Seeding rate for small grains

Small grains have the ability to tiller and produce several stems that can produce grain. Research shows the main stem and the first tiller contribute the majority of the grain yield. It’s important to adjust the seeding rate to produce a plant population with a main stem and one or two tillers.

Another advantage of crops with few tillers is that most stems will be in similar development stages. This narrow window for each crop stage improves the timing for crop inputs, such as herbicides or fungicides, especially for growth-stage-sensitive inputs.

Varieties that produce few tillers may require higher seeding rates. Excessive seeding, however, can lead to lodging and poor root development. You need at least one tiller for optimal root development.

If planting is delayed past the optimum seeding date for spring-planted small grains, increase seeding rates by about 1 percent for each day planting is delayed. Do this up to a maximum rate of 1.6 million seeds per acre.

An increased seeding rate will partially compensate for the decrease in grain yield and the reduction in tillering. This happens because the crop will go through its development faster as average temperatures increase during the growing season. For winter wheat, increase seeding rates if planting is delayed to compensate for a potentially higher risk of winterkill.

An average optimum stand for hard red spring wheat, when planted early, is 28 to 30 plants per square foot, or approximately 1.25 million plants per acre. This number should increase by 1 to 2 plants per square foot for every week planting is delayed past the early optimum seeding date.

Expected stand loss, even under good seedbed conditions, is 10 percent to 20 percent and will increase with a poor seedbed or improper seed placement due to poor depth control.

The general formula for calculating a seeding rate is:

Seeding rate (pounds per acre) = [(desired stand in plants per acre) / (1 - expected stand loss)] / [(seeds per pound) x (percentage germination)]

Calculate the seeding rate for each seed lot and calibrate the drill accordingly.

Example

An example for calculating the planting rate for wheat:

1. Desired population is 1.25 million plants per acre at harvest.

2. Historic field stand loss is 10 percent.

3. Seed lot germination is 95 percent.

4. Seed lot has a seed count of 15,000 seeds per pound.

5. Calculate:

   1. 15,000 x 0.95 = 14,250 viable seeds per pound.

   2. 1,250,000 seeds x 110% = 1,375,000 viable seeds needed per acre.

   3. 1,375,000 seeds divided by 14,250 seeds per pound = 96.5 pounds per acre seeding rate, or 28 seeds per square foot.

Seeds per pound

The number of seeds per pound differs for each variety and can vary considerably between seed lots of the same variety.

If the seeds per pound of a seed lot is not known, the most practical way to obtain this information is to count out 100 seeds two or three times, weigh each sample and calculate the average weight per 100 kernels. Use this number to calculate the number of seeds per pound. The accuracy improves as more seeds are counted.

Pounds of seeds

Table 2 summarizes the pounds of seed needed for seed lots with different weight and for different seeding rates for a range of kernel weights and for different desired stand densities.  It assumes 15 percent stand loss and 95 percent germination.