Effects Of Irrigation Of Biogas Slurry On Plant Growth,Soil Nutrient Content And Nitrogen Loss

Returning biogas slurry to farmland is an effective way to treat aquaculture istewater.In Guangxi,the planting area of Eucalyptus(Eucalptus urophylla x E.grandis)and Sugarcane(Saccharum officinarum)is larger,while the Forage Grass(Pennisetum purpureumSchum)has larger biomass.The biogas slurry absorption potential of these three plant systems is large.At present,little is known about the safe uptake of biogas slurry,nutrient transfer and loss,especially the volatilization characteristics of nitrogen after the application of biogas fertilizer,such as Eucalyptus and Sugarcane.In order to explore the potential and environmental effects of the combination of Eucalyptus×Forage Grass to absorb biogas slurry from aquaculture farms,pot experiments are carried out to irrigate four planting patterns of Eucalyptus,Forage Grass,Sugarcane,Eucalyptus×Forage Grass.The characteristics of plant growth,soil nutrient content changes and nitrogen volatilization and leaching under different planting types and irrigation rates are analyzed in order to determine safer and more efficient in the future.The types of cultivation modes for digestion and cultivation of cultivated land biogas slurry and the safe capacity for irrigation of biogas slurry provide the basis.The following major advances have been made:(1)As a whole,the biomass of plants increased first and then decreased with the increase of the amount of biogas slurry irrigation,but the change trends of different treatments is different.Forage Grass yield irrigated with biogas slurry in pot experiment Eucalyptus×Forage Grass treatment only 1/3-1/2 of pure Forage Grass treatment.With the increase of biogas slurry irrigation,the nitrogen,phosphorus and chlorophyll content of Eucalyptus leaves in the combination of Eucalyptusx Forage Grass crops increased,and the height and diameter of Eucalyptus increased faster with the increase of irrigation amount until the growth rate decreased when the irrigation amount increased to 2400 m3/hm2.The yield of forage in Eucalyptusx Forage Grass treatment also increased with the increase of irrigation,but not significantly,Eucalyptus intercropping with Forage Grass did not affect the growth of Eucalyptus,but greatly increased the capacity to absorb biogas slurry.(2)In general,soil nutrients also increased with the increase of the amount of biogas slurry irrigation,and the effects of biogas slurry and chemical fertilizer on soil is different.Under 600 m3/hm2 biogas slurry irrigation in pot experiment,the soil total nitrogen content of Eucalyptus xForage Grass combination is lower than that of other plants,and there is no significant difference between other plants.Biogas slurry is more conducive to the sustained release of fertilizer than chemical fertilizer to increase the content of nitrogen and phosphorus organic matter in soil.Biogas slurry and chemical fertilizer have the effect of reducing soil pH,but the effect of chemical fertilizer is more severe.Soil nutrients of Eucalyptus xForage planting structure increase with the increase of biogas slurry irrigation,but soil nutrients do not increase when the irrigation amount exceeds 1800 m3/hm2.(3)On the whole,the nutrient concentration of leachate increased significantly with the increase of irrigation biogas slurry,and the change trends of different fertilization treatments and plant treatments is different.Fertilizer application can reduce the pH of leachate water,but chemical fertilizer is more obvious than biogas slurry;ammonium nitrogen content in leachate of Eucalyptus×Forage Grass under 600 m3/hm2 biogas slurry irrigation is significantly lower than that of other plants,nitrate nitrogen content in leachate of Sugarcane is significantly lower than that of other treatments,and there is no significant difference between other planting modes;biogas slurry can significantly reduce the risk of leachate pollution after land absorption,and Application When the amount of fertilizer and biogas slurry irrigation exceeds 1800 m3/hm2,the content of nitrogen and phosphorus in the leachate of potted plants will be higher.Under the same nutrient input,the biogas slurry irrigation is more difficult to cause the eutrophication of the leachate than the chemical fertilizer irrigation.(4)With the increase of irrigation biogas slurry,nitrogen volatilization increased,but the proportion of nitrogen volatilization to nitrogen input decreased first and then increased.The ammonia volatilization and nitrous oxide volatilization of all plant types reached the highest level on the same day after the irrigation of biogas slurry,and then decreased day by day.The ammonia volatilization tended to zero on the fifth day after the irrigation of biogas slurry and the nitrous oxide on the third day.Their emissions increased sharply with the increase of the amount of biogas irrigation.The rate is 4.5%-11.3%.Under 600 m3/hm2 biogas slurry irrigation,the loss of nitrogen caused by ammonia volatilization from Sugarcane and Eucalyptus×Forage Grass soil is greater than that of Eucalyptus and Forage Grass,and the loss rate of nitrogen oxide emission is much lower than 0.1%.In the combination of Eucalyptus×Forage Grass,ammonia volatilization caused by the amount of biogas slurry irrigated at 1200 m3/hm2 and 1800 m3/hm2 resulted in the lowest nitrogen loss rate;ammonia volatilization is positively correlated with light intensity,soil moisture and air temperature after the irrigation of biogas slurry,but the correlation with soil moisture and air temperature is not significant except for the very significant correlation between light intensity,while the correlation of ammonia emission in the experiment correlated with soil temperature is small.(5)It is found that irrigation of marsh liquids in farmland is more beneficial to plant growth and pollution caused by nutrient loss than fertilization.After irrigation with biogas slurry,most of the nutrients accumulated in the soil under the action of plants,while the loss of nitrogen was mainly caused by water leaching and ammonia volatilization.In this experiment,the biogas slurry capacity of the 4 planting modes is Eucalyptus×Forage Grass>Sugarcane>Eucalyptus>Forage Grass;the maximum safe capacity of the biogas slurry for EucalyptusxForage Grass is 1200-1800 m3/hm2,which is equivalent to the amount of biogas slurry generated from 10-15 pigs per mu(667m2).