Huancahuari M, F Pensati, A Rongoni, M Carrieri, R Bellini
Bulletin of Insectology 69 (1): 131-141, 2016
The possibility to reduce the nitrogen input into rice cultivations thanks to the organic nitrogen input derived from the predator fish Gambusia holbrooki Girard used for the biological control of mosquito species was studied. Trials were conducted on three rice varieties, „Koral‟, „Gladio‟ and „Loto‟, measuring the impact of different fish density and nitrogen inputs on phenological parameters (number of culms per square meter, culm height, spike length, number of fertile seeds per spike, and yield per hectare) and on the ammoniacal nitrogen concentration during the cultivation period. Trials were repeated for 2-3 years consecutively, and in all varieties we observed a positive effect of G. holbrooki on some phenological parameters (above all on the number of culms per square meter and on the number of seeds per spike) which in turn determined an increase of the yield per hectare, especially in those parcels with low nitrogen input. We hypothesize that the introduction of G. holbrooki in rice paddies exerted a positive role in maintaining the proper concentration of ammoniacal nitrogen thanks to the fish excreta, thus positively affecting rice cultivation during particularly sensitive phenological phases, like culm and spike formation. This practice could concur to reduce the need of nitrogen fertilization and, in turn, nitrogen pollution, while reducing mosquito larval density.
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