Interactive effects of growth stage and nitrogen fertilization on herbage characteristics and nutritive value of Paspalum atratum

Paspalum atratum is a tropical grass with potential to contribute to forage availability in areas dominated by waterlogged acidic soils. However, little is known of the interactive effect of N fertilization and stage of harvest on its nutritive value. Therefore, the objectives of this study were to evaluate the interactive effects of N fertilization and harvesting stage on herbage characteristics and nutritive value of P. atratum (Cv. Ubon) and to determine the optimum N fertilization rate at each stage of regrowth. P. atratum seedlings were planted in 18,631-cm(3) plastic pots containing growth media amended with 0, 25, 50, and 75 kg N/ha. Forage was harvested after 6- and 12-weeks regrowth. Nitrogen fertilizer had a significant effect (p < 0.05) on herbage yield, sward height, crude protein yield, crude protein concentration, and 12- and 24-h in vitro ruminal organic matter digestibility (IVOMD). P. atratum fertilized with 50 kg N/ha produced the highest dry matter yield (1,133 kg DM/ha) at 12-week regrowth. Crude protein (CP) was highest (133 g/kg DM) in 6-week regrowth forage that received 50 kg N/ha. IVOMD at 12 and 24 h of incubation was highest in 6-week regrowth forage amended with 0 and 50 kg N/ha, respectively. Herbage characteristics and nutritive value of P. atratum showed a quadratic response to N fertilization at both regrowth stages. Response surface optimization indicated that N fertilizer application rates of 56.0 and 52.3 kg N/ha maximized P. atratum herbage yield, CP content, and 12-h IVOMD at 6- and 12-week regrowth, respectively. It was, therefore, concluded that the herbage yield and nutritive value of 6- and 12-week regrowth P. atratum is optimized with N fertilizer rates of 56.0 and 52.3 kg N/ha, respectively.