| Topography,parent material and fertilization are important factors affecting soil physical and chemical properties and micronutrient content in soil.The contents of soil organic matter,available phosphorus and available potassium,the balance of large,medium and trace elements in soil,and soil nutrient content in different soil spaces are all important factors affecting nutrient absorption of fruit tree roots.Most of the previous studies are about the nutrient status of orchard surface soil and the balance of input and output of nitrogen,phosphorus and potassium based on the macro survey data.There are few systematic studies on the primary nutrient barriers and secondary nutrient barriers caused by excessive fertilization from the parent materials of orchard soil and the dynamic changes of soil nutrients in different soil layers.Based on the secondary soil survey data(1980-1985),this paper systematically analyzed the characteristics of soil available iron,available zinc and water-soluble boron in orchard soil under different landforms and soil forming parent materials,and studied the status of primary nutrient barriers in different regions;studied the changes of soil nutrients in apple orchards in Hebei Province through the positioning monitoring of soil nutrients,and studied the nutrient distribution characteristics of 0-80cm soil layer in Hebei Province;soil nutrient status,soil secondary salt status and balance degree of large,medium and trace elements were studied by soil nutrient measurement of representative orchards in large area;The soil nutrient status and its influencing factors in orchard under different cultivation modes were studied by combining the soil nutrient status measurement of arrow-tree and dwarf apple orchard;It provides the basis for scientific management of orchard soil nutrients.The main results are as follows:1.In the main apple planting area of Hebei Province,the parent material of soil formation is mainly flood alluvial,hill slope deposit and Quaternary loess;the parent material of soil formation is an important factor affecting the available iron and zinc in the soil of each area,and the content of water-soluble boron in each area is low without obvious difference.The status of soil available iron in different terrain:Yanshan hill area>Taihang hill,piedmont plain>low plain area.There was a significant positive correlation between soil organic matter and available zinc,but no significant correlation between soil organic matter and available iron and water-soluble boron.There was no significant correlation between the percentage of clay particles<0.01mm and the available iron and zinc in the soil,but there was significant correlation between the percentage of clay particles<0.01mm and the soluble boron in the soil.2.Based on the fruit tree yield(6000-7500 kg/hm2)and fertilization status in the orchard for 20 years,the apparent balance of soil N,P and K was calculated as follows:the average amount of N,P2O5 and K2O in orchard be used was 1154-1977,823-936 and 711-1043 kg/hm2;the apparent surplus of soil N,P and K was 758.5,591.5 and 277.0 kg/hm2 respectively.3.The accumulation of available P and K in 0-20cm soil in apple orchard leads to the secondary salinization of surface soil,which highlights the problems of low organic matter,relative lack of available iron,water-soluble boron and available zinc.The average contents of organic matter,total nitrogen,available phosphorus,available potassium,available iron and available zinc in 0-20cm soil were 18.05g/kg,1.34g/kg,113.00mg/kg,286.13mg/kg,20.21mg/kg and 4.27mg/kg,respectively.Compared with the cultivated land nutrients in Hebei Province during the second Soil Census,the nutrient contents increased by 0.57,0.84,16.9,1.23,1.46 and 7.06 times,respectively.The soil nutrient status of dwarf and dense orchard:the available P and available K in the surface layer of 0-20cm ridge were obviously accumulated,highlighting the secondary salinization of soil.The contents of organic matter,available phosphorus and available potassium in 0-20cm were 19.48g/kg,135.85mg/kg and 392.70mg/kg respectively.Compared with 0-20cm,the contents of organic matter,available phosphorus and available potassium in 20-40cm were reduced by 34.2%,34.3%,39.1%respectively,and those in 40-60cm were reduced by 56.5%,71.I%and 60.5%respectively.4.Dynamic changes of soil nutrients in apple orchard:mainly reflected in the accumulation of soil available P and K,highlighting the imbalance between a large number of elements and trace elements in the soil,and secondary salinization and other nutrient barriers.Compared with 1993,organic matter,available phosphorus and available potassium in 0-20cm soil of apple orchard in 2018 increased by 12.51g/kg,182.55mg/kg and 426.80mg/kg respectively,with average annual growth of 0.50g/kg,7.30mg/kg and 17.07mg/kg;available iron and available zinc increased by 4.09mg/kg and 1.52mg/kg respectively,with annual growth of 0.27mg/kg and 0.10mg/kg respectively.There was a significant correlation between available P,K and EC value.There was a significant positive correlation between tree age and soil available phosphorus and available potassium.5.The accumulation of soil nutrients in the surface layer and the misalignment of the root layer of fruit trees in the soil space lead to low soil nutrient utilization efficiency.Soil organic matter,available phosphorus and available potassium in 20-40 cm and 40-60 cm soil layers were 50.8%,59.8%,74.0%and 42.3%,27.0%and 55.9%of 0-20 cm soil layers,respectively.In 2018,the contents of organic matter,available phosphorus and available potassium in 20-40 cm soil layer decreased by 49.2%,40.2%and 26.0%respectively compared with that in 0-20 cm soil layer,and the nutrient content in 40-60 cm soil layer decreased by 57.7%,73.0%and 44.1%respectively.6.In the orchard with 30-40 years of planting,the soil pH decreased significantly.The soil pH in 0-20cm,20-40cm and 40-60cm soil layers decreased 1.09,0.41 and 0.27 units compared with that in the orchard with less than 10 years.Main conclusion:the main influencing factors of primary nutrient obstacle in apple orchard are soil parent material,which is mainly manifested in the difference of available iron in orchard soil in different regions.The secondary nutrient obstacle is mainly manifested in the accumulation of available phosphorus and available potassium in 0-20cm soil caused by excessive application of chemical fertilizer,the significant increase of secondary salt content in surface soil and the imbalance of soil nutrients.The soil nutrient accumulation layer and the root distribution layer of fruit tree absorbing nutrient are misplaced in soil space. |
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