Réduire les fuites de nitrate au moyen de cultures intermédiaires : conséquences sur les bilans d'eau et d'azote, autres services écosystémiques

La présence de nitrate en excès dans les eaux de surface et les nappes phréatiques pose des problèmes de santé publique et de dégradation de l’environnement. C’est d’abord un enjeu de santé publique notamment pour les nappes phréatiques, avec la nécessité de distribuer une eau de boisson présentant une teneur inférieure à la norme de potabilité qui est de 50 mg de nitrate par litre. C’est aussi un enjeu de protection de l’environnement pour les eaux de surface, en particulier pour certains bassins versants proches de la mer, comme en Bretagne ; le transfert rapide du nitrate des zones agricoles vers la mer induit une eutrophisation des zones côtières

Réduire les fuites de nitrate au moyen de cultures intermédiaires : conséquences sur les bilans d'eau et d'azote, autres services écosystémiques : Synthèse du rapport d'étude

Synthèse du rapport d'étude. Le présent document constitue la synthèse de l’étude sollicitée conjointement par le Ministère de l'Ecologie, du Développement Durable et de l'Energie et le Ministère de l’Agriculture et de l’Agroalimentaire et subventionnée par le Ministère de l'Ecologie, du Développement Durable et de l'Energie (étude n° 2100450303). Son contenu n'engage que la responsabilité de ses auteurs. Le rapport d’étude, source de cette synthèse, a été élaboré par les experts scientifiques sans condition d’approbation préalable par les commanditaires ou l’INRA. La synthèse a été validée par les auteurs du rapport

Réduire les fuites de nitrate au moyen de cultures intermédiaires : conséquences sur les bilans d'eau et d'azote, autres services écosystémiques : Synthèse du rapport d'étude

Synthèse du rapport d'étude. Le présent document constitue la synthèse de l’étude sollicitée conjointement par le Ministère de l'Ecologie, du Développement Durable et de l'Energie et le Ministère de l’Agriculture et de l’Agroalimentaire et subventionnée par le Ministère de l'Ecologie, du Développement Durable et de l'Energie (étude n° 2100450303). Son contenu n'engage que la responsabilité de ses auteurs. Le rapport d’étude, source de cette synthèse, a été élaboré par les experts scientifiques sans condition d’approbation préalable par les commanditaires ou l’INRA. La synthèse a été validée par les auteurs du rapport

Which model species for weed seedbank and emergence studies? A review

International audienceModels predicting the effects of cropping systems on weed demography are important tools for testing new rules for integrated weed management that may reduce the use of herbicides and preserve the biodiversity of agro-ecosystems. Such models already exist for a few species and should now be extended to a larger flora, in order to predict and understand the effects of agricultural practices on the evolution of weed communities. This review analysed the literature from 1973 to 2006, focusing on 45 species, to identify past reasons for choosing particular species when modelling the effects of cropping systems on the processes leading to seedling emergence. The frequency or harmfulness of the species were the main reason for studying them. It appears that the studied species were mainly autumn-emerging in north-western Europe cropping systems and summer-emerging in North America; the effects of deep soil tillage were studied mainly in Europe, as simplified sowing techniques are more often practised in North America. A voluminous literature exists on seed persistence in the soil, dormancy, germination and emergence, but rarely with the attempt of establishing generic relationships between species characteristics and model parameters. Until now, such an approach has been mostly developed in ecological studies. Taxa, as well as ecological preferences, seed size and the relationships of these characteristics with weed emergence model parameters should be considered when selecting a range of species for multi-specific modelling purposes

Prediction of germination rates of weed species: Relationships between germination speed parameters and species traits

International audienceIn fields, the timing of weed emergence flushes is mostly related to the timing and rate of seed germination, which depend on seed dormancy level, soil temperature and water potential conditions as well as soil tillage and crop sowing date. Seed germination parameters are essential in weed dynamics models to account for the effects of soil conditions on weed demography. Since these parameters are difficult to measure, our objective was to test the possibility of estimating them from easily accessible information. Seed germination parameters (germination lag-time, time to mid-germination and mid-germination rate) were measured or collected from the literature for 25 weed species with contrasted seed characteristics. Correlations were then searched for between these parameters and morphological, chemical and physiological seed traits as well as seed dormancy level. The dormancy level was positively correlated with speed of germination parameters. Earliness of germination was positively correlated with seed lipid content and the seed area to mass ratio. Germination was also earlier and faster in species with a high base temperature for germination. These relationships explained about half the observed variability in germination speed parameters but should be further tested before being used to predict the germination behaviour of weed species in the field in different seasons

Effects of seed depth and soil aggregates on the emergence of weeds with contrasting seed traits

International audienceTillage has a strong impact on weed emergence by burying seeds in the soil and modifying soil structure. Its influence can vary according to seed and seedling characteristics. This article focuses on shoot and radicle elongation in the soil and on seedling mortality caused by soil obstacles. Germinated seeds of nine contrasting weeds were planted in pots and grown in the dark to measure shoot and radicle elongation. Second, the proportion of seedlings blocked under aggregates (20–50 mm) was measured. Shoot growth rate, maximal shoot and radicle lengths were positively correlated with seed mass. Large-seeded species (e.g. Avena fatua) were more likely to emerge from greater depths (exceeding 20 cm deep). Seedling mortality increased with increasing obstacle size for all species; it was greater for monocotyledonous than for dicotyledonous species and decreased with the shoot diameter. Weed seed depth and soil structure influence emergence of weed species differently, depending on seed mass, shoot diameter and taxa. Including the results of this study in a cropping system-weed dynamics model would help to predict responses of weeds species to tillage

Effects of seed traits on weed seedbank dynamics in response to seed depth and soil structure

International audienceWeed seedling establishment in fields strongly depends of soil tillage because it determines both seed depth and soil structure. Species can differ in their ability to develop after germination a shoot able to grow towards the soil surface. The length of the pre-emergent shoot growth is limited and seed size could be a key functional trait related to the maximum shoot growth. Besides, during pre-emergent growth, a proportion of seedlings can remain blocked under obstacles into the soil. This mortality could be linked to the hypo- or epicotyl morphology. This trait could be correlated to the emergence force exerted at the extremity of the shoot in the soil. The maximal length of the pre-emergent shoot and the effects of soil structure through the shoot probability to be blocked under different sizes of clods were studied in controlled conditions for 11 contrasted species. A strong relation (maximal shoot length = 67.5 x seed weight 0.48; r² = 0.85) was observed between seed mass and maximal shoot length. Shoot elongation in the soil occurs without light and is therefore directly dependent on the seed characteristics such as embryo size or the amount of reserves which are more or less positively correlated to seed weight. For each species, the probability of a shoot to be blocked was linked to clod size; the parameters of this relation, i.e. the response to soil structure could then be related to the hypo- or epicotyl diameter. The relationships between seed traits and emergence processes make it possible to predict more easily the behaviour of any species. These data, completed by seed survival in soil, dormancy and germination will be introduced into a plurispecific model in order to predict weed seedbank dynamics and their interactions with agricultural practices

Modeling the dynamics and emergence of a multispecies weed seed bank with species traits

International audienc

How to choose model weed species for analysing the emergence processes in cropping systems? A review

International audienc

Evolution of weed beet (Beta vulgaris L.) seed bank: Quantification of seed survival, dormancy, germination and pre-emergence growth

International audienceWeed beet is an important weed of sugar beet crops. Weed and cropped beets can cross easily and the management of weed beet is therefore crucial in the case of the advent of GM sugar beet, especially herbicide-tolerant cultivars, in order to ensure the co-existence of GM and non-GM crops and to avoid the appearance of herbicide-resistant weed beet. The inability of weed beet to compete in most other crops of the rotation makes the seed bank evolution a crucial stage of the life-cycle because in the rotation, sugar beet is at the most cultivated only every 3 years. The present study used seed burial experiments and laboratory analyses to characterise each step of the evolution of the weed beet seed bank and the external factors that could modify seed persistence in the soil. A monthly seed mortality of 10% was observed between October and December, while mortality was nil during the other seasons. Equations were then developed to describe the observed seasonal variations in seed survival. Seed dormancy also varied with season: the proportion of non-dormant seeds increased during winter (appearance of secondary dormancy) and decreased during the remaining seasons (loss of dormancy). In addition, the germinating seeds decreased with seed age and seed depth, while the presence of light stimulated germination. These observations were also translated into equations. Last, the pre-emergence hypocotyl growth and its variability were studied according to seed age, but no significant effect was observed. The results confirm the importance of the effects of cropping system on the evolution of the weed seed bank, especially the effect of soil tillage, which determines the date and conditions of seed burial, seed excavation and germination stimulation