Effects Of Continuous Application Of Different Amounts Of Biogas Slurry On Soil Material Transferring Lengthwisely Under Rice And Rape Rotation Test

The study countered the problem of security of biogas slurry as a fertilizer using several years.In the field trial,the biogas slurry used as irrigation fertilizer was completely anaerobic fermentation by the raw material of pig manure and piss coming from a large scale pig farm,which using the Tongwei fodder feeding the pigs. Twelve treatments have been made (one control applied with clean water, one applied with conventional fertilizer, and ten applied with different quantities of pure biogas slurry), on the rice-planted yellow soil in Qionglai City of Sichuan Province. The objects of the study were the soil samples collected from 0-20cm(soil layer A),20-40cm(layer B),40-60cm(layer C),60-80cm(layer D),80-100cm(layer E) soil layers.The aim of the research is to study the accumulation and migration characteristic of soil material of rice-rape rotation soil after the continuous application of biogas slurry. The main conclusions are as follows. 1) Application of Biogas slurry can increase clay content in the 0-80cm soil layers, to a certain extent. As the application amount of Biogas slurry increasing,the impact on the mechanical composition in the deep soil layer were increased,while the effect on the mechanical composition by the chemical fertilizer were mainly in the A and B layer of soil.2) Both of biogas slurry and chemical fertilizer can improve the aggregate structure of 0-80cm soil,and promote the formation of> 0.25mm waterstable aggregate.Besides, biogas slurry make for the transforming of<0.25mm aggregate to>0.25mm aggregate,because the fractal dimension of A、B、C、 D soil layers have the trend of decrease as the increasing amount of biogas slurry. With the increase of soil depth,water stability aggregates in small size are increased.Compared with chemical fertilizerma certain amount of biogas slurry can promote more 2-5 mm, 1-2mm particle size of aggregate formulated in A,B soil layer,and more 1-2mm particle size of aggregate formulated in C soil layer,more 2-5mm、0.25-0.5mm particle size of aggregate formulated in D soil layer,and more 0.25-0.5mm particle size of aggregate formulated in E soil layer. What’s more,biogas slurry improves the aggregate composition in 0-40cm, 60-80mm soil layer and Biogas slurry treatment 9-12 improves the aggregate composition in 40-60mm soil layer,which are more effective than chemical fertilizer treatment.3) Application of large amount of biogas slurry (biogas slurry treatment 6-12)have higher efficiency of improving the pH of acid soil,as the value of pH in different treatment showing a tendency of increasing with the increase of the applied amount of biogas slurry.However,both of the application of small amout of biogas slurry(biogas slurry treatment 3-6) and the chemical fertilizer can lead to the decrease of pH value.4) Application of biogas slurry promote the migration of water soluble K,Ca,Na,Mg.With the increase amount of biogas slurry,the content of water soluble Ca,Na in each of 0-80cm soil layer and the content of water soluble Mg in each of 0-60cm soil layer have a tendency of increasing generally.White the content of water soluble K in 0-60 cm soil layer show the tendency of first increasing then decreasing,but the content of water soluble K in 60-100 cm soil layer show a tendency of increasing. The type of impact of Chemical fertilizer and biogas slurry on soil salt accumulation are the surface-accumulation type,both of them can improve the migration of the soil salt in 0-80cm soil layers,but biogas slurry are more efficient,and application of large amount of biogas slurry treatments soil accumulate more soil salt than chemical fertilizer.However,three yeres application of biogas slurry do not have problem of soil salinization in 0-100cm soil layer, on contrast, biogas slurry can improve the soil available nutrient status.5) Application of biogas slurry promote the accumulation of Zn,Cu,Cd,Cr,As,Hg in the surface soil layer,as for the content of Zn,Cu,Cd,Cr,As increasing with the amount of biogas slurry increasing, the content of Hg first in increasing then decreasing(still more than water treatment). But application of biogas slurry will not promote the accumulation of Pb in the surface soil layer, firstly,.Second,0-20cm soil layer is the main layer accumulating heavy metals, the larger amount of biogas slurry is, the more heavy matels in deep soil layer accumulate:in 20-40cm soil layer,the content of Pb,Cr,As decrease by the increase of biogas slurry applicating amount(still more than water treatment),but Zn,Cu,Cd,Hg increase with the increase of the amount of biogas slurry;in the 40-60cm, the content of Zn,Cr,As,Hg increase,the content of Cu,Cd increase generally, Hg decrease, with the increase of the amount of biogas slurry;in 60-80cm soil layer,the content of Pb,Zn,Cr increase with the the increase of the amount of biogas slurry, the content of Cu,Cd,As,Hg have a slight increase;in 80-100cm soil layer,with the increase of the amount of biogas slurry,the content of Pb has a slight increase but showing variability, the content of Zn increase generally.the content of Cu,Cr have no significant changes, the content of Cd have a slight increase, the content of As,Hg do not have an obvious change trend. Third,as a compared treatment,chemical fertilizer mainly lead to the increase of Pb,Cd,Cr,As,Hg in 0-20cm,20-40cm soil layers, and the decrease of Zn,Cu.Compared with chemical fertilizer,application of biogas slurry can promote the migration of Pb,Zn,Cu,Cd,Cr,As,Hg to accumulate in deep soil layers.6) The single factor pollution indexes of Pb,Zn,Cu,Cr,As,Hg of each biogas treatment in 0-100cm soil layer are less than l,but the Nemerow comprehensive pollution indexes of each biogas treatment in 0-20cm are more than 1,indicating that the soil are under mild contamination,and Cd is the contribution factor for the contamination;the 20-40cm soil layer of each treatment are under security alert state,and Cd,Cu are the contribution factors for the contamination, the 40-100cm soil layer of each treatment are at the good state,and have low environmental pollution.In conclusion,three years application of certain amount of biogas slurry,which can improve the soil structure and the composition,have an improving effect on the pH of soil,which can lead to the migration and accumulation of soil salt and heavy matels in the surface and deep soil layers,but don’t have the problem of soil salinization in 0-100cm soil layer and have low environmental pollution of heavy matels of Pb,Zn,Cu,Cr,As,Hg,but will aggravate soil Cd pollution problem.