Forage Rice Yield and Quality Response to Harvest Timing and Nitrogen Management

Because forage rice (Oryza sativa L.) must be cost competitive with other forages, high dry matter (DM) and total digestible nutrient (TDN) yield are essential. To optimize forage rice production, it is important to maximize nutritional value in the leaf and stem rather than in the panicle because the hull restricts cattle's (Bos taurus) ability to digest rice grain. In particular, it is important to maximize TDN concentration and yield in the leaf sheath plus stem (stem) due to the high proportion of this component in the crop rather than in the leaf blade (leaf). The objective in this study was to evaluate the effects of timing of first harvest [95 or 116 days after transplanting (DAT) (booting or full heading stage, respectively)], N application rate (150 or 300 kg N ha−1), and N application method (100–0N method, applying N at 100 and 0% in the first and second crops, respectively; 67–33N method, applying N at 67 and 33%, respectively; 33–67N method, applying N at 33 and 67%, respectively) on TDN concentration and yield in double-harvest of forage rice systems in southwestern Japan. With the 100–0N method, stem TDN yield in the second crop was 39 g m−2 lower when the first crop was harvested at 116 DAT than at 95 DAT. However, with the 100–0N and 67–33N methods, stem TDN yield in the first crop was 152 and 163 g m−2 higher when the first crop was harvested at 116 DAT than at 95 DAT, respectively. When the first crop was harvested at 116 DAT, stem TDN yield in the first crop was 152 and 161 g m−2 higher with the 100–0N and 67–33N methods than with the 33–67N method, respectively. In contrast, stem TDN yield in the second crop was 115 and 142 g m−2 higher with the 67–33N and 33–67N methods than with the 100–0N method, respectively. To obtain high stem TDN yield in total of the first and second crops, harvesting the first crop at full heading and applying 300 kg N ha−1 at 67 and 33% in the first crop and second crops, respectively, is effective. Management practices that increase forage quality will help southwestern Japan to be more sufficient in forage production.