Studies: In drought conditions, organic farming methods give crops better water-holding capacity

Corn in the legume-based, left, and conventional plots six weeks after planting during the 1995 drought. The conventional corn is showing signs of water stress.
Rodale Institute photo  

As the Midwestern drought has hung on and more states are reporting damage to their impending corn crop, Tom Philpott of Mother Jones reflected on a recent Nature study that found that industrial agricultural methods were found to produce higher yields than farms that used organic methods. (He notes he was not convinced by the study but he continues on that, in any case, "under conditions of extreme weather, things absolutely change. "Soils managed with organic methods have shown better water-holding capacity and water infiltration rates and have produced higher yields than conventional systems under drought conditions and excessive rainfall," Philpott reports. In other words, he explains, organically managed soils deal with water better -- both in conditions of drought and heavy storms, the frequency of which is also expected to increase as the climate changes. Soil rich in organic matter  -- well-decayed remnants of plants and other living creatures -- bolster soil in weather extremes by helping store water in times of scarcity and by holding together and not eroding away during heavy rains.

And why would organically managed soils contain more organic matter? It quite likely, Philpott writes, that this has to do "with the ways conventional and organic farmers feed the soil. If you're a conventional farmer, you probably fertilize annually with synthetic nitrogen fertilizer in the form of anhydrous ammonia. This is isolated plant food, free of any organic matter. (It's the equivalent of taking a vitamin pill—pure nutrients without actual food.) The only organic matter your soil gets comes from the crop residues that you leave in your field. This brings the advantage of convenience—crop nutrients come from tanks that can efficiently be sprayed on to fields. And it also gives crops a quick jot of ready-to-use nitrogen. If you're an organic farmer, you don't have the luxury of blasting your soil with straight nitrogen. To replenish nutrients, you have to have physical stuff that contains nitrogen bound up in organic matter—think compost and manure. You can also grow legume cover crops that trap nitrogen from the air and deliver it to the roots of plants in a form that can be taken into the soil. In this case, too, you're adding a nice dose of organic matter along with nitrogen, in the form of the plants that rot in the ground when the cover crops does. And, like conventional farmers, you get the benefit of crop residues left in the field. As a result of these difference, organically managed soils trap more carbon in the soil—and all of that carbon allows these soils to hold in water and nutrients better. (Note that carbon stored in soil in a stable fashion is carbon that isn't in the atmosphere trapping heat and causing the planet to warm. So organically managed soils don't just help farmers adapt to climate change—they also help help mitigate climate change.)"

The oldest U.S. tests plots comparing organic and conventional farming, the Rodale Institute's fields in Pennsylvania, bear this out. (See the institute's latest report here.) In the latest report on its side-by-side experiment, which started 1981, Rodale found that "organic corn yields were 31 percent higher than conventional in years of drought." Researchers theorize that this is because the organic fields continue storing more carbon year after year, while the conventional ones have "shown a loss in carbon in more recent years." Another long-term study, Iowa State University's Long-Term Agroecological Research Experiment, found similar results.