• Energy Research

The effect of the location of wheat residues (soil surface vs. incorporated in soil) on their decomposition and on soil bacterial communities was investigated by the means of a field experiment. Bacterial-automated ribosomal intergenic spacer analysis of DNA extracts from residues, detritusphere (soil adjacent to residues), and bulk soil evidenced that residues constitute the zone of maximal changes in bacterial composition. However, the location of the residues influenced greatly their decomposition and the dynamics of the colonizing bacterial communities. Sequencing of 16S rRNA gene in DNA extracts from the residues at the early, middle, and late stages of degradation confirmed the difference of composition of the bacterial community according to the location. Bacteria belonging to the γ-subgroup of proteobacteria were stimulated when residues were incorporated whereas the α-subgroup was stimulated when residues were left at the soil surface. Moreover, Actinobacteria were more represented when residues were left at the soil surface. According to the ecological attributes of the populations identified, our results suggested that climatic fluctuations at the soil surface select populations harboring enhanced catabolic and/or survival capacities whereas residues characteristics likely constitute the main determinant of the composition of the bacterial community colonizing incorporated residues.

AbstractCrop 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.

L’autonomie d’alimentation électrique des stations météo mobiles est un problème récurrent. L’une des manières d’assurer la plus longue autonomie possible est d’espacer l’intervalle des mesures élémentaires pour un capteur donné. La question est alors de savoir quel intervalle de mesure conservera une qualité de mesure proche des mesures de capteurs de référence. La mesure du rayonnement global est précisément l’une des mesures pour laquelle cet intervalle doit être déterminé avec rigueur.

Abstract We adapted the STICS agro-environmental model to simulate the effects of cultivation practices on the biomass production and nitrogen accumulation of perennial crops undergoing regular defoliation, using alfalfa as an example. A unique set of parameters was used to simulate both establishment and regrowth phases over several years, with the assumption that crop growth is driven by interaction between crop development stage and abiotic stresses. The model accurately simulated the total biomass (stems + leaves + crown + taproot + roots) and aboveground biomass of the crop, with model efficiencies of 0.75 and 0.70, respectively, and relative root mean squared errors (rRMSE) of 42% and 36%, respectively. The evaluation results were also satisfactory with respect to total nitrogen content and the aboveground biomass nitrogen content, with model efficiencies of 0.90 and 0.60, respectively, and rRMSE values of 29% and 31%, respectively. The model thus enabled simulations of both the establishment and regrowth of alfalfa and accurately reproduced its seasonal patterns of growth, even though it tended to underestimate spring biomass production. It also produced accurate simulations of the water and nitrate contents of the soil during cropping and after crop destruction. It could therefore be a useful tool regarding the multi-criteria assessment of cropping systems based on alfalfa with respect to their sustainability.

Bioenergy woody biomass production shortens the life cycle of carbon and secures energy supplies. However, using fast growing trees in these woody crop systems such as in short rotation coppices (SRCs), implies an increasing risk of depleting the soil nutrient stocks by direct biomass removal and low nutrient return. The aim of this study was to quantify the impact of these woody crop systems after 4 years of growth on the soil quality (C and nutrient cycling) by monitoring tree components (i.e. shoot, litterfall, root system) instead of soils; C and nutrient contents in weed strips were also included into these analyses. Our results indicated that shoot biomass was similar in SRC-P and SRC-W 2 years after planting (4 t ha−1). However, after 4 years, willow outperformed poplar (21.9 vs. 8.6 t ha−1, respectively) removing until 30 % of K soil pool. Litterfall increased between first and second rotation coppices (0.85 vs. 4 t ha−1) similarly for SRC-P and SRC-W, indicating biomass exportation and return were strongly imbalanced in SRCs crop systems. N pool in weed strips represented a significant contribution to N cycling in these SRC woody crop systems due to the presence of N2-fixing plants. However, no differences were detected between poplar and willow crops. In low quality agricultural soils, which are the likely host for SRC implementation, we demonstrated that willow has a higher nutrient accumulation rate than poplar, particularly for K, Mg and P. Weed strips constitute an important reservoir of C and nutrients and should be studied further.

Aujourd’hui, les résidus de culture ne sont plus considérés comme des déchets : leur contribution aux équilibres agronomiques et environnementaux des systèmes de culture est reconnue. Dans ce contexte, connaître leur quantité à la surface d’un sol, après une récolte, devient un enjeu important de la gestion des matières organiques dans la rotation des cultures. Généralement, l’estimation quantitative se réalise par prélèvement d’échantillons, afin d’en déterminer la masse sèche (MS) au laboratoire. L’objectif de ce travail est de proposer une méthode rapide de quantification des résidus au sol, dont l’hypothèse est basée sur une méthode d’estimation de biomasse prairiale sur pied. Ce travail a été réalisé sur des exploitations pratiquant l’agriculture de conservation en région de grandes cultures. Les résidus ont été broyés lors de la récolte ou lors d’une opération spécifique suivante. Les données de biomasse ont été collectées à l’aide de cadres de 0,5 × 0,5 m, tandis que les mesures d’épaisseur ont été effectuées à l’aide d’un aspérimètre. Ce travail compare deux méthodes de mesure d’épaisseur : soit par répétitions aléatoires de positionnement de l’aspérimètre le long d’un transect perpendiculaire au sens de progression de la moissonneuse, soit par répétitions côte à côte. Un test du nombre de mesures d’épaisseur a été réalisé pour connaître l’espacement maximal à conserver pour réaliser une estimation précise. Les résultats montrent qu’il est préférable de réaliser les mesures d’épaisseur des résidus sur l’intégralité d’un transect de moissonneuse pour estimer avec précision cette information, et qu’il faut maintenir 100 mesures d’épaisseur pour conserver une estimation proche de la mesure d’épaisseur de référence, l’espacement entre deux mesures ne devant pas excéder 6 cm. Par ailleurs, ce travail montre qu’il est possible d’obtenir une approximation de la biomasse présente au champ avec une bonne qualité d’estimation, en retenant qu’un millimètre d’épaisseur de résidu représente 50 g MS.m−2.