Couverts végétaux et semis directs. Une réalité et une nécessité au Brésil

National audienc

A contribution to the modelling of cropping systems with permanent ground cover and zero tillage

*UMR d'Agronomie, Bibliothèque, 78850 Thiverval-Grignon Diffusion du document : UMR d'Agronomie, Bibliothèque, 78850 Thiverval-GrignonInternational audienc

Vers des systèmes de culture avec non labour et couverture permanente du sol en grande culture en France

*UMR Agronomie, Bibliothèque, 78850 Thiverval-Grignon Diffusion du document : UMR Agronomie, Bibliothèque, 78850 Thiverval-GrignonNational audienc

Y a-t-il un intérêt agronomique à associer une culture commerciale et une plante de couverture ?: Cas d’une association blé (Triticum aestivum L.) fétuque rouge (Festuca rubra L.)

Cover crops, which have proven to be efficient in increasing the sustainability of tropical cropping systems, are much less used in temperate ones. The aim of this work is triple: i) to study the way to undersow a cover crop simultaneously with a cash crop in temperate areas without impacting too strongly the yield of the cash crop ; ii) to measure the overproduction of organic matter to be buried into the soil due to the lengthening of the period of the PAR use in such systems ; iii) to measure their impact on the risk of pollution of the ground water by nitrogen. Two two-year cycles of experimentation were carried out at Grignon in 1999-2001 (E1) and 2000-2002 (E2) to analyze the effect of red fescue (Festuca rubra L.), a turf grass selected as cover crop, on the wheat (Triticum aestivum L.) yield and its components and to observe its role during the following inter-crop. Several conditions of competition between the two species were analyzed: undersowing two wheat varieties at two sowing rates, two red fescue varieties, sole crops being compared with undersown ones. The wheat yield target was 9 t/ha. Wheat yields depended more on the wheat variety (Isengrain: 8.8 t/ha, Scipion: 7.0 t/ha) than on the red fescue undersowing (sole wheat: 8.6 t/ha ; undersown wheat: 7.8 t/ha). Undersowing had statistically significant effects for the lower wheat sowing rate. Yield component analysis showed that the undersowing had a depressive effect on the number of kernels per m 2. This effect was partially compensated for by a higher kernel weight in undersown wheat than in sole wheat. The red fescue variety and wheat sowing rate had no effect. During the time period between the wheat harvest and the sowing of the next cash crop, previously undersown fescue produced 3.3 t/ha in E1 and 2.7 t/ha in E2. The amount of soil mineral nitrogen in the 0-0.9 m layer decreased under the 2 g/m 2 threshold.Les plantes de couverture, de plus en plus utilisées en zone tropicale en raison de leur intérêt pour la durabilité des systèmes de culture, le sont très peu en zone tempérée. C'est pourtant un moyen efficace de développer les services écosystémiques à cette échelle. L'objet de ce travail est triple : i) analyser la possibilité de les implanter en même temps qu'une culture commerciale sans entraîner de trop forte baisse de rendement ; ii) mesurer le supplément de matière organique susceptible de retourner au sol par l'allongement de la période d'utilisation du rayonnement photosynthétiquement actif ; iii) mesurer leur effet sur les risques de pollution des eaux par l'azote minéral. Un essai a été mis en place à Grignon en 1999-2001 (E1) et 2000-2002 (E2) pour étudier l'association d'une fétuque rouge (Festuca rubra L.) et d'un blé (Triticum aestivum L.), avec plusieurs modalités de compétition, obtenues en associant deux variétés de blé, à deux densités de semis, et deux de fétuque. Les blés ont été conduits avec un objectif de rendement en grains de 9 t/ha. Ces rendements (moyenne de E1 et E2) ont été plus affectés par le choix de la variété de blé (Isengrain : 8,8 t/ha, Scipion : 7,2 t/ha) que par la présence de la fétuque (blé seul : 8,6 t/ha ; blé associé : 7,8 t/ha). La fétuque a un effet dépressif sur l'élaboration du nombre de grains mais cet effet a été partiellement compensé par le poids d'un grain. La variété de fétuque n'a pas eu d'effet, ni la densité de semis du blé. Dans la période entre la récolte du blé et le semis de la culture suivante, les fétuques antérieurement associées ont produit 3,3 t/ha de biomasse en E1 et 2,7 t/ha en E2. Elles ont fait baisser la quantité d'azote minéral du sol dans la couche 0-0,9 m sous le seuil de 2 g/m 2

Utilisation des composés phénoliques pour le marquage de pools géniques de Tournesol cultivé

International audienc

Evaluation of environmentally-friendly crop management systems based on very early sowing dates for winter oilseed rape in France

We assessed new crop management systems for winter oilseed rape based on very early sowing dates, with a view to improving environmental performance without decreasing economic benefits. In a network of 36 trials conducted over 3 years in France, the new systems turned out to be more effective than current systems in terms of environmental variables: absorption of almost all the mineral N present in the soil in autumn, even after organic manure spreading; nitrate concentration of the percolated water below 50 mg $\cdot$ l$^{-1}$, and lower levels of molluscicide use, even in years of heavy slug infestation. The gross margin was optimised by very early sowing, which in most trials resulted in yields equal to or greater than those for crops sown at the usual date. We typed the trials, linking the difference in yield between the two crop management systems to various limiting factors (crop establishment, stem canker and nitrogen nutrition), to identify situations appropriate for the new crop management systems.Évaluation en France d'itinéraires techniques du colza d'hiver favorables à l'environnement, basés sur des semis très précoces. Notre objectif est l'évaluation de nouveaux itinéraires techniques du colza basés sur des semis très précoces, afin d'améliorer le bilan environnemental de cette culture sans affecter son bilan économique. Sur un réseau de 36 essais pendant 3 années en France, les nouveaux itinéraires techniques se sont avérés plus efficaces que les itinéraires techniques actuellement recommandés au niveau des performances environnementales : absorption, au cours de l'automne, de la quasi totalité de l'azote minéral du sol même après épandage d'effluent organique ; teneur en nitrate de l'eau percolée inférieure à 50 mg $\cdot$ l$^{-1}$ ; réduction de l'emploi de molluscicides, même en année de forte infestation de limaces. En terme de marge brute, les résultats moyens furent favorables aux semis très précoces qui permirent, sur la majorité des essais, un rendement supérieur ou égal à celui des semis à date normale. Une typologie des essais reliant la différence de rendement entre les deux itinéraires techniques à différents facteurs limitants (implantation de la culture, phoma, nutrition azotée), est utilisée afin de définir le domaine de validité des nouveaux itinéraires techniques

Evaluation en France d'itinéraires techniques du colza d'hiver favorables à l'environnement, basés sur des semis très précoces

International audienc

Undersowing wheat with different living mulches in a no-till system. I. Yield analysis

The classical management of no-till wheat has several environmental and economic drawbacks such as the use and cost of herbicides, and the degradation of soil physical quality. Recent investigations suggest that undersowing crops with a living mulch could be a sustainable alternative. Therefore, we studied during three growing seasons the effect of undersowing wheat with living mulches on wheat grain yield. Treatments were wheat grown on a conventionally-tilled soil, on a no-till soil, and on a no-till soil with various living mulches. The living mulches were red fescue, sheep's fescue, alfalfa, bird's-foot-trefoil, black medic and white clover. Our results show that the use of living muches during wheat cropping decreased wheat yield of 19–81% by comparison with wheat cropped alone. This decrease is linked to the biomass of living mulches and weeds at the time of flowering. As a consequence, the control of living mulch and weed biomass is a major issue. Our findings also reveal that the wheat yield decrease is mainly the consequence of a decrease in grain number from 37 to 32 grains per spike on average, and of a decrease in spike number from 0.7 to 0.4 spikes per stem. We thus conclude that stem elongation, flowering and fecundation are the major stages of stress for wheat grown with living mulches. Our findings will help to design innovative crop management systems that take into account the biological interactions in agro-ecosystems better

Undersowing wheat with different living mulches in a no-till system. II. Competition for light and nitrogen

No-till wheat management systems with a living mulch is a possible means to improve agricultural sustainability. Nonetheless living mulches may affect wheat production by competition for light and nutrients. Therefore, here we studied competition for light and nitrogen between wheat and different living mulches under no-till. We grew wheat using three different practices: (1) conventionally-tilled wheat, (2) no-till wheat and (3) wheat undersown with various living mulches. Living mulches were: red fescue, sheep's fescue, alfalfa, bird's-foot-trefoil, black medic, and white clover. We measured: leaf area index and height of wheat and living mulch, and radiation partitioning between species; above-ground biomass of wheat and living mulch; nitrogen uptake of wheat and living mulch; and wheat nitrogen status using a nitrogen nutrition index. Our results showed that at flowering, competition for light between mixed species occurred in sixteen out of the eighteen situations, i.e. in three experiments times six no-till/living mulch treatments. Further, the biomass of wheat grown with living mulches was 24–84% lower than no-till wheat alone. At flowering, competition for nitrogen only occurred in seven out of the eighteen situations. Our findings showed that competition for light was due to light partitioning between mixed species. Furthermore, we found that the light competitive ability of wheat undersown with a living mulch was the highest when wheat was much taller than living mulch, and also when wheat leaf area in the mixed canopy layer was greater than that of living mulch. We conclude that the negative effects of living mulches on wheat yield should be solved by a careful choice of living mulch species and the control of living mulches by mechanical or chemical means

Does intercropping winter wheat (Triticum aestivum. L) with lucerne (Medicago sativa. L) improve nitrogen resource utilization (nitrogen uptake and atmospheric nitrogen fixed)?

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