| Soil acidification,low organic matter,enrichment of nitrogen and phosphorus and lack of potassium are the prominent problems limiting the sustainable utilization of agricultural soil resources in southern China.Shifang City was known as "the town of cigar in China".Tobacco planting often required a large amount of fertilizer,and p H,organic matter and nitrogen,phosphorus and potassium contents of tobacco soil had already changed.However,there was a long-term lack of relevant studies on the characteristics and change trends of p H,organic matter and nitrogen,phosphorus and potassium contents of tobacco planting soil in Shifang City.Therefore,based on the data of p H,organic matter,total nitrogen,alkali-hydrolytic nitrogen,available phosphorus and available potassium of totobacco planting soil in Shifang City in 1984,2009 and 2019,this study used multivariate statistics,geostatistics and GIS to reveal the spatio-temporal evolution of p H,organic matter and nitrogen,phosphorus and potassium of totobacco planting soil in Shifang City.The change characteristics of soil comprehensive fertility quality were further studied to provide reference for the improvement of tobacco planting soil quality.The main research results are as follows:(1)The mean p H value of tobiot soil in Shifang City decreased by 0.43,0.01 and0.02 respectively from 1984 to 2009.The average organic matter content increased by31.77% from 1984 to 2019,with an average annual increase of 0.11 g/kg in the first 25 years and 0.56 g/kg in the last 10 years.The average content of total nitrogen and alkali-hydrolyzed nitrogen increased by 0.14 g/kg and 75.99 mg/kg,respectively.From 1984 to 2019,the average available phosphorus content increased by 0.92 mg/kg annually.The average available potassium content increased by 1.65 mg/kg during 1984 to 2019,0.34mg/kg during 1984 to 2009,and 4.93 mg/kg during 2009 to 2019.(2)In 1984,2009 and 2019,the p H of tobaccotic soil was mainly weak acid and neutral,alkaline soil disappeared in 2009,and acidic soil was 4.75% in 2019.In 1984,soil organic matter content in tobacco-growing areas was mainly at high level,accounting for 78.86% of the total tobacco-growing soil area.In 2009,the proportion of high level tobacco-growing fields increased to 84.80%.By 2019,the total proportion of high level and high level tobacco-growing fields reached 98.02%.In 2009,most of the total nitrogen content(84.67%)was at the appropriate level,and the proportion of tobacco fields at high level decreased from 79.03% in 1984 to 75.23% in 2019.In 1984,most of the alkali-hydrolyzed nitrogen content was at the appropriate level.In 2009,the majority of the fields were at the excessively high level,accounting for 58.29%.In 2019,58.29% of the fields reached the excessively high level.In 1984,60.22% of the tobacco fields had an appropriate level of available P,and 80.02% of the tobacco fields had a high level of available P in 2009.In 2019,61.94% of the tobacco fields had an excessive level of available P.In 1984 and 2009,soil available potassium content in tobacco fields was mainly at low level,accounting for98.19% and 89.51% of the total area of tobacco planting soil,respectively.In 2019,soil available potassium content in tobacco fields at low level accounted for 73.18%,and only8.14% of the area was at the appropriate level.(3)53.51% of tobacco planting soil has shown an acidification trend in the past 35 years(Δ PH <-0.3),11.63% of the soil exhibits alkaline characteristics(Δ p H > 0.3)。 From 1984 to 2019,79.96% of tobacco planting soil organic matter content was increasing.The main range of organic matter content changes from 1984 to 2009 was-5 to 5 g/kg,and from 2009 to 2019,it was mainly between0 to 15 g/kg.Compared with 1984,55.09% of the regional soil total nitrogen content in 2019 was increasing,with changes mainly ranging from 0 to 0.5 g/kg.In the past 35 years,the content of soil alkali hydrolyzable nitrogen has shown an increasing trend in the vast majority of regions(96.85%),with a rate of increase being lower in the central region than in the southern and northern regions;The increase from 1984 to 2009 was mainly between 0-50mg/kg,and from 2009 to 2019,the sum of the area ratios between 0-50 mg/kg and 50-100mg/kg accounted for 81.52% of the total tobacco planting soil area.95.67% of the available phosphorus content in tobacco planting soil showed an increasing trend over the past 35 years,with a slow rate in the middle and a fast rate in the north and south;The increase from1984 to 2009 was mainly between 0-30 mg/kg,while the increase in 78.83% soil available phosphorus content from 2009 to 2019 was between 0-60 mg/kg.From 1984 to 2019,the soil available potassium content in nearly 100% of the regions showed an increasing trend,with a significant increase in the southern part of Majing Town,the northeastern part of Jiandi Town,and the central part of Luoshui Town;From 1984 to 2009,there was a significant increase of 0-30 mg/kg in a large area,and from 2009 to 2019,the change was mainly between 0-60 mg/kg,accounting for 76.12%.(4)The average comprehensive fertility quality of tobacco planting soil in Shifang City in1984,2009,and 2019 were 0.49,0.62,and 0.54,respectively;In 1984,the overall soil fertility quality of tobacco fields in Shifang City was mainly at the third and fourth level.By2009,72.58% of tobacco planting soil was at the second level.In 2019,the area with soil fertility quality at the second and third level accounted for 29.20% and 68.77% respectively.From 1984 to 2019,63.74% of the soil comprehensive fertility quality in the Shifang tobacco growing area was increasing,with a variation range mainly ranging from-0.20 to0.20;From 1984 to 2009 and from 2009 to 2019,the area ratio with a variation of 0 to 0.20 was the largest. |
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