The Effects Of Biogas Slurry On Soil Improvements

In recent years, the rapid development of large and medium biogas projects played an important role in domains such as the new energy development, rural environment improvement, and so on. However, the anaerobic fermentation residues such as biogas slurry have the characteristics of continuous, large amount and centralization, its harmless treatment have become bottleneck for the normal operation of biogas projects. Biogas slurry contains a variety of water-soluble nutrients, which are available and high efficient for crops. When applied in field, the biogas slurry could not only improve crop yield and quality, but also prevent disease and improve soil structure. Thus, biogas slurry is considered as an ideal organic fertilizer. However, the antibacterial mechanism of biogas slurry and the way of effective utilization as fertilization are not yet entirely clear. In this research, the antibacterial mechanism of biogas slurry was investigated; impacts of biogas slurry subsurface irrigation on soil fertility characteristics and microbial community in soil were studied. Based on results of above research, the key components of biogas slurry fertilizer machine are designed. The main research results are as follows:(1) Antibacterial mechanism of biogas slurry1) With the concentration increased from20%to100%by step of20%, inhibition rate of both biogas slurry and supernatant on five kinds of pathogens(Rhizoctonia solani, Fusarium nivale, Fusarium oxysporum, Fusarium solani, Sclerotinia sclerotiorum) gradually improve, and the concentration of100%biogas slurry has the best inhibitory effect, but inhibition rate decline with time.100%biogas slurry has significant inhibition on Rhizoctonia solani, Fusarium nivale, Fusarium oxysporum, Fusarium solani, inhibition rates are70%,40%,68%,70%, respectively. Inhibitory rate of Sclerotinia sclerotiorum is poor, only25%.100%sterilized biogas slurry has little inhibition effect, and the maximum inhibition rates were30%,15%,35%,25%and10%, respectively.100%supernatant has tiny inhibition effect, and the maximum inhibition rates were48%,35%,47%,55%and18%, respectively.while the sterilized100%supernatant is far less than before, with inhibition rate of23%,14%,22%,20%and13%, respectively.2) In order to find the inhibitory factors in the biogas slurry, the slurry was pretreated by five methods, namely, untreated, sterilization, centrifugal supernatant, sterile filtration and bacteria solution. Then the antibacterial test was carried out. The result showed that the antibacterial effect: bacteria solution is the best, and the others are untreated, centrifugal supernatant, sterile filtration and sterilization, respectively. The inhibition rate of bacteria solution were74%,45%, 68%,64%and24%, respectively, and the inhibition time are longer than raw slurry. This suggested that the microbial of bacteria solution played a main role in inhibiting pathogens. In addition, the inhibition rate of sterilization was still the smallest.3) After the isolation, screening and purification for the microbe from biogas slurry, finally,8fungi,48bacteria and3strains of Actinomycetes were obtained (No.1-59). Then, the co-culture experiments were respectively conducted using each microbe with the pathogens. As a result, there were two strains showing stronger inhibitory effect to the pathogens was detected, namely, nfd-9and nfd-16. The scan electron microscope observation showed that the mycelia of pathogens was firmly tangled or pierced by the mycelia of nfd-9, thus, the growth space of r. solani was limited. Additionally, nfd-9could rival the necessary nutrients for growth with pathogens, thus playing the inhibitory effect. These results suggested that the mycoparasitism was an important mechanism for nfd-9as antagonistic microorganism. The antibacterial mechanism of nfd-16was constantly to invade the growth space of pathogens, or covered, or intruded into the pathogenic colony, which could form a ring of encirclement to prevent the pathogens get in touch with the plant root and leaf surface, thereby playing the inhibitory effect. The inhibitory effect of Antagonistic bacteria against R.solani and Sclerotinia sclerotiorum was best, and the inhibition rate of above90%. Moreover, the inhibitory rate for Fusarium solani, Fusarium fungi and Fusarium nivale was at the range of70-80%.4) strains are identified by molecular biological technology, strain nfd-9and nfd-16were Rhizopus oryzae and Trichoderma harzianum. Antagonistic bacteria are mainly belonging to bacillus, illustrating huge bacteria in biogas slurry.(2) Soil fertility characteristics and microbial diversity1) Biogas slurry can improve the pH, content of ammonium nitrogen, nitrate nitrogen, available phosphorus, available potassium and organic matter. The pH of T3treatment can increase from7.3to7.6, improved about4.11%, T2is the next, about3.91%, the worst one is T1, only2.61%. The pH of three groups of water control is unchanged. With the increase of biogas slurry, ammonium nitrogen increased. Soil ammonium nitrogen of T3has the highest content,34.52mg/kg, and the control treatment has almost no change. The effects of biogas slurry on available phosphorus is less than nitrogen, and T3treatment has the biggest available potassium content in soil, about364.42mg/kg, improved32.55%compared with the pre-implantation, T2and T4are the next, about26.98%and36.7%, respectively. Biogas slurry has superior and significant effect on soil organic matter to conventional chemical fertilizers. Soil organic matter content of T3, T2and T1is23.48g/kg,23.13g/kg and22.84g/kg, respectively.2) With the increased of biogas slurry, the number of bacteria also corresponding increase, the number of bacteria of T3after fertilization is the most, counting up by32×105CFU/g to59.97×105CFU/g, T2is to53.13×105CFU/g, and T1reach49.00×105CFU/g. But the control did not change significantly. The number of soil fungi has similar laws with soil bacteria; however, the level of increase is low. The largest number soil fungus of T3is approximately31×104CFU/g, an increase of about40.91%, and T2and T1increased about36.36%and31.81%. Conventional chemical fertilizers reduce slightly the number of fungi. The maximum number of actinomycetes is about27×104CFU/g, increased by26.09%, compared to the average initial number of actinomycetes of23.67×104CFU/g. Actinomycetes of control treatment Conventional chemical fertilizers has almost no change, which are between22×104CFU/g and24×104CFU/g, and less than biogas slurry tretments.3)27categories bacterial strains are derived from the DGGE profiles of bacteria and actinomyces in soil. The diversity index is4.16, slightly higher than in the control treatment, and evenness indexes are basically the same. Biogas slurry significantly reduced species of bacteria in the soil.13major bands are derived from the DGGE profiles of soil fungi, and these bands are clear and bright, belonging to the common bands, lack of peculiar bands. Biogas slurry has little impact on fungi compare with bacteria.(3) Design of biogas fertilizer machineThe total design scheme is that forward and turning power of biogas slurry tanker is provided by tractor, while fertilization and other operations are carried out by fertilizing machine behind the tanker. An antiblocking type distributor is designed to slave the problem of high viscosity and blockage of the biogas slurry, and its principle and structure are discussed.