By Kay Ledbetter
Texas A&M AgriLife scientists are conducting several research projects to improve producers’ understanding of guar and the legume’s value to their operations in the Rolling Plains and South Plains.
Guar has been grown in Texas for more than a century, but acreage of the crop in the state is relatively low, said Dr. Curtis Adams, Texas A&M AgriLife Research crop physiologist in Vernon,
Lack of nodulation on guar roots is one of the producer concerns addressed in a recent AgriLife Research study by Adams and Dr. Calvin Trostle, Texas A&M AgriLife Extension Service agronomist in Lubbock, along with Dr. Santanu Thapa, AgriLife Research postdoctoral research associate in Vernon.
Dr. Curtis Adams, Texas A&M AgriLife Research crop physiologist, Vernon, tested the effects of contrasting soils, a sandy loam and a clay loam, and Rhizobium inoculants on nodulation and plant growth in two guar varieties in the greenhouse.
Nodulation is the process of forming nodules on the roots of legume plants. Nodules are root structures that legumes make to house bacteria capable of using nitrogen gas from the air to form fertilizer that the plant can use to grow.
The team conducted a controlled environment study to compare the impact of environmental and management factors on guar nodulation and crop nitrogen uptake, Adams said.
Guar is grown in semi-arid regions and produces a seed containing galactomannan gum, which is a product used in a variety of food and industrial applications as a lubricant, binder, thickener or hardener, he said.
Rhizobium bacteria in the soil will associate with guar roots and potentially develop nodules where the bacteria converts atmospheric nitrogen into fertilizer for the plant and soil.
“As a legume, Rhizobium bacteria in the soil will associate with guar roots and potentially develop nodules where the bacteria converts atmospheric nitrogen into fertilizer for the plant and soil,” he said, adding that “the plant is also drought tolerant and uses relatively little water.”
Thapa said guar is unfamiliar to most people, but it is a part of their lives nonetheless.
“Guar gum is a common ingredient in the food we eat every day,” he said. “It is used extensively in oil and gas exploration, and in so many other ways.”
The majority of the world’s guar is grown in India and Pakistan, and the U.S. has had variable and relatively low acreage over time, Trostle said. In the U.S., guar is mostly grown across the Southern Great Plains region where the climate is suitable.
Guar has been grown in Texas for more than a century, but acreage of the crop in the state is relatively low.
“Guar being a legume and adapted to a semi-arid region’s dryland agriculture is important,” Trostle said. “There are few legumes that would be adapted in this type of environment. That is why this work is especially important, to get potential nitrogen fixation in a legume rotational crop where it doesn’t rain a lot.”
Adams said despite the potential nitrogen benefits of the crop, there is a worldwide perception that guar does not nodulate effectively.
“So, we tested the effects of contrasting soils, a sandy loam and a clay loam, and Rhizobium inoculants on nodulation and plant growth in two guar varieties,” he said.
Although Rhizobia bacteria often occur naturally in soils, Rhizobium inoculants are crop-specific bacterial cultures prepared in the lab and applied to the seed or in-furrow at planting to increase the likelihood of root nodulation, Adams said.
He said because guar acreage is not large in the U.S., there is a lack of inoculant products specific to guar.
“In our study, we tested one commercially available inoculant and a custom inoculant prepared by a microbiologist colleague, both containing bacterial strains thought to create nodules on guar roots that fix nitrogen,” he said.
Thapa said two iterations of the 50-day study were run in 2017. Plant growth, plant nitrogen concentration, measures of yield potential, root nodule number, nodule weight and other parameters were determined.
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