BUSHLAND — A long-term study by scientists at the USDA- Agricultural Research Service cropping field laboratory here shows that a fixed wheat- fallow-sorghum rotation is preferable to an “opportunity” cropping system .
“We used 32 years of historical soil water and yield data from stubble mulch tillage on wheat-sorghum-fallow (WSF) and continuous annual cropping of wheat and sorghum to evaluate the potential of opportunity cropping,” said O.R. (Reggie) Jones, USDA-ARS soil scientist.
With the opportunity system, explained Jones and USDA-ARS biometrician Thomas Popham, the same crop–wheat or sorghum–is planted back to back if the soil is wet to a depth of three feet at planting. Moisture depth is determined with a soil probe. If not sufficiently moist, the land is fallowed and planted to the next scheduled crop in the wheat-sorghum-fallow rotation.
“We compared grain production on the opportunity system with a fixed three-year wheat-sorghum-fallow rotation,” Jones said. “The average annual precipitation for the 32 years (1958-1978 and 1986- 1996) was 18.5 inches.”
Cumulative 32-year production on the fixed WSF system was 193 bushels of wheat (10 crops) and 463 bushels of sorghum (11 crops). This compares with opportunity cropping production of 135 bushels of wheat (nine crops) and 524 bushels of sorghum (16 crops), the scientists said.
“There were only three times in the 32 years that wheat crops could be planted back to back, but there were 10 times that sorghum could be repeated,” Jones said. “We assumed in this analysis that the yield of the second crop in back to back planting was the same as was obtained with annual cropping of sorghum or wheat.”
The scientists concluded that a fixed WSF rotation is preferable to opportunity cropping “due to greater yields on the WSF crops and a reduced number of crop harvests, thus reducing (harvesting) expense.” They said adoption of a fixed rotation also allows a wider spectrum of herbicide use for reduced tillage or no-tillage management.