I know you can buy local or buy organic, but I’ve heard that some crops are simply more resource-intensive than others, regardless of how or where they are grown. So what’s the key to picking foods that have the smallest environmental footprint?

We’ve already been over the environmental benefits of choosing poultry over beef and anchovies over haddock. But you’re right to suggest that the same sort of logic can apply to picking vegetarian foodstuffs. Certain crops require loads of phosphate fertilizer, for example, which is mined from the ground and can eventually cause stream-choking algal growth. Other fruits and veggies are grown with heavy doses of pesticides, fungicides, and other chemicals that can pollute waterways and cause reproductive problems in animals. So how do you know which crops are best to eat? Here’s the Lantern’s rule of thumb: Try to keep your more extravagant fruit cravings in check, but don’t sweat the low-impact calories that come with your carbs.

As it turns out, it’s not hard to find digestible data on the use of fertilizers. The United Nations Food and Agriculture Organization offers a handy list of various crops and their associated fertilizer loads. Bananas consume the most by a very large margin, requiring a whopping 427 pounds of nitrogen, phosphate, and potash fertilizer per acre of cultivation. Sugar beets and citrus crops are next, followed by vegetables, tubers, and grains. Peas and beans require just 35 pounds per acre, in part because they have capacity to absorb nitrogen from the air. In short, eat more beans.

Numbers on pesticide use can be found in a database of California crops maintained by the Pesticide Action Network. According to the information compiled there, raspberries are the worst offenders, accounting for an average of 20.2 pounds of chemicals dumped on every acre of treated land. Other particularly noxious crops include carrots and strawberries. Wild rice also fares poorly by this metric, requiring nearly 6 pounds of pesticide per acre. In the middle of the pack are the tree crops, like avocados and oranges, and at the clean end of the list you’ll find broccoli, leafy greens, beans and grains—which are grown with an average of less than 3 pounds of pesticide per acre. (Remember, we’re talking about risks to the planet here, not risks to individual health. The Environmental Working Group has a list of the fruits and veggies that show up in stores—and on your plates—with the highest levels of pesticide residue. But that doesn’t make them the worst offenders against the environment.)

It’s useful to know the amount of pesticide or fertilizer that goes into each acre of a given crop, but there’s more to the story. Some crops make more efficient use of the land than others, so their environmental impacts may be less intense on per-calorie basis. To figure out how all this fits together, the Lantern whipped out his solar-powered pocket calculator and compared overall pesticide and fertilizer use with California’s agricultural yields from 2007 and nutritional information for each of 12 conventionally grown crops. White rice came out the big winner here, returning more than 2 million calories per pound of pesticide used and 82,000 calories per pound of phosphate. Onions and sweet corn ranked nearly as efficient as rice when it came to pesticide, but were only so-so in terms of fertilizer; the opposite was true for oranges and apples. Lingering at the bottom of both lists were strawberries, which returned just 121,000 calories per pound of pesticide, and 5,300 per pound of fertilizer.

What does all this fancy number-crunching mean? Considering that about one-third of greenhouse gases (PDF) emitted from agriculture in the United States come from fertilizers and pesticides, identifying low-impact crops can be at least as important as sourcing your foods locally. For instance, switching from strawberries to oranges in your fruit salad cuts pesticide use by half and fertilizer use by a factor of 10. For those who can’t do without their berries, your best bet may be to buy from a truly sustainable source that avoids the worst pesticides, sticks to manure and other organic fertilizers, and prevents excess nutrients from flowing into waterways. Major organic growers like Cascadian Farms and others provide limited information about their agricultural practices on their Web sites.

What about organic versus conventional produce? When it comes to dietary staples like corn, wheat, and rice, the choice isn’t so clear. David Pimentel of Cornell has estimated that it takes about 30 percent less energy to grow organic soy and corn than it does to grow the conventional kind. On the other hand, organic doubters, including the father of the Green Revolution, Norman Borlaug, have suggested that the spread of fertilizer and pesticide-free agriculture would result in more land being cleared for crops to match today’s conventional yields, a view that has been supported by a British government report. The USDA has just started surveying some organic crops, and we’ll have to wait until all the data is in to issue a final verdict on that front. As for fruits and vegetables, going organic is the eco-friendly choice. The switch will reduce your impact on the soil and water and won’t require a vast expansion of the agricultural footprint.

For all this, one of the simplest ways to ballpark the impact of a conventionally grown fruit or vegetable is to glance at its price. The trick doesn’t always work, but, in general, the cheaper one probably required less fertilizer, pesticide, land, and energy.

Is there an environmental quandary that’s been keeping you up at night? Send it to ask.the.lantern@gmail.com, and check this space every Tuesday.