A Comparison Of Nitrogen Transfer And Transformation In Conventional Rice Cultivation And The Rice-Duck Farming System By ¹⁵N Tracer Method

Rice is an important staple food and is also the most important cereal for a large population in the world.In China,rice accounts for a large proportion of total grain production.However,cultivable natural land resources are limited.In order to respond to food security and the growing population more strategies are required.The integrated rice-duck farming system has been recommend into cultivation practices in many Asian countries,particularly Japan,China,Indonesia,Vietnam,Korea,and the Philippines.Rice-duck co-culture in a paddy rice creates a yield-increasing for rice production and,more importantly,duck breeding.Thus,the rice-duck mutualism system may benefit for rice growing and duck breeding.Compared to conventional rice farming,rice-duck co-culture is considered as one of the forms of organic agriculture.Ducks in paddy field play several roles.For example ducks are very strong predators that prey on insects,weeds,and small animals such as golden apple snails.Duck activities include walking,swimming,eating,grooming,paddling,and rubbing improve microclimate,and rice disease prevention.However,this study not only emphasize on the mutualism benefit rice-duck farming,and conventional farming,but also the effect of chemical fertilizer applied alone,chemical and organic fertilizer applied in combination,chemical fertilizer 30%decreased and organic fertilizer the amount unchanged.Therefore,except the effect of ducks in the field,this study also demonstrated the importance of organic fertilizer in the field over chemical fertilizer.Farmers often employ fertilizers in excessive quantity in order to increase plant production and ignore environmental threats.But,in our study the amount of chemical fertilizer was reduced in order to avoid heavy N loss to the environmental.Moreover,inappropriate use of fertilizers may cause damage to the health of soil and also to the plant growth.In our field study,eight（8）treatments were established at both duck and without duck field as follows:CK-ND（Control+no-duck）,CK-D（Control+ducks）,CF-ND（Chemical fertilizer+no-duck）,CF-D（Chemical fertilizer+ducks）,CM-ND（Chemical fertilizer+organic fertilizer+no-duck）,CM-D（Chemical fertilizer+organic fertilizer+ducks）,CD-ND（Chemical fertilizer 30%off+organic fertilizer+no-duck）,and CD-D（Chemical fertilizer 30%off+organic fertilizer+ducks）.Greenhouse pot experiment included six rice varieties,Jin U99（JU 99）,Jinyuan 98（JY 98）,Jindao 89（JD 18）,Jinyuan（JY 89）,Jinhei 1（JH 1）,Jindao 201（JD 201）,separated into duck and no-duck soil.N and P concentration of rice plant organs were measured.The objectives of this doctoral dissertation were as follows:1.to evaluate the ecological effects of duck presence or absence on N and P concentration in rice field,2.to demonstrate the application effect of organic fertilizer in the field,3.to determine N uptake by rice and N use efficiency,4.to measure ¹⁵N abundance in plant and soil.We highlighted the important results and conclusions as follow:1.In the first rice season（2017）,grain N concentration significantly differed amongControl（CK）,chemical fertilizer（CF）,chemical and organic fertilizer（CM）when comparing the presence and the absence of ducks in the field,whereas chemical fertilizer 30%off and organic fertilizer（CD）did not differ significantly between duck and no-duck in the field.Straw N concentration was not affected whether ducks were present in the field or not.Neither grain or straw N concentration nor leaf and root P concentration was affected by the presence of ducks.Our results showed that the presence of ducks alone did not show any significant differences between treatments.2.Effects of organic fertilizer:in most of our results whether chemical and organic fertilizer in combination（CM）or chemical fertilizer 30%off and organic fertilizer（CD）was higher over chemical fertilizer applied alone（CF）and control（CK）.3.The means comparison of variance analysis between ducks presence and ducks absence on rice land showed significant differences on rice,fresh grain,and fresh husk yield.4.N concentration in rice season 2（2018）in grain,leaf,and root N concentration significantly differed among duck and without duck treatment,whereas straw N concentration was not significantly affected whether ducks were present in the field or not.5.There were interactive effects between duck levels and treatment on grain and leaf N concentration in 2017,while there was an interactive effect between duck levels and treatment only on leaf N concentration compared to other parts of rice plant.However,there was no interactive effect between year and treatment in all rice plant organs with ducks presence on rice land.In contrast,there were interactive effects between year and treatment on grain and leaf N concentration in the absence of ducks.There were interactive effects between year and chemical fertilizer（CF）on grain,straw,and leaf N concentration,whereas root was not affected.The interactive effect between year,chemical fertilizer and organic fertilizer（CM）was observed on grain and root N concentration,whereas straw and leaf were not affected.Grain,straw,leaf,and root N concentrations were not affected by the interaction between year and chemical fertilizer 30%off and organic fertilizer（CD）.The interaction between year,duck levels and treatment significantly affected leaf N concentration.6.The results of greenhouse pot experiment showed that the mean N content of Japonica rice varieties grown under duck’s soil was higher when compared to the same varieties grown under no-duck soil.7.Total ¹⁵N was significantly affected among treatments by the presence of ducks in the field at0-20cm soil layer,while total ¹⁵N was not significantly affected by the presence of ducks at 20-40cm soil layer.Likewise,total ¹⁵N was not significantly affected by the absence of ducks in the field at0-20cm or 20-40cm soil layer.Grain,straw,leaf,and root ¹⁵N-labelled indicate different trend when ducks were present or not.In addition,the percentage of nitrogen derived from the soil with ducks and without duck in the field was higher than that nitrogen derived from the fertilizer.Furthermore,N uptake and N use efficiency were not significantly affected whether ducks were in the field or not.Based on our results,this study elucidated the mutualism benefit of rice-duck farming system in paddy field and also demonstrated the importance of organic fertilizer in the field.