Bioenergy sorghum offers traditional row crop farmers flexibility for rotation and end uses for the versatile crop.
“Biomass sorghum is versatile. Farmers may produce forage or biomass feedstock, depending on demand,” said Dr. Jason Wight, of Texas AgriLife Research.
Because biomass sorghum is an annual row crop, it offers farmers the versatility to be able to go into and out of production as markets and farm needs change. “It’s also a higher biomass producer versus corn and switchgrass,” he said.
“Bioenergy sorghum could play a more prominent role in the future,” said Wight, speaking at the Texas Plant Protection Association annual meeting last December in College Station.
Energy demand may encourage more production. “Bioenergy production will demand 50 million acres of cropland by the year 2022,” Wight said.
He said sorghum provides an efficient biomass option. “It is tolerant of many stress factors, including drought. It can go dormant and waits for rainfall. Also, pests such as midge are not problems since we’re not producing for grain.”
Wight said sorghum offers flexible planting dates as well and he expects improved varieties in the near future with even more promise. “The genetic potential is virtually untapped,” he said. “Until now, biomass sorghum has not been a breeding priority.”
Wight has also looked at biomass sorghum management, especially the effect of removing biomass on soil nutrient levels and yield potential. Field trials have targeted yield, nutrient uptake and changes in soil properties.
“In high fertility soils we saw no nitrogen response in 2009 and a minimal response to 70 pounds of nitrogen per acre in 2010, with limited irrigation.”
With proper management, biomass sorghum yielded more than 12 dry tons per acre, three to five times as much as for corn silage. “And we harvest the entire plant, stalk, grain and all.”
Wight is also looking at rotation effects versus continuous sorghum. “Rotation with corn has a significant effect,” he said. “Rotation is a strong determinant for crop growth and nutrient uptake, increasing yields by about 25 percent. Nitrogen fertilization increased crop growth and yield but to a lesser extent than with rotation.”
He said data from trials in Weslaco and College Station, Texas, show a 10 percent increased yield with nitrogen fertilization. “Fertilization raised yields significantly and uptake of nutrients was also higher. We’re pulling more than 300 pounds of potassium per acre from the soil and are not adding potassium. We’re also pulling out about 30 pounds of phosphorus per acre. We’ll see what the drawdown is over time.
“After only two years of sorghum production we are beginning to see changes in soil quality. Fertilization generally increased soil organic carbon throughout the profile. Continuous sorghum increased soil organic carbon near the soil surface and to 20 inches deep. Fertilization increased nitrogen at the soil surface and continuous sorghum increased total nitrogen.”
Plant material produced under continuous sorghum and fertilization increased soil organic carbon even though the above-ground material was harvested. Phosphorus and potassium levels also increased in the top two inches of soil with continuous sorghum but were drawn down at deeper depths.
“These high sorghum yields may increase nutrient uptake below the soil surface,” Wight said.
Removal of potassium and phosphorus also may have long-term effects on soil properties,
“So far, our biomass sorghum systems have maintained high yields and increased soil organic carbon. However, we’ve seen a drawdown of nutrients in the subsurface that may lead to a future loss of productivity. We will continue to monitor these systems to determine the long-term economic and environmental viability.”