The partnership between rice growers in the Mississippi Delta and USDA's Delta Water Management Research Unit in Jonesboro, Ark., is helping growers understand the relationship between irrigation techniques and greenhouse gases, as well as prepare them to take advantage of carbon credits.
"The unit started in 2011," said Michele Reba, research hydrologist and acting research leader of the unit. "I started in March of 2011 and our mission then, and now is still the preservation of water quantity and water quality for agriculture and for the Lower Mississippi River Basin."
For three years, Reba worked as the only research scientist at the unit and helped farmers manage to improve their yields while keeping an eye on the environmental side of resource management.
In 2014 the site became a stand-alone research unit and brought researchers Joe Massey and Arlene Adviento-Borbe, both research agronomists, on board to broaden the program.
"It has been phenomenal," Reba said. "They both came to us with a lot of experience and really good ideas."
While their work encompasses most row crops of the region, including cotton and soybeans, some of the rice research projects have provided information for rice growers that have helped to boost their bottom line and have helped them increase environmental benefits in the crop.
Two important projects spearheaded by the unit include field comparisons of row rice and multiple inlet rice irrigation (MIRI) in relation to greenhouse gas emissions and providing technical assistance for the issuance of carbon credits for rice.
Greenhouse gases in rice
The unit set up a two-year field trial collaboration with a Mississippi County, Ark., farmer comparing row rice and MIRI for irrigation water use efficiency, greenhouse gas emissions, and economics.
MIRI uses multiple inlets to manage a series of descending paddies, calculating water application to end in the final paddy with little surface runoff. Row rice is furrow irrigated, similar to conventional row crops but uses end-blocking to reduce runoff. It typically uses less water and requires less maintenance than paddy irrigated rice.
They found considerable irrigation savings with row rice, but no net change in global warming potential.
"If you look at the warming potential in the flooded rice system, you will get a number in which methane is the dominant greenhouse gas," said Adviento-Borbe. "But in a row rice field, you would assume that maintaining much of the field aerobic would reduce methane. It's correct. From our data, methane was reduced by 40% to 60% compared to a continuous flood."
But she noted that when they measured the emissions of nitrous oxide, its output was higher with row rice because more fertilizer was added to compensate for nitrogen losses in the non-flooded portions of the row fields.
"So overall, there was no reduction in global warming potential, although there was a significant water use reduction," she said. "You just changed the dominant greenhouse gas from methane to nitrous oxide when moving from flooded to row rice. We were concerned that increased nitrous oxide emissions with row rice would more than offset reductions in methane but, the good news is that, at least for this clay soil, this was not the case."
The unit will continue to study gas emissions, as well as other opportunities that may give rice growers an advantage in the marketplace.
"My view of our efforts is looking at the long view of how we can help farmers manage their resources a little bit better," said Reba.
"An example of this would be our unit’s involvement in the first carbon credits being issued to rice growers in the United States in 2017," said Massey. "That multi-year process involved the creation of field procedures that guided participating farmers through this new program created by the California Air Resources Board."
A total of seven U.S. rice farmers received carbon credits with five farmers being in the Midsouth, according to Massey. The Midsouth farmers received credits because they reduced methane emissions using alternate wetting and drying (AWD) rice irrigation and had the documentation necessary to validate these claims.
The Jonesboro unit provided data on methane reductions and aided growers in documenting their practices using a variety of sensors.
"It didn’t turn out to be a lot of money for these farmers because of the low price of carbon and costs associated with verification, but we all learned by participating in this process," said Massey. If carbon credit activity increases, it is hoped that these initial efforts will benefit other growers in the region.
Reba notes that a major strength of the unit is that the approach work from a systems perspective.
"Not just focusing on the production season," she said. "But also looking at what happens in the winter, what happens with crop residue, how does that then influence what is happening in the production season.
"Not only are we looking at greenhouse gas emissions, but also runoff which provides information on irrigation efficiency and potential impacts on water quality. Not just looking at yield but looking at return on investment, since we feel that sound agronomics is good for the environment and, ultimately, the bottom line."
She notes that they are interested in the long-term management of crops and helping producers to understand what their options are now and into the future.
"When I first came on board I would often be told, 'we know how to grow rice,'" she said. "But we need to understand that our systems are not stagnant and that we can shift practices as conditions require us to change."