Christian Gary

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.

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.

An open platform to build, evaluate and simulate integrated models of farming and agro-ecosystems

Due to significant changes in agro-ecological contexts, farmers need new solutions to produce goods. Modelling complements field experiments in the design of new farming systems. French researchers involved in such design issues developed a specific modelling platform to help model, simulate and evaluate cropping systems. After testing several existing environments, the RECORD platform was developed under the VLE environment, allowing the design of atomic and coupled models. It integrates different time steps and spatial scales and proposes some standard formalisms used to model agro-ecosystems (e.g. difference equations, differential equations, state charts...). A graphic user interface was designed to simplify coding tasks. A variety of research projects already use this platform. Examples are given showing the ability to recode simple models, encapsulate more complex models, link with GIS and databases, and use the R statistical package to run models and analyse simulation outputs. The option to use web interfaces enables application by non-scientist end-users. As the models follow a given standard, they can be placed in a repository and used by other researchers. Linking RECORD to other international platforms is now a compelling issue.

Optimal temperature regimes for a greenhouse crop with a carbohydrate pool: A modelling study

Abstract A simple crop model with two state variables, namely structural biomass and carbohydrate pool, was used to explore the effect of alternative temperature regimes on greenhouse crop production. Assuming a repeated environmental cycle, certain qualitative predictions could be made. (1) The smaller the plants and the higher the light integral and CO2 enrichment, the higher are the temperatures which lead to maximum production. (2) Day temperatures higher than night temperatures usually lead to higher production. On winter days, however, an inverse temperature regime may result in energy saving without loss of production. (3) Temperature variations may often be tolerated, provided that the mean temperature (temperature integral) is maintained at the level appropriate for maximum production. A limited amount of published experimental data was used to fit the model, leading to a satisfactory agreement.

Source-sink balance affects reproductive development and fruit quality in cantaloupe melon (Cucumis melo L.)

Summary Competition for assimilates affects fruit quality in many species, while seed content is reported to influence only fruit weight. Our study was aimed at determining whether and/or how source-sink balance and seed content in cantaloupe (Cucumis melo L.) could affect flowering, fruit set, growth and fruit quality including the physiological disorder “water-soaking” which is important for the market-value of this fruit. We followed standard cultivation practices for early cantaloupe production under greenhouse conditions and studied fruit and flower removal over 2 years with two “Charentais” cantaloupes cultivars, and limited hand-pollination treatment for 1 year on one cultivar, and recorded the quality attributes of the fruit. Reproductive development in both cultivars was characterised by the production of a large number of female flowers on plants bearing a single fruit. Fruit set and fruit growth rate were affected by the intensity of pollination, probably by the ability of fertilisation to promote cell division and increase the sink strength of the young ovary. Fruit load did not affect the average number of seeds per fruit, yet individual seeds were lighter under high fruit load. A significant difference in final fruit weights obtained with similar cultivars and treatments between the 2 years is discussed. Fruit quality was affected by source-sink balance. Seed content within a fruit correlated with individual fruit weight, affected flesh firmness, the sweetness of the flesh and slightly affected the occurrence of “water-soaking”. Competition for assimilates within a plant decreased the sweetness of the flesh and dramatically increased the occurrence of “water-soaking” in both years and in both cultivars. Climacterium also increased with a low source-sink balance, and an ethylene burst was confirmed to be closely-related to flesh firmness.

Modelling adaptive management of intercropping in vineyards to satisfy agronomic and environmental performances under Mediterranean climate

In the Mediterranean area, rainfed viticulture is exposed to irregular rainfall distribution. The impacts on production and environment can be mitigated by appropriate management practices like, for instance, the introduction of cover crop in the inter-rows in vineyards. This paper presents the VERDI simulation model created to study various adaptive intercrop management strategies at field scale. The purpose is to design management strategies that are responsive to the water status of the biophysical system (soil - grapevine - intercrop) and the past and current climatic conditions. VERDI realistically reproduces the dynamic interactions between the biophysical system and the decision system in varying Mediterranean rain regime. The decision system works as an interpreter of a management strategy, defined as a set of soil surface management activities (e.g. mechanical weeding of the intercrop) that are linked by temporal constraints (e.g. sequencing, synchronisation) and organisational or programmatic specifications (e.g. iteration). The adaptive capabilities of the strategies are distinguished according to the different sources of flexibility to be exploited at operational, tactical, and strategic levels. A simulation study is reported that involves more or less flexible strategies under different climate scenarios. The simulation results proved that, in case of severe drought, the most flexible strategy yields the best trade-off between agricultural production and environmental services over the years.

Influence of cultivar, fruit position and seed content on tomato fruit weight during a crop cycle under low and high competition for assimilates

SummaryThe control of tornato fruit weight during a crop cycle may be of commercial benefit. To assess the main causes of variability in the potential and actual fruit weight of mature fruit, both were measured together with the seed content on three tomato cultivars. Potential and actual weight were appraised on plants with single-fruit and seven-fruit trusses, respectively, until maturation of the fifteenth truss. Variability in the potential weight was mainly related to the cultivar, whereas differences between proximal and distal fruits were significant for beefsteak tomatoes only. In the long term, no truss effect on this potential could be detected. Under competitive growth conditions, the weight of distal fruits was reduced more than that of proximal fruits especially for the beefsteak cultivar. All trusses were not equally affected, inducing a large variability along the stem. The relation between fruit weight and seed number was closer as the range of variability in fruit weight was reduced, that...

Changing the soil surface management in vineyards: Immediate and delayed effects on the growth and yield of grapevine

In a changing context, farmers adapt their cropping systems and, in this respect, the response time of the soil-crop system (changes in the soil resources and in the grapevine vegetative or reproductive development) has to be considered to maintain its agronomic performances. This is particularly true for perennial crops such as grapevine. This paper aims to analyse the short- and long-term effects of changes in soil surface management on grapevine performances. A vineyard in which bare soil inter-rows had been compared with a tall fescue intercrop since 2002 had each of these treatments split into two in 2007, with half of the intercrop being ploughed in and half of the bare soil being sown with fescue, resulting in four treatments whose effects were studied in 2008–2009. Grapevine growth, yield formation and grape quality were assessed. After intercrop destruction, grapevine vegetative growth was enhanced by the mineralization of organic matter from the first year, whereas after intercrop introduction, the competition for soil resources affected growth only in the second year. The grape yield depended on the number of bunches, elaborated the year before. One year after the change in soil surface management, the ranking of yield was as follows: permanent intercrop < intercrop destroyed < intercrop introduced < bare soil. The second year, this ranking altered (still in relation to the number of bunches) to: intercrop introduced < permanent intercrop < bare soil = intercrop destroyed. This study shows that the response times of the processes of grapevine vegetative growth and yield formation to a change in the cropping system vary from one to two years, and therefore, have to be considered carefully to manage the cropping system well.

GPSF: a generic and object-oriented framework for crop simulation

Abstract In this paper we present the result of an effort to reengineer an existing plant growth and development simulation program and model (TOMGRO) originally written in FORTRAN. The program was completely redesigned in terms of the OO paradigm and implemented in the Smalltalk OO programming system. Much thought and effort was put into the design and implementation of a conceptual framework that the authors believe has potential as a generic toolbox and specification for the construction of a whole family of plant growth and development simulation models. A relatively detailed description of the OO framework and of the OO implementation of TOMGRO is given. The objective is to provide neophyte readers with a practical example of an OO implementation of a non-trivial model and to interest readers who are more familiar with software engineering issues in general through the presentation and discussion of the various software constructs.

Primary and Secondary Yield Losses Caused by Pests and Diseases: Assessment and Modeling in Coffee

The assessment of crop yield losses is needed for the improvement of production systems that contribute to the incomes of rural families and food security worldwide. However, efforts to quantify yield losses and identify their causes are still limited, especially for perennial crops. Our objectives were to quantify primary yield losses (incurred in the current year of production) and secondary yield losses (resulting from negative impacts of the previous year) of coffee due to pests and diseases, and to identify the most important predictors of coffee yields and yield losses. We established an experimental coffee parcel with full-sun exposure that consisted of six treatments, which were defined as different sequences of pesticide applications. The trial lasted three years (2013–2015) and yield components, dead productive branches, and foliar pests and diseases were assessed as predictors of yield. First, we calculated yield losses by comparing actual yields of specific treatments with the estimated attainable yield obtained in plots which always had chemical protection. Second, we used structural equation modeling to identify the most important predictors. Results showed that pests and diseases led to high primary yield losses (26%) and even higher secondary yield losses (38%). We identified the fruiting nodes and the dead productive branches as the most important and useful predictors of yields and yield losses. These predictors could be added in existing mechanistic models of coffee, or can be used to develop new linear mixed models to estimate yield losses. Estimated yield losses can then be related to production factors to identify corrective actions that farmers can implement to reduce losses. The experimental and modeling approaches of this study could also be applied in other perennial crops to assess yield losses.