Analyzing and improving corn irrigation strategies with MODERATO, a combination of a corn crop model and decision model

International audienc

Assessing the uncertainty when using a model to compare irrigation strategies

International audienceA major use of crop models is to evaluate management strategies. An important question is how accurate models are for such evaluations. The purpose of this study was to determine how to use a combined crop and decision model to evaluate irrigation strategies for corn (maize, Zea mays L.) and to estimate the uncertainty in the criteria used for evaluation. The uncertainty estimation has three steps. First, the sources of uncertainty are identified. We considered uncertainty in the model parameters and model residual error. Second, the uncertainty in each source is quantified. We used a Bayesian approach to obtain a posterior distribution of the model parameters and variances of residual error. Finally, the uncertainties are propagated through to the quantities of interest. In our case, this included calculations for observed quantities—these posterior predictive checks allowed us to verify that our uncertainty estimates were reliable—and predictions of the criteria used to evaluate the irrigation strategies. We considered several criteria including multiyear average yield and interannual yield variability. The uncertainty in average yield was quite small (standard deviation of about 0.2Mg/ha). This is due to the fact that much of the error in yield prediction cancels out when looking at average yield. Three major conclusions are that this model can be a powerful tool for evaluating irrigation strategies, that prediction of average yield can have much less uncertainty than prediction of yearly yield, and that it is essential to verify the reliability of uncertainty estimates using data

A conceptual model of farmers’ decision-making process for nitrogenfertilization and irrigation of durum wheat

International audienceWith a 2 millions of tons production, France is the second country in the European Union to produce durum wheat. Durum wheat production requires high grain nitrogen concentration. Irrigation and nitrogen fertilization must be managed simultaneously to maximize grain yield and also avoid low protein concentration and environmental impacts. To help advisors and farmers to better manage together these two agricultural operations and to develop innovative managements, developing a biodecisional model is an interesting possibility. However, knowledge is still missing on how farmers already managed these operations and how these two operations are linked. We developed the conceptual model for the decision part of this computer model. We performed a survey of 28 farmers conducted over the five French production areas investigating a diversity of growing conditions to identify the set of possible constraints and farmers’ decision rules. To analyze the survey, we first used a general inductive approach on individual cases and then built a conceptual model of the decision with a bottom-up approach. We identified four decision sequences for fertilization (N splitting, choice of N fertilizer, rate of application, fertilization triggering) and five for irrigation (irrigation period, anticipated number of irrigation cycles, irrigation cycles organization, irrigation triggering and irrigation cycle specificities). For each operation, the first three decision sequences refer to strategic decisions. The other decision sequences refer to tactical decisions. Coupling this model with a crop model could provide guidelines for managing durum wheat in the current climatic and economic changing context

Le Réservoir Utilisable : Evaluation - Concepts - Incertitudes

National audienc

A modelling chain combining soft and hard models to assess a bundle of ecosystem services provided by a diversity of cereal-legume intercrops

International audienceCereal-legume intercropping is known to improve the sustainability of crop production. However, it remains uncommon on commercial farms in Europe due to a number of socio-technical lock-ins and the many practical issues raised when integrating intercrops in cropping systems (e.g. which species, cultivars, sowing densities). Crop modelling is an option to explore integration scenarios and support farmers' decisions. However, available crop models are not able to simulate bundles of ecosystem services provided by a large diversity of binary cereallegume intercropping scenarios. To address this challenge, we developed a hybrid modelling chain that combines process-based, statistical and knowledge-based models to benefit from the strengths of these three different modelling approaches. The chain (i) simulates potential biomass of the sole cereal and legume crops independently using the crop model STICS; (ii) uses statistical interaction models built in R to convert potential biomass in sole cropping into attainable biomass in intercropping by considering competition effects among species, using a field trial database; (iii) converts attainable biomass into actual biomass by considering pest damage using a knowledge-based multi-attribute DEXi model, and also assesses control of pests (i.e. weeds, insects and diseases); and (iv) uses another set of multi-attribute models to assess five additional ecosystem services (i.e. cereal and legume grain yields, cereal protein content, nitrogen supply to the following crop and impact on soil structure) from the actual biomass of the intercrop at harvest and/or cropping system features. The chain was calibrated for grain cereal-legume intercrops sown simultaneously in a random pattern under low-input French conditions. We used an expert-based approach to assess the performances of each model and evaluate the accuracy of the entire modelling chain. In 18 simulated scenarios, 79% of the predicted levels of ecosystem services were consistent with experts' opinion. Predictions were more accurate for intercropping scenarios that included species from the trial database used to build linear interaction models (relative RMSE of 27-31%) but remained satisfactory for other intercropped species (relative RMSE of 32-37%). This is the first modelling chain able to assess bundles of ecosystem services provided by multiple cereal-legume intercrops in function of their cropping system contexts. This chain is intended to be included in an educational tool that is used face to face with farmers or students to design cropping systems that include intercrops

Early rhythm-control therapy in patients with atrial fibrillation

BACKGROUND Despite improvements in the management of atrial fibrillation, patients with this condition remain at increased risk for cardiovascular complications. It is unclear whether early rhythm-control therapy can reduce this risk. METHODS In this international, investigator-initiated, parallel-group, open, blinded-outcome-assessment trial, we randomly assigned patients who had early atrial fibrillation (diagnosed ≤1 year before enrollment) and cardiovascular conditions to receive either early rhythm control or usual care. Early rhythm control included treatment with antiarrhythmic drugs or atrial fibrillation ablation after randomization. Usual care limited rhythm control to the management of atrial fibrillation–related symptoms. The first primary outcome was a composite of death from cardiovascular causes, stroke, or hospitalization with worsening of heart failure or acute coronary syndrome; the second primary outcome was the number of nights spent in the hospital per year. The primary safety outcome was a composite of death, stroke, or serious adverse events related to rhythm-control therapy. Secondary outcomes, including symptoms and left ventricular function, were also evaluated. RESULTS In 135 centers, 2789 patients with early atrial fibrillation (median time since diagnosis, 36 days) underwent randomization. The trial was stopped for efficacy at the third interim analysis after a median of 5.1 years of follow-up per patient. A first-primary-outcome event occurred in 249 of the patients assigned to early rhythm control (3.9 per 100 person-years) and in 316 patients assigned to usual care (5.0 per 100 person-years) (hazard ratio, 0.79; 96% confidence interval, 0.66 to 0.94; P=0.005). The mean (±SD) number of nights spent in the hospital did not differ significantly between the groups (5.8±21.9 and 5.1±15.5 days per year, respectively; P=0.23). The percentage of patients with a primary safety outcome event did not differ significantly between the groups; serious adverse events related to rhythm-control therapy occurred in 4.9% of the patients assigned to early rhythm control and 1.4% of the patients assigned to usual care. Symptoms and left ventricular function at 2 years did not differ significantly between the groups. CONCLUSIONS Early rhythm-control therapy was associated with a lower risk of adverse cardiovascular outcomes than usual care among patients with early atrial fibrillation and cardiovascular conditions