Researchers' crumpled cover extends growing season and deters pests. WHAT WOULD PETER RABBIT DO?

IT'S a cool but bright spring day in northern New England, and Prof. Otho Wells's enthusiasm shows as he greets a visitor. The snow has all but vanished and the prospect of vacating the greenhouse for research opportunities in the open field is immensely satisfying to the vegetable-crops specialist at the University of New Hampshire. Once again, he will be involved with research on spunbonded polyester or polyethylene - a material that started out as stiffening in men's ties and collars and went on to revolutionize agriculture.

Even after eight years, the revolution is far from over. New uses for the material are still cropping up, says Dr. Wells, who adds: ``We still don't know why it works so well.'' He did his pioneering work with Prof. Brent Loy, also of UNH.

The agricultural world knows these spunbonded plastics as floating row covers, the ultra-lightweight blankets that, when draped over crops like a rumpled bed sheet, promote even germination, boost yields, advance the harvest, and cut back, or even eliminate the need for pesticides on everything from beets to tomatoes.

More recent discoveries: Lettuce and spinach seedlings can overwinter under the covers even in icy New Hampshire, and spring strawberry production is significantly boosted with similar winter-long protection.

As a result, growers around the world, particularly in the United States, Europe, and Japan, say it's a product they never want to be without. Home gardeners, too, are increasingly valuing its use.

Wells and Dr. Loy say the discovery of the floating row cover was ``inevitable'' somewhere in the world. But ``We were the ones who stumbled across it, so we'll happily take the credit,'' they say with a grin. It happened this way:

In 1981 Wells and Loy began experimenting with slit clear plastic as row tunnels held up by wire hoops. The idea was that the plastic would provide protection from the cold, yet allow excess heat to vent naturally out through the slits on warm days, eliminating the need for human judgment.

The idea worked so well that slit plastic row covers have become a successful commercial product. But when the professors wrote up their findings in the American Vegetable Grower, an alert DuPont Company employee phoned up to say that his company made a fabric that might prove similarly useful.

Reemay, a nonwoven fabric made by ``ironing'' threads of polyester together, had until then been used solely as an interfacing in the garment industry. It was porous to both air and water, transmitted 80 percent of the sunlight, and would offer some protection from chilling winds and late cold snaps.

Wells and Loy found that Reemay did all that they expected of it and that it had yet another very valuable feature. It was so light that a square yard weighed a mere 0.6 ounce. That meant it would need no supporting hoops but could be laid directly on top of the seedlings or newly sown rows. If the cover were given enough slack (hence the rumpled-sheet look), the growing plants would simply lift up the material as they grew. The cover would ``float'' on top of the growing plant leaves.

Although not a frost protector, the floating cover proved to be a growth enhancer, raising temperatures slightly, creating a more uniformly moist environment, and cutting back on stress caused by chill spring winds. The compacting effect of heavy rains on cultivated soil was also reduced. The cumulative effects of all these findings showed up in increased yields (in the case of muskmelons by more than 100 percent) on most crops and produced earlier yields on every one. In effect it proved a great ``growth enhancer,'' to quote Wells.

For many growers, though, the greatest value of the floating covers is in pest control. Shepherd Ogden, a grower of guaranteed pesticide-free produce, says: ``I grow greens for restaurants. If the flea beetle gets them, there goes the sale.''

Wells says of the covers, ``They keep all flying insects at bay for as long as the cover is on.'' He's not so certain about slugs. It's too easy for them, or their eggs, to be in the soil before the covers go on. Another significant plus: Rabbits, deer, birds, and woodchucks are all deterred by the covers.

Despite its many pluses, Wells hastens to point out that the row cover is not a panacea. In the spring it protects plants down to no more than 3 degrees F. of frost, or 7 degrees in the fall because of warmer soils at the close of the growing season. What promotes good crop growth also enhances weed growth, so Wells suggests using the covers in association with a weed-defeating mulch. Finally, it can get too hot for a plant even under a naturally ventilating cover. If it is going up to 90 degrees that day, Wells suggests folding back the cover.

How long plants remain under the cover varies with the crop, Wells says. Four to six weeks is average in the spring, and the cover can act as a season extender for a similar length of time in the fall.

A more recent surprise came when the floating covers went over lettuce seedlings in the fall. Though temperatures under the cover dropped to as low as the outside readings and stayed there all winter long, all the seedlings survived and grew to maturity the following spring. In contrast, not one plant lived through the winter in the uncovered control plot.

This success with winter lettuce so far north surprised both Wells and Loy. ``We get an extraordinary amount of protection from a very thin layer,'' says Wells, ``and we don't yet know why.''

Finding out ``so we can develop better management strategies'' will be the major thrust of the ongoing experiments at New Hampshire in the coming months.