Planting Considerations and Population Assessment

Achieving consistently high yields in corn and soybean production requires uniform crop emergence and plant spacing.
Planting Considerations and Population Assessment - Articles

Updated: August 8, 2017

Planting Considerations and Population Assessment

This is a great time to review key goals in stand assessment. With planting season upon us it is best to have some idea of the goals this spring. If weather remains cool at night chilling injury to seed corn is at risk and we already have reports of slugs and other pests so keep an eye on any early planted fields. Here are some things to think about with stands and making stand decisions. The 2 inch soil map still indicates below average soil temperatures in the 40 degree range. Check your location at the PA PIPE website. This useful site assists in plant timing.

Key points to consider when planting corn and soybeans

Soybean population drop from a planter or drill should be in the 150,000 ppa to achieve a final stand of 120,000ppa at harvest and corn is 28-34,000 ppa or higher depending on hybrid. This represents final stands that are even and uniform indicating same day germination and subsequent emergence. Now that we have an idea of the goal one can ensure that the planting operation achieves the goal. Compensations for seed drop will need to include primarily germination differences and planting conditions. Planter, tillage, pests, weather; take control of the items you can control. With No Till I commonly add 20% to the seed drop from the goal. For instance if desire 30,000 final stand one would drop 36,000 to achieve the desired goal. On seed depth I do not like to see soybeans planted too deep 1.25 inch is ideal (unless specified on herbicide label) and with corn I do not like to see more than 1.5 inch in depth and that is the depth of soil over top of the seed, just setting the planter is not enough inspection of the seed trench to determine depth is preferred.

Once you begin to see germination one will need to determine the population in the field. To determine populations you must first know the width of planting. 6", 7", 8" for small grains 7", 15" or 30" for beans and 15" or 30" for corn.

  1. Now to determine population you simply convert the row width from inches to feet by dividing by 12."
  2. Then divide the square feet per acre(43560) by the foot of row. This gives you linear feet
  3. Then, take the number of plants you find per foot in the field and multiply by that number to get the ppa.
  4. Let's take corn for an example. Thirty-inch rows divided by 12 is 2.5 feet. 43560 square feet in an acre divided by 2.5 gives us 17424 linear feet. Now if you get 1 plant in a foot you have 17,424 plants per acre. If you get 2 then you have 34,848. To simplify this you could now take 17424 and divide by 1000 to get the number of feet you need to represent 1/1000th of an acre. In this case it would be 17.4 feet. So you could go to the field measure 17.4 feet count the plants multiply by 1000 and you will have your plants per acre. Do this in several places and you could find the average of the field.

Assess the plant evenness in the field. In fact Penn State research suggests that within row unevenness robs 12% of yield while between rows only rob 5% according to his research. At this time one can also assess the stand deviation. For each inch of deviation University research suggests a 2.5-5 bu/inch loss. This is more critical as populations are increased. Most No Till Corn Club participants that shoot for over 300 bu/acre of corn record stand deviations of below 2. A survey of Pa growers by county agents showed an average deviation of 4 so there is some room for improvement.

Know the key planting times and relation to yield. This will come into play as stands are deemed inadequate and a replant is in question. We know that planting April 25th for corn is 100%, the 19th of May is 90% and the 29th of May is 80% a full 20 % loss just by delaying the planting date by three weeks. Knowing this allows us to say, "well if I want to replant today May 29th I will lose 20% of my yield and if I don't replant I will only lose 12% so it probably will not pay."

What will the loss in population do to pests? Weeds will invade anywhere light is allowed through to the soil. For this reason weeds can over run poor stands and this is one critical issue when considering replants.

Review any pesticides applied and re-crop restrictions.

Check with dealer to determine policy for replant support. For more information see the Agronomy Guidefor details.


Agriculture/Agronomy Plant Science

More by Del G. Voight, M.S