What’s changed since the 1960s?

The Iowa State University publication “How a Corn Plant Develops” has stood the test of time. First developed in the 1960s, ISU agronomist John Hanway and his colleagues developed a classic known across the country and probably in most corn growing areas around the world. But a lot of things have changed since the 1960s.

Advances in corn management practices and genetics have allowed us to consistently produce higher yields than in the past. Modern hybrids better tolerate stress when planted at higher plant populations than older hybrids, resulting in more biomass and grain per acre. With increased biomass and grain, do modern hybrids require more nutrients and demand them at different times during the growing season?

We investigated biomass and nutrient accumulation in a two-year field study using two popular commercial hybrids from each of five decades: 1960s, 1970s, 1980s, 1990s and the 2000s. Hybrids were planted at seeding rates recommended in the decades in which they were grown.

The idea was to determine how hybrids have changed over time. We collected total aboveground biomass at 10 sampling dates beginning at V6, the sixth leaf stage, through physiological maturity, R6. Total biomass, nitrogen, phosphorus and potassium uptake were determined and analyzed on an area basis and as percent of total uptake for each sampling date and decade.

Grain yields increased nearly 100 bushels per acre from hybrids grown in the 1960s to those produced today (see table). Total biomass, nitrogen, phosphorus and potassium uptake were greater in the modern hybrids as well. However, when comparing hybrids from the different eras on percentage of total uptake at any given sampling date, biomass, nitrogen, phosphorous and potassium only varied on a few scattered sample dates from which we could determine no pattern.

When averaged across all eras at silking, R1, 45% of total biomass was present. At the same growth stage, nitrogen, phosphorus and potassium uptake was 72%, 58% and 97%, respectively. Potassium uptake was the most rapid of all nutrients, whereas phosphorus uptake was the slowest. However, percent biomass accumulation and nutrient uptake were similar across hybrids from all decades.

What are the implications?

At typical plant populations for each decade, the more modern the hybrid, the greater the biomass, nitrogen, phosphorus and potassium accumulated on an area basis. Modern hybrids require more nutrients.

However, when considering the percent uptake at any given growth stage, biomass and nutrient uptake patterns of modern hybrids didn’t differ greatly. So, to answer our main question, modern hybrids require more nutrients than older hybrids, but the timing of nutrient demands during the growing season are similar among both old and modern hybrids.

In addition to an increase in biomass and nutrient uptake in more recent hybrids, when looking at all 10 hybrids across the five decades, grain yield increased 2.2 bushels per acre per year. That’s very similar to the actual increase in Iowa grain yield from 1960 to 2010.

The fact that biomass and nutrient accumulation on a percent basis was similar with old and modern hybrids tells us that the accumulation curves in the classic publication “How a Corn Plant Develops” are still representative for today’s hybrids.

Nevertheless, findings from the modern hybrids in this research are now incorporated into the biomass and nutrient accumulation figures found in “Corn Growth and Development,” ISU Extension Publication PMR 1009.

Elmore is the ISU Extension corn agronomist. Boyer was a graduate assistant.

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This article published in the March, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.