Wheat replanting decisions
Where heavy rains occurred on October 8-9, some wheat fields were washed out and may have to be replanted. Replanting is expensive and time-consuming, but may be advisable under certain conditions.
The first thing producers will need to do when making this decision is evaluate the existing stand. One way to do this is to count the average number of plants per square foot. That will give you a rough idea of the level of yield potential at this point in time – although obviously many other factors will ultimately affect yield potential between now and harvest.
As a place to start, you might expect about one bushel per acre of yield for every head per square foot. This isn’t exact by any means because a lot of other factors (such as number of kernels per head and kernel weight) are involved, but it’s not a bad estimate this early in the season. So if you want a yield of 60 bushels per acre, you’d want about 60 heads per square foot. To get 60 heads per square foot, you’ll need at least 15 plants per square foot – and that’s assuming each plant produces four tillers, which may be a bit on the high side. If the stand is very thick, plants may only have two tillers each – or less. But where the stand is more open and the growing environment in winter and spring is close to normal, it’s reasonable to assume four tillers per plant.
To count the number of plants per square foot, you can simply go out and randomly toss a one-square-foot grid in the field and count the number of plants within that square. Or if your field is in 12-inch rows, just count the number of plants per foot of row at several locations in the field. Multiply the average number of plants you have per square foot by four (or however many tillers per plant you expect based on the thickness of your stand) and that will give you a rough idea of the number of heads per square foot you’ll have – and possibly your yield potential if you assume that each head per square foot will result in about one bushel per acre.
So, what kind of yield potential are you willing to accept? If you have only four plants per square foot, multiply that by four and you have about 16 tillers per square foot at harvest. That projects out to about 16 bushels per acre. If you have five plants per square foot, you might have a yield potential of about 20 bushels per acre. Not enough? Then you should consider replanting.
There are two major concerns to consider other than yield potential in deciding whether to replant: the susceptibility of the ground to wind erosion and the potential for weed and grass infestations. Where stands are less than 40 percent of normal, these become major concerns, even if yield potential is not a concern. In fact, research in western Kansas indicates that 260,000 to 320,000 plants per acre (or about six to seven plants per square foot) can produce within 90 percent of expected yields – especially if the plants are able to tiller well and the stand is uniform. But if the soil is blowing or weeds and grass infestations become severe, the stand should probably have been replanted and thickened.
If possible, replanting should be done at a 45 degree angle to the original stand to minimize damage to the existing stand.
Until the end of October, producers could cross-drill at the rate of 30-40 pounds per acre in western Kansas and 40-60 pounds per acre in central and eastern Kansas, using a double-disc opener drill if at all possible to minimize damage to the existing stand. If the replanting is done in November or later, increase the seeding rates to 60-75 pounds per acre in western Kansas and 75-90 pounds per acre in central Kansas. If stands are less than 30 percent of normal, increase the seeding rates just mentioned by 20-30 pounds per acre. If a hoe drill is used, the seeding rate should be higher than if a disc drill is used because the hoe drill will destroy much of the original stand. With a hoe drill, add about 20-30 pounds per acre to the seeding rates mentioned above.
Where there was no emergence in all or parts of the field, producers would have to use a slightly higher seeding rate than used initially -- 75 to 90 pounds per acre in western Kansas and 100 to 120 pounds in eastern and central Kansas, using the higher end of those ranges when planting in November or later.
Seeding rates on non-irrigated fields should not be higher than 90 lbs/acre in western Kansas or 120 lbs/acre in central and eastern Kansas. Under irrigation, seeding rates should never be higher than 150 lbs/acre.
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