Explore Your Roots

By Pam Smith
DTN Progressive Farmer Crops Technology Editor

Neither leaf cuts nor mud nor summer heat nor the itch of pollen can keep Adam Watson from his appointed rounds. This time of year, the most critical tool on his farm is a spade. Uncovering the truth behind what is happening in his fields provides answers that pave the way for choices he makes the following season.

CHECK FOR CLUES

Noticeable symptoms such as goose-necked plants are obvious crime scenes to investigate. However, Watson sees roots as more than an anchor to guard against lodging. Roots are the gateway to yield. "Anything that restricts them from running true and deep is a stress on the plant that limits uptake of water and nutrients," says Watson, who farms near Villa Grove, Ill.

"Mostly, I'm a curious farmer," he says. "For example, I want to see for myself if the in-furrow treatments we're trying are contributing to a more robust root mass. And, if so, how long that advantage holds through the growing season."

He starts checking roots soon after emergence and continues to dig four or five times throughout the growing season. Plants exhibiting stress are particularly ripe for probing. Washed roots -- georeferenced and tagged with diagnostic comments -- often litter the farm shop floor and serve as teaching tools for the rest of the farm team.

"Understanding roots can be complex and definitely not as convenient as scouting above-ground symptoms," Watson admits. "There are also not a lot of in-season rescue treatments for what I discover this time of year, but the information helps validate decisions or adjust management moves, such as how we set a planter or whether we continue to use a Bt trait."

DON'T JUMP TO CONCLUSIONS

Bruce McVicker, technical sales agronomist for DuPont Crop Protection in western and central Illinois, says environmental factors can challenge any trait or treatment. Sometimes plant damage perceived as a product failure can be misinterpreted if growers aren't digging for real answers.

"Last year [2014], for example, the cool, early-dry spring in this region allowed preapplied anhydrous to move down the soil profile, and we saw some root pruning because of high salt concentrations," McVicker recalls. "It was isolated, but if we hadn't been digging, we might have assumed it was something else."

Here are five things Watson will look for as he digs roots this season:

1: Catch Compaction. Sidewall compaction became a concern as cool, rainy conditions lingered and caused some growers to rush planting this spring. "I'm willing to sacrifice timeliness for good planting conditions," Watson says. "But at some point, you have to roll."

Dave Shenaut, Monsanto technology development representative, expects to see what he calls "hatchet roots" this season. "It will be an important year to dig roots, because some early corn was planted in less-than-ideal conditions," Shenaut says.

Sidewall compaction tends to happen when the soil on top often seems near perfect, but the soil below the surface is too wet. Planter double-disk openers can smear the side of the seed trench and pressure-pack the soil too tightly.

The compacted sidewalls act as barriers that keep the corn roots from expanding to their full potential. Instead, roots get trapped in the planting trench, grow straight down and don't spread between rows. They often take a horizontal turn until they can clear the compacted zone. "Sometimes, if soils stay moist, corn roots can push through compaction layers," Shenaut adds. Symptoms don't always show up until mid-season, or conditions turn dry. Potassium deficiencies are common when roots can't penetrate into the soil profile.

Root digs can also reveal density layers from tillage or no tillage. A compacted root ball breaks apart in layers, exposing a flat area where roots do not penetrate.

2: Root Out Rootworms. Shallow or weak root systems aren't always a sure sign of insect injury. Some weather conditions—high winds and wet soils can combine for lodging problems. Still, Western corn rootworm is an annual visitor for Watson, and digging is the only way to evaluate how control programs are holding up. Adult beetles that emerge to clip silks are no indication of how much larval feeding took place below ground prior to emergence.

Cool temps and plenty of rainfall made for a lighter rootworm year in 2014, but Watson still found greater-than-expected feeding damage on some corn-on-corn acreage. Although his agronomist assured him it was below economic levels, he took more precautions in 2015 by planting pyramided hybrids on corn-on-corn acres. He also used a soil insecticide on first-year corn acres planted to hybrids containing a single mCry3A trait (Agrisure RW). "Our Herculex traits seem to be holding up fine," he says. Watson is a DuPont Pioneer seed dealer and therefore sticks with the traits offered within the brand.

The decision to use insecticide on trait was a $21-per-acre decision. He knows the additional insecticide won't reduce rootworm populations or reduce Bt selection pressure. His goal is to protect the main root ball and preserve yield in those fields containing single-trait hybrids.

So far, crop rotation is still an option that he's also exercising. But he's monitoring it, too, since rotation-resistant rootworm has been confirmed in nearby counties. Larval damage counts can also help him assess if an adult rootworm spray program should be a consideration.

3: Size Up Sidedressing. Split nitrogen applications have become popular as a way to cut usage and deliver a late shot of nitrogen at just the right time. Watson puts out 70% of the crop's nitrogen (32% liquid) needs at preplant, and the rest is injected with a Hagie toolbar from V5 through V10, depending on seasonal conditions and plant needs. Nitrogen uptake accelerates rapidly between V8 and V10, but root growth is also extending into the row middle (and below the corn stalk) by this time. Root digs indicate he's not experiencing any excessive root pruning by sidedress placement, but he is watching, analyzing and taking care to thread those row middles.

4: Evaluate Inputs. Untreated check strips allow Watson to evaluate product efficacy. In the case of Bt rootworm corn hybrids, comparison to the refuge is helpful. However, he's constantly testing all sorts of products, from new biologicals to old standby seed treatments. Side-by-side evaluations helped determine the value of the biostimulant BioForge, for example, which he's found encourages plant response during periods of drought and heat by regulating the stress hormone ethylene.

"Digging and comparing check strips helped us confirm the value of a pop-up fertilizer program," Watson says. The advantage of starters shows up around the V3 stage of development when the plant begins the transition from kernel reserves to nodal root support. If growing conditions have compromised nodal root development, the nodal roots find help when they tap into the starter fertilizer band.

5: Gather Hybrid Information. Rooting characteristics vary between hybrids, says Bob Nielsen, Purdue University agronomist. "You might think the root systems are constricted, but it may just be a genetic characteristic," he notes. "So you have to be a little careful about drawing too hard of conclusions. Nevertheless, digging year after year gives one a feel for what the roots should look like and what they are suggesting."

Some seed companies provide root characteristics, and Nielsen suggests those ratings can be helpful when making hybrid selections. "Root digs fall into information gathering to make management decisions. There are terrific smartphone apps to help keep track of what you are finding," he says.

HOW TO DIG IT

Root digs are a chore, but they don't have to be complicated. Grab a shovel, and dig far enough away from the stalk to get the whole root mass. Don't pull -- you want as many roots as possible.

Try to avoid breaking roots by placing the root ball on its side. Adam Watson prefers to soak roots in a bucket -- rootworm larvae, if present, will float to the top of the water. A pressure hose is used to clean off the remaining dirt.

The best time to dig in and inspect root damage is after the rootworm grub has finished feeding. Timing is weather dependent. Wade in well beyond border rows, and sample from several areas within each field. Continuous corn fields and areas with persistent corn rootworm populations should be your highest priority.

Keep in mind the larvae must eat a little for the Bt trait to work. Roots may also show some signs of regrowth. Look for telltale rootworm injuries on the root tissue: feeding scars, browning and pruning of the tissue back to the base of the plant. Iowa State University's Interactive Node-Injury Scale (www.ent.iastate.edu/pest/rootworm/nodeinjury/nodeinjury.html) can help you calculate root injury. Iowa State analysis shows, on average, a 15% yield loss for every root pruned.

(BAS)

Copyright 2015 DTN/The Progressive Farmer. All rights reserved.