| The co-cultivation of rice and fish is an integrated agri-aquaculture system(IAAS)that combines rice cultivation with aquaculture.The transformed rice paddy are used for planting and farming activities to form a rice-fishing coculture system.Through the mutual benefit of rice and fish coculture,it is possible to produce green and ecological agricultural products under the premise of effectively reducing the application amount of pesticides and chemical fertilizers,thereby achieving the goal of increasing rice yield and increasing income,and is a sustainable agricultural model.This model provides an opportunity to improve the economic benefits and farmers'income,improve the quality and safety of production from the paddy and improve the ecological environment of the paddy.The Qingtian rice-fish coculture system in Qingtian County,Zhejiang Province has a long history and deep roots.It began in the Tang Dynasty and has a history of more than 1,300 years.So,it is an original ecological agricultural method.In 2005,Food and Agriculture Organization of the United Nations(FAO)established the Qingtian rice-fish coculture system as the first pilot site of Global Important Agriculture Heritage System(GIAHS),which advocates“dynamic protection”for agricultural heritage systems.The meaning of dynamic protection is that the innovation and optimization under the premise of protection can be allowed.Based on this concept,it is feasible and necessary to rationally optimize it after scientific research.The reasonable optimization can improve production efficiency of the coculture system and farmers'enthusiasm for production,and it is beneficial to better inherit and retain the system.At present,most of the researches on this traditional system focus on investigation.There are few reports on the density of rice in this coculture system and the reports have evaluated the yield of rice and fish under different rice cultivation densities.The research on the growth of the rice and fish(Cyprinus carpio var.color),nutritional value of fish and the quantification of soil fertility is rare,which makes the study of rice cultivation density in the Qingtian rice-fish coculture system lack systematic and comprehensive scientific basis.From the perspective of rice,fish and soil nutrient,our study tracked the growth,stem traits and yield of rice in the rice-fish coculture system under different rice cultivation densities,and compared the survival rate,specific growth rate and muscle nutrients of the fish under different rice densities,and also explored the variation of soil nutrient content under different rice densities.The purpose was to comprehensively evaluate different rice cultivation densities and find the best value.Three density treatments were set up by controlled the row spacing of rice:20 cm×30 cm,30 cm×30 cm and 40 cm×30 cm,which were recorded as high,medium and low density,respectively.Each treatment was set up with 3 parallels.Two seeding per hill in the paddy.After 20 days of rice transplanting,the fish were placed at a density of 9000/hm~2,with a specification of 50 g/tail and uniform size.Three days after the release of the fish,the feed was started,and the daily feed amount was 2~5%of the weight of the squid.The feed was fed twice in the morning and evening,and the feed amount was increased according to the growth and feeding of the fish.The main findings are as follows:1.The tiller number and biomass of rice under low density(40 cm×30 cm)were significantly higher than those of the high density groups after elongation stage.And there was obvious advantages of the rice stem characters under low density(40 cm×30cm)among the 3 densities;the cultivation density had no significant effect on rice yield,but the highest rice yield was in the high density;the number of effective panicles in the low density was significantly higher than that in the high density,and panicle setting rate in the low density was significantly higher than that in the medium and high density.The grey correlation analysis showed that the greatest correlation with rice yield was the panicle length among the rice stem characters,and the greatest correlation with rice yield was the 1000-grain weight among rice yield compositions.Based on rice growth and production efficiency considerations,the Qingtian rice-fish coculture system can use low-density(40 cm×30 cm)to save labor costs while ensuring rice yield.2.The specific growth rate(SGR)of fish reached the highest value(4.54±0.03)in the medium density(30 cm×30 cm),which was extremely significantly higher than that in the high density(20 cm×30 cm)(3.62±0.04).The survival rate(SR)of fish was not significantly different among treatments.The nutritional value of fish in the paddy fields was excellent on the whole,and the contents of crude fat(CF),crude protein(CP),amino acid(AA)and fatty acid(FA)were not significantly different among the treatments.The content of essential amino acid(EAA)in fish muscle under the high,medium and low rice cultivation densities were(37.35±1.07)%,(37.35±0.27)%,(32.20±1.29)%,respectively.The first limiting amino acids were Met;the total essential amino acid(TEAA)and the essential amino acid index(EAAI)in the medium and high density were all slightly higher than those in the low density.The contents of polyunsaturated fatty acid(PUFA)included in fish muscle under the medium and low density were all slightly higher than that under the high density.3.The pH of the tested paddy soil was varied between 5.50~6.13,which was weakly acidic.The contents of soil nutrients(such as the soil total nitrogen,soil organic matter,available phosphorus and available potassium)decreased until and reached the lowest values at the booting stage,which were recovered to the similar higher levels with the initial before rice harvesting,indicating that the activity of the field fish and perhaps fish feces could help maintain the soil fertility.According to the results of Grey relational analysis(GRA)between rice yield and soil nutrient,it was found that soil pH and available potassium were most closely related to rice yield.Compared with the richful nitrogen,available phosphorus and soil organic matter,the less suficiently available potassium and low pH might be responsible for the limited growth and yield of rice.On the whole,in our trial of the Qingtian rice-fish coculture in this season,the optimal rice density was 30 cm×30 cm. |
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