Soil Nitrogen And Phosphorus Leaching Characteristics Of Typical Land Use Types In The Three Gorges Reservoir Area

The Three Gorges Reservoir area is not only an important water source protection area in China,but also a strategic water resource bank.At present,due to the excessive application of chemical fertilizer to the economic returns of the garden area,the soil nutrients such as nitrogen and phosphorus enter the water body of the reservoir area,which leads to the serious eutrophication of the water body of the reservoir area and the frequent occurrence of "water bloom" in the tributaries.Runoff loss is the main way of soil nutrient loss.During the early stage of monitoring and research,soil nitrogen and phosphorus surface runoff loads were paid more attention,and soil nutrient leaching process was also an important way of nutrient transport.Based on the analysis of the related data of land use types in the Three Gorges Reservoir area,and after the investigation of agricultural activities,the area of the garden area?tea garden,citrus garden and chestnut garden?and the types of farmland were selected.The 6 treatments were as follows: no fertilization(0kg N·hm^-2,0kg P2O5·hm^-2),reduced fertilization(250kg N·hm^-2,0kg P2O5·hm^-2),constant fertilization(500kg N·hm^-2,0kg P2O5·hm^-2)and incremental fertilization(750kg N·hm^-2,0kg P2O5·hm^-2),constant compound A fertilization(500kg N·hm^-2,250 kg P2O5·hm^-2),constant compound B fertilization(500kg N·hm^-2,138.89 kg P2O5·hm^-2).The characteristics and regularity of nitrogen and phosphorus leaching loss under different fertilization conditions and soil depth were studied by the method of soil column simulation test?soil column height: 20 cm,40cm,60cm?.The response of soil nitrogen and phosphorus leaching solution concentration and load to the change of fertilizer amount and the distribution characteristics of soil layers were revealed.The amount of fertilizer and its corresponding control way.The conclusion of the experiment is as follows:?1?the effect of fertilizer amount on the leaching concentration of nitrogen and phosphorus.Under different nitrogen application,the average range of total nitrogen leaching concentration in soil column soil of 4 land use types is 48.52¹10.81 mg·L^-1.The average range of nitrate leaching concentration is 26.23⁵4.40 mg·L^-1,the proportion of total nitrogen is 54.06%⁶0.46%,the average range of ammonium nitrogen leaching concentration is 2.67⁵.89 mg·L^-1,and the proportion of total nitrogen is 5.50%⁶.36% in 60 cm soil column soil..The order of leaching of total nitrogen,nitrate nitrogen and ammonium nitrogen is incremental fertilization > constant fertilization > reduced fertilization > no fertilization.Nitrate nitrogen is the main leaching form in nitrogen,accounting for more than 50% of total nitrogen.Under constant fertilization,nitrate nitrogen and ammonium nitrogen account for the largest proportion of total nitrogen.The average phosphorus leaching loss of total phosphorus was 0.35⁰.85 kg·hm^-2,and the leaching loss of total phosphorus was 1.99³.61 mg·L^-1 without fertilizer application,constant compound A and constant compound B.The order of total phosphorus leaching and leaching is constant A,constant B and no fertilizer.The results of the experiment showed that the amount of nitrogen and phosphorus leaching could be increased significantly,and the conversion of nitrate nitrogen and ammonium nitrogen could be inhibited after the amount of fertilizer reached a certain degree.?2?soil nitrogen and phosphorus leaching and loss of land use typesThe leaching amount of total nitrogen in the 60 cm soil column of citrus orchard,agricultural land,tea garden and chestnut forest were 11.75³0.79,10.79²6.30,8.88²4.61,10.12²2.70kg·hm^-2,and the total nitrogen leaching concentration was 37.16¹63.07,30.68¹47.33,40.9¹38.22,29.65¹24.07 mg·L^-1.The leaching amount of total phosphorus in the 60 cm soil column of citrus orchard,agricultural land,tea garden and chestnut forest were 0.42¹.29,0.27⁰.89,0.29⁰.80,0.27⁰.51kg·hm^-2,and the concentration of total phosphorus leaching was 1.07⁷.69,0.92⁵.62,1.04⁵.99,0.83³.11mg·L^-1.The order of total nitrogen leaching loss and leaching concentration are citrus orchard,agricultural land,tea garden and chestnut forest.The order of total phosphorus leaching loss and leaching concentration are citrus orchard,tea garden,agricultural land and chestnut forest.There is no significant difference in the leaching loss and leaching rate of total nitrogen and total phosphorus in 4 typical land use types.In this experiment,land use type has no significant influence on soil nitrogen and phosphorus leaching loss,not the main influence factor.?3?soil layer distribution of soil nitrogen and phosphorus leaching lossThe average total nitrogen leaching loss in 20 cm soil column is 165.00 kg·hm^-2,the total phosphorus leaching loss of total phosphorus is 5.05 kg·hm^-2,nitrate nitrogen is 49.95% of total nitrogen,and ammonium nitrogen is 5.50% of total nitrogen.The average total nitrogen leaching loss in 40 cm soil column is 114.13 kg·hm^-2,the total phosphorus leaching loss of total phosphorus is 3.98 kg·hm^-2,nitrate nitrogen is 53.36% of total nitrogen,and ammonium nitrogen is 6.61% of total nitrogen.The average total nitrogen leaching loss in 60 cm soil column is 126.89 kg·hm^-2,the total phosphorus leaching loss of total phosphorus is 3.65 kg·hm^-2,nitrate nitrogen is 51.75% of total nitrogen,and ammonium nitrogen is 5.96% of total nitrogen.There is no significant difference in the leaching amount of total nitrogen and total phosphorus under the depth of the 3 soil columns.In this experiment,the depth of soil column has no significant influence on the leaching loss and leaching rate of soil nitrogen and phosphorus,not the main influencing factor of nitrogen and phosphorus leaching.However,the depth of soil column affects the migration and transformation process of ammonium nitrogen and nitrate nitrogen in soil.According to the above test results,fertilization is the main factor affecting soil nitrogen and phosphorus leaching.The amount of nitrogen and phosphorus leaching in soil decreased significantly,reduced the risk of eutrophication in the reservoir area,increased the effective utilization of fertilizer,and slowed down the pollution of agricultural non-point sources in the reservoir area to a certain extent,and provided data support for the research on rational fertilization in the vicinity of the reservoir area.