Corn Stand Uniformity in Wisconsin

Mike Rankin
Crops and Soils Agent - Fond du Lac County
University of Wisconsin - Extension

Introduction

         As you drive down the road in early summer, most corn fields appear uniform. However, a closer examination often reveals a wide variation in how evenly plants are spaced within the row.  When planters are not operated or functioning properly, a high number of doubles or gaps may occur.  Some researchers have suggested using standard deviation (SD) as a measure of in-row corn stand uniformity (Nielson, 1991).  At Purdue University, Nielson (1991) has suggested that corn grain yield declines about 2.5 bu/acre for each 1 inch increase in standard deviation above a value of 2 inches.  Conversely, many researchers have seen very little impact of corn spacing SD on final grain yield (Butzen, 1998).  Nafziger (1996) has suggested that SD alone is not a good means of predicting yield responses to stand variability because of the differing and interactive effects of row skips, doubles, and plant density.

         Few studies have been done in the upper Midwest to quantify in-row stand uniformity of production corn fields and measure its effect on grain yield.  To investigate this question, a research project was initiated in 1998.

Methods

Stand uniformity in production fields
        County UW-Extension faculty were asked to select fields for stand uniformity evaluations.  Forty-two fields were evaluated in 1998 and 45 fields were evaluated in 1999.  The 87 total fields represented at least one field from 16 different Wisconsin counties.  Plant to plant spacing was measured between 30 consecutive corn plants for each row unit of the planter at two different locations of each field evaluated.  Fields and areas of fields were selected that had good emergence so that factors other than planter performance (e.g. diseases, insects, and environmental conditions) would not confound final results. Stand uniformity was characterized by determining SD, plant density, average plant spacing, row gaps per 50 ft., and seed doubles per 50 ft. using a Microsoft Excel^® spreadsheet program. Plant doubles were defined as any plants within 2 inches of each other and gaps for 30, 36 or 38-inch row spacings were defined as spaces of 12 inches or more without an emerged plant.  For 20-inch row spacings, gaps were defined as 18 inches or more without a plant.  Data was summarized for both individual fields and in total.  Each cooperating corn grower was given a summary sheet with data derived from their individual field (see Attachment 1).

Interactions of planting speed, stand uniformity, and grain yield
        In 1998, corn was planted at 4, 6, and 8 MPH on two Fond du Lac County farms (Lamartine and Eden locations) in an effort to force differences in stand uniformity.  Similar field plots were established in 1999 on two Fond du Lac County farms (Byron and Malone locations) and at the Arlington Agricultural Research Station in Columbia County.  Field plots were established using a randomized complete block design with three or four replications. After corn emergence, the distance between 30 consecutive plants was measured for each row of every plot.  Stand uniformity was characterized by determining SD, plant density, average plant spacing, row gaps per 50 ft., and seed doubles per 50 ft. using a Microsoft Excel^® spreadsheet program.  Grain yields were measured in the fall.  Statistical analysis was done using AgStats2 (Karow, 1990).  At four other locations (Malone, Two Rivers, Mason, and Saxon) in 1998 and three other locations (Brownsville, Gillett, and Saxon) in 1999, the same treatments were imposed and data was collected with the exception of grain yield.  Planting information for all plot locations is presented in Table 1.

Table 1.  Planter and field information for 1998 and 1999 corn stand uniformity trials

Location

Year

Planter Make/model

Seed Delivery System

Row number/
width

Planting Date

Planting Rate

(#/in.)

(seeds/acre)

Lamartine

1998

IH Cyclo 800

air

6/30

6 May

32,000

Eden

1998

JD 7000

finger

6/30

21 May

35,600

Malone

1998

JD 7200

finger

6/30

11 May

30,900

Two Rivers

1998

JD 7200

air-vac

6/30

14 May

28,500

Mason

1998

JD 1770

air-vac

12/30

15 May

30,000

Saxon

1998

White 5400

air

4/30

16 May

26,000

Malone

1999

JD 7200

finger

6/30

11 May

30,200

Byron

1999

Kinze 2000

finger

6/30

4 May

31,000

Brownsville

1999

JD 7200

finger

6/30

2 May

29,600

Gillett

1999

JD 7000

finger

6/30

13 May

27,000

Saxon

1999

White 5400

air

4/30

28 May

26,000

Arlington

1999

Kinze

finger

4/30

10 May

30,000

Standard Deviation Primer

         SD is a mathematical measure of variability within a group of measurements.  For example, a “perfect” corn stand with every plant exactly the same distance away from the next plant would have a SD of 0 inches.  This of course never happens even with the best of planter maintenance programs and operation.  The more variability that exists among plant-to-plant measurements, the higher the SD value.  Effectively, SD describes how close all measurements cluster around the sample average.  Nielson (1991) suggested that a SD of 2 inches is about the best a producer can obtain in actual production fields because of planter performance limitations and the fact that a small percentage of seed will not germinate.

A Survey of Stand Uniformity in Wisconsin Corn Fields

         Eighty-seven Wisconsin corn fields have been evaluated for in-row stand variation during the 1998 and 1999 growing seasons.  It is again important to emphasize that fields with good to excellent emergence were targeted in an effort to measure corn planter performance rather than other variables inhibiting germination and emergence.  Success in accomplishing this goal is indicated by the fact that actual stands averaged 97.1% of farmer-reported planting rates.  Corn planter characteristics and planting rates for these fields are presented in Table 2.  

Planting speed, stand uniformity, and grain yield

         We’ve determined that a large range of in-row plant-to-plant stand variability exists in Wisconsin corn fields.  The next logical question is:  “Does this variability impact corn grain yield?”  Planting speed was used as a mechanism to force differences in stand variability and measure the effects on grain yield with field scale equipment.  Nielson (1995), in a series of on-farm strip trials conducted in Indiana, showed that planting speed can have negative effects on stand uniformity.

         At the 5 locations where yield measurements were taken, yields tended to decline as planting speed increased (Figure 3).  When averaged across all locations, a significant yield loss from 183 bu/acre at the 4 MPH planting speed to 176 bu/acre at the 8 MPH speed occurred (Figure 4).  Along with this decline in grain yield, there was a significant increase in SD from 3.3 inches at 4 MPH to 4.2 inches at 8 MPH (Figure 4).

        Because these fields had good initial emergence, and changes in plant population were not large enough to explain the yield reductions (Table 4), it can be assumed that yield declines were primarily attributed to differences in plant-to-plant spacing.  A fair question to ask is why did we see a larger response in yield decline relative to increased SD (about 4% for a 1-inch increase in SD) than has been documented in other Midwestern states?  Perhaps it is simply a function of the type of growing seasons we had.  Both 1998 and 1999 were exceptional years in Wisconsin for growing corn.  Another possible reason is that we may see more response to uniform stands in the northern states where growing seasons are shorter.  Certainly it appears this is the case with narrowing corn row spacing to attain more equidistant plant spacing (Lauer, 1996).  Small plot, replicated research is currently being conducted at the University of Wisconsin to evaluate a wider range of stand variability with different frequencies of doubles and row gaps.  Until more data is collected, we will reserve further judgment other than it appears growers would be well served to strive for uniform stands.

A closer look at planting speed and stand variables

        Stand uniformity data was collected on a total of 12 planting speed trials during the 1998-99 growing seasons.  Of these, 7 were finger-type planters and 5 were air planters (either positive or negative pressure).  Stand uniformity data for the 12 sites is presented in Table 4.  Although there were differences in results depending on location and year, some trends are apparent.  It is important to note here that it is the trends that are important rather than the performance of a specific planter make, model, or type of seed delivery system.  These trials were done over a range of different field conditions, target plant densities, and planter maintenance schedules.