Romain Roche

An overview of the crop model stics

Abstract stics is a model that has been developed at INRA (France) since 1996. It simulates crop growth as well as soil water and nitrogen balances driven by daily climatic data. It calculates both agricultural variables (yield, input consumption) and environmental variables (water and nitrogen losses). From a conceptual point of view, stics relies essentially on well-known relationships or on simplifications of existing models. One of the key elements of stics is its adaptability to various crops. This is achieved by the use of generic parameters relevant for most crops and on options in the model formalisations concerning both physiology and management, that have to be chosen for each crop. All the users of the model form a group that participates in making the model and the software evolve, because stics is not a fixed model but rather an interactive modelling platform. This article presents version 5.0 by giving details on the model formalisations concerning shoot ecophysiology, soil functioning in interaction with roots, and relationships between crop management and the soil–crop system. The data required to run the model relate to climate, soil (water and nitrogen initial profiles and permanent soil features) and crop management. The species and varietal parameters are provided by the specialists of each species. The data required to validate the model relate to the agronomic or environmental outputs at the end of the cropping season. Some examples of validation and application are given, demonstrating the generality of the stics model and its ability to adapt to a wide range of agro-environmental issues. Finally, the conceptual limits of the model are discussed.

Simulation of carbon and nitrogen dynamics in arable soils: a comparison of approaches

Although mechanistic soil-crop models are increasingly accepted as valuable tools in analysing agronomical or environmental issues, potential users are faced with an equally increasing number of available models. In principle, model selection should be based on a rational assessment of its merit with respect to the objectives pursued. Such information may be obtained by comparing the ability of candidate models to predict given sets of experimental data. However, because the basic components of soil-crop models interact strongly in producing model outputs, little can be drawn as to the validity of the approaches used for the individual components. Here, we focused on the soil carbon and nitrogen turnover module of four soil-crop models (CERES, NCSOIL, SUNDIAL, and STICS), which were selected based on their representativity of currently used models, and the range of complexity and process approaches they offered. The C-N modules of models other than CERES were extracted and linked within CERES, so that they were all supplied with the same physical and chemical data. Inputs and outputs other than those involved the N cycle were provided with good reliability by the common CERES shell. The performance of the various modules was assessed according to two criteria: short-term response of topsoil inorganic N to climate and crop residues input, and long-term dynamics of soil organic matter (SOM). Accordingly, data sets involving net mineralization and topsoil inorganic N dynamics under contrasting bare or wheat-cropped soils, and long-term soil carbon data were used to test them. The results highlight a trade-off between the prediction of N mineralization in the short-term (day to year) and SOM dynamics in the long-term (year to decade). On a yearly basis, NCSOIL over-estimated immobilization of inorganic N associated with the decomposition of crop residues, and CERES predicted extremely low mineralization fluxes. STICS and SUNDIAL gave good predictions of soil N supply, but over-estimated the rate at which soil carbon from slow-turnover pools was degraded as a result. Comparison with a model dedicated to predicting SOM turnover (RothC) showed that the discrepancy may be attributed to a strong under-estimation of the turnover of below-ground plant material by the plant modules of CERES. Crop models should thus be improved from this point of view before coupling with SOM models.

Effects of nitrogen deficiencies on autumnal growth of oilseed rape

Several field experiments were carried out to define the effects of temporary N deficiency in autumn on the growth and yield of winter oilseed rape. N deficiencies are described in terms of nitrogen nutrition index (NNI) i.e. methodologies of Lemaire et al. (Proceedings of the XVI International Grassland Congress, Nice, France, 1989, p. 179) and Lemaire and Gastal (In: G. Lemaire (Ed.), Springer, Berlin, Diagnosis of the Nitrogen Status in Crops, 1997, p. 3). The growth components analysed were shoot and tap root biomass, leaf area index (LAI) and radiation use efficiency (RUE). In all the experimental conditions, N deficiencies were severe (NNI near 0.60) and had significant effects on all growth components. These growth variables and NNI were fitted by various functions. The effects of N stress on winter oilseed rape are discussed and compared to another crop. Despite severe autumn N deficiencies, no difference in yield was apparent because these deficiencies probably allow all the time enough growth in autumn to ensure sufficient regrowth in spring.

Late Foliar Diseases in Wheat Crops Decrease Nitrogen Yield Through N Uptake Rather than Through Variations in N Remobilization

BACKGROUND AND AIMS French wheat grains may be of little value on world markets because they have low and highly variable grain protein concentrations (GPC). This nitrogen-yield to yield ratio depends on crop nitrogen (N) fertilization as well as on crop capacity to use N, which is known to vary with climate and disease severity. Here an examination is made of the respective roles that N remobilization and post-anthesis N uptake play in N yield variations; in particular, when wheat crops (Triticum aestivum) are affected by leaf rust (Puccinia triticina) and Septoria tritici blotch (teleomorph Mycosphaerella graminicola). METHODS Data from a 4-year field experiment was used to analyse N yield variations in wheat crops grown either with a third or no late N fertilization. Natural aerial epidemics ensured a range of disease severity, and fungicide ensured disease-free control plots. The data set of Gooding et al. (2005, Journal of Agricultural Science 143: 503-518) was incorporated in order to enlarge the range of conditions. KEY RESULTS Post-anthesis N uptake accounted for a third of N yield whilst N remobilization accounted for two-thirds in all crops whether affected by diseases or not. However, variations in N yield were highly correlated with post-anthesis N uptake, more than with N remobilization, in diseased and also healthy crops. Furthermore, N remobilization did not significantly correlate with N yield in healthy crops. These findings matched data from studies using various wheat genotypes under various management and climatic conditions. Leaf area duration (LAD) accurately predicted N remobilization whether or not crops were diseased; in diseased crops, LAD also accurately predicted N uptake. CONCLUSIONS Under the experimental conditions, N yield variations were closely associated with post-anthesis N uptake in diseased but also in healthy crops. Understanding the respective roles of N uptake and N remobilization in the case of diseased and healthy crops holds the promise of better modelling of variations in N yield, and thus in GPC.

Ozone and aging up-regulate type II metacaspase gene expression and global metacaspase activity in the leaves of field-grown maize (Zea mays L.) plants

Maize plants (Zea mays L. cv. NK Perform) were exposed to O(3)-enriched air, using a new field fumigation system. Transcriptional changes for three type II-metacaspase genes were studied in the leaves (ranks 10 and 12), using quantitative real-time PCR. Global metacaspase activity was measured using metacaspase-specific synthetic tripeptide Boc-GRR-AMC. Aging had little effect on mRNA accumulation whereas four to six-fold increases were observed for the most O(3)-responsive type II metacaspase genes, in the older leaves 10. Global metacaspase activity increased by 257% and 333% in leaves 12 and 10, respectively, in response to the highest cumulated concentration. In non-fumigated plants, metacaspase activity progressively increased over the course of the experiment and always was higher in the older leaves 10. Together, these results suggest that metacaspase-mediated proteolysis is a crucial step in leaf responses to both O(3) and age-mediated senescence.

Comparison of different models predicting the date of beginning of flowering in pea (Pisum sativum L.)

Abstract In pea, the time of flowering is mainly related to the photoperiod ( P ) and mean temperature ( T m ) during the vegetative period. In field conditions, both variables depend mainly on the latitude (LAT) and the date of sowing (RDS). On the basis of these four variables, several empirical models simulating the time to flowering either in days or in degree-days were calibrated (the parameters determined) and compared for pea (cv. Solara). Data were from trials in various locations throughout France over 8 years and with several sowing dates (from mid-November till mid-April). Surprisingly, the model with the more explicative variables ( P and T m ) did not give the most reliable results in field conditions as assessed with a validation sample of situations including many years and locations. The best fit and MSEP (mean square error of prediction) were obtained by combining P , RDS and LAT in the model. Models can be constructed to use days or degree-days: models in days are very useful for crop management, whereas models in degree-days are well-adapted for crop modelling. The case of autumn sowings was analysed separately: models were recalibrated to give a good account of the whole range of sowing dates.

Identification and characterization of MOR-CP, a cysteine protease induced by ozone and developmental senescence in maize (Zea mays L.) leaves

Among the different classes of endoproteases, cysteine proteases are consistently associated with senescence, defense signaling pathways and cellular responses to abiotic stresses. The objectives of this work were to study the effects of various concentrations of ozone on gene expression and enzymatic activity for papain-like cysteine proteases (PLCPs), in the leaves of maize plants grown under field conditions. Leaves from ranks 12 and 10 (cob leaf) were harvested regularly over a long-term artificial ozone fumigation experiment (50 d). Tissues were tested for transcriptional and activity changes concerning cysteine proteases, using qRT-PCR for the newly identified ozone-responsive PLCP gene (Mor-CP) and synthetic oligopeptide Boc-Val-Leu-Lys-AMC as a PLCP-specific substrate, respectively. Results showed that developmental senescence induced a significant and progressive rise in CP activity, only in the older leaves 10 and had no effect on Mor-CP gene expression levels. On the other hand, ozone dramatically enhanced Mor-CP mRNA levels and global PLCP enzymatic activity in leaves 12 and 10, particularly toward the end of the treatment. Ozone impact was more pronounced in the older leaves 10. Together, these observations concurred to conclude that ozone stress enhances natural senescence processes, such as those related to proteolysis.