Features Agronomy Corn
Throw away the square metre

Obtaining optimum stand establishment is key in getting the crop off to a healthy,
competitive start. But how do you accurately assess plant stands in the field?
The first thing to do is throw away the quarter-square metre tool for measuring
plant stands.

Determining crop stand density. Source: Westco.

"I don't find a quarter-square metre tool useful and a one-square foot
is even worse," says agronomist Rick Taillieu with Alberta Reduced Tillage
Linkages (RTL) at Camrose. "Even with multiple sampling, if you throw the
quarter-square metre down in the wrong spot, it can skew your numbers badly
one way or the other."

The problem with quarter-square metre sampling, especially with wider row spacings,
is that a quarter-square metre can fall on one side or the other of a seedrow.
Instead, Taillieu recommends counting plant emergence in individual rows and
then converting the results to plants per square foot.

"If you count individual rows, then the assessment of stand establishment
will be much more accurate," explains Taillieu.

How to use seedrow counting for plant populations
When conducting plant counts, cereal crops should be assessed at the two to
three leaf stage. In field peas, once the first node stage is reached, counts
can be done since all the peas should have been placed into moisture and emerged
at the same time. Count canola when one or two leaves have developed, since
these are the plants that will produce most of the yield. Later emerging canola
plants indicate a soil-to-seed contact problem, or moisture problem at seeding.

Taillieu recommends counting plants in several randomly selected rows. First,
always count three feet of plants in the seedrow. He says you need to count
three feet because air-drills do not equally space the plants so you get plants
close together with significant gaps. Shorter measurements bias this further,
especially in low plant counts like peas. A good pea stand is seven plants per
square foot, but it is not uncommon to have a six inch gap in a seedrow. "Counting
three feet is very important," he stresses.

Next, take the three foot count and divide by three to get an average plant
count for one foot of seedrow. Then, divide the one foot count by the row spacing
and then multiply that figure by 12. That will give plants per square foot.

Plants per square foot =
Number of plants in 3ft of row divided by 3
divided by row spacing x 12.

For example, if the average barley count was 42 plants per three feet of seedrow
and the row spacing was nine inches, then the average plant population would
be 18.66 plants per square foot – just on the low range of target plant
stands for barley.

If the field has fairly uniform emergence, then five to six seedrow counts
should be adequate. If the field is patchy, try eight or more counts to assess
plant populations.

The square foot number is most useful in assessing planter performance, since
the row spacing of air-drills is still quoted in inches or feet. The only time
this technique does not work is if the opener system creates a solid or random
seeding pattern, such as a wide-sweep opener that scatters the seed over most
of the seedbed. In this case, a quarter-square metre tool would be required.

An alternative to this technique is the Crop Stand Density chart used by Westco
as part of its AgroManager program. With it, you count the number of plants
in one foot of row length and then cross-reference that number to the seedrow
spacings. Where the numbers intersect on the grid indicates the number of plants
per square foot. As with Taillieu's recommendation, a good idea would be to
count three foot lengths and divide by three to get an average one foot plant
count. The chart also indicates the target plant population zones for peas,
canola and cereals.

A significant difference between anticipated plant population, based on seeding
rates and the actual count, indicates there is a problem with the seeding system.
"The starting point is to assess your plant stands. After that, you can
decide how best to correct any seeding problems," explains Taillieu.

Using one metre or quarter metre squares for counting plant populations can be misleading. Photos Courtesy Of Rick Taillieu, Reduced Tillage Linkages.

Why worry about plant populations?
Stand establishment is directly related to crop health. Studies at Agriculture
and Agri-Food Canada showed that competitive varieties and proper seeding rates
achieved optimum plant populations, increased competition with weeds and enhanced
herbicide efficacy. That also led to better weed suppression and reduced weed
pressure over several years.

The research also showed that seed mortality is generally much higher than
estimated by farmers and extension information. Other surveys done in central
Alberta found that barley stands are often well below 15 plants per square foot
even though plant populations of 22 to 24 plants per square foot is optimum.
So, RTL and the Alberta Applied Research associations took that research out
to the field, where they established five replicated demonstration sites looking
at five barley, 10 canola and six pea seeding trials in 2005. Funding came from
the Alberta canola, pea and barley associations. The goal is to see how more
competitive crops can contribute to improved herbicide efficacy, better economic
returns and greater farming sustainability.

Taillieu says that one year of data will provide some base information on how
seeding rates affect crop health, but that the benefits build up over the years.
"If you look at the Lacombe research, higher seeding rates increased crop
competitiveness and yields. But after four or five years of using the same approach,
you saw even greater effects."

The starting point in increasing plant populations is to get away from seeding
bushels or pounds per acre. Rather, seeding rates should be calculated on the
basis of 1000 kernel weight, germination rate and estimated seedling mortality.
Seed rate calculators, such as the one found on Alberta Agriculture's website,
make the calculations simple. And then once the crop comes up, throw away the
square metre and start counting seed rows.

The Bottom Line
Knowing 1000 kernel weights is critical. Treated hybrid canola seed
is massive in comparison to bin-run seed. Not compensating for big seed could
result in a very thin stand, which is susceptible to much more competition from
weeds. The significance of thin stands partially depends on the herbicide system
being used. Thin stands of Roundup Ready canola can be kept clean fairly cheaply
with multiple herbicide applications, whereas other herbicide systems will be
very expensive to spray more than once. John Waterer,
Winnipeg, Manitoba.

Plant establishment has always been a critical part of high yielding crops.
Seed size, germination, seed vigour, moisture, temperature, soil quality and
weed competition are all factors that play a role in the establishment of a
good plant stand.

Measuring emergence is a good tool for making the decision to stay with what
you have or to reseed. The outcome can vary widely. I have had a thin stand
out-yield a thick stand and vice versa.

The environment is the biggest single factor. Actually measuring plant stand
is more difficult as the field is more uneven. The idea of row counts and averaging
should be helpful to establish an accurate count. Dave
Hegland, Wembley, Alberta.