Nitrogen management of organic winter wheat Decision-making through model-based explorations

In organic wheat, nitrogen is one of the key limiting factors responsible for irregular productivity and low quality (David et al, 2005b), 5 to 50 % less than conventionally managed crops (Nieberg and Schulze Pals, 1996). On arable farms, the decreasing use of N-organic sources such as forage legumes, manures and composts relative to mixed-farms requires the development of suitable fertility strategies based on the use of off-farm organic fertilizers. Numerous mechanistic crop models simulating the dynamics of crop requirements and N supply in the soil (e.g. CERES, EPIC, APSIM, ARCWHEAT STICS) have previously been developed (Whisler et al, 1996). Although these models are highly used in research, their complexity and input requirements have limited their practical use for farmers and advisers. The aim of this study was to develop an engineering approach (Passioura, 1996) by the development of a decision-making tool for assessing N management of organic wheat on commercial farms. Azodyn-Org crop model was developed in organic agriculture to predict the influence of spring N fertilization strategies on grain yield, grain protein content, mineral N in the soil at harvest and gross margin (David et al., 2004). This simpler model requires little input data, which are easily measured in farmers’ fields (soil characteristics, climatic data, crop biomass and mineral N in the soil at the end of winter). The performance of Azodyn-Org was relevant for selecting appropriate strategies in a large range of environment and crop management conditions (David et al., 2005a). This paper focuses on the potential contribution of model-based explorations from Azodyn-Org for managing N fertilization in organic wheat crops at the regional scale

Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma

Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe

La conduite du champ cultivé : points de vue d'agronomes

L'amélioration des systèmes de culture et la conception d'innovations en conduite culturale peuvent aujourd'hui s'appuyer sur l'utilisation de modèles de fonctionnement des cultures et de leur environnement. Dans une première partie, on met en évidence le rôle que jouent les modèles aussi bien pour la conception de règles de décision élémentaires que pour celle d'itinéraires techniques, de successions de cultures ou d'agencement des systèmes de culture dans l'espace. Dans une seconde partie, on passe en revue différentes difficultés méthodologiques de la démarche : étude des qualités des indicateurs d'aide à la décision ; choix des modèles utilisés pour la prévision de l'effet des techniques sur la production et l'environnement ; principes de la conception et de l'évaluation de systèmes de culture innovants. (Résumé d'auteur

Diagnosis of limiting factors of organic oilseed rape yield. A survey of farmers' fields

The yield of organic winter oilseed rape (WOSR) crop is low and variable in organic farming, but the reasons responsible for this problem are not clear. Aiming to identify the factors affecting organic oilseed rape yields, we carried out a diagnostic study on a network of 19 farmers' fields in four contrasting regions of France over a two-year period. Weed density and biomass, nitrogen absorption by the crop and by weeds, and nutrient availability in the soil, as well as the occurrence of pests and diseases, were assessed at four developmental stages. A range of possible limiting factors throughout the crop cycle led us to use a regression procedure for different periods, using the yield components during spring and biomass during autumn as dependent variables. We identified factors limiting yield and the critical time points at which they acted, which has never been done. Yield variation was strongly correlated with number of grains.m$^{-2}$. Dry biomass of weeds, nitrogen uptake by weeds and density of weeds appeared to explain 39% of variation in crop biomass in early winter, while pollen beetle and rape stem weevil damage explained 4.5% and 12% of variation in the number of flowers.m$^{-2}$ and the number of branches.m$^{-2}$, respectively. Crop nitrogen deficiencies occurring before branching were strongly correlated with weed biomass in flowering. Analysis of covariance showed that sowing date, soil management and the quantity of organic manure application may have significantly affected the nitrogen nutrition index, nitrogen uptake by plants and ratio of weed biomass: a late sowing date and shallow soil tillage were related to a low crop nitrogen nutrition index and high ratio of weed biomass. From a practical point of view, this study demonstrated that it should be possible to reduce weed competition by ensuring that the amount of nitrogen in soil before sowing is around 100 kg/ha

Re-design and co-design of farming systems. An overview of methods in practices

Agriculture is considered to be responsible for environmental degradation. At the same time, the demands for food and non-food products are increasing and the contribution of agriculture to a sustainable development of territories is at stake. All these elements require a shift towards new production systems. In line with Farming Systems Research, farmers and other stakeholders cannot be considered as recipients of inventions, but are actors of innovation processes. We present definitions and applications on how the design of innovative farming systems can be organised. Two approaches, i.e. ‘de novo’ and ‘step-by-step’ design, are described. Innovative design must mobilize a collective and distributed intelligence. We present concrete examples of interactive design processes either with heterogeneous stakeholders or with extension and public bodies, as well as the methodologies that support these processes

Sistemas de cultivo alternativos desarrollados por productores en el sudeste de la provincia de Buenos Aires

El proceso de expansión de la soja (denominado sojización) en la pampa argentina ha tenido como consecuencia la especialización de numerosas explotaciones agrícolas en el cultivo de soja. Sin embargo, muchos actores del sector agrícola cuestionan la sustentabilidad de los sistemas especializados en ese cultivo. Aun así, cabe preguntarse si las afirmaciones que se hacen sobre la sojización consideran la diversidad de los sistemas de cultivo practicados en las explotaciones agrícolas pampeanas. Este artículo presenta los resultados de un trabajo que se realizó con el fin de identificar y analizar sistemas de cultivo alternativos desarrollados por productores en el partido de Balcarce. El trabajo se dividió en cuatro etapas: (i) caracterización de un sistema predominante basado en el cultivo de soja en la zona de estudio, (ii) identificación de productores que practican sistemas de cultivo alternativos, (iii) descripción y análisis de los distintos sistemas, (iv) evaluación agroambiental y económica de esos sistemas. Se identificaron sistemas alternativos en el partido de Balcarce con prácticas agrícolas distintas de las del sistema predominante. Los sistemas alternativos son caracterizados por rotaciones largas y diversificadas, la combinación de siembra directa y labranza mínima, el uso limitado de plaguicidas, etc. La evaluación reveló que dichos sistemas podían tener mejores resultados agroambientales que el sistema predominante, lo cual nos permitió identificar algunas líneas y preguntas para futuras investigaciones agronómicas

Relationship between the amount of reduced nitrogen accumulated in winter wheat shoots and the activity of nitrate reductase measured in situ

3 tables 7 graph.International audienc

Devising fertiliser recommendations for diverse cropping systems in a region: the case of low-input bean/maize intercropping in a tropical highland of Haïti

Variability of the efficiency of N, P, K and Mg fertilisation on a low-input bean/maize intercrop (BMI) was analysed in an upland of Haïti using the combination of a simple equation predicting the fertiliser requirements and an agronomic diagnosis in farmers' fields. The study results in a classification of cropping systems according to factors limiting the fertiliser response of the intercrop species (mainly bean root necrosis and high soil K supply) and in fertilisation rules specifically adapted to the diversity of agronomic conditions. Bean root necrosis due to a parasitic complex with Fusarium solani f. sp. phaseoli decreased the fertiliser efficiency and was higher wherever the topography of a field was concave and where beans were frequent in the rotation. High soil exchangeable K content was generally found where the preceding crop was cabbage, a cash crop that is given large amounts of N-P-K fertiliser. Additional fertiliser applied to the BMI decreased nodulation of the bean, N and Mg uptake and bean yield. Because of the competition from the associated bean crop, the maize did not respond to fertiliser.Élaboration de règles de fertilisation pour la diversité des systèmes de culture d'une région : le cas d'une association haricot/maïs à bas intrants dans une région d'altitude d'Haiti. La variabilité de l'efficience d'un engrais complet (N, P, K, Mg) sur une association culturale haricot/maïs à bas niveau d'intrants cultivée dans une petite région d'altitude en Haïti, est analysée en combinant l'utilisation d'une équation simple de calcul de dose d'engrais et un diagnostic en parcelles d'agriculteurs. Une classification des systèmes de culture en fonction des facteurs limitants de la réponse à l'engrais de l'association (principalement les nécroses racinaires du haricot et la richesse du sol en K) permet d'adapter la fertilisation à la diversité des conditions agronomiques de la région. Les nécroses des racines du haricot, dues à un complexe parasitaire dominé par Fusarium solani f. sp. phaseoli, sont à l'origine d'une faible efficience de l'engrais sur cette espèce ; elles sont importantes sur les sols à topographie concave, et dans les rotations où le haricot revient fréquemment. Une teneur élevée du sol en K échangeable est observée sur les parcelles antérieurement cultivées en chou, culture de vente fortement fertilisée. Sur ces parcelles, l'apport d'engrais à l'association haricot/maïs entraîne une diminution de la nodulation et du rendement du haricot, ainsi que du prélèvement de N et de K par cette culture. à cause de la structure de l'association, la concurrence du haricot empêche toute réponse du maïs aux apports d'engrais

Model-based explorations to support development of sustainable farming systems: case studies from France and the Netherlands.

Sustainable land use requires development of agricultural production systems that, in addition to economic objectives, contribute to objectives in areas such as environment, health and well-being, rural scenery and nature. Since these objectives are at least partially conflicting, development of sustainable farming systems is characterized by negotiation about acceptable compromises among objectives. Four phases can be distinguished in the course of farming systems development: diagnosis, design, testing and improvement, and dissemination. During the last decade an approach coined 'prototyping' has emerged as a promising method for empirical farming systems development in Western Europe. Limitations of the approach include: (1) the limited number of systems that can be evaluated, resulting in a lack of perspective on conflicts among objectives, and (2) the expertise-based nature of rules used during systems design which unduly narrows the range of available options and obscures understanding of systems behaviour. In the paper, explorative studies based on transparent models of agronomy and management are put forward to supplement empirical prototyping and to remedy its shortcomings. To illustrate the potential of model-based explorations, two case studies are presented. The first case study deals with diagnosis and design of wheatbased rotations in the Paris Basin of France, aimed at alleviating tactical problems of poor resource-use efficiency within the constraints imposed by existing crop rotations. The second case study addresses design of sustainable bulb-based farming systems in the Netherlands with the purpose of investigating strategic options at crop rotation and farm level to resolve conflicts between economic and environmental objectives. In the discussion, methodological elements of model-based explorations, and interaction with stakeholders are addressed, and opportunities for enhanced development of sustainable farming systems are identified