Application Of Vegetable Waste Fermentation Broth For Regulating Nitrate Accumulation And Vegetable Growth In Greenhouse Soil

In China,a large quantity of vegetable.waste is not properly treated and utilized in the process of harvesting,transportation,processing and sales,causing environmental pollution.On the other hand,high-intensity fertilization in greenhouses has caused serious over-accumulation of nitrate in the soil,not only affecting crop yield and quality,but also increasing non-point source pollutionJn order to reduce the cost of nitrate control in greenhouse soil and broaden the utilization approach of vegetable waste,this paper adopted the method of acidic fermentation to obtain the fermentation broth containing water-soluble organic carbon(SOC)from vegetable waste,and then,the fermentation broth was used at different rates based on the extent of soil nitrate accumulation to regulate the accumulation of nitrate in greenhouse soil and vegetable.In the acidic fermentation experiment of vegetable waste,using Chinese cabbage vegetable waste as test material,40-day anaerobic fermentation(hydrolysis acidification)at a water-to-Chinese cabbage vegetable waste ratio of 2.4:1 was carried out in greenhouse environment(15-30?)with 4 treatments being set up,including inoculation of denitrifying activated sludge and pH regulation in the middle of the fermentation(day 15)using magnesium oxide(0.40g·L-1).Results show that the pH was lowered below 5 after 5 days of fermentation.the addition of magnesium oxide increased the pH to 5.0 or higher in a short time and promoted the formation of SOC.At the end of fermentation,the pH of each treatment was above 4.2,and the accumulation of organic acids exceeds 20mmol·L-1.The treatment with pH adjustment and denitrifying activated sludge inoculation averagely had the highest level of COD.After 30 days of treatment,the fermentation broth became stable,with the COD level around 10.0g·L-1,the C/N ratio greater than 40,the K/Na ratio greater than 10,and multiple types of available mineral nutrients at proper ratios,which could be used to regulate soil nitrate accumulation and vegetable growth.In the experiment of using the fermentation broth of vegetable waste to regulate the accumulation of soil nitrate and vegetable growth in a low-nitrate soil(49.9mg·kg-1),ammonium bicarbonate(0.25 or 0.5g·kg-1)was applied in the low-nitrate soil,and SOC from the fermentation broth was added through irrigation at 90 or 180mg·kg-1 COD once to create short-term soil moisture saturation(water content of 40%)respectively in the early and middle stages of lettuce growth.through experimentation found that the fermentation broth promoted nitrate accumulation in low-nitrate soil(20.12%-46.29%),and the soil pH value increased slightly,which was beneficial to alleviate soil acidification.The vegetable yield increased(4.69%-27.41%),and the nitrate content of lettuce in each treatment was reduced(3.81%-28.63%).In the experiment of using the fermentation broth to regulate nitrate accumulation and vegetable growth in a moderate-nitrate soil(164.3mg·kg-1),no chemical fertilizer was not applied,and SOC(360-720mg kg-1 COD)from the fermentation broth was added once through irrigation to create temporal soil moisture saturation(water content of 40%)respectively in the early and middle stages of lettuce growth.The test results showed that the addition of the fermentation broth could significantly reduce nitrate accumulation in the moderate-nitrate soil(14.68%-33.21%),slightly increased the soil pH,increased the lettuce yield(5.76%-14.07%)and reduced the nitrate content in lettuce(19.30%-33.27%).In the experiment of soil reduction treatment of a high-nitrate soil(502mg·kg-1),the effects of vegetable fermentation broth and other types of carbon sources(sugar,straw fermentation broth,denitrifying sludge,straw)on soil nitrate accumulation were studied.The study found that the fermentation broth was very effective at supporting denitrification-based nitrate transformation to lower soil nitrate accumulation(41.65%),with a capacity only slightly weaker than sucrose.The vegetable waste fermentation broth could be used as a composite carbon source for soil reduction treatment of high-nitrate greenhouse soil,reducing the extent of nitrate over-accumulation and supplementing various mineral nutrients at proper ratios.Anaerobic fermentation treatment of vegetable waste is of low control requirements,but can efficiently transform/mobilize its organic matter and mineral elements.The obtained fermentation broth can not only control nitrate accumulation in greenhouse soil,but also promote vegetable growth and improve environmental quality.