Effects Of Different Plant Assembling Patterns On Vertical Leaching Process Of Soil N And P

The loss of nitrogen and phosphorus is the main cause of agricultural non-point source pollution,and leaching loss is also one of the pathways that cannot be ignored for nitrogen and phosphorus loss.Therefore,studying the vertical leaching process of nitrogen and phosphorus in soil is of great significance.This study focuses on the Jinning phosphate mining area in the Dianchi Lake Basin,including the original mixed forest（CQH）that has grown for over 50 years,the artificial forest community（CGM）that has been restored for40 years after mining,the artificial forest community（CAC）that has grown for 10 years,the artificial forest community（CMX）that has been restored for 7 years,and the community that has grown naturally on the slope of the waste dump for 1 year（CMB）.The southern bank of Yilong Lake,including the Yangmei forest（1770 meters above sea level）,the Yangmei acacia（CJY）,and the 1440 meters Yangmei Yunnan pine（CYY）1300 m Myrica rubra Japonica（CLY）community as the experimental area,the species diversity and the vertical distribution characteristics of N and P in the plant community were investigated;The soil in the original vegetation area of Jinning phosphate mine area in the Dianchi Lake basin and the soil in the bayberry picking garden in Baxin Town,Shiping County,on the south bank of Yilong Lake were selected,and the method of indoor simulation of leaching soil column was used to construct different plant composite pattern（black wattle,ryegrass,black wattle+ryegrass,cockgrass+myrica,alfalfa+myrica,cockgrass+alfalfa+myrica）to simulate the impact of rainfall（annual average rainfall level1000 mm,extreme heavy rain event daily rainfall 121 mm）on soil N The impact of P vertical migration and leaching loss process.The research results are as follows:（1）The species richness of Alnus cremastogyne Pinus armandii mixed forest（CQH）in plant community in the phosphate mine area was significantly higher than that of the other four communities,and the contribution rate of herb layer was 50.0%;The species richness of the Yangmei Yunnan Pine community（CYY）in the Yangmei forest on the south bank of Yilong Lake is the highest,with a contribution rate of 41.7%from the herbaceous layer.There is a significant positive correlation between species richness and Shannon Wiener index H’in the herbaceous layer of the community and total phosphorus（TP）and available phosphorus（AP）in the soil.The distribution of total nitrogen（TN）and available phosphorus（AP）content in the soil profile of the Jinning phosphate mining area in the Dianchi Lake Basin shows obvious surface aggregation phenomenon（0-20 cm soil layer）,while total phosphorus（TP）shows a continuous downward migration pattern.The distribution of alkaline hydrolyzable nitrogen（AN）and available phosphorus（AP）content in the soil profile of Yangmei on the south bank of Yilong Lake shows a significant surface aggregation phenomenon.There is a significant negative correlation between soil p H value and total nitrogen（TN）and alkaline nitrogen（AN）,electrical conductivity（EC）and total nitrogen（TN）,cation exchange capacity（CEC）and available phosphorus（AP）,while organic matter（OM）is significantly positively correlated with total phosphorus（TP）and available phosphorus（AP）.（2）The soil simulation leaching experiment in the original vegetation area of Jinning phosphate mining area showed that in six leaching experiments,the leaching amount of the first layer of leachate showed a gradual decrease trend.Compared with the black clover model,the leaching amount of the ryegrass model and the black clover+ryegrass model decreased by 56.9%～95.9%and 12.1%～48.7%,respectively.The leaching losses of total phosphorus（TP）and soluble total phosphorus（TDP）in the black clover model were 1.51and 0.92 kg/hm²,respectively,indicating the best reduction effect.Compared with the ryegrass model,the leaching losses of total phosphorus（TP）and soluble total phosphorus（TDP）were reduced by 7.4%and 18.6%,respectively;Compared with the black clover+ryegrass model,the leaching of total phosphorus（TP）and soluble total phosphorus（TDP）decreased by 31.1%and 41.0%,respectively.（3）After 6 leaching cycles,different modes had a significant impact on the total nitrogen（TN）and total phosphorus（TP）content in different soil layers（P<0.05）.Compared with CK,the total nitrogen（TN）content in the 0-20 cm soil layer of the black clover model,ryegrass model,and black clover+ryegrass model decreased by 17.0%,44.8%,and 33.9%,respectively.The height of black wattle is significantly positively correlated with the total nitrogen（TN）content in different depths of soil layers.The root characteristics（total root length,total root surface area）of ryegrass are significantly negatively correlated with the total nitrogen（TN）content in the 0-20 cm soil layer.Compared with CK,the total phosphorus（TP）content in the 0-20 cm and 20-40 cm soil layers decreased by 39.0%to 41.2%,44.2%to 44.9%,and 40.9%to 43.0%in the black clover model,ryegrass model,and black clover+ryegrass model,respectively.The soil total phosphorus（TP）loss in the ryegrass model was significantly higher than that in the black wattle model and the black wattle+ryegrass model（P<0.05）,and the soil TP showed a downward migration pattern.The height of black wattle is significantly positively correlated with the total phosphorus（TP）content in the 0-20 cm soil layer,while the root characteristics of ryegrass（total root length,total root surface area）are significantly negatively correlated with the total phosphorus（TP）content in the 0-20 cm soil layer.（4）The simulated leaching experiment of soil in the Yangmei picking orchard showed that in 5 leaching cycles,the leaching amount of the first layer of leachate showed a gradual decrease trend.Compared with the alfalfa+bayberry model,the leaching amount of the duckweed+bayberry model and the duckweed+alfalfa+bayberry model decreased by19.4%～42.5%and 23.9%～59.7%,respectively.The dynamic trends of total phosphorus（TP）and soluble total phosphorus（TDP）concentrations in different leaching modes are consistent,with the maximum total phosphorus（TP）concentration appearing in the fifth leaching,reaching 1.51 mg/L,1.46 mg/L,and 1.65 mg/L,respectively.The variation trend of soluble total nitrogen（TDN）concentration in different leaching modes is similar to that of TN,and overall,it shows a trend of first decreasing,then increasing,and then decreasing with the increase of leaching times.The total phosphorus（TP）,soluble total phosphorus（TDP）,and ammonium nitrogen（NH₄⁺-N）leaching amounts of the duckweed+alfalfa+bayberry model were 1.27,0.62,and 0.22 kg/hm²,respectively.Compared with the duckweed+bayberry model,the leaching amounts decreased by 6.6%,16.2%,and 18.5%,respectively;The total nitrogen（TN）,soluble total nitrogen（TDN）,ammonium nitrogen（NH₄⁺-N）,and nitrate nitrogen（NO₃^--N）leaching amounts of the duckweed+alfalfa+bayberry model were 63.79,57.97,0.22,and 25.46 kg/hm²,respectively.Compared with the alfalfa+bayberry model,the leaching amounts decreased by 33.9%,36.1%,5.7%,and 56.4%,respectively.Overall,the model of duckweed+alfalfa+bayberry has the best reduction effect on nitrogen and phosphorus.（5）After 5 leaching cycles,there were significant differences in the content of alkali hydrolyzed nitrogen（AN）and available phosphorus（AP）in different soil layers of different models（P<0.05）.Compared with CK,the content of alkaline hydrolyzable nitrogen（AN）in the 0-20 cm soil layer decreased by 16.1%,8.1%,and 40.0%in the duckweed+bayberry model,alfalfa+bayberry model,and duckweed+alfalfa+bayberry model,respectively.The inhibition and control effect of soil alkaline nitrogen（AN）loss in the alfalfa+bayberry model is higher than that in the duckweed+bayberry model and the duckweed+alfalfa+bayberry model（P<0.05）.There is a significant positive correlation between the root characteristics（average root diameter and total root volume）,underground phosphorus content,and alkaline nitrogen（AN）content in the 0-20 cm soil layer of duckweed.Compared with CK,the available phosphorus（AP）content in the 0-20cm soil layer decreased by 28.4%,58.0%,and 9.2%in the duckweed+bayberry model,alfalfa+bayberry model,and duckweed+alfalfa+bayberry model,respectively.The inhibition and control effect of available phosphorus（AP）loss in the duckweed+alfalfa+bayberry model was higher than that in the alfalfa+bayberry model（P<0.05）.The root characteristics（total root length,total root surface area,and total root volume）and underground nitrogen content of alfalfa were significantly negatively correlated with available phosphorus（AP）in 0-20 cm and 20-40 cm soil layers.In summary,the black wattle model has a certain control effect on phosphorus loss in the Dianchi Lake basin,while the duck grass+alfalfa+bayberry have a significant control effect on nitrogen and phosphorus loss in the southern bank of the Yilong Lake bayberry forest.