Cropping Systems

Grain sorghum needs warm, moist soil that is well-supplied with air and fine enough to provide good seed-soil contact for rapid germination. Farmers can use a number of different tillage and planting systems to achieve these conditions. These systems may involve primary tillage, secondary tillage or no-tillage operations prior to planting.

Any seedbed preparation should provide a means of profitable crop production while minimizing soil erosion due to wind and water. Conservation tillage systems, such as reduced till, mulch till, ecofallow, strip-till, ridge-till, zero-till and no-till, provide protection from erosion. These systems also provide the added benefits of moisture, energy, labor and equipment conservation.

For successful dryland sorghum, the soil profile must have stored as much precipitation as possible. In addition, runoff from high-intensity rainfall events can be greatly reduced by maintaining residue on the soil surface. Every time the soil is tilled, some moisture is lost.

Strip-till resembles both no-till and minimum tillage systems and allows for the use of anhydrous ammonia, the least expensive nitrogen fertilizer. Small strips, generally a width of 8 inches or less, are tilled and fertilizer is applied below where the seed is planted. Strip till is more like traditional tillage, where the residue is removed and the seed is planted into a clean soil surface. However, similar to no-till, the residue between the strips remains. For dryland grain sorghum production, strip-till could be a good intermediate step for a farmer who does not want to switch to no-till.

No-till grain sorghum planting is best suited for moderately drained and well-drained soils. Many growers find it easier to plant in standing stubble rather than in stubble lying on the ground following reduced tillage. Soils often remain cooler and wetter through the growing season under no-till conditions, which is particularly true in heavy residue. While wetter soils are an advantage during dry periods, wetter soils at planting time can require that planting be delayed to allow soils to warm up, resulting in reduced yields, particularly in cool, wet springs and on poorly drained soils. Other conservation tillage systems, such as reduced till or strip-till, may be better choices in those conditions.

A 10-year study was completed in 2015 that examined two four-year winter wheat and grain sorghum rotations. The study consisted of three crop rotations: continuous annual wheat (WW), wheat/wheat/sorghum/fallow (WWSF) and wheat/sorghum/sorghum/fallow (WSSF).

When sorghum followed wheat in the rotations, the yield was 78 bushels per acre compared to 49 bushels per acre when sorghum following sorghum. The difference was a 58% increase in yield.

Reference: Schlegel, A. et al. Yield and soil water in three dryland wheat and grain sorghum rotations. Agron. J. 109:227-238 (2017).

Water use efficiency of sorghum in the rotations also was improved when following wheat, increasing from 179 pounds per acre with 1 inch of water when sorghum followed sorghum to approximately 268 pounds per acre with 1 inch of water when sorghum followed wheat.

Corn and sorghum are complementary warm-season grasses at many levels:

• Sorghum and corn share almost no common diseases. Crops struggling with issues such as Goss’ wilt, a bacterial disease related to short corn rotations, and extended diapause corn rootworm can break these disease and insect cycles while still maintaining a high proportion of warm-season grasses in a rotation.
• Sorghum is normally planted later than corn, spreading the workload and equipment over two windows for increased efficiency. Farmers could achieve this same efficiency by simply planting sorghum in one-half of the fields designated for corn rather than changing the rotation design.

In northern areas, sorghum is most commonly planted first in the sequence, followed by corn. Reasons for this include:

• More short-residual herbicides are available for use in corn than in sorghum.
• Sorghum does a better job of catching snow and provides a seedbed conducive for planting corn.
• Sorghum can struggle when seeded into heavy corn residue in northern areas due to the shorter growing season and cooler temperatures.

An Oklahoma State University trial has shown a benefit to corn yields when following sorghum. Corn grain yields were over 18% higher when following sorghum compared to continuous corn. Similar yield results occurred when corn was rotated with soybeans.

Note: Number in parentheses indicates yield increase percentage as compared to continuous corn.

Sorghum yields were not affected in a rotation with corn or soybean when compared to continuous sorghum.

Reference: Kochenower, Rick. Utilizing Grain Sorghum in Irrigated Crop Rotations. Oklahoma State.

In a more recent study, Dr. Allen Schlegel at the Kansas State University Agricultural Experiment Station near Tribune, Kansas, reported an 8.4% increase in corn yields following sorghum in a five-year study where continuous corn and continuous sorghum were compared to corn/sorghum and corn/wheat rotations. Sorghum yields improved 6.7% over continuous sorghum when rotated with corn.

Reference: Schlegel, A. Alternative Cropping Systems with Limited Irrigation. Southwest Research -Extension Center Field Day Report 2018.