Pascal Denoroy

Development and evaluation of a CERES-type model for winter oilseed rape

Abstract Because of its large N fertiliser requirements and long growth cycle, winter oilseed rape (Brassica napus L.) is considered to expose its environment to substantial risks of N losses. Soil–crop models provide unique tools to analyse such impacts, with an accuracy that primarily relies on the simulation of crop C and N budgets. Here, we describe a model simulating the growth and development of oilseed rape that was adapted from CERES-N Maize and a previously existing rape model. In addition to its soil components, the model, called CERES-Rape, has modules for crop phenology, net photosynthesis, leaf area development and grain filling, as influenced by crop N status. A new feature compared to previous rape models is the ability to predict the crops C and N budgets throughout its growth cycle, including losses from leaves by senescence. It also contains a mechanistic description of N translocation from vegetative parts to pods and grains after the onset of flowering. The model has been calibrated on a one-year experiment with three fertiliser N levels conducted in France, and subsequently tested on a similar experiment from Denmark for which no parameters were adjusted. In the vegetative phase, the time course of biomass and N accumulations in the various plant compartments was well simulated, with predicted values falling within one or two standard deviations from the mean in the measurements, except for the low-N treatments for which the high rates of leaf senescence could not be mimicked. After the onset of flowering, some bias appeared in the simulation of crop N uptake which impaired the predictions of final grain N yields. Simulated grain dry matter yields matched observations within ±15% for the calibration data set, but were over-estimated by a factor of 2 for the other data set. Despite the above shortcomings, the simulation of fertiliser effects on the dynamics of crop N uptake and dry matter was judged sufficiently satisfactory to allow an investigation of N losses from rapeseed–cropped soils with the CERES-Rape model.

A MODEL OF LEAF AREA DEVELOPMENT AND SENESCENCE FOR WINTER OILSEED RAPE

Abstract In winter crops, leaf area is a major determinant of the final yield, and is substantially affected by losses occurring during vegetative growth. Here, we propose and test a submodel simulating the development of leaf area and pod area, along with leaf senescence, for winter oilseed rape ( Brassica napus L.), which was included in a CERES-type model for rape adapted from CERES-N Maize. This crop model, called CERES-Rape, has components for crop phenology, net photosynthesis, N uptake, and assimilate partitioning. As a new feature compared to previously published work, the leaf area submodel includes senescence from shading due to competition for light in the canopy, and from leaf N deficiencies. The model has been developed and parameterised on a 1-yr-long experiment with three fertilizer N treatments in northeastern France, during which measurements of senescing parts allowed calibration of the equations for leaf area index (LAI) senescence and total generated LAI. The leaf area submodel, once coupled to the CERES-Rape model, was tested against two additional experiments from Denmark and northern France. This process-oriented submodel proved accurate for the simulation of actual LAI whether in the calibration or in the validation phase, with an overall Root Mean Square Error (RMSE) of 0.496 m 2 m −2 , falling close to the mean experimental standard deviation. Extrapolation did not require any further adjustment, although a different cultivar was involved.

Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments

Morel, C., Ziadi, N., Messiga, A., Bélanger, G., Denoroy, P., Jeangros, B., Jouany, C., Fardeau, J. C., Mollier, A., Parent, L. E., Proix, N., Rabeharisoa, L. and Sinaj, S. 2014. Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments. Can. J. Soil Sci. 94: 377-387. Long-term field experiments on phosphorus (P) fertilization were originally designed to study crop needs in different soil types by analyzing the effects of several rates of P fertilization on yields, their P concentrations and dynamics of plant-available soil P. The objective of this study was to test a computer-based model to simulate the P dynamics at the field scale using plant database and analyzing for plant-available P by a hierarchical process-based approach. It predicts both the concentration (CP) of phosphate ions (Pi) in soil solution and the associated Pi amounts that in time equilibrate with Pi in solution. Five experiments, representative of contrasting soil types, land-use, and climates were selected. Our model equilibrates the change in plant-available P in the upper soil layer to the P budget between annual P inputs and outputs. Rates of P fertilization affected simulations following the same expected pattern across sites. Field-observed and simulated values are in good agreements in all sites. The field-observed variations of CP per unit of P budget ranged from 0.007 to 2.49 (µg P L-1) (kg P ha-1)-1. The predictions are of the same order of magnitude. Predictions were compared with empirical long-term data and mismatches were discussed. This investigation highlights the scientific interest of long-term field P experiments to test and validate models describing P dynamics at the scale of the agricultural fields under different agricultural management practices.

A method for assessing available phosphorus content in arable topsoils over large spatial scales

Human activities, and more specifically agricultural activities, have modified the way the ecosystem functions through the use of fertilizers. When these inputs are not being utilized reasonably, they can lead to a degradation in both soil and water quality. As a result of the subsequent environmental problems and socio-economic constraints, the concept of sustainable fertilization was born. The main goal behind sustainable fertilization is to reduce the amount of fertilizers used while maintaining soil fertility and farmer revenues. We have designed herein a methodology for assessing the phosphorus bioavailability in arable topsoils on France’s national scale, on the basis of this sustainable fertilization concept. We will consider the sustainability of a cropping system that requires balancing nutrient removal from the soil by fertilization, in order to avoid environmental risks. The originality of this method lies in quantitative results stemming from the French Soil Test Database (BDAT) and their evaluation using the RegiFert® software, which incorporates soil characteristics and crop sensitivity to nutrient availability. According to the proposed procedure, we determined the phosphorus bioavailability class of French arable soils at the cantonal scale. Cantons are areas of average surface of 140 km2. This methodology constitutes an attempt to gather all analytical results into a common diagnostic framework on the national scale (for France), while taking into account the local pedological context and crop production requirements. With this procedure, we are able to conclude that 77% of cantons are situated below the critical level regarding crop needs. Furthermore, this diagnosis suggests that the available phosphorus content in soils is considered insufficient with respect to any crop potential requirement. From an environmental standpoint, however, this situation could be considered as generating the lowest pollution risk. Nevertheless, 23% of the cantons exhibit a soil phosphorus accumulation that is not necessary with regard to agricultural uses. In this case, no fertilization is required and the pollution risk is increased. On the national scale, bioavailability class frequencies are structured spatially, with gradients correlated to soil parameter spatial distribution, and tend to reflect land use patterns.