When Mary was asked How does your garden grow, she didn't compare the relative merits of conventional versus organic farming. But results published online this week by the Proceedings of the National Academy of Sciences suggest that her silver bells and cockleshells could have lived longer and better under sustainable agriculture techniques.

To test how plants fare under different growing conditions, Autar K. Mattoo of the U.S. Department of Agriculture and his colleagues set up two patches of tomato plants at a Maryland farm site. The team covered one section with a typical chemical treatment known as black polyethylene (BP), whereas the other received natural fertilization from the hairy vetch legume (HV), which acts as an organic mulch. The researchers analyzed differences in growth patterns, gene expression and overall plant health between the two groups over three different growing seasons. After 65 days in the fields, the researchers noticed clear signs of improved health from the HV-fertilized tomatoes compared with the BP-treated plants. In addition, the plants growing in organic mulch lived longer and could more successfully fend off disease.

When they analyzed the plants, the scientists found that five types of genes were more highly expressed in the organically grown tomatoes compared with the traditionally cultivated ones. The team posits that the increased expression stems from the more regulated supply of nutrients, including carbon and nitrogen, that the legume cover provides. The authors write that it is imperative that we understand the mechanism(s) underlying the beneficial aspects of legume cover crop, because it can provide the scientific legitimacy for adopting alternative farming practices.