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Corn planting dates, plant populations interact in final yield levels

With corn acres expected to be at record are near-record highs in the Southeast this spring, many growers are fine-tuning their production practices — tweaking things such as plant populations and planting dates — to guarantee the greatest return on their investment.

A study conducted by Auburn University researchers in 2011 and 2012 at the Gulf Coast Research Center in Fairhope, Ala., evaluated the impact of plant population on yield, and the impact of the interaction between plant populations and planting dates on corn yields in non-irrigated conditions.

It’s well known that plant population can positively or negatively affect corn yield, but yield potential also can be influenced by planting date, which is strongly linked to the at-planting and in-season weather and climatic conditions.

“When considering management changes, farmers need to keep in mind that the optimum plant population will not only vary between regions of the state, but from season to season, and from field to field on the same farm,” according to the research report.

Currently, there is a big push to increase plant population in order to increase production, states the report. However, this change is typically recommended under non‐limiting conditions, such as those with an ample water supply and adequate fertilization.

Corn genetics have evolved to the point to where farmers can delay planting to take advantage of favorable environmental conditions, while maintaining a good insect protection and water-use package.

Researchers say that a combination of the currently available corn hybrids along with a growing knowledge of climate variabilities within regions allow them to investigate how plant populations and/or planting dates should be modified in order to increase production and profitability and reduce potential production risks.

The Fairhope, Ala., research — conducted on Malbis fine sandy loam soils — consisted of four different plant populations of 18,000, 22,000, 26,000, and 30,000 seeds per acre planted at two different times during the growing season: mid‐March (standard date by farmers in the area) and three weeks later.

The corn hybrid planted was Pioneer 31P42 with a relative maturity of 119 days. Experimental plots were four rows wide by 30 feet long with 38-inch row spacing. Plots were fertilized with 150 pounds of urea ammonium nitrate. Yield data was recorded after harvesting the middle two rows of each plot.

Regardless of the plant population and planting dates chosen for the study, corn yield in the 2011 season was lower than in the 2012 season. The year‐to‐year yield changes could be associated with differences in the climatic conditions.

When comparing 2011 and 2012 monthly precipitation and maximum temperature deviations with respect to historic values (1970‐2000), the main differences were observed from May to July which corresponds to the months of flowering and grain filling.

Time of rainfall

Even though precipitation was lower than normal early in the season for both years, the low yields in 2011 could be a consequence, not only of the low precipitation during the flowering period, but also the permanent precipitation deficit and the elevated temperatures throughout the season.

During the 2012 growing season, above-normal precipitation values were observed during the months of May and June, and maximum temperature was below normal for the months of June and July. These specific climatic conditions could favor pollination and grain filling.

According to the research, plant population has a strong effect on final yield, but the interaction between populations and the environment defines final yield.

As plant population increases, competition between plants for resources (light, water, and nutrients) increases.

The 2011 and 2012 growing seasons are good examples of the plant response to the environment, states the report.

During the 2011 growing season, a negative yield trend towards high population was observed with yield decreasing as plant populations increased, and that was independent of the planting date.

The precipitation deficit and the high temperatures observed in the 2011 season strongly affected the high plant population treatments (26,000 and 30,000) compared to the low population treatments (18,000 and 22,000).

Under the 2011 environmental conditions, the best corn production choice was the 22,000 plant population.

In 2011, changes in planting date had an overall impact on yield, but did not influence the yield response to plant population.

Corn planted on the April 12 (three and a half weeks later than the standard planting date) performed better than the standard planting date (March 17) which might be due to the rainfall and temperature observed during flowering.

Corn planted on March 17 received less precipitation during the period of flowering than the crop planted on the April 12.

There was also a sharp increase in maximum temperature after flowering of plants corresponding to the first planting date (March 17) compared to the second planting date which may have affected pollination and grain filling.

The increase in precipitation around mid‐July certainly favored ear development of the plants from the second planting date (April 12) which were harvested at the end of August, compared to the first planting date harvested in the first week of August.

In 2012, yield increased as plant populations increased, but reached a maximum at 26,000 seeds for both planting dates. The positive yield response to increases in planting density could be due to water availability from precipitation during the months of May, June and July.

Although there were yield differences between planting dates for all plant population treatments, the greatest difference was observed for the 26,000 plant population treatment.

Reasons for lower yield

The lack of precipitation and the increase in maximum temperature during the last two weeks of May (flowering period) and the last two weeks of June (grain filling) for the first planting date (March 20) could explain the lower yield associated with the 26,000 plant population treatment compared with the second planting date (April 13).

Determining the economically optimum plant population and planting date combination is influenced by five pieces of information: yield, price of corn, price of seed, variable costs associated with corn production, and climate forecast, according to the report.

Each farming operation is different and producers should use their actual costs of production to make management decisions such as planting date and plant population.

If the corn price increased ($6 or $ 7.75), revenue from corn production covered direct expenses for the delayed planting and lower plant populations (18,000 or 22,000) treatments.

Data from 2011 show that if a dry season is expected, a plant population of 22,000 seeds per acre is the best economical choice for the conditions in Fairhope, Ala., and the estimated cost of production.

In 2012, higher plant populations increased returns over direct expenses independent of the price of corn. The later planting date resulted in higher returns over direct expenses. Higher returns over direct expenses were realized when corn was planted on about April 13, compared with corn planted on March 20.

Based on the conditions in Fairhope in 2012, and the estimated costs of production, a seeding rate of 26,000 seeds per acre planted on about April 13, provided the highest returns over direct expense, regardless of price.

Aside from returns over direct expenses, there are other factors to consider prior to making decisions on planting date.

When the planting of one crop is delayed, it may negatively impact the ability to plant additional crops due to available labor and machinery hours.

Furthermore, delaying planting may negatively impact harvesting of other crops and planting of winter commodity crops or cover crops.

The report recommends that decisions regarding the management of planting dates should be made considering the needs of the entire operation, not just one crop.

“There are financial tradeoffs to all production decisions when considering all crops grown on the operation and the role they each play in the profitability of the operation.”

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Lastly, land rent is not considered in the direct expenses due to the variability across operations. This cost should be considered a direct expense and considered as part of the decision-making process.

The overall results from this two-year experiment show that the yield potential of corn grown under multiple plant populations and seeded at two different dates can vary depending on the weather and climate conditions.

Yield and profitability data shows that, under dry conditions, the use of low plant populations, especially 22,000 seeds per acre, may be a good option if planted about the second week of April.

In comparison, if normal precipitation is expected, an increase in plant population will result in higher returns over direct expenses.

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Gardens: Starting seeds

Photo by Katie Jackson

Now’s the time to start seeding for the season

By Katie Jackson

April heralds the start of the “serious” gardening season, which means it’s time to get serious about planting those late spring and summer annuals (and some perennials) that will grace our tables with food and flowers.

But should we be planting seeds or seedlings? The answer is some of both, but starting from seed offers a number of advantages.

Seedling transplants, also called “starts,” are in abundant supply at local garden centers these days and are often the easiest, most sure-fired way to get many plants, both edible and ornamental, to succeed. However, if you want to grow less mainstream varieties, such as heirloom plants, or want to save a little money, planting from seed is a great option. The key to seed success is getting those seeds started off right.

By now, soil and air temperatures are warm enough to plant many vegetables and flowers directly in the garden, a practice called direct seeding, which is often ideal for large-seeded plants such as squash, peas and melons as well as such flowers as sunflowers and marigolds. Certainly, even small-seeded plants like tomatoes, peppers and a number of other herbs and flowers can be sown directly into well-prepared beds. But giving many plants a leg up by starting them in containers often helps.

Start with the correct growing container

Start your own seedling nursery by choosing some appropriate growing containers such as peat pots or reusable seed-starting trays or even repurposed items like paper cups, slated wooden boxes, small pots or yogurt, milk and egg cartons. Any container that is at least a couple of inches deep and has drainage holes in the bottom will do, though repurposed containers should be thoroughly washed and disinfected in a diluted bleach solution (nine parts water to one part bleach) before they are used.

Aside from the seeds, the most important ingredient for seed-starting success is a high-quality growing media. Do not use yard or garden soil as it may contain pathogens or pests that can harm sprouting plants. Instead, use a sterile media such as prepackaged seed-starting mixes or a homemade media of equal parts peat moss, vermiculite and perlite.

The most important ingredient for successful seeding is high-quality growing media. Photos by Katie Jackson

If you want to save a little money, planting from seed is a great option

Fill each container at least three-fourths full with the growing media (it often helps to wet the media before you put it in the containers, though make sure it is moist, not soggy). Press it in firmly into the containers to eliminate any air pockets then follow the recommended planting instructions found on each seed packet. Typically larger seeds are buried about two times deeper than their width while smaller seeds are sprinkled on top of the growing media then lightly covered with another thin layer of media.

Place the seed containers in a sunny spot (this time of year that can be indoors or out) that has good air circulation but is protected from harsh winds or hard rains. Water the containers lightly about once a week or when the top of the growing media is dry to the touch, but be careful not to overwater — soggy growing media can promote diseases or rot the seed. Once the seedlings emerge, apply a small dose of balanced liquid fertilizer to give them a little extra boost as they grow.

Most seedlings are ready to transplant when they have produced two to three “true” leaves (the first leaves that emerge are cotyledons or “seed leaves”; the second set and all thereafter are “true” leaves). Try to plant the seedlings in the garden late in the afternoon on a calm, overcast or cloudy day so they won’t be stressed by sun, heat or wind as they acclimate to their new surroundings.

If you direct-seed into the garden, make sure your beds are fully prepared and pre-moisten the soil before planting or water gently just after planting, then keep the soil moist (again, not too wet) until the new plants emerge. Applying a thin layer of mulch will help retain moisture around the seeds, though once seedlings begin to pop their heads up, make sure the mulch does not hinder their growth.

Whichever method you use, you may have to thin the new plants once they come up so they won’t be overcrowded, but you can move the extra seedlings to pots or to other spots in the garden if you can’t bring yourself to toss them out. And once those little darlings are up and thriving, you can take great pleasure in seeing your hand-raised garden grow.

April Tips

  •  Plant peas, Irish potatoes, strawberries, blueberries, raspberries and blackberries.
  •  Sow seeds for beans, corn, squash, melons and other summer vegetable crops.
  •  Begin planting tomatoes, peppers and eggplants once the threat of a hard freeze is past.
  •  Weed garden beds.
  •  Fertilize warm-season lawns and plant new lawns.
  •  Plant summer annual flowers and summer-blooming bulbs.
  •  Prune spring-flowering shrubs such as spirea, flowering quince, azalea, jasmine and forsythia after they have bloomed.
  •  Clean dust from the leaves of indoor plants.
  •  Plant container-grown roses and keep an eye out for insect and disease problems on all roses.
  •  Start a new compost pile and turn the contents of existing ones.

Katie Jackson is a freelance writer and editor based in Opelika, Alabama. Contact her at [email protected]

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