As water becomes more scarce and more expensive to pump in the High Plains, more farmers are likely to turn to grain sorghum as one of their main crops. This is supported by the fact that sorghum is more drought-tolerant than corn and produces higher yields during moderate to severe drought conditions.
However, some questions need answering before farmers commit to the crop under irrigation, according to Susan O’Shaughnessy, a USDA Agricultural Research Service engineer. For instance, what is sorghum’s yield response to deficient irrigation? Farmers also have questions about whether to plant early-maturing varieties (that are seeded later in the season and are, thus, less vulnerable to drought) or late-maturing varieties (that have higher yields but only if they are given enough moisture).
field trials answer questions
O’Shaughnessy and her colleagues at the ARS’s Soil and Water Management Research center in Bushland, Texas, set up field trials using early- and late-maturing sorghum varieties. Additionally, those varieties were grown under four deficit irrigation conditions.
Those water-moisture conditions included applying water to meet 80%, 55%, 30%, and 0% water-replenishment levels. “You could consider the 80% replenishment level to be mild deficit irrigation and the lower replenishment levels to be moderate to extreme deficit irrigation,” O’Shaughnessy explains.
The research team planted the late-maturing sorghum variety in late May or early June, while the early-maturing crop was seeded in late June. Both varieties were harvested at about the same time in the fall.
These field trials were conducted for three consecutive seasons. Also, the team tracked weather data and rainfall levels, and the researchers also measured evapotranspiration rates, which is an indicator of the plant’s overall water needs.
Over the three seasons of their evaluation, the researchers found that crop water-use efficiency (the water used by the crop in relation to the crop yield) was typically greatest at the 55% replenishment level. Yet, even a 30% replenishment level at least doubled the yields when compared with no irrigation.
At 80% replenishment, the late-maturing variety consistently produced higher yields than the early-maturing one. The early-maturing variety, however, produced sufficient yields to make it a viable alternative if there was limited well capacity or if a crop planted earlier in the season (such as corn or cotton) had failed due to hail, flood, or drought.
Higher-Yielding sorghum plant
In related research, USDA ARS researchers in Lubbock, Texas, have developed a mutant sorghum plant that produces 30% to 40% more seeds.
The researchers developed the higher-yielding sorghum by taking advantage of a plant part called a spikelet. A spikelet is a cluster of florets within the panicle, a type of flower cluster found in some other grasses, such as millet or rye.
Sorghum produces two types of spikelets: sessile spikelets and pedicellate spikelets.
Normally, only the sessile spikelets are fertile. The scientists developed a sorghum plant, however, that produces seeds in both types of spikelets.