Abstract: Herbage drymatter accumulation, and nitrogen and phosphorus absorption responses of three forage species following addition of nitrogen as urea (N) or phosphorus as superphosphate (P) fertilizer were studied over 2 seasons (2015 and 2016), in a field experiment with a randomized block design. The leguminous forage, Stylosanthes guianensis cv. Seabrana, and the forage grasses black spear grass (Heteropogon contortus) and ‘kong ying' grass (Bothriochloa pertusa) were compared with nil-fertilizer and N or P fertilizer treatments. In general, fertilizer application (especially N) delayed crop phenological development by 5-10 days. Averaged over the two growing seasons, addition of either N or P fertilizer increased forage yield by approximately 11%, but data were variable, and the yield, except B. pertusa responses to N and P were not statistically significant. Crop N and P yields (kg·ha^-1) of S. guianensis were almost double those of the two grasses tested, but only in the case of N addition to B. pertusa, was there a significant fertilizer-induced increase in forage N or P yield. Root mass of H. contortus was reduced by N or P fertilizer (P<0.05), especially by N addition. This study has provided a theoretical basis for planning the application of nitrogen and phosphorus in sub-tropical forage production. In this article, proper application of nitrogen and phosphorus is beneficial to increase the yield of the three herbages.

Key words: nitrogen, phosphorus, three pasture, growth, absorption