By Kay Ledbetter
In a season plagued by drought and high fertilizer prices, Texas A&M AgriLife scientists appreciate what guar provides in a crop rotation.
"Guar is a drought-tolerant, low-input crop that doesn't require expensive fertilizers," said Waltram Ravelombola, Ph.D., organic and specialty crop breeder at Texas A&M AgriLife Research and Extension Center -Vernon and Department of Soil and Crop Sciences. "We know guar improves soil health and increases the yield of the wheat that follows, making it a good rotational crop for producers to consider in the Southern Great Plains."
Ravelombola is working on the final year of a project funded by a U.S. Department of Agriculture National Institute of Food and Agriculture grant, titled "Enhancing Ecosystem Services Through Integration of Guar into Wheat Cropping Systems of the Southern Great Plains." The project started in 2018 and will finish up this year.
Guar is a legume, which means its roots can associate with Rhizobium bacteria in the soil to convert atmospheric nitrogen into fertilizer for the plant and soil. It's adapted to the semi-arid conditions of Texas and is among the most drought-tolerant crop plants, with relatively low water use.
However, new research is needed to improve production and nitrogen-fixing qualities of the crop. Ravelombola said the guar varieties this project is working to improve were released 35 years ago or more.
"We want to provide farmers with more options to diversify their cropping systems," he said. "For instance, with the fertilizer prices as high as they are now, if we had a variety that nodulates better, it could fix more atmospheric nitrogen and leave residual nitrogen for the following crop, thus reducing the requirement of synthetic fertilizer for the following season."
Long-term and short-term goals of the research
The study's long-term goal is to increase and stabilize guar production in the U.S. and increase the sustainability of wheat cropping systems in the Southern Great Plains region.
The immediate goal is to quantify wheat and guar crop development, productivity, nitrogen uptake and nodulation, and precipitation-use efficiency. Additionally, Ravelombola is studying the dynamics of soil nitrogen cycling and nitrogen-use efficiency, soil organic carbon storage and soil biological activity.
AgriLife Research is growing about 400 types of guar on approximately 8 acres in small plots. Two research plots are at Chillicothe, on 4 acres, and at Lockett, on 2 acres. His project also includes on-farm research on 1 acre with New Deal Grain Co. Another 1-acre plot is near Lubbock, grown in cooperation with Calvin Trostle, Ph.D., Texas A&M AgriLife Extension Service, Lubbock agronomist.
"Guar is a heat-tolerant, drought-tolerant crop," Trostle said. "To the extent that climate change makes our climate warmer and drier and may influence Texas cropping, guar will perform relatively better compared to other crops we grow."
He said older literature reports that dryland cotton yields are increased up to 15% after guar vs. in a cotton-cotton crop rotation, but more research is needed to evaluate this finding with modern varieties.
"Again, guar is a legume, and any time we can get a legume that grows well in a dry climate—and nodulates to fix nitrogen—this a potentially great benefit to farmers and cropping system stability," Trostle said.
Guar is planted mid-May to July and harvested after the first freeze, which is used to defoliate the plants, typically in October or early November. Guar can be harvested using combines most grain producers already own.
In this final year of the grant-funded project, Ravelombola said he will work to improve the phenotyping of guar using technologies such as unmanned aerial vehicles, UAV, and 3D crop modeling. He also will investigate the genetic basis of nitrogen fixation in guar.
Maximizing nitrogen fixation of guar crop
Nitrogen fixation is the ability of the crop, in cooperation with soil-borne bacteria, to take in atmospheric nitrogen and thus reduce the need for commercial nitrogen fertilizers. The nitrogen from those legumes is a way to reduce the incorporation of synthetic nitrogen fertilizers.
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