Control Of Nitrogen And Phosphorus Loss From Paddy Fields By Carbon-based Fertilizer Substitution And Ecological Ditch Interception Approaches

The reduction of agricultural non-point source pollution is very important to improve the quality of agricultural water environment in China.This research is guided by source control and process intercept technology,supported by‘the Major Science and Technology Program for Water Pollution Control and Treatment’.Investigating the basic physical and chemical properties of paddy soils and monitoring the law of nitrogen and phosphorus loss of paddy fields runoff,examining the influence of carbon-based fertilizer application on nitrogen and phosphorus loss,exploring the interception effect of ecological ditch on nitrogen and phosphorus loss.It is expected to provide support for controlling nitrogen and phosphorus loss in intensive rice-growing areas.The main conclusions of this study are as follows:（1）According to the investigation in the paddy fields of experimental area,it was found that the application rate of chemical fertilizer in the local paddy fields was large,the soil total nitrogen and total phosphorus content and loss risk were high.It was found that the average fertilizer application rate reached 295 kg N hm^-2 and 60 kg P hm^-2.The average contents of total nitrogen and total phosphorus were 2.20 g kg^-1 and 0.60 g kg^-1,respectively.In two consecutive years,the monitoring results of nitrogen and phosphorus showed that the loss of nitrogen and phosphorus in paddy fields runoff was significantly affected by rainfall and fertilization.The average runoff values of total nitrogen（TN）and total phosphorus（TP）were 2.37 mg L^-1 and 0.35 mg L^-1,respectively.The main form of nitrogen loss was soluble nitrogen（DN）,while the main form of phosphorus was particulate phosphorus（PP）.（2）It was found that the application of carbon-based organic fertilizer had an obvious control effect on soil nutrient loss through the field verification experiment.There were four treatments about no fertilizer（CK）,conventional fertilization（CF）,carbon-based organic fertilizer replace 15%chemical fertilizer according to phosphorus content（OFSB15）,carbon-based organic fertilizer replace 30%chemical fertilizer according to phosphorus content（OFSB30）,respectively.The results showed that the window phase of nitrogen and phosphorus loss in runoff was within 7 days after fertilization.The loss load of TN and TP under CF treatment was 5.46 kg ha^-1 and 1.06kg ha^-1,respectively.Compared with CF,OFSB30 significantly reduced the load loss of TN（29.1%）and TP（10.1%）.（3）Ecological ditch could intercept nitrogen and phosphorus in paddy runoff.The adsorption capacity of TN and TP was 1.66 g kg^-1 and 1.03 g kg^-1,respectively,when the adsorption material reached saturation after 60 days.The average uptake of N and P of Thalia dealbata was 59.09 g plant^-1 and 5.19 g plant^-1 at the harvest stage,respectively.By monitoring 16 runoff events,the interception rates of TN,NH₄⁺-N,NO₃^--N,TP,PP and PO₄^3--P by ecological ditch were 42.1%,43.4%,36.5%,33.4%,51.3%,38.5%,respectively.