Rice Field Ecosystem Research Articles

Indonesia

There are approximately 1.4 million hectares of swampy area in South Sumatera, but only 12% of those are being used as farm and plantation. The purpose of this research was to investigate the similarity of arthropod community inhabiting swampy rice field and its surrounding area. This research was conducted in South Sumatera Province covering regency of Musi Banyuasin and Palembang. Four types of swampy area were selected from each location, i.e. rice field, thicket, bush, and swampy land inhabited by broad-leaf weeds. Pitfall trap used to collect arthropod and it installed at five different times. i.e. 15 days before rice planting, one month, two months, and three months after planting, and 15 days after harvest time. The result showed that relative abundance of predatory arthropod dwelling soil in rice field was 95.03%, and habitat surrounding rice field was 95.12–97.21%. The level of similarity of arthropod species between rice field ecosystem and its surrounding area ranged from 0.73 to 0.84. Thus, the surrounding area of rice field probably can be used as catchment area of predatory arthropod and other pests during planting season.

Food and Feeding Habits of the Mola Carplet Amblypharyngodon mola (Hamilton, 1822) in Rice Field Ecosystem with Consideration of Water Quality Parameters

The present investigation was conducted in the Agronomy field laboratory of Bangladesh Agricultural University, Mymensingh, Bangladesh during May 1999 to August 1999 to reveal the food and feeding habits of Amblypharyngodon mola in the rice field ecosystem. Percentage of frequency of occurrence and percentage in number methods were used for the qualitative and quantitative estimation of plankton population. Results showed that, during the present study, the water quality parameters were within the suitable range for optimal fish growth and plankton population was abundant in the water of the rice plots. Gut content analysis of A. mola revealed a sum of 32 genera of phytoplankton belonging to Chlorophyceae (17), Euglenophyceae (2), Cyanophyceae (7) and Bacillariophyceae (6) and 8 genera of zooplankton under Rotifera (3), Cladocera (2) and Copepoda (3). In general, Navicula, Fragilaria, Chlorella, Chrysococcus, Closterium, Oscillatoria and Gomphosphaeria were found abundant both in the water of the rice plots and in the gut contents of A. mola indicating that, these genera are preferred food of this fish in the rice field ecosystem. Gut content analysis also exposed that, phytoplankton was the major food item constituting 94.38% of the gut contents’ composition of A. mola whereas zooplankton comprised only 5.62%. The results of this study conclude that, the A. mola is planktivorous in nature, feeding mostly on phytoplankton and could be a suitable species for integrated rice-fish farming.DOI: http://dx.doi.org/10.3126/on.v11i1.8245 Our Nature Vol.11(1) 2013: 61-75

Residues of cyantraniliprole and its metabolite J9Z38 in rice field ecosystem

A simple and reliable analytical method was developed to detect cyantraniliprole (HGW86) and its metabolite J9Z38 in rice straw, paddy water, brown rice, and paddy soil. The fate of cyantraniliprole and its metabolite J9Z38 in rice field ecosystem was also studied. The target compounds were extracted using acetonitrile, cleaned up on silicagel or strong anion exchange column, and analyzed by ultra-performance liquid chromatography–tandem mass spectrometry. The average recoveries of cyantraniliprole and J9Z38 in rice straw, paddy water, brown rice, and paddy soil ranged from 79.0% to 108.6%, with relative standard deviations of 1.1–10.6%. The limits of quantification of cyantraniliprole and J9Z38 were 18 and39μgkg−1 for rice straw, 2.8 and 5.0μgkg−1 for paddy water, 4.3 and 6.3μgkg−1 for brown rice, and 3.9 and 5.3μgkg−1 for paddy soil. The trial results showed that the half-lives of cyantraniliprole were 3.2, 4.4, and 6.3d in rice straw and 4.9, 2.0, and 6.2d in paddy water in Zhejiang, Hunan, and Shandong, respectively. The respective final residues of cyantraniliprole and J9Z38 in brown rice were lower than 0.05 and 0.02mgkg−1 after 14d of pre-harvest interval. The maximum residue limit of cyantraniliprole at 0.1mgkg−1 and dosage of 100g a.i.hm−2, which could be considered safe to human beings and animals, were recommended.

Degradation of metaflumizone in rice, water and soil under field conditions

The degradation behavior of metaflumizone was studied in a rice field ecosystem, and a simple and reliable analytical method was developed for determination of metaflumizone in soil, rice straw, paddy water and brown rice. Metaflumizone residues were extracted from samples with acetonitrile. The extract was cleaned up with QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method, and determined by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The average recoveries of metaflumizone were 75.2–105.1 percent from soil, rice straw, paddy water and brown rice. The relative standard deviations were less than 15 percent. The limits of quantitation (LOQs) of metaflumizone were 3.0μg/L for paddy water and 3.0μg/kg for other samples. The results of the kinetic study of metaflumizone residue showed that metaflumizone degradation in soil, water and rice straw coincided with C=0.08564e−0.0505t, C=0.04984e−0.1982t, C=2.2572e−0.1533t, respectively; the half-lives were about 13.7d, 3.5d, and 4.5d, respectively. The final residues of metaflumizone on brown rice were lower than maximum residue limit (MRL) of 0.05mg/kg after 28d Pre-Harvest Interval (PHI) at the recommended dosage. Therefore, a dosage of 450mLa.i.ha−1 with 28 days before harvest was recommended, which could be considered as safe to human beings and animals.

Influence of Soil Amendments on Mitigating Methane Emissions and Sustaining Rice Productivity in Paddy Soil Ecosystems of Bangladesh

Two field experiments were conducted at two different rice ecosystems, one in the upland rice field of Bangladesh Agricultural University farm, Mymensingh and the another one in the low lying area of Bhaluka, Mymensingh to investigate the effects of soil amendments on mitigation of methane emissions and sustaining rice productivity. The experimental treatments were urea (250 kg ha-1), urea plus coal ash (1t ha-1), urea plus phosphogypsum (90 kg ha-1), urea plus silicate fertilizer (150 kg ha-1), ammonium sulphate 400 kg ha-1, ammonium sulphate plus silicate fertilizer (150 kg ha-1), urea (25% less than the recommended doze) plus cyanobacteria plus azolla (1t ha-1). In case of BAU upland rice field, the total seasonal CH4 emission was decreased by 12-21% and rice grain yield was increased by 4.0- 18.0% respectively, whereas 11.0-26.0% reduction in total CH4 emission and 4.5-24.0% increase in rice grain yield was recorded from the low lying rice field of Bhaluka with the application of soil amendments. Among the amendments silicate fertilization with urea and silicate in combination with ammonium sulphate reduced total CH4 flux by 18- 23% and 21-26% respectively, whereas rice grain yield was increased by 18-24% and 16-18%, respectively in both ecosystems. Although maximum reduction in total seasonal CH4 flux was recorded with silicate and sulfate of ammonia amendment in paddy soil, however soil acidity was developed which might affect soil fertility and rice productivity in the future. Therefore, silicate fertilizer could be introduced with the nitrogenous fertilizer sources, preferably with 50% urea plus 50% ammonium sulphate for reducing CH4 emissions and increasing rice productivity under both irrigated upland and lowland rice field ecosystems. DOI: http://dx.doi.org/10.3329/jesnr.v5i1.11574 J. Environ. Sci. & Natural Resources, 5(1): 179 - 185, 2012

Integrated Rice-Fish Farming: Safeguarding Biodiversity and Ecosystem Services for Sustainable Food Production in the Mekong Delta

A comparison of agricultural practices, with a specific focus on pesticide use, between rice and rice-fish farmers in the Cần Thơ and Tiền Giang provinces of the Mekong Delta in 2007, shows that integrated rice-fish farming can provide a competitive alternative to intensive rice mono-cropping, if the farmer restricts the use of pesticides and takes full advantage of the ecosystem services provided by the rice-field ecosystem. In Cần Thơ, rice-fish farmers had significantly higher income (43.6 million dong ha−1 year−1) than other farmer groups, while this was not seen among rice-fish famers in Tiền Giang (32.4 million dong ha−1 year−1), which partly could be due to a high use of insecticides (0.9 kg active ingredient ha−1 crop−1) and comparatively low fish yield among these farmers. The study emphasizes the need to rethink current agricultural systems and to provide opportunities for more diverse systems that maintain and enhance a range of ecosystem services and protect human health. Future production systems should not be optimized to only provide a single ecosystem service, such as rice, but designed to deliver a variety of interlinked ecosystem service such as rice, fish, pest control, and nutrient recycling.

Natal nest locations of the Asian house rat (Rattus tanezumi) in lowland rice–coconut cropping systems: a coconut penthouse or rice bunds with water frontage?

Context Rattus tanezumi is a serious crop pest within the island of Luzon, Philippines. In intensive flood-irrigated rice field ecosystems of Luzon, female R. tanezumi are known to primarily nest within the tillers of ripening rice fields and along the banks of irrigation canals. The nesting habits of R. tanezumi in complex rice–coconut cropping systems are unknown. Aims To identify the natal nest locations of R. tanezumi females in rice–coconut systems of the Sierra Madre Biodiversity Corridor (SMBC), Luzon, during the main breeding season to develop a management strategy that specifically targets their nesting habitat. Methods When rice was at the booting to ripening stage, cage-traps were placed in rice fields adjacent to coconut habitat. Thirty breeding adult R. tanezumi females were fitted with radio-collars and successfully tracked to their nest sites. Key results Most R. tanezumi nests (66.7%) were located in coconut groves, five nests (16.7%) were located in rice fields and five nests (16.7%) were located on the rice field edge. All nests were located above ground level and seven nests were located in coconut tree crowns. The median distance of nest sites to the nearest rice field was 22.5 m. Most nest site locations had good cover of ground vegetation and understorey vegetation, but low canopy cover. Only one nest location had an understorey vegetation height of less than 20 cm. Conclusions In the coastal lowland rice–coconut cropping systems of the SMBC, female R. tanezumi showed a preference for nesting in adjacent coconut groves. This is contrary to previous studies in intensive flood-irrigated rice ecosystems of Luzon, where the species nests mainly in the banks of irrigation canals. It is important to understand rodent breeding ecology in a specific ecosystem before implementing appropriate management strategies. Implications In lowland rice–coconut cropping systems, coconut groves adjacent to rice fields should be targeted for the management of R. tanezumi nest sites during the main breeding season as part of an integrated ecologically based approach to rodent pest management.

Residues of chlorantraniliprole in rice field ecosystem

The fate of chlorantraniliprole was studied in rice field ecosystem, and a simple and reliable analytical method was developed for determination of chlorantraniliprole in soil, rice straw, paddy water and brown rice. Chlorantraniliprole residues were extracted from samples with acetonitrile. The extract was cleaned up with QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method, and determined by high-performance liquid chromatography electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS). The average recoveries were 76.9–82.4% from soil, 83.6–89.3% from rice straw, 95.2–103.1% from paddy water and 84.9–87.7% from brown rice. The relative standard deviation was less than 15%. The limits of detection (LODs) of chlorantraniliprole calculated as a sample concentration (S/N ratio of 3) were 0.012μgL−1 for paddy water, 0.15μgkg−1 for soil, brown rice and rice straw. The results of the kinetics study of chlorantraniliprole residue showed that chlorantraniliprole degradation in soil, water and rice straw coincided with C=0.01939e−0.0434t, C=0.01425e−0.8111t, and C=1.171e−0.198t, respectively; the half-lives were about 16.0 d, 0.85 d and 3.50d, respectively. The degradation rate of chlorantraniliprole in water was the fastest, followed by rice straw. The final residues of chlorantraniliprole on brown rice were lower than maximum residue limit (MRL) of 0.02mgkg−1 after 14d Pre-Harvest Interval (PHI). Therefore, a dosage of 150mL a.i.hm−2 was recommended, which could be considered as safe to human beings and animals.

Population structure and dynamics of Nerothemis tulla (Odonata: Libellulidae) with water availability in rice field ecosystem

Dragonflies are important insects in rice field ecosystem (RFE) as pest predators. Rice fields in return serve as a good breeding and feeding ground for dragonflies though RFE undergo several changes during a crop cycle. However habitat conditions vary mainly on the climatic regions and farming practices. The selected RFE in wet zone lowland for sampling comprised deferent habitats, two shallow streams, non cultivated fields, cultivated fields, small water pools, ponds and water wells. The most common dragonfly in marshes and paddy fields, Nerothemis tullia (Pied Parasol) was studied to understand its population structure and dynamics with the water availability. Sampling was conducted from May 2010 to November 2010 covering one cultivation cycle. Two sampling methods i.e., random sampling along 5m X 50m transects and systematic sampling in pre-identified colonies were used. Colonies were identified in advanced, numbered consecutively and every third colony was observed. Nerothemis tulla adult male, adult female, juvenile male and terneral female were distinguish by general mophological characters and recorded separately. Activeness of Nerothemis tulla individuals were recorded as number of catches (of prey) or tries for per 10 minutes. Other associated dragonflies and damselflies were also recorded. Water level and flow rate in streams were measured as indicators of water availability in RFE. Systematic sampling recorded higher density (2.50 individuals/m2) while random sampling produced lesser density (0.19 individuals/m2). However random sampling method recorded higher diversity of Odonata in RFE. Number of individuals were positively correlated (r =7.68) with water level. Flow rate had no significance relationship with individual density. Activity of colony peaks between 9.00 hr to 11.00 hr and minimum around 13.00 hr. Second peak occurred around 16.00 hr - 17.00 hr. Number of both male and female juveniles sharply reduced towards the drier months whilst number of both adult male and female increased. During the dry period in September, density reduced to minimum and juveniles became scares. In November with the beginning of rain, number and activity of Nerothemis tulla increased and more colonies observed at water holes and in field proper of paddy fields. Sampling along transects can be recommended for study of odonata diversity whilst systematic sampling is more suitable for study of population dynamic and structure. The study is being continued for second crop cycle. Though common species are neglected in conservation practices, consequences of sudden decline in common species that occur in higher number, such as Nerothemis tulla is unpredictable. This study implies the necessity of their conservation as they have complex ecosystem interactions and intense ecosystem service.

Taxocoenosis and Distribution of Nektonic Fauna in the Rice Fields of Kashmir (J and K) India

Present study attempts to identify the taxocoenosis and distribution of nektonic fauna harbouring the rice field ecosystems of Kashmir. The main objective of the study was to provide an overview of the nektonic community composition and physicochemical characteristics of flood waters. 6 sites were selected in Kupwara, Bandipora, Budgam, Srinagar, Pulwama and Anantnag districts of valley Kashmir. A total of 26 taxa belonging to 13 different orders were reported during the study which commenced through 2 consecutive crop cycles. The taxocoenosis was dominated by Coleoptera (10 taxa) followed by Hemiptera (3 taxa), Diptera (2 taxa), Diplostraca (2 taxa), Acarina, Anostraca, Anura, Amphipoda, Basommatophora, Cypriniformes, Cyprinodontiformes, Odonata and Pulmonata (1 taxa each). Diversity was calculated using Simpsons Index (D), Simpsons Index of Diversity (1-D), Simpsons Reciprocal Index (1/D), Shannon-Weiner Index (H'), Margalef Richness Index (d) and Evenness Index (e). Kupwara (34 degrees 02'N; 74 degrees 16'E) formed the most diverse site registering a total of 2384 individuals belonging to 24 taxa. A perusal of the primary data related to the physicochemical attributes of flood waters exhibited that average water temperature varied between 19-30 degrees C, average air temperature varied between 21 and 33 degrees C. pH depicted a variation between 6.0 and 9.0, Dissolved Oxygen varied between a minimum of 1.0 mg L(-1) and a maximum of 10 mg L(-1). Free CO2 ranged between 0 mg L(-1) and 6.1 mg(-1). The results pressed the need for recognizing and preserving rice fields as potential habitats for organisms that have successfully adapted to the highly manipulated and eutrophic conditions of rice paddies.

Residues and dynamics of pymetrozine in rice field ecosystem

The fate of pymetrozine was studied in rice field ecosystem, and a simple and reliable analytical method for determination of pymetrozine in soil, rice straw, paddy water and brown rice was developed. Pymetrozine residues were extracted from samples, cleaned up by solid phase extraction (SPE) and then determined by high-performance liquid chromatography electrospray ionization tandem mass spectrometry (LC–ESI–MS–MS). The average recovery was 81.2–88.1% from soil, 83.4–88.6% from rice straw, 87.3–94.1% from paddy water and 82.9–85.3% from brown rice. The relative standard deviation (RSD) was less than 15%. The limits of detection (LODs) of pymetrozine calculated as a sample concentration were 0.0003 mg kg −1 (mg L −1) for soil and paddy water, 0.001 mg kg −1 for brown rice and rice straw. The results of kinetics study of pymetrozine residue showed that pymetrozine degradation in water, soil, and rice straw coincided with C = 0.194e −0.986t, C = 0.044e −0.099t, and C = 0.988e −0.780t, respectively; the half-lives were about 0.70 d, 7.0 d and 0.89 d, respectively. The degradation rate of pymetrozine in water was the fastest, followed by rice straw. The highest final pymetrozine residues in brown rice were 0.01 mg kg −1, which was lower than the EU’s upper limit of 0.02 mg kg −1 in rice. Therefore, a dosage of 300–600 g a.i.hm −2 was recommended, which could be considered as safe to human beings and animals.

MENINGKATKAN KEPEDULIAN SISWA TERHADAP LINGKUNGAN EKOSISTEM PERSAWAHAN DENGAN MODEL PENULISAN BUKU AJAR BIOLOGI SMA BERWAWASAN LOKAL DAN EKOLOGI

A study using Research and Development design was conducted to produce a model of Biology hand book writing which is ecology and local oriented as an effort to increase students’ care toward environment. The background of this research is the reality which is still going on so far that the awareness and care of the school graduatee toward the environement safe is still low. Besides, hard science instructional at school could not affect or intervene the graduatee’s characteristics, for instance in keeping the environment awareness. Meanwhile, there are many concepts of environment which had been taught through hard science especially biology. So in the researcher’s point of view, biology subject has strategic role to prevent or mitigate the environment disaster caused by human activities. The model was validated at rice field environments. The analysis of the research result includes three aspects, namely: 1) text comprehension, 2) environment care attitude, and 3) handbook readibility. Based on the result of rice field ecosystem data analysis, it was found that (1) there was a significant difference between experimental class and control class in the rice field ecosystem which is shown by tcalculation > ttable (6.150 > 2.00); (2) there was strong correlation between students’ comprehension and attitude which is shown by coeficient correlation (r) 0.769. While the text readability test (Cloze test) shown (1) the readability of rice field ecosystem text is 56,72% (moderate). Therefore, the conclusion is that all of the texts in the developed book are fit and proper for SMA students of grade X. Kata kunci: Penulisan buku ajar, orientasi ekologi dan lokal, kepedulian terhadap lingkungan

Nutritional composition of aquatic species in Laotian rice field ecosystems

The population of Laos PDR has increased rapidly in recent years, reaching 2.5% per annum. This growth threatens food security, which in Asia is often equated with rice production. The country has to feed almost 50% more people now than 16 years ago. The role of aquatic rice field species in rural Laotian diets has been underestimated, as almost 200 species are consumed, supplying a range of nutrients needed by the villagers. Nevertheless, national and regional food composition databases contain limited information on the nutritional composition of these species. Field sampling was undertaken in Champasak and Savannakhet provinces for nine species of aquatic animals, including fish, amphibians, crustaceans, molluscs and insects. Four samples of fermented fish products were included. The objective was to gain knowledge on the nutritional composition of the aquatic species included in Laotian diets. The aquatic animals consumed on a daily basis contained high amounts of protein (11.6–19.7% for fish, crustaceans, molluscs, amphibians and insects and 3.3–7.8% for fermented fish), and a generally acceptable essential amino acid profile. They were also excellent sources of calcium, iron and zinc. However, they had low contents of fat (0.1–4.6%), fatty acids and vitamin A. Essential amino acids, iron and zinc are nutrients that are scarce in rural Laotian diets. As the food supply of rural households in rice farming areas of Laos is critically dependent on the environment, the sustainable existence of the rice field aquatic animals is a crucial factor for the nutritional status of the Laotians.

湛水管理による休耕田の雑草制御

In Japan, fallow paddy fields and abandoned paddy fields have increased through the rice acreage reduction policy for dealing with surplus rice, depopulation, or aging of the population. It is important to manage and maintain those paddy fields in a condition in which they are immediately and easily available for use as rice fields in the future. Control of weeds cannot be neglected in order to use fallow paddy fields as a rice fields soon. We think that much manpower and a cost are not necessary, and that the herbicides that have a bad influence on the surrounding environment, especially the rice field ecosystem should not be used for managing fallow paddy fields. As a way of satisfying these conditions, an examination of the control of water by the deeper ponding method was made. First, we examined the relations of the ponding depth of water and the growth of weeds in an experimental rice field. As a result, the abundance of weeds decreased as the ponding depth increased. Also, grass did not grow at all in water 5cm or more in depth during winter and in water over 15cm depth during summer. We arrived at the standard ponding depth of water for managing fallow paddy fields from this examination. Therefore, we proved that though some kinds of waterweed appeared, a grass did not appear as a result of managing the ponding depth of water at about 15cm in summer in an actual fallow paddy field.

Applying stable isotope probing of phospholipid fatty acids and rRNA in a Chinese rice field to study activity and composition of the methanotrophic bacterial communities in situ

Methanotrophs in the rhizosphere play an important role in global climate change since they attenuate methane emission from rice field ecosystems into the atmosphere. Most of the CH(4) is emitted via transport through the plant gas vascular system. We used this transport for stable isotope probing (SIP) of the methanotrophs in the rhizosphere under field conditions and pulse-labelled rice plants in a Chinese rice field with CH(4) (99% (13)C) for 7 days. The rate of (13)CH(4) loss rate during (13)C application was comparable to the CH(4) oxidation rate measured by the difluoromethane inhibition technique. The methanotrophic communities on the roots and in the rhizospheric soil were analyzed by terminal-restriction fragment length polymorphism (T-RFLP), cloning and sequencing of the particulate methane monooxygenase (pmoA) gene. Populations of type I methanotrophs were larger than those of type II. Both methane oxidation rates and composition of methanotrophic communities suggested that there was little difference between urea-fertilized and unfertilized fields. SIP of phospholipid fatty acids (PLFA-SIP) and rRNA (RNA-SIP) were used to analyze the metabolically active methanotrophic community in rhizospheric soil. PLFA of type I compared with type II methanotrophs was labelled more strongly with (13)C, reaching a maximum of 6.8 atom-%. T-RFLP analysis and cloning/sequencing of 16S rRNA genes showed that methanotrophs, especially of type I, were slightly enriched in the 'heavy' fractions. Our results indicate that CH(4) oxidation in the rice rhizosphere under in situ conditions is mainly due to type I methanotrophs.

Activity and composition of methanotrophic bacterial communities in planted rice soil studied by flux measurements, analyses of pmoA gene and stable isotope probing of phospholipid fatty acids

Methanotrophs in the rhizosphere of rice field ecosystems attenuate the emissions of CH(4) into the atmosphere and thus play an important role for the global cycle of this greenhouse gas. Therefore, we measured the activity and composition of the methanotrophic community in the rhizosphere of rice microcosms. Methane oxidation was determined by measuring the CH(4) flux in the presence and absence of difluoromethane as a specific inhibitor for methane oxidation. Methane oxidation started on day 24 and reached the maximum on day 32 after transplantation. The total methanotrophic community was analysed by terminal restriction fragment length polymorphism (T-RFLP) and cloning/sequencing of the pmoA gene, which encodes a subunit of particulate methane monooxygenase. The metabolically active methanotrophic community was analysed by stable isotope probing of microbial phospholipid fatty acids (PLFA-SIP) using (13)C-labelled CH(4) directly added to the rhizospheric region. Rhizospheric soil and root samples were collected after exposure to (13)CH(4) for 8 and 18 days. Both T-RFLP/cloning and PLFA-SIP approaches showed that type I and type II methanotrophic populations changed over time with respect to activity and population size in the rhizospheric soil and on the rice roots. However, type I methanotrophs were more active than type II methanotrophs at both time points indicating they were of particular importance in the rhizosphere. PLFA-SIP showed that the active methanotrophic populations exhibit a pronounced spatial and temporal variation in rice microcosms.

Molecular identification of methane oxidizing bacteria in a Japanese rice field soil

By using cultivation-independent techniques, community changes of methane-oxidizing bacteria (MOB) in rice bulk soils were investigated under field conditions in a Japanese rice field. The representative soil samples were collected during the typical rice growing season and nonrice growing period all year round. Statistical characterization of denaturing gradient gel electrophoresis (DGGE) community patterns of MOB pmoA/amoA functional gene fragments showed that MOB community structures in the rice bulk soils remained largely unchanged throughout the investigated period. The total intensity of six common DGGE bands that appeared consistently throughout the investigated period accounted for 64% of the total intensity of all 18 different DGGE bands detected. The low squared distance of the Ward cluster analysis of the DGGE pattern and the high Sorensen similarity coefficient (81%) also implied the high similarity of the MOB community structures. The stable MOB community structure did not couple well with the wide variation of soil water contents all year round. Sequencing analysis of the nine characteristic bands including six common bands revealed the presence of Type I, Type II methanotrophs, and β-proteobacterial ammonia oxidizers in rice bulk soils. In comparison with MOB type species, three DGGE bands showed a wide variation of the highly conserved amino acid residues, implying the presence of novel MOB bacteria inhabiting the rice bulk soil. The high diversity of MOB composition suggested that rice bulk soils might serve as an ideal reservoir for the dynamic changes of MOB in a rice field ecosystem in response to environment changes.

Contribution of Rice Field Ecosytems to Food Security Strategies in Northwest Cambodia

ABSTRACT Rich in biodiversity, Cambodia's rice field ecosystems are an important source of livelihood and food security. Foraging of aquatic plants and animals alongside the cultivation of rice has been the main characteristic of food and income systems of traditional Cambodian rural society. Participatory action learning involving 30 farmers in three different villages located in three different lowland ecosystems of northwest Cambodia showed that fish and other aquatic animals collected (between 111 kg and 267 kg/family based on ecosystems) from rice field ecosystems constitute an important source of food and income. It is also true for plants collected from the ecosystems. In lowland environment of Cambodia, and considering the rice economy only, there is very little economic advantage growing rice with traditional cultivation techniques over importing it. However, if we take into consideration the total production of nutrients from cultivated and non-cultivated sources Cambodian rice fields are highly productive. Unsustainable interventions for economic development and modernization (such as increased use of agro-chemicals, development of irrigation, and drainage structures) may reduce the productivity of rice field ecosystems and affect livelihood patterns and food security. The paper argues that a focus on increasing the rice production without any regard to the total bio-productivity of the rice field ecosystems could result in higher ecological costs, which could make the increase in rice production ecologically as well as nutritionally unsustainable.

The rodent species of the Ifugao Rice Terraces, Philippines – target or non-target species for management?

We investigated the species diversity and habitat use of rodents in the Ifugao Rice Terraces (IRT), Luzon, Philippines, as a first step in their assessment either as pest species of rice or as potential non-target species of rodent control practice. Trapping was carried out in caneland and forest habitats adjacent to rice cropland using trap lines of 10 – 15 cage-traps. Four trapping rounds, each consisting of 5 nights trapping, were replicated at two sites during the months of May and June. A diverse rodent fauna was recorded, including the non-native pest species, Rattus tanezumi, and the native species, Rattus everetti and Chrotomys mindorensis. Results from trapping and spool-and-line tracking suggested that these native species do not contribute to rice damage and that several may actually be beneficial in the ricefield ecosystem as vermivores that feed on invertebrate pests. Control should therefore be directed at the pest species, R. tanezumi, minimising non-target effects on the non-pest rodent species.

Combining fish and rice production.

Abstract The combination of rice and fish production into one system is considered to be an efficient means of agricultural land use for small-scale farmers. In some of these so-called rice-fish systems rice and fish are grown in the same field, at the same time; in other systems they are grown in the same field, but in rotation. Rice-fish farmers pay most attention to the maximization of the rice yield. This is a logical choice because the rice field is not the most ideal environment for fish production as the rice crop shades the field floodwater, thus hampering aquatic primary production. Still, practically all-major freshwater species being farmed, worldwide, have been successfully raised in rice field ecosystems. Farmers usually opt to stock several fish species in a polyculture in an attempt to make optimal use of all ecological niches in the rice field. Fish yields are usually low but can be substantially increased when additional feed or manure is added to the system. One of the advantages of rice-fish culture is that it gives farmers new and sustainable opportunities to apply integrated pest management (IPM). Indeed, the presence of fish in the rice fields shifts the economic threshold for pesticide applications to a level which is unlikely to be reached by pest populations. Fish are also known to control weeds in rice fields. The rice yields in rice-fish systems are sometimes higher, and sometimes lower, when compared with those from rice monoculture systems. The mechanisms for this are not always well understood. The increase in household income might be substantial, but the high input costs associated with the system often deter farmers from adopting it. Nevertheless, rice-fish farming can provide a sustainable alternative to rice monoculture, both from an economic as well as an ecological point of view.