UVALDE – Limited water resources and increasing input costs make the development of more effective cropping systems crucial for agricultural producers in Southwest Texas, according to Texas AgriLife Research scientists.
“Efficient cropping systems allow for better management of natural resources, water use and nutrient inputs, providing a holistic approach to crop management,” said Dr. Daniel Leskovar, interim resident director of the Texas AgriLife Research and Extension Center in Uvalde.
Leskovar said what makes efficient cropping systems economically feasible is that they should allow agricultural producers to be more profitable compared to monoculture systems while, at the same time, conserving valuable natural resources and maintaining long-term soil quality.
The Cropping Systems Program at the Uvalde center was developed initially by Dr. Diane Rowland with collaboration from Drs. David Forbes, Jason West, Cristine Morgan and Leskovar, all of Texas A&M AgriLife. In mid-2010, Forbes became the on-site manager of the project with Bethany Speer serving as the project’s field technician. The project currently is being funded by the Texas AgriLife Research Cropping System Initiative.
The Uvalde group’s research is focused on using cropping systems to address issues including climate change and fluctuations in production input costs and commodity prices in Southwest Texas. Another group of cropping systems program researchers has been investigating new row crop systems in East Texas at the Texas AgriLife Research and Extension Center in Overton.
“Demands for water resources are increasing even while we’re still recovering from recent drought conditions in Southwest Texas,” Forbes said. “Meanwhile, fuel and fertilizer prices continue to increase, diminishing farm profitability.”
Forbes said he and the others recognized the need “to develop new systems and novel approaches” to improving farm profitability and conserving natural resources — especially water resources — in a closed agro-ecosystem. For their research, they decided to evaluate a conservation tillage production system against a conventionally tilled row crop system.
“This involved using a cool-season legume and grass cover crop, followed by a warm-season row crop strip-tilled after removal of the cover crop,” he said. “We also incorporated cattle grazing as a cost-recovery and nutrient-cycling element of the research.”
Forbes explained cover crops improve the soil by adding organic matter, enhancing soil structure, and soil’s water-holding and nutrient-cycling capacity. They also assist in erosion control as well as weed and pest management.
A native burr medic legume, white clover and annual ryegrass were mixed and seeded for the 2010 season cover crop, explained Speer, who has worked with the cropping systems program in Uvalde since its inception. Legumes have been studied extensively as a cover crop and are known to effectively fix nitrogen into soil, which reduces the need for fertilizer.
Legume rotations in the cropping systems evaluated were used to enrich the available nitrogen while simultaneously providing a “foundation” cover crop which would further open up the soil and enhance its moisture retention for conservation tillage, Speer said.
“We incorporated ryegrass as part of a cover crop as it too helps with erosion control and soil improvement,” she said.
Forbes noted there is some expense involved in planting the winter cover crop, so grazing cattle may provide a means for recovering some of that cost.
“Cattle are also an important industry for this region, he said, “so incorporating them into a cropping system makes good sense.”
The researchers also decided to measure nitrogen and carbon isotope ratios to find out which systems had the potential to decrease the use of water and fertilizer.
Conventional and conservation tillage systems were established at the Uvalde center on a 48-acre circular center-pivot irrigation system divided into four 12-acre plots. Three of the quarter sections were planted with different crops, including corn and cotton. Conservation tillage, or strip-till, sections were planted with a legume/ryegrass mixture in Oct. 2009, and cattle grazing was allowed on these sections.
“The reason behind using two different tillage treatments was to see how yields will differ,” Speer said. “Conventional tillage is plowed every year before planting and will dry out faster than strip tilling. Strip tillage creates a 6-to-8-inch or deeper trench that tends to obtain more moisture since the soil is more compact around the seed.”
Different irrigation treatments also were tested to find out if it was possible to lower the amount of water per crop and reduce the amount of electricity and fuel needed.
“These are huge factors when it comes to farming. In a dry season, pivots almost run nonstop just to keep the crop from stressing too much,” she said.
Speer said scientific measurements were taken throughout the project, including soil-moisture measurements using profiler probes and employing rhizotron tubes for taking root-development images for the cotton crop. Yield and fiber quality were determined by stomatal conductance/photosynthesis and disease rating.
“We also measured carbon and nitrogen isotopes and measured nighttime respiration and sap flow in the cotton crop to help determine the effectiveness of irrigation,” she said.
In the spring of 2010, the legume cover crop was removed in the areas being strip tilled, and strip tilling began just prior to planting. Conventional tillage in the system was managed through deep tillage, bedding and rod-weeding during the spring.
Different irrigation methods were applied to the crops to determine their comparative impact on yield and quality. Pie slices of the quartered sections of the 48-acre plot were irrigated at 70 percent of normal seasonal irrigation, 100 percent of normal and a combination of 70 percent of normal for the first half of crop development and 100 percent after flowering.
“The 70 percent initial irrigation followed by 100 percent irrigation is a technique called primed acclimation,” Forbes said. “Basically, the lower irrigation rate initiates a drought-stress reaction in the plant, forcing it to become more drought tolerant. The plant then makes physiological compensations which enable it to grow better during the second, full irrigation, rate.”
The crops were harvested in late summer or fall, depending on the crop, at which time yield and quality were determined, Speer said. Burr medic and ryegrass cover crops were then replanted to begin the second year of grazing treatments.
Crop yields were determined by taking crop weight per foot of row as appropriated for each crop after harvesting with industry-standard combines and pickers. Quality was assessed using crop-specific industry protocols.
“We’re still waiting for the quantitative results from nitrogen and carbon cycling aspects of the research and still want to find out more about the results of grazing cattle on these plots,” Forbes said. “But based on the research to date we can make some assessments of cropping system efficiencies, as well as hypothesize on how to maximize cropping system benefits.”
He said one of the most valuable results of the cropping system research was information obtained on use of the primed acclimation method of irrigation.
“We learned that primed acclimation at the early stage of crop development does not reduce yields and also may provide a substantial water savings,” Forbes said.
He added that research also has shown that over time, strip or conservation tillage is likely to increase the amount of organic matter in soil and give it better moisture-holding capacity.
“And grazing cattle as part of cropping system activities not only helps recoup some of the costs associated with establishing a legume or grass cover crop, it also helps speed up the transfer of nutrients to the soil through cattle excretions,” he said.
Forbes extrapolated that some vegetable crops may be well-suited as a component of cropping systems for the Southwest Texas region.
“A crop with a larger seed is more suited to this area, so watermelon or cantaloupe likely would work well in this area if it were to be substituted for corn or cotton in a cropping system,” he said. “You also have to consider there is a lot of clay in the soil around here, which can make strip-tillage more difficult … and the soil here also has a higher pH level. Legumes do not like alkaline soil, so it’s best to choose a native legume for your cover crop.”
He said ultimately a “properly designed and maintained self-sufficient, self-sustaining cropping system” promotes environmental health, recycles valuable nutrients, maximizes water-use efficiency, improves soil structure and provides the foundation for more profitable agricultural production.
“We hope the results of our cropping system research will benefit the growers in the area by helping them use less fuel and less water to produce higher yields,” Forbes said.