Yield Response to Soybean Population
Dordt College
2016 Growing Season
Author: Ross Schreur
Introduction
Soybean population is a popular topic when it comes to planting soybeans. Soybean seed is getting more expensive as more traits get added to it, so farmers want to know what is the least amount of soybean seed they can plant and still achieve maximum yield. If there are too many plants per acre, there will not be enough nutrients and water to get to each plant to allow it to reach its full potential. If there are too few plants per acre it can result in not fully utilizing all of the growing spaceand nutrients that are in the field and can result in lower yields. The benefit to planting the right soybean population is having maximum yield while not spending too much on seed costs. Some risks of planting low population soybeans are late canopy cover, weeds, and not utilizing all of the ground, sunlight and nutrients. Some risks to planting high population soybeans are disease, plant competition with each other, and spending too much on seed costs. There is a lot that goes into finding the right soybean population.
Materials and Methods
The two soybean varieties that were used were Pioneer® P18T85R and P27T03R. They were planted no-till on May 5th and 21st. There were three different populations of 100,000, 125,000, and 150,000 seeds per acre planted in 30-inch rows. This study was done at the Dordt College Agricultural Stewardship Center in Sioux County, Iowa. There were three reps of six rows of each population and this was a randomized complete block study. There were no fertilizer applications to the field prior to planting. The post-emerge herbicide application was Warrant Ultra® and that was done twice. The cost of a bag of these soybeans is $74.94 and there are140,000 soybean seeds in one bag and both hybrids cost the same.
Results and Discussions
The results that were collected showed(Table 1) that there was no statistical difference between different populations and yield. The p-value for the test was 0.36, which is not statistically significant. The 100,000 seeds per acre soybeans yielded 76.13 bushels per acre. The 125,000 seeds per acre soybeans yielded 77.78 bushels per acre. The 150,000 seeds per acre soybeans yielded 79.09 bushels per acre.
Table 1 – Average Yield
Population (seeds per acre) / Yield (Bu per acre)100,000 / 76.13
125,000 / 77.78
150,000 / 79.09
The soybeans were sold for around $9 a bushel and the soybean seed costs $74.94 per 140,000 seeds. 25,000 soybean seeds cost $13.49. So it is not cost effective to plant 150,000 seeds per acre.
Acknowledgements
Mike Schouten- Agriculture Stewardship Center Manager