Guitong Li

The growth of Brassica chinensis in heavy-metal-contaminated sewage sludge compost from Hong Kong

Abstract A plant growth experiment was performed to evaluate the growth of Chinese cabbage (Brassica chinensis) in a sewage sludge compost derived from both industrial and domestic sewage containing high metal and salt contents. A loamy soil was amended with sewage sludge compost at application rates equivalent to 0, 5·9, 11·7, 29·2 and 58·5 tonne ha−1 on dry weight basis. Addition of sludge compost caused a slight increase in soil pH, and a significant increase in electrical conductivity (EC) and soluble K, Ca, Mg, NH+4 and PO3−4 contents. DTPA-extractable Cu and Zn contents increased significantly according to the compost application rate, while a significant increase was noted only in soil with the highest compost application rate for Cd, Pb and Ni. The yield of Chinese cabbage was significantly increased with sludge compost amendment as compared to the control without fertilizer and with the highest yield at 5–10% application rate. An accumulation of Cu, Cd, Zn, Ni and Pb was observed with an increase in compost amendment. Among the metals studied, only Cd had a tissue content higher than the maximum permitted concentration of Cd in vegetables at a compost amendment rate of 10%. Therefore, stringent guidelines should be set for the sludge compost produced in Hong Kong for edible crop production. Besides, the long-term effect of the sludge compost on the accumulation of trace metals in edible plants should also be investigated.

Effects of livestock grazing intensity on soil biota in a semiarid steppe of Inner Mongolia

Intensive livestock is known to significantly affect soil physical and chemical parameters in steppe ecosystems. However, the effects on soil biological parameters still remain unknown. We hypothesized that intensive grazing would significantly decrease the size and diversity of soil biota due to deterioration of the soil environment and reduction in vegetation cover, while the adapted grazing intensity would improve the biological parameters. Soil samples were collected from five sites with different grazing intensities and history in a semiarid steppe of Inner Mongolia in August 2005. Two sites were long-term ungrazed since 1979 (UG79) and 1999 (UG99), one had been moderately grazed in winter (WG), one continuously grazed moderately (CG) and one long-term site was heavily grazed (HG). Soil microbial biomass carbon (C), basal respiration (BR), catabolic diversity of soil microbial communities, protozoa and nematodes abundance were measured. Soil physicochemical variables were also measured to establish the relationships between soil biological parameters and key soil physical and chemical properties. Soil microbial biomass C, BR, biomass specific respiration (qCO2) and soil protozoa abundance were significantly lower at the HG site compared to the UG79 site, but no clear differences were found in the other sites. However, soil nematodes abundance increased with increasing grazing intensity, and the abundance of soil amoeba were greater in CG than in the other sites. Principal component analysis (PCA) of Biolog data revealed large differences in catabolic capacity of soil microbial communities between UG79, HG and UG99, WG, CG. However, Shannon’s diversity index did not indicate marked effects of grazing intensity on substrate catabolic community structure. In conclusion, heavy grazing negatively affected soil microbial biomass, activity and protozoan abundance, but positively influenced soil nematodes abundance and did not affect soil microbial catabolic diversity. Based on these results, CG may provide an appropriate grazing intensity to be used in the long term in the semiarid steppe of Inner Mongolia.

Efficiency of sewage sludge biochar in improving urban soil properties and promoting grass growth

It is meaningful to quickly improve poor urban soil fertility in order to establish the green land vegetation. In this study, a series rates (0%, 1%, 5%, 10%, 20% and 50%, in mass ratio) of biochar derived from municipal sewage sludge was applied into an urban soil and then turf grass was grown in pots. The results showed that biochar amendment induced significant increases in soil total nitrogen, organic carbon, black carbon, and available phosphorus and potassium by more than 1.5, 1.9, 4.5, 5.6 and 0.4 times, respectively. Turf grass dry matter increased proportionally with increasing amount of added biochar (by an average of 74%), due to the improvement in plant mineral nutrition. Biochar amendment largely increased the total amounts of soil heavy metals. However, 43-97% of the heavy metals in the amended soil were concentrated in the residual fraction with low bioavailability. So the accumulation of heavy metals in turf grass aboveground biomass was highly reduced by the addition of biochar. These results indicated that sewage sludge biochar could be recommended in the poor urban raw soil as a soil conditioner at a rate of 50%. However, the environmental risk of heavy metal accumulation in soil amended with sewage sludge biochar should be carefully considered.

Hydrochar production from watermelon peel by hydrothermal carbonization

Watermelon peel waste was hydrothermally carbonized under 190°C and 260°C for 1h, 6h, and 12h, respectively. The hydrochar and spent liquor were collected and assayed for their properties. The results indicated that hydrochar yield was 2-5% and 46-95% on fresh and dry matter, respectively. Low temperature (190°C) was conducive to high conversion efficiency. The hydrochar had higher C/N ratio (22.19-26.86), more alkyl C, aryl C, and carbonyl C, but lower H/C (0.98-1.22) and O/C ratios (0.13-0.38), and less O-alky C, carboxylic C, compared with feedstock. So the aliphaticity decreased, whereas aromaticity increased significantly, especially under severe conditions. It should be watchful for that the toxic compounds in hydrochar may induce environmental risk while it is amended into soil. The spent liquor with abundant nutrients could be used as a fertilizer. Further work is required for testing the application in soil.

Soil microbial biomass carbon and phosphorus as affected by frequent drying–rewetting

Drying and rewetting (DRW) events are very common in arable land. However, it is not clear how the frequency of DRW stress history influences soil carbon (C) and phosphorus (P) dynamics under field conditions. In this study, an arable loam calcareous soil was treated with simulated farming practices that included wheat straw and nitrogen incorporation and three DRW cycles at intervals of 14 days during a 90-day experimental period of incubation at 25°C. The DRW events significantly increased cumulative CO2-C evolution, but the increase rate of cumulative CO2-C evolution declined with increasing DRW cycles. Microbial biomass C (MBC) and P (MBP) decreased by 9–55% and 9–29%, respectively, following each DRW event, but recovered to the level before DRW treatment within 7 days. Frequent drying and rewetting caused significant increases in both extractable organic C and NaHCO3-extractable P, by 10–112% and 10–18%, respectively. The fluctuation of the tested parameters became less with increasing frequency of DRW cycles. Changes in microbial biomass, either MBC or MBP, were poorly correlated with those of extractable organic C and NaHCO3-extractable P. Overall, frequent DRW cycles had much stronger and longer lasting impact on soil biomass P dynamics than biomass C. These findings may imply certain links among soil moisture, microbial activity and nutrient bioavailability that are important in water and nutrient management.

Interference of Soil-Extractable Phosphorus in Measuring Soil Microbial Biomass Phosphorus

Abstract Soil microbial biomass contains a labile phosphorus (P) fraction and is an important source of phosphorus for plant nutrition. It is therefore essential to estimate soil microbial biomass P accurately. Two calcareous alluvium soils with low (soil 1, 8.9 mg kg−1) and high (soil 2, 460 mg kg−1) Olsen P were collected. Soil 1 was amended with a series of dipotassium phosphate (K2HPO4) solutions (0, 37.5, 75, 150, 375, 750 mg P kg−1 soil). The objective was to investigate the interference and removal methods of soil‐extractable P when measuring soil microbial biomass P. The results showed that the soil microbial biomass could not be determined in those soils where Olsen P was greater than 60 mg kg−1. This part of the soil P should be removed by either anion resin or 0.5 M sodium bicarbonate (NaHCO3) solution (pH 8.5) prior to fumigation. The recovery rates of the added phosphate in the two soils tested were greater than 150%. Calibration was not necessary when calculating soil microbial biomass P. The microbial biomass P values of the two soils were 12.42±1.02 and 15.00±1.06 mg kg−1, respectively.

Does soil amendment alter reactive soil N dynamics following chloropicrin fumigation

Chloropicrin fumigation had strong inhibitory effect on soil N cycling. Knowledge gap existed about the performance of reactive N in soil applied with different amendments used to improve the fumigation function or soil quality. In this study, we employed four amendments, i.e., wheat straw residue, manure, biochar and ammonium thiosulfate, incorporated into soil at the regular application rate. Simultaneously, bare soil was selected as control (CK). Based on a three months incubation assay, soil reactive N and activity of three enzymes governing N-mineralization was measured, i.e., protease, arylamidase and l-glutaminase, as well the soil fluorescein diacetate (FDA) hydrolysis, basal soil respiration, and dissolved soil organic carbon (DOC). Result showed that, compared with the bare soil, the addition of straw or manure to soil markedly enhanced the FDA and the resistance of arylamidase and l-glutaminase to the fumigation, while significantly decreased the concentration of DON, NH4+N and NO3--N. The addition of biochar to soil had no effect on the reactive N, but contrasting effects on the three enzymes, i.e., suppressed protease activity, and enhanced arylamidase activity. The ammonium thiosulfate showed an inert effect on the measured microbiological indices and reactive N except the enhanced concentration of NH4+N. DOC content of amendments governed microbial activity under fumigation condition. In synthesis, our findings suggested that under chloropicrin fumigation the use of straw or manure enhanced the microbial abundance and the activity of N-mineralization enzymes, which may lead to low reactive N by the microbial N immobilization for a longer period.

Portable integrated system of waste water treatment and drip irrigation and its effect on heavy metal removing

Municipal waste water (WW) treatment plant, usually in large scale, centralized location, and high running cost, was not suitable in countryside, where waste water discharge was scattered and in small amount. In an European Commission Framework Plan 6th Project, SAFIR, a new concept of waste water treatment and resue was developed. In the concept, nitrogen, phosphorus, and dissoved organic matter as plant nutrition in WW were mostly kept after treatment, whereas heavy metals and pathogenic microorganisms were removed in the most degree, and drip-fertlized irrigation device was integrated into the system. To do the work, the system was composed of water store tank, pump, sandy filter, heavy metal adsorption tank, on-line UV lamp, fertilization device, and control part of Single Chip Micyoco (SCM), in which all components were portable. The benefits of this system were its nutrient recycling and water reuse, effective in harmful component remove, low cost, high automotization, quantification in irrigation, and easy extentable and portable. Result of 3 yearss running showed that the system was effective, stable, and easy to operate.