Bigger corn plants bully smaller neighbors in no-till fields

January 25, 2010 Brian Wallheimer

WEST LAFAYETTE, Ind. - It might not look like there's much going on in those roadside corn fields, but a Purdue University researcher has shown that corn plants are in a fierce battle with each other for resources.

Tony Vyn, a professor of agronomy, said it's been known for a long time that young corn plants are, on average, shorter in no-till, corn-on-corn fields, but that doesn't mean there is an overall stunting of growth among all plants. Instead, residue left over from last year's corn crop is changing soil conditions and creating a disadvantage for some plants fighting for sunlight, water and nutrients.

"There is a hierarchy that is formed, even though the plants are genetically the same and should be equal in size and stature," Vyn said about his findings, which were published in the early online version of the journal Soil & Tillage Research. "No-till corn yield reductions have little to do with an overall height reduction early in the season. They have more to do with height variability during vegetative growth."

Vyn said yield losses of up to 14 percent can be attributed to this competition in no-till fields where corn is planted the year after corn. In those fields, the leftover corn residue creates patches of soil with lower temperatures and different water and nutrient content. Seeds planted there are at a disadvantage.

"These conditions created by the field residue can affect root development," he said. "Plants that have better access to resources grow faster and then dominate their smaller neighbors."

Vyn studied plant height data over 14 years and found that there were pronounced height differences among plants by four weeks. It had been thought that a no-till field situation with high residue cover and no soil loosening uniformly reduced the height of all plants because of overall cooler soil temperatures, but Vyn said significant height differences were observed from plant to plant.

The negative consequences of this plant competition are exacerbated as planting density increases.

"For example, competition for nitrogen increases as crowding increases," Vyn said. "The higher the density, the greater the intensity of the competition for all resources."

Weather conditions, such as a lack of rainfall during a critical development period, also can affect the final yield from plants fighting for limited resources.
While some plants dominate and grow to their full potential, the smaller, dominated plants decrease the field's overall yield.

Vyn said growers should ensure during the previous year's harvest that residue cover will be uniform, that fields are drained adequately, that surface soil compaction is avoided and that nutrients are evenly distributed. No-till fields are desirable because they decrease the amount of nutrients running off into nearby water, but Vyn said newer tillage options, such as vertical tillage, are less disruptive than the traditional intensive tillage and could ensure more uniform conditions for seeds.

The next step in the research is to investigate how vertical tillage systems and nutrient banding affect plant height uniformity and yield in corn-on-corn fields and whether hybrids developed for rootworm resistance are as susceptible to plant height variations. 

Pioneer Hi-Bred International and Purdue University funded the research, and Beck's Hybrids provided corn seed.

Writer: Brian Wallheimer, 765-496-2050,

Source: Tony Vyn, 765-496-3757,


Maize Grain Yield Responses to Plant Height Variability Resulting from Crop Rotation and Tillage System in a Long-term Experiment

Christopher R. Boomsma, Judith B. Santini, Terry D. West, Jason C. Brewer, Lauren M. McIntyre and Tony J. Vyn

Research emphasizing slower plant growth and delayed maturity in continuous maize (Zea mays L.), no-till (MM–NT) systems has often led to the conclusion that lower grain yields in this environment are associated with reduced plant heights. Yet prior research has shown that early-season and mature plants are not always shorter in MM–NT systems, suggesting that overall plant height may not be an accurate morphometric indicator of decreased yield in MM–NT environments. Given that plant-to-plant morpho-physiological uniformity is strongly associated with higher yield in maize, we hypothesized that greater plant height variability would provide a better agronomic explanation for yield loss in MM–NT environments than overall plant height reductions. This 14-year study primarily examined the effects of crop rotation {maize–soybean [Glycine max (L.) Merr.] and continuous maize} and tillage system (no-till and moldboard plow) on the yield, 4-week plant population, and 4- and 8-week plant height and plant height variability of a single maize cultivar. Due to sizeable year-to-year variation, actual crop response means for the MM–NT; maize–soybean, no-till (MB–NT); and continuous maize, moldboard plow (MM–PL) treatment combinations were expressed relative to the accompanying means for the maize–soybean, moldboard plow (MB–PL) treatment. In numerous years, the MM–NT system exhibited reduced actual and relative yields and lower 4- and 8-week plant heights compared to the other treatment combinations. Both actual and relative 4- and 8-week plant height variability were rarely greatest for the MM–NT treatment, and in only a few years were actual and/or relative plant density lowest for this system. However, single-factor regression analyses between relative yield and the aforementioned relative agronomic measures revealed that a decline in relative MM–NT yield was most strongly associated with an increase in relative 4-week plant height variability. Multi-factor regression analyses between relative yield, relative 4-week plant height variability, and various weather parameters suggested that this strong inverse relationship was potentially a manifestation of (i) non-uniform germination, emergence, and early seedling growth and (ii) later-season intra-specific competition. Regression analyses between relative 4-week plant height variability and various weather parameters suggested that phenomenon (i) was potentially promoted by cool and moist or warm and dry pre-plant weather conditions while phenomenon (ii) was possibly encouraged by low precipitation and/or high temperatures during rapid stem elongation. While MM–NT systems should be managed to limit plant density reductions and minimize growth and developmental delays, increased focus should be placed on minimizing the occurrence of plant-to-plant variability in these environments.

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