The Potential of a Double Cropping System for Biomass Production.

The production of biomass through double cropping systems has the advantage of producing more feedstock for refineries by extending the growing season, while also providing many environmental benefits, such as the reduction of erosion. Double cropping systems also have the benefit of incorporating two different species to take advantage of seasonal growing environments, such as the use of cool and warm season grasses.  The objective of this study was to evaluate the biomass production potential of various sorghum genotypes grown in a double cropping system with winter annuals compared to a single cropping system.  For the 2007-08, twelve sorghum genotypes (four sweet and forage sorghums, and four sorghum x sudangrass) were grown in rotation with three winter annuals (triticale, Tifton burclover, and triticale/burclover mixture) and as a season long crop in a split plot design at the Sorenson farm in Ames, IA.  Because of a severe winter, the stands of Tifton burclover did not establish for the spring of the year, and were not considered with the total yield for the growing season. The triticale and triticale/burclover stands were found to have a similar yield (6,603 vs. 6,256 kg/ha) and chemical composition (NDF: 65.28 vs. 63.69, ADF: 37.85 vs. 36.67, ADL: 3.45 vs. 3.47, Lignin: 2.90 vs. 2.89). The sorghum compositions varied considerably depending on the rotation and cultivar, with no consistent relationship being attributed to a specific rotation or genotype.  There was no difference between yields the sorghum types, with the season long treatment of the biomass sweet sorghum (Sugar T) having the highest yield with 21,577 kg/ha. The total dry matter production for the season was not significantly different for the season long sorghum and triticale/sorghum, triticale/burclover/sorghum rotations (16,565, 17,442, and 17,479 kg/ha) when averaged across genotypes.  Overall it may be concluded that with equivalent production between systems, the double cropping system would be more acceptable because of the favorable conservation attributes.