Water Use and Irrigation
Water sources covering the Sorghum Belt, like the Ogallala Aquifer, are being depleted at a much faster rate than they are being replenished. According to a research study by Kansas State University and the Kansas Geological Survey, if no action is taken within the next 50 years, the Ogallala will be 70% depleted and 40% of the area irrigated by the aquifer will not support a 400 gallon per minute well. In many cases, water availability and well yield are declining, resulting in reduced irrigated capacity. As water supplies decline, risk increases for growers. Many farmers are looking for an effective alternative to help sustain their water supplies and economy. Sorghum’s ability to produce when other crops wither make it a smart choice in areas with unpredictable water availability.
Sorghum and Water
Sorghum has a long planting season and a diverse hybrid portfolio, offering farmers a broad window to take advantage of moisture patterns. While other crops require close to 12 inches of water to produce the first bushel, it only takes six inches of total water from soil, rainfall, or irrigation to produce the first bushel of grain sorghum. In low-water settings, sorghum can produce more grain per inch than comparable grain crops.
The total amount of water needed to grow grain sorghum without limiting yield is often referred to as its evapotranspiration (ET) demand. ET is the sum of water lost through evaporation from the soil and the water that moves through the plant and evaporates from the leaf surface, mostly through the stomata. Sorghum’s ET demand is dependent on the environment in which it is being grown. ET is largely determined by radiation, humidity and wind speed. As environmental conditions change, so does the amount of water required to grow grain sorghum. Tropic and subtropic regions will require less water for sorghum production than temperate regions, which require less water than arid and semi-arid regions.
Water use efficiency (WUE) is the amount of yield produced per inch of water used. In areas where water is in short supply, it is important to implement cultural practices that maximize WUE. In research conducted by USDA scientists near Amarillo, Texas, WUE of grain sorghum under well-managed conditions yielded 329 pounds of grain per acre-inch of water used. In this environment, 20 inches of the total water used by the plant would be expected to produce a yield of 6,580 pounds or 118 bushels.
In the semi-arid region of the southern Great Plains, growers have changed production practices in recent years to maximize the ability of the soil to store water. No-till and limited till practices greatly reduce the amount of water lost from the soil as evaporation while decreasing the amount of water from rainfall events that are lost through runoff. In addition, planting in more narrow rows shortens the time the sorghum leaves need to canopy over and shade the soil which also reduces evaporation.
Efficiencies in the use of irrigation water take into account losses during storage, transport and application. In the southern Great Plains, growers over the years have moved from inefficient furrow irrigation to low and mid-elevation sprinkler heads to subsoil drip irrigation systems.