38 research outputs found
Introduction de jachÚres florales en zones de grandes cultures : comment mieux concilier agriculture, biodiversité et apiculture ?
Les abeilles au sens large reprĂ©sentent plus de 20 000 espĂšces dans le monde. Or, un dĂ©clin des populations d'abeilles a Ă©tĂ© rĂ©cemment observĂ© en Europe (Biesmeijer et al., 2006 ; Rasmont et al., 2006). Il pose le problĂšme du risque de disparition de ces insectes auxiliaires et de sa rĂ©percussion sur les activitĂ©s humaines qui leur sont liĂ©es comme lâapiculture, la production de fruits, de lĂ©gumes, de semences. La FAO (Nations-Unies) a lancĂ©, en 1996, un cri dâalarme Ă lâattention de tous les gouvernements pour sauvegarder cette faune dâauxiliaires. Les causes possibles de ce dĂ©clin sont multiples (Kearns et al., 1998 ; Ghazoul, 2005). Les plus citĂ©es concernent la destruction et la fragmentation de lâhabitat des abeilles (Richards, 2001 ; Steffan-Dewenter et al., 2006) et l'impact des produits phytopharmaceutiques (Kevan, 1975 ; Johansen et al., 1983 ; TasĂ©i, 1996 ; Haskell et McEwen, 1998)
Predicting field NO emissions from crop residues based on their biochemical composition: A meta-analytical approach
Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (NO). Previous meta-analyses have linked various biochemical properties of crop residues to NO emissions, but the relationships between these properties have been overlooked, hampering our ability to predict NO emissions from specific residues. Here we combine comprehensive databases for NO emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on NO emissions. On average, crop residue incorporation increased soil NO emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in NO emissions. Crop residue effects on NO emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and NO emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate NO emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated NO emissions, whereas mature residues with opposite characteristics had marginal effects on NO. The most important crop types belonging to the immature residue group â cover crops, grasslands and vegetables â are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high NO emissions
Challenges of accounting nitrous oxide emissions from agricultural crop residues
Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2O emissions
Challenges of accounting nitrous oxide emissions from agricultural crop residues
Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2O emissions
Challenges of accounting nitrous oxide emissions from agricultural crop residues
Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (NO) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for NO emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil NO production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on NO could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for NO emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate NO emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on NO emissions
Mesure de lâhumiditĂ© du sol en continu en sols caillouteux Ă lâaide de capteurs capacitifs
La mesure de lâhumiditĂ© du sol est une composante agronomique indispensable au suivi de lacroissance des cultures, trĂšs utilisĂ©e en agriculture de prĂ©cision (Camilli et al., 2007 ; Garcia-Sanchezet al., 2011). Câest Ă©galement une variable indispensable au fonctionnement de nombreux modĂšlesde simulation de la dĂ©composition de la matiĂšre organique, du suivi de la dynamique du stock dâeaudu sol (Gabriel et al., 2010). Plusieurs matĂ©riels permettant le suivi permanent de la mesure de lateneur en eau du sol existent sur le marchĂ© ; mais peu dâentre-eux sont adaptĂ©s Ă une utilisation ensols caillouteux. Or, dans le cadre de la production de biomasse destinĂ©e Ă la fabrication decarburants de seconde gĂ©nĂ©ration, les cultures destinĂ©es Ă cette production sont avant toutimplantĂ©es sur des parcelles intĂ©ressant peu ou plus le monde agricole. Ces sols de faible qualitĂ©agronomique sont parfois trĂšs caillouteux. Dans ces conditions, la majoritĂ© des matĂ©riels de mesuresde lâhumiditĂ© du sol en continu prĂ©sents sur le marchĂ© ne peuvent ĂȘtre utilisĂ©s. Dans le cadre dâuntravail sur le suivi de croissance dâarbres cultivĂ©s en taillis Ă courte ou trĂšs courte rotation (ThiĂ©beauet al., 2013), nous avons utilisĂ© des capteurs capacitifs en sols possĂ©dant une forte proportion degraviers (2 Ă 13%) et de cailloux (18 Ă 44%), afin de disposer de mesures dâhumiditĂ© du sol en continuen nous Ă©quipant de sondes ECH2O (Decagon Device Inc.) de deux types : EC5 de 5 cm et 10HS de 10cm de longueur.Les deux types de matĂ©riels testĂ©s ont Ă©tĂ© mis en oeuvre sur deux types de sols contrastĂ©s : sablolimoneuxen rĂ©gion Centre (Loiret) et argilo-limoneux en rĂ©gion Champagne-Ardenne (Aube). LesrĂ©sultats dâĂ©talonnage obtenus au cours de quatre annĂ©es dâutilisation au champ montrent de bonsrĂ©sultats par rapport Ă lâhumiditĂ© de rĂ©fĂ©rence : lâhumiditĂ© massique du sol. Au regard des capteursutilisant le principe de la rĂ©flectance temporelle (TDR), ces rĂ©sultats sont obtenus en faisantabstraction de la mesure de la densitĂ© apparente du sol et de sa tempĂ©rature, ce qui simplifiebeaucoup les conditions dâemploi au champ. Dans nos conditions de travail, nous avons pu utiliserune seule et mĂȘme Ă©quation pour lâobtention de lâhumiditĂ© massique Ă partir de donnĂ©es initialesdĂ©livrĂ©es en millivolt
Production de biomasse et immobilisation de carbone et dâazote sur des sols marginaux : cas de taillis Ă trĂšs courte rotation conduits sans fertilisation
National audienceDescription of the subject. This article presents the aboveground and belowground biomass balances of young non-fertilized short-rotation coppices, planted on marginal soils. Objectives. On two contrasting soils, the growth of willow, poplar and black locust was monitored firstly, to estimate their harvested biomass production, and the immobilization of root-derived carbon and nitrogen, and secondly, to quantify the restitutions occurring at the soil surface through leaf senescence. A comparison of two densities of black locust (2,500 vs 5,000 feet·ha-1) was carried out. Method. The devices used were instrumented to quantify the levels of carbon (C) and nitrogen (N) involved in: i) leaf senescence returning to the soil, ii) exports by the two harvests. Results. The total C immobilized in the second harvest oscillated from 7.8 to 16.1 t·ha-1, and the total N from 125 to 393 kg·ha-1. Leaf senescence corresponded to 15 to 22% of the total C on the soil surface, while 17 to 31% was immobilized in the roots. The N released into the soil by senescence varied from 48 to 79 kg·ha-1, i.e. 38 to 20% of the total respectively, and ranged and the one in the roots ranged from 22% to 48% of the total. We did not find an effect of planting density on different compartments of black locust. Conclusions. Willow and black locust have adapted better to the difficult conditions encountered than poplar. The symbiotic nitrogen fixation of black locust should be better exploited to increase the biomass production of other species, in mixed crops for example.Description du sujet. Cet article prĂ©sente les productions de biomasses aĂ©riennes et souterraines de jeunes taillis Ă trĂšs courte rotation, non fertilisĂ©s, plantĂ©s sur des sols marginaux. Objectifs. Deux sols contrastĂ©s ont permis de suivre la croissance de saule, peuplier et robinier pour estimer leur production de biomasse exportable, lâimmobilisation de carbone et dâazote dans les racines, et quantifier les restitutions au sol par la sĂ©nescence foliaire. Une comparaison de deux densitĂ©s de robinier (2 500 vs 5 000 pieds·ha-1) est Ă©galement rĂ©alisĂ©e. MĂ©thode. Les dispositifs sont instrumentĂ©s afin de quantifier le carbone (C) et lâazote (N) impliquĂ©s dans i) la sĂ©nescence foliaire retournant au sol, ii) les exportations et immobilisations de deux rĂ©coltes. RĂ©sultats. Le C total immobilisĂ© en seconde rĂ©colte varie de 7,8 Ă 16,1 t·ha-1 et lâazote de 125 Ă 393 kg·ha-1. La sĂ©nescence foliaire restitue au sol 15 Ă 22 % du C total fixĂ©, tandis que 17 Ă 31 % est immobilisĂ© dans les racines. Lâazote restituĂ© au sol par la sĂ©nescence a variĂ© de 48 Ă 79 kg·ha-1, soit respectivement 38 Ă 20 % du total, et celui retrouvĂ© dans les racines a variĂ© de 22 Ă 48 % du total. Nous nâavons pas constatĂ© dâeffet de la densitĂ© de plantation sur les diffĂ©rents compartiments des robiniers. Conclusions. Saule et robinier ont su mieux sâadapter que le peuplier aux conditions difficiles rencontrĂ©es. La fixation dâazote symbiotique du robinier pourrait ĂȘtre mieux exploitĂ©e pour accroitre la production de biomasse dâautres espĂšces, en cultures mixtes par exemple
Luzerne sous couvert de pois protéagineux. Un seul travail du sol pour implanter deux cultures principales
National audienc
Une méthode pour estimer l'interception du rayonnement par un couvert bas: application au colza avant montaison
National audienc
Effet précédent de cultures intermédiaires, seigle et ray-grass, sur l'implantation et la production d'une luzerne semée au printemps
National audienceSowing a catch crop between two main crops at the end of summer, in this case between a cereal crop and a spring-sown lucerne (Medicago sativa L.), gives the possibility of putting to good use the soil, which otherwise would generally remain bare, and to reduce the leaching of nitrate. In addition, the catch crop can be used on the farm itself as green manure or silage. The object of this work was to compare the effects of two catch crops, rye (Secale cereale L.) and Italian ryegrass (Lolium multiflorum Lam.), and of the bare soil, on the establishment and growth of spring-sown lucerne. The two catch crops tested were harvested and/or incorporated into the soil at three different dates during March and April (D1, D2, and D3). These dates were in agreement with those usually practiced for the sowing of lucerne in spring. They had an effect on the yield of the lucerne crop in the sowing year, which was depressed for the two later dates (D2, D3), as compared to the first date. However, for these dates D2 and D3, the total dry matter yield of the catch crop and the lucerne crop was equivalent to the dry matter yield of the lucerne crop alone, sown at D1. In the first year after sowing, there was no effect of the catch crops on the yield of lucerne, as compared to the bare soil.Une culture intermĂ©diaire, seigle ou ray-grass, entre la rĂ©colte d'une cĂ©rĂ©ale et le semis d'une luzerne au printemps, a un rĂŽle de piĂšge Ă nitrates. Elle peut aussi ĂȘtre valorisĂ©e sous forme d'engrais vert ou d'ensilage. Mais quel est son impact sur la production de la luzerne semĂ©e au printemps ? On a Ă©tudiĂ© l'effet de 2 cultures intermĂ©diaires (seigle et ray-grass d'Italie) sur l'implantation de la luzerne. Les cultures intermĂ©diaires ont Ă©tĂ© dĂ©truites Ă 3 dates diffĂ©rentes au printemps suivant, correspondant Ă 3 dates de semis de luzerne. En conditions climatiques normales, la rĂ©serve hydrique du sol n'est pas affectĂ©e par leur prĂ©sence. Une date tardive de semis de la luzerne a un impact nĂ©gatif significatif sur sa production l'annĂ©e d'implantation mais cet impact est compensĂ© par la production de la culture intermĂ©diaire, laquelle contribue Ă faire diminuer la teneur en nitrate de l'eau drainĂ©e pendant l'interculture. La production de matiĂšre sĂšche de la luzerne au cours de l'annĂ©e suivante n'est affectĂ©e ni par la date de semis, ni par le prĂ©cĂ©dent