Ecological Functions Of Cultivated Species Interaction In Farming System

The intensified use of agrochemicals e.g. herbicides, pesticides and inorganic fertilizers, and the simplification of crop species or varieties in modernized agricultural systems have produced some by-side effects such as environmental pollution and emergence of agrochemical-resistant population of weeds, pests and diseases. Species diversified cropping systems or farming systems by increasing the number of crop species grown has been concerned and proposed as a solution of these problems currently. As a major agricultural country, China has a long history of farming with diversified farming systems such as diverse crop variety mixture, intercropping and crops coexisting with animals. However, what ecological effects of species interaction in the species-diversified farming systems and how species interaction impacts on production of the farming systems were less known. Therefore, field experiments were conducted to exam species interaction and their effects in a Chinese 1200-year-history traditional rice-fish system, which was listed by FAO and UNDP as Globally-important Ingenious Agriculture Heritage Systems (GIAHS) in 2005. The results are as follows.1 Rice and fish productionFor rice production) tiller numbers per rice plant and yield in rice-fish cropping pattern were significantly higher than that in the monoculture of rice plant. Rice yield in rice-fish treatment increased by 12.48% compared to monoculture of rice plant.For fish production, growth rate of fish and gross fish production in rice-fish treatment were significantly higher than that in single pisciculture and rice-fish system with artificial pollen-free. Fish production decreased by 13.79% and 36.28% respectively under single pisciculture treatment and pollen-free rice-fish system compared to rice-fish treatment.2 Pest and weed controlPopulation of rice brown hopper was significantly restrained by rice-fish interaction in this experiment. Numbers of rice brown hopper under rice-fish treatment were significantly lower than that under single rice treatment. Rice brown hopper density decreased by 48.84% in rice-fish system compared to monoculture of rice plant. Weedy species occurred in rice field during the experiment mainly were Echinochloa oryzicola (Ard.) Fritsch, (Heleocharis plantagineiformis Tang et Wang), (Salvinia natans) , (Leptochloa chinensis (Linn.) Nees). Monochoria vaginalis (Burm.f.) Presl.ex Kunth. No difference was found in species component of weed community but significant difference of total weed density was found among various treatments. During the experiment total weed density were significantly higher under rice-fish treatment than that in the monoculture of rice plant. One week after rice harvested, total weed biomass in rice monoculture plot was 56.01g/ m² while in rice-fish plot it was only 6.14g/m². Total weed biomass decreased by 89.05% in rice-fish plots compared to single rice plots.3 Micro-environmental states in rice fieldIn higher temperature season during the experiment, field water temperature measured in the morning, at noon and in the evening was significantly lower in the experimental plots with rice covering than the plots without rice covering. Compared to rice plant cover-free fish plots, water temperature in rice-fish plots was lower by 0.43℃,2.60℃and 0.78℃in the morning, at noon and in the evening respectively. Rice plant cover in field provided shade for fishes in the rice-fish plots. Compared to the fish monoculture plots without rice cover, solar radiation intensity in the rice-fish plots decreased by 1820-2800μmol.m^-2.s^-1. No significant difference of dissolved oxygen was found between fish monoculture treatment and rice-fish treatment. However, dissolved oxygen increased by 13.25% in rice-fish plots compared to rice monoculture plots, implying that fish activity could enhance oxygen diffluence into water in the rice-fish system.4 A comprehensive evaluation of modern and traditional rice varieties in rice-fish systemOur experiment showed that modern and traditional rice varieties differed in some agronomical traits. Generally speaking, modern variety (e.g. hybrid rice) possessed of ideal plant type and showed the advantage in dry matter production. However, in rice-fish system with low fertilizer and agricultural chemicals input, no significant difference of rice yield between modern variety and traditional variety was found. Among traditional varieties, some types (e.g. glutinous rice) presented highly resistance to pest and weed infestation, implying that traditional variety could be also used in rice-fish system and diversify the genetic background of this rice-fish system.