Effects Of The Reduction Of Nitrogen And Phosphorus Application And Ecological Ditch Interception On Nitrogen And Phosphorus Non-point Source Pollution In Farmland

Long term excessive fertilization has brought serious environmental problems.It is an important measure to prevent and control agricultural non-point source pollution by controlling nitrogen and phosphorus loss in farmland and constructing ecological ditch to eliminate nitrogen and phosphorus in water body.With two years field experiments,we studied the effects of nitrogen and phosphate reduction on middle rice growth and nitrogen and phosphorus loss in paddy field surface water.In the meantime,with ecological ditch and intercepting test,the effect of ecological ditch on the interception and elimination of nitrogen and phosphorus were also demonstrated in a small watershed.The main conclusions are as follows:1.Effects of nitrogen and phosphorus application on yield and nutrient uptake in middle season riceThere were five fertilization applications in this study: CK: no N and P fertilizer,Com:conventional fertilizer,0.8N: controlled release urea with 20% N reduction,0.8NP:controlled release urea with 20% N and 20% P reduction,and 0.8OM+0.2FN: organic manure substitution 20% fertilizer N.The results showed that both N and P fertilizer can significantly increase middle rice yield.Compared to the control,the yield of four fertilizer applications increased by 18.31%,21.62%,19.59%,14.97% respectively,though there was no significant differences between the four treatments.During this two years,compared with the Com treatment,the yield of 0.8N and 0.8NP increased by 5.55% and 3.22% respectively,while 0.8OM+0.2FN reduced by 20% on average.Compared with conventional fertilization,the shoot N accumulation of 0.8N and 0.8NP applications increased by 19.01% and 13.66%,and N partial factor productivity(NPFP)increased by 31.94% and 28.83%,and N agronomy efficiency increased by 47.52% and33.75%,and N utilization efficiency increased by 95.30% and 73.31%.Compared with the0.8N treatment,0.8NP increased PPFP by 22.08%,but with little effect on shoot P accumulation and PUE.When added with organic manure,0.8OM+0.2FN treatment decreased P accumulation and PUE by 11.14% and 36.04% respectively.However,the Naccumulation,NPFP,N agronomy efficiency,NUE,PPFP and P agronomy efficiency were less affected by 0.8FN+0.2ON manipulation.2.Effects of the reduction of nitrogen and phosphorus application on nitrogen and phosphorus content in paddy field waterThe main form of nitrogen in field water is ammonium.The application of ordinary urea will rapidly increase total nitrogen content in field water.The application of controlled release nitrogen fertilizer could obviously reduce the nitrogen content in the field water.The total nitrogen concentration in the 20%-reduction controlled release nitrogen treatment decreased by 93.69 and 89.76% in the 9 days after the base fertilizer,and the average decreased by 84.09 and 79.64% in the 17 day after fertilizer application in the two experiments,respectively.The total phosphorus content in the field water increased rapidly to the maximum after the fertilizer application and then decreased quickly.The reduction of the amount of phosphate fertilizer can reduce the total phosphorus content in field water.3.Effects of ecological ditch on nitrogen and phosphorus interception in small watershedThe ecological ditch can effectively intercept the nitrogen and phosphorus in the runoff water.In two years,the average removal rate of total nitrogen in the channel is 58.49% and47.61% respectively.The average removal rate of ammonium nitrogen is 77.29% and69.72% respectively.The average removal rate of nitrate nitrogen is 58.77% and 47.79%,respectively.The average removal rate of total phosphorus is 67.07% and 54.47%respectively.4.Removal rate of nitrogen and phosphorus in ditch with different interception plant speciesThe removal rate of total nitrogen,ammonium nitrogen,nitrate nitrogen and total phosphorus per square meter in the ditch with different interceptor plant species all showed:the treatment with myriophyllum spicatum + pontederia cordata > pontederia cordata >sorbaria sorbifolia > myriophyllum spicatum > natural vegetation.Pontederia cordata had good effect when using single plant species,which would be better when combining with myriophyllum spicatum.