K. Ampongnyarko et Sk. Dedatta, EFFECTS OF NITROGEN APPLICATION ON GROWTH, NITROGEN USE EFFICIENCY AND RICE WEED INTERACTION, Weed Research, 33(3), 1993, pp. 269-276
Responses of upland rice (Oryza sativa L.) and the weeds Amaranthus sp
inosus L., Cyperus rotundus L., Eleusine indica (L.) Gaertn., and Rott
boellia cochinchinensis (Lour.) W. D. Clayton to nitrogen (N) and time
of N application were studied in the glasshouse both in monoculture a
nd in mixture. The N response of two rice cultivars and R. cochinchine
nsis in monoculture levelled off between 69 and 103 mg N kg-1 air-drie
d soil, whereas the other weed species continued to respond beyond 103
mg N kg-1 air-dried soil. At high N application rates, N uptake by we
eds was higher than that by rice; weeds used N more efficiently. Weeds
, which had high dry matter production at high N application rates in
monoculture, were most competitive at low N and least sensitive to low
applied N. Nitrogen application levels sub-optimal to rice reduced th
e competitive ability of rice when in mixture with E. indica, R. cochi
nchinensis, and A. spinosus, but not with C rotundus. Although N respo
nse of a plant species generally declined with age, interspecific diff
erences were observed. Timing of N application can be exploited in ric
e-weed management.