Henry Mascagni | 10/12/2016 7:30:07 PM
Grain sorghum is often used as a rotation crop with soybeans and cotton. The most important management practice is planting date, and early planting maximizes yield and enhances the ability to “ratoon” or produce a second crop from the original stubble. For a ratoon crop to be practical, enough time is required after the main harvest for the second harvest to develop and dry down. The yield potential of both the first and ratoon crops and input costs associated with insect and disease management, particularly for the late-developing ratoon crop, need to be determined in order to fully evaluate the viability of a ratoon-cropping system.
Field experiments were conducted on Commerce silt loam in 2013 and 2014 and Sharkey silty clay in 2015 to evaluate the feasibility of ratoon-cropping sorghum in northeast Louisiana. The official variety trials were used each year for evaluating treatment effects. Hybrid entries numbered 24 in 2013, 29 in 2014 and 31 in 2015. Cultural information is presented in Table 1. Because of severe bird damage, the 2013 trial had to be replanted. The ratoon crop began developing after the main crop stubble was mowed the day after harvest. The main crop was fertilized with 150 pounds of nitrogen per acre, and the ratoon crop was fertilized with 100 pounds of nitrogen per acre. Insecticides were applied whenever a pest reached threshold levels. The Sharkey silty clay trial in 2015 was irrigated.
Grain was harvested with a small-plot combine and weight was adjusted to 14 percent grain moisture. To avoid potential bird damage, particularly for the late ratoon crops, mesh bags were placed over the grain heads during the grain fill period for four hybrids in 2015 to ensure a true yield without bird damage. These heads were hand-harvested and threshed with a small mechanical thresher, and yield was adjusted to 14 percent grain moisture.
The 2014 ratoon crop was not harvested because of incomplete grain development resulting from an early freeze. Additionally, time between planting and harvesting the main crop was 132 days compared to 112 days in 2013 and 118 days in 2015, leaving fewer days for the ratoon crop to develop.
Yields averaged 109 bushels per acre in the main crop and 14 bushels per acre in the ratoon crop for the 24 entries in 2013 and 104 bushels per acre in the main crop and 21 bushels per acre in the ratoon crop for the 31 entries in 2015. Thus, the ratoon crop equaled only 13 percent of main crop yield in 2013 and 20 percent of main crop yield in 2015.
Grain yield and yield components for both the main crop and ratoon crop for the four hybrids with bird protection were evaluated. The main crop was combine-harvested and the ratoon crops were hand harvested and threshed. Yield for the four hybrids averaged 106 bushels per acre for the main crop and 54 bushels per acre for the protected ratoon crop. Although yields were higher when grain was protected from bird damage, they still were only about 50 percent of main crop yield.
A major concern about the feasibility of sorghum ratoon cropping is the costs for pesticide applications. Multiple applications were applied each year on the ratoon crop for insect pests, including aphids, armyworms and sorghum midge.
Producing a second crop requires timely planting and harvesting of the main crop to best ensure that the ratoon crop has time to completely develop and dry down. Both limited yield potential and need for multiple pesticide applications for the ratoon crop suggests that grain sorghum ratoon cropping may not be feasible for northeast Louisiana.
Rick Mascagni is a professor at the Northeast Research Station in St. Joseph.
A ratoon-cropping test at the Northeast Research Station, St. Joseph. Photo by Rick Mascagni
Table 1. Cultural information for main and ratoon crops in St. Joseph, 2013-2015.