Les légumineuses, une alternative dans les systèmes visant à réduire leurs intrants azotés

Leguminous, an alternative for farming systems looking for a low level of nitrogen input

Context

In organic farming, to which Walloon area wants to convert 10 % of its UAS before 2010, crop nitrogen fertilisation management, at different plant development key stages, remains one of the main brakes to good yield performing.In order to face this problem of nitrogen supplying, farmers use organic fertilisers with a more or less rapid effect, range from the compost till cattle slurry, and manage their rotations to take the best out of leguminous species. So they take profit from the direct and the long term effects of different crops such as temporary grasslands, leguminous rich fallow, grain legumes crops, …

Objectives

The main target of this project lies in the definition of alternatives that allow to include leguminous species in the rotation while taking into account the technical itinerary to adopt to obtain high quality yield.

The aspects that are or have been taken into account are :

* the management and the use of cereal-grain legume associations, to harvest at maturity, in livestock farming systems : which association and which species ratio to promote?

* the definition of the advantage to use high diversity grassland mixture instead of traditional ‘Perennial Ryegrass – Timothy – Red Clover’ association.

* the potentialities of a cereal under-sowed in a white clover sward to extend rotation length within organic farming systems.

* leguminous drying management : a key stage to limit quantity and quality losses.

Results obtained

Grain legume – cereal associationsCereal-pea mixtures introduce plant protein in organic livestock farming systems and nitrogen to the actual and following crops. However the mixture equilibrium is difficult to reach. In order to define it, a trial associating different cereal (oat and barley) and pea densities and this for different pea varieties.A clear yield impact of the cereal species has been observed : barley based associations have a yield of 1.3 T/ha higher than oat based associations. These better yields are mainly linked to the better pea development in associations with barley, less competitive. Indeed, in these associations, oat yield was, in mean, of 2.5 T/ha against 2.1 T/ha for barley.Species rich association for meadowUnder a mowing exploitation scheme, after nine years of records and analysis, associations of more than 5 leguminous and 5 graminae species do not present, under our soil and climatic conditions, any clear advantage and this neither on a qualitative nor on a quantitative point of view, in comparison to the classical perennial ryegrass – white clover association.Species rich sward showed often an advantage the implantation year but, linked to a lower persistence of the clover species used, saw their performance decreased more rapidly. These observations are of value with or without the use of a cover crop the implantation year.We can also underline the quick decrease of the initial floristic diversity in these mixtures : species adapted to a cutting regime, like cocksfoot, perennial rye-grass, red clover, …, are the more persistent.In order to explore this problematic ahead, we have set up, in the context of an INTERREGIV ‘Wallonie-Flandre-France’ project, an experiment aiming to record species rich mixtures performances under contrasted management schemes. (1) Under mowing with two fertilisation levels and two cut frequencies, under grazing and under mowing – grazing mix schemes with different levels of organic fertilisations. These trials, set up in 2008, will be followed up from 2009 till 2011. The impact of these different management schemes on biodiversity, on sward productivity and on the stabiity of this productivity will be quantified. Winter cereal implantation in a white clover swardThe aim of this trial is to length the rotation scheme of ‘3 years of temporary grassland – 3 years of cropping’ usually applied in organic farming in ‘ 3 years of temporary grassland – 6 years of cropping’ with the under-sowing of a white clover cover, on the 4^th year of cropping, in the spring cereal. This culture will be followed by two winter cereals that will be sowed, without deep tillage, in the white clover cover.During this first year, different modalities of soil preparation, before winter cereal (spelt) implantation in the white clover sward, have been tested. These modalities went from the deep tillage to the direct sowing technique, by the way of different lighter tillage techniques. Their objectives were to slow white clover development before spelt implantation. The results obtained underlined the interest of a stubble barrowing followed up by a rotary barrowing.Under such a scheme, the recorded yields were lower than after normal ploughing itinerary that destroy all the clover cover. However, in such a scheme, clover effect is expected to be not significant during the second year after ploughing.Some approaches are running to quantify the nitrogen effect of the white clover cover.Drying losses during hay and silage makingThese trials have been settled to quantify quantitative and qualitative losses observed during leguminous rich sward drying. Indeed, leguminous leaflets break off easily during forage drying. Different technical itineraries were evaluated.Associations taken into account are the perennial ryegrass – white clover (PRG-WC), the PRG – red clover (RC), the timothy – red clover (T – RC) and the cocksfoot – lucerne (C-L) ones.Technical itineraries taken into account in 2003 are, during the first cut (with hay production), the impact of mower type, to say with or without conditioner, and, during the second cut (with silage making), the impact of the tedder rotation speed (270 versus 540 rotations per minute (r/min) at the power plug). Leguminous composed, in mean, 65 and 80 % of the dry matter (DM), respectively, during the first and the second cut.Losses observed, on a DM basis, were of 41 and 27 %, respectively during hay and silage making. There was no effect of the mower type while the increase of the tedder rotation speed had increased the protein losses from more than 11 % without significant impact on the final DM content. As expected, the main losses were observed at the level of leguminous leaflets. This was confirmed through the development of a NIRS calibration allowing to quantify leguminous leaflets proportion in a graminae – leguminous mixed sward (see the project ‘Adaptation of grass varieties to grazing : persistence and palatability’).These results support the high losses that could be observed during leguminous rich sward drying, losses that are more than twice the ones observed with a pure graminae sward. This parameter must be taken into account while making the promotion of leguminous use in farming system wanting to decrease their nitrogen input dependency.

This study is on the run while testing other technical itineraries.

Contribution

The Farming System Section is the project leader. It is occupied of the establishment and the follow-up of the project, as of the analysis of the results.

Partners

E. Montignies, Centre for organic farming and horticulture trials (B, Wallonie).P. Luxen and D. Knoden, Better Forage npo (B, Wallonie).C. Ducatillon, CARAH (B, Wallonie).L. Delanote, PCBT (B, Vlanderen).

A. Lecat, Chambre d’Agriculture du Nord (F).

J. Zaoui, GABNOR (F).