Remediation Technologies for Cadmium Contamination in Greenhouse Vegetable Fields

Based on the literature and experimental results, three kinds of soil amendments, namely rice biochar, hydroxyapatite and potassium dihydrogen phosphate(KH2PO4), and deeper ploughing were selected to evaluate the field application effect of soil amendments and agronomic measures on the remediation of Cd contamination in greenhouse vegetable fields. Cd-contaminated greenhouse screening was conducted from 2015 to 2017. In September 2017, comparative tests of eight treatments were performed, and a preferred test was performed in September 2018. The screening results of the contaminated areas indicated that the distribution of over-standard sites was uneven, and Cd content was significantly different. Over-standard rate of No.4 greenhouse was 83.33% and was the highest, and the average content of Cd in soil was 0.535 mg/kg. It was used as a comparative test greenhouse for eight treatments. No.1 greenhouse was selected as the preferred test greenhouse, with three over-standard plots having average Cd concentrations of 0.530, 0.568 and 0.792 mg/kg. The comparative test results showed that after 8 months of remediation, the content of available Cd in the treatment of hydroxyapatite+rice biochar+deeper ploughing(T6) was reduced by 32.55% compared with CK(the control) and 24.96% than 2 months of remediation. The content of available Cd using the treatment of potassium dihydrogen phosphate+rice biochar+deeper ploughing(T7) decreased by 47.88% compared with CK and 31.00% than 2 months of remediation. The preferred remediation test results showed that in the treatment of hydroxyapatite+rice biochar+deeper ploughing: the mean Cd content decreased from 0.489 to 0.372 mg/kg, reducing by 23.86%, and the mean did not exceed the standard. Compared with CK, the mean content of available Cd decreased by 10.71% after 8 months, and the lowest content of available Cd in three treatments was 0.133 mg/kg. In addition, the Cd content, bioconcentration factor(BCF) and translocation coefficient(TF) of bean aboveground plants were decreased by 15.86%, 23.68% and 25.77%, respectively when compared with CK. Rice biochar+hydroxyapatite +deeper ploughing is a favoured technology for the remediation of Cd-contaminated greenhouse vegetable fields.

A Study on Remediation Technologies for Cadmium Contamination in Greenhouse Vegetable Fields

Based on the literature and experimental results, three kinds of amendments, namely, rice biochar, hydroxyapatite and potassium dihydrogen phosphate(KH2PO4), and deeper ploughing were selected to evaluate the field application effect of soil amendments and agronomic measures on the remediation of Cd contamination in greenhouses. Cd-contaminated greenhouse screening was conducted from 2015 to 2017. In September 2017, comparative tests of eight treatments were performed in September 2017, and a selective test was performed in September 2018. The results of the screening of contaminated areas indicated that the distributions of over-standard sites and Cd content were significantly different. Greenhouse No. 4, in which the highest over-standard rate was 83.33% and the average content of Cd in soil was 0.535 mg/kg, was used as a comparative test experimental site for eight treatments. Greenhouse No. 1 was selected as the optimum test greenhouse for selective testing, with three plots having average Cd concentrations of 0.530, 0.568 and 0.792 mg/kg. The 8 months following comparative treatment showed that the content of available Cd following the treatment of rice biochar+hydroxyapatite+deeper ploughing(treatment T6) was reduced by 32.55% and 24.96% compared with the CK(the control) and 2 months following treatment, respectively. The content of available Cd using rice biochar+KH2PO4+deeper ploughing(treatment T7) treatment decreased by 47.88% and 31.00% compared with the CK and 2 months following treatment. The selective test results showed that in rice biochar+hydroxyapatite+deeper ploughing: the total Cd content of decreased from 0.489 to 0.372 mg/kg(23.86% lower), compared with the CK, and the mean content of available Cd decreased by 10.71% after 8 months, which was the lowest available Cd measured(0.133 mg/kg). In addition, the bean plant Cd content, bioconcentration factor(BCF) and translocation coefficient(TF) decreased by 15.86%, 23.68% and 25.77%, respectively. Rice biochar+hydroxyapatite+deeper ploughing is a favoured technology for the remediation of Cd-contaminated protected vegetable fields.

NITROGEN USE AND MANAGEMENT IN ORCHARDS AND VEGETABLE FIELDS IN CHINA: CHALLENGES AND SOLUTIONS

China is the largest producer and consumer of fruits and vegetables in the world.Although the annual planting areas of orchards and vegetable fields(OVF)account for 20%of total croplands,they consume more than 30%of the mineral nitrogen fertilizers in China and have become hotspots of reactive N emissions.Excess N fertilization has not only reduced the N use efficiency(NUE)and quality of grown fruits and vegetables but has also led to soil acidification,biodiversity loss and climate change.Studies using 15N labeling analysis showed that the recovery rate of N fertilizer in OVFs was only 16.6%,and a high proportion of fertilizer N resided in soils(48.3%)or was lost to the environment(35.1%).Nitrate accumulation in the soil of OVFs is the main fate of N fertilizer in northern China,which threatens groundwater quality,while leaching and denitrification are the important N fates of N fertilizer in southern China.Therefore,taking different measures to reduce N loss and increase NUE based on the main pathways of N loss in the various regions is urgent,including rational N fertilization,substituting mineral N fertilizers with organic fertilizers,fertigation,and adding mineral N fertilizers with urease inhibitors and nitrification inhibitors.

Soil microbial communities as potential regulators of N2O sources in highly acidic soils

●Soil pH was a key driver of N2O emission and sources in acidic soils.●N2O emission was significantly positively associated with the ratio of ITS to 16S.●N2O was significantly correlated with bacterial and fungal community composition.●Fungi contributed to N2O in highly acidic tea plantations and vegetable fields.Acidic soil is a main source of global nitrous oxide(N2O)emissions.However,the mechanism behind the high N2O emissions from acidic soils remains a knowledge gap.The objective of this microcosm incubation study was to pin-point the microbial mechanisms involved in N2O production processes in acidic soils.For that purpose,the isotopic signatures and microbial community structure and composition of four soil samples were examined.The results showed that highly acid soils(pH=3.51)emitted 89 times more N2O than alkaline soils(pH=7.95)under the same nitrogen(N)inputs.Fungal denitrification caused high N2O emissions in acidic soils.ITS to 16S abundance ratio was positively correlated with cumulative N2O emissions from the tested soils.The highly acid soils(pH<4.5)showed greater fungal nirK gene abundance and lower abundance of AOA-amoA,AOB-amoA,nirK,nosZ I and nosZ II genes.The unclassified Aspergillaceae fungi(63.65%)dominated the highly acidic soils and was the most strongly correlated genus with N2O emissions.These findings highlight that soil microbial community structures,denitrifying fungi in particular,shaped by low pH(pH<4.5)lead to high N2O emissions from acidic soils.