Is a population change warranted in irrigated corn?

decrease font size  Resize text   increase font size       Printer-friendly version of this article Printer-friendly version of this article

Following the 2012 drought, many Nebraska growers are faced with water allocations and looking for ways to reduce evaporation and transpiration (ET) or are wanting to ensure more efficient irrigation applications.

This year many growers have asked whether they should reduce irrigated plant populations to reduce ET. Let’s take a look at the dynamics of this suggestion.

click image to zoom First we must consider Leaf Area Index (LAI). The LAI defines the amount of leaf surface area available to transpire water. The leaf area index is the ratio of leaf surface area (one side) to land surface area. For example, if there is an average of 15 square feet of leaf surface for each 5 square feet of land surface, then the LAI would be 3.0.

When this value is greater than 2.7, the crop’s evapotranspiration is determined only by atmospheric demand and is not limited by leaf area, provided that the plant is not under water stress. For irrigated plant populations for corn, a LAI value of 2.7 is reached when the crop has about 14 fully emerged leaves or is five to six feet tall. For many irrigated corn hybrids the LAI approaches 6.0 during the growing season.

Figure 1 shows a typical leaf area index curve as it changes throughout the growing season for irrigated corn in various populations. Before the crop reaches the peak LAI value in the figure, it crosses the full ET threshold of 2.7. From that point on, leaf area becomes a non-limiting factor for crop water use.

The figure also illustrates the effect of plant population on leaf area index over the growing season. The curves represent four populations of corn planted on the same date and with the same hybrid. Once the “high” and “medium” populations cross the full ET threshold (LAI = 2.7), the rate of water use is essentially the same for both populations. Leaf area index is not the limiting factor in water use in either case; however, the high population crosses the threshold level sooner than the medium population. After the high population has passed a leaf area index of 2.7 and before the medium population reaches it, transpiration by the high population would be greater for a few days. While this is happening, soil evaporation would typically be greater for the low plant population so overall ET is about the same.

To get any significant reduction in water use under irrigation, populations of modern, upright leaf corn varieties (115-120 day maturity) would have to drop below about 18,000 plants per acre. Substantial water conservation would come only when populations are in the range of 8,000-10,000 plants per acre. For shorter season hybrids (with fewer leaves), populations can be 10-20 percent greater and conserve water, but the principle is the same.

The bottom line is that there may be good reasons to reduce plant populations on some soils or in certain areas of an irrigated field; however, water conservation is probably not one of them.


Buyers Guide

Doyle Equipment Manufacturing Co.
Doyle Equipment Manufacturing prides themselves as being “The King of the Rotary’s” with their Direct Drive Rotary Blend Systems. With numerous setup possibilities and sizes, ranging from a  more...
A.J. Sackett Sons & Company
Sackett Blend Towers feature the H.I.M, High Intensity Mixer, the next generation of blending and coating technology which supports Precision Fertilizer Blending®. Its unique design allows  more...
R&R Manufacturing Inc.
The R&R Minuteman Blend System is the original proven performer. Fast, precise blending with a compact foot print. Significantly lower horsepower requirement. Low inload height with large  more...
Junge Control Inc.
Junge Control Inc. creates state-of-the-art product blending and measuring solutions that allow you to totally maximize operating efficiency with amazing accuracy and repeatability, superior  more...
Yargus Manufacturing
The flagship blending system for the Layco product line is the fully automated Layco DW System™. The advanced technology of the Layco DW (Declining Weight) system results in a blending  more...
Yargus Manufacturing
The LAYCOTE™ Automated Coating System provides a new level of coating accuracy for a stand-alone coating system or for coating (impregnating) in an automated blending system. The unique  more...
John Deere
The DN345 Drawn Dry Spreader can carry more than 12 tons of fertilizer and 17.5 tons of lime. Designed to operate at field speeds up to 20 MPH with full loads and the G4 spreader uniformly  more...
Force Unlimited
The Pro-Force is a multi-purpose spreader with a wider apron and steeper sides. Our Pro-Force has the most aggressive 30” spinner on the market, and is capable of spreading higher rates of  more...
BBI Spreaders
MagnaSpread 2 & MagnaSpread 3 — With BBI’s patented multi-bin technology, these spreaders operate multiple hoppers guided by independent, variable-rate technology. These models are built on  more...


Comments (1) Leave a comment 

Name
e-Mail (required)
Location

Comment:

characters left

ryan    
nw ks  |  March, 21, 2013 at 08:57 AM

If have less than 2.5 gallons per acre and have population of 30,000 crop burns up if have population of 18 to 22,000 have a harvestable crop. LAI does not work in the real world the way they indicate. Also, does not take into account ear flex, drought tolerance, or root strength of each hybrid. Have not even covered no-till and full tillage methods. LAI is only a small component of a large complex system.


Portable Conveyors

Convey-all portable conveyors are designed to handle your crops gently and efficiently. We offer an extensive line of high capacity ... Read More

View all Products in this segment

View All Buyers Guides

Feedback Form
Feedback Form