Cowpeas could add sustainability to cropping systems

Ground left fallow in the High Plains to store soil moisture between crops may be better off with a legume crop such as cowpeas, according to a Texas Agricultural Experiment Station researcher.

Dr. Bill Payne of Amarillo said he is trying to make the region’s wheat-sorghum-fallow cropping system more sustainable by getting rid of the fallow component.

Leaving the land idle for one cropping season is a way to retain soil moisture for the following crop. However, Payne said, this practice doesn’t store that much moisture. And it oxidizes the soil organic matter, leaving the land subject to erosion and releasing carbon into the air, thereby contributing to global warming.

Planting a legume crop, such as cowpeas, allows the producer three crops in three seasons, rather than two crops in three seasons, he said. The residue from the cowpeas also adds organic matter, which tends to decompose faster than cereal crop residue, Payne said.

“What we’d like to do is plant it the year after sorghum and before fall-planted wheat,” he said. “What we’re trying to do now is find the right maturity group among cowpea varieties.”

Cowpeas can be grown in as little as 65 days, allowing for a brief fallow period before the wheat is planted. A longer-season variety can go until a killing frost, Payne said. The research is aimed at finding a balance between biomass production and water conservation, he said.

“The options would be to hay it or graze it as a forage, or if there’s a market for the peas, a producer could go for that,” Payne said.

The crop can be harvested at flowering for forage and at pea production, as with blackeyed peas. By doing both, he can compare water usage and determine potential water stress on the next crop.

“Our hope is the wheat yields will increase following cowpeas, as well as the sorghum,” Payne said. “We see that in other parts of the world, but here we have to be careful of the water component.”

Preliminary data shows the more cowpea biomass produced, the larger the yield increase of the following cereal crop, he said. However, the study must run for at least six years or two entire crop rotations to confirm the results.

Determining the sustainability characteristics — changes to the soil physical and chemical properties — will take even longer, he said.

“We can show now that growing cowpeas results in less soil water storage at wheat planting than fallowing,” Payne said. “But so far, it has been such a small amount, it’s insignificant as far as yield goes.”

Cowpeas’ water requirements depend on the maturity group, but the goal is to find a variety that will survive on 12 inches of rainfall, he said.

During 2003’s dry growing season, Payne said, the sorghum died off before the cowpeas, which means cowpeas is a very drought tolerant crop.

Payne said some experts are concerned that cowpeas grown on any significant scale in the U.S. would flood the human consumption market and lower the price. However, as forage, cowpeas shows a lot of potential, he said.

In Africa, tests show cattle’s weight gain doubles when cowpea fodder is added to their diet, Payne said.

“I think producers are looking for a high-protein forage crop,” he said. “There’s a reason cowpeas are called ’cow’ pea. Earlier on, cows grazed it throughout the South.”

The protein value of cowpeas ranges from 22 percent to 30 percent, Payne said.

“We’ll have to work with producers and (Texas Cooperative) Extension agents to see how it works into a production system,” he said. “Timing of pasture availability will be important. We want to try to time its availability with the greatest demand, so there are still things to work out.”