This paper aims to study the influences of introducing frogs in the paddy fields on soil ecology and rice growth.The 2-year field experiments were conducted in the suburb of Shanghai in 2013 and 2014. No pesticides, herbicides, and chemical fertilizers were applied within the rice growing season to prevent the possible poisonous effects of agrochemicals on frogs.The results indicated that immigrant frogs in the fields could reduce the populations of rice leaf rollers, stem borers, and planthoppers effectively due to frog predation, and could control rice sheath blight indirectly through reducing insects that transmit disease pathogens. The frog treatment could raise soil nutrient status, improve rice growth, and increase the contents of soluble protein, chlorophyll, and soluble sugar in rice leaves to some extent, thus increasing grain yield significantly. Moreover, it also raised soil microbial biomass and enhanced the activities of soil enzymes such as dehydrogenase, catalase, urease, and acid phosphatase.To raise the survival rate of immigrant frogs in the fields, it should be protected from human hunting and chemical poison, and its habitats in the nearby fields should be properly reserved. Introducing frogs in the paddy fields not only showed a potential of pest and disease control but also improved soil fertility and rice growth. Such eco-modified method is beneficial to establish a low-input integrated farming system in the suburb of Shanghai in the future.

This paper aims to study the ecological effects of rice-duck integrated farming on soil fertility and weed and pest control.A field experiment was carried out in the suburb of Shanghai in 2014, which included a rice-duck integrated treatment and non-duck treatment (CK) under organic management. Each treatment was in triplicate, and the experiment included six plots in total, with each plot 667 m2 in area.(1) The number of weeds in the plots with the duck treatment was significantly lower than that with CK (p < 0.01). (2) The incidence of stem borers (Chilo suppressalis) with the duck treatment was significantly lower than that with CK (p < 0.05). The incidences of rice leaf rollers (Cnaphalocrocis medinalis), rice sheath blight (Rhizoctonia solani), and planthoppers with the duck treatment were extremely significantly lower than those with CK (p < 0.01). (3) The contents of NH4+-N, alkali-hydrolyzable N, available P, and available K in the soils with the duck treatment were higher than those with CK, and the activities of urease, phosphatase, sucrase, and catalase in the soils with the duck treatment were also much higher than those with CK. The grain yield with the duck treatment was 1.9 times that with CK. (4) The number of soil nematodes with the duck treatment was significantly higher than that with CK in the late rice growing stage (p < 0.01).Raising ducks in the paddy fields not only showed a potential of controlling weed hazards and reducing rice pests and diseases but also raised soil fertility, improved soil biodiversity, and increased grain yield effectively. Implementing the rice-duck integrated farming could highly reduce the amount of pesticides and herbicides and was beneficial to develop the organic rice farming in the suburbs of Shanghai, Southeast China.

Located in Central South China, Hunan province is rich in mineral resources. To study the influence of mining on Cd pollution to local agricultural eco-system, the paddy soils and rice grain of Y county in northern Hunan province were intensively monitored. The results were as follows: (1) Total Cd (T-Cd) content in the soils of the county ranges from 0.13 to 6.02 mg kg−1, with a mean of 0.64 mg kg−1, of which 57.5 % exceed the allowable limit specified by the China Soil Environmental Quality Standards. T-Cd in the soils varies largely, with the coefficient of variation reaching 146.4 %. The spatial distribution of T-Cd in the soils quite matches with that of mining and industries. The content of HCl-extractable Cd (HCl-Cd) in the soils ranges from 0.02 to 2.17 mg kg−1, with a mean of 0.24 mg kg−1. A significant positive correlation exists between T-Cd and HCl-Cd in the soils (r = 0.770, ρ < 0.01). (2) Cd content in the rice produced in Y county ranges from 0.01 to 2.77 mg kg−1, with a mean of 0.46 mg kg−1. The rate of rice with Cd exceeding the allowable limit specified by the Chinese Grain Security Standards reaches 59.6 %; that with Cd exceeding 1 mg kg−1, called as “Cd rice,” reaches 11.1 %. (3) Cd content in the rice of Y county is positively significantly correlated with HCl-Cd (r = 0.177, ρ < 0.05) but not significantly with T-Cd in the soils (r = 0.091, ρ > 0.05), which suggests that the amount of Cd accumulating in the rice is more affected by its availability in the soils, rather than the total content. (4) The dietary intake of Cd via rice consumption in Y county is estimated to be 179.9 μg day−1 person−1 on average, which is far beyond the allowable limit specified by FAO/WHO and the target hazard quotients of Cd much higher than 1, suggesting the high risk on human health from Cd exposure.

•Rice plants chemically fertilized were more susceptible to pests and diseases.•Infestations of pests and diseases were related to excessive N nutrients.•Incidence of migratory pests was linked to hits of summer storms.•Grain yield was primarily determined by the infection rate of pests and diseases.To implement organic rice farming around a drinking water source in the western suburbs of Shanghai, pioneering field experiments on the relationships between fertilizer applications and occurrences of rice pests and diseases were performed without the use of pesticides and fungicides from 2012 to 2014. The rice plants treated with chemical fertilizers (CF) accumulated higher content of available nitrogen (NH4+ + NO3−) and grew higher and more luxuriantly, but they were more susceptible to pests and diseases. Comparatively, the plants treated with organic manure demonstrated higher resistance to rice pests and diseases and grew more healthily. However, excessive application of organic manure also increased the risks of pests and diseases. The unfertilized plants were highly deficient in nutrients, but they maintained the lowest rates of pests and diseases. This suggests that rice pests and diseases were easily triggered by a high content of N-related nutrients in plant tissues and inhibited by nutrient deficiency. Annual climatic conditions also deeply affected the occurrences of rice pests and diseases. Long-term warm and humid weather in the growing areas favored the development of herbivorous pests and fungal diseases. The incidence of migratory pests in Shanghai is also linked to violent summer storms. Frequent rain storms in southern or southwestern China increased the chance of infestations of migratory pests in Shanghai. Rice yield was primarily determined by the infestations of pests and diseases. In the pest-infested year of 2012, the grain yield for the different fertilizers was only 40%–44% of that under conventional farming practices, and the yield in CF was even significantly lower than that in the unfertilized CK. In 2013, with lower infestation rates, the grain yield of the different fertilizers was more than 80% of the conventional yield. The application of a lower amount of organic manure, 2100 kg ha−1 of cake manure, was recommended for the implementation of organic rice farming in the water source areas in Shanghai.

•Paddy fields were polluted by heavy metals due to release of mining wastewater.•Rice grain produced in the polluted fields was contaminated by Cd.•Activities of soil enzymes were highly inhibited by the heavy metal pollution.•DH and MBC could be used as eco-indicators of heavy metal pollution of soils.To study the effects of mining activities on the agricultural environmental quality, four representative paddy fields distributed at different towns (HSG, SNJ, NT and THJ) of Y County, northern Hunan Province, were investigated. It was found that the paddy fields at HSG, SNJ and NT were heavily polluted by heavy metals, especially Cu, Zn and Cd, due to long-term irrigation with the nearby stream water contaminated by mining wastewater. In contrast, the paddy field at THJ, far away from mining sites, was not polluted by heavy metals and regarded as a control. The rice grain produced at the fields of HSG, SNJ and NT had a high risk of Cd contamination. Soil enzyme activities and microbial biomass were significantly inhibited by the heavy metal pollution. Microbial biomass carbon and microbial biomass nitrogen at a severely polluted site of the field at HSG were only 31.6% and 64.4% of the controls, respectively. The activities of dehydrogenase, urease, catalase, acid and neutral phosphatase and sucrase were only 25.2%, 49.3%, 52.4%, 94.7%, 53.2% and 87.8% of the controls, respectively. The microbial parameters were mostly negatively significantly correlated with the contents of Cu, Zn, Cd and Ni in the paddy fields, fully suggesting that the heavy metals had toxic effects on microbial processes. Furthermore, the principal component analysis and cluster analysis indicated that the activities of dehydrogenase and microbial biomass carbon were the most sensitive to the toxicity of heavy metals and could be used as eco-indicators of soil pollution in the study areas.

The environment of estuarine wetlands has been attracting worldwide attention. To study the spatial distribution of pollutants in the tidal flats of the Yangtze Estuary, Southeast China, the Eastern Tidal Flat of Chongming Island (EC) and the Jiuduansha Shoal (JS) of the estuary were selected as the study sites. At each of the two sites, a cross-transect from land to sea was established and topsoil and soil core samples in the cross-transect were collected spatially and seasonally to determine their contents of heavy metals (Cu, Zn, Pb, Cd, Cr, Ni, Mn, and Fe) and grain-size characteristics. The results showed that the heavy metal loads were commonly higher in the soils of nearshore high tidal flats and had a tendency of decreasing from land to sea at both of the study sites. The contents of heavy metals in the soils of the high and medial tidal flats were mostly higher in April and November but lower in July. Corresponding spatial and seasonal variations in grain size of the intertidal soils were also observed at the two study sites. The soils in the nearshore high tidal flats were finer and gradually got coarser seawards; they were relatively finer in April and November but coarser in July. Furthermore, the contents of heavy metals in the intertidal soils of both the sites EC and JS were significantly positively correlated with the clay (< 2 μm) and 2–20 μm fractions, but negatively with the sand (> 63 μm) and 20–63 μm fractions, which suggested that the heavy metals in the intertidal soils were primarily combined with the fine particulate fraction (< 20 μm), especially clay, and hence the spatial and seasonal variations in heavy metals were actually caused by the change of the grain-size characteristics of the intertidal soils due to the different sedimentary environments in the estuary. The results of this study may also contribute to a better understanding of the soil formation and classification in the tidal flats of the Yangtze Estuary.

•Colors of the red clay in southern China were quantitatively measured.•Redness (a⁎) of the red clay has paleoclimatic implications.•The amount of hematite formation is closely related to the weathering degree.•Temporal variation of a⁎ in the red clay reflects local paleoclimatic changes.•Spatial variation of a⁎ in the red clay is correlated with latitudinal positions.The red clay and red weathering crust are widely distributed in southern China. To study the possible relationship between soil color and paleoclimatic environment, three color parameters, lightness (L⁎), redness (a⁎) and yellowness (b⁎), of twelve Quaternary Red Clay (QRC) profiles in southern China were measured using a colorimeter. Colors of the QRC profiles vary vertically: a⁎ and b⁎ generally increase downward and L⁎ decreases downwards. Colors of the QRC also show spatial variation: a⁎ and b⁎ generally increase towards the equator; whereas L⁎ increases away from it. Both a⁎ and b⁎ are positively significantly correlated with clay (< 2 μm) content, free Fe (Fed), Fed/Fet ratios and other soil weathering indices of the QRC (ρ < 0.05), and the correlations between a⁎ and the weathering indices are much stronger than those between b⁎ and the indices. a⁎ mainly reflects hematite content in soils. Compared with magnetic susceptibility (χ), a⁎ of the QRC is a more promising paleoclimatic indicator, although it is sometimes disturbed by uneven parent materials and dissolution of hematite by water logging. The upward decrease of a⁎ of the QRC profiles reflects a cooling and drying paleoclimate since the end of the Last Interglacial, and the spatial variation of a⁎ coincides with more optimum hydrothermal conditions in lower-latitude areas of southern China.

Magnetic properties, free and active Fe oxides, grain size distribution and mineral assemblage of a Quaternary loess–Tertiary red clay (TRC) section in Lingtai County in the Chinese Loess Plateau were studied. The results suggest that the TRC of the Lingtai section shares similar aeolian characteristics with the overlying Quaternary loess-paleosol sequence (QLPS), but the former is generally more intensively weathered than the latter, as indicated by its higher citrate–bicarbonate–dithionite (CBD) extractable Fe (Fed), finer grain size and lower content of easily weathered primary minerals. However, magnetic susceptibility (χlf) and magnetic remanence (χarm, SIRM and SOFT etc.) of the main part of the TRC are significantly lower, implying the decline of ferrimagnetic minerals (FM). In contrast, hematite and goethite in the TRC is significantly enhanced, as indicated by its higher HIRM. The acid ammonium oxalate (AAO) extractable Fe (Feo) of the whole section sharply decreases with increasing age. Feo and Feo/Fed values of the section are significantly correlated with χlf. Especially in the TRC, the low values of Feo and Feo/Fed correspond to weak χlf. This suggests a significant influence of the age-related transformation of Fe oxides on the decline of FM in the TRC. Lower FM and higher hematite and/or goethite in the TRC further suggest the transformation of FM into hematite with the aging of Fe oxides during post-depositional processes, though more evidence is needed to understand the processes involved. χlf of the TRC in the Chinese Loess Plateau mostly cannot be regarded as a promising paleoclimatic proxy because its weak magnetism does not correlate to its strong pedogenesis.

To study the feasibility of using magnetic techniques for monitoring soil pollution in Shanghai, magnetic properties and heavy metals in the topsoils in an urban site (Songnan Town) and a less-urbanized agricultural site (Luojing Town) in Baoshan District, Shanghai, were studied. Compared with the background, magnetic signals of the urban topsoils are extremely enhanced with magnetic susceptibility (χlf) from 127.3–1959 × 10− 8 m3 kg− 1; while those of the agricultural topsoils are only slightly increased. However, both the urban and agricultural topsoils contain few pedogenic SP grains, as indicated by their low χfd% (< 3.6%). Ratios of χarm/SIRM, χarm/χlf and SIRM/χlf indicate that the grain size of magnetic minerals in the urban topsoils is significantly coarser than that in the background and the agricultural topsoils. Furthermore, the urban topsoils show low coercivity and magnetic soft behaviors, as indicated by higher SOFT%, lower HARD%, higher IRM300 mT/SIRM (close to 1) and lower IRM− 200 mT/SIRM (close to − 1). It suggests that the urban topsoils have received some coarse ferrimagnetic particles. Heavy metals are highly enriched in the magnetic fractions of the topsoils. Geochemical properties of the magnetic fraction of the urban topsoils are significantly different from those of the agricultural topsoils, further indicating that the extra magnetic minerals accumulated in the urban topsoils are neither inherited from soil parent materials nor from pedogenic processes, but originate from anthropogenic activities. The significant correlations between heavy metals and χlf, χarm, SIRM, SOFT and HIRM of the topsoils in the district indicate that the magnetic techniques can be used for monitoring soil pollution in Shanghai. The soils with χlf from 39–50 × 10− 8 m3 kg− 1 in the district are tentatively defined as “slightly polluted soils”; those with χlf > 50 × 10− 8 m3 kg− 1 are defined as “polluted soils”.