Rooting Down to Find Nitrogen: Corn Root Architecture and Nitrogen Placement Effects on Nitrogen Use Efficiency

By Bob Gunzenhauser, Director of Agronomy

The primary means for corn to access nitrogen is through its rooting system.  Nitrogen can be taken up into the roots through either mass flow, where water moving to the roots is carrying nutrients (like nitrate-nitrogen) with them, or through root interception, where the growing roots absorb nutrients as they come in contact (like ammonium-nitrogen). 

Rooting depth and architecture can be affected both by environmental conditions and genetics.  Soils with higher clay content and shallower water tables will cause corn to develop shallower rooting systems.  This is a problem during wet vegetative growth periods; if the weather turns drier during reproductive stages, when root development has ceased, the plant will be more susceptible to drought conditions due to a reduced volume of soil in which roots can draw nutrients and water. 

On the other hand, looser, well drained soils will encourage deeper rooting.  In drier periods during fast vegetative growth, roots will go deeper, seeking both water and nutrients to keep the plant well supplied. 

Utilizing nitrification stabilizers in banded ammonium-containing fertilizers, like N-Serve for anhydrous ammonia, will keep the ammonium form longer before converting to nitrate-nitrogen.  Ammonium-nitrogen is typically affixed to soil and does not move as much as nitrate-nitrogen, the form that is created through nitrification.  While this preserves the nitrogen in a stable form longer, the roots must encounter the ammonium ions in the soil to be taken up by the corn plant.  Some amount of nitrification of ammonium-containing fertilizers is beneficial, especially before or during the rapid nitrogen uptake in the mid to late-vegetative growth stages (V6 to VT). 

Rooting depth and architecture can be affected by genetics as well.  Some varieties have increased root surface area and length density as compared to others.  In fact, some varieties have a certain level of plasticity to grow into nitrogen or water-rich zones, either laterally or deeper. 

A study performed in China (Liu et al, 2024) compared the corn root architecture of older hybrids to newer hybrids at both 0 and 150 kg/ha nitrogen applications.  It was found that older hybrids had significantly shallower brace and crown root angles than newer hybrids, and that newer hybrids had statistically more brace and crown root nodes than the older hybrids.  When comparing the 0 vs 150 kg/ha N treatments, both older and newer hybrids had slightly but statistically shallower rooting angles for brace and crown roots and more brace and crown nodes at the higher nitrogen rate.  Rooting depth was statistically greater at 0 kg/ha N than 150 kg/ha N, and newer hybrids had statistically deeper roots than the older hybrids. 

These findings would suggest that varieties with broader root systems (or those created due to environmental conditions) may benefit from broadcast/incorporated nitrogen applications, whereas those varieties with deeper, narrower root systems would thrive where nitrogen was banded below or near the seed.  Nitrification will convert ammonium-containing nitrogen fertilizer into nitrate with temperature, and soil moisture will move nitrate through the soil-water solution, but certainly for early to mid-vegetative growth, corn with broader rooting architecture and nitrogen placement that is more dispersed would be needed to intercept and be nitrogen efficient. 

Another study (Postma et al, 2014) utilized a root architecture simulation process to determine the best lateral root branching density (LRBD) for either nitrate or phosphorus.  This illustration from the paper shows the difference between roots with low or high LRBD: 

Lateral Root Branching Density Comparison

In this illustration, the root structure on the left represented 40-day old corn roots with 2 branches per centimeter, the right being the same age of corn but with 20 branches per centimeter.

Through this simulation it was found that sparsely spaced (< 7 branches per cm) lateral roots that were longer were optimal for nitrate interception, whereas lateral roots that were densely spaced (> 9 branches per cm) and were shorter were ideal for phosphorus acquisition.  There is a tradeoff between nutrient acquisition and carbon budget (more roots = more carbon expended).

Beck’s Hybrids’ Root Reveal Research program is a project to characterize hybrids by their root architecture.  Plants are grown in empty chemical totes with a soil-like medium and strung with line to support the roots.  The plant is grown until tassel, then water and nutrients are cut off and the plant is left to dry.  The medium is carefully removed to reveal the roots.

Beck’s research team has found varieties that range from 20 to 80-degree angles of rooting.  Hybrids with more vertical roots are suggested to have better water and nutrient scavenging capability, performing better in low nitrogen environments.  Hybrids with more horizontal roots may be considered better for no-till, poorly drained or lower population rates.  In addition, hybrids with smaller root volumes are more likely to respond to deep-banded P and K than with larger volume root hybrids.

Summary:

Corn rooting architecture is affected by both genetics and the environment.  Nitrogen availability can also be affected by product, placement, and timing.  Considering these dynamics when selecting corn varieties and nitrogen fertilizer options, along with the environmental conditions of your farm, can help you increase nitrogen use efficiency.

• If nitrogen is broadcast applied or even banded but between rows, medium to horizontal architecture roots may be beneficial.

• If nitrogen is banded below or closer to the corn plant, a vertical architecture root structure may be useful.