A. Seedbed Preparation:
A seedbed similar to the one prepared for corn is also good for grain sorghum. The use of a cultipacker or corrugated roller after seeding often gives better stands. In warmer regions, reduced- and no-tillage systems are used for grain sorghum. Soil temperatures may be too cold for these systems in much of the Upper Midwest.
B. Seeding Date:
Grain sorghum should be planted when soil temperatures reach 60 to 65°F. Generally this is 15 to 20 days after corn planting or
between May 15 and early June. Grain yields decrease as planting is delayed after early June. Most hybrids require 90-120 days to reach maturity, therefore late-planting as an emergency crop is not recommended.
C. Method and Rate of Seeding:
[*]Method of Planting: Plant grain sorghum in rows at a depth of 1 inch in heavy soil and 1 1/2 to 2 inches in sandy soil. Corn planters are probably the most common seeding equipment. It is important to place the seed in moist soil to obtain fast emergence of the seedling. A grain drill can also be used to plant the seed in narrow rows. Some adaptations in the grain seedbox may be necessary to isolate the seed above the hole. Some growers have attached small gas funnels above the holes in the seedbox and place the seed in the funnels. Commercial equipment is also available for most newer drills.
[*]Rate of Planting: Seed size will influence the pounds of seed to plant per acre. As a general rule, there are approximately 16,000 sorghum seeds per pound. Most sorghum hybrids average about 75% emergence. On soils of good fertility and adequate moisture, the recommended rate of seeding is 8- 10 pounds of seed in rows of 30-40 inches in width. At this rate of planting, seeds will be I to 1 1/2 inches apart in the row with a population of 100,000 to 120,000 plants per acre.
On soils that are less fertile or more droughty, the seeding rate should be 5-6 pounds per acre.
[*]Row Width: The row width used will likely depend on the equipment available. During the last few years, there has been considerable interest in planting grain sorghum in narrow rows to boost grain yields. With narrow rows, greater distance between plants in the row must be planned in order to get the optimum plant population per acre. The main advantage of narrow rows is to attain more efficient use of moisture, soil fertility, and sunlight. Grain yields in Minnesota studies were 10-15% higher in 10-inch rows than in 40-inch rows. The primary disadvantage is that cultivation is not possible and weed control is dependent entirely on chemical herbicides.
D. Fertility and Lime Requirements:
Nutrient needs of sorghum closely resemble those of com in that sorghum uses relatively large amounts of nitrogen and moderate amounts of phosphorus and potassium. The grain in a 100-bushel per acre grain sorghum crop removes
about 100 lbs. of nitrogen, 14 lbs. of phosphorous, and 14 lbs. of potassium.
A soil test is the most practical method of determining fertilizer needs. Apply phosphate and potash according to soil test recommendations where soil tests for P and K are low (L) or very low (VL). Use the nitrogen and maintenance phosphate and potash recommendations shown in Table 1. Lime soils to a pH of 6.0 to 6.5.
Nitrogen can be applied in the spring as a preplant application, at planting, or as a side dressing at cultivation. Appropriate N credits should be taken for manure and previous legumes to reduce N fertilizer rates. A starter fertilizer may be beneficial.
Table 1: Annual nitrogen, phosphate, and potash recommendations for grain sorghum.
<TABLE border=1 cellSpacing=1 cellPadding=3><TBODY><TR><TD vAlign=bottom rowSpan=3>Yield level
</TD><TD vAlign=bottom colSpan=4>Nitrogen recommendation
</TD><TD vAlign=bottom rowSpan=2 colSpan=2>Phosphate and Potash
recommendation<SUP>1</SUP>
</TD></TR><TR><TD vAlign=bottom colSpan=4>Organic matter %
</TD></TR><TR><TD vAlign=bottom>< 2
</TD><TD vAlign=bottom>2-5.0
</TD><TD vAlign=bottom>5.1-10
</TD><TD vAlign=bottom>> 10
</TD><TD vAlign=bottom>P<SUB>2</SUB>O<SUB>5</SUB>
</TD><TD vAlign=bottom>K<SUB>2</SUB>O
</TD></TR><TR><TD vAlign=top>bu/a
</TD><TD vAlign=top colSpan=6>lb/a
</TD></TR><TR><TD vAlign=top>50 to 100
</TD><TD vAlign=top>120
</TD><TD vAlign=top>100
</TD><TD vAlign=top>80
</TD><TD vAlign=top>60
</TD><TD vAlign=top>30
</TD><TD vAlign=top>30
</TD></TR></TBODY></TABLE>
F. Weed Control:
Early spring seedbed preparation followed by one or two shallow cultivations, just before planting sorghum will kill several generations of weed seedlings and give sorghum a chance to get ahead of the weeds. Timely cultivations of sorghum planted in 20-inch or wider rows during the early growing stages are highly important. Sorghum planted in narrow rows can not be cultivated, but it is a highly competitive crop and can dominate many weeds. Several herbicides are available to compliment cultural and mechanical practices. Quackgrass can be controlled with I qt/A of Roundup applied when the weed is actively growing and has 3 to 4 leaves. Other perennial weeds such as Canada thistle, milkweed and hemp dogbane should be suppressed the year before sorghum is planted.
Several selective herbicides can be used in sorghum.
Atrazine can be applied as a preplant incorporated, preemergence or postemergence herbicide.
Application rates are similar to those used in com, as are the concerns of atrazine carryover. If crops other than corn will be planted next year, do not use atrazine in sorghum. On the other hand, sorghum could be safely planted in fields with atrazine residues from previous years.
Dual and Lasso can be used as a preplant or preemergence treatment
only when sorghum seed is treated with a safener. Your seed dealer may be able to obtain safener-treated seed for you. Dual and Lasso are excellent annual grass herbicides and could be used in combination with atrazine. If incorporated into the upper 2 inches of soil, they suppress yellow nutsedge.
Ramrod is chemically related to Lasso and Dual but can be used preemergence in sorghum without a chemical safener applied to the seed. It controls many annual grasses and can be mixed with atrazine to control a broader spectrum of weeds.
Buctril, Banvel and 2,4-D are labeled for use in grain sorghum for postemergence broadleaf weed control. Their use directions and rates are similar to those for corn.