Research On The Influence Of Rice Planting On The Water Body Of Rice Field And The Rice Soil

More people and less land is a major problem facing China,and the per capita arable land in China falls far short of international standards,so the pressure on food is enormous.In order to increase production on limited arable land,farmers apply a large amount of chemical fertilizers and pesticides during rice cultivation.Although the application of chemical fertilizers and pesticides can increase the yield,the residual chemical fertilizers and pesticides in the farmland will enter the receiving water body with surface runoff,especially in the tropical monsoon area,due to the high amount of rainfall,the frequent drainage of farmland will inevitably increase the risk of pollution of the surrounding environment,in addition if In addition,if rice soilheavy metals exceeds the standard,it will also increase the risk of riceheavy metals exceeding the standard.Therefore,the study of rice fieldwater body and rice soil quality in tropical monsoon area is of practical significance.In this study,five rice fields of five farmers in Ledong County,Hainan Province were used as research objects.（1）The analysis of residues of chlorpyrifos and deltamethrin in rice field water body were used to evaluate their pollution status in rice field water body,as well as the purification pattern of chlorpyrifos and deltamethrin in water body and their influencing factors were analyzed by simulated experiments;（2）The residues of chlorpyrifos and deltamethrin in（2）to monitor the content of heavy metals in water body of paddy fields at the time of rice nodulation（T1）and maturity（T2）,to investigate the distribution characteristics of the content of heavy metals in water body of paddy fields in different cultivation periods,and to evaluate the potential pollution risk of heavy metals in water body of paddy fields in different cultivation periods.（3）To monitor the content of carbon and nitrogen and heavy metals in rice soil at the time of rice nodulation（T1）and maturity（T2）,we also investigate the spatial and temporal distribution characteristics of carbon and nitrogen and heavy metals that in rice soil during different cultivation periods,the spatial and temporal distribution characteristics of rice soil were evaluated during different cultivation periods;（4）Analysis of sources of heavy metals in paddy soil.The main results were as follows The main findings are as follows:（1）The six types of heavy metals,including Cr,Cu,Zn,Cd,As and Pb,in the water bodies of five farmers’rice fields at the time of rice nodulation（T1）and maturity（T2）did not exceed the standard values,but the heavy metals Hg exceeded the standard values.The range of the single factor index of Hg in the paddy water of the five farmers was 2.0 to 3.3 and 1.3 to 2.0,respectively,and the maximum values were 3.3 and 2 times of the standard values of water quality in irrigated farmland,respectively.At the time of rice maturity,only the paddy water body of N5s was in light pollution,and the paddy water bodies of N1s to N4s were in moderate pollution.This indicates that the water body of paddy field will be polluted under the additive effect of several heavy metals.（2）After the first d of chlorpyrifos and deltamethrin application,the levels of chlorpyrifos and deltamethrin in the water bodies of five farmers’paddy fields exceeded the standards,and the levels of chlorpyrifos were 28.67 times、23.33 times、31.0 times、25.33 times、40 times higher than the standard value(0.03 ug.m L^-1);the levels of deltamethrin were 37.5 times、35.50 times、44.5 times、42.0 times、45 times higher than the standard value(0.02 ug.m L^-1).（3）The contents of TN and TOC in rice soil showed that the content of uprooting（T1）was higher than that of maturing（T2）,while the content of TC was slightly higher in maturing（T2）than that of uprooting（T1）.The highest values of TN,TC and TOC in rice soil were concentrated in the middle of the rice field（M2）,which were5.64,1.77 and 5.11 times higher than the background values（M0）in the study area,respectively;the content of TC and TN at the ridge（M4）was second only to the middle of the rice field（M2）.The TOC and TN contents of rice rice soil at the plucking and maturity stages in this study area were higher than the organic carbon contents of rice soil in the Sichuan basin and red soil rice soil in Jiangxi;but lower than the organic carbon contents of rice soil in the Heilongjiang region,Taihu Lake region and Dongting Lake region.The rice soil in the study area was at an intermediate level and showed accumulation,and the accumulation level of TN in rice soil was higher than that of TOC.The C/N values of rice soil at the rice nodulation stage（T1）and maturity stage（T2）were lower,ranging from 11.99 to 15.47 and 11.20 to 16.65,respectively,indicating that the rate of organic matter decomposition and mineralization of rice soil at the rice nodulation and maturity stages was greater than the accumulation rate,which was not conducive to the accumulation of organic matter.（4）The contents of heavy metals Zn,Ni,Hg,As,and Cd in the rice soil of the five farmers were basically the highest in the middle of the paddy（M2）,the second highest at the ridge（M4）,followed by the diagonal of the drainage outlet（M1）,and the lowest at the drainage outlet（M3）.At the rice plucking stage（T1）and maturity stage（T2）,Cd in five farmers’rice soil was 1.95 times、2.1 times、2.18 times、1.83 times、2.18 times and 1.95 times、2.03 times、1.58 times、1.6 times、1.58 times of the standard limits for soil pollution risk control of agricultural land for soil environmental quality;and 14.60 to17.40 times and 12.60 to 16.20 times of the background values of soil environmental elements in Hainan Province.（5）Geo-accumulation index and potential ecological risk index were applied to evaluate tne paddy soil of farmers,the geological accumulation index showed that the I_geoof Cd was greater than 3 at both the rice nodulation and maturity stages,and100%of the sampling sites were in strong contamination;at the rice nodulation stage,the I_geoof Cr in the five farmers’rice soil was greater than 1,and the rice soil was in moderate contamination;at the rice maturity stage,the I_geoof Cr was greater than 0,and 40%of the sampling sites In addition,some farmers were also contaminated with Cu and As,and they were in light-medium contamination at the rice nodulation and maturity stages;the Igeo of Ni,Zn and Pb in the rice soil of five farmers were≤0,and they were in no contamination.The potential ecological risk parameters（Eir）of Cd in rice soil at the rice nodulation（T1）and maturity（T2）were all greater than 240,which were at very high risk of pollution;while the Eir of single metals of Cr,Ni,Cu,Zn,As,and Pb were all less than 30,which were at no risk.In terms of the potential ecological pollution index of multiple metals（RI）,the multiple metals in the rice soil of all five farmers at the time of rice nodulation was greater than 440,which was at very high risk of pollution;at the time of rice maturity（T2）,40%of the sampling points had RI values greater than 440,which was at very high risk of pollution,and 60%of the sampling points had RI values less than 440,which was at high risk of It can be seen that the pollution of heavy metals Cd in rice soil is serious.（6）Correlation analysis showed that TN,TOC and Cr,Zn,As,Hg,Pb and Cd in rice soil were significantly correlated with each other,and the correlation coefficient was above 0.9,with the highest value reaching 0.984;heavy metals Pb was significantly correlated with Cr,Cd,As and Hg,with the highest value reaching 0.995.This indicates that these elements are closely related,have common influencing factors and may have similar sources.The tests on various fertilizers applied by farmers showed that the content of heavy metals Cr,Cu,Zn,As,Hg,Pb,and Cd in phosphate fertilizers and compound fertilizers was high,among which the content of heavy metals Cd,Zn,and Hg exceeded the limit value of soil environmental quality soil pollution risk control standard for agricultural land,and the exceedance rates were 30%,20%and 50%respectively.Among the three fertilizers applied,phosphate fertilizer had the highest content of heavy metals Cd and Hg,with Cd 5.05 times and Hg 1.58 times of the standard value;compound fertilizer had the second highest content,with heavy metals Zn and Hg 1.64 times and Hg 1.08 times of the standard value;urea had the lowest content of heavy metals content was the lowest,and none of them exceeded the limit value of the soil pollution risk control standard for agricultural land of soil environmental quality.（7）Simulation experiments on the degradation of deltamethrin and chlorpyrifos showed that basalt and sand placed in the water body had a certain effect on the purification of deltamethrin and chlorpyrifos;and the purification effect of sand was better than that of basalt.The alkaline environment helps to accelerate the purification of chlorpyrifos and deltamethrin in water body.