Abstract
Subtropical grasses were compared in pot culture experiment in their responses to nitrogen fertilizer as a first step to investigate the effect of nitrogen fertilization on controlling the competition among species in subtropical pasture. The grasses used were Rhodesgrass (Chloris gayana Kunth.), dallisgrass (Paspalum dilatatum poir.) and bahiagrass (Paspalum notatum Flugge.). They were grown in a glasshouse at Faculty of Agriculture, Miyazaki University from 10 July to 29 August 1973. Nitrogen fertilizer was applied at five levels, 0, 0.25, 0.50, 1.00, 2.00g-N/pot, in the form of ammonium nitrate solution on three weeks after seeding and plants were harvested four weeks after nitrogen application. The average daily maximum and minimum temperature in the glasshouse during the experimental period were 35.8 and 20.7℃, respectively. Results were summarized as follows: 1. Rhodesgrass showed the highest dry matter yield with increment of N rate, followed by dallisgrass and bahiagrass. Also, N rate at which dry weight reached the maximum was the highest in Rhodesgrass and the lowest in bahiagrass. Similar trends were shown in their stem numbers. 2. The nitrogen yield of Rhodesgrass was increased almost linearly up to the highest N rate (2.00g-N/pot) and recovery of applied-N in whole plant of Rhodesgrass was ranged from 84.0 to 76.0%. Nitrogen yields of dallisgrass and bahiagrass, however, were not always increased with increasing applications of nitrogen, and their nitrogen recovery was declined from 87.0% at 0.25g-N/pot to 44.6% at 2.00g-N/pot in dallisgrass and from 71.0 to 17.3% in bahiagrass, respectively. 3. The value of dry matter yield per N yield (W/N) was declined with increase of N-applied in all species, however, Rhodesgrass always showed the highest W/N value at the same N-applied level. These results suggest that differences of W/N value in relation to species and Napplied are one of important factors which influence the efficiency of dry matter production and the plant competing ability for nutrient under high nitrogen fertilization in the pasture. Therefore, further study will be needed to clarify the factors influencing W/N value.
