This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Planting Grain Sorghum: II. In-row Spacing
In a previous Sorghum Tip, I discussed row spacing (see http://texassorghum.org/sorghum-tips Feb. 20, 2017). Now what about spacing of seeds within the row?
On this smaller scale of about two to six inches within the row, it may seem that the uniformity of spacing is not that important. Yes, it is true that the root system, for example, will basically still explore the same area and leaf area will be about the same. Some hybrids, though, do respond differently to spacing around the individual plant with more tillering than others. This can be a positive effect (a plant accounts for extra space and yield potential by tillering to compensate for a gap in the row) and negative (excess tillering is not desirable in moisture-limited production). Research beginning in the early 2000s from Dr. Bobby Stewart’s program at West Texas A&M demonstrated that for West Texas dryland conditions suppression of tillering by placing 4 to 6 seeds (thus subsequent plants) within 1.5” or less would essentially eliminate tillering. Resulting yields tended to be higher (the plant does not direct resources into unproductive tillers) than uniform spacing, but the potential for less shading of soil of clumped plants may lead to more weeds and higher evaporation of soil moisture.
Still having uniform spacing with the row is a plus. We are most immediately concerned about larger gaps of 12” or more—they are obvious, especially if you are planting 3 to 6 seeds per foot of row. But the same principle applies like I discussed in row spacing, uniformly distributed plants is favorable.
The faster you plant on rough ground you will also lose incrementally some of your uniform spacing in the seed drop. I am not the first one to advise producers to “slow down” when you are planting.
I have already planted my grain sorghum. I will consider this next year…
Actually, when your crop is young, it is a good time to evaluate the stands you have in individual rows. Do you have skips? Do you have a row that looks thick? Or thin? Usually you can tell from the tractor tire track ribs which direction the planter was moving so you know which row unit of the planter may have thickly or thinly seeded row. The planter unit needs to be checked for a malfunction. If you are using a plate planter you can’t expect quite the uniform spacing (or even favorable control of seed drop), but for planters that meter seed in an air-vacuum system, you should expect all rows to very closely drop the same number of seed. And if you see a row that departs from the general appearance, you need to check that planter unit.
Planter Unit Seed Drop Confirmation
In testing on a late model John Deere 8-row planter at one of our AgriLife research facilities, I found that two rows dropped 17% or more seed than they should have, and one rows was -20% from what was targeted. Pending the production conditions this creates a potentially non-agronomic plant population. I recommend that farmers, once they have their seed on hand for grain sorghum—or any other crop—set the planter up, turn the drive wheel a set distance and catch seed to calculate the number of seeds per foot. How does this match with your planter book? In this case, a correction can be made before you go to the field, otherwise you await the stand to see if one of your planter units may be off. For an individual row with the seeding rate off, that is like having the whole field at that population in that row. You have too many or too few plants. It needs to be corrected.