Nitrogen Requirements of Sweet Pearl Millet and Sweet Sorghum As Energy Crops in Eastern Canada.

Arable land is increasingly used to grow crops for ethanol production. Those crops must provide high yields, be suitable to the local pedo-climatic conditions, offer useful byproducts and have a high net energy balance (NEB): the difference between energy output and input for biomass production and processing.

Hybrids of sweet pearl millet (Pennisetum glaucum [L.] R. BR.) and sweet sorghum (Sorghum bicolor [L.] Moench) have recently been developed for climate conditions of eastern Canada. A sweet juice can be extracted from these crops for ethanol production, whereas the pressed stalk residues can be used as silage. However, there is limited knowledge on the NEB of these crops when produced under the pedo-climatic conditions of eastern Canada.

The optimal N requirements for sustainable production of sweet pearl millet and sweet sorghum as energy crops in eastern Canada (46°44’N, 71°31’W) was determined over two growing seasons on a well-drained sandy loam using different N rates (0, 40, 80, 120 and 160 kg N ha^-1 as ammonium nitrate; or 80 kg available N ha^-1 from dairy cattle and pig slurries).

Sweet pearl millet and sweet sorghum produced 13.0 and 12.6 t DM ha^-1 with optimum N rates as low as 75 and 55 kg N ha^-1, respectively. Low N requirements could lead to a favorable NEB in comparison with corn, an N-demanding biofuel crop currently grown in this area. For an equivalent available N rate (80 kg N ha^-1), sweet pearl millet offered higher yields with ammonium nitrate, than with dairy cattle and pig slurries. For sweet sorghum, there were no significant differences between yields obtained with ammonium nitrate and pig slurry, while lower yields were obtained with dairy cattle slurry. The low N requirements of these crops suggest a superior efficiency in soil N uptake.