Yield Response of Corn Products to Seeding Rate - Marble Rock, IA

Trial Objective

  • Several years of research have indicated that corn yield has a positive correlation with plant population until a threshold was reached, beyond which, yield decreases. Defining this threshold for each corn product is difficult as it is highly influenced by several factors including management practices and the environmental conditions during the growing season.
  • Knowing the threshold is critical as it forms the basis upon which other management practices, such as nitrogen rate, are based.
  • The objective of this study was to determine the yield response of corn products at different seeding rates to find the optimum seeding rate.

Research Site Details

  • Eight corn products were planted at 32,500 (32.5K), 35,000 (35K), 37,500 (37.5K), and 40,000 (40K) seeds/acre.
  • The trial was carried out in 30-inch row spacing, with four rows in 150-ft-long plots with two replications.
  • Fertilizer application consisted of nitrogen and potassium with the strip tillage operation followed by 70 lb nitrogen side-dressed using 32% UAN.
  • Weed management consisted of a pre- and post-emergence program.
  • Delaro® 325 SC fungicide was applied at VT.

Understanding the Results





  • Corn product response to seeding rate varied. The optimum yield for most products was realized at either 35K or 37.5K seeds/acre, such as in K4R-9706 and K0708SS brand blends. In K4R-9900 brand blend, yield decreased with increasing seeding rate whereas there was no clear trend in K4R-9608 brand blend (Figure 1).
  • In all products except K4R-9608 brand blend, the seeding rate of 40K seeds/acre produced the lowest grain yields (Figure 1).
  • The average grain yield across all products indicated similar performance between the 35K and 37.5K seeds/acre seeding rates (Figure 2).

What Does This Mean for Your Farm?

  • We consider a 3 bu/acre response in a 2.5K seeds/acre increment to be economical. Thus, the seeding rate of 35K seeds/acre was economical in 50% of the products, with 32.5K and 37.5K seeds/acre each being economical in 25% of the products (Figure 1). The most economical seeding rate, with more than a 14 bu/acre yield advantage, was 35K seeds/acre (Figure 2).
  • Marble Rock had a tough growing season with a tremendous amount of rainfall. Such growing conditions affect nutrient levels and do not favor high populations. This may be part of the reason for the poor performance of the 40K seeds/acre seeding rate across the products. However, this doesn’t represent every year or what we should expect for a response next season.