David Y. Lanclos, Jay Geaghan and Robert Ferguson
Over the past decade, Louisiana producers harvested an average of 129,000 acres of wheat annually. In 2005, the wheat crop had an economic impact to the state of around $19.6 million. Historically in Louisiana, producers will double-crop 95 percent of all wheat acreage with soybeans, so proper management of wheat stubble is critical in maximizing soybean yields.
Combines have changed over the years. Today, most producers harvest wheat with “straw choppers,” which chop and shred the straw into much smaller pieces than the older “straw throwers,” which essentially just toss the straw on the ground after it is thrashed.
Producers across the state employ numerous cultural practices for managing wheat straw after a late-spring harvest. The predominant practices include burning, burning and disking, disking without burning, planting directly into the wheat stubble or a combination of any of these.
Traditionally, a large number of wheat acres are burned before planting soybeans because burning removes any straw and stubble that may inhibit proper stand establishment for producers who do not use no-till drills. Producers have tried repeatedly to establish stands using conventional drills without burning, but it is generally difficult. In addition, the practice of burning wheat stubble eliminates some soil nutrients and reduces soil organic matter. The reduction of soil organic matter can potentially reduce soil tilth, hindering crop establishment and overall crop health.
Burning wheat straw also is becoming less popular as urban sprawl continues into more traditional rural areas. However, complete elimination of wheat straw is not possible at this time without burning, so it is imperative that alternatives to burning wheat be explored.
Research conducted in Arkansas reported that leaving wheat straw in the field could be either detrimental or beneficial on the subsequent soybean crop. Because of this, a two-year replicated study at the LSU AgCenter's Dean Lee Research Station
in 2003 and 2004 evaluated eight different straw-management treatments. They included leaving 6-, 9-, 12- and 15-inch stubble in the field, burning, disking, burning and disking, and conventional tillage, which employs disking twice in different directions. All tillage treatments were packed down to standardize the seedbed. Winter wheat was planted in November at approximately 80 pounds per acre, and the wheat crop was followed by maturity group V soybeans planted on 15-inch row spacing in May.
Data collected in the study included stand counts, plant height at growth stages V1 and R5, and yield. The V1 growth stage is when the first node appears and the unifoliate leaves are fully developed opposite of each other, and the R5 growth stage is “beginning seed,” where seed is 1/8 inch in a pod at one of the four uppermost nodes on the main stem. Stand counts in both years showed no statistical differences among all treatments, but numerically the disked and conventional-tillage treatments were higher at 10.12 and 10.5 plants per 3 feet of row.
Plant height at V1 showed no statistical differences among treatments; however, the 12 and 15-inch stubble treatments had the tallest plants. Data results for plant height at R5 were similar to results at V1 with no statistical differences. Once again, however, the 15-inch stubble had plants approximately 1.5 inches taller than the next tallest treatment, which was the 12-inch stubble.
Likewise, yield showed no statistical differences, although a numerical linear trend developed among the stubble treatments – the 15-inch stubble treatment yielded 34 bushels per acre followed by the 12-inch stubble at 31 bushels per acre, the 6-inch stubble at 29 bushels per acre and the 9-inch stubble at 28 bushels per acre. These results suggest that leaving stubble higher than 1 foot can influence yield positively. For the remaining treatments, the burned treatment yielded more when compared to all tillage regimes. This may have been caused by increased moisture retention because the soil had not been disked. These results suggest disking wheat stubble does not improve yield.
It appears that the best way to handle wheat stubble is to cut it high or burn the residue off completely. Leaving the stubble at 12 inches or higher causes the plants to stretch more for sunlight, which positively influences biomass, which could increase yields. Studies will continue.(This article was published in the fall 2006 issue of Louisiana Agriculture.)