Effects of heavy metal pollution of highway origin on soil nematode guilds in North Shenyang, China.

Soil samples were collected with distance at 5, 20, 40, 80, 160, and 320 m from the Shen-Ha (Shenyang-Harbin) Highway, Northeast China, to investigate the effect of heavy metals of highway origin on soil nematode guilds. The contents of soil Pb, Cu, Zn, and the nematode community structure were analyzed. The results showed that the contents of total and available Pb, Cu, Zn varied significantly with the different distances from the highway. Pb was the main pollutant in the soils in the vicinity of Shen-Ha Highway. The zone from 20 to 40 m away from the highway was the most polluted area. The highest abundance of soil nematodes was found at 5 m while the lowest at 20 m away from the highway. Thirty six genera of nematodes belonging to 23 families were identified. Nematode guilds having different responses to soil heavy metals were classified into four types. Soil nematode guilds may act as a prominent indicator to heavy metal pollution of highway origin.

[Dynamics of aquic brown soil enzyme activities under no-tillage].

This paper studied the effects of no-tillage on the dynamics of invertase, urease and acid phosphatase activities in an aquic brown soil during maize growing season. The results showed that in 0 - 10 cm soil layer, the invertase activity at jointing, trumpet-shaped and ripening stages, urease activity at jointing and booting stages, and acid phosphatase activity at booting and ripening stages were significantly higher under no-tillage (NT) than under conventional tillage (CT). In 10 - 20 cm soil layer, the invertase activity at seedling, jointing and trumpet-shaped stages was significantly different between NT and CT, and the urease activity during whole growing season except at booting stage was significantly higher under NT than under CT. In 20 - 30 cm soil layer, the invertase activity during maize growing season was significantly lower under NT than under CT, and urease activity at seedling stage and acid phosphate activity at ripening stage were significantly different between these two treatments. Under NT, there was a decreasing trend of soil enzyme activities with increasing soil depth; while under CT, soil invertase and acid phosphatase activities increased, but urease activity decreased with increasing soil depth.

Effects of slow-release urea fertilizers on urease activity, microbial biomass, and nematode communities in an aquic brown soil.

A field experiment was carried out at the Shenyang Experimental Station of Ecology (CAS) in order to study the effects of slow-release urea fertilizers high polymer-coated urea (SRU1), SRU1 mixed with dicyandiamide DCD (SRU2), and SRU1 mixed with calcium carbide CaC2 (SRU3) on urease activity, microbial biomass C and N, and nematode communities in an aquic brown soil during the maize growth period. The results demonstrated that the application of slow-release urea fertilizers inhibits soil urease activity and increases the soil NH4+-N content. Soil available N increment could promote its immobilization by microorganisms. Determination of soil microbial biomass N indicated that a combined application of coated urea and nitrification inhibitors increased the soil active N pool. The population of predators/omnivores indicated that treatment with SRU2 could provide enough soil NH4+-N to promote maize growth and increased the food resource for the soil fauna compared with the other treatments.

Spatial heterogeneity of DTPA-extractable zinc in cultivated soils induced by city pollution and land use.

The spatial heterogeneity of DTPA-extractable zinc in the cultivated soils of Shenyang suburbs in Liaoning Province of China was investigated, and its map was drawn by the methods of geostatistics combined with geographic information system. The data of soil DTPA-extractable zinc fitted normal distribution after logarithm transformation, and its semivariogram fitted a spherical model. The semivariogram indicated that the spatial dependence of soil DTPA-extractable zinc content was moderate, with the spatial dependence range of 1.69 km and the fractal dimension of 1.96. Stochastic factors contributed to 49.9% of the spatial variability, while structural factors contributed to 50.1% of it. The spatial heterogeneity of soil DTPA-extractable zinc shown by a kriged interpolation map was deeply influenced by stochastic factors such as city pollution, land use pattern and crop distributions. For example, the average content of Zn in vegetable garden soils was 2.5-4 times as much as in their originated soils, and was lower in paddy soils than in their originated soils. The areas with a higher content of soil DTPA-extractable zinc appeared in the near suburbs and the riverside along Hunhe River and the wastewater drainage of Xihe River, and the extremely high values in the near suburb of the city's residential area were a striking feature, indicating the key role of city pollution in the spatial heterogeneity of soil DTPA-extractable zinc. When recorded in the form of a soil pollution map, the results of such a survey make it possible to identify the unusually polluted areas, and to provide more information for precise agriculture and environmental control.

[Analysis of paddy field evapotranspiration in North China and calculation of crop coefficient].

The potential evapotranspiration (ET0) values from 1951 to 2002 for the lower reaches of Liaohe Plain, North China, were estimated by Penman-Monteith equation, and the annual change in ET0 was analyzed. By using non-weighting lysimeters at Shenyang Experimental Station of Ecology (CAS) in North China, the daily evapotranspiration of flooded rice (Oryza sativa L.) at the interval of 10-11 days was determined for eight seasons from 1993-2002 (except for 1997 and 1999). The results showed that the total evapotranspiration ranged from 581 mm to 695 mm during 1993 and 2002, averaged 634 mm. Both in dry and wet seasons, supplemental irrigation was essential in this region for the uneven distribution of rainfall and time. The average crop coefficient (Kc) for eight years from 1993 to 2002 during the whole growth period was 1.32, with a second-degree polynomial change for the values of Kc during different rice growth stages.

[Effects of tillage method and herbicide on cornfield weed community].

By the method of community ecology, this paper surveyed the weed community in a cornfield at the Shenyang Experimental Station of Ecology, CAS, and studied the effects of tillage method and herbicide on the weed composition, species diversity, and biomass at the experimental site. The results showed that the dominant weed species in the cornfield were Eriochloa villosa, Abutilon theophrasti, Bidens frondosa and Commelina communis, of which, Eriochloa villosa had the highest important value. In non-tillage field without herbicide application, the weed community had larger biomass, higher richness (S) and concentration (C), but lower species diversity (D) and species evenness (J). Herbicide could decrease weed species and inhibit biomass growth significantly in non-tillage field. It was clear that tillage method and herbicide could affect the weed composition, diversity and stability significantly.

[Effects of urease/nitrification inhibitors on soil available N and microbial biomass N and on N uptake of wheat].

With an aquic brown earth as test soil, this paper studied the effects of urease inhibitor (NBPT), nitrification inhibitor (DCD) and their combinations on the dynamics of soil available N and microbial biomass N. The results showed that the treatments of inhibitors, especially the combined application of NBPT and DCD, could increase soil NH4+-N by 2%-53%, inhibit NH4+ oxidation, decrease soil NO3(-)-N concentration, increase soil total available N by 34%-44%, and increase wheat N uptake by 0.26%-6.79%. The best treatment was urease inhibitor combined with nitrification inhibitor. The application of inhibitors increased soil microbial biomass N immobilization at the early growth stage of wheat, and promoted soil N mineralization at filling stage.

[Effects of intermittent irrigation on ecological and physiological water requirement of rice in north China].

The ecological and physiological water requirement of rice was studied in a paddy field of north China, and the field experiment was conducted at Shenyang Experimental Station of Ecology, Chinese Academy of Sciences. Under continuous flooding irrigation (CSF) and intermittent irrigation (IT) conditions, the evapotranspiration and soil evaporation of paddy fields were measured by non-weighing lysimeters and micro-lysimeters, respectively. The results showed that compared with continuous flooding irrigation, the transpiration under intermittent irrigation condition was not significantly reduced, but 16% and 24% of water amounts were reduced by decreasing the water losses through soil water evaporation and percolation, respectively. The water use efficiency of intermittent irrigation was increased 10%, without any adverse effects on biomass and grain yield of rice. Although the amount of water requirement under IT treatment was reduced significantly compared with CSF treatment, about 60% of total water requirement was still lost through deep percolation. Based on the results obtained, the corresponding countermeasures to reduce the amounts of soil water evaporation and percolation and to increase the water use efficiency were put forward in this paper.

[Effects of water managements on soil nematode communities in a paddy field].

This paper studied the effect of water managements on the abundance, trophic groups and community composition of soil nematodes in a paddy field in the Lower Reaches of Liaohe Plain at the depths of 0-10 cm, 10-20 cm and 20-30 cm during rice (Oryza sativa L.) growth season. The total number of nematodes at 0-10 cm soil depth was lower in percolation-controlling treatments than in control during pre-tillage and yellow ripeness stage. No significant difference was found in the total number of nematodes at 10-20 cm soil depth during the study period, but significant difference was observed in 20-30 cm soil depth during pre-tillage and yellow ripeness stage. Sixteen families and 22 genera were observed, and Plectus, Tylenchus and Monhystera were the dominant genera. Plectus and Tylenchus were sensitive to different water managements. Significant difference was found in the number of bacterivores at 0-10 cm soil depth during pre-tillage and yellow ripeness stage in percolation-controlling treatments, which exhibited a similar trend with the total number of nematodes. Bacterivores and plant-parasites were the most abundant trophic groups in all plots and at all soil depths during the study period, averaging 60.8% and 33.8% of the nematode communities, respectively, and omnivores-predators were the least abundant groups.

[Dynamics of organic C in black soil of Northeast China, simulated by CENTURY model I. Accumulation of soil organic carbon under natural conditions].

By using CENTURY model, this paper simulated the dynamics of organic carbon and its fractions, including active, slow and passive pools, in black soils under natural condition at Nenjiang, Beian, Hailun and Harbin in Heilongjiang Province and at Gongzhuling in Jilin Province. The results showed that soil organic carbon had increased for a long time, and tended to reach the steady state. In the steady state, soil organic carbon reached 7914.72-11672.78 g x m(-2), which decreased from north to south in geperal. The active, slow and passive fractions were 3.36%-4.62%, 50.54%-55.47% and 36.47%-41.95% of soil organic carbon pool, respectively, which indicated that slow and passive fraction were the main body of soil organic carbon in native ecosystem. The simulated results were in agreement with some observed results, which can be used as the original data in the study on the dynamics of soil organic matter after cultivation.

[Water requirement of paddy field under different soil water conditions].

Field experiment with three irrigation treatments, i.e., continuous flooding irrigation (CSF), moisture condition irrigation (MTC), and intermittent irrigation (IT) were installed to study the water requirement of paddy fields. The results showed that in field experiment, the evapotranspiration(ET) was 889.1, 635.9 and 775.9 mm, and the evapotranspiration rate was 6.9, 4.9 and 6.0 mm.d-1 for CSF, MTC and IT, respectively during the entire growing season. MTC and IT were less than CSF by 28.5 and 12.7%. Under sufficient water supply, the evapotranspiration calculation by Penman formula was less than that from field experiment by 29.3%, during stages from returning green to milk. The biomass was 16438.22, 15887.94 and 15757.88 kg.hm-2, and the grain yield was 8014.01, 7828.91 and 7853.93 kg.hm-2 for CSF, MTC and IT, respectively. No significant differences were found among three treatments. The water use efficiency (WUE) was 9.01, 12.31 and 10.12 kg.hm-2.mm-1 for CSF, MTC and IT, respectively. The WUE of MTC and IT were higher than that of CSF by 26.8 and 11.0%, showing that MTC was a comparatively water-saving irrigation treatment.

[Spatial variability of soil nutrients in cultivated surface soil of Sujiatun District, Shenyang City].

The spatial variability of organic matter (OM), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) in 0-20 cm horizon in cultivated soils of Sujiatun District, Shenyang City were investigated using geostatistics and geographic information system (GIS). Data of each variable fitted normal distribution or normal distribution after log transformation, and a spherical model for semivariogram fitted all the variables. Semivariograms indicated that OM content strongly spatially dependent with the ratio of nugget to sill of 24.11%. The contents of AN, AP and AK were moderately spatially dependent with the ratio of nugget to sill of 29.53%, 60.77% and 58.82%, respectively. The ranges of spatially dependent for OM, AN, AP and AK were 26.051, 28.293, 15.132 and 23.813 km, respectively. The spatial variability for OM and AN was fundamentally affected by structural factors such as soil formation factors, and that for AP and AK was by random factors such as fertilization. Kriging maps showed the spatial distributions of the four variables, which were useful in monitoring nutrient changes and providing quantitative support to decision and policy making for agriculture and environment management.

[Comparison of soil organic matter models].

Soil organic matter is a soil carbon pool, and its content and dynamics is very important to global C cycling, soil fertility, and soil quality. SOM models can simulate soil organic matter dynamics and predict its content, especially for which some of data are difficult or impossible to obtain by experiential hypotheses and existing data. Therefore, SOM models have become the most important quantitative means to study SOM decomposition and accumulation, and can help us to identify the mechanism about SOM dynamics. SOM models can also predict CO2 emission and plant growth, and evaluate agricultural management practices. Several SOM models, especially RothC model and CENTURY model, were summarized and analyzed in this paper.

[Research directions of agroecosystem health in the early 21st century].

Agroecosystem health refers to the state of an agroecosystem where it is free from 'distress syndrome' and to cope with stress, or capability to produce agricultural products in a sustainable way. At present, the research of agroecosystem health focuses on assessment methods, soil and water quality, human health, ecologically based pest management, integrated weed management, ecopathology, nematode communities, transgenic crops, agricultural input policy, landscape ecology and green food development. Firstly, the present state of agroecosystem health research was described; then a case study of agroecosystem health, biological indicators of soil health, was introduced; finally, the research directions of agroecosystem health were put forward. This paper could provide a basis for ensuring agricultural product security and increasing human health.

[Landscape ecological studies on autumnal Chinese cabbage fields in Shenyang city suburb. I. Features of autumnal Chinese cabbage field patches].

Some typical patches of autumnal Chinese cabbage fields in the agricultural landscapes of Shenyang city suburb were investigated, and their basic features, such as areas, shapes, neighborings and connections, were recorded. Their mosaic features were also analyzed and discussed. In the region of less 5 km distance from city, many Chinese cabbage patches neighbored each other and connected to highways, while in the region of 5-10 km distance from city, they neighbored with corn patches and connected to countryside roads. In the region over 10 km distance from city, many Chinese cabbage patches are surrounded by corn patches and connected to countryside roads.

[Landscape ecological studies on autumnal Chinese cabbage fields in Shenyang city suburb. II. Relationship between Chinese cabbage field patches and their neighboring landscape elements].

The relationship between autumnal Chinese cabbage patches and their neighboring other lanascape elements were studied in Shenyang suburb. The groups and quantities of arthropods moving through a boundary between a Chinese cabbage patch and its neighboring corn patch in certain period, were investigated and the 7 oders of arthropods moving through the boundary with an average flow of 10.3 individuals.m-1.d-1 were observed. The changes of falling dust rates on a Chinese cabbage patch near a countryside road are analyzed. Some principles of agroecosystems in an agricultural landscape were discussed on the basis of these observation results.