Nutrient Surplus Status And Impact On Water Quality In Kiwifruit Region

With the large-scale centralized planting of cash crops,the problem of excessive input of chemical fertilizer is becoming more and more serious,and the resulting problems such as resource waste,nutrient surplus and water pollution cannot be ignored.The excessive investment of fertilizer in cash crops is largely due to the traditional thinking of farmers,who believe that the more fertilizer they apply,the higher the yield and better quality will be.Therefore,it is urgent to find out the current situation and problems of fertilization for cash crops represented by fruit trees.Shaanxi Province as the largest kiwifruit planting province,planting area and output account for more than 60%of the country,ranking first in the country,at the same time in the world kiwifruit production occupies a pivotal position.In recent years,the application of fertilizer to kiwifruit in this area and the problems caused by it have aroused people’s attention.However,there are few reports about the effect of nutrient input and transport at village level on soil nutrient content and regional water quality in kiwifruit peach orchard.Therefore,in this experiment,Yujia village located in Zhouzhi County at the northern foot of the Qinling Mountains as the object,the field survey of the village kiwifruit planting area,the number of permanent population,the application of fertilizer in the kiwifruit orchard and the diet of farmers,and the analysis of the village nutrient surplus with kiwifruit as the main crop;The surface and profile soil of rhesus monkey peach orchard and grain field were collected to find out the abundance and deficiency of phosphorus and potassium and the accumulation of nitrate nitrogen in soil.The groundwater and surface water of Yujia village were further collected to analyze the pollution of nitrate nitrogen to water body.The results are as follows:（1）The income and expenditure of nutrient（N,P₂O₅,K₂O）in Yujia village was investigated.It was found that the nutrient was in surplus at the village level,and the main reason was the excessive input of chemical fertilizer.The input of chemical fertilizer N,P₂O₅,K₂O was 544 kg/ha,474 kg/ha,and 470 kg/ha,respectively.The average annual surplus of N,P₂O₅ and K₂O reached 453 kg/ha,378 kg/ha and 359 kg/ha,respectively.The biggest contribution to the surplus was the input of fertilizer.N,P₂O₅ and K₂O fertilizer input contribution rates were 67%,97%and 86%,respectively,among which fertilizer accounted for41%,61%and 55%.It can be seen that the nutrients in kiwi producing areas are in excess surplus state,which poses a potential threat to the local environment.（2）The soil basic nutrients of Yujia village rhesus peach orchard and grain field were determined.The results showed that the nutrient content of rhesus peach orchard was higher than that of grain field,and the p H of rhesus peach orchard was significantly lower than that of grain field.The average contents of organic matter,total nitrogen,available phosphorus and available potassium in 0-20 cm soil layer were20.92 g/kg,1.09 g/kg,50 mg/kg and 245 mg/kg,and the proportion of samples in low nutrient was 12%,33%,11%and 11%,respectively.From the point of view of p H,the average value of the macaca orchard is 6.18,showing that the soil is weakly acidic,and the sample of weak acid accounts for 54%,while the average value of the grain field is 7.25.After extreme rainfall,0-8 m nitrate was washed,and there was no difference between different tree ages and grain fields of kiwifruit.Extreme rainfall results in large amounts of nitrate leaching downward.After the extreme rainfall in 2021,the accumulation of 0-4 m nitrate nitrogen in the same orchard decreased from 1536 kg/ha in 2018 to 163 kg/ha,with 1373 kg/ha of nitrate nitrogen leaching below 4 m.Nitrate nitrogen accumulated in normal rainfall years.In 2022,remining of 2021 orchards showed an increase of 349 kg/ha in 0-3 m nitrate nitrogen accumulation.In conclusion,phosphorus and potassium nutrients in the orchard were abundant and accumulated in the orchard soil,and the orchard showed acidification trend.Nitrogen is likely to enter groundwater under the action of rainfall,causing pollution to local water bodies.（3）The plasma contents of p H,EC,K^+,Na⁺,Ca²⁺,Mg²⁺and NO3^--N in groundwater and surface water of the main producing areas of kiwifruit in Zhouzhi County were continuously monitored at a fixed point for a year.The results showed that:The NO₃^--N contents of shallow groundwater,surface water and deep groundwater（drinking water）in Zhouzhi County were 22.90,8.99 and 5.50 mg/L,respectively,and the corresponding over standard rates were 75%,57%and 16%,among which the shallow groundwater in the administrative village where kiwifruit was mainly planted（>80%）exceeded the standard.The content of NO₃^--N in shallow groundwater had two peaks during the growth period of kiwifruit in one season.The first one was at the end of September 2021 when fertilization was stopped after harvest,and its average content reached 25.35 mg/L;the second one was low in April after the first topdressing in the next year,and its content reached 25.52 mg/L.The contents of each cation(K⁺,Na⁺,Ca²⁺,Mg²⁺)in groundwater and surface water are in the order of shallow groundwater>surface water>production groundwater,the contents of each cation in shallow groundwater is in the order of Ca²⁺>Mg²⁺>Na⁺>K⁺,and NO₃^--N in shallow groundwater has a significant positive correlation with each cation.In conclusion,nutrients in the main producing areas of kiwifruit were in surplus at the northern foot of the Qinling Mountains,and phosphorus and potassium accumulated in the surface layer of soil（0-40cm）.Nitrogen migrated downward into groundwater under the condition of rainfall and irrigation,and caused pollution to the shallow groundwater.