Response to Nitrogen of Sweet Pearl Millet and Sweet Sorghum Grown for Ethanol in Eastern Canada

Sweet pearl millet [Pennisetum glaucum (L.) R.BR.] and sweet sorghum [Sorghum bicolor (L.) Moench] are considered for ethanol production in eastern Canada, but their response to N fertilization is not well established. Our objectives were (i) to compare both species for dry matter (DM), water-soluble carbohydrate (WSC), and estimated ethanol yields and (ii) to determine their response to mineral N rate (0, 40, 80, 120, and 160 kg N ha−1), (iii) mineral vs. organic N (liquid swine and dairy manures at 80 kg total N ha−1), and (iv) single vs. split N application (80 kg ha−1 mineral N). The two species were grown for 2 years on sandy loams in two ecozones (Mixedwood Plains [MWP] and Boreal Shield [BS]) with contrasting temperature regime. Both species responded similarly to mineral N fertilization, with maximum WSC yield at 86 kg N ha−1 at MWP and 91 kg N ha−1 at BS, and maximum DM yield at 121 kg N ha−1 at MWP and 107 kg N ha−1 at BS. Mineral N fertilization at 80 kg ha−1 resulted in higher DM and WSC yields than the manures, which showed fertilizer N equivalences varying from 15 to 52 %. Splitting mineral N rate between seeding and the four-leaf stage did not improve yield compared to a single application. Sweet sorghum had higher averaged WSC concentration and yield than sweet pearl millet (249 vs. 134 g WSC kg−1 DM; 3.41 vs. 2.02 Mg WSC ha−1) and appears more promising for ethanol production in eastern Canada.