This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Planting Grain Sorghum: I. Row Spacing Width
The average Texas grain sorghum field has narrower row spacing than 20 and 30 years ago. The impetus to do so incudes better understanding of plant growth response, improved sorghum shading of the soil for reducing evaporation and suppressing small weeds, more conservation tillage, and in some cases the desire to push for higher yields with more uniformly spaced plants. And finally, when sorghum producers (as well as corn, cotton, and other crops) push for higher yields there is a common belief that higher plant populations may enable you to realize that most years. But as any Texas farmer knows, weather varies from year to year, and a crop will not respond the same way each year. Higher plant populations can limit your sorghum’s ability to respond to environment, especially rainfall.
Whether a farmer moves from 40” rows to 30” rows in the High Plains, from 36” or 38” rows to 30” in South Texas, or to 15” or 20” row spacing anywhere in the state, there is tendency to increase seed drop thus resulting in a higher population. I tend to believe this increased seed drop is a neutral to negative effect in most Texas sorghum fields because many farmers are in fact already at the upper end—or beyond—what seed drop they should be using (see below where to get AgriLife suggestions). I recommend that farmers initially do not increase seed drop when they reduce row spacing width. Instead, let the more uniform spacing of plants in the field be your friend and potentially increase your yield. That alone is likely an improvement in agronomic practices.
I will cover in-row spacing in a future Sorghum Tip.
What if I am drilling my grain sorghum?
Some Texas sorghum farmers, at least in the High Plains, may even drill their grain sorghum. Compared to 30” rows or even 40” rows, should they increase their grain sorghum seeding rate? I usually say ‘no.’ First, it is hard to set drills to plant a targeted seed drop. They are designed to plant seed in volume, like wheat. You may not be able to get a sorghum seeding rate low enough without taping off 1 in 3 drill rows, or even 1 in 2 drill rows. Again, let the spacing of your seed and the subsequent plant be your friend. I will concede, though, a 10% increase in seeding rate if drilling due to the inferior ability of a drill to place seed like a planter does. If the ground is rough and thus seedbed planting conditions are less than desirable, I might increase seeding rate 20%, but know that if you get the rain you hoped for, all the seed could germinate, and you are immediately overpopulated.
What grain sorghum seeding rates should I be using?
In some areas of the state we truly don’t have good data, or it may be 30 or more years old. We don’t discount the data from the distant past, but as hybrids have changed some, tillering ability may be different, etc. it would be good if AgriLife could bring you recent multi-year and multi-site data for each region of the state. For our current general suggestions see the United Sorghum Checkoff Program pocket grain sorghum production guides at http://www.sorghumcheckoff.com/farmer-resources/grain-production/ There are three editions that cover Texas (South & Central Texas; South Plains/Concho Valley/Rolling Plains (the West Texas edition), and a third edition that covers the Texas Panhandle. The former two guides were prepared by Texas A&M AgriLife staff, the Panhandle edition was a joint effort between Texas A&M and Kansas State.