Christophe Naudin

Traits affecting early season nitrogen uptake in nine legume species

Legume crops are known to have low soil N uptake early in their life cycle, which can weaken their ability to compete with other species, such as weeds or other crops in intercropping systems. However, there is limited knowledge on the main traits involved in soil N uptake during early growth and for a range of species. The objective of this research was to identify the main traits explaining the variability among legume species in soil N uptake and to study the effect of the soil mineral N supply on the legume strategy for the use of available N sources during early growth. Nine legume species were grown in rhizotrons with or without N supply. Root expansion, shoot and root biomass, nodule establishment, N2 fixation and mineral soil N uptake were measured. A large interspecific variability was observed for all traits affecting soil N uptake. Root lateral expansion and early biomass in relation to seed mass were the major traits influencing soil N uptake regardless of the level of soil N availability. Fenugreek, lentil, alfalfa, and common vetch could be considered weak competitors for soil N due to their low plant biomass and low lateral root expansion. Conversely, peanut, pea, chickpea and soybean had a greater soil N uptake. Faba bean was separated from other species having a higher nodule biomass, a higher N2 fixation and a lower seed reserve depletion. Faba bean was able to simultaneously fix N2 and take up soil N. This work has identified traits of seed mass, shoot and root biomass, root lateral expansion, N2 fixation and seed reserve depletion that allowing classification of legume species regarding their soil N uptake ability during early growth.

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.

Enhancing planned and associated biodiversity in French farming systems

In a context of global change involving uncertainty in agricultural production, agroecological systems need to reduce their dependency on inputs and increase their resilience. Biodiversity-based techniques are promising, as they provide production services based on biological processes. Tracking farmer practices is an original approach aiming at identifying and analysing alternative systems and supporting the development of these techniques. We studied, for the first time, the on-farm implementation of six biodiversity-based techniques: (i) agroecological infrastructures, (ii) cropped varietal mixtures, (iii) agroforestry, (iv) intercropping, (v) cover cropping and (vi) crop rotation diversification. We first analysed the combinations of these techniques in a large sample of 194 French farmers. A multiple correspondence analysis followed by a hierarchical cluster analysis on principal components resulted in groups of farms with different combinations of these techniques. Then, deeper interviews were conducted with 29 farmers across three regions to analyse the various methods of applying the techniques in the context of their farm and to identify the conditions for their successful implementation. Taking advantage of this large and rare sample of almost 200 interviewed farmers, we identified six different groups of farms. From farms applying mainly cover cropping to comply with European regulations to much diversified farms implying the redesign of the farming system, we support the idea that different strategies of implementation of such biodiversity-based techniques co-exist. The in-depth interviews demonstrated that the level of diversification is related to farm characteristics and four factors mainly favoured the development of such techniques on farms: (1) available labour force and (2) specialised machinery (internal factors) as well as (3) access to market opportunities and (4) the exchange of knowledge through networking (external factors). Surprisingly, the conservation agriculture farmers of our sample did not apply significantly more biodiversity-based techniques. However, our results indicated that organic farmers applied significantly more of these techniques. Our results suggest that enhancing knowledge exchange through networks would favour the broader application of such techniques. It could also be relevant to gather farmers, industries and public authorities to favour the emergence of market opportunities.

Differences for traits associated with early N acquisition in a grain legume and early complementarity in grain legume–triticale mixtures

We grew a grain legume in rhizotrons, alone and mixed with a cereal. There were differences between some of the genotypes of the grain legume but they all demonstrated slow early growth and low ability to absorb mineral soil nitrogen compared to the cereal. The two species were complementary for nitrogen acquisition in the first 2 months of growth. Mixtures showed a higher total soil mineral nitrogen uptake than pure grain legume. Complementarity allowed higher cereal biomass production than in pure cereal, without compromising grain legume growth.