This risk the report says have few solutions

It took 25 experts, a bibliography of some thousands of scientific publications and a 350-page report to this observation: the monoculture of maize mortgage the sustainability of water resources. This is in any case finding unofficial of the authors of the work of expertise that comes from making the Inra with academic partners. To prevent the bad faith of many producers of corn, the report is much more nuanced. "We are not pointing the farmers but lead them to the discussion", temper Bernard Itier, the head of the Inra report.

Launched in 2005 at the request of the Ministry of Agriculture, the expertise ambition to study the influence of agriculture on the drought and vice versa. So far, agronomists were especially interested in the impact of agriculture on water quality. Drought in 2003, 2004, 2005 and 2006 have relaunched the research on the problem of the quantity of water, neglected since the 1970s.

The experts through the scientific literature to gather the State of the art of knowledge on the subject. First observation, most research focus on the aridity, structural situation of lack of water, more than on drought, insufficient rainfall episode limited in time and space. Bernard Itier recalled that the France is affected by the drought, 930 mm of water per year dousing its soils. More than rainfall, it is especially the configuration of watersheds that can be a problem. South-East of the France needs of 400 millimetres of water on average he gets with external resources from the Alps and transported by the channel. In the Southwest, the needs are three times lower but its sources are insufficient: it must tap into groundwater and rivers. The report also analysed the reasons for the drought in Poitou-Charentes, very touched by the phenomenon. Once again, the rainfall there is be deficit averaged but its geology denies generous groundwater: water falls in the winter but stores is not for the summer. Modelling of climate scientists leave hope no improvement: all converge on the degradation of the drought in the South of the France. More to the North, the winter will be more rainy but it was dry.

However it is this summer as summer crops, corn in mind, grow the most and therefore pump more water. Agronomists recall that corn uses more water than the winter wheat species. So-called "C4" (type of metabolism), it is even more efficient in water than other plants in C3 which lost by transpiration 600 grams of water against 300 grams for the C4. The problem of corn is its summer growth requiring six times more irrigation. The report states: "In many cantons, grain corn irrigation rate exceeds 75." From 1970 to 2000, irrigation has been multiplied by three in France.

This risk, the report says have few solutions. Very surprising, agronomists do not believe in particular to the improvement of plants. François Tardieu geneticist is categorical: "can not grow without water, plants need strongly to the level of the stomata to absorb CO2 and produce biomass. Their metabolism causes evapotranspiration of 6 litres per metre squared per day. This represents 200 of their mass, humans sweat them 2 of their body. Increase the resistance of plants to drought, progress has been made, dry yields increased by 50 kilograms per hectare per year in fifty years. Transgenesis is likely to resolve the issue, no scientific communication is currently credible on the subject.

Use of other species

The researcher is expected nevertheless to what different search strategies to win 10 percent of additional performance. Agronomists are looking earlier genotypes to move forward the dates of crop seedlings and therefore limit the summer periods during which plants such as corn pump more water. Another trick is to decrease their evaporation. It is possible to limit the size of the leaves or to close the stomata of the plants to reduce photosynthesis from the appearance of moisture stress. But Bernard Itier warned: "If it decreases too evapotranspiration, are the pay by an increase in temperature of the atmosphere." The water absorbs much energy from the liquid state in the soil in the gaseous state. Full day of summer, on 500 watts received from the Sun, a tract absorbs 350 to 400. "A bare soil can increase the temperature of 20 to 30 C in the hot region." Some teams also managed the strategy of the roots of plants, up to 40 centimetres to facilitate deep depletion. But still, the complexity of the plant world makes modest researchers: "this technique can be catastrophic if the plant is no reserve of water deeper." Other research in the Mexico studied a strain of plants sorted in every generation for their resistance to the dryness. A fifth generation, researchers found that the best organisms were those with shorter roots... ", relativizes François Tardieu.

Finally, the approach of the engineering plant to maintain the development of the functions of the plant in times of famine seems promising but she returned to barter the safety against a maximum yield. We know require corn to continue its flowering and therefore its production of biomass, risking increased mortality.

The skepticism of agronomists is shared by another report on the water presents the Academy of sciences today. Its author, Ghislain de Marsily, recalled that "the water-carbon exchange at the level of the stomata seems too complex genetic to let hope an artificial reduction of the amount of water lost in Exchange".

For the authors of the report of the Inra, the most promising solution is "cropping cycles and species diversification." On some terroirs like clay-limestone in Midi-Pyrénées, only the winter crops are acceptable. On the more generous soils, agronomists recommend replacing corn by cultures close but more tolerant to drought as sorghum or sunflower. Crops of corn, they should be reserved for the soils of valleys.

To the work of agronomists, the maïsculteurs stream continues to kick into touch. At the recent symposium for the restitution of expertise, in Paris, his representative, Henri-Bernard Cartier, recalled the economic importance of this global market. Other farmers, as Luc Sevran, of the Chamber of agriculture of Poitou-Charentes, were more open by calling a change of system of crops, while recalling the difficulties into new channels such as the sunflower. One thing is certain, "globally, agriculture is fundamental because it is the largest user of water", sinking the Academy of sciences.