How Many Seeds per Acre?
NDSU Extension Service/Burke County
January 21, 2013
How many seeds per acre?
Do you know how many seeds you are planting per acre? With the many different crops producers are growing today and an increasingly wide variation in seed sizes between varieties and even within varieties producers need to be thinking about plant populations not just bushels of seed per acre.
Much of the research done with hard red spring wheat from 1950 through the 1970’s indicated that seeding rates near 1 million live seeds per acre would maximize yield potential under good growing conditions while the driest areas of the state maximized yields at lower populations. Changes and improvements in varieties with higher yield potentials continually change those optimums. Research done at several locations in the early 90’s with Grandin HRSW found that yield was optimized at about 34 plants per square foot (1.48 million plants per acre) but with very little difference from 26 plants per square foot to 41 plants per square foot.
Based on that research a producer would shoot for a minimum of 26 plants per square foot or 1.2 million plants per acre. Should that be your seeding rate? No, you still have to factor in emergence percentage which generally decreases as seeding rates go up and you also need to know your germination percentage and the number of seeds per pound.
The same research with Grandin HRSW found a 95% emergence based on pure live seed (PLS) planted at only .5 million PLS per acre but only 85% emergence when planted at 1.5 million PLS per acre.
Pure Live Seed is your total number of seeds times the germination percentage.
Now let’s look at seeds per pound, There are big differences in varieties but there can be big differences within the same variety from various seed lots grown in different conditions. You can count and weigh seeds yourself or you can get a seed count test from the State seed Department when submitting samples for purity tests. Hard red spring wheat varieties have been known to exceed 18,000 seeds per pound but are often 14,000 or even less.
Let’s compare seeding rates for a lot of Norpro at 14,099 seeds per pound and 90% germination with a seed lot of Keene at 18,160 seeds per pound and 95% germination. For this example let’s assume we will have an 85% emergence rate for both varieties. That means 1.5 million pure live seeds will give us about 1.27 million plants per acre or slightly more than the 1.2 million minimum I suggested above.
Norpro: 14,099 seeds per pound x .9 (90% germination) = 12690 pure live seeds per pound.
1,500,000 divided by 12690 = 118 pounds of seed needed per acre or nearly two bushels.
Keene: 18,160 seeds per pound x .95 (95% germination) = 17,252 pure live seeds per pound.
1,500,000 divided by 17,252 = 87 pounds of seed needed per acre or just under 1 ½ bushels.
You can see that there can be a big difference in the pounds of seed needed based on these two different seed lots. And remember that the example provided you with only slightly higher than the minimum stand based on early 90’s research. Based on increasing stand requirements for optimum yields on research from the 1950’s through the 1990’s it is probable that today’s varieties may need higher plant populations for those maximum yields. The 85% emergence factor which I used came from research with good planting conditions. It is reasonable to assume that excessive moisture, drought or other conditions may reduce emergence even further and require a higher seeding rate to achieve the desired plant population.