Agronomic Cropping for Maximum Biomass Production

With recent widespread awareness of dwindling petroleum supplies, considerable attention has been directed towards plants as photosynthetic energy converters. The purpose of this 3-year study was to investigate the bioproductivity of agronomic crops as a potential energy source in Minnesota. Experiments were conducted in the field at St. Paul on a Waukegan silt loam (Typic Hapludoll) and at Waseca on a Webster clay loam (Typic Haplaquoll). Both double-cropping and monocropping systems were evaluated. The double-cropping system consisted of growing fall-planted winter rye (Secale cereale L.) at recommended seeding rates and harvesting it on 15 June, near the peak of its vegetative production and before the formation of acceptable grain. After the rye was harvested, the plots were fertilized, disked, and planted to corn (Zea mays L.). Three corn hybrids: ‘Pioneer 3780’ (full season), ‘NKPX74’ (14% more than full season), and ‘Pioneer 3030’ (28% more than full-season) were grown at each of two populations that exceeded normal production populations by approximately 25% and 100% (75,000 plants/ha and 125,000 plants/ha). Corn was chosen to follow the rye for double-cropping since, in a preliminary study, we determined that it produced more biomass than sorghum (Sorghum bicolor [L.] Moench) or sudangrass (Sorghum blcolor [L.] Moench) when grown on rye plots following the rye harvest. A corn-only or monocropping system was established adjacent to the double-cropping plots. The same three corn hybrids were grown at the same two populations, but they were planted as early in the season as possible and grew uninterrupted. Rye produced an average biomass yield (dry weight of aboveground portion) of 9.6 metric tons/ha (MT/ha) by June. The largest average biomass yield from corn planted after the rye harvest (double cropped) was 16.3 MT/ha, produced by NXPX74 at 125#00 plants/ha. The rye plus corn double-cropping yields thus averaged 25.9 MT/ha. The largest average monocropped corn yield of 18.8 MT/ha (produced by NKPX74 at 125,000 plants/ha) was 7.1 MT/ha below the double-cropped yields. Due to interactions and yield fluctuations across environments, however, the two systems were not determined significantly different. Since costs and risks of successfully producing two crops per season would be an important consideration, we suggest that monocropped corn would be preferred over rye-corn double cropping as a biomass production system in Minnesota.