| Soil fertility is the basic attributes and the essential characteristics of soil, the material composition of soil and organization of the state and natural conditions determine the level of soil fertility, soil fertility affects the growth of plants, it is the material basis of crop yield formation. Currently, the second national soil survey over35years, many studies have shown that soil nutrients and soil fertility has changed compared with the second soil survey data. Chongqing Fertilization tested142,641soil samples, soil pH, organic matter, potassium trend is clearly lower, and phosphorus and other content increased, while Yongchuan arable soil acidification phenomenon is more serious, pH, phosphorus, potassium down, organic matter, nitrogen increase, but all in the middle level. Due to the adjustment of national administrative divisions (Chongqing Municipality), the construction of the Three Gorges Reservoir, the main contents of the huge changes in agricultural production and production methods, regardless of the jurisdiction of Chongqing regional agricultural production accounted for the proportion of the national economy (agricultural achieve self-sufficiency) are completely different from the "old Chongqing"; meanwhile, with the changes in agricultural production systems, the improve the level of agricultural science and technology.Chongqing is necessary to comprehensively statistics and updates comprehensive the base of farmland condition. The full range of regional farmland soil types in Chongqing, distribution, characteristics and levels of fertility, changes in the trends of soil properties and other issues, Make a comprehensive analysis and summarize, in order to provided the based foundation of efficient development of agriculture in Chongqing. In this regard, this study intends to Chongqing "Fertilization Project" implementation process35districts (counties) of agricultural land "soil profile" survey (a total of about629cross-section), combined with the analysis of the measurement results of "agricultural soil samples", to comprehensively summarize the basic situation of agricultural soils in Chongqing, and on this basis, analysis and comprise the major agricultural soil types fertility characteristics, obstacle factors, deepening trend and so on, using Comprehensive Index to judge the live of topsoil, in addition to the statistics of the cultivated the area of each soil type level. The main findings are as follow:(1) Chongqing is located in the hills southeast of Sichuan Basin and Basin Mountain junction, on the geological structure belonging to the three major sections:southeast belonges Neocathaysian Sichuan, Hubei, Hunan and Guizhou Long fold belt:middle and west region, mainly due to the Sichuan Basin in East fold belt edge control; Chongqing Northeast is among Da Bashan fold fault. Total agricultural districts (county) are35in Chongqing; they will be divided into "Mountain agricultural area northeast of Chongqing,""Yuzhong, Yuxi Gao hilly agricultural area","Southeast Chongqing Karst Mountains-hilly agricultural area," Affected by geological structure, three regions’ soil parent material three regions are different, the "Mountainous agricultural area northeast of Chongqing" of soil parent material is impacted by chemical differentiation, such wide distribution of yellow soil in the area;"Yuzhong, Yuxi Gao hilly agricultural area," of soil parent material is impacted by physical weathering, the degree of development of soil shallow, soil in the area is purple soil more;"Karst Mountains of Southeastern-hilly agricultural area" soil parent material by the effects of chemical differentiation, mostly karst area based, thus limestone soils are mainly distributed in the area. The total cultivated area in Chongqing area is2,162,740hm2,dry land area is1,135,000hm2. The arable of each farmland soil type account for different proportion of total arable land, paddy soil account for47.7%of the total cultivated area, purple soil type account for29.7%of the total cultivated area, tide soil type account for0.5%of the total cultivated area, lime soil type account for approximately9.89%of the total cultivated area, yellow soil type account for11.4%. The distribution of each type agricultural land, subclasses, and the soil partition are different. This paper chooses these five major types analysis chemical properties of soil, comparing the fertility level of the five types.(2) The respect of soil pH, the size distribution of pH in the entire sequence of the Chongqing region:acidic soil＞neutral soil＞alkaline soil; Different geographical areas in Chongqing, the area distribution of the acidic soil is Yuxi, Yuzhong district＞Southeast Chongqing＞Chongqing Northeast, Fuling which is the largest acidic soil Southeast Chongqing, which may be long-term cultivation of mustard, resulting in acidification. Neutral soil, alkaline soil distribution area in descending order is:West Chongqing Yuzhong district＞northeast Chongqing＞southeast Chongqing. The distribution of pH area account for the proportion of the total cultivated area in different geographic area, the distribution ratio of acidic soil is:Southeast Chongqing＞Yuxi, Yuzhong＞Chongqing northeast, the distribution ratio of alkaline soil is:Northeast Chongqing＞West Chongqing Yuzhong district＞southeast Chongqing, therefore, from the distribution area and the distribution ratio of the Chongqing region, the alkaline soil of northeastern region is more than Southeastern, acid soil is in the contrary, showed a trend Northeast acidic and southeast bases. The pH distribution ratio is inconsistent in the five soil types. Such as paddy soil mainly in4.5-5.5,5.5-6.5and≥7.5range, and yellow soil type≤4.5,4.5-5.5,5.5-6.5. The distribution ratio in the range of strong acid (4.5-5.5) is yellow soil type＞paddy soil type＞purple soil type＞tide soil type＞lime soil type, the distribution ratio of slightly acidic (5.5-6.5) is:yellow soil type＞lime soil type＞paddy soil type＞tide soil type＞purple soil type, and the distribution ratio of the neutral range is:lime soil type＞purple soil type＞tide soil type＞paddy soil type＞yellow soil type, the distribution of alkaline is purple soil type (tide soil type)＞lime＞paddy soil type＞yellow soil type.(3)Compared with the second soil census, the organic matter, nitrogen and phosphorus of surface soil were improved but potassium was nearly unchanged. The total nitrogen, alkali solution nitrogen and organic matter of yellow soil, lime soil and paddy soil were significantly higher than Chao soil and purple soil in Chongqing. The differences of organic matter and total nitrogen of the first three soil types were not significant, and the content of organic matter, total nitrogen and alkali solution nitrogen was also not significant between Chao soil and purple soil. The content of the organic matter and nitrogen of the paddy soil, lime soil and yellow soil was more between the medium level and rich level, on the contrary, most of the purple soil and Chao soil were in lacking and very lacking situation, which leaded to the content and abundance of the organic matter and nitrogen of the kind of paddy soil, lime soil and yellow soil were higher than the purple soil and Chao soil. The content of the total phosphorus, effective phosphorus and available potassium of the Chao soil and paddy soil were lower than calcareous soil, purple soil and yellow soil. The abundant degree level of the rapidly-available potassium of every soil type is given priority to with the lack of level. The content size of total potassium is the class purple soil＞the calcareous soil＞the rice soil> the Chao soil＞the yellow soil type. The content of the total potassium of yellow soil and Chao soil were significantly lower than the purple soil, lime soil and paddy soil. Most of the total potassium of all kinds of soil is in medium level, but the turn is slightly different to the content of the total potassium, for example the total potassium content in the soil of lime soil types higher than paddy soil type and Chao soil type, But the percentage of moderate abundance and above is less than paddy soil type and Chao soil type.(4) The order of exchangeable Ca2+content is:yellow soil＜tide soil＜limestone soil＜purple soil＜paddy soil. The order of exchangeable Mg2+content:purple soil＞paddy soil＞tide soil＞calcareous soil＞yellow soil, exchangeable K+content in limestone soil is the highest. Exchangeable Na+in paddy soil is the highest, the exchangeable K+of limestone soil is slightly larger than the content of exchangeable Na+, while other soil types of exchangeable K+content is less than exchangeable Na+. From the surface soil to the bottom soil, the exchangeable Ca2+content of the paddy soil and yellow soil content increased with soil depth is reduced, and in the purple soil, tide soil, limestone soil performance the first increase and then decreases. But no matter what kind of trends, exchangeable Ca2+content in the topsoil and subsoil layer, topsoil and bottom soil, subsoil and bottom soil has no significant difference; the exchangeable Mg2+content of the paddy soil, purple soil, tide soil and yellow soil increased with soil depth is increased, in addition to the purple soil in the topsoil and bottom soil have significantly difference, the other four types of soil exchangeable Mg2+content in the topsoil and subsoil layer, topsoil and bottom soil, subsoil and bottom soil is not significant difference; either content of exchangeable Ca2+or Mg2+content in subsoil layer and bottom soil have changed in this five types. Subsoil layer exchangeable Ca2+in purple soil is significantly higher than paddy soil, tidal soil lime soil, yellow rice soil, paddy soil, tide soil, lime soil are no significant difference, but all with the yellow soil exchangeable Ca2+levels is significantly different; Two soil layers, exchangeable Mg2+content differences between soil types have the same resistance, no significant difference in the paddy soil, purple soil and tide soil, but all are significantly higher than lime soil and yellow soil, the content of Mg2+in lime soil and yellow soil showed have no significant differences. From the surface soil to the bottom soil, the exchangeable K+content in each types increased with soil depth is reduced, in addition to the topsoil and subsoil layer of yellow soil, topsoil and bottom soil have significant difference, there is no significant difference between the other soil types. The exchangeable Na+content changes little from the topsoil to the bottom soil, there was no significant difference between exchangeable Na+content of the soil in each of the three soil types, while the descending order of exchangeable K+content and the exchangeable Na+content in each soil type has changed.(5)From the surface soil to the bottom soil, almost no change in total potassium content, and each soil type of organic matter, nitrogen, phosphorus, potassium content decreased with the soil depth increased, and the topsoil and subsoil layer, topsoil and bottom soil have significant difference. The order of content has a slight change in each soil types of surface soil and subsoil, but the same with topsoil, organic matter and nitrogen in yellow soil, limestone soil, paddy soil is higher than the purple soil and the tide soil, phosphorus in limestone soil, paddy soil has turned into lower than in the yellow soil, tidal soil type and purple soil, potassium lime in limestone soil type, paddy soil type and purple soil type is higher than in yellow soil type and tide soil type.(6) Based on fuzzy comprehensive evaluation, the nutrient composite index descending order for each soil type:limestone soil, yellow soil, paddy soil, purple soil, tidal soil; paddy soil nutrient Composite Index is significantly higher than the purple soil (a≤0.01) and Chao soil (a≤0.05), but significantly lower than the limestone soil (a≤0.01) and Yellow (a≤0.01), the nutrient index between purple soil and tide soil nutrient is not significant difference, but both types with limestone soil, yellow soil has highly significant differences. The soil nutrient of composite index in yellow soil type is also significantly lower than the limestone soil (a≤0.01). |
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