| The wheat-maize rotation district in north China is one of the major grain producing areas in China.The implementation of precision agriculture,better management of soil nutrients,improvement of fertilizer utilization rate and reduction of fertilizer pollution to the environment are key guarantees for the sustainable development of agriculture in China.In this paper,27 cities and 185 counties(cities and districts)in north China wheat-maize rotation district of Hebei province,Henan province and Shandong province were selected as the research areas.The spatial and temporal variations of soil pH,organic matter,macroelement and medium trace elements were studied by using the geostatistical analysis method of GS+software and kriging interpolation method of ArcGIS.Using the single factor analysis method(ANOVA)of SPSS software,the effects of four categories of influencing factors,namely climate factor,altitude factor,soil factor and human factor,and seven categories of influencing factors,including accumulated temperature,precipitation,elevation,soil type,surface texture,irrigation and drainage conditions and fertilization level refinement,on soil nutrient variability were studied.A random forest regression model was constructed by coding in Python language,and the effects of various factors on total nitrogen,available phosphorus,available potassium and the sum of nitrogen,phosphorus and potassium were determined.Using the NDVI data from MODIS remote sensing image,the growth status of wheat and maize was obtained,and the relationship between the growth,yield variation of wheat and maize and the main nutrients in soil was analyzed.The comprehensive index of soil nutrients was constructed by using the analytic hierarchy process(ahp)through three indexes of organic matter,macroelement and medium trace elements,and the nutrient management zoning of wheat-maize rotation district in north China was conducted by using the fuzzy c-means clustering method of FuzME software.The target yield method and fertilizer effect function method were combined to carry out the fertilization formula zoning.The main research results are as follows:(1)The general characteristics of soil nutrients were studied.The variation of soil nutrients in the study area is slightly different.From the coefficient of variation,pH belongs to the degree of weak variation,organic matter and large and medium elements to the degree of medium variation,and most trace elements to the degree of strong variation.In the degree of spatial autocorrelation,pH,total nitrogen,available potassium,slowly available potassium,available zinc,available boron,available copper and available molybdenum have strong spatial autocorrelation,and spatial variation is mainly influenced by structural factors.Organic matter,available phosphorus,available sulfur,available iron and available manganese have moderate spatial autocorrelation,spatial variability is the result of the combination of random and structural factors.In terms of spatial distribution of nutrients,soil pH is characterized by homogeneity in spatial distribution.Organic matter and total nitrogen have similar spatial distribution pattern,and the content is at medium level.The spatial distribution pattern of available phosphorus,available potassium and slowly available potassium is relatively complex,and the distribution of available potassium and slowly available potassium is similar,and the distribution pattern was higher in the north and lower in the south.The distribution of available sulfur is higher in the north and lower in the south,with little difference between the north and the south.The contents of available boron,available iron,available molybdenum and available iron are relatively low on the whole in space,generally showing the characteristics of low content in the northern region and high content in the southern region.In terms of the dynamic changes of nutrients,pH was maintained at the level of weak alkalinity on the whole,and acidity,weak acidity and alkalinity were improved to different degrees.The contents of organic matter and macroelements were increased to different degrees,and the contents of trace elements were also increased on the whole.(2)The effects of different factors on soil nutrient variability were studied.The average contents of different soil nutrients in different factor grades or classifications were different.With the increase of accumulated temperature,precipitation and altitude,the pH of soil presented a decreasing trend.With the increase of accumulated temperature,the mean value of organic matter and total nitrogen decreased first and then increased.The mean values of organic matter and total nitrogen increased with the increase of precipitation and altitude.With the increase of accumulated temperature,the mean values of available p and available k increased slowly at first and then decreased.With the increase of precipitation and altitude,available phosphorus and available potassium decreased.For soil types,the mean values of nutrient contents in fluvo-aquic soil,cinnamon soil and lime concretion blacksoil were higher.In terms of surface texture,the contents of soil organic matter,total nitrogen,available phosphorus and available potassium showed the most consistent change trend in different soil textures,and the contents of various nutrients increased in sand,loam and clay.For human factors,soil nutrient levels were generally higher in areas with better irrigation and drainage conditions and higher fertilization levels.(3)The effects of various factors on soil main nutrients were analyzed.Through random forest regression analysis,it is concluded that irrigation capacity and topsoil texture have the most significant influence on the content of a large number of elements including total nitrogen,available phosphorus and available potassium in the soil,and neither accumulated temperature nor precipitation are important factors affecting the main nutrients in the soil.The degree of influence of various influencing factors on the total nitrogen content of soil is from the largest to the smallest,followed by the irrigation capacity>topsoil texture>elevation>NDVI>precipitation>accumulated temperature.The degree of influence on soil available phosphorus content is from the highest to the lowest in the order of topsoil texture>elevation>irrigation capacity>NDVI>precipitation>accumulated temperature.The degree of influence on the content of available potassium in soil was from the highest to the lowest,followed by the topsoil texture>irrigation capacity>elevation>NDVI>accumulated temperature>precipitation.The influencing factors of total NPK in soil were from high to low in the order of topsoil texture>irrigation capacity>elevation>precipitation>NDVI>accumulated temperature.(4)Crop growth and yield levels were analyzed.In the wheat-maize rotation district of north China province,the overall growth of wheat was lower in the north than in the south,and the growth of maize was higher in the north than in the middle and lower in the south,and the growth of maize was better than that of wheat.The yield distribution and growth distribution of wheat and maize are similar.The average yield of wheat in the wheat-maize rotation district of north China was 6927.90 kg/hm~2,and the average yield of maize was7787.40 kg/hm~2.There was a positive correlation between growth and yield of wheat and corn.At the level of 0.01(both sides),the correlation coefficients were 0.386 and 0.425,respectively.(5)Nutrient management zones of wheat-maize rotation district in north China were studied.The soil nutrient status of wheat-maize rotation area in north China was generally in good condition,the nutrient level in the middle of the study area was higher,and that in the surrounding area was lower.In the nine nutrient management regions divided,the area with the nutrient comprehensive index above 60 was 8.9957 million hm~2,accounting for 78.87%of the cultivated land area.The soil nutrient status in the wheat-maize rotation area of north China was in a good state on the whole.The nutrient level in the middle part of the study area was relatively high,with an area of 2.0937 million hm~2,accounting for about 20%of the total area.A few areas in the northeast and northwest had low nutrient levels,with an area of1.3695 million hm~2,accounting for about 10%of the total area.(6)The precise fertilization division of wheat-maize rotation district in north China was studied.In the wheat-maize rotation district of north China,the proportions of N,P,K and fertilizer required in the whole growth cycle of wheat-maize were 1:0.31~0.47:-0.11~0.45,respectively.The main lack of NPK in the whole region was mainly concentrated in the middle of the rotation area,with an area of 1,508,600 hm~2,accounting for 13.23%of the study area.The amount of fertilizer needed in the northern and southern regions was relatively less than that in the central region.Its area is 6.5702 million hm~2,accounting for57.59%.Among them,the area that does not need K-fertilizer is 418,800 hm~2,accounting for3.61%of the total cultivated area in the research area.This paper systematically studied the soil nutrient status of wheat-maize rotation district in North China.Using qualitative and quantitative scientific means,the temporal and spatial variability of soil nutrient and its influencing factors were found out.Nutrient management and fertilization zoning were established.It has certain reference value and guiding significance for fertilization and management of wheat-maize rotation district in North China. |
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