So, in our case, if we include in the carbon balance, the emissions of CH₄ and NO₂ (these two greenhouse gases have a higher global warming potential on the atmosphere than CO₂), we end up with a positive GHG balance. Is this bad news for cattle-rearing as practiced in Wallonia? The researcher from Gembloux is careful not to draw any such conclusions. She specifies that, in the first instance, while the grassland studied at Dorinne is grazed on by Belgian Blue cattle which are so prevalent in Wallonia, this fact cannot alone account for the diversity of cattle-rearing practiced in the south of the country both in relation to breeds and pedoclimatic conditions. "In terms of the soil and climatic conditions, Condroz is neither the High Ardennes nor the Pays de Herve.". The grassland studied in Dorinne, moreover, is characterized by intensive farming methods: the use of fertilizer is quite important there and the number of head of cattle that grazed there (on average, two livestock units per hectare per year). It is also probable (even though this could not be significantly demonstrated), that the two episodes of drought that occurred during the period under consideration (summer of 2010 and spring of 2011), had the effect of reducing the production of plant biomass and therefore the absorption of CO₂ by the plot.

Ongoing benefits

It will be useful to make some further basic comments on the results obtained. The meadow in Dorinne is old. Studies have demonstrated that the capacity of grassland to play a carbon-storing role dwindle over time. “This could explain why our plot is neutral from the point of view of the carbon balance for the three years studied”, comments the researcher. Finally, and this is certainly not the least of the qualifications to be applied to the results, the carbon balance  must not exclude the fact that: “The grassland predominance in the walloon landscape justifies itself by climatic and agronomic constraints. Indeed, in some regions,  the sum of temperatures and the length of active vegetation are weak so it limitates considerably the choice of growing likely to reach ripeness with certainty before harvest. In other regions, grasslands establish itself because of the ground nature, plot positioning or even territory relief. That’s why meadows in Wallonia cannot, for the most part, be replaced by crops and are therefore grassland that can only be efficiently used by grazing animals. Thanks to the presence of a rumen above the stomach, bovine animals are the only ones capable of transforming the grassy biomass into products that have a nutritional value for humans, such as milk and/or meat. This type of breeding based on the use of grassland products also makes it possible for farms and the families on them to survive and benefit the ecosystems which provide important ecological services benefits such as the slowing of water run-off, protection against soil erosion, improvement of soil fertility, maintenance of biodiversity etc.”

Given the variability of CO₂ flux results demonstrated by this work (the Dorinne meadow also seems to have been an important sink of CO₂ in 2014, the year that Elisabeth Jérôme continued her long-term studies. “This is the only way to test the reliability of the carbon balance results”. But from here on, as farm management was the factor that had probably the most effect on the variability of fluxes (CO₂ and the others); it seems that possible ways of improving the carbon balance (increased storage of carbon in the soil) exist. One of them, which is currently being studied, consists of factoring grazing intensity. How could this be done? On an adjacent plot to the one studied in the thesis, a rotational grazing was introduced. Instead of allowing the entire herd of cattle to graze continuously or at least during quite lengthy periods, the duration of grazing was limited to two or three days, and on a plot that was greatly reduced in size. The animals were allowed to enter the plot once the plant cover reached a height of 10 to 15 centimeters. The herd was removed when the grass was down to 5 cm (the herd was then conducted to another plot). “Each system has its advantages and disadvantages”, comments the bio-engineer. “In general, good rotating pasture management makes it possible to maximize the production potential of the meadow and to use it in an optimal way. Permanent grazing can sometimes cause the over-grazing of some areas and the under grazing of others. The objective is to establish, by the end of this study, the complete carbon balance on the scale of the two adjacent plots, and in this way, to see whether the change in grazing management increases-or not-the storage of carbon by the meadow”. It follows from this that breeders should be informed as to how they can make a contribution to the struggle against climate change.