Concilier performances économiques et environnementales au sein des exploitations herbagères

Conciliate economic and environmental performances in dairy farms based on grassland

Context

Since 2007, the nitrogen directive defines, in the Walloon area, new vulnerable zones including the area located north of Sambre-Meuse, the southern part of Namur and the Herve Country. This alarm underlines the necessity to improve nitrogen management, even in livestock farming system based on grassland, and this even if the positive impact of grassland on nitrogen leaching reduction is recognized. On this basis, the Walloon regulation has adopted new standards of organic nitrogen input since the 1^st January 2007. These standards are of 115 kg organic N/ha in cultivated land and 230 kg organic N/ha in grassland, restitution under grazing included and this with a maximum of 250kg/ha of total nitrogen in cultivated land and of 350kg/ha in grassland. In vulnerable zone, an additional constraint is to respect the 170 kg of organic nitrogen per ha, imposed by the European Community. In such zone, the exploitations with at least 48 % of their utile agricultural surface under grassland can derogate to this additional constraint and increase the 170 kg limit in consequence. In such a case they will accept to quantify nitrate leaching risk in a representative sample of their parcels.

So a special attention was given to indicators of N losing risk in the environment such as to (1) the N balance and (2) the nitrogen leaching risk, reflected by the soil nitrogen content in autumn. However, in its actual version, this last indicator does not integrate parameters such as the date or type of fertilizer application and so badly reflect the real risk of water pollution under grassland and more especially under grazed grassland characterized by a strong heterogeneity of urine patch deposition.

Objectives

The main objective of this project is to complete and validate the list of factors to take into account, together with the definition of their critical thresholds, in order to set up the “survey of the agricultural surfaces” define in the Walloon government arrest of the 10 October 2002 for "sustainable nitrogen management in agriculture”.

To do so we focus on :

– the identification, the validation and the diffusion of the agronomic practices allowing to reduce the nitrogen balance in dairy farming systems based on grasslands valorisation;

– the validation and the definition of the critical limits for different environmental pressure indicators;

– the integration of the available data in a Decision Support System that will allow an evaluation of the nitrogen loses risk, at the parcel scale.

Results obtained

With the collaboration of the Technico-Economic Service of the AWE, 232 specialized dairy farms (OTE 411) were selected in the Herve County, the Ardenne and the High Ardenne areas. This selection was based on economic performance and nitrogen balance sheet. Selected criteria were the part of milk in the total production (>70%) and the economical efficiency of the production process (Gross Margin and cost/litre of milk), and that during three consecutive years (2000, 2001 and 2002). The nitrogen balance sheet of these exploitations, during the same period, allowed to distinguish 3 groups : a first one with a N balance sheet smaller than the average minus two standard deviations, expected to exert a smaller environmental pressure, a second one with the exploitations having a N balance sheet included between the average ± 2 standard deviations, and a third one having their nitrogen balance greater than the average added of 2 standard deviations, expected to exert an higher environmental pressure. Twenty-six exploitations were chosen in the first and third groups.The evaluation, with the IDEA method, of the environmental, economical and social sustainability of these 26 exploitations showed, as expected following choice criteria, that these exploitations were efficient from the economical point of view, even if the way followed to reach such good efficiency was not always the same. The environmental sustainability was rather weak, due to the high specialization of these farms.A typology has been performed, leading to the constitution of 4 exploitations groups. Criteria used to set up this typology were:– The level of production intensification, expressed throughout the number of litter of milk produced per hectare (> or < 9000 l/ha);– The presence or absence of maize in the cropping system.These 26 dairy farms were followed during the pasture season, in 2004, while 19 of them remained in 2005. The farmers recorded all the management operations performed on their pastures (fertilisation, grazing time, stocking rate, …) while swards, animal performances, manure, … were characterised during monthly visit. Soil analyses were also performed at the end of the grazing season in 4 grazed grasslands per farm in 2004 and in 3 grazed grasslands per farm in 2005. All these data had allowed to quantify the nitrogen balance at the paddock scale. Nevertheless, even if some tendencies were highlighted, no significant relation was obtained between the nitrogen balance and the technical practices recorded.We develop a decision support system, based on regression and classification trees method, aiming to classifies the paddocks according to the risk they have to develop important nitrogen residue in the soil in function of the agricultural techniques applied by the farmer. The techniques took into account had to be easy to apprehend. This tool shows the important impact of the stocking rate, either during the whole season or in autumn, on such nitrate leaching risk (fig 1).

Contribution

The Section is the project leader. In collaboration with the STE-AWE, we have selected 26 dairy farms and set up the first contact with these farmers to present the project.

The farming system section was in charge of the monthly visit, of samples collection, of nitrate sampling in 4, of results analysis and discussion.

The Section also establishes (2004) and will follow up (2005-2006) drained grasslands, in Mussy-la-Ville, to link grazed grassland management to nitrate leaching risk under our pedo-climatical conditions.