The Agro-ecological Geochemistry Evaluation Based On GIS

Neijiang city locates in the middle part of Chengdu-Chongqing economic zone.It is the main producing area of foodstuff and economic crops,the experimental city for aquatic product industrialization in Sichuan and the national production base of commodity grain.With the guidance of eco-geochemical theory,this paper implements agro-ecological geochemical evaluation on Shuangqiao village,Dongxing district, Neijang city.By way of finding out the background values,reference values and dispersion and enrichment features of soil element in the study area,understanding the content and distribution of elements and related geochemical index in the media(soil, water,air and biology) in ago-ecosystem.Using GIS space analysis technology and space attribute information extraction function,implement eco-geochemical survey and map filling.Establish a comprehensive agro-ecological geochemical evaluation project,combining basics of the soil environment and fertility,with the supplement of the evaluation result on air,water and biology,grounding on space congruence analysis technology,carry out comprehensive agro-ecological geochemical evaluation and spatial pattern analysis,and on this basis to do agro-ecological regionalization,adjust the structure and spatial layout of agricultural planting,and and establish suitable agricultural ecological models.The main evaluation results are as follows:(1)The relative abundance ratio value of Cd and CaO in the evaluation area is higher than that in the national soil of horizon.Compared with the soil background values of Chengdu economic zone,most elements' background values are close to,with high relative abundance ratio value of CaO.Comparing the background values of shallow soil in the study area with the benchmark values of deep soil,most elements' background values are close to,with the ratio range from 0.77 to 1.54.The variation coefficient(Cv₁) of most elements is under 40%,of which the distribution is relatively concentrated,the variation degree is comparatively low.The Cv₁ of S,Hg,Org.C is comparatively high,reaching 71.71%,71.70%,57.15%respectively.Excluding the discrete abnormal values,the variation coefficient(Cv₂) reduces quite a lot,indicating the topsoil is greatly influenced by the human activities.(2)The soil environmental quality is generally good in the evaluation area,with quite clean soil,which accords with the soil environmental quality request of pollution-free food producing area.Some regions reach the request of green food producing area.The rudimental quantity of organic contamination is lower than the soil environmental quality standard.The content of Cd and Ni in soil is relatively high:The content of Cd is within the primary and secondary standard of national soil environment quality.The soil of entire study area belongs to the Categoryâ…¡.73.89%of the area containing Ni belongs to Categoryâ…¡soil.(3)Through classification evaluation on single target of N,P,K and Org.C in soil by using GIS space analysis,it indicates the following results:the content of P is generally low,and with concentrated distribution;K has high content and balanced distribution;the content of N and Org.C substances differs greatly,and the region content is out of balance.Through classification evaluation on available state,it indicates the following results:the content of hydrolysable nitrogen and available phosphor differs greatly, with distribution out of balance.The content of available molybdenum and boron is low in general.Measures should be taken according to different region,supplementing the lacking nutrients of each region.Through Nemerow Synthetical Pollution Index,the comprehensive analysis on soil nutrition total content and available state indicates the following results:there is a lack of A Grade enrichment region.The comprehensive analysis on soil nutrition through repeated multiplication indicates that the regions are general ones of B Grade, and no A Grade enrichment regions exist.(4)Compared with the atmospheric dust data in Chengdu economic zone,such as Chengdu,Deyang,Meishan,Mianyang,Ya'an and Leshan six cities,the content of Cu, Zn,Ni is relatively high in the study area,with Cu content higher than three cities of Mianyang,Meishan,Ya'an.Zn higher than Ya'an.Ni higher than four cities of Meishan, Mianyang,Ya'an,Leshan.The content of other elements is all lower than that of the six cities in Chengdu economic zone. (5)The irrigation water can reach the quality standard of farmland irrigation water, and the request for pollution-free food and green food producing area.The content of heavy metals in bottom mud is far under the standard of pollutants control of agricultural sludge.Therefore,the bottom mud formed in irrigation canals can be utilized.The drinking water generally can reach the quality standard of drinking water, the content of total rigidity,Mn,TFe and NO₃^- are partially out of standard,especially the content of TFe is over out of standard.It is necessary to find out the pollution origination and enhance inspection,prevention and cure.(6)Compared with the pollution-free health index and green food health index,the grain all meets the requirements,except one sample has comparatively high Pb content which is near the stand limited value.Each target of all the corn and orange samples is under standard.Within the element targets of peanut,As,Hg,Pb all measure up,only Cd exceeds the pollution-free food health index and is a little higher than the green food health index.(7)Combine soil environment,soil nutrients,water environment and ecological effect factors,to implement comprehensive agro-ecological geochemical evaluation and spatial pattern analysis by using GIS spatial overlay analysis.Regions with over-standard air mainly distribute in Fujia village,Dongshan village and Malong village.Regions with over-standard soil centralize in Yuanjue village.Regions with over-standard crops lie in Yuanjue village,Dongshan village and Malong village.As the low content of soil nutrients in the whole area,fertility should be supplied according to different regions.(8)Based on the environment standard of pollution-free food and green food producing area,and combined the agro-ecologieal geochemical comprehensive analysis by using GIS technology,it suggests to set up fruit-medicine production base, green rice-vegetables production base,pollution-free rice-vegetables production base, and freshwater aquaculture production base.Develop suited agro-ecological model: fruit-medicine-livestock agricultural models,rice-vegetables planting models,and fruit-grass around pound ecological models,establish ecological agriculture.