| As the material basis of crop growth,soil fertility is very important to ensure national food security.Through defining the temporal and spatial evolution characteristics of paddy soil fertility in typical county of Northeast China,grasping the status quo of paddy soil fertility in typical county,providing scientific basis for the rational management of paddy soil fertility in this region,and promoting the development of regional agriculture.Taking Fangzheng County of Heilongjiang Province as an example,and collectted 900 paddy soil data sample points in 2007.In 2017,114 representative paddy soil points were selected in the research area.p H,organic matter,alkalide nitrogen,available phosphorus and available potassium were selected as factors of soil fertility evaluation.The weight of each factor was determined by principal component analysis.According to the characteristics of the northeast paddy soil,appropriate membership function curves and turning points were selected to determine membership values.According to the multiplication principle of fuzzy mathematics,the soil integrated fertility index was calculated by weight values and membership values.The method of combining GIS and geostatistics was used to determine the spatial variability and distribution pattern of various fertility factors and soil integrated fertility index of paddy soils in Fangzheng County in 2007 and 2017 at two different time periods.The results are as follows:(1)2007~2017,pH of the paddy soil in Fangzheng County showed a downward trend,and the overall soil acid-base level decreased from neutral to slightly acidic.The average soil pH in 2017 was 5.83.2007~2017,the average soil organic matter content in rice fields increased from 25.63 g/kg to 36.46 g/kg,with an average annual increase of 1.08 g/kg.2007~2017,The average value of alkaline nitrogen content in paddy soil decreased from 191.36 mg/kg to 177.56 mg/kg.2007~2017,the average content of available phosphorus in paddy soil increased from 28.16 mg/kg to 38.23 mg/kg,and the average annual increase was 1.00 mg/kg.2007~2017,the average value of available potassium in the paddy soil of Fangzheng County increased from 121.53 mg/kg to 171.77 mg/kg.The coefficients of variation of various soil fertility indicators in the rice field of Fangzhe ng County were as follows:available phosphorus > alkaline nitrogen > available potassium > organic matter > pH(2007),available phosphorus > organic matter > alkaline nitrogen > available potassium > pH(2017 year).(2)The spatial distribution of soil p H in 2007 was relatively uniform,with pH values ranging mainly from 6.50 to 7.00.In 2017,the soil pH of the rice fields in Fangzheng County gradually increased from the middle of the rice fields to the east-west direction.2007~2017,the organic matter change trend in Fangzheng County showed that the organic matter content growth rate gradually decreased from southeast to northwest.In 2017,Fangzheng County mainly focused on paddy fields with organic matter content at the first and second levels,accounting for 22% and 75%,respectively.In 2007,the soil alkaline nitrogen content of paddy soil in Fangzheng County showed a distribution pattern of high in the south and low in the north,with more island-like patches.The content of soil alkaline nitrogen in 2017 showed a gradual decrease from northwest to southeast.In 2007 and 2017,91% of the paddy soil's alkaline nitrogen content was at the first level.The distribution characteristics of available phosphorus in paddy soils in Fangzheng County in 2007 and 2017 showed a gradual increase from the middle to the northeast and southwest.In 2017,Fangzheng County mainly focused on paddy fields with soil available phosphorus content at the first and second levels,accounting for 46% and 63%,respectively.In 2007,available potassium content in the paddy soil of Fangzheng County was evenly distributed,and 89% of the available potassium content in the paddy soil was at the third level.In 2017,the content of available potassium in paddy soil was low in the midd le,and high in the south and northeast.It was mainly rice paddies with a second-level soil available potassium content,accounting for 96%.(3)Under different conditions of soil parent material and soil type,soil p H,available phosphorus and available potassium content did not show significant differences at different time points.In 2017,soil organic matter content of the three soil-forming parent materials in Fangzheng County was as follows: slope deposits > alluvial proluvial deposits > alluvial deposits.The organic matter content of the four soil types in Fangzheng County in 2017 was alluvial soil > albic soil > meadow soil > black soil.In 2007,alkaline nitrogen content of albic soil in Fangzheng County was significantly lower than the other three soils(P <0.05),and the black soil alkaline nitrogen content was the lowest in 2017.In 2017,the content of alkaline nitrogen in the paddy soil formed by slope deposits in Fangzheng County was significantly higher than that in the other two soil-forming parent materials(P <0.05).2007~2017,soil organic matter,available phosphorus,and available potassium content of alluvial soil in Fangzheng County increased the most,and pH decreased the most.(4)The overall fertility of the paddy soil in Fangzheng County is on the rise.In 2007,98% of the paddy soil was below the middle level,and in 2017,61% of the paddy soil was above the middle level.2007~2017,the average value of soil integrated fertility index of the rice field in Fangzheng County increased from 0.41 to 0.60.In 2007,soil integrated fertility index of the rice field in Fangzheng County Exponential distribution is uneven.The distribution of soil integrated fertility index in Fangzheng County in 2017 was generally high in the south and low in the north. |
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