The objective of this paper is to present the contribution of a new dielectric constant characterisation for the modelling of radar backscattering behaviour. Our analysis is based on a large number ...of radar measurements acquired during different experimental campaigns (Orgeval'94, Pays de Caux'98, 99). We propose a dielectric constant model, based on the combination of contributions from both soil and air fractions. This modelling clearly reveals the joint influence of the air and soil phases, in backscattering measurements over rough surfaces with large clods. A relationship is established between the soil fraction and soil roughness, using the Integral Equation Model (IEM), fitted to real radar data. Finally, the influence of the air fraction on the linear relationship between moisture and the backscattered radar signal is discussed.
Trois principaux facteurs conditionnent les caractéristiques physiques (taille des dépôts) et chimiques (teneur en eau, en nutriments…) des déjections des herbivores domestiques au pâturage : ...l’espèce, l’état physiologique de l’animal et la qualité de l’herbe ingérée, qui dépendra elle-même de la composition du tapis végétal et des conditions climatiques. À travers les déjections solides s’opère une restitution de matière organique et d’éléments nutritifs non assimilés vers le système sol-plante. L’importance énergétique de ce retour est telle que la dissémination des déjections est source d’hétérogénéité à l’échelle de la pâture. Cette hétérogénéité, elle même conditionnée par le comportement des animaux et les modalités de conduite, est à son tour source de diversité, tant floristique que faunistique. L’élimination de l’excrément de la surface du sol dépend des conditions climatiques et de l’activité de la faune saprocoprophage. L’activité de cette faune modifie à la fois les propriétés de la déjection et celles du sol (porosité, aération), ce qui favorise les activités microbiennes. A court terme, les déjections de grande taille ont un effet néfaste sur la végétation et entraînent un phénomène de refus de consommation de la part des bovins et des équins. A plus long terme, les déjections entraînent une augmentation de la croissance des plantes situées à proximité, effet qui peut persister jusqu’à deux ans. Si les transformations physicochimiques et les impacts des déjections sur la faune et la flore sont assez bien connus, en revanche nos connaissances sont lacunaires lorsqu’il s’agit de faire le lien entre le fonctionnement des communautés d’insectes coprophages et les fonctionnalités écosystémiques associées.
Gibberellin (GA) levels in leaf sheaths and in elongating leaf bases of perennial ryegrass (Lolium perenne L. cv. Bravo) were monitored in undefoliated and defoliated plants. Nine C‐13‐hydroxylated ...GAs (GA8, GA97, GA29, GA1, GA20, GA44, GA19, GA17, GA53) and one C‐13‐non‐hydroxylated GA (GA9) were identified by combined gas chromatography‐mass spectrometry in leaf extracts. The total level of GA8, GA29, GA1, GA20, GA44, GA19 and GA53, determined by selected ion monitoring, was 7 times higher in elongating leaf bases than in mature leaf sheaths. In both leaf tissues, defoliation induced an increase in GA53 level, while GA20 and GA1 levels decreased, suggesting that the GA53→GA44, as well as GA19→GA20, conversions were slowed down. The roles of GA1 in the control of leaf elongation and fructan mobilization following defoliation are discussed.
The objectives of this study were (i) to evaluate the relative involvement of fructans from leaf sheaths and from elongating leaf bases to regrowth after defoliation of Lolium perenne L. by following ...fructan exohydrolase (FEH), sucrose‐sucrose fructosyl transferase (SST) and invertase (INV) activities and (ii) to examine whether gibberellins could be implicated in regulation of FEH activity. In stubble, 36% of fructans are located in leaf bases and 64% in leaf sheaths. During the first phase of regrowth, the depletion of carbohydrates was mainly due to the decline of fructans, which represented 76% and 50% of the carbohydrates mobilized from leaf sheaths and elongating leaf bases respectively. Despite a decrease in protein content, FEH activity increased 2·5‐fold in leaf sheaths and six‐fold in elongating leaf bases, so that the fructan‐hydrolysing activity was four times higher in growing leaves than in leaf sheaths, 2 d after defoliation. INV activity also increased, whereas the pattern of SST activity was inversely related to the variations of both hydrolysing activities. SST activity, which is highest in growing leaves, declined approximately threefold in leaf sheaths and elongating leaf bases at the beginning of regrowth.
The increase in activity of FEH in stubble was strongly inhibited by an inhibitor of the biosynthesis of gibberellin, uniconazole. FEH activity was decreased to c. 67%, 45% and 33% of the level in nontreated plants 24, 48 and 72 h following defoliation, respectively. The inhibition could be overcome by a subsequent treatment with gibberellic acids (GAs). For the first time, data are provided to support the view that GAs might play a role in the regulation of FEH activity, and the implication of this result is discussed.
The objective of this paper is to present the contribution of a new dielectric constant characterization for the modelling of radar backscattering behavior. Our analysis is based on a large number of ...radar measurements acquired during different experimental campaigns (Orgeval'94, Pays de Caux'98, 99). We propose a dielectric constant model, based on the combination of contributions from both soil and air fractions. This modelling clearly reveals the joint influence of the air and soil phases, in backscattering measurements over rough surfaces with large clods. A relationship is established between the soil fraction and soil roughness, using the Integral Equation Model (IEM), fitted to real radar data. Finally, the influence of the air fraction on the linear relationship between moisture and the backscattered radar signal is discussed.
The objectives of this study were (i) to evaluate the relative
involvement of fructans from leaf sheaths and from
elongating leaf bases to regrowth after defoliation of Lolium perenne L.
by following ...fructan exohydrolase (FEH),
sucrose-sucrose fructosyl transferase (SST) and invertase (INV) activities and
(ii) to examine whether gibberellins
could be implicated in regulation of FEH activity. In stubble, 36% of fructans
are located in leaf bases and 64%
in leaf sheaths. During the first phase of regrowth, the depletion of
carbohydrates was mainly due to the decline
of fructans, which represented 76% and 50% of the carbohydrates mobilized
from leaf sheaths and elongating leaf
bases respectively. Despite a decrease in protein content, FEH activity
increased 2·5-fold in leaf sheaths and six-fold in elongating leaf bases,
so that the fructan-hydrolysing activity was four times higher in growing leaves than
in leaf sheaths, 2 d after defoliation. INV activity also increased,
whereas the pattern of SST activity was inversely
related to the variations of both hydrolysing activities. SST activity, which
is highest in growing leaves, declined
approximately threefold in leaf sheaths and elongating leaf bases at the
beginning of regrowth. The increase in activity of FEH in stubble was strongly inhibited by an
inhibitor of the biosynthesis of
gibberellin, uniconazole. FEH activity was decreased to c. 67%, 45%
and 33% of the level in nontreated plants
24, 48 and 72 h following defoliation, respectively. The inhibition could
be overcome by a subsequent treatment
with gibberellic acids (GAs). For the first time, data are provided to
support the view that GAs might play a role
in the regulation of FEH activity, and the implication of this result is discussed.
Groundnut [leaf analysis Gillier, P. (Groupes d'Etudes et de Recherches pour le Developpement de l'Agronomie Tropicale, Paris (France). IRHO. Institut de Recherches pour les Huiles et Oleagineux); Bockelee-Morvan, A
1984
Book
References acquisition about nitrogen fertilizer value of livestock organic products (LOP), which represent an important source of nitrogen, has mainly concerned short term nitrogen effects. But mid ...and long term nitrogen effects are not yet well quantified because there are very few references from long term experiments. 25 trials on 15 sites have been analysed, mainly settled on loamy soils from west of France in crop rotations with forage maize, wheat with straw removed. 9 types of LOP (manures, composts, slurries) from livestock cattle, pig or poultry, were studied. Cattle manure most widespread organic product from livestock was present on most of trials. 10 years of annual supply or 20 years of biannual supply which cumulated from 1000 to 3000 kgN.ha-1, led to a significant storage of organic C and N in soil, compared to a mineral fertilization. In trials with crop system where crop residues were mainly exported, where organic C stock decreased with time, LOP supply made it possible to stabilize or increase this stock. For each type of LOP, C storage in soil was well correlated with the amount of C from LOP for a given trial but widely differed among sites. Site effect seemed to be linked to agro-soil-climate context and LOP composition. Organic C and N from LOP storage in fine (0-50 E) and intermediate (50-200 E) fractions of soil organic matter with slow turn over suggested that effects on soil nitrogen mineralization will last for a long time. Soil organic N originated from cattle manure dynamics was simulated by annual step time « Decay series » model (Pratt model). The model was adjusted both on organic N storage and mineralization supplement (SMIN-N) compared to a mineral fertilization, which were measured at the end of the experiments, showed that SMIN-N values were increasing with time for regular input scenarios. Evolution with time of nitrogen annual extra absorption of crops, due to repeated supply of LOP, did not allowed to account for SMIN-N increase with time. Then it seems that 10 years of annual supply of LOP represent a too short delay to evidence SMIN-N with nitrogen absorption of crop measurement.
La recherche de références sur la valeur fertilisante azotée des produits organiques issus d’élevages (PROE), qui constituent un gisement important d’azote, a surtout porté jusqu’à présent sur l’évaluation des effets à court terme (année de l’apport). Par contre, les effets azote à moyen et long terme sont encore mal quantifiés, car les références issues d’expérimentations de longue durée sont rares. 25 essais répartis sur 15 sites ont été analysés, implantés en majorité sur des sols limoneux de l’Ouest de la France, dans des rotations maïs fourrage/blé pailles exportées. 9 types de produits organiques (fumiers, fumiers compostés, lisiers) issus d’élevages bovins porcins ou avicoles, ont été étudiés. Les fumiers de bovins, produit organique le plus répandu, ont été étudiés sur la majorité des essais. 10 ans d’apports annuels ou 20 ans d’apports bisannuels de PROE qui cumulent de 1000 à 3000 kgN.ha-1, conduisent le plus souvent à un stockage significatif de C et N organique dans les sols, comparativement à une fertilisation minérale seule. Dans des essais principalement conduits en systèmes de cultures exportant la majeure partie des résidus de récolte, où le stock de C organique a diminué au cours du temps, de tels apports de PROE ont permis un maintien ou une augmentation de ce stock. Le stockage est corrélé à la dose apportée, pour un essai donné, mais varie fortement d’un site à l’autre, pour un même type de produit à des doses voisines, l’effet « site » étant lié à la fois au contexte agropédoclimatique et à la composition des PROE. Le stockage du C et N organiques apportés par les PROE dans des fractions fines (0-50 E) et intermédiaires (50-200 E) de la matière organique du sol à turn over lent suggère que les effets sur la minéralisation d’azote du sol vont s’exercer sur des temps longs. La dynamique d’évolution du N organique apporté par les fumiers de bovins, approchée avec un modèle à pas de temps annuel (modèle « Decay series » de Pratt), ajusté à la fois sur le stockage et le supplément de minéralisation (SMIN-N) par rapport à une fertilisation minérale seule, mesurés après l’arrêt des apports, conduit à calculer des valeurs de SMIN-N croissantes avec le temps pour des scénarios d’apport réguliers. L’analyse de l’évolution au cours du temps des suppléments annuels d’absorption d’azote des cultures réceptrices, induits par les apports répétés de PROE, ne permet pas de rendre compte d’un accroissement de SMIN-N au cours du temps. Il semble donc que 10 ans d’apports annuels de PROE représentent un délai encore trop court pour qu’un supplément significatif de minéralisation de N puisse être mis en évidence par la mesure de l’absorption de N des cultures.
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