Does increasing plant population density alter sugar yield in high stalk-sugar maize hybrids?

Escalating demands for food and green energy have renewed interest in the dual-purpose use of maize (Zea mays L.) for a biofuel and high-energy forage crop. Recently, maize hybrids with high stalk-sugar (sugarcorn) have been developed. It is important to determine how agronomic practices, for example altering plant population density (PPD), affect stalk-sugar yields of these newly developed hybrids and to advance knowledge required for producing sugarcorn as a dual-purpose bioenergy-high energy silage crop in short-season regions unable to grow sugarcane. A field experiment was conducted for 3 years to assess the effect of PPD on stalk-sugar accumulation, dry matter production, silage and sucrose yields of sugarcorn compared with two commercial silage hybrids. Targeted PPD ranged from 75000 to 150000 plants ha(-1) in increments of 25000 plants ha(-1). We found that increasing PPD from 75000 to 125000 plants ha(-1) increased stalk sugar concentrations by up to 25% in some of the sugarcorn hybrids, with minimum change in the conventional check hybrids. The sugarcorn hybrid CO348xC103 had the highest stalk sugar concentration (128gkg(-1)) and sucrose yield of up to 3.8Mgha(-1) at the targeted PPD of 125000 (or actual 118000 +/- 7000) plants ha(-1). By contrast, the check silage hybrids produced at most 2.0Mgha(-1) of sucrose yield with much lower stalk sugar concentrations (53-65gkg(-1)). Sugarcorn hybrids had generally lower grain yield with greater plant barrenness (the failure of a plant to produce a normal ear) and severer head smut infestation than the conventional silage hybrids. Our results suggest that as a silage crop, the current recommended PPD of 75000-85000 plants ha(-1) for commercial silage maize production in the region is likely suitable for sugarcorn, and a higher PPD is required if sugarcorn hybrids are designated as a biofuel crop or for dual-purpose use.