Sorghum, often referred to as milo, is a cereal grain belonging to the grass family that originated in Africa several thousand years ago. It is the world’s fifth-most important cereal crop, cultivated primarily for grain used in human food, animal feed, and ethanol production. Sorghum’s global significance is rooted in its exceptional ability to thrive in challenging environments, making it a reliable staple in regions considered too hot and dry for other major grains.
The Climate Requirements of Sorghum
A successful sorghum growing zone requires high temperatures and tolerance for limited water availability. Optimal growth requires warm conditions, with the ideal temperature range between $27^\circ \text{C}$ and $30^\circ \text{C}$ ($80^\circ \text{F}$ and $86^\circ \text{F}$). While the crop can survive a wider range, extreme heat above $38^\circ \text{C}$ can harm yields.
To track progress toward maturity, grain sorghum requires the accumulation of Growing Degree Units (GDUs). Medium-maturity hybrids generally require a cumulative $1,400$ to $2,000$ GDUs to reach mid-bloom, which is important for growers in northern latitudes with shorter seasons. The plant’s physiological adaptations are the basis of its superior drought tolerance compared to corn.
Sorghum has a more efficient, deeper root system and a waxy leaf cuticle that reduces water loss through transpiration. This mechanism allows it to delay development during severe drought and then resume growth when moisture returns. In water-limited environments, sorghum consistently demonstrates a higher Crop Water Use Efficiency (CWUE), producing more grain per unit of water than other major cereals. This resilience cements its role in arid and semi-arid regions.
Global and Regional Sorghum Production Zones
The heat and drought tolerance of sorghum dictates its placement in the semi-arid tropics and subtropics globally. This distribution is split between regions focused on human consumption and those focused on industrial uses. Africa and India, where the grain originated, rely on sorghum as a primary food source, with countries like Nigeria and Ethiopia ranking among the top global producers.
In the Western Hemisphere, the United States is the world’s largest producer, with cultivation concentrated in the Sorghum Belt. This belt spans the Great Plains, including states like Kansas and Texas, characterized by hot summers and limited rainfall. Here, the grain is predominantly utilized for livestock feed and ethanol production. Mexico is another major producer, growing sorghum for both human consumption and livestock feed, thriving in hot conditions where crops like maize would require costly irrigation.
Soil and Planting Requirements
Sorghum is adaptable to a wide array of soil conditions, contributing to its broad cultivation footprint. While it can grow in heavy clay and sandy soils, the plant thrives best in well-drained loamy soils that prevent waterlogging. The crop exhibits a high tolerance for varying soil acidity, with a $\text{pH}$ range between $5.0$ and $8.5$.
For optimal growth, a $\text{pH}$ between $5.5$ and $7.5$ is preferred, as lower acidity can lead to increased aluminum toxicity. Successful planting begins when the soil temperature consistently reaches $17^\circ \text{C}$ to $18^\circ \text{C}$ ($63^\circ \text{F}$ to $64^\circ \text{F}$) to ensure quick and uniform germination. Planting the seed at a depth of $1$ to $1.5$ inches is typical, though it can be planted up to $3$ inches deep to reach moisture in dry conditions.
Like all cereal crops, sorghum requires a balanced supply of macro-nutrients, particularly nitrogen, phosphorus, and potassium, for healthy development. Nitrogen is applied to support high yields, with specific rates determined by soil testing and expected yield goals.