Tropical Rice Research Articles

MACRONUTRIENT RATES AND MULTIFUNCTIONAL MICROORGANISMS IN A TROPICAL FLOODED RICE CROP

ABSTRACT Tropical flooded rice production systems require a high input of fertilizers and chemical defensive. The use of plant growth-promoting rhizobacteria (PGPR), a sustainable component of this system, can increase nutrient-use efficiency and lead to significant increases in the grain yield of tropical flooded rice crop. This study aimed to determine the effect of the microorganism BRM 32110 (Bacillus thuringiensis) in combination with nitrogen (N), phosphorus (P) and potassium (K) application rates on the physiological and agronomic performance of tropical flooded rice plants. Trials were performed in the 2016/2017 growing season in Formoso do Araguaia, a city in Tocantins state, Brazil. Three independent experiments (E1, E2, and E3) were performed in a randomized block design in a 4 x 2 factorial scheme with three replications. E1 comprised four N application rates (0, 40, 80 and 120 kg N ha-1) with and without the addition of BRM 32110, E2 comprised four P2O5 application rates (0, 40, 80 and 120 kg P2O5 ha-1) with or without BRM 32110, and E3 comprised four K2O application rates (0, 20, 40 and 60 kg K2O ha-1) with and without BRM 32110. In fertile soil, there were no interactions between the rhizobacterium BRM 32110 and the N, P or K application rates. BRM 32110 improved nutrient uptake and, on average, increased shoot dry matter by 8%, photosynthesis rate by 14% and grain yield by 11% in the flooded rice plants. Our results suggest that the use of multifunctional microorganisms is a good strategy for improving flooded rice grain yield sustainably.

Farmer participatory research in agricultural extension programs: A case study of fertilizer management in tropical rice

AbstractAgricultural extension requires close communication with farmers, and researchers must consider farmers’ perspectives on crop management. Farmers tend to take into account the canopy appearance when they decide on fertilizer application, and this is often neglected in crop management recommendations by researchers. Our objectives were to dissect the growth characteristics that farmers implicitly account for in nutrient management of tropical rice. Farmer participatory trials were conducted in irrigated and rainfed lowlands in the Philippines during the wet seasons of 2014, 2015, and 2016. Each year, 30 participating farmers made decisions on fertilizer management for plots with different seedling ages and planting densities. These treatments greatly changed the canopy appearance, and affected farmer decisions on nitrogen (N) management, particularly in the first year. We found that plant height and leaf greenness were the major determinants of their decisions in irrigated lowlands. Under rainfed conditions, the risk of drought made farmers focus on tillering rather than plant elongation and leaf color during early growth stages, and on canopy cover and plant elongation during later stages. Across years and water regimes, farmers applied 78% more N than researchers without generally increasing grain yield. Since crop diagnosis is a key for successful management by farmers, guidelines for efficient nutrient management should include numerical targets for the traits emphasized by farmers. That will help farmers better understand their crops, and the guidelines will be more user-friendly than providing only a fertilizer application prescription.

Development of Bt rice potential for yellow stem borer control

Rice (Oryza sativa L.) production is always threatened by biotic and abiotic stresses. Both stresses can reduce rice productivity and quality. Yellow stem borer (YSB; Scirpophaga incertulas Walker) is one of the biotic stresses and is reported as the most destructive pest of tropical rice insects. The application of pesticides is less effective since the insect larvae live and feed inside the stem, thus inhibiting pesticides to reach the larvae. Planting YSB-resistant cultivars is a good strategy besides environmentally friendly. However, no sufficient level of resistance to YSB has been identified among rice germplasm collection, making the use of conventional breeding methods is difficult. Bacillus thuringiensis (Bt) is a Gram-positive bacterium produces insecticidal proteins, Cry toxins that are toxic to YSB. The introduction of cry genes from Bt into rice plants by using genetic engineering has been widely and successfully carried the out. A number of strategies have been conducted to increase the expression level and to prolong the effectiveness of Bt toxins in transgenic rice, including plant codon usage-optimized genes, the use of strong promoters and wound-inducible promoters and gene stacking. Insect bioassays under laboratory, greenhouse and field conditions showed that transgenic rice plants harboring and expressing cry genes are highly resistant to YSB compared to the original cultivars from which transgenic plants were developed. Thus, the development of transgenic rice plants harboring and expressing cry genes from Bt is a good strategy to build plant resistance against YSB.

Stable Carbon Isotope Studies of CH4 Dynamics Via Water and Plant Pathways in a Tropical Thai Paddy: Insights Into Diel CH4 Transportation

AbstractSeparate evaluation of methane (CH4) emission dynamics (e.g., oxidation, production, and transportation) at the soil‐plant‐atmosphere and soil‐water‐atmosphere interfaces has been limited in tropical rice paddies, but it is crucial for comprehending the entire CH4 cycles. We investigated CH4 oxidation, production, and transportation through plant and water pathways during the reproductive stage in a tropical Thailand rice paddy field using natural abundance carbon stable isotope ratios (δ13CH4 and δ13CO2). Mass balance equations using δ13CH4 and δ13CO2 in soil gases indicated that CH4 oxidation in the planted soil exceeded those in the interrow soil due to oxygen supply through rice roots. In addition, at 1–11 cm depth acetate fermentation was the dominant process in the planted soil, whereas in the interrow soil the dominant process was H2/CO2 reduction. The water pathway showed a significant negative correlation between CH4 flux and released δ13CH4 over 24 hr, driven by a diel change in episodic ebullition, steady ebullition, and diffusion, all due to diel changes in soil temperature and atmospheric pressure. In contrast, the plant pathway showed a significant positive relationship between CH4 flux and emitted δ13CH4 throughout one day. A comparison of the diel change in emitted δ13CH4 between the water and plant pathways showed that the rice plants transported CH4 in soil bubbles without any large isotopic fractionation. The diel change in the plant‐mediated CH4 transportation was mainly controlled by diel changes in soil bubble expansion and CH4 diffusion through plants, which were probably regulated by diel changes in soil temperature and atmospheric pressure.

Modelling rice yield with temperature optima of rice productivity derived from satellite NIRv in tropical monsoon area

Tropical rice production is at risk from rising temperature. Understanding regional and seasonal heterogeneity of optimum temperatures for rice production is important for model simulation to predict rice yield change under climate change. However, studies or tools for widely observation of crop responses to temperature over broad spatial scales with long time spans are limited. In this study, we detected optimum temperature range for rice gross primary production (ToptGPP) in the lower Gangetic plains and delta region using the near-infrared reflectance of vegetation (NIRV), which is a new photosynthetic proxy, to improve ORYZA model performance in high-temperature season and assessed how tropical rice would respond to temperature increase in the study area. According to satellite observations of NIRV from 2001 to 2015, current ambient air temperature has exceeded the mean ToptGPP of Boro rice (24.8 ± 1.8 °C) and Aman rice (26.7 ± 1.2 °C) in the lower Gangetic plains and delta region, suggesting a downtrend of rice production under future warming. The detection results show that rice has lower ToptGPP in the regions with more drought stress and lower background temperature under water-limited conditions. Furthermore, the model modified by NIRv-ToptGPP shows better performance in potential yields, especially in high-temperature seasons on the region scale. Without CO2 fertilization effect, each degree-Celsius increase is expected to reduce rice potential yields by 4.9 ± 1.6% based on the default ToptGPP range in ORYZA model and by 7.0 ± 1.2% based on the detected NIRv-ToptGPP range in the study area. This study implies that global grid-based model simulation may underestimate sensitivity of tropical rice yield to temperature rise due to the neglect of regional and seasonal heterogeneity of ToptGPP. NIRV makes it possible to determine local optimal temperatures for crop production, and to improve grid-based modelling across various agricultural systems in different growing seasons at the regional scale.

Identification and characterization of high-yielding, short-duration rice genotypes for tropical Asia.

Previous efforts to increase the yield of tropical rice (Oryza sativa L.) have focused on medium‐duration varieties. However, there is increasing demand for high‐yielding short‐duration varieties that can adapt to intensified cropping systems and climate change. Our goal was to identify physiological traits associated with high yield in elite short‐duration genotypes suitable for tropical Asia. We conducted field experiments in five consecutive growing seasons at the International Rice Research Institute, the Philippines. We selected genotypes in the first two seasons, then performed a detailed characterization of the most promising genotypes in the following three seasons. Of the 50 advanced‐generation genotypes, three had consistently high yield and early maturity, with yields 11 to 38% higher than that of ‘IRRI104’ (‘IR50404‐57‐2‐2‐3’), a short‐duration variety that is widely grown in Southeast Asia. These genotypes were 20 to 32 cm taller than IRRI104. We found that for grain growth, low source capacity, defined as stem nonstructural carbohydrates at heading plus biomass accumulation after heading, was the major factor for the low yield of IRRI104. Although sink capacity (spikelets m−2 × grain weight) in the promising genotypes was comparable to that of IRRI104, they had a 25 to 53% higher source–sink ratio (source capacity/sink capacity) than IRRI104, which was attributed to larger leaf area and greater biomass accumulation during the grain‐filling stage. This result suggests that slight changes in plant development to promote height combined with increased leaf area around heading would improve the yield of short‐duration rice varieties in tropical Asia.

Genetics, Molecular Mechanisms and Deployment of Bacterial Blight Resistance Genes in Rice

Rice is the principal food crop for people in South and South-East Asia and is life for millions of rural households worldwide. Bacterial blight (BB) is a very common, widespread, and highly destructive disease of rice. By the introduction of nitrogen-responsive high-yielding rice varieties, there was many-fold increase in the productivity level of tropical rice in recent years. Continuous cropping of rice with high nitrogen use and general wet conditions aggravated the disease incidence. The cost of chemical control measures is high and often shows adverse effects on the environment. Development of host-plant resistance is therefore a preferred approach to control the disease. Evolution of pathogen differentiation in the Xanthomonas oryzae pv. oryzae (Xoo) isolates often causes the breakdown of resistance against the disease. Efforts to deploy R-genes combinations are more important for managing the disease. Durable and broad-spectrum resistance may be achieved in host plants by precise gene incorporation through gene-pyramiding approach. To date, 45 genes conferring resistance to this disease have been identified in rice. The gene-for-gene concept of resistance governs the race-specific interaction between the host and the Xoo strains. Plants have developed different intrinsic mechanisms to defend the pathogen invasion. The pathogen also evolves to produce effectors with variation to counter the patterns-triggered immunity and convert the host plants response for effector-triggered susceptibility. This review discusses the progress in the identification of resistance genes, mechanisms of resistance, and deployment of resistance genes for durable and stable resistance in rice.

Quantitative assessment of water soluble fractions of organic carbon in deep soils under rice and non-rice ecology

Soil is the largest terrestrial sink of Carbon (C). Carbon sequestration in soil is important for soil quality as well as to mitigate CO2 loading in atmosphere. Study on C of surface soil layer is going on for long time. Only in the recent past, scientists have noticed the importance of subsoil as a store house of stable C. On the contrary, study of C dynamics in tropical rice soil is important in countries like India where rice is the predominant crop and soil C sequestration is at risk due to high temperature. In this context, this study tried to understand the dynamics of soil C in deep soil under rice and non-rice ecology. Three distinct long term experimental sites were selected for soil sampling from three eastern states of India. Results indicated high total C and total organic C in surface soil in comparison to subsoil. On the other hand, rice soils had higher C than non-rice soil. The soil C was further divided into labile and recalcitrant pools using water extraction. As per water solubility, water soluble (room temperature) and hot water soluble C was highest in surface soil. This is natural as these pools represent labile C and surface soil receives maximum fresh C input in terms of deposited leaf and litter. The remaining C, not dissolved in water, was considered as recalcitrant C. While considering the water soluble pools as well as recalcitrant C as % of total organic C, trend indicated more labile C (water soluble) in surface soil while subsoil has more recalcitrant C. Therefore, this study conclusively indicated the potential of subsoil layer to act as a C sink in comparison to surface soil. The rice soil also has been identified as a niche for soil C sequestration.

Use of NDVI for indirect selection of high yield in tropical rice breeding

Plant breeders evaluate large numbers of breeding lines/accessions and measure various traits in the field in order to identify and select elite genotypes with high yield. Therefore, information on highly correlated yield-related traits and simple high-throughput methods to predict grain yield would be useful for rice breeders. The objective of this study was to examine the usefulness of various traits as indirect selection criteria for high yield in tropical rice breeding, with an emphasis on rapid and non-destructive measurements. We evaluated a wide range of germplasm, including popular varieties, elite genotypes, and donor parents, in the irrigated rice breeding program at the International Rice Research Institute, in the Philippines, during the 2015 wet season and 2016 dry season. We measured the normalized-difference vegetation index (NDVI), leaf chlorophyll content (SPAD value), agronomic traits, and grain yield. Harvest index, NDVI at the heading and late grain-filling stages, and SPAD value at the late grain-filling stage were significantly correlated with yield during the wet season, whereas plant height, panicle length, and NDVI from panicle initiation to the booting stage during the dry season. Our results indicate that pre-harvest analysis of primary and secondary traits such as NDVI has potential for selecting high-yielding accessions in tropical rice breeding programs. By using low-cost portable equipment, NDVI measurements could be incorporated into breeding programs. Trait associations with yield differed between the dry and wet seasons, which has important implications for breeding new varieties and germplasm evaluation in different seasons.

Spatiotemporal Patterns of Latrine-Site Use by Small-Clawed Otters in a Heterogeneous Rice Field Landscape

Tropical rice fields with asynchronous growth stages provide a good model to investigate the effects of landscape heterogeneity on the use of agricultural landscapes by wildlife. The small-clawed otter (Aonyx cinereus) uses rice fields as latrine sites in Southeast Asia. Through a 53-week survey of latrine sites, we analyzed the spatiotemporal patterns of latrine-site use by small-clawed otters in an asynchronous rice field in West Sumatra, Indonesia. Based on a generalized linear mixed model incorporating local environmental factors, otter latrine-site visitation was positively associated with the vegetative stage of rice cultivation and the biomass of a major prey item, the golden apple snail (Pomacea canaliculata). The vegetative stage of rice cultivation and golden apple snail biomass were closely associated with deep water in rice fields; therefore, water availability in rice fields is likely important in determining the spatiotemporal patterns of small-clawed otter latrine-site use in the asynchronous rice field landscape. To consistently provide latrine sites for small-clawed otters, we recommend that asynchronous rice cultivation be maintained, or zoning of synchronous and asynchronous rice cultivation areas be planned in the region.

Nitrous Oxide (N2O) Estimation from Tropical Rice Paddy Under the Influence of Growth-Regulating Compounds

Nitrous Oxide (N2O) Estimation from Tropical Rice Paddy Under the Influence of Growth-Regulating Compounds

Effect of Long Term Manuring on Carbon Sequestration Potential and Dynamics of Soil Organic Carbon Labile Pool Under Tropical Rice-Rice Agro-ecosystem

ABSTRACTSoil carbon sequestration is a complex process influenced by agricultural practices, climate and soil conditions. Labile organic carbon is sensitive to soil management practices and thus provides better management of carbon dynamics than total carbon alone. Thus, an attempt is made here to investigate the Carbon sequestration potential and labile pool of soil organic carbon (SOC) in post kharif-2014 in flooded tropical rice (Oryza sativa L.) under long-term fertilizer experiment started in the year 2005–06 in the central farm of Odisha University of Agriculture and Technology (OUAT) under All India Coordinated Research Project (AICRP) taking rice as a test crop. The experiment was laid out in a Randomized Block Design with quadruplicated treatments. The treatments include no fertilization, 100% N, 100% NP, 100% NPK, 150% NPK and 100% NPK+FYM. The results revealed that cultivation over the years caused a 14% decrease in SOC in unfertilized control over uncultivated soil. The carbon sequestration potential (1.77 Mg ha−1) was highest in 100%NPK +FYM treatment. The greater accumulation of microbial biomass C, water and extractable carbon (WEO-C), potassium permanganate oxidizable C (KMnO4-C) was recorded in 100%NPK + FYM treatment. The highest carbon management index (CMI) was computed in 100%NPK with FYM. CMI can be used as a more sensitive indicator of the rate of change of SOC in response to soil management changes. Results suggested that 100% NPK+ FYM are adequate for maintaining SOC stock and this practice may help in maintaining the sustainability of rice-rice cropping system.

Fertilizer management through coated urea to mitigate greenhouse gas (N2O) emission and improve soil quality in agroclimatic zone of Northeast India.

Agricultural soils are an important source of greenhouse gas nitrous oxide (N2O) emission. The comprehensive effects of nitrogen fertilizer management on N2O emission from paddy fields of India have not been evaluated under field conditions. A 2-year field study was conducted to evaluate the effect of different nitrogen fertilizers, namely, conventional fertilizer (NPK), starch-coated urea (SCU), neem-coated urea (NCU), and normal urea alone (NUA) on soil quality, grain yield, and N2O emission from rice field. Gas samples were collected from the field at weekly intervals by static chamber technique and analyzed in a gas chromatograph. During the crop-growing season, the application of NPK resulted in the highest cumulative N2O emission (2.49kg N2O-Nha-1) followed by NUA (2.34kg N2O-Nha-1), NCU (2.20kg N2O-Nha-1), and SCU (1.97kg N2O-Nha-1). As against the application of conventional fertilizer (NPK), the application of SCU and NCU reduced the total N2O emission by 21% and 12%, respectively (p < 0.05), during the rice-growing period. The results indicate a good correlation of N2O emissions with soil organic carbon, soil mineral nitrogen, and urease activity (p < 0.05) at different stages of crop growth. Application of SCU significantly increased the rice grain productivity by 12%, 10%, and 3% over NPK (control), NCU, and NUA respectively without affecting the soil quality and nutrient status. The use of SCU improved the nitrogen use efficiency (NUE) and was the effective substitute for conventional fertilizer in terms of reducing N2O emissions from tropical rice paddy.

Evaluating differential effect of deltamethrin and carbofuran on growth characteristics of Westiellopsis prolifica Janet, a dominant nitrogen fixing cyanobacterium of tropical rice field ecosystem

Recent trends of indiscriminate use of synthetic pesticides in different tropical rice fields has been affecting the soil flora and fauna including the most beneficial nitrogen fixing cyanobacteria . As nitrogen fixing cyanobacteria play an important role in soil fertility and acts as a natural bio fertilizer, the present study was carried out to investigate the differential effects of deltamethrin and carbofuran on Westiellopsis prolifica , an abundantly grown nitrogen fixing cyanobacterium in the rice fields of tropics. The study was conducted considering its dry biomass, protein, carbohydrate along with chlorophyll-a, and carotenoid content in a time- and dose-dependent exposure for 16 days. The resultant effect of both the pesticides was found to be pleiotropic for different concentrations of deltamethrin (25–75ppm) and carbofuran (20–60ppm). Results revealed that the growth parameters were more affected with carbofuran treatment than that of deltamethrin at their highest treated concentrations. Carbohydrate showed a gradual increase with carbofuran in a time and dose dependent manner whereas deltamethrin enhanced carbohydrate content up to 16th day from the day of inoculation only at 25ppm. Carotenoid showed a little but insignificant increase at the initial concentrations of both the pesticides whereas protein showed positive enhancement up to 4th day of inoculation when treated with deltamethrin. Though low concentrations stimulated some of the growth characteristics of the test organism, higher concentrations of both the pesticides were observed to be detrimental.

Description of 'Ca. Methylobacter oryzae' KRF1, a novel species from the environmentally important Methylobacter clade 2.

Members of the genus Methylobacter (Mtb) have been identified to be the most dominant methanotrophs in aquatic as well as terrestrial habitats. Methylobacter shows four species with validly published names and these are grouped in two clades based on phylogenetic and genomic comparisons. Mtb luteus and Mtb marinus (synonym: Mtb whittenburyi) belong to clade 1 Methylobacter. Clade 2 Methylobacter comprises of two species: Mtb tundripaludum and Mtb psychrophilus (type strain, no longer available). We isolated a yellow pigmented, rod-shaped methanotroph, strain (KRF1), from a tropical rice field in India, which might represent a putative novel species within Methylobacter clade 2. The cells are long, thick and motile rods. The strain grows under variable oxygen concentration (5-80% air) and also in nitrogen free media (5-50% air). The morphological, chemotaxonomic and genomic features of KRF1 were investigated in details. The digital DNA-DNA hybridization values and average nucleotide identity (ANI) comparisons with the members of its closest species, Mtb tundripaludum, were in the range of 20-26% and ~ 73-81%, respectively. The fatty acid methyl esters profile of KRF1 was different from the profile of Mtb tundripaludum SV96T. The major cell wall fatty acids of strain KRF1 are 16:1 ω7c/16:1 ω6c summed feature (55.4%) and 16:1 ω5c (28.6%). The draft genome of KRF1 is of 5.04 Mbp in size with a GC content of 49.3% and the whole genome shotgun sequencing project has the accession number RYFG00000000 (version: RYFG02000000). Due to the difficulties in the maintenance and cryopreservation of this culture, it could not be deposited in two international culture collections. We thereby propose KRF1 to be member of a Candidatus species, 'Candidatus Methylobacter oryzae' KRF1. The culture is maintained live in our laboratory and also in our institutional WDCM approved culture collection (MACS Collection of Microorganisms) as MCMB-1471.

Stabilization of Functional Soil Organic Matter Fractions in Response to Long-Term Fertilization in Tropical Rice–Rice Cropping System

ABSTRACT Soil organic matter (SOM) and its fractions play an important role in many soil chemical, physical, and biological properties. We studied functional groups of SOM fraction using a physical and chemical fractionation scheme in long-term application of a fertilization in a rice–rice system, which started in 2005 (sandy loam). Replicated soil samples of experimental plots of four different manure and fertilizer treatments and one unfertilized control were evaluated. The unprotected coarse particulate organic matter (POM) (cPOM), pure physical protected POM (iPOM), and the biochemically silt-sized fractions (NH-dSilt) contributed the major carbon storage fractions constituting 32.16–40.37%, 13.78–23.32%, and 14.44–28.66% of the total soil organic carbon (SOC) content, respectively. Combined application of organic manure like farmyard manure along with fertilizer improved the SOC content in all unprotected, physically protected, and chemically protected, silt and clay-associated physico-biochemically, clay-associated physicochemically protected and silt-associated biochemically protected fractions compared to control. Besides, the SOC increase expressed as SOC content per unit of total SOC for iPOM, cPOM, silt associated physicochemically and physico-biochemically protected fractions (H-µSilt and NH-µSilt) were the highest and as large as 70%, 60%, 45%, 38%, respectively. Our study indicates that long-term addition of manure with fertilizer for a long period of soil submergence under rice cultivation promoted the formation of more stabilized pools of C through physical and chemical protection mechanism.

THE TESTING OF THE VIETNAMESE RICE SAMPLES IN THE ROSTOV REGION

Rice ( Oryza sativa L. ) is one of the most important food crops in the world. The development of rice varieties for the conditions of Russia and especially the Rostov region requires a thorough study and introduction of the polymorphic gene pool for breeding work. The purpose of this study was to study comprehensively 45 collection Vietnamese rice samples (AGI), to estimate some of the key traits, and to select the best forms for breeding stress-resistant rice crops. These samples show a wide range of resistance to blast disease, bacteriosis, pests, lodging, salinization and flooding. The study was carried out in the Proletarsky district of the Rostov region. The standard varieties were the varieties “Boyarin” and “Yuzhanin” of ARC “Donskoy”. The study of the collection tropical rice gene pool according to a number of important economic and biological quantitative traits identified significant polymorphism. The vegetation period “sproutsflowering” varied from 85 to 142 days. All samples had a modern low-growing habit of plants with vertical rigid leaves and long drooping panicles (17.3–24.3 cm). Plant height ranged from 61.7 cm to 90 cm. Grains are long (9–10 mm), narrow (2–3 mm), with a weight to 29 mg, often with aroma. There was established a positive correlation between plant height and such traits as “kernel weight per panicle”, “1000 kernel weight”, “number of heavy kernels per panicle” and “fertility”. Kernel weight per panicle also correlated with the above-listed traits. Nine rice forms resistant to stress factors and well adapted to the region conditions have been selected for the breeding process. There has been carried out hybridization of the samples “OM 1401”, “OM 6106”, “OM 6561” with the local early ripening variety “Kontrakt”.

Effects of Vegetation Strips, Fertilizer Levels and Varietal Resistance on the Integrated Management of Arthropod Biodiversity in a Tropical Rice Ecosystem.

Integrated biodiversity management aims to conserve the beneficial species components of production ecosystems and reduce the impacts of pests. In 2011 and 2013, experiments were conducted at Los Baños, Laguna, Philippines, to compare arthropod communities in rice plots and on levees with and without vegetation strips. Vegetation strips included spontaneous weeds, sesame and okra (2011), or mung bean (2013). The plots were treated with one of three nitrogen levels and in one experiment were planted with planthopper-resistant (IR62) and susceptible (IR64) rice varieties. Parasitoids and predators of lepidopteran pests and of the ricebug, Leptocorisa oratorius, were more abundant in high-nitrogen rice plots where their prey/hosts also had highest densities. Planthoppers and leafhoppers were more abundant in low-nitrogen plots. Weedy and sesame/okra bunds provided habitat for a range of natural enemies including spiders, parasitoids and predatory bugs, but did not have higher pest numbers than cleared bunds. Higher abundances of the predator Cythorhinus lividipennis and higher parasitism of planthopper (Nilaparvata lugens) eggs by Anagrus sp. were associated with sesame/okra bunds in late season rice plots. Mung bean also provided habitat for key predators and parasitoids that spilled over to adjacent rice; however, mung bean was also associated with higher numbers of lepidopteran and grain-sucking pests in the adjacent rice, albeit without increased damage to the rice. For ricebug in particular, damage was probably reduced by higher parasitoid:pest ratios adjacent to the vegetation strips. Varietal resistance and mung bean strips had an additive effect in reducing abundance of the planthopper Sogatella furcifera and the leafhopper Nephotettix virescens. Reduced numbers of these latter pests close to vegetation strips were often compensated for by other plant-sucking bugs, thereby increasing the intensity of potentially stabilizing interspecific interactions such as competition. We highlight the benefits of diversifying rice landscapes and the need to optimize vegetation strips, e.g., by including lepidopteran trap-plants, for intensive rice production systems.

Influence of long-term fertilization on soil microbial biomass and dehydrogenase activity in relation to crop productivity in an acid Inceptisols

An effective approach for improving nutrient use efficiency and crop productivity simultaneously through exploitation of biological potential for efficient acquisition and utilization of nutrients by crops is very much needed in this current era. Thus, an attempt is made here to investigate the impact of long term fertilization in the soil ecology in rice-rice cropping system in post kharif - 2015 in flooded tropical rice (Oryza sativa L.) in an acidic sandy soil. The experiment was laid out in a randomized block design with quadruplicated treatments. Soil samples at different growth stages of rice were collected from long term fertilizer experiment.The studied long-term manured treatments included 100 % N, 100% NP, 100 % NPK, 150 % NPK and 100 % NPK+FYM (5 t ha-1) and an unmanured control. Soil fertility status like SOC content and other available nutrient content has decreased continuously towards the crop growth period. Comparing the results of different treatments, it was found that the application of 100% NPK + FYM exhibited highest nutrient content in soils. With regards to microbial properties it was also observed that the amount of microbial biomass carbon (MBC) and microbial biomass nitrogen ( MBN) showed highest accumulation in 100 % NPK + FYM at maximum tillering stage of the rice. The results further reveal that dehydrogenase activity was maximum at panicle initiation stage and thereafter it decreases. Soil organic carbon content, MBC, MBN and dehydrogenase activity were significantly correlated with each other. Significant correlations were observed between rice yield and MBC at maturity stage( R2 = 0.94**) and panicle initiation stage( R2 = 0.92**) and available nitrogen content at maturity stage( R2 = 0.91**).

Enchytraeid Community (Annelida, Clitellata, Enchytraeidae) and Its Dependence on Edaphic Conditions in Rice Agroecosystems in Russia

Communities of soil animals (meso- and macrofauna) in rice paddies tend to be fragmented, and have extremely low abundance. Nevertheless, some groups, such as enchytraeids, may become dominant in flooded conditions, as shown in tropical rice agroecosystems. However, the fauna and functional composition of enchytraeids (Annelida, Clitellata, Enchytraeidae) under such conditions have not yet been studied at temperate latitudes. We have investigated enchytraeid communities and the ratio of their functional groups in the main rice-growing regions of Russia: Krasnodar krai, Primorsky krai, and the Republic of Kalmykia. Samples were taken in summer–early autumn of 2016 in four habitat types: flooded rice paddies, drained paddies occupied by upland crops, adjacent bunds, and undisturbed grasslands (control). Generalized linear model analysis showed that the factor habitat type and its interaction with the factor region had a significant effect on the total enchytraeid abundance, with the factor region alone having no such effect. Their abundance was the highest in the control habitats and bunds (mean and standard error for all the regions: 3278 ± 1131 and 3255 ± 762 ind./m2, respectively), being insignificantly lower in the paddies under upland crops (1282 ± 850 ind./m2) and decreasing to a minimum of 415 ± 323 ind./m2 in the flooded paddies. A comparison between the last two habitat types shows that enchytraeids can relatively quickly restore their abundance in the rice paddies after draining. Principal component analysis revealed a positive correlation between the density of enchytraeids belonging to basophilous ecological group and bioavailable phosphorus content. The correlation between the abundance of acidophilous enchytraeids and this parameter was negative. Thus, the abundance ratio of enchytraeid ecological groups could be used as an informative indicator of the concentrations of nutrient elements and depends on physical and chemical characteristics of paddy soils. Despite the low abundance of enchytraeids in these soils, they can be an important component of the detrital food webs during periods of paddy-drainage in intensive rice agroecosystems at temperate latitudes.