Xue-Feng Hu

Affects of mining activities on Cd pollution to the paddy soils and rice grain in Hunan province, Central South 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 6.02xa0mgxa0kg−1, with a mean of 0.64xa0mgxa0kg−1, of which 57.5xa0% 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 146.4xa0%. 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 2.17xa0mgxa0kg−1, with a mean of 0.24xa0mgxa0kg−1. A significant positive correlation exists between T-Cd and HCl-Cd in the soils (ru2009=u20090.770, ρu2009<u20090.01). (2) Cd content in the rice produced in Y county ranges from 0.01 to 2.77xa0mgxa0kg−1, with a mean of 0.46xa0mgxa0kg−1. The rate of rice with Cd exceeding the allowable limit specified by the Chinese Grain Security Standards reaches 59.6xa0%; that with Cd exceeding 1xa0mgxa0kg−1, called as “Cd rice,” reaches 11.1xa0%. (3) Cd content in the rice of Y county is positively significantly correlated with HCl-Cd (ru2009=u20090.177, ρu2009<u20090.05) but not significantly with T-Cd in the soils (ru2009=u20090.091, ρu2009>u20090.05), 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 179.9xa0μgxa0day−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.

Influences of introducing frogs in the paddy fields on soil properties and rice growth

PurposeThis paper aims to study the influences of introducing frogs in the paddy fields on soil ecology and rice growth.Materials and methodsThe 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.Results and discussionThe 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.ConclusionsTo 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.

Ecological effects of rice-duck integrated farming on soil fertility and weed and pest control

PurposeThis paper aims to study the ecological effects of rice-duck integrated farming on soil fertility and weed and pest control.Materials and methodsA 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 667xa0m2 in area.Results and discussion(1) The number of weeds in the plots with the duck treatment was significantly lower than that with CK (pu2009<u20090.01). (2) The incidence of stem borers (Chilo suppressalis) with the duck treatment was significantly lower than that with CK (pu2009<u20090.05). 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 (pu2009<u20090.01). (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 (pu2009<u20090.01).ConclusionsRaising 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.

Effects of different fertilisers on rice resistance to pests and diseases

A field experiment was conducted in Shanghai in 2013, to study the effects of different fertiliser applications on the occurrence of rice pests and diseases. The experiment included four treatments: a non-fertilised control (CK); rapeseed cake manure (CM) at a low (CML) and a high (CMH) rate; and a synthetic chemical fertiliser (CF). No pesticides were applied within the rice-growing season. The rice plants treated with CF grew tallest, and had higher contents of NH4+-N, NO3–-N, chlorophyll and soluble proteins than those in the other fertiliser treatments and CK. However, the incidence of leaf rollers (Cnaphalocrocis medinalis), stem borers (Chilo suppressalis) and planthoppers on the rice plants treated with CF was significantly higher than in the other fertiliser treatments and CK (Pu2009<u20090.05). In particular, the incidence of stem borers in the plants treated with CF was about 10 times higher than in the other treatments and CK, and the density of planthopper populations on the plants treated with CF was 1.73, 1.42 and 3.04 times that on plants treated with CMH, CML and CK, respectively. The application of fertilisers increased soil microorganisms, and the effects of rapeseed cake manure on the increase in microorganisms were most significant. Numbers of soil bacteria, fungi and Actinomyces were the highest in soils treated with CMH. Application of rapeseed cake manure also significantly raised the activity of soil dehydrogenase. The CF treatment inhibited dehydrogenase activity but raised urease activity significantly. Average theoretical grain yields in treatments CML, CMH, CF and CK were 7.45u2009×u2009103, 8.85u2009×u2009103, 7.41u2009×u2009103 and 3.70u2009×u2009103u2009kgu2009ha–1, respectively. The application of CF stimulated rice vegetative growth more effectively but finally led to lower grain yield due to higher incidence of pests and diseases.