On the ground floor

If he were a tree, David Granatstein says he would enjoy a nice mulch blanket. “Where we put on organic mulches in the orchard, we often see roots grow from the soil up into the mulch,” says the Washington State University sustainable agriculture specialist.

Tillage, on the other hand, “destroys all of the roots at the surface,” he adds. “Mulch has been a steady performer in our research, but there are risks,” Granatstein warns.

Wood chip mulch is producing the best results in WSU tests to date, he reports. Importantly, rodents, which can be a major problem in other treatments, hate chips, he says.

What’s more, he finds a 25% reduction in irrigation needs in orchards with chip floors. “This is very achievable over the course of a growing season,” he says.

Key Points

• Wood chip mulch is producing good results in WSU tests; rodents hate it.

• New tillage equipment better competes with cost of some herbicide applications.

• Fabric materials used on the ground are showing promise in limited tests.

Tilling the ground

Orchard tillage, particularly dominant among organic growers who avoid using herbicides, has become more popular recently as new tillage equipment has reduced the cost of doing this job. Among conventional growers, the practice is also gaining due to the new equipment, which Granatstein says is now competing in cost with applications of some herbicides. Breaking up rodents’ habitat, he says, is also a benefit of tillage.

In his work with the Center for Sustaining Agriculture and Natural Resources, Granatstein is investigating not just the cost of tillage, but also the impact it has in terms of fruit size and yield. Growers using tillage are urged to check the impact the practice might have on their trees.

Another option for the orchard floor is cover crops. Granatstein warns cover crop roots can compete with tree roots. Apple tree root density, for example, is “extremely low,” he says, making it difficult to compete with the cover crop.

Managing tree needs while using cover crops is a delicate balancing act, Granatstein says.

Covering up for winter

Use of winter annual cover crops may be best, says Granatstein, since their growing period won’t overlap with the tree growing season. Cover crops have produced “tremendous” improvements in soil quality, he notes.

Rodents are perhaps the biggest downside to cover crops. “Consistently we have seen almost any kind of cover crop in the tree row exacerbates rodent problems,” he says. “White clover is the favorite food of the voles in our region.”

Some cover crops may actually deter voles, says Granatstein. One possibility is sweet woodruff.

Another alternative for the orchard floor that holds promise is fabric covers, Granatstein says. In Hood River, Ore., a cherry planting study used black fabric, which added $2,500 an acre to costs but resulted in a net increase of $3,000 in the first harvest year, he reports. That dollar benefit, he says, continued for several years.

Black and white

But Granatstein is concerned that black fabric could push soil temperatures above optimum in some regions. His solution was to use a fabric that’s black on the bottom and white on top.

A USDA research report shows that this technique suppressed weeds, cooled soil temperatures, increased the quality (sugar-to-acid ratio) of the fruit, and boosted soluble solids in the crop.

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weed control: Washington State University’s David Granatstein, a sustainable agriculture specialist, says using a white fabric with a black backing has had some success in weed control on the orchard floor.

This article published in the September, 2010 edition of WESTERN FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2010.