The fact that field water levels
of 25 cm are a common practice in Bangladesh (Haroon and Pittman, 1997a) and the fact
that the Bangladeshi experiments only lasted for 2– 3 days (Haroon, 1998) might explain
why Haroon (1998) did not find intraspecific competition in his experiments. Farmers in
Vietnam prefer water levels of 10 –15 cm because rice yields decrease 0.06 ton/ha with
every 1 cm increase in the water level (Vromant et al., in press). As such, the increasing B.
gonionotus standing biomass goes together with an increasing rice biomass at an
increasing height, out of reach of the species. Besides that, rice becomes less palatable
as the plant matures.