On-farm research in Washington shows that strip-tilled soil warmed up more quickly than residue-covered soil.

The research conducted at several farms in the Columbia Basin was part of an ongoing effort from Washington State University to help farmers adopt profitable conservation tillage systems.

Andy McGuire, WSU Extension ag specialist for Grant and Adams counties, worked with four farmers who irrigate to demonstrate the feasibility of direct seeding corn into wheat stubble and measure the effects on crop yield and soil quality.

McGuire and the farmers also examined the relationship between corn growth, soil temperature and residue cover and measured the results of strip-tilling vs. leaving high amounts of residue on the soil.

The researchers used a Deere 1730 planter modified for high residue levels. The planter had heavy-duty downpressure springs, Deere row cleaners, Keeton seed firmers and Exapta Mojo wires, Exapta closing wheels and a popup-fertilizer system.

Soil Temperatures

High-residue farming demonstration sites (two fields in corn after wheat) and during connected to either one or two temperature probes were used to collect the data.

Three or four locations in each field were used with a pair of temperature probes at each location, one under residue and one under bare soil. Due to a limited number of data loggers, researchers could not monitor temperatures at all sites at the same time.

Soils varied with the three fields being Quincy fine sand or Royal loamy fine sand. The north demonstration field soil has Ephrata/Malaga gravely sandy loam and the south demo field soil has Shano silt loam. All fields were under center-pivot sprinkler irrigation.

The demonstration fields were in wheat in 2007 with corn direct seeded in 2008. At each logger location, one probe was placed under a bare soil area was created by removing all residue without tillage. The other probe was placed beneath existing residue.

The farmer fields were all strip-tilled: One in the fall and two in the spring. At each logger location, one probe was placed beneath the soil in the strip of mostly bare soil, while the other probe was placed beneath the undisturbed residue in the center between the strips.

In the comparison of the temperature of untilled soils vs. bare or residue covered, the measurements showed that the daily range of the temperature of the bare soil was greater than that of the residue covered soil.

The high temperatures were higher and the low temperatures were lower for the bare soil as the residue moderated daily temperature changes. This could be seen throughout the season, even after the canopy closed around the beginning of July.

Yield Results

The north site yielded 5.2 tons of corn per acre, or 184 bushels per acre, while the south site produced 6.2 tons per acre, or 222 bushels per acre.

"The study achieved the goal of successfully direct-seeding corn into the undisturbed wheat stubble, as shown by the successful stand establishment," McGuire says. "However, the yields were lower than the target, mainly due to cooler than normal weather during the 2008 spring and summer.

"Compared to the 10-year average, the 2008 season was 12 to 16 days shorter based on corn growing degree days (GDD) and early planted corn suffered from prolonged cold weather and even killing frosts in the Columbia Basin."

McGuire says better pre-plant weed control and early fertility and later water control and, possibly, a slightly shorter relative maturity hybrid may have increased yields.