It's Earth Day, and I imagine the vegetable sprouts on the South Lawn of the White House are now above ground. Michelle Obama could hardly have chosen a better way to send a green message to America than by engaging fifth graders from a Washington elementary school in digging and planting a garden.

Obama said the garden was meant to help kids and their parents get excited about growing, cooking, and eating more healthful food. But she was also offering indirect encouragement to advocates of local, sustainable food production. Intentionally or not, her garden spoke to one of the chief ills of the global economy and the environment: corporate agriculture.

It may seem shortsighted to criticize industrialized agricultural practices that in the last half-century have produced more food per year than ever before. But our food-production system, so uniquely productive in the short term, is uniquely destructive in the long term.

Agriculture, our largest industry, accounts for many of our environmental problems. The 2005 U.N.-sponsored Millennium Ecosystem Assessment named agriculture a chief culprit in reducing biodiversity and harming ecosystems worldwide. Agriculture is also a prime contributor to global warming, razing forests for fields of soybeans.

Also as a result of large-scale food production, erosion rates run far ahead of soil-replacement rates - and topsoil is replaceable only in geological time, not in our lifetimes. Soil suffers from the heavy application of chemical fertilizers, too, and the runoff makes water unsafe to drink in some rural communities.

Industrial-scale agriculture is also our largest consumer of fresh water and one of our heaviest consumers of fossil fuels. The average farm product travels 1,500 miles or more to the shelves of our supermarket, using up increasingly scarce oil resources.

The good news (sort of) is that Americans will not be eating this way 50 years from now, nor will anybody else. The resources to sustain it simply will not exist.

The only real question is, what kinds of food production will replace our industrialized practices? There is no single answer. Part of the answer must be political, and that is why agricultural critics such as Wendell Berry and Wes Jackson are urging the Obama Administration to pass a 50-year farm bill directly addressing the dangers of soil degradation, pollution, and petroleum dependency.

A long-term farm bill would also strengthen the economic base of rural communities, which are the first victims of our agricultural practices. Farmers have long been experiencing the economic recession the rest of us have now entered; the cheap food on supermarket shelves has robbed many rural communities of their livelihoods. And the people who grow food are further devalued when their land is irreparably damaged.

Michelle Obama's garden is not an overtly political act, but it highlights some of the problems of the way we eat. Teaching kids to grow a vegetable garden in the nation's capital, at the very epicenter of its power structure, is an act of agricultural criticism.

As a biblical scholar, I am tempted to say it is a kind of prophetic act. The essence of biblical prophecy is to show where the social order is broken, where human action threatens the created order, and where possibilities for healing lie.

Remarkably, there is good evidence that biblical prophecy itself had its roots in agricultural criticism. Three millennia ago, Amos and Micah spoke out against a system of food production that drove farmers into debt and off their land, leaving the poor without enough food and the land damaged.

If we are now in a similar situation, then we need contemporary prophetic actions - however small and varied - that show us a better way. Maybe the White House garden is one of those.

Ellen F. Davis is a professor of Bible and practical theology at Duke Divinity School. She can be contacted at edavis@div.duke.edu.