Characteristics Of Nutrient Input And Soil Nutrient Accumulation In New And Old Apple Orchards Of The Loess Plateau

Apple production has developed rapidly in the Loess Plateau since the 1990s.At present,the area and yield of apple productions in this region account for 50.9%and 43.4%of total apple production in China,respectively.It plays an important role in the market supply of apple in China.Apple production is becoming a pillar industry which can promote local economy and increase farmers’income.Compared with cereals,orchards had higher fertilizer application rates.The overused fertilization is very common,which has severely restricted the sustainable development of apple production.Therefore,we analysed the impact of land use change from cereals to apple orchards on nitrogen,phosphorus and potassium nutrients balance in soil of Luochuan county,a typical apple producing region on the Loess Plateau.We also compared the fertilization and soil nutrients accumulation of apple orchards in Luochuan（new apple producing county）and Liquan（old apple producing county）on the Loess Plateau.Our study can provide a scientific basis for nutrient management of apple orchards in the Loess Plateau.The main conclusions show as follows:（1）We selected the Luochuan county as the typical apple producing region of the Loess Plateau,to evaluate the land use change from cereals to apple orchards on soil nutrients balance in Luochuan county from 1990 to 2015.The results showed that cropping systems in Luochuan was changed from cereals to apple orchards in past 25 years,and the proportion of apple planting area was increased from 19.2%in 1990 to 76.9%in 2015.The nutrients input from chemical fertilizer increased significantly,particularly for potassium fertilizer;and the proportion of chemical fertilizer to total nutrient input in the region increased from 55.6%in1990 to 93.0%in 2015.Soil nitrogen,phosphorus and potassium nutrients input and output in1990-2005 remained near balance;however,since 2005,soil nutrients becomes excess gradually.By the end of 2015,the surplus of nitrogen,phosphorus and potassium in the regions were 7202,10446 and 12105 t,respectively.It indicated that the land use changes had large impact on nutrient balance at regional level.（2）We investigated the situations of fertilization inputs of more than 400 apple orchards in Luochuan（new apple producing county）and Liquan（old apple producing county）in the Loess Plateau,and 15 orchards were taken from each county,to determine soil nutrient content in the 0-40 cm layers.The results showed that excessive application of nitrogen,phosphorus and potassium fertilizers was very common in apple orchards of the Loess Plateau,and the average application rates of N,P₂O₅ and K₂O fertilizers in Liquan county were 1115,656 and 968 kg/hm²,respectively;and the percentages of excessive application of N,P₂O₅and K₂O fertilizers were 95.3%,91.3%and 100%,respectively.The average application rates of N,P₂O₅ and K₂O fertilizers in Luochuan county were 1208,828 and 1114 kg/hm²,respectively;and the percentages of excessive application of N,P₂O₅ and K₂O fertilizers were99.3%,98.7%and 100%,respectively.The available phosphorous and potassium contents of the apple orchards in two counties were generally excessive,the available phosphorous and potassium contents in 0-20 cm layers in old apple orchard of Liquan were 118 mg/kg,622mg/kg,respectively;the available phosphorous and potassium contents in 0-20 cm layers in new apple orchard of Luochuan were 40 mg/kg,344 mg/kg,respectively.And the available phosphorous and potassium contents of old orchards were significantly higher than that of new orchards.（3）15 apple orchards were collected from both in Luochuan and Liquan counties in the Loess Plateau and then surveyed the fertilizer application,calculated the nitrogen apparent balance,and measured NO₃^--N contents in the 0-200 cm soil profiles in apple orchards;and the relationships between orchard age,N application rate and NO₃^--N accumulation were also analyzed.The result showed that excessive N fertilization was very common both in new and old apple orchards in the Loess Plateau;the N fertilization application rates averaged were1287±244 and 1193±300 kg/hm² for the two counties,respectively.It resulted in high N surplus in the soil profiles.The accumulations of NO₃^--N in the 0-200 cm soil profile in apple orchard of Luochuan and Liquan were 2724 and 5226 kg/hm²,respectively.Nitrate accumulations of old orchards were significantly higher than that in new orchards.The NO₃^--N accumulation in soil profile was significantly increased with the increased N application rate and orchard ages.