Sweet Pearl Millet Yields and Nutritive Value as Influenced by Fertilization and Harvest Dates

Abstract

Sweet pearl millet [Pennisetum glaucum (L.) R.Br.] can be used for ethanol production from the extracted juice with residues used as livestock feed, but optimal fertilization and harvest dates are unknown for this “sugary stem” hybrid developed from forage pearl millet. We evaluated the effects of five equally spaced N fertilization rates (0–200 kg ha−1), K fertilization rates of 0 and 66 kg ha−1, and four harvest dates (approximately every 15 d from early or mid‐August in 2007 and 2008) on water soluble carbohydrate (WSC) concentration and yield, dry matter (DM) yield, and nutritive value of sweet pearl millet, at two sites with 2300 to 2500 and 2900 to 3100 crop heat units (CHU) in Québec, Canada. Delaying harvest dates increased DM (22–99%) and WSC yields (98–173%), and WSC concentration but decreased N concentration by 36% and neutral detergent fiber digestibility (dNDF) by 19%. Increasing N fertilization increased DM and WSC yields, and N concentration, but had no effects on WSC concentration, and decreased dNDF moderately. Potassium fertilization had limited effects on DM and WSC yields, WSC concentration, and on most attributes of nutritive value. Fertilization with 78 to 90 kg N ha−1 and an accumulation of 2100 to 2200 CHU corresponding to harvest dates in September are required to maximize WSC yield (1.86–2.83 Mg ha−1) of sweet pearl millet in eastern Canada. Maximizing WSC yield with the goal of producing ethanol, however, would result in reduced nutritive value.