Yield and nutritive value response to row spacing and cultivar in forage rice

Although the forage rice (Oryza sativa L.) cultivar 'Ruriaoba' has very high dry matter (DM) yield, it readily lodges after heading because of its high plant height. As a result, seed production and conventional cultivation of 'Ruriaoba' are very difficult. To improve this situation, we examined the effects of cultivar ('Ruriaoba' or 'Tachiaoba') and row spacing (30 [30-30-30-30]cm, 45 [30-30-30-45]cm, or 60 [30-30-30-60]cm) on the yield and nutritive value of forage rice. The lodging score of 'Tachiaoba' did not differ among row spacings but that of 'Ruriaoba' decreased with increasing row spacing. 'Ruriaoba' had lower grain yield than 'Tachiaoba'. Among its components, 'Ruriaoba' had fewer spikelets per m(2), fewer spikelets per panicle and lower 1000-grain weight than 'Tachiaoba'. 'Ruriaoba' had fewer grains per m(2) than 'Tachiaoba'. Grain yield and its components did not differ among row spacings, nor did the number of grains per m(2). Thus, 'Ruriaoba' planted at 60-cm row spacing may not decrease the grain yield and number of grains without lodging. This type of low-density planting of 'Ruriaoba' may be useful for seed production. At heading and yellow ripe stages, 'Ruriaoba' had higher DM yield than 'Tachiaoba' because 'Ruriaoba' had higher number of panicles than 'Tachiaoba'. Furthermore, 'Ruriaoba' had higher total digestible nutrients (TDN) yield than 'Tachiaoba'. At heading, DM yield decreased with increasing row spacing because the number of panicles decreased with increasing row spacing. Total digestible nutrients yield was lower at 45- and 60-cm row spacings than at 30-cm row spacing. However, at heading and yellow ripe, 'Ruriaoba' planted at 60-cm row spacing had DM and TDN yields similar to those of 'Tachiaoba' planted at 30-cm row spacing. Such low-density planting of 'Ruriaoba' may be an option for forage rice production.