02 Jun Double Crop Sorghum Management
With sorghum prices remaining strong for fall delivery, planting sorghum after wheat harvest is a great idea. Double crop sorghum management does not change very much compared with normal sorghum plantings.
Applying 100 lbs of N is recommended for double crop sorghum because an 80 bu/acre yield goal is reasonable. If your yield goals are substantially different, use those yield goals to determine N recommendations. Nitrogen must be applied despite the temptation to try and hedge your N applications based on carryover from wheat. If you grew enough straw for 40 bu/acre wheat, regardless of the final yield, most of the N you applied to your wheat is tied up in the wheat straw. Relying on carryover N from your wheat might result in disappointing sorghum yields.
Since P and K levels are managed in a long term fertilizer system, you can take this opportunity to add more P and K to your systems if you are trying to build soil levels. If your P and K levels are where you want them, applying P and K to your double crop sorghum is an option.
Since you are planting during the summer months and night temperatures are at their highest, tiller production will be low in double crop sorghum (Figure 1). To compensate for lower tiller production, it is recommended that you increase seeding rates 15 5o 20% over seeding rates you used a month sooner for full season sorghum production.
Volunteer wheat will be one of your biggest weed threats in double crop sorghum. To control what may be emerged at or near planting as well as to control other weeds that may be lurking in the wheat straw a glyphosate burn down mixed with a pre-emergence herbicide is recommended. Pre-emergence herbicides that contain a chloroacetamide and atrazine provide the best early season weed control and the probability of getting a rain to activate them are quite high this time of year.
Your typical post emergence sorghum herbicides can be used if necessary to control weeds that may come up later. In double crop sorghum, the sorghum grows very fast and post emergence applications are often not necessary.