed to assess performances of a wide variety of bispecific crucifer-legume mixtures designed to provide soil S catch-crop and S green-manure services.MethodsA two-year field experiment was conducted at two sites near Toulouse, France (silt clay loam soil) and Orléans, France (sandy loam soil) in which cultivars from eight crucifer species and nine legume species were tested as sole and bispecific cover crops.ResultsCrucifer-legume mixtures and crucifer sole cover crops provided the same level of S catch-crop service (12xa0kgxa0Sxa0ha−1), significantly higher than that of legume sole cover crops (4xa0kgxa0Sxa0ha−1). Similarly, crucifer-legume mixtures provided almost the same level of S green-manure service (5.5xa0kgxa0Sxa0ha−1) as crucifer sole cover crops (6.5xa0kgxa0Sxa0ha−1).ConclusionOur results demonstrate the compatibility and complementarity of certain crucifer and legume species when grown together to provide S and N catch-crop and green-manure services. For a same cover crop species no strong cultivar effect has been highlighted in our growing conditions.

Correction to: Yield gap analysis extended to marketable grain reveals the profitability of organic lentil-spring wheat intercrops

Due to an unfortunate turn of events, the names of the authors appeared incorrectly in the original publication as given names and family names have been reversed. The correct representation of the authors’ names is listed above and below and should be treated as definitive.

Main Lessons Drawn from the Simulation Study

The study of the literature relative to the impact of cover crops on nitrate leaching, and hence their primary role as “nitrate-trapping” catch crops in annual cropping systems, reveals a lack of data relating to certain regions in France. The same is true concerning their impact on other variables, such as the water balance or the yield of the next crop. However, since the planting of cover crops has become compulsory in all vulnerable zones since 2012, it is of the utmost importance to assess how effective they are in terms of reducing the nitrate concentration of drainage water, as a function of the soil and climate context in a broad range of French conditions. By doing so, it will be possible to optimize the associated management technique and identify situations in which their use may have negative consequences on the next crop and, potentially, on groundwater recharge.

Main Lessons Drawn from the Analysis of the Literature

Planting and destruction are the two main phases in cover crop management techniques. Their dates and implementation conditions play a key role in terms of the various functions targeted for these crops (nitrate-trapping, erosion prevention, weed control, effect on next crop, etc.). The analysis of the literature therefore focused on cover crop planting and destruction techniques. The aim was to identify the different methods and, if possible, their effectiveness with respect to the success of sowing and destruction. The issue of the implementation of these techniques by farmers was then examined by analysing the constraints in terms of organization of labour and implementation costs.