| Animal husbandry is an important part in agriculture and also in the whole national economy.In many countries in the world,the output of animal husbandry surpasses more than 50%of the total output of agriculture.In recent years,however,with the development of animal husbandry,especially the rapid development of large-scale livestock farming,the problems of environmental pollution caused by livestock and poultry breeding have become increasingly apparent.A new trend of livestock pollution in China at this stage is the growing-point source pollution,and it has been a threat to the safety of the ecological environment,in particular a threat to the water environment.Some of the world's developed countries,such as Japan,Finland and the United States,began their environmental pollution control work caused by livestock and poultry manure in the seventies of the last century.In China,in the early nineties of the last century,a number of cities(Shanghai,Beijing,etc.) have begun to carry out regional governance of livestock and poultry manure,and have achieved some results.Directly under the Chongqing Municipality since 1997,a lot of work,including in the social and economic aspects,have been done to combat environmental pollution,and the city's environmental protection investment has increased year by year.The city's environmental protection work in general has made remarkable results,but,as a point source pollution in rural areas,the main source of animal waste pollution has little effect in recent years.Meanwhile little research has been done in this area in the city.Prior to this,comprehensive and systematic study and investigations have not been carried out from the aspects of the pollutional features of livestock and poultry manure and its temporal and spatial dynamics of the city's.Over the years,the main way to proceed our livestock and poultry manure is to put it into the fields as an organic manure.Applied into fields,livestock and poultry manure not only provides nutrients for crops and improves the quality of the soil,it is also a simple means of waste disposal.However,within a certain time and space,the rapid growth of livestock and poultry manure does not have enough farmland to digest and absorab it, resulting in agricultural and pastoral touch,breaking the original ecological model of a virtuous cycle,and coupled with heavy use of fertilizers,finally limiting the way of livestock and poultry manure,so that within a certain region,livestock and poultry manure surpasses the carrying capacity of farmland and great pressure has been brought on the environment.Therefore,the rational use of livestock and poultry manure is of great significance for agricultural production and environmental protection.But questions are: how to make rational use of it? How much livestock and poultry manure is appropriate for per unit area of soil each year ? In practice,the peasants have summed up a saying "One pig,one mu of fields.",which means that by breeding a pig all year round,its manure can be used as fertilizers for each mu of fields of crops,so the growth of crops can be maintained,and no environmental pollution being resulted in.But how is it in science? No one has made an in-depth study on it.And in the real practice,not only pigs are bred,other types of livestock and poultry are also bred.So such a problem has been proposed:how much livestock and poultry manure on earth is appropriate for each mu of land a year,that is:what is the load of livestock and poultry manure suitable fort the soil.For this reason, taking Chongqing as the research object,based on the principle of material balance,to meet crop needs for nitrogen as the premise,this study first regards the whole city of Chongqing as an open system with nutrient input and output.Second,through extensive research and data collection,basic data can be obtained from the macro and micro aspects to determine the input and output items.Finally,under the principle of material balance, within the Chongqing municipality,the difference between nitrogen input and output in each year is equal to the net accumulation of nitrogen within the system.Thus,nitrogen demand of crops per unit area per year can be theoretically calculated.Suppose that all nitrogen comes from livestock and poultry manure,and according to the amount of livestock and poultry manure,nitrogen can be converted to the corresponding pig equivalent,and then divide the year's farming area,we can calculate the theoretical load of livestock and poultry manure each unit area of the soil per year in Chongqing,that is the theoretical load of livestock and poultry manure suitable for soil to meet the needs of crops of Chongqing Municipality for nitrogen In fact,the suitable soil load of livestock and poultry manure is affected by a wide range of factors,such as nutrient levels of the farmland,the different nutrient needs,the nutrient contents of different types of livestock and poultry manure,and regional conditions of manure application(types of land use,soil textures,topographies,seasons,climate,economy,population,etc.).These factors are a dynamic variation.And therefore the appropriateness of livestock and poultry manure is also a dynamic load variation.Based on and obtained from the theoretical analysis of nitrogen balance,whether the theoretical suitable load of livestock and poultry manure in Chongqing is suitable for crop growth,should take the value the theory to test the authenticity in practice.This study takes asparagus lettuce as materials,and is based on the suitable load of theoretical study, and according to the size of basins,pig manure is converted into the corresponding amount and then increases and decreases respectively 100 grams of pig manure for different test levels,with the total of 8 treatment levels,pot experiments are carried out in a greenhouse. The growth of asparagus lettuce is observed every day,and after 85 days it is harvested. The biomass is measured,so is nitrogen and phosphorus and other nutrients and iron and copper and other heavy metals in soil and asparagus lettuce.And analysize and process these data to obtain the results of pot experiments.Applying livestock and poultry manure into the soil increases in it the contents of nitrogen,phosphorus,potassium and metallic elements.As one of the metallic elements in the soil is easy to accumulate,a long-term application of manure will produce contamination of metallic elements on the soil and crops.So even if the soil is applied appropriate amount of manure,livestock and poultry manure should be controlled not to be continuously applied to the same plot during a period of time.In this study,metal element copper is taken as a benchmark to identify the environmental capacity of copper in the soil, the soil background value,the value of copper content in pig manure,and through a certain mathematical formula,the time amount that the pig manure could be applied continuously to the same block of soil can be figured out.Due to the differences in the structures of livestock and poultry breeding,in different regions and during different periods,the livestock manure emissions are variable,and have not the same impact on the environment,which also results in the differences in the emporal and spatial distribution of livestock and poultry manure in Chongqing.This study takes 39 districts and counties in Chongqing City in 2007 as its space units,and such main animals bred in Chongqing as pigs,cattle,poultry(chickens,ducks,geese),and sheep as the research object,with a total of 13 years from 1995 until to 2007.According to the amount of emissions by a single head of livestock and poultry,manure and its major components are to be measured.Combined with the studies at home and abroad,the emission parameters of livestock and poultry in Chongqing are selected.Then according to the number of livestock and poultry bred in Chongqing each year,the annual emissions from various types of livestock and poultry manure and its composition can becalculated. The major nutrient of nitrogen in livestock and poultry manure is taken as the benchmark, and the main livestock-the pigs' emission as units,pig manure equivalent can be converted.With these data,a study can be carried out about the changes in emissions from livestock and poultry manure in Chongqing from 1995 until 2007 each year,and thus comes to the time-varying features of livestock and poultry manure in Chongqing.In spatial distribution,the latest year 2007 is selected as the research object.Combined with geographic information systems,the method of spatial analysis is analyzed to study regional spatial distribution characteristics of emissions from livestock and poultry manure.Finally,according to the established value of suitable soil load of livestock and poultry manure and the emporal and spatial distribution of livestock and poultry farming in Chongqing Municipality,the assessment of environmental impact by breeding livestock and poultry is to be conducted,and the layout of livestock and poultry breeding in Chongqing is proposed.The results show that the theoretical suitable load of livestock and poultry manure in Chongqing is 44.37 t·hm-2.a-1,which is 4.437 kg.m-2.a-1.After the examination of crop pot experiments,it is proved that the load value is the most suitable load value of livestock and poultry manure for the growth of crops.Thus,it can be considered that the suitable load of soil for livestock and poultry manure in Chongqing Municipality is 44.37 t·hm-2.a-1.This value is basically consistent with the " A pig burdens an acre of fields".Poultry manure being applied into the soil,after normal growth of crops,the levels such as nitrogen,phosphorus,potassium and metal elements,copper,iron,zinc in the soil increase significantly,and with the increase in the amount of manure applied into in the soil,nitrogen,phosphorus,copper,zinc and other substances increases linearly.It is appropriate for the same land to be applied to pig manure continuously within 42 years.In Chongqing,the emissions from the main livestock and poultry manure(pigs,cattle, poultry,etc.) are increasing with the changing of time,while the total amount of various types of livestock and poultry manure is also increasing with the changes over time.The biggest change is poultry droppings,an increase of 4.85 times from 1995 to 2007;the smallest change is cattle dung,only an increase by 1.23 times between 1995 and 2007; livestock and poultry manure in Chongqing is 8600.27 million tons in 1995,and 10974.45 million tons in the year of 2007,with an increaseof 1.28-fold,but the development of poultry is the most prominent.The pig equivalent of changes and the changes in the total emissions in Chongqing have the same trend.The value of equivalent load of pig manure ranges between 21.343t.hm-2a-1.and 27.74t.hm-2a-1,the changes being relatively stable,but the overall trend is that as time goes by,the load increases year by year,and the correlation has reached an extremely significant level.The amount of nutrient emissions and loads of livestock and poultry manure in Chongqing are increasing year by year.The biggest annual emissions of organic matter is in 2007,1151.96 million tons,and the smallest in 1995,935.57 million tons,the fluctuation value being 216.39 million tons.Annual emissions of nitrogen is much smaller than the organic matter,the largest being in 2007,to 61.31 million tons the smallest in 1995,to 47.26 million tons.Among these four substances from livestock and poultry manure,the smallest annual emission is phosphorus,only from 24.33 to 31.05 million tons each year,equivalent to about one fortieth of organic matter of the year.The nitrogen load of livestock and poultry manure in Chongqing per year fluctuates between 0.13--0.17t·hm-2,the phosphorus load 0.06--0.08 t·hm-2 and the potassium load 0.15--0.19 t·hm-2. The general trends of load changes of nitrogen,phosphorus,potassium are almost the same, the load incrasing with the changes of time.The load change of phosphorus is relatively small,the changing trend line almost being straight.Emissions from various types of livestock and poultry manure have shown a strong regional characteristics.Pig manure is concentrated in Hechuan,Banan,Wulong,Fuling, Kaixian and so on.The maximum area is Hechuan,with 464.13 million tons,the smallest area is Shuangqiao,with 5.91 million tons Sheep manure is concentrated in Youyang, Fengjie,Chengkou and other places.The largest region is Yunyang for 21.14 million tons, and the smallest area is Nanan 0.014 million tons.Cattle manure is concentrated in Tongliang,Yubei,Nanan and other places.The largest region is Youyang for 220.75 million tons,and the smallest region is Shuangqiao for 0.18 million tons.Poultry droppings are concentrated in Bishan,Yongchuan,Tongliang,Changshou and so on.Large differences in Chongqing exist among the pig manure equivalent load of regional distribution.The largest pig equivalent region lies in the suburbs,such as Dadukou,Jiulongpo,etc.;while the smallest are located in the remote mountainous areas, such as Chengkou,Wuxi,Wushan and other counties.Large Organic load areas are mainly located in the Three Gorges reservoir area such as Youyang,Rongchang,the main corridors of the West Chongqing,and Jiangbei City,Jiulongpo and other areas;large nitrogen load areas are mainly concentrated in the main city of Jiangbei,Shapingba, Jiulongpo and Rongchang,Hechuan and Youyang--the Three Gorges reservoir area.Large phosphorus load areas are focused on Rongchang,Hechuan,and Jiangbei.The environmental assessment of Chongqing's livestock and poultry breeding shows that with livestock and poultry breeding,2.6%of Chongqing's districts and counties have no pollution on the environment,68.4%of them have a little pollution on the environment, 23.7%of them have environmental pollution,and 5.3%of them have more serious environmental pollution.Under the existing amount of aquaculture,in Rongchang and Jiangbei District,the breedings have already been more than the carrying capacity of arable land.These two regions should be limited in quantity and be controlled of livestock and poultry breeding structure,and other regions still have a certain degree of culture space for development.To take breeding pigs as the standard,districts and counties which can further develop more than 2 million pigs include Fuling,Hechuan and other six districts and counties,accounting for 15.8%of the number of districts and counties in Chongqing; Those which can develop more than 1 million include 15 districts and counties such as Qijiang,Changshou,accounting for 39.5%of the number of districts and counties;Those which can develop no more than 1 million have 15 districts and counties of Chongqing: Beibei,Nanan,and so on,accounting for 39.5%of the number of districts and counties.
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