Differential responses of soil nematode community to pig manure application levels in Ferric Acrisols.

Excessive pig manure application probably degrades arable soil quality in some intensive pig farming areas. The responses of the nematode community to dosages of pig manure were investigated in Ferric Acrisols under 3-season peanut monoculture. Varying dosages of manure (1.75, 3.5, 7, 14 and 28 t·ha-1·yr-1) in combination with chemical fertilizer were applied to field plots, and chemical fertilizer alone was also applied as a control. With increasing manure application, the abundance of bacterivores and omnivores-predators increased, the abundance of plant parasites decreased, and fungivores abundance exhibited hump-shaped variation. Simpson diversity index and plant parasite index/maturity index of the nematode communities increased to a maximum level at a manure application rate of 3.5 t·ha-1·yr-1 and then sharply decreased. The changes in the soil nematode community were further determined to be correlated with chemical properties; available phosphorus had the strongest quadratic correlation with the two indices, implying that available phosphorus had a better indicative effect than other soil properties to nematode community. Available phosphorus in soil was deduced from 49 to 64 mg·kg-1 with the best nematode communities. Our results emphasized the importance of regular applications of manure in agriculture field to balance nematode diversity and build healthy agro-ecosystems.

Experimental Studies on the Flammability and Fire Hazards of Photovoltaic Modules.

Many of the photovoltaic (PV) systems on buildings are of sufficiently high voltages, with potential to cause or promote fires. However, research about photovoltaic fires is insufficient. This paper focuses on the flammability and fire hazards of photovoltaic modules. Bench-scale experiments based on polycrystalline silicon PV modules have been conducted using a cone calorimeter. Several parameters including ignition time (tig), mass loss, heat release rate (HRR), carbon monoxide (CO) and carbon dioxide (CO2) concentration, were investigated. The fire behaviours, fire hazards and toxicity of gases released by PV modules are assessed based on experimental results. The results show that PV modules under tests are inflammable with the critical heat flux of 26 kW/m². This work will lead to better understanding on photovoltaic fires and how to help authorities determine the appropriate fire safety provisions for controlling photovoltaic fires.

The composition of root exudates from two different resistant peanut cultivars and their effects on the growth of soil-borne pathogen.

The high incidence of various soil-borne diseases in the monoculture field of peanut is a major production constraint in the red soil regions of southern China. The peanut root exudates are generally thought to play an important role in regulating soil-borne pathogens. The responses of the soil-borne pathogens, Fusarium oxysporum and F. solani to the peanut root exudates were studied using one susceptible cultivar Ganhua-5 (GH) and one mid-resistant cultivar Quanhua-7 (QH) as the test materials. The components and contents of the amino acids, sugars and phenolic acids in the peanut root exudates were determined. The results demonstrated that the root exudates from both susceptible and mid-resistant cultivars significantly promoted the spore germination, sporulation and mycelial growth of soil-borne pathogens, F. oxysporum, F. solani compared with the control. The extent of the stimulation was depended on the strains of the Fusarium tested, and gradually increased with the increased concentrations of peanut root exudates. HPLC analysis showed that the contents of sugars, alanine, total amino acids in the root exudates of GH were significantly higher than that in QH, whereas the contents of p-hydroxybenzoic acid, benzoic acid, p-coumaric acid and total phenolic acids were significantly lower than that in QH. Results of the study suggested that the differences in the root exudates from the different peanut cultivars were considered to regulate the wilt-resistance mechanism in the rhizosphere of peanut. The results are therefore crucial important to illustrate the mechanism of peanut replanted obstacle, and to develop its control techniques in the red soil regions of southern China.

[Effects of intercropping peanut with medicinal plants on soil microbial community].

With pot experiment, this paper studied the quantitative variations of bacteria, actinomyces, mould and yeast in soils of peanut intercropped with medicinal plants, aimed to test if such an intercropping pattern could remove the obstacles of peanut's continuous cropping. The results showed that Atractylodes lancea and Euphorbia pekinensis had the strongest inhibitory effect on mould. Compared with CK (mono-cropping peanut), the CFU of mould in the treatments intercropped with A. lancea and E. pekinensis was decreased by 53.87% and 29.59%, respectively during flowering-pegging stage of peanut, but increased after harvesting, which was in favor of substance circulation and nutrient returning. The CFU of bacteria in treatments intercropped with A. lancea, E. pekinensis and Pinellia ternate was all increased, and that of yeast in all five intercropping treatments was increased during the flowering-pegging stage of peanut. No familiar pathogens were found in the treatments intercropped with A. lancea, E. pekinensis and Diosoren zingiberebsis. Peanut intercropped with medicinal plants could regulate soil microbial community effectively.

[Bio-environmental effects and index of remediation of multi-heavy metals polluted red soils].

A pot experiment was conducted to study the bio-environmental effects of lime and organic manure application on red soil and paddy soil derived from red sandstone and polluted by multi-heavy metals. The results indicated that liming decreased the content of soil bioavailable Cu and Pb extracted with 0.05 mol/L HCl, while applying hog manure increased that of Cd. Soil bioavailable heavy metals (HMs) showed an apparent relationship with soil dissolved carbon. Applying lime and organic manure has a positive physiological effect on soil microorganisms and sweet potato. Many indexes, i.e. the number of soil actinomycetes, the content of HMs in the root of sweet potato, showed the remarkable relationship with soil bioavailable Cu, Cd and Pb. However, some indexes of soil and plant only relative to one or two soil bioavailable HMs. For example, soil microbial biomass carbon correspondent with soil bioavailable Cd. Only the content of Cu in the stem and leaf showed a notable relationship with soil effective Cu. Soil effect Cu and Pb rather Cd showed remarkable relation with mean transpiration rate, total biomass and leaf area index of sweet potato. The daily mean value in the seedling stage showed a stronger relationship with soil bioavailable Cu and Pb. Therefore these two physiological indexes can reflect the change of soil metallic contamination.

Soil CO2 flux in relation to dissolved organic carbon, soil temperature and moisture in a subtropical arable soil of China.

Soil CO2 emission from an arable soil was measured by closed chamber method to quantify year-round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil moisture content. Soil CO2 flux, soil temperature, DOC and soil moisture content were determined on selected days during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil, the Chinese Academy of Sciences, in a subtropical region of China. Soil CO2 fluxes were generally higher in summer and autumn than in winter and spring, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The estimation was 2.23 kgCO2/(m2 x a) for average annual soil CO2 flux. Regressed separately, the reasons for soil flux variability were 86.6% from soil temperature, 58.8% from DOC, and 26.3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained approximately 85.2% of the flux variance, however by stepwise regression, soil temperature was the dominant affecting soil flux. Based on the exponential equation developed from soil temperature, the predicted annual flux was 2.49 kgCO2/(m2 x a), and essentially equal to the measured one. It is suggested the exponential relationship between soil flux and soil temperature could be used for accurately predicting soil CO2 flux from arable soil in subtropical regions of China.