Jean-François Sigrist - Numerical Simulation, An Art of Prediction, Volume 2

More than 20 years ago, this mode of production was not understood. At the beginning of the 2000s, it became a guarantee of quality and consumers were not mistaken, meeting the offer proposed by the two brothers and by other producers in their region. Their bet proved to be a win–win situation for all.

Models developed by researchers in digital agriculture can support the decision and transition required by such reconversions (Figure 1.11). Hélène Raynal explains:

“Models contributing to decision-making are a delicate matter. They reproduce, at the farm level, the calculations made, for example, for the whole country in the context of public policies. Including detailed data – such as the equipment available for irrigation or exploitation, crop organization and location on the land, possible polyculture rotations, cohabitation with livestock, etc. In addition, the models also seek to capture farmers’ preferences: the risks they are willing to take in their investments, the balance they want to favor between short- and long-term productivity, the time they spend at work and how they can integrate environmental issues”.

Simulations are carried out on the plots and make it possible to develop an overview of everyone’s practices. By enriching them with climate change data, they offer farmers the opportunity to anticipate some of their consequences in the long term.

“The criteria for analyzing simulation data are developed with the farmers involved in the process: this joint approach is essential to ensure its relevance and quality. While the most traditional indicators are those of investments and returns, operators also include those of quality of work, such as the possibility of taking days off… This criterion is, for example, a determining factor in the choices of certain operators – and it is highly contextual”.

Many professionals are on the lookout for new practices and the models proposed by researchers give them the means to make profitable decisions.

Figure 1.11. Working hours (per ha and per year) required by a farmer for “conventional” agricultural production (yellow squares) and pesticide-free production (orange triangles), as part of a durum wheat and sunflower crop rotation, in southwest France [RAY 17]. For a color version of this figure, see www.iste.co.uk/sigrist/simulation2.zip .

NOTE.– Statistical models to predict yields .

Complementing or replacing equation-based modeling, statistical models allow yield projections of new crops. A protein-rich legume the planting of which allows crop rotation does not require nitrogen fertilizers and offers to diversify production; soya is the subject of European agronomic studies, while its production is largely carried out in other continents, North America and Asia in particular.

Figure 1.12. Soya is a legume valued for its nutritional qualities and whose intensive cultivation in some parts of the world also has a negative influence on the environment

(source: www.123rf.com )

Where to grow soybeans in Europe? Following which practices (using phytosanitary products whose harmful effects on the environment are feared… or by means of organic farming)? What are the expected yields? How could climate change affect its implementation? Numerical modeling helps to answer these questions, as Nicolas Guilpart, an agronomy researcher, explains:

“Data-based modeling exploits the statistical relationships between yields recorded in regions of the world and climatic conditions recorded during growing periods. Such modeling uses automatic learning techniques and characterizes ecological niches, the regions in which a culture can potentially develop”.

Performance data for soybeans, or any other crop, around the world can predict areas suitable for cultivation in other regions, whose climatology – and other factors, such as soil quality – are similar . Based on global data, the prediction is still limited to regions the size of a French department. The models also reveal the likely evolution trends of these areas with climate change.

Figure 1.13. Calculation of wheat crop yields in France and worldwide: the figure represents yield increases estimated by statistical methods, in different countries of the world and for the French departments. The unit is the ton of wheat per hectare cultivated and per year [MIC 13]. For a color version of this figure, see www.iste.co.uk/sigrist/simulation2.zip .

Fertilizers are organic substances, of plant or animal origin, or mineral substances (synthesized by the industrial fixation of atmospheric nitrogen) intended to provide plants with nutrient supplements. They contribute to improving their growth and increasing the yield and quality of production.

Figure 1.14. Fertilizers promote plant growth but their overintensive use has long-term harmful effects on the environment or may be dangerous for human health

(source: www.123rf.com/ )

COMMENT ON FIGURE 1.14.– Often used in a mixture, fertilizers are mainly composed of three elements: nitrogen contributes to the vegetative development of all overground parts of the plant, phosphorus strengthens their resistance and participates in root development, and potassium promotes flowering and fruit development. They also provide plants with complementary elements (such as calcium or magnesium) and trace elements (such as iron, manganese, sodium or zinc), useful for plant life and development. Their use dates back to the early days of agriculture and, nowadays, the development of the chemical industry encourages their use, sometimes to an excessive extent .

Their widespread use worldwide (Figure 1.15) supports the yields expected by some farmers, often at the expense of soil, water and air quality. Used in excessive quantities, fertilizers are responsible for the depletion, or even destruction, of ecosystems – inhibiting the ability of soils to regenerate naturally or permanently polluting groundwater reserves.

Figure 1.15. Global use of nitrogen, potassium and phosphate fertilizers worldwide in 2014: major agricultural countries are making massive use of fertilizers. The quantities used are expressed in kilograms per hectare of cultivated land (source: Our World in Data/ https://ourworldindata.org/fertilizer-and-pesticides ). For a color version of this figure, see www.iste.co.uk/sigrist/simulation2.zip .

Sophie Genermont, a researcher at INRA, has been working for more than 20 years on the development of a platform for simulating ammonia emissions resulting from the use of fertilizers [GEN 97, RAM 18], which contribute to the degradation of air quality: