ISU researcher to get to root of many aspects of sustainable organic vegetable production

AMES, Iowa - As the number of organic vegetable growers continues to increase, there has been startlingly little research done on the sustainability of these organic practices.

An Iowa State University researcher is now examining which organic vegetable growing practices are best for the soil, water, yields and even nutrition.

Kathleen Delate, professor of horticulture and agronomy, is undertaking perhaps the most comprehensive study of organic vegetable-growing practices by looking at the use of cover crops, manure, tillage and mulch.

"We are measuring a lot of things," said Delate. "We are hoping to provide organic producers with science-based information that they can use to make wise decisions affecting the sustainability of their operations. And we think much of this data can be used for conventional crops as well."

Using 36 farm plots that each employ different combinations of variables, Delate hopes to discover which practices work best. The vegetables in the research include tomatoes, broccoli, onions, beans, squash and lettuce.

The vegetables will be grown in rotation with one crop planted in the spring, followed in the fall by another.

Early-stage organic soybeans grow through now-dead crushed rye cover crop in this organic no-till system. The yields from these organic soybeans ranged from 35 to 45 bushels per acre, without any cultivation for weed control.

"The first parameter we're looking at is cover crops. For cover crops, we are using hairy vetch and rye," said Delate. "That combination is one that we've had really good luck with for our vegetable farming."

In the research, the rye and hairy vetch are planted in the fall after the second vegetable crop is harvested. The cover crops are allowed to stay in the ground all winter and are then destroyed in the spring prior to the first vegetable crop planting.

Cover crop systems have been shown to improve soil quality and Delate hopes that they have other advantages.

"One of the theories we'll be testing is that cover crops can actually attract beneficial insects," said Delate.

"We also have some data that the straw from the cover crop could prevent some aerial diseases, but it also keeps the soils moist, which could lead to some root rot and a whole suite of soil quality issues. We're eager to see the outcomes," she said.

In keeping with the organic nature of the research, rather than destroying the cover crops with chemicals, Delate's research team will use a large roller to break the plant stems of the plants.

"The blades of the roller crush and kill the cover crops," said Delate. "It physically breaks the transfer of water and nutrients in the plant."

None of the cover crop will be harvested and the plants will remain on the field and will add to the organic matter in the soil, said Delate.

The second parameter is the use of composted manure. Organic farming requires that farmers compost manure and apply it at least four months prior to harvesting.

Delate's team will see if these practices have an effect on soil quality and nutrient runoff.

The third input being measured by the Delate study is till versus no-till farming.

Delate says that using no-till practices may be challenging. The crushed cover crop may present problems as vegetables are planted through it.

The final parameter is using plastic mulch in the crop production. Using plastic mulch involves growing crops through slits in thin, plastic sheets. Plastic mulch provides benefits such as soil moisture retention and weed suppression, and allows for earlier planting dates.

During the research, soils will be tested regularly using lysimeters from the United States Department of Agriculture's Agricultural Research Service National Laboratory for the Agricultural and the Environment to see if nutrients are leaching through the soil.

One other aspect of the study involves food properties of the organic produce.

"On top of everything else we're studying," Delate said, "our colleagues in Florida are going to run a nutritional analysis, including vitamins and minerals, of the crops in this study."

The research is conducted in partnership with the University of Florida, Gainesville, and funded by the Department of Agriculture through the National Institute for Food and Agriculture.