Mid-season nitrogen and iron deficiency in sorghum
The rains this week don’t yet make our crop for the summer for dryland unless you received many inches; they just put us back in the ballgame. The NEXT rains will determine where we go. With that in mind as Pete Dotray, Wayne Keeling, and others will note, keep an eye on your weed issues. Some areas of the South Plains finally have enough moisture to trigger potentially major weed activity.
Is it truly too late to take a chance on grain sorghum?
Yes. Of course we can find those in the past that have had a successful crop planting this late, but it may be early next week before some fields dry out enough to plant. One Lubbock County grower asked on July 17 about still planting early maturity grain sorghum and “see what happens.” But it will be several days before he can plant so it is truly too late. For a Lubbock Co. example, if we could get a true early maturity hybrid in the ground on July 21 (allowing for drying), then at 55 days to half bloom (half of the plants in the field initiating bloom), that takes us to Sept. 14, then allow another five weeks to reach reasonable physiological maturity in the seed—that’s Oct. 19. Growth by then has for all practical purposes has ceased by about a week earlier. Remember that 1 day of heat accumulation in these days of July is worth 2 to 3 days in early October.
A more suitable alternative is sorghum/sudan or haygrazer. You do not need a physiological seed maturity and, with favorable conditions the rest of the summer, yield of 1.5 tons/A is certainly feasible. For dryland for seeds of ~15,000 seeds/lb. then 15 lbs./A is a good target, but even 10 lbs./A will give adequate results. Some haygrazers like the “three-way cross,” or the sorgo-sorghum/sudans, may have seed size of near 20,000 seeds/lb. If that is the case you can reduce your per-acre seeding rate.
Mid-Season Nitrogen on Grain Sorghum
With rainfall support some producers may now actually consider fertilizing grain sorghum that was planted late. This will depend on the amount of N you might have had on cotton ground that failed. Grain sorghum’s requirement is about 2 lbs. of N per acre per 100 lbs. of yield goal. I like for this N to be applied within 30 to 35 days of planting to ensure the N is “in the system” at the time when the all-important growing point differentiation occurs.
If you are irrigated, the bulk of this N should still be applied by 30-35 days after planting, but if you trickle out smaller amounts of N, then you might hold back 20% and fertigate, but for a medium-early maturity hybrid I recommend you still complete N applications with 50 days of planting.