Dynamic Characteristics Of Nutrient Loss In Surface Runoff And Its Relationship With Soil Nutrient For A Carya Cathayensis Stand

Chinese hickory?Carya cathayensis Sarg?belongs to a member plant of walnut genus in the Carya Nutt family and is a unique high-grade dried fruit and woody oil tree species in Chin.Since1990's,Chinese hickory has become an important source of income for farmers in main producing areas.As Chinese hickory stands are mostly located on the poor and steep slopes with>25 degrees,and in addition,in recent years,farmers have continuously cleared the undergrowth vegetation,increased chemical fertilizer rates and applied other undesirable management,which has led to the intensification of loss of soil,water,and nutrients as well as the pollution of water body around the woodland.Therefore,it is of great practical significance to explore the status and dynamic change of nutrient loss as well as the relationship with nutrient loss and soil nutrients in Chinese hickory stand land.To improve the shortcomings of the traditional method of runoff plot in soil erosion monitoring,the representative bayonet station of the closed area was established according to local conditions.In order to reveal the characteristics of nutrient loss in the runoff and to study the relationship between nutrient concetrations in runoff and available nutrient contents in the soils under Chinese hickory stand,the runoff in a year was collected and analyzed by monitoring the runoff in a closed plot.The runoff produced after each natural rainfall was collected,and the concentrations of nitrogen?N?,phosphorus?P?,potassium?K?,sodium?Na?,calcium?Ca?,magnesium?Mg?in the runoff were measured.In addition,the contents of available N and P in the surface soil corresponding to the runoff occurring were determined in the same time.The results of this study can provide a technical support for the control of non-point source pollution of Chinese hickory stand land.The main results and conclusions were as follows:?1?The rainfall and runoff of each rainfall in a year were recorded in a bayonet station of the closed area.The results showed that the runoff amount was larger and the maximum was 312.50t·hm^-2.There was a significant correlation between volume of runoff and rainfall?y=1.209 3x+56.1770,R2=0.884 8,P<0.05?,which indicating that the greater the rainfall,the greater the runoff.?2?The results showed that the average concentrations of total nitrogen?TN?and total phosphorus?TP?in the runoff ranged from 2.01-3.70 mg·L^-11 and 0.01-0.11 mg·L^-1,respectively,which suggesting that the content of P in runoff was very low.The contents of different forms of nitrogen decreased in the following order:hydrolyzed nitrogen>nitrate nitrogen?NO₃^--N?>ammonium nitrogen?NH₄⁺-N?,in which hydrolyzed nitrogen was the main form of nitrogen loss,accounting for 60.7%of TN.Furthermore,there was no significant correlation between the loss of N in the runoff and the content of available nutrients in the soil.The content of available phosphorus in the soil was also low,but there was a significant linear relationship between the content of available P and the P loss in the runoff?y=0.0658x-0.0287,R²=0.319 5,p<0.05?.The average concentrations of Ca²⁺,Mg²⁺,K⁺,and Na⁺in the runoff was in order of Ca²⁺>Mg²⁺?Na⁺>K⁺.The average concentrations in the runoff were relatively low.?3?The loss of N and P in runoff in Chinese hickory stand land exceeded the critical value of eutrophication,which suggesting there was a great risk of non-point source pollution.The loss of N and P respectively reached 11.02 kg·hm^-2·a^-11 and 134.82 g·hm^-2·a^-1,respectively.The nutrient loss in the sediment was less than that in the runoff.The loss amount of N was greater 81 times than that P.The soil degradation of Chinese hickory stand land was serious.Thus the future forest management should focus on increasing the surface vegetation coverage,effectively intercepting surface runoff and thickening the soil layer.In addition,to improve fertilizer utilization rate and reduce soil and water loss,farmers should reduce greatly nitrogen fertilizer rate and apply soil testing and fertilizer recommendation according to the fertilizer requirement of Chinese hickory stands.