Sorghum Production

Overview:

Sorghum is a relatively drought-tolerant crop that can be produced over a range of irrigation levels, from rain-fed (dryland) to deficit to full irrigation. It is often a feed grain of choice where irrigation capacity is limited.

Objectives:

1. Increase understanding of water requirements (peak water use, seasonal water use, critical growth stages, drought sensitivity/tolerance, and water quality requirements) of sorghum.
2. Increase water use efficiency and profitability in sorghum production through application of appropriate best management practices.

Key Points:

1. Sorghum is relatively resistant to drought and salinity. Grain sorghum has an extensive root system, and its drought tolerance makes it suitable for limited irrigation.
2. Seasonal water use for sorghum in the Texas High Plains is approximately 13 to 24 inches per season. Seasonal water demand is approximately 24 inches. Deficit irrigation management (water available is less than crop demand) is common practice, often due to limited water supply.
3. Peak water use occurs just before and during boot stage.
4. Late-season water stress during grain filling can result in shriveled seeds, which reduces yield.

Assess your knowledge:

1. What is the peak water use of sorghum in you area? When (growth stage and calendar range) does this occur?
2. What is the maximum effective root zone depth for sorghum? Are there other factors in your field or management program that you would expect to limit this effective root zone depth? What practical significance do these limitations have with respect to your irrigation and nutrient management programs?
3. Are there water quality (salinity) concerns for sorghum production on your farm? If so, what are they? How can they be managed?
4. What irrigation method do you currently use to irrigate sorghum? What best management practices (BMPs) are you using to optimize water use efficiency? Identify other methods and BMPs that would be applicable to your operation.

Irrigation Management for Sorghum Production

Grain sorghum is a tropically adapted plant that can survive under drought and adverse conditions. Because of its ability to survive in unfavorable conditions, sorghum is often produced in poor soils and with poor management. However, profitable sorghum production requires sufficient water at critical points in the crop’s development. Good crop management, including good irrigation management, is key to high yields and profitability.

Sorghum can produce an extensive fibrous root system as deep as 5-6 feet, but it generally extracts more than 75 percent of its water and nutrients from the top 3 feet of soil. As moisture is depleted from the top 3 feet, the crop will extract water (if available) from deeper in the root zone.  Plants can use about 50 percent of the total available water without undergoing stress.

Water availability is most critical during the rapid growth stage and before the reproductive stage.  If plant maturity is delayed due to water stress, the crop may face frost damage in the event of an early freeze. Late-season water stress during grain filling can result in shriveled seeds, which reduces yield.

Grain sorghum’s peak use begins at approximately initiation of the reproductive stage; this peak can be 0.3 inches per day (or temporarily higher in hot, dry weather conditions). Seasonal water demand for grain sorghum is 24-28 inches (from rainfall, stored soil moisture and irrigation). Grain sorghum has an extensive root system, and its drought tolerance makes it suitable for limited (deficit) irrigation.

Irrigation of grain sorghum on sandy soils requires more frequent and smaller irrigation applications than on soils with higher water holding capacity. Center pivot irrigation is an excellent option for irrigating in these conditions.  Irrigation scheduling using evapotranspiration or by maintaining a given soil water depletion balance may be especially useful where soils with low water holding capacity and/or restricted root zones present challenges to irrigation management.

Common mistakes affecting sorghum water use

• Waiting too long to apply the first irrigation. The head begins to form about 35 days after planting. If the plant is stressed during this period, the number of seeds per head will be reduced.
• Irrigating too late. Do not irrigate after the hard dough stage or after the plants have reached physiological maturity.
• Over-planting. For irrigated production, do not exceed 70,000 to 80,000 established plants per acre; dryland production should not exceed 50,000 to 60,000 plants per acre. Excessive plant population increases plant competition, reduces head size, increases the chance of charcoal rot and lodging, and reduces water use efficiency.

References

• Irrigating Sorghum in South and South Central Texas (L-5434)