No-tillers using a wheat/row crop/fallow rotation may find that row-crop yields in such a rotation are higher — in years with relatively normal weather — when the wheat-stubble height is taller.

Kansas State University research in western Kansas by Lucas Haag, agronomy graduate student, and Alan Schlegel, agronomist-in-charge at the Southwest Research Extension Center at Tribune, Kan., has found that corn yields increased as stubble height increased.

Grain sorghum yield response to stubble height was less apparent, but exhibited a response to moderately higher cutting heights.

"Wheat residue provides numerous benefits, including evaporation suppression, delayed weed growth, improved capture of winter snowfall and reduced soil erosion," Schlegel says. "Stubble height affects wind velocity, surface radiation interception and surface temperatures, all of which will reduce evaporation potential and increase winter snow catch."

The researchers add that taller wheat stubble is also beneficial to pheasants in postharvest and overwinter fallow periods.

Using stripper headers leaves taller wheat stubble than previously attainable with conventional headers. In theory, increasing wheat-cutting heights or using a stripper header should further improve the effectiveness of standing wheat stubble.

Studies were conducted from 2007 through 2010. Corn and grain sorghum were planted into standing wheat stubble of three heights: short, optimal and stripped.

• The short-cut treatment was half of optimal cutter bar height.
• Optimal cutter bar height is the height necessary to maximize both grain harvested and standing stubble remaining (typically two-thirds of total plant height).
• The third treatment was stubble remaining after stripper header harvest.

In 2007, these heights were 7, 14 and 22 inches. In 2008, heights of 10, 20 and 30 inches were obtained. In 2009, the heights were 7, 14 and 23 inches. In 2010, the stubble measured 8, 16 and 25 inches.

Corn was seeded at the rate of 15,000 seeds per acre and grain sorghum was seeded at the rate of 33,000 seeds per acre. In 2010, the sorghum plots were split and an additional seeding rate of 41,000 seeds per acre was added to the study.

Nitrogen was applied to all plots at a rate of 80 to 100 pounds per acre. Starter fertilizer (10-34-0) was applied in-row at rates of 7 and 9 gallons per acre for corn and sorghum, respectively.

Plots measured 40-by-60 feet. Soil water measurements were obtained by neutron attenuation to a depth of 6 feet in 1-foot increments at seeding and harvest to determine water use and water-use efficiency.

Results 2007-10

Over the 4 years, corn grain yield increased from 80 to 92 bushels per acre as stubble height increased. Increased grain yields are the result of the effect of stubble height on one primary yield component, kernels per ear, which increased with increasing stubble height from 467 for the low cut to 521 for the stripped stubble treatment.

Another key yield component, ear population, also increased numerically with increasing stubble height, suggesting that increasing stubble height also may reduce in-season plant mortality and ear abortion.

Corn grown in stripped or optimal-cutter-bar-height stubble resulted in higher water-use efficiency, which increased from 305 pounds per inch in short-cut stubble to 361 pounds per inch in the stripped stubble treatment.

Over the 4 years, sorghum grain yields exhibited a quadratic response to stubble height, with optimal-cutter-bar-height stubble producing grain yields of 4 to 5 bushels per acre higher than either the stripped or short-cut treatment.

An examination of yield components revealed that kernels per head generally increased with increasing stubble height. Although no statistical differences were observed, heads per plant exhibited a positive response to increasing stubble height.

"Future efforts in this study will involve more emphasis on yield components, specifically tillers per plant, in an effort to identify any interaction between tillering and the production environment created by stripped stubble," Haag says. "Data from prior years suggested that sorghum planted into stripped stubble was yielding less than sorghum planted into optimal-cutter-bar-height stubble due to reduced tillering.

"The addition of the 41,000 seeding rate was designed to further investigate this possibility. Interestingly, in 2010, the increased seeding rate resulted in only a very small increase in plant and head population.

Conclusions

Increasing stubble height has improved subsequent corn grain yields and water-use efficiency. The impact of stubble height on grain sorghum yields is less apparent at this time and requires further study, the researchers says.

"Surprisingly, this study has found little impact of stubble height on profile available soil water," Schlegel says. "This is in direct contrast to other studies and anecdotal field observations.

"Corn-grain yield differences in the absence of differences in available soil water at planting indicate a more pronounced impact of stubble harvest height on in-season, plant-water dynamics than previously thought. Additional years of observation are needed to identify any potential effect of stubble height on the yield components of grain sorghum and to provide a more robust dataset across multiple years in which to evaluate the effects of stubble height on soil water storage."