Characteristics Of Nitrogen And Phosphorus Runoff In Dryland Cropland Of The Pearl River Delta And The Effect Of Ecological Ditch Resistance And Control

In recent years,agricultural non-point source pollution has seriously threatened the quality safety of water environment,and it has become an important factor affecting nitrogen?N?and phosphorus?P?pollution in water bodies.Therefore,such as the comprehensive policy,the implementation of"source-control-end reduction treatment"on N and P pollution became an important strategy for the prevention and controlling of N and P pollution in cropland.Meanwhile,the characteristics of N and P runoff in cropland were systematically investigated under different planting patterns,and the effects of ecological ditches,constructed wetlands and ponds on controlling of N and P runoff in cropland were also studied.These will help to further understand N and P runoff,migration mechanism and purification effect of cropland,which is also important significance for the prevention of agricultural non-point source pollution caused by N and P runoff in cropland.In this paper,the fertilization reduction and non-point source pollution control of typical dryland sweet corn in the Pearl River Delta were studied.At first,the formula fertilizer,organic fertilizer,bio-charcoal and controlled release fertilizer was used for reducing the amount of conventional fertilizer?CF?and controlling the generation of non-point source pollution from the source.Meanwhile,the crop yield and N and P runoff characteristics using different fertilization treatments were also analyzed.In addition,the plant selection of ecological ditches was carried out and the simulation experiment of controlling N and P in water by ecological ditches was also conducted.The major conclusions are given below:?1?The amount of nitrogen fertilizer used in CF was reduced by 20%and that of phosphate fertilizer was reduced by 57.6%.OFFF has a significant yield increase effect compared with CF,with increasing yield by 17.8%.The enhanced effect of OFFF with yield was the most significant.?2?The total nitrogen?TN?concentration and runoff of surface runoff during the growth period of sweet corn showed a gradual decline trend,and the total amount of N lost by CF was the highest,reaching 3.48 kg/hm².The TN runoff of sweet corn using reduced fertilization decreased significantly,with a decrease of 36.49%⁵0.86%,but the effect of treatment with FF was the best?with a decrease of 50.86%?.The main form of N runoff from surface runoff was nitrate nitrogen?NO₃^--N?,which accounts for 35.09%-61.18%of the total nitrogen runoff.The total phosphorus?TP?runoff of CF was the highest,reaching 0.045kg/hm².?3?Thaliadealbata,Cyperusalternifolius,Echinodorus major and Hydrilla verticillate had a large amount of growth under static conditions,and these plants had strong absorption capacity for nitrogen and phosphorus.TN removal rates of Thaliadealbata and Cyperusalternifolius were 98.5%and 63.89%,respectively.While TP removal rates of Thaliadealbata,Echinodorus major and Hydrilla verticillata were 81.87%,81.21%and69.62%,respectively.?4?The effect of N and P removal on the ecological ditches was related to the influent flow.Under different influent flows,the biomass growth of C2?Thalia dealbata-Eichhorniacrassipes-Hydrilla verticillata?was higher than that of C1?Thalia dealbata-Pistia stratiotes-Echinodorus major?,but the absorption of N and P by C1 was higher than that of C2.In general,a low influent flow rate?60 L/h?was favorable to the plant growth and resistance to N and P.Under this flow rate,within 26 day,TN removal rates of C1 and C2 in ecological ditches were 36.74%and 34.91%,respectively.The removal rate of NH₄⁺-N was over 97%and TP removal rate was over 95%.TP with NH₄⁺-N concentrations reached the national surface water environmental quality standard II and I,respectively.