Effects Of Different Fertilization Treatments On Nitrogen And Phosphorus Loss And Crop Benefit In Purple Soil Of Arid Sloping Farmland

The Three Gorges Reservoir?TGR?area is an important agricultural production area and a population gathering area at the upper reaches of the Yangtze river,as well as a relatively eco-fragile region in China.The water quality of the TGR area has directly influence on the health of downstream residents and the sustainable development of economy.However,most of farmlands of the TGR area are sloping farmlands,which pose a conflict between living and farming.Moreover,the sediment loss from sloping farmland erosion accounts for 73%of total soil erosion at the TGR area in one year.Therefore,the controlling of soil erosion,non-point source pollution and the quality improvement of farmland at the TGR area are necessary and urgent.Excessive fertilization is a major source of non-point source pollution in agricultural area.High input of mineral fertilizers not only promotes the emission of greenhouse gases?e.g.,nitrous oxide?,but also results potential eutrophication risk by nutrient leaching?e.g.,nitrate and phosphate?from soil.Currently,studies related to the effects on mineral fertilizer reduction coupling with biochar or straw incorporation on nutrients retention have been reported.However,the most of studies were focused on paddy soils;few study has been conducted on the arid sloping farmland with purple soil.This study was conducted at the Zhongxian station of Chengdu Mountains Institute of Chinese Academy of Sciences.Sloping farmland with purple soil was selected and runoff plot?projection area of 100 m²?method was used to study the effect of biochar and straw combined with different mineral fertilizer application on soil nitrogen and phosphorus loss at two slope conditions?10°and 15°?.Rape/maize rotated plantation was used and five fertilizer treatments?no fertilizer?CK?,conventional fertilization,optimized fertilization,reducing fertilizer coupling with biochar?referred as?biochar treatment??,and reducing fertilizer coupling with straw?referred as?straw treatment???were included.The effects of biochar and straw mulching on the reduction of soil nitrogen and phosphorus nutrient loss and plant benefits were further analyzed in combination with soil nitrogen and phosphorus content measurement,plant yield and fertilizer agronomic efficiency calculation during cultivation.in order to provide scientific understandings on nutrients management in purple soil of sloping farmland.Main results are as follows:?1?During the experiment?from November 2017 to October 2018?,the total runoff in the straw treatment?9515 L?was the lowest at 10°plots among different fertilizer treatments.The largest total runoff at 10°plots was found in the optimized fertilization treatment with 20737 L.In 15°plots,the largest and lowest total runoff were found in the conventional fertilization treatment?16133 L?and biochar treatment?11893 L?,respectively.With the exception of straw treatment,the total runoff in10°plots were all higher than those in 15°plots.Subsurface flow was the dominated runoff which contributed 60.14⁸8.56%of total runoff.All fertilization treatments reduced soil erosion in both10°and 15°slope plots.Straw treatment reduced surface runoff and sediment erosion effectively.?2?Surface runoff was the major way for ammonium nitrogen?AN?loss.The loss fluxes of AN in 10°plots ranged from 0.16 to 0.85 kg·hm^-2·a^-1,which accounted 79.91⁹4.04%of total loss fluxes.In the plots with a slop of 15°,the loss fluxes for AN ranged from 0.17 to 0.69 kg·hm^-2·a^-1and accounted 82.23⁹6.58%of total loss fluxes.Among different treatments,the highest loss fluxes were all found in the biochar treatment at two slopes.Fertilization increased the concentration of particulate nitrogen?PN?in the runoff,and the highest loss fluxes for PN were found in the optimized fertilization(1.753 kg·hm^-2·a^-1)and conventional fertilization(2.874 kg·hm^-2·a^-1)treatments for 10°and 15°plots,respectively.Straw treatment reduced the loss fluxes of PN than those of other treatments both at 10°and 15°plots.Significant positive correlations between total nitrogen?TN?and nitrate nitrogen?NN?concentrations under different fertilization treatments were found.Nitrate nitrogen was the dominant species in TN and mainly lose by subsurface flow in soil.The loss fluxes for TN in subsurface flow accounted for 86.56⁹5.93%and 72.88⁹2.35%for 10°and 15°plots,respectively.The maximum loss flux of TN was found in the conventional fertilization treatment(61.30 kg·hm^-2·a^-11 for 10°plots and 35.58 kg·hm^-2·a^-11 for 15°plots).The minimum loss flux of TN was found in the straw treatment(18.31 kg·hm^-2·a^-11 for 10°plots and 20.07 kg·hm^-2·a^-1for 15°plots).Straw application reduced soil nitrogen loss in purple soil of arid sloping farmland,while biochar application increased soil nitrogen loss in surface runoff.?3?In the arid sloping farmland with purple soil,surface runoff was the major way for phosphate loss.Under the same fertilizer treatment,the phosphate loss fluxes of 10°and 15°plots accounted 55.35⁸7.49%and 59.85⁸8.83%for total loss flux,respectively.Straw treatment reduced the loss flux of phosphate for 63.67%and 63.37%in 10°and 15°plots,respectively.With the exceptions of CK and the conventional fertilization treatments,the loss fluxes of phosphate at15°plots were lower than those at 10°plots.The loss flux of particulate phosphorus?PP?was found increased by fertilization.The largest increase of PP loss fluxes were found in the conventional fertilization treatment at 10°plots and the biochar treatment at 15°plots.While,straw treatment decreased the PP loss flux effectively,which decreased 60.28%and 85.56%with the optimized fertilization treatment.Sediment erosion was the major way for total phosphorus?TP?loss.The ranges of TP loss by sediment erosion were 63.74⁷8.74%and 53.34⁹0.74%for 10°and 15°plots,respectively.Among all fertilizer treatments,the biochar treatment contributed the highest TP loss fluxes(1.01 kg·hm^-2·a^-1 for 10°plots and 1.44 kg·hm^-2·a^-1 for 15°plots),while the straw treatment contributed the lowest(0.41 kg·hm^-2·a^-1 for 10°plots and 0.30 kg·hm^-2·a^-1 for 15°plots).Biochar application increased TP loss flux of purple soil in arid sloping farmland,but reduced phosphate loss flux;and no significant changes of PP loss flux was found.The application of straw presented an ideal effect on phosphorus retention in soil.?4?The contents of ammonium nitrogen?AN?and alkali-hydrolyzable nitrogen in soil during maize season were all found higher than those during rape season.The highest AN contents in 10°and 15°plots soils were 16.88 and 15.82 mg·kg^-1 respectively,and both of them were found in the conventional fertilization treatment.The highest alkali-hydrolyzable nitrogen contents in soil were40.83 mg·kg^-11 in 10°plots?biochar treatment?and 49.29 mg·kg^-11 in 15°plots?straw treatment?.Available phosphorus was increased by straw application when comparing with other fertilizer treatments.The highest total nitrogen?TN?contents in soil during maize season were 0.59 g·kg^-1?10°plots?and 0.60 g·kg^-1?15°plots?,but no significant difference was found among different treatments.Soil total phosphorus?TP?content was also increased by fertilization,but the difference between different seasons as well as different treatment were not significant.The yields of rape and maize under each fertilization treatments were significantly higher than those under CK treatment.The total yields for rape and maize for the plots with a slop of 10°were2030²606 kg·hm^-2 and 6056⁷607 kg·hm^-2,respectively.The total yields for rape and maize for the plots with a slop of 15°were 1962²328 kg·hm^-2 and 4765⁵838 kg·hm^-2,respectively.The contents of TN and TP in rape and maize were concentrated in grain.The contents of TN in root and stem of rape were lower than that in shuck,while the content of phosphorus in stem,root and shuck had no significant difference.The lowest nitrogen and phosphorus contents of plant cobs under different fertilization treatments were in maize.During rape season,the reducing fertilization treatment all improved the utilization rate of nitrogen and phosphorus.While,during the maize season,the highest utilization rate of mineral fertilizers was found in the biochar treatment at 10°plots and in the straw treatment at 15°plots.