Effects Of Biodiversity On Planthoppers And Barnyard Grass Control In Paddy Fields

Developing species-diversified cropping systems by increasing the number of crop species has been becoming main approach to harmful organisms control in agroecosystems.Two experiments were conducted to exam whether and how agro-biodiversity could control pests and weeds and thus enhance productivity in rice system in this study:(1) effects of species diversity on pests and weeds were investigated through field experiment in a Chinese 1200-year-history traditional rice-fish system that was listed by FAO and UNDP as Globally-important Ingenious Agriculture Heritage Systems(GIAHS) in 2005;2) effects of rice genetic diversity on barnyard grass(Echinochloa crus-galli) by mixed-planting two weed-suppressive rice (Oryza sativa) varieties Guodao No.1(GD) and PI312777(PI),and three non-suppressive varieties Xiushui No.63(XS),Zhongjian No.2(ZJ) and Chunjiang No.016(CJ).The main results were as follows:1 Pest and weed controlCompared to rice treatment(rice monoculture),density of rice brown hopper in rice-fish treatment(rice co-culture with fish in the plot) decreased by 24.6%-37.1%. However,the density in both rice-fish treatment and rice monoculture treatment was significantly higher than that of conventional rice treatment(rice monoculture with pesticide).There was no significant difference in numbers of rice leaf roller (Cnaphalocrocis medinalis) in both treatments rice-fish and rice monoculture,but numbers of rice leaf roller were significantly lower in conventional rice treatment than that in rice-fish and rice monoculture.The result showed that the density and biomass of weed in rice-fish treatment were significantly lower than rice monoculture.The biomass decreased by 89.05%in rice-fish treatment compared to rice treatment in 2006.The biomass and density decreased by 82.14%and 88.91%respectively in 2007.2 Mechanisms of pest and weed control by species diversityTo reveal why rice brown hopper density in rice-fish treatment were lower than that in rice monoculture,the relation between fishes and plant hopper was further examined through scanning technology.Results showed that predation and swimming activities of fishes could reduce the population of plant hopper in rice-fish co-culture system.Each hill of rice was hit by fishes 1.52 times and 4.9 plant hoppers fell down onto water surface and were eaten by fishes in one hour.Spiders,one of plant hopper's natural enemies,also contributed to plant hopper reduction by directly feeding on adult plant hoppers.3 Rice and fish productionThe yield of rice increased by 12.48%in rice-fish treatment compared to rice treatment.There was no significant difference among rice-fish treatment,rice monoculture treatment and conventional rice treatment.The yield of fish in rice-fish treatment was higher than that in fish treatment(only fish cultivated without rice) in both 2006 and 2007.4 Weed control by rice genetic diversityCompared to monocultures of non-suppressive rice varieties Xiushui No.63(XS), Zhongjian No.2(ZJ) and Chunjiang No.016(CJ),mixed-planting of non-suppressive rice varieties with weed-suppressive varieties Guodao No.1(GD) and PI312777(PI) could significantly reduce barnyard grass infections.Weed density and biomass were reduced by 28.9%-54.3%and 10.2%-40.8%respectively in mixtures compared to monocultures.Rice yield increased by 32%-115%in mixtures with non-suppressive rice varieties compared to monoculture.