Herbicide-free systems based on under-the-row grass cover in French vineyards

Abstract

Context and purpose of the study – In a context of reducing herbicide use, the most part of French vineyards are developing permanent grass cover crops on inter-rows alleys, while under the row chemical weeding remains the general case. The setting up of a controlled grass cover crop under the vine row could be a complementary alternative to mechanical weeding – which one is very restrictive – interesting from a technical and economical point of view. The present study aimed at assessing agronomic impacts of grass cover crop under the row in different climatic conditions and production objectives.

Material and methods – Two soil management treatments – under-the-row grass cover and chemical weeding, i.e. bare soil – were compared on two experimental plots in South-west and Mediterranean regions of France. Maximum percentage of grass cover per plot was 100% on South-west site and 30% on Mediterranean site. Experiments were implemented since 2007 on Malbec grape variety within AOP Cahors and since 2010 on Syrah within IGP Vin de Pays d’Oc. Each treatment was replicated three times in a complete randomized block design. Experimental monitoring was carried out over the medium to long term (six to nine years). Data were annually collected on grapevine production – yield, vigour – and water and nitrogen status (water potentials dynamics, leaf chlorophyll index, must assimilable nitrogen).

Results – On Mediterranean site, introduction of under-the-row grass cover has not resulted in a significant decrease in yield or vigour. On South-west site, yield was reduced for this treatment in comparison to bare soil most of the years of monitoring, with variation according to climate. AOP production objective was nevertheless achieved for more than 50% of the vintages studied. Regarding vigour, over the first four years of study, an increasing rise of the relative difference between under-the-row grass cover treatment and bare soil was registered, until it reaches -45%. Proportion of grass coverage per plot seems to be a more important factor than climatic context to explain the impact of under-the-row grass cover on the vine. Monitoring of water and nitrogen status indicators highlighted that competition from under-the-row grass cover focuses on nitrogen rather than water. In South-west region, foliar nitrogen fertilisation was applied after four years of grass cover under the row. A strong reduction of the relative difference between under-the-row grass cover treatment and bare soil was then observed in terms of vigour and leaf nitrogen. The setting up of a grass cover under the row of vines appeared to be a viticultural practice compatible with different sets of constraints and objectives pertaining to the adaptation of production system such as management of the proportion of grass coverage and adaptation of the fertilisation practices.