Nutrient Surplus And Environmental Effects In Kiwi Fruit Production Areas In Northern Slope Region Of Qinling Mountains

The northern part of the Qinling Mountains located in Shaanxi Province is one of the dominant kiwifruit planting areas in the country.The planting area and output of kiwifruit rank first in the country in terms of productivity.However,with the increase of kiwifruit orchard planting area,nutrient input rate was also increasing causing several problems due to the fertilization use.This situation is a concern because kiwifruit orchards in northern slope region of Qinling Mountains are mostly planted on slopes zone and high rainfall.Therefore,excessive fertilization will not only increase the cost of production,but also polluted groundwater which is a threat for the health of the population and the sustainability of the kiwifruit industry.In this paper,Meixian and Zhouzhi County which are the main producing areas of kiwifruit in northern slope region of Qinling Mountains,Shaanxi,were used as a study site.The industrial changes and nutrient input of kiwifruit in these areas from 1992 to 2017 were investigated by means of experimental investigation and field experiment.The accumulation and migration characteristics of nitrate nitrogen in soil under different planting patterns were measured.Moreover,the changes of nitrate and base ion contents in surface water and groundwater caused following different land use patterns in this area were monitored,and the following main conclusions were drawn:（1）Since 1992,layout of crops in Meixian County has undergone significant changes.The crop planting pattern has changed from wheat and corn to kiwifruit.The sown area of corn and wheat dropped from 46.56%and 37.07%to 26.61%and 23.02%respectively.Kiwifruit accounted for 42.44%in 2017.Nitrogen use rate in the study area has always been in a surplus with 9271 t while phosphorus surplus increases significantly,from 2661t in 1992to 10268 t in 2017,with an increase of 286%.Potassium rate turned into a surplus from 2000by 280.07%with an amount of 6841 t.Therefore,it is crucial to reduce the input of N,P₂O₅and K₂O nutrients,and more pay attention about the problem caused by the excessive nutrient surplus in the groundwater.（2）The nutrient input of the kiwifruit orchard in the study area is too high.Excessive application of nitrogen fertilizer and phosphate accounted for more than 80%,and that of potassium fertilizer was 79.2%.We observed that the accumulation of nitrate in 0～200 cm soil was large,increases with the increase of tree age and was higher in grain fields.The average nitrate nitrogen content of orchard within 0～200 cm soil layers were 571,1045,1459kg·hm^-2,and the average nitrate nitrogen accumulation of each tree age reaches 1025 kg·hm^-2and that of grain field was 179 kg·hm^-2.The content of available phosphorus,potassium,and organic matter in the soil reached a high level,and the orchard was higher than that of the grain field.Same observation was observed for soil nutrient content.It is recommended to appropriately reduce nitrogen,phosphorus,and potassium nutrients rate of application.（3）Finally,the nitrate content of surface water in natural vegetation area at northern slope region of Qinling Mountains,Shaanxi,ranged between 1.95 and 4.80 mg N·L^-1,with a stable change while the nitrate content in the water did not exceed the standard.The average nitrate content in surface water of kiwifruit concentrated producing areas was 16.12～36.28 mg N·L^-1,indicating that the planting of kiwifruit significantly increased the nitrate pollution in surface water.Groundwater nitrate in the main production area of kiwifruit in northern slope region of Qinling Mountains in Shaanxi was over standard by 93.27%in the surface water(average value,29.68 mg N·L^-1)and exceeding by 57.41%in the groundwater(average value,15.06mg N·L^-1).The variation trend of nitrate content in groundwater and surface water was basically consistent with that in Meixian County during fertilization period,and the peak value mainly appeared in June and November during fertilization period.The peaks mainly occur during the fertilization period from June to November;groundwater nitrate content decreased significantly in September,which is consistent with the long-term high rainfall occurring in September.There was a significant positive correlation between the nitrate content of groundwater and surface water and the water EC,Ca²⁺,Mg²⁺,and Cl^-content,indicating that leaching of nitrate also aggravates the loss of Ca²⁺and Mg²⁺plasma and increases water hardness.The nitrate rate application in the groundwater of kiwifruit areas in northern slope region of Qinling Mountains,Shaanxi Province is extremely high and effective measures should be taken to solve this problem.In summary,with the development of the kiwifruit production area in northern slope region of the Qinling Mountains in Shaanxi,long-term excessive fertilization has resulted in a large surplus of nutrients in the county.Soil nutrients,especially nitrate nitrogen,accumulate in the soil profile,causing serious damage to the local surface water and groundwater quality.influences.Therefore,in kiwifruit planting,source control should be adopted to reduce fertilization,reduce nutrient input,reduce soil nitrogen accumulation and loss,and closely monitor surface water and groundwater quality,protect the ecological environment,and promote the sustainable development of the local kiwifruit industry.