Dryland Sorghum Management in Arid Environments
By Russell French
Dryland Sorghum Management
Research has shown wheat-sorghum-fallow rotation or continuous sorghum is the most profitable cropping system for dryland grain production on the Texas High Plains. Research has also shown no-till or minimum-till sorghum outperforms conventional tillage due to soil moisture preservation.
Dryland sorghum fertility guidelines should be built on soil testing and yield goals based on depth of subsoil moisture at planting. Heavy soils with more than 1.3% organic matter (OM) need 1.0 pound nitrogen per bushel yield goal or 1.8 pound nitrogen per hundredweight yield goal. It is recommended that sandy soils with 1.3% OM or less receive 1.2 pounds per bushel or 2.1 pounds nitrogen per hundredweight yield goal.
Phosphorus (P) is recommended for low and very low testing soils. When soils test in the medium range, applying phosphorus should be considered if subsoil moisture is available (4-6 feet) at planting. Potassium (K) should be applied only if the soil test is low. Most High Plains soils have adequate potassium for dryland sorghum. Zinc (Zn) should also be applied if the soil test is very low for this element. Zinc deficiency can delay sorghum maturity, possibly exposing the crop to freezing conditions before harvest.
Phosphorus, potassium and zinc are immobile nutrients and must be incorporated with tillage or placed in the soil (banded) in no-till situations. Broadcast rates of P, K and Zn can be reduced by as much as 50% if applied in a band at planting. Banding reduced rates of fertilizer helps reduce costs on dryland production. Fertilizer decisions can be delayed until subsoil conditions are ascertained at seeding, when planting equipment has the capability of banding nutrients.
If moderate to heavy grass pressure is anticipated, safened sorghum seed and a grass herbicide such as dimethenamid, metolachlor or alachlor are recommended. There is no reliable post-emerge grass herbicide for sorghum. Banding a pre-emergence grass herbicide behind the planter, along with cultivation, can be cost effective.
Where possible, any amount of 2,4-D should be a voided. If 2,4-D must be used, apply with a ground rig with drop nozzles and spray below the whorl. For broadleaf weed control, pre-emergence atrazine or atrazine and crop oil used as a post-emergence treatment are options. However, neither will be effective against triazine-resistant weeds, which are becoming very prevalent throughout the high plains. Tank mixes of atrazine with dicamba, bromoxynil, or Peak¹ have been the most effective against triazine-resistant weeds. These mixes are also effective against other tough broadleaf weeds and some perennial weeds. These post-emergence herbicides provide good crop safety if applied according to labeled directions. For large weeds, 3-way tank mixes (such as atrazine, dicamba and bromoxynil) are the most effective.
Scout dryland sorghum regularly throughout the entire growing season. Early season sorghum pests include wireworms, greenbugs, false chinch bug, chinch bug and cutworm. Late season sorghum pests include corn leaf aphid, greenbug, fall armyworm, spider mite, sorghum midge and headworm.
Greenbug populations on the High Plains have shifted from biotype-E to biotypes-K and I. Organophosphate insecticide resistance in greenbug populations has also increased. Cruiser¹ insecticide seed treatment is an option for high plains dryland sorghum growers. At a 1.5 to 2.0 pounds per acre seeding rate, this treatment will cost from $2.00-$3.00 per acre, which is more cost effective than an aerial application of insecticide.
Always read and follow label direction for pesticide applications. Check with your crop consultant, extension specialist or agricultural chemical supplier for the latest recommendations.
Growers have several hybrid options for dryland sorghum production on the high plains. Pioneer offers a diverse lineup of hybrids for dryland production on the high plains that ranges from 95 to 118 CRM, and includes both red-bronze and yellow-white hybrids. Dryland sorghum growers should use 3 primary factors in selecting a hybrid and planting rate; planting date, subsoil moisture at planting time, and hybrid availability.
Growers should select a hybrid that will begin to boot/head near the wettest part of the summer, and mature approximately 2-3 weeks before the average first fall freeze date. In the Texas and Oklahoma Panhandles, Eastern New Mexico and southwestern Kansas, the ideal situation would be to have sorghum boot/head in mid-August and mature by October 1. In northwestern Kansas, grain sorghum should reach boot/head stage in early August and mature by mid-to-late September.
Figure 1. Average monthly precipitation for High Plains locations
By following the guidelines listed above, sorghum should head in mid-August under normal conditions. This is typically the wettest part of the summer growing season in the southern high plains. Growers should avoid planting early maturing varieties prematurely as they will head in mid to late July, which is historically the hottest and driest part of the summer.
Subsoil Moisture Related to Planting Rate
Dryland sorghum growers should use a 6-foot soil penetrometer to determine subsoil moisture depth in several locations in the field. Sorghum hybrids vary in seeds per pound. It is important to plant in terms of seeds per acre. Planting dryland grain sorghum in 30-inch rows at rates of 20,000-35,000 seeds per acre has proven to give the most consistent yield performance across a wide range of environments, over a period of years. Research has shown when early maturity sorghum hybrids are planted in dryland conditions in late June to early July, a planting rate of 64,000 seeds per acre on 15-inch rows is preferred, if subsoil moisture is adequate (4 feet or more.)
Dryland Sorghum Strategies
Table 1. Hybrid maturity recommendations for planting dates - High Plains & Kansas
|Planting Dates - High Plains & Kansas||CRM Range|
|Mid-May to early June||112 – 118 CRM|
|Early- to late- June||106 – 112 CRM|
|Late June to early July||95 – 106 CRM|
There are 3 planting date options for sorghum. The first is mid-May to early-June, for which there are 3 planting rates and time frames:
- With 5-6 feet of subsoil moisture, plant an adapted medium-maturity hybrid at 25,000-30,000 seeds per acre.
- With 3-5 feet of subsoil moisture, plant an adapted medium-maturity hybrid at 20,000-25,000 seeds per acre.
- If less than 3 feet of subsoil moisture, wait until mid-to late-June and plant a medium or medium-early hybrid. If you feel you must plant immediately, use a medium maturity hybrid at 18,000-20,000 seeds per acre.
The second planting option date, of early- to late-June, offers these strategies for planting:
- With 5-6 feet of subsoil moisture, plant an adapted medium maturity hybrid at 30,000-32,000 seeds/acre.
- With 4-5 feet of subsoil moisture, plant an adapted medium maturity hybrid at 25,000-30,000 seeds per acre.
- With 3-4 feet of subsoil moisture, plant an adapted medium-maturity hybrid at 20,000-25,000 seeds/acre
- If there is less than 3 feet of subsoil moisture, it is recommended to wait until late June to early July and plant an adapted early maturity hybrid. If planting cannot be postponed, plant a medium maturity hybrid at 18,000-20,000 seeds per acre.
The third planting date option is late June to early July, with the following planting strategies:
- With 5-6 feet of subsoil moisture present, plant an early maturity hybrid at 30,000-32,000 seeds per acre, or try a high-density strategy and plant 64,000 seeds/acre in 15-inch rows. High-density planting is not recommended for less than 4 feet of subsoil moisture.
- With 3-5 feet of subsoil moisture, plant an early-maturity hybrid at 20,000-25,000 seeds/acre.
- If there is less than 3 feet of subsoil moisture, plant an early-maturity hybrid at 18,000-20,000 seeds per acre.
The recommended seeding rates can be increased 10-15% for marginal topsoil moisture at planting, cloddy seedbed, or cold soils in early no-till situations. Growers located above 4,000 feet elevation, northwest Kansas, or eastern Colorado, check with your local Pioneer Sales representative for area cutoff dates.
Plan to plant sorghum to reach heading stage in early August in western Kansas and eastern Colorado and plan for heading in mid-August for Texas and Oklahoma Panhandles.
Adjust planting rates to available subsoil moisture at planting time. Under short subsoil moisture conditions, delay planting when possible and utilize shorter-season sorghum hybrids, which require less water. Lowering seeding rates with short subsoil moisture conditions keeps sorghum out of stress longer and improves standability. Sorghum can compensate very well at lower planting rates in favorable years due to tillering potential. Most Pioneer® brand grain sorghum hybrids have excellent emergence characteristics, which improves low rate planting success.
¹Trademark of a Syngenta Group Company.
Russell French holds a Bachelor of Science degree in agriculture and crop protection from Kansas State University. He currently serves as a District Sales Manager for Pioneer, with prior experience as a crop consultant to sorghum producers in western Kansas. He has been with DuPont Pioneer since 1992.