Impact of crayfish densities on wet seeded rice and the inefficiency of a non-ionic surfactant as an ecotechnological solution

In order to compare the effects of crayfish (Procambarus clarkii) on rice production, with and without the use of a non-ionic surfactant (Genapol OX-80) at a concentration of 0.005%, 12 enclosures at 1 m(2) containment area were built in each of two experimental fields. Crayfish densities used in the experiment were: 0, 1, 3, and 5 adult crayfish per m(-2). In each field, at harvest time, five randomly chosen areas of 1 m(-2) were also sampled for rice, infestants and sediment characteristics. Additionally, the number of filled grains per panicle, the percentage of empty grains and the 100 grains weight were determined. One of the experimental fields was used as the treatment (field T) and another one as the control (fit ld C), and no statistically significant differences (p > 0.05, Mann-Whitney U test) were found between them. No perceptible reduction in crayfish damaging effects was observed after the use of the surfactant in field T. Results of an ANOVA performed on the effects of crayfish density on rice production at each field were statistically significant (p < 0.05). There was a total destruction (100%) of rice in the enclosures with densities of 3 and 5 crayfish m(-2). Some infestant macrophytes survived at 3 crayfish m(-2) in both fields and at 5 crayfish m(-2) in field C. At lower densities (1 crayfish m(-2)) the average decrease in grain production attributable to crayfish was 41.61%. Results provided data to calibrate a management model and suggested that the surfactant is not effective in field conditions. (C) 2000 Elsevier Science B.V. All rights reserved.