Be prepared for drought in sorghum
By Larry Dreiling
As spring planting time arrives, there's plenty of hope beneficial rains will fall, if not to completely break the drought that particularly affects the High Plains, but to at least enable dryland farmers to get their crops under way.
With the rise in thought about climate change, sorghum's popularity--not just as a rescue crop but also as a crop of primary intent--has risen slightly, not just in the U.S., but globally.
Over the past decade, world sorghum production has risen slightly from 2.4 billion bushels 2.6 billion bushels.
Worldwide, it is the fifth most important cereal crop based after wheat, corn, rice and barley, according to the United Nations' Food and Agriculture Organization. Sorghum is a staple food crop for millions of people in arid and semiarid regions, primarily in Africa and parts of Asia.
Still, in terms of global utilization, almost half of the grain sorghum produced is used as animal feed. More recently sorghum has also been proposed as a dedicated cellulosic bioenergy feedstock.
While the U.S., Argentina and Australia account for only about 23 percent of this production, they remain the top exporters of sorghum, accounting for 97 percent of total world exports.
U.S. farmers grew 247 million bushels of sorghum in 2012, up 15 percent from last year on 4.96 million harvested acres, up about 14 percent from 2011. Yields at 49.8 bushels per acre are down 4.8 bushels from last year.
Ram Perumal, Ph.D., sorghum breeder at the Kansas State University Agricultural Research Center-Hays, sees the numbers, senses drought has caused this falloff in production of what ought to be a true dryland crop, and says help is on the way soon through drought-tolerant sorghum.
Still, that won't help farmers this season. As research continues to find acceptable drought-tolerant varieties, Perumal offers some advice in sensing potential problems for sorghum production.
"Sorghum has high drought tolerance as it is compared with other cereal crops," Perumal said. "However, this crop experiences drought stress at three critical stages in development.
Those stages are:
--Early to vegetative stage: Where signs of poor germination and plant stands, stunted growth and poor root development are seen.
--Pre-flowering: Characterized by traits like leaf rolling, leaf tip and margin burn, poor panicle size.
--Post-flowering, from grain-filling to maturity: Stalk lodging and reductions in seed numbers and size.
"The majority of sorghum is grown under dryland conditions on the High Plains, which are characterized by spare and erratic precipitation coupled with high evaporative demand. This results in severe water stress during grain filling stage as the crop utilizes stored soil moisture during their vegetative stage. This leads to loss of a greater percentage of grain yield and outright crop failure," Perumal said.
The average annual rainfall at KSU-ARCH is about 17 inches. Travel another 50 miles toward the west and the average annual rainfall decreases by another one inch. Therefore, Perumal asserts, water stress has become the key factor that constrains crop production in western Kansas. Due to these limitations there are urgent needs to increase the yield and water use efficiency under water limiting conditions.
It's why Perumal is taking a "future is now" attitude toward production of drought-resistant varieties, with a goal of making such varieties available as soon as possible.
"The further west you go, the more stresses you face," Perumal said, "while east toward our researchers on the Manhattan campus you find primarily post-flowering stresses. With two breeders working in the state, we are working to find suitable lines for all sorts of producers."
Sorghum is vulnerable to freezing temperatures and suffers chilling injury when subjected to non-freezing temperatures below 50 degrees. Chilling injury occurs during germination, early vegetative growth and during mid- to late-grain-filling stages when sorghum is planted during late April and May.
This usually results in poor seedling establishment of sorghum because of slow emergence rate, reduced emergence percentage, and reduced growth rate after emergence. The average last freeze day in spring is May 15, while the first fall freeze starts sometime in second or third week of September.
"So we want to plant as early as possible to get harvest in September," Perumal said. "It's also why we need to include, in equal consideration, some cold tolerance traits in these new varieties. "
Again, the statewide consideration for new sorghum varieties is toward post-flowering water stress, primarily because stalk rot and charcoal rot, two yield-robbing fungal diseases, have an effect on more crops.
"Stalk rot disease usually develops at later growth stages during grain filling period and is characterized by degradation of the pith tissue at or near the base of the stalk causing death of stalk pith cells that accompanies maturation and grain development," Perumal said. "This results in slow down (of) the grain filling process and thus results in shriveled seeds.
"Charcoal rot is the most widespread and destructive stalk rot disease of sorghum caused by root inhabiting fungus. Once the roots are invaded, the pathogen quickly moves to above ground basal stalk portions attacking the lower internodes eventually resulting in poor grain filling or premature death of the plant."
Another thing Perumal saw last year was a high amount of sorghum suffering from poor panicle size.
"When a panicle is of small size, covered in boot leaves, it results in significant yield loss. You can also see panicle blasting, which isn't due to just drought, but to a constant high heat index."
Perumal's idea is to develop sorghum varieties that eventually can do all things well, since farmers' bottom line is most important. The drought year of 2012 presented challenges to the plant breeder, but it also increased the resolve to make better selections.
"By seeing all the drought and water stress we've had in the last couple of years, along with climate change, we need to look seriously at drought-tolerant crops so that farmers won't face any more losses," Perumal said.
"We need to keep all these different factors in mind in making selections. You can't separate one issue from another. They are all interrelated. We face a lot of problems, so we need to make selections that will work well under a lot of different situations. It's quite a challenge."
More than 44,000 different types of sorghum germplasm were reduced to 840 converted sorghum lines for testing. Out of those lines, taken from 242 accessions from sorghums grown in 57 different countries, 220 lines have been selected by K-State researchers for further testing.
"From these lines, we will develop the hybrids that will eventually make crosses both here in Kansas and in greenhouses and test plots in Mexico," Perumal said. "These can either be seed parent lines or pollinator lines. With the drought situation and high heat index we were able to make significant progress toward developing quality lines that will lead to outstanding hybrids. Producers turn to sorghum when other crops fail due to drought or other factors. With the progress we are making, sorghum will remain key to Great Plains crop production in the 21st century."
Larry Dreiling can be reached by phone at 785-628-1117, or by email at firstname.lastname@example.org.