Effect Of The Continuous Application Of Biogas Slurry On Quality Of Soil And Rice Under The Mode "Rice-Cole-Rice"

Biogas slurry is a nutrient-rich liquid organic fertilizer. The rational application of biogas slurry could improve soil fertility, improve soil physical and chemical properties, improve the resistance to pests and improve crop quality and yields. Meanwhile, usage of biogas slurry in agriculture could reduce the use of chemical fertilizers, pesticides and reduce its harm to environment.In present study, rice was cultivated on the farmland with yellow-brown paddy soil. The farmland was divided into several parts. Experimental groups were fertilized by different amount of biogas slurry which mainly contained pig waste as a fermentation raw material. The control group was fertilized by water and chemical fertilizer. The farmland had been cultivated successively for3quarters with rice, cole and rice, respectively. The appropriate amount of biogas slurry applied in the southern massif district and the soil endurance on the application of biogas slurry were studied. From the above research, some conclusions could be drawn as follows:(1) In comparison with the original soil, after the continuous application of biogas slurry for3quarters in the same farmland, the pH value, content of available potassium (AK), cation exchange capacity (CEC) in current soil increased. Content of alkali-hydrolyzable nitrogen decreased except for the one (increased by2.4%) treated by the biogas slurry concentration of6000kg/666.7m2. content of organic matter, total nitrogen, available phosphorus in current soil also decreased.(2) In comparison with the original soil, the content of available iron increased when the amount of biogas slurry applied was3600-4800kg/666.7m2, while treatment of other amount of biogas slurry continuously decreased. Content of available manganese in soil decreased in all treatments except when applied biogas slurry of6000kg/666.7m2; content of available manganese decreased most by52.81%when treated with water. Content of available copper decreased except treated with biogas slurry of3600kg/666.7m2whose content increased by11.96%. Available zinc in all the treated soils increased, of which the one treated with biogas slurry of3600kg/666.7m2increased the most by87.33%.(3) Compared with original soil, content of lead in current soil declined a lot. Nickel content increased in all the treatment, of which applied biogas slurry of6000kg/666.7m2increased the most by18.42%. Content of chromium in all treated soil had an increase. Cadmium content in current soil increased when treated with large dosage of biogas slurry, while decreased when treated with low dosage of biogas slurry. Arsenic content in all treated soils had huge increase, of which the content increased by76.40%when treated with the biogas slurry of3600kg/666.7m2. While mercury content in all the treated soil decreased slightly.(4) With the increase of treated biogas slurry, protein content in polished rice, brown rice rate and zinc content in rice gradually increased. The content of total amino acid, Mn, Cu, Ca and Mg in rice increased first and then decreased. While content of Fe in rice continuously decreased. Content of Ca and Mg in polished rice of the second quarter was higher than that of the first quarter, while content of the other inorganic elements in current rice were lower.(5) Under the "rice-cole-rice consecutive farming" mode, content of Pb, Cr, Cd and As in polished rice would increase with the consecutive application of biogas slurry. Content of Ni increased first and then decreased in polished rice, while Hg was not detected in rice. Content of Pb、Cr、Cd and Ni in polished rice were lower in the second quarter than that in the first quarter, while content of As was higher in polished rice of the2nd quarter.(6) Under the "rice-cole-rice consecutive farming" mode, the application of biogas slurry to cultivate rice could affect the quality of soil and rice. If take soil quality as the first goal, the amount of biogas slurry applied should controlled at3600-4800kg/666.7m2in the second quarter. This amount was better for the enhancement of soil fertility, environmental quality and environmental benefits. While if take the rice quality as the first goal, the amount of biogas slurry applied should controlled at3000～4200kg/666.7m2, when the rice could get the highest yield and best quality as well as good environmental and economic benefits. If take soil quality, rice yield and quality and some other factors as a consideration, the best application amount of biogas slurry for farming was3600～4200kg/666.7m2, when the environmental and economic benefits achieved the best balance. The maximum endurance of biogas slurry applied on the farmland was 4200kg/666.7m2,when the quality of soil and rice could achieve a good level.