Something to that effect...

But what does it mean?

To grass or not to grass, that is the question. Big debate, and of course the relative merits of each solution will depend on circumstances (rainfall, potential for erosion, sun exposure, etc.).
In a paleo-New-World approach, at least, the effects, positive or negative, or growing grass between rows would have been - and by most probably still are - addressed, by most at least, from a scientific angle rather than from the wishy-washy all-encompassing terroir approach, hence the ref. to "phenolics" in one of the references below.
Personally I am unconvinced by laisser au terroir une plus large expression. And I'm not sure non-French speakers, even wine afficianados, would be impressed or even pretend to understand, especially when you consider the debate about the pros and cons of grass. Particularly when you consider that if growing grass is beneficial for the terroir, then why have they been herbiciding it out of existence for decades if not centuries while still vaunting the qualities of that same terroir? Yes, I am over-critical/cynical.

I'd keep it simple, in "plain English", and just as vague.

Maintaining BARE SOIL BETWEEN CROP ROWS OF ANY KIND HAS MANY ADVANTAGES; crops are not subject to competition for water and nutrients, the risk of disease transmission is minimised and air movement is promoted within crop rows. The NEGATIVE EFFECTS OF BARE INTER-ROW SOIL can include poor water penetration, degradation of soil structure and organic matter, and reduced activity of beneficial soil organisms.
http://www.corbansviticulture.co.nz/news/2009/0111-inter-row...

ucce.ucdavis.edu/files/repositoryfiles/ca2206p10-65386.pdf

In agriculture, weeds have often been identified as the enemy. Although they use water and nutrients, they can be managed in organic farming by mulching, mowing, mechanical weeding, and by naturally occurring growth suppressants which are not harmful or residual. MID VINE ROW GRASS/PLANT COVER REPLENISHES SOIL HUMUS NATURALLY, INSULATES SOIL AND REDUCES EVAPORATION, PROVIDES FOOD FOR MICROBES AND MAINTAINS SOIL AERATION THROUGH GRASS ROOT PENETRATION. Organic farming discourages clean cultivation of soils and accepts the benefits of naturally occurring ground covers.

Continuous use of various herbicide chemicals to kill weeds results in:
- Reduction of soil biology responsible for mineral breakdown and nutrients available to vines
- Resultant reduced organic matter in soil, soil water retention, soil permeability, soil oxygen
availability and natural soil nutrient replenishment cycle
http://www.tamburlaine.com.au/public/what-organic.html

We begin in this postcard-perfect vineyard, where Patty Skinkis points out something unusual among the vines. Some have more foliage, longer shoots, and deeper green leaves. The reason, she explains, lies at our feet, in the alleyways between the vines where some rows are bare soil and others are carpeted with grass.

Skinkis is a vine expert at OSU, and she’s been studying these vineyard alleyways at Stoller Vineyards for the past three years to see how they impact the growth of vines and the quality of the grapes. Her study suggests that USING A COVER CROP IN ALLEYWAYS YEAR-ROUND IN A MATURE VINEYARD PRODUCES HIGHER-QUALITY GRAPES AND A BETTER BOTTOM LINE.
To understand why, it helps to know a little about vineyard management practices in the north Willamette Valley. Vineyard managers in the area often plant cover crops, like grass, to keep soil from eroding during the rainy winter and to provide traction for machinery. But this costs money. When spring rolls around, some managers plow up the grass so that it doesn’t compete with the vines for water during the drier summer. This, too, costs money. Managers also often fork out cash to prune back leafy canopies, which grow rampantly during the Valley’s wet spring.
It seems that the Valley’s fertile soil and abundant spring rain may encourage too much growth from the grapevines. Overzealous canopies increase the possibility of diseases and make it harder for the sun and air to reach the fruit. But Skinkis has found that VINES THAT ARE SANDWICHED BETWEEN GRASS-COVERED ROWS DON’T GROW AS VIGOROUSLY AS THOSE THAT ARE NEXT TO BARE ROWS. THAT’S BECAUSE THE GRASS STEALS SOME OF THEIR NUTRIENTS, BUT IT DOESN’T COMPETE WITH THE VINES FOR WATER.
Better yet, Skinkis has found that GRAPES FROM THESE SAME VINES WITH GRASS ALLEYWAYS SCORED THE HIGHEST IN TERMS OF PHENOLICS, which affect how wine feels in the mouth, and anthocyanins, which are pigments that produce a more intense red—a desirable trait in Pinot noir and many other red wines. That increased quality could translate into higher prices for Oregon grapes and for the wine made from them.
http://oregonprogress.oregonstate.edu/fall-2009/oregon-wine