When farmers decide to implement cover crops on their farms, they usually lack available data regarding the performance of species and/or cultivars in their own pedo-climatic context.
Testing different species and/or cultivars of cover crops on the farm generates useful local data on the performance of species and/or cultivars. The French MERCI tool (Méthode d’Estimation & des Restitutions par les Cultures Intermédiaires) facilitates their evaluation.
The acquired information on biomass production and expected nutri-ent release of cover crop species and/or cultivars will provide greater certainty for the selection of suitable varieties and the estimation of fulfilment of the nutrient requirements of the subsequent crop.
Method and results of practical testing
MERCI is an easy-to-use tool which simplifies:
• Estimation of the dry matter produced per hectare (tonnes per hectare);
• Calculation of the nitrogen trapped (or stored) by the cover crop;
• Definition of the nitrogen refund levels for the subsequent crop (kg/ha).
The references used in the calculations are based on more than 10 years of trials on cover crops in Poitou-Charentes/France. Simulations are carried out with INRA's STICS software.
ITAB, together with a group of farmers, tested the MERCI method, undersowing different cultivars of white clover in a winter wheat field on a farm in Central France (Saint Fargeau, Yonne). The following 6 cultivars were grown: 3 dwarf cultivars (Huia, Rivendel and Pirouette), 2 intermediate “Hollandicum” cultivars (Merwi and Jura) and 1 giant cultivar (Excell). The cultivars were compared to a mixture of species as a control.
The white clover species was sown on 26 March 2017 into winter wheat. Weeds, cover crop development (plant den-sity) and winter wheat development were monitored along the cover crop cycle (3 times). The performances of 4 cultivars were estimated in early November, using the MERCI method. Weeds were identified and their total ground cover was estimated. For each cultivar, the fresh biomass from three 1 m² plots was sampled (Fig. 1), weighed and used as an input in the MERCI tool. The most promising results were identified for Merwi cultivar (Tab.1).