我国热作地区绿色食品生产与质量安全控制探讨

通过对我国主要热作地区的农产品生产现状和绿色食品标志使用现状的调查研究,分析影响热带农产品质量安全生产的主要因素,提出热区绿色食品质量安全控制的建议,为热作地区绿色食品的发展和产品质量安全的控制提供参考。

Nutrient Discharges from a Typical Watershed in the Hilly Area of Subtropical China

Agriculture is still the biggest contributor of non-point source (NPS) pollution to water bodies andrunoff discharges of nutrients and other chemicals are one of the most important pathways. This studywas conducted during 1998～1999 in a typical watershed with complex agriculture and forestry systems aswell as dotted farmer villages, in a transitional region between the mid- and northern subtropical zones ofChina. Continuous sampling of stream water was performed regularly at a weekly frequency, with additionalsampling after all major rainfall events. The discharges of N and P nutrients and suspended materials weremeasured and the total and area-averaged annual discharges of all components were calculated. The resultsshowed an uneven seasonal distribution of nutrient discharges with summer storms contributing most tothe total fluxes. This study demonstrated a high dependence of runoff volume on rainfall but the overallrunoff coefficients were dependent on land use type and watershed size. The area-averaged annual dischargesvaried greatly among the sub-watersheds with different sizes and land use structures. This is the first studyestimating the area-averaged annual discharges of N and P in the hilly areas of subtropical China, which were1.5 g m-2 a-1 and 0.1 g m-2 a-1, respectively, providing important reference values for the assessment ofregional agricultural non-point source pollution.

Effect of Decadal Changes in Air-Sea Interaction on the Climate Mean State over the Tropical Pacific

Collaboration of interannual variabilities and the climate mean state determines the type of E1 Nifio. Recent studies highlight the impact of a La Nifia-like mean state change, which acts to suppress the convection and low-level convergence over the central Pacific, on the predominance of central Pacific （CP） E1 Nifio in the most recent decade. However, how interannual variabilities affect the climate mean state has been less thoroughly investigated. Using a linear shallow-water model, the ef- fect of decadal changes of air-sea interaction on the two types of El Nifio and the climate mean state over the tropical Pacific is examined. It is demonstrated that the predominance of the eastem Pacific （EP） and CP E1 Nino is dominated mainly by relationships between anomalous wind stresses and sea surface temperature （SST）. Furthermore, changes between air-sea interactions from 1980-98 to 1999-2011 prompted the generation of the La Ninalike pattern, which is similar to the background change in the most recent decade.

Soil Microbiological and Biochemical Properties as Affected by Different Long-Term Banana-Based Rotations in the Tropics

Soil microbiological and biochemical properties under various field crop rotations such as grains, pastures and vegetables have been studied intensively under short-term period. However, there is limited information about the influence of banana-based rotations on soil organic C, total N(TN), microbial biomasses and enzyme activities under long-term crop rotations. A field experiment arranged in a randomized complete block design with three replicates was carried out at the Wanzhong Farm in Ledong(18?37′–18?38′N, 108?46′–108?48′E), Hainan Province, China, to compare the responses of these soil parameters to long-term(10-year) banana(Musa paradisiaca)-pineapple(Ananas) rotation(AB), banana-papaya(Carica) rotation(BB) and banana monoculture(CK) in a conventional tillage system in the Hainan Island. Soil p H, total organic C(TOC), dissolved organic C(DOC), TN, total P(TP) and available P(AP) were found to be significantly higher(P < 0.01) in AB and BB than CK at 0–30 cm soil depth. Microbial biomass C(MBC) and N(MBN) were observed 18.0%–35.2% higher in AB and 8.6%–40.5% higher in BB than CK at 0–30 cm. The activities of urease(UA), invertase(IA), dehydrogenase(DA) and acid phosphatase(APA) showed a mean of 21.5%–59.6% increase in AB and 26.7%–66.1% increase in BB compared with CK at 0–30 cm. Higher p H, TOC and DOC at 0–10 and 10–20 cm than at 20–30 cm were obtained despite of the rotations. Soil MBC and MBN and activities of UA, IA and DA decreased markedly(P < 0.01) with increasing soil depth in the different rotation soils as well as the monoculture soil. In general, soil microbial biomass and enzymatic activities were more sensitive to changes in banana-based rotations than soil chemical properties, and consequently they were well-established as early indicators of changes due to crop rotations in the tropics.

Analytical study on coordinative optimization of convection in tubes with variable heat flux

The laminar heat transfer in the thermal entrance region in round tubes, which has a variable surface heat flux boundary condition, is analytically studied. The results show that the heat transfer coefficient is closely related to the wall temperature gradient along the tube axis. The greater the gradient, the higher the heat transfer rate. Furthermore, the coordination of the velocity and the temperature gradient fields is also analysed under different surface heat fluxes. The validity of the field coordination principle is verified by checking the correlation of heat transfer coefficient and the coordination degree. The results also demonstrate that optimizing the thermal boundary condition is a way to enhance heat transfer.

Responses of Soil Nematode Abundance and Diversity to Long-Term Crop Rotations in Tropical China

A field experiment was carried out from 2003 to 2013 in the Wanzhong Farm of the Hainan Island, China, to determine the effects of two long-term banana rotations on the abundance and trophic groups of soil nematode communities in the island. The experiment was set out as a randomized complete block design with three replications of three treatments： banana-pineapple rotation （AB）, banana-papaya rotation （BB） and banana monoculture （CK） in a conventional tillage system. Soil samples were taken at depths of 0-10, 10-20 and 20-30 cm, and nematodes were extracted by a modified cotton-wool filter method and identified to the genus level. Nematode ecological indices of Shannon-Weaver diversity （Ht）, dominance index （A）, maturity index （MI）, plant parasite index （PPI）, structure index （SI）, enrichment index （EI）, and channel index （CI） were calculated. A total of 28 nematode genera with relative abundance over 0.1% were identified, among which Tylenchus and Paratylenchus in the AB, Thonus in the BB, Tylenchus and Helicotylenchus in the CK were the dominant genera. The rotation soils favored bacterivores, fungivores and omnivores-predators with high colonizer-persister （c-p） values. Soil food web in the rotation systems was highly structured, mature and enriched as indicated by SI, MI and EI values, respectively. Higher abundance of bacterivores and lower values of CI suggested that the soil food web was dominated by a bacterial decomposition pathway in rotation soils. Nematode diversity was much higher after a decade of rotation. Soil depth had significant effects on the abundance of soil nematodes, but only on two nematode ecological indices （λ and MI）.