Want to increase corn yield potential? Aim for increasing kernel numbers! Yield is a function of kernel number and kernel weight. The number of kernels per acre will vary based on other components including plants per acre, ears per plant, and kernels per ear. We discussed the proper seeding rates in an April 10 Integrated Crop Management article, What is the best seeding rate for corn based on seed prices and yield level?. The number of ears per plant is primarily influenced by hybrid. Most hybrids grown in Iowa have one dominant ear, although some "prolific" hybrids are available that produce more than one ear per plant at normal seeding rates.

The number of kernels per ear is a function of ear length (kernels per row) and kernel rows per ear. Each of these begins development sometime between V6 and V8 as the ear shoots are formed. Let's talk for a bit about both of these components of kernels per ear.

Kernels per row

The maximum number of ovules (potential kernels) per row is set a week or so before silks emerge. Some researchers estimate there are up to 1,000 potential ovules per ear. An ovule develops into a kernel when its silk receives pollen, is fertilized, and then develops without aborting. Ear length is based on a hybrid's genetics but can be significantly altered based on stresses. Potential kernels per row are highly dependent on growing conditions prior to silking while actual kernels per ear are determined by conditions during and after silking.

A 16-row ear (left) and a 14-row ear (right). Number of rows per ear is influenced mainly by a hybrid’s genetics and some by growing season stresses. (Roger Elmore)

Rows per ear

The number of rows on an ear will usually be even, assuming a normal environment. The number is even because of a split of the first kernel initials, thus forming two rows from one. A hybrid's genetics is instrumental in determining the potential number of rows per ear; environmental factors have a lesser influence. Yet, the amount of water received as well as varying plant populations will affect the number of kernels per row.

Research investigating the influence of nitrogen timing shows how early-season stresses can also influence ear development (see figure). A deficiency in nitrogen before V8 clearly caused an irreversible decrease in ear diameter and ear length as well as kernels per ear. By looking at treatment N1, we can see that if nitrogen is not applied until after V8, there is a significant yield reduction. Nitrogen was supplied the rest of the season, but this did not help increase yield because the ear parameters were set earlier.

Many stresses can affect row number and kernels per row. Thus, kernels per ear are affected by stresses beginning at V6 and ending prior to silk emergence. These include:

• Nutrient deficiencies (especially N, see figure)
• Drought
• Insects (e.g., corn rootworm feeding or insect defoliation)
• Hail or frost
• Root pruning by cultivation

Controlling or limiting these stresses when possible during vegetative stages will help maintain yield potential.

(2.54 cm = 1 inch) Effect of different nitrogen treatments on ear diameter, ear length, and number of kernels per ear (averaged over three hybrids). Nitrogen treatments are as follows: N1 (N supplied from V8 to maturity); N2 (N supplied from emergence to V8); N3 (N supplied from emergence to silking); N4 (N supplied from emergence to 3 weeks after silking); and N5 (N supplied from emergence to maturity). If columns have the same letter within each parameter, they are not significantly different from one another (at P = 0.05). Source: Subedi, K.D., and B.L. Ma. 2005. Crop Sci. 45:740–747.