| The mudflat saline soil in the eastern China can be used as an important reserve land resource,especially under the current situation of arable land shortage caused by the rapid industrialization and urbanization in China.The newly reclaimed mudflat saline soil must be amended before agricultural production due to its adverse soil properties characterized by high soil salinity and extremely low soil fertility.Massive input of organic matters from outside is the key approach for rapid mudflat amendment.Being rich in organic matter,nitrogen,phosphorus,and other nutrients,it is an important topic to study whether sewage sludge can be used as a low-cost exogenous organic matter for high-efficiency fertilizer improvement in mudflat saline soil,and to realize the recycling of waste resources and nutrients and energy materials.In order to study the effects of sewage sludge addition on mudflat soil amendment under different utilization modes(paddy cultivation and upland cultivation)of mudflat,field trials were carried out at reclamation areas of Sheyang and Fangling.Rice,sweet sorghum,and barley were used as test crops to study the effects of sewage sludge application on soil salt reduction,fertilization and crop growth in mudflat soil,as well as the corresponding environmental effects of heavy metals.In addition,we studied the effects of sewage sludge addition on rice root growth in mudflat soil through pot experiment.In order to reduce and stabilize heavy metals in the process of mudflat amendment by sewage sludge,we used maize and barley as test trial plants and studied the effects of vermicompost addition on mudflat soil amendment and plant growth,especially the environmental effects of heavy metals in Tiaozini reclamation area.The main results were as follows:(1)One-time sewage sludge and vermicompost addition all significantly reduced soil salinity in mudflat under paddy cultivation and upland cultivation.During the three-year experimental periods,soil salinity in the maximum sludge addition treatment(180 t ha-1)was reduced from 5.25‰ to 2.38‰ in mudflat under paddy cultivation,and soil salinity in the maximum sludge addition treatment(250 t ha-1)was reduced from 8.35‰ to 2.31‰ in mudflat under upland cultivation,and soil salinity in the maximum vermicompost addition treatment(250 t ha-1)was reduced from 4.04‰ to 1.96‰ in mudflat under upland cultivation With the increase of sewage sludge and vermicompost addition rates,the decreases in soil salinity caused by the application of unit sludge and vermicompost gradually decreased.After one-time application of sewage sludge and vermicompost,soil salinity decreased gradually during the three-year experiment.The decreases in soil salinity in sludge and vermicompost treatments were significantly higher than those in control treatments.Sewage sludge and vermicompost addition decreased soil pH in mudflat under paddy cultivation and upland cultivation,and soil pH decreased with the increase of sewage sludge and vermicompost addition rates and amending years(2)One-time sewage sludge addition promoted soil aggregate formation in mudflat under paddy cultivation and upland cultivation.Sewage sludge and vermicompost addition decreased soil bulk density in mudflat under paddy cultivation and upland cultivation,and soil bulk density decreased with increasing sludge addition rates and amending years during the three-year experiment.(3)Sewage sludge and vermicompost addition all increased soil organic carbon contents in mudflat under paddy cultivation and upland cultivation,and soil organic carbon contents increased with increasing sludge addition rates and amending years during the three-year experiments.Sewage sludge addition increased soil fertility by increasing soil nitrogen and phosphorus contents,and soil total N,alkaline N,total P,and available P contents in sludge-amended mudflat were significantly positively correlated with sludge addition rates.Vermicompost addition also increased soil total N,alkaline N,total P,and available P contents in mudflat under upland cultivation.(4)The application of sewage sludge significantly increased rice yield for 3 consecutive seasons in mudflat under paddy cultivation.Compared with rice yield in control treatment,rice yield in the maximum sludge addition treatments in 2016,2017 and 2018 increased by 125.2%,124.7%and 127.9%,respectively.According to the relationship between rice yield and sludge addition rate,in the range of 0-210 t ha-1 sludge addition rates,rice yield would increase with increasing sludge addition rates.Meanwhile,the increment of rice yield per unit sludge addition was gradually reduced.Rice yield in sludge-amended mudflat increased during the three-year experiment.The highest economic benefit was found in the treatment with 120 t ha-1 sludge applied.Sludge addition increased rice yield,promoted rice root growth,enhanced the bleeding sap of rice plant,and increased the solubility sugar and amino acid contents in the bleeding sap in pot experiment,and at the same time increased rice root activity,and the higher the amount of sludge application,the stronger the rice root activity.(5)Sewage sludge addition promoted sweet sorghum growth,and increased the stem and leaf dry weight of sweet sorghum.According to the relationship between sweet sorghum biomass and sludge addition rate,in the range of 0-450 t ha-1 sludge addition rates,for each 100 tons sewage sludge added into mudflat soil,approximately 2.02 tons of sweet sorghum biomass can be obtained.With the increase of sludge addition rates,the gross energy content of sweet sorghum increased continuously.Sewage sludge addition increased the biomass and yield of barley in mudflat under upland cultivation.(6)Vermicompost addition promoted the growth of maize and barley in mudflat under upland cultivation,and the biomass and yield of maize and barley increased with increasing vermicompost addition rates.Meanwhile,the increments of crop yields per unit vermicompost addition were gradually decreased.One-time application of vermicompost had a continuous effect on the increase of maize and barley production.The yields of maize and barley increased during the three-year experiment,and the annual increases in yields of maize and barley were 11.8%and 31.8%.respectively.(7)Sewage sludge addition increased soil total and available metal concentrations in mudflat under paddy cultivation and upland cultivation.While soil total metal concentrations were lower than relevant national standards.Soil total metal concentrations in sludge-amended mudflat decreased and soil available metal concentrations increased during the three-year experiments.Sewage sludge addition increased the uptake of metals by rice and barley plant in mudflat.The uptake of heavy metals by rice and barley organs as a whole was:root>stem>leaf>grain.With the increase of sludge addition rates,the concentrations of Cd,Cr,Cu,Ni,Pb,and Zn in root,stem and leaf of rice and barley gradually increased.Cd,Ni,and Zn concentrations in rice grain and Cd,Cu,Ni,Pb,and Zn concentrations in barley grain also increased with increasing sludge addition rates,while Cr,Cu,and Pb concentrations in rice grain and Cr concentrations in barley grain did not change significantly.The metal concentrations in rice and barley plants decreased in sludge-amended mudflat during the three-year experiments,and the concentrations were all lower than relevant national standards.(8)Vermicompost addition increased soil total and available metal concentrations in mudflat under upland cultivation.Soil total metal concentrations decreased and soil available metal concentrations increased in vermicompost-amended mudflat during the three-year experiment.Compared with sludge addition under the condition of maintaining equal carbon input,vermicompost addition allowed heavy metals to accumulate in a more stable binding form in the top 20-cm layer of mudflat soil.Vermicompost addition increased the uptake of metals by maize and barley plant in mudflat The uptake of metals by maize and barley organs as a whole was:root>stem>leaf>grain.Cd,Cr,Cu,Ni,Pb,and Zn concentrations in root,stem and leaf of maize and barley and Cd,Cr and Pb concentrations in maize grain and Cd,Cr,Ni and Zn in barley grain gradually increased with the increase of vermicompost addition rates.While Cu,Ni and Zn concentrations in maize grain and Cu,Pb and Zn in barley grain did not change significantly.The metal concentrations in maize and barley plant decreased in vermicompost-amended mudflat during the three-year experiment,and the concentrations were all lower than relevant national standards.Compared with sludge addition under the condition of maintaining equal carbon input,vermicompost addition can effectively reduce the accumulation risk of heavy metals in maize plants. |
PDF Full Text Request