The integrated rice-duck co-culture is a type of integrated production system used in paddy fields and a major model of planting and breeding in south China, opening a new way of sustainable development for rice and waterfowl production. This paper discusses the effects of stocking rates of ducks on the species, quantities, diversity and biomass of algae. The field experiment was designed including conventional paddy ecosystem (CK) and rice-duck co-culture (RD).

The results showed 6 algal phyla (Cyanophyta, Chlorophyta, Bacillariophyta, Euglenophyta, Cryptophyta, Pyrrophyta), 57 algal genera and 108 species found in all paddy water during sampling period. The difference of the algal numbers in the two treatments was not obvious, but the algal density and biomass in RD was lower than those in CK. Under CK treatment, the predominant algal species during the early stages of rice growth were Merismopedia glanca, Sceaedsmus quadricauda, Euglena viridis, Cryptomonas erosa, but in the late stages (45th day after putting into ducks), the predominant species were Closterium acerosum, Cosmarium quadrum, Cosmarium formosulum, belonging to Chlorophyta phylum. However, the predominant algal species in RD were Euglena viridis, Euglena oxyuris, Phacus longicauda, belonging to Euglenophyta. Compared with CK, the algal density and biomass in RD decreased significantly within 15 days after putting into ducks. The content of total P increased, and the content of total N and the genus diversity reduced during the late periods of rice growth (45th day after putting into ducks). Correlation analysis between the algae and the environment factors showed that there were positive relationships between the content of total P, Euglenophyta density and the total biomass of algae.