To Fallow... Or Not to Fallow

Crop and soil management systems in dryland agro ecosystems

Most masters make mosaics from small pieces of glass or tile, sometimes dedicating years to one big picture. Gary Peterson and Dwayne Westfall, Colorado State University soil and crop sciences professors, work within a mosaic of nature, using little pieces of a rain cloud here, sandy soil or a dab of evaporation next, and holding it all together with the seeds of a crop. Like most who make mosaics, they've spent years finding small pieces that make a big picture.

For Peterson, building the big picture started with the search for an answer to one small question. Fifteen years ago, a student in his soil management class asked him if crop and soil data from one part of the state applies to other parts of that state. Peterson had to tell him that he didn't really know.

"There was no way to expand data from one region across different climates and conditions," says Peterson. "So I started to look at consistent variations across crops within certain climates."

Peterson and Westfall chose several plots on farms scattered across most of eastern Colorado to conduct a study. They started testing crop production and the soil's moisture retention with different crop cycles. Each of the test plots had three different soil types.

"Once we had the data about how to manage soil in all of these different conditions," says Peterson, "I could start to answer the student's question."

First, they tested results with the most common crop rotation: wheat fallow, i.e. – plant wheat one year, no crop the next.

"If someone fallows well, they only save about 25 percent of the rainfall. The rest is lost to evaporation, runoff, or weeds," said Peterson. "Farmers fallow to save water, but as they till the land, they expose it to evaporation because moist soil is turned to the top of the ground. Even with herbicides to control weeds, fallow is an insufficient situation."

The researchers set up crop rotations with less fallow. They started with one year of wheat, then corn, then fallow; on another plot, they tried wheat, corn, proso millet, then fallow.

They discovered that the fewer years of fallow in a rotation, the more productive the land. They developed the opportunity crop system – plant a crop every year – a concept foreign to traditional farming but which requires more intensive management.

"Another problem with fallow, especially after a wheat crop, is that few crops put much organic matter back into the soil," said Peterson. "We wondered if growing crops and decreasing fallow leads to higher organic matter. The answer is yes."

Peterson and Westfall use no-till to maximize water conservation and organic matter accumulation. The soil is only stirred when a new crop is planted, which preserves organic matter and moisture. Fertilizer is added as needed. Herbicides control weeds between harvest and planting.

"After 15 years, we have solid conclusions," said Peterson. "Growing a crop every year is the most productive system. Grain production jumped by up to 75 percent, and profit went up 25 to 40 percent. No one needs to fallow. It's a win-win deal. Save water, produce more crops, make the soil more productive. Farmers come out ahead."

But even with these solid answers, Peterson and Westfall continue to piece together a mosaic of information from Colorado's farmlands. The weather, as always, affects a farmer's profits. The smaller pieces like evaporation, erosion, and altitude do, too. They hope that long-term experiments will continue to provide more information so farmers can learn from the long-term effects of crop rotations.

"In England," says Peterson, "there is an experiment that's been going since 1840. Some things you learn over time can't be learned any other way."