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L'Unité Expérimentale de Gotheron développe des programmes d'expérimentation-recherche sur les systèmes de production durable en  ARBORICULTURE  fruitière (abricotiers, pêchers, pommiers, poiriers). © MAITRE Christophe

Water and agriculture

The impact of drought on permanent grasslands

The livestock sector is always the hardest hit during a drought. Spring droughts affect forage production on temporary and permanent grasslands, with permanent grasslands requiring more time to recover. Research at INRA provides tools for better permanent grassland management in periods of drought.

Today, permanent grasslands cover nearly one-third of farmland in France. In the Limousin region, for instance, they represent half of grasslands and are an important source of food for livestock herds, especially pastures. Moreover, permanent grasslands are currently viewed at the European level as an important lever for maintaining environmental quality. These areas are synonymous with plant and animal biodiversity, serve as carbon stores and slow down erosion.

 

Grassland “recovery” after drought

Permanent grasslands cover nearly one-third of farmland in France. © TOILLON Sylvie
Permanent grasslands cover nearly one-third of farmland in France. © TOILLON Sylvie
While temporary grasslands can be reseeded, permanent grasslands often require several years to return to normal after a severe drought. Research carried out by INRA on experimental plots show that certain species can languish (grasses and legumes), while weeds such as thistles and dock weed can thrive in the “holes” created. According to Pascal Carrère, director of the Joint Research Unit on Grassland Ecosystems at INRA Clermont-Ferrand, “When well-managed and looked after, permanent grasslands can withstand extreme stresses and the diversity of plants there makes regeneration possible once the drought is over. It is important to keep in mind the mix of flora, the number of animals, fertilisation and the rotation between pasture and cutting.” On plots where machinery can be used, oversowing can compensate after the fact once the superficial layer of soil has been worked to replant original dominant species. Current research by INRA on grasslands is broken down by typologies. Agricultural advisors can then pass on comprehensive information to farmers on the distribution of flora, agricultural and environmental values, and the services that can be expected from the land. These typologies are precious points in discussions with livestock farmers so they can adapt their practices to the production potential of their grasslands (www.prairies.aop.net).

 

Optimising grass harvest according to temperature

 

INRA Toulouse (Joint Research Unit – Agrosystems, agriculture, resource management, innovation and rurality, www.agir.toulouse.inra.fr/agir) has created software, Herb’âge, that enables grass harvests from permanent grasslands to be optimised by calculating the maturity level of the vegetation depending on the sum of temperatures since the last cutting. Certain chambers of agriculture use this tool to give advice on the date to cut via “grass management” network newsletters. The team at INRA Toulouse has also developed more complex research models that aim to create less risky systems with regards to climate variability and long-term climate evaluation.

 

Forecasting the yield of permanent grasslands

The darker the colour, the lower the growth. Regions in white: no growth. ISOP system. Source: Agreste. © INRA, ISOP system
The darker the colour, the lower the growth. Regions in white: no growth. ISOP system. Source: Agreste © INRA, ISOP system
Since the production of grasslands is essentially consumed on farms by the livestock, without any sale, estimating the forage production is difficult by the traditional methods used for arable crops, based on the data of sales companies. Hence the formulation of a request in 1997 by the French Ministry of Agriculture which led to the setting up of ISOP (information and objective monitoring of grasslands). This system is the result of a joint effort between Météo-France, INRA and the French Ministry for Agriculture (department of statistics and foresight), and provides the Ministry with an objective outlook of damage by region. It calculates the quantity of dry matter per hectare, day by day, over small forage regions considered as having homogeneous climates, while respecting a variety of soils and practices within each of the 228 defined forage regions. To do so, the STICS plant development model, which has parameters characterizing the grasslands, must be provided with spatial input data, which is carried out using a base designed specifically and which concerns agricultural practices (statistical survey), soil (map of soils of France) and the daily climate.

The role of grasslands and forests in soil water regulation

Ground cover plays a key role in soil water regulation during heatwaves. Recent results show that forests and grasslands especially do not react in the same ways. At the start of a heatwave, forest land warms up faster, but conserves humidity better over a longer period of time. Grasslands, however, experience increased evapotranspiration, which slows down soil heating but accelerates drying. These phenomena can have significant consequences on the regional climatic system. This could offer an explanation for the situation observed during the 2003 heatwave.

Publication:

Adriaan J. Teulinget al.(2010). Contrasting response of European forest and grassland energy exchange to heatwaves. Nature Geoscience, 3 (10), 722-727