A U.S. Department of Agriculture (USDA) scientist is providing much needed guidance to sorghum farmers in the Texas High Plains who are trying to save water by using less-than-optimal amounts of it.
Farmers in the area are turning to sorghum because many of them suffered major losses raising corn during recent droughts and water shortages. Sorghum is more drought tolerant than corn, but growers need to know if they will get sufficient yields using less water. They also must decide whether to raise early-maturing sorghum varieties (which are planted later and are less vulnerable to drought) or late-maturing varieties (which produce higher yields if given enough water).
Susan O'Shaughnessy, an agricultural engineer with the USDA's Agricultural Research Service (ARS) in Bushland, TX, evaluated yields and water-use efficiency of early- and late-maturing sorghum varieties produced under four levels of deficit irrigation. She and her colleagues planted late-maturing and early-maturing varieties at optimal times and harvested both types at about the same time in the fall. They grew the crops for three seasons, tracked weather data and rainfall levels, and measured evapotranspiration rates an indicator of the plant's overall water needs. Above-average rainfall occurred in 2009 and 2010, and much lower-than-average rainfall occurred in 2011.
They found that on average, over the three growing seasons, crop water-use efficiency (the water used by the crop in relation to the crop yield) was typically greatest at the 55-percent replenishment level, but even a 30-percent replenishment at least doubled the yields when compared with no irrigation. At 80-percent replenishment, the late-maturing variety consistently produced higher yields than the early-maturing one, but the early-maturing variety produced sufficient yields to make it a viable alternative. Growers also risk severe or total losses if they practice even moderate deficit irrigation during droughts. In fact, total crop failures are likely without at least some irrigation in drought years like 2011.
The results from this research should help farmers in regions with a growing season that has erratic rainfall, widely varying temperatures and extreme weather (hail, flooding and lightning).
Read more about this research in the July 2015 issue of AgResearch magazine. ARS is USDA's principal intramural scientific research agency.