Different Growth Stages Of Rice Research Articles

Correlations Between Different Extractable Cadmium Levels in Typical Soils and Cadmium Accumulation in Rice

Pot experiments were used to study the correlations between different extractable cadmium levels in typical soil and cadmium accumulation in rice. To analyze the pH, Cd in soil solution(SSE-Cd), TCLP extractable Cd level(TCLP-Cd), and Cd accumulation in rice at different growth stages of rice, we conducted pot experiments which selected the reddish clayey soil(developed from quaternary red clay parent materials) and purple paddy field(developed from purple sandy shale parent materials), meanwhile added with exogenous Cd with the gradients of 0, 0.5, 1, 2, 5, 10 mg·kg-1. The results showed that, during the rice growth period, the content of SSE-Cd in reddish clayey soil was in the range of 0 and 2.5 μg·L-1, and the average content was 0.57 μg·L-1; TCLP-Cd was in the range of 0 and 0.25 μg·L-1 with the average content of 0.10 mg·kg-1;The content of SSE-Cd in purple paddy field was in the range of 0 and 1.6 μg·L-1 with the average content of 0.48 μg·L-1; TCLP-Cd was in the range of 0 and 0.2 mg·kg-1, and the average content was 0.07 mg·kg-1. It showed that the cadmium concentrations in soil solution and the TCLP extractable Cd levels were both significantly reduced in two types of soil with the extension of rice growth period, and the content in reddish clayey soil was higher than that in purple paddy. The TCLP extractable Cd level was significantly positively correlated with Cd concentration in soil solution. The total Cd accumulation in rice plants gradually increased with increasing exogenous Cd concentration. There were significant positive correlations between Cd concentration in soil solution and Cd concentration in rice, Cd concentration in soil extracted by TCLP method and Cd concentration in rice and total Cd accumulation in rice plant. The soil environmental capacities of the two different parent materials varied greatly,and the safety threshold of Cd in purple paddy field was 2.06 times of that of reddish clayey soil. There were significant differences in Cd uptake and accumulation in different soils, so different measures may be needed to control Cd pollution in different parent materials. TCLP extractable Cd was more relevant with total Cd accumulation in rice, and had more extraction amount. Therefore, the TCLP method can more accurately evaluate the biological availability of soil Cd.

Evaluating Hyperspectral Vegetation Indices for Leaf Area Index Estimation of Oryza sativa L. at Diverse Phenological Stages.

Hyperspectral reflectance derived vegetation indices (VIs) are used for non-destructive leaf area index (LAI) monitoring for precise and efficient N nutrition management. This study tested the hypothesis that there is potential for using various hyperspectral VIs for estimating LAI at different growth stages of rice under varying N rates. Hyperspectral reflectance and crop canopy LAI measurements were carried out over 2 years (2015 and 2016) in Meichuan, Hubei, China. Different N fertilization, 0, 45, 82, 127, 165, 210, 247, and 292 kg ha-1, were applied to generate various scales of VIs and LAI values. Regression models were used to perform quantitative analyses between spectral VIs and LAI measured under different phenological stages. In addition, the coefficient of determination and RMSE were employed to evaluate these models. Among the nine VIs, the ratio vegetation index, normalized difference vegetation index (NDVI), modified soil-adjusted vegetation index (MSAVI), modified triangular vegetation index (MTVI2) and exhibited strong and significant relationships with the LAI estimation at different phenological stages. The enhanced vegetation index performed moderately. However, the green normalized vegetation index and blue normalized vegetation index confirmed that there is potential for crop LAI estimation at early phenological stages; the soil-adjusted vegetation index and optimized soil-adjusted vegetation index were more related to the soil optical properties, which were predicted to be the least accurate for LAI estimation. The noise equivalent accounted for the sensitivity of the VIs and MSAVI, MTVI2, and NDVI for the LAI estimation at phenological stages. The results note that LAI at different crop phenological stages has a significant influence on the potential of hyperspectral derived VIs under different N management practices.

Arsenic mobility and bioavailability in paddy soil under iron compound amendments at different growth stages of rice

Iron (Fe)-based solids can reduce arsenic (As) mobility and bioavailability in soils, which has been well recognized. However, to our knowledge, there are few studies on As uptake at different growth stages of rice under Fe compound amendments. In addition, the formation of Fe plaques at different growth stages of rice has also been rarely reported. Therefore, the present study was undertaken to investigate As mobility and bioavailability in paddy soil under Fe compound amendments throughout the whole growth stage of rice plants. Amendments of poorly crystalline Fe oxides (PC-Fe), FeCl2+NaNO3 and FeCl2 reduced grain As by 54% ± 3.0%, 52% ± 3.0% and 46% ± 17%, respectively, compared with that of the non-amended control. The filling stage was suggested to be the key stage to take measures to reduce As uptake. At this stage, all soil amendments significantly reduced As accumulation in rice plants. At the maturation stage, PC-Fe amendment significantly reduced mobile pools and increased immobile pools of soil As. Besides, PC-Fe treatment promoted the transformation of Fe fractions from dissolved Fe to adsorbed, poorly crystalline and free Fe oxides. Moreover, significant positive correlations between soil Fe fractions and As fractions were found. Accordingly, we hypothesized that Fe compound amendments might affect the concentration distribution of Fe fractions first and then affect As fractionation in soil and its bioavailability to rice plants indirectly. The formation of Fe plaques varied with growth stages and different treatments. Significantly negative correlations between mobile pools of As and Fe or As in Fe plaques indicated that Fe plaques could immobilize mobile As in soils and thus affect As bioavailability. Overall, the effect of the soil amendments on reduction of As uptake varied with growth stages and different treatments, and further research on the key stage for reducing As uptake is still required.

Efficacy of Potassium Humate and Chemical Fertilizers on Yield and Nutrient Availability Patterns in Soil at Different Growth Stages of Rice

ABSTRACTPotassium humate (PH) is a promising natural resource to be utilized as an alternative for increasing crop production. A pot experiment was conducted during 2009 and 2010 to assess the efficacy of application of potassium humate (0, 5, and 10 mg kg−1 soil) alone and in combination with chemical fertilizers (75% and 100% recommended dose of nitrogen–phosphorus–potassium) on yield and nutrient availability patterns in soil at different growth stages of rice. Two doses of zinc, viz. 0 and 12.5 mg kg−1, were also applied. Sole and combined application of potassium humate with nitrogen–phosphorus–potassium (NPK) and zinc significantly (p < 0.05) improved the yield and availability of nitrogen, phosphorus, potassium, sulfur, zinc, and dehydrogenase activity in soil. Application of 10 mg kg−1 potassium humate along with 100% NPK and 12.5 mg kg−1 zinc sulfate proved significantly superior when compared to 75% and 100% of NPK alone.

Effect of rodenticides and traps against lesser bandicoot rat,(Bandicota bengalensis) in rice field

An investigation was carried out at Regional Agricultural Research Station (RARS), Titabor and Instructional-Cum- Research Farm, Assam Agricultural University, Jorhat during 2013-14 and 2014-15 in boro and sali season respectively. The field trials were conducted to evaluate effectiveness by combining rodenticides with local bamboo traps against field rodents in rice. Combined effect of rodenticides and traps were evaluated at different growth stages of rice against Bandicota bengalensis in terms of live burrow count (LBC/ha), trapping index (TI) as well as per cent cut tillers in both boro and sali rice, respectively. Baiting with bromadiolone (0.005%) at panicle initiation stage and bamboo traps at milky stage recorded the highest reduction in rodent population (72.39% LBC/ha, 70.57% TI and 68.13% cut tillers) in boro and (72.27% LBC/ha, 77.13% TI and 70.77% cut tillers) in sali rice over control at harvesting stage. The second best treatment in respect of per cent reduction of LBC/ha, trap index and cut tillers was bamboo traps at maximum tillering stage and bromadiolone (0.005%) at panicle initiation stage in both boro and sali rice, respectively which recorded a reduction of 65.89% LBC/ha, 66.19% TI and 65.66% cut tillers in boro rice and 68.33% LBC/ha, 71.04% TI and 62.83% tiller damage in sali rice

Regional heavy metal pollution in crops by integrating physiological function variability with spatio-temporal stability using multi-temporal thermal remote sensing

Heavy metal stress in crops is characterized by stability in space and time, which differs from other stressors that are typically more transient (e.g., drought, pests/diseases, and mismanagement). The objective of this study is to assess regional heavy metal stress in rice by integrating physiological function variability with spatio-temporal stability based on multi-temporal thermal infrared (TIR) remote sensing images. The field in which the experiment was conducted is located in Zhuzhou City, Hunan Province, China. HJ-1B images and in-situ measured data were collected from rice growing in heavy metal contaminated soils. A stress index (SI) was devised as an indicator for the degree of heavy metal stress of the rice in different growth stages, and a time-spectrum feature space (TSFS) model was used to determine rice heavy metal stress levels. The results indicate that (i) SI is a good indicator of rice damage caused by heavy metal stress. Minimum values of SI occur in rice subject to high pollution, followed by larger SI with medium pollution and maximum SI for low pollution, for the same growth stage. (ii) SI shows some variation for different growth stages of rice, and the minimum SI occurs at the flowering stage. (iii) The TSFS model is successful at identifying rice heavy metal stress, and stress levels in rice stabilized regardless of the model being applied in the two different years. This study suggests that regional heavy metal stress in crops can be accurately detected using TIR technology, if a sensitive indicator of crop physiological function impairment is used and an effective model is selected. A combination of spectrum and spatio-temporal information appears to be a very promising method for monitoring crops with various stressors.

Effect of Soil Water Deficit on Yield and Its Components at The Different Growth Stages in Rice (Oryza sativa)

Effect of Soil Water Deficit on Yield and Its Components at The Different Growth Stages in Rice (Oryza sativa)

Zinc fractionation of tropical paddy soils and their relationships with selected soil properties

Knowledge of zinc (Zn) distribution among various fractions will help to predict the potential of the soil to supply sufficient Zn for crop production. The present study was done to investigate Zn fractions, Zn availability factor (AF) and their relationship with soil properties of Zn-deficient tropical paddy soils. The samples of two soil orders (six soil series) were sequentially extracted with chemical extractants in two different growth stages of rice (maximum tillering and flowering stages). The proportion of Zn fractions extracted at the maximum tillering stage followed the order, water soluble plus exchangeable (WE) < crystalline sesquioxide (Cry) < manganese oxide (MN) < organically bound (Org) < amorphous sesquioxide (Amor) < residual Zn (Res), whereas the order at the flowering stage was as follows: WE < Mn < Cry < Org < Amor < Res. Cation exchange capacity (CEC), clay content and organic carbon (OC) were the most important factors controlling the distribution of Zn in soils. The AF was low in Tok Young (1.79%), high in Telemong (17%) and medium in the rest of soil series (around 8%). A stepwise multiple linear regression and principal component analyses showed that OC, clay content and CEC were the main variables that explained the predictability of Zn fractions. The result of the length of submerging showed that the WE, Org and Cry concentrations decreased, while Amor, MN, and the sum of all Zn fractions increased with increase in the flooding period. The extractability and solid-phase fractionation of Zn in two different times of soil sampling showed the importance of timing of Zn fertilizer application and flooding or pre-flooding in Zn availability.

Potential of Controlled Irrigation and Drainage for Reducing Nitrogen Emission from Rice Paddies in Southern China

The effect of controlled irrigation and drainage (CID) at different growth stages of rice on nitrogen (N) from rice paddy was studied. Submergence at different stages was imposed in specially designed experimental tanks in 2009 and 2010 based on alternate wetting and drying technology (AWD, the control, CK). Treatments include CID treatment at tiller stage (T1), jointing-booting stage (T2), panicle initiation stage (T3), and milky stage (T4). Results showed that fertilization could significantly increase the concentration ofNH4+-N and TN in surface water but had a little influence onNO3--N. The concentrations ofNH4+-N andNO3--N in surface water increased at first and then decreased after fertilization, while the concentrations ofNH4+-N and TN in groundwater kept on being relatively stable. Compared to CK, CID significantly increased the concentration ofNH4+-N in surface water at four stages. However, it reduced the concentration ofNO3--N. Consistent with the reduction of drainage, CID at four stages could significantly decrease the amount ofNH4+-N andNO3--N losses by runoff in relation to CK.

Impacts of controlled irrigation and drainage on the yield and physiological attributes of rice

Taking into account the likely contribution of rainwater to crop water requirements, is an alternative option for increasing the productivity of water in irrigated agriculture. We evaluated the response of yield and physiological characters to controlled irrigation and drainage (CID) at different growth stages of rice (Oryza sativa L.). Submergence at different stages was imposed in specially designed experimental tanks in 2009 and 2010 based on alternate wetting and drying technology (AWD, the control). Treatments include CID treatment at tiller stage (CID-Stage I), jointing–booting (CID-Stage II), panicle initiation (CID-Stage III), and milky stage (CID-Stage IV). Compared to the control, we observe a strong reduction in root length, root weight and root–shoot ratio were observed in the CID treatments. Under CID-Stage I and CID-Stage II, rice was characterized by faster shoot elongation, larger single leaf area extension, and more total dry mass, as a higher photosynthetic rate was maintained during and after submergence. The CID-Stage I and CID-Stage II treatments increased photosynthesis rate (PN) and transpiration (Tr) significantly compared to the control, but decreased average leaf water use efficiency (WUEL, defined as the ratio of PN to Tr) by 3.3% (2009) and 5% (2010). The PN and Tr also demonstrated close linear and quadratic relationships with stomatal conductance. Cultivation of rice under CID-Stage II resulted in 6% and 3% yield reduction over the control. This insignificant decrease in grain yield was due largely to the reduced percentage of filled gain. The lowest yields were obtained under CID-Stage I in 2009 and CID-Stage III treatments in 2010, respectively. The submergence-induced decrease in the number of panicles per unit area and number of spikelets per panicle were responsible for the lower yields obtained from those two stages. CID-Stage II had an average irrigation water productivity of 1.77kgm−3 for the two years, an increase of about 9% from the control.

Study on Denitrification Intensity in Rice Rhizosphere Soil under Water Management Model

A typical rice field ecosystem as the research object, using the indoor pot experiment to study the three kinds of water driven (shallow layer of continuous irrigation (C), alternating wet and dry (J), and water control mode (G)) on the effect of rice rhizosphere soil denitrification intensity. Effect of changes in soil moisture caused by the three different irrigation patterns on different growth stages of rice on rhizosphere denitrification was comparatively analyzed,referring to the rhizosphere denitrification capacity during different rice growth stage.The results showed that: soil denitrification intensity with different water managements changed significantly, showing C&gt;J&gt;G. And with the growth of plants, under three different water managements, denitrification intensity showed a downward trend. Mature reached to a minimum. All have to be higher than control groups.

Ammonia Emission from Rice–Wheat Cropping System in Subtropical Soil of India

Ammonia (NH3) emission from rice (July–October) and wheat (November–April) cropping system was measured using the chemiluminescence method at the subtropical agricultural land of Delhi, India during 2009–2010 and 2010–2011. The measurement was carried out from the canopy height (1.2–1.3 m) during the different growth stages of rice and wheat crops to quantify NH3 emission and assess the variations in emission during the crop growth stages. The background atmospheric concentration of NH3 was measured at 5 m height at the study site and subtracted from the NH3 concentration at crop canopy height to quantify the emission of NH3 from crops. The NH3 emission in wheat crops were 35.9 ± 6.3, 24.5 ± 5.5, 15.8 ± 4.5, 18.6 ± 3.9, and 20.8 ± 3.8 µg m−2 d−1 during sowing, crown root initiation, panicle initiation, grain filling, and maturity stages, respectively. In rice crops, the emissions during transplanting, tillering, panicle initiation, grain filling, and maturity stages were 29.7 ± 7.4, 16.2 ± 3.7, 19.0 ± 3.7, and 18.4 ± 3.9 µg m−2 d−1, respectively. The emission was higher during sowing/transplanting compared to other stages in both the crops. About 9 % of applied fertilizer N was emitted as NH3 from the rice–wheat cropping system in the subtropical soils of India.

Diversity of Microbial Community in a Paddy Soil with cry1Ac/cpti Transgenic Rice

Two types of cry1Ac/cpti transgenic rice (GM1 and GM2) and their parental non-cry1Ac/cpti rice (CK1 and CK2) were planted in the field at Wufeng, Fujian Province, China for four years to investigate the influence of genetically modified rice on diversity of bacterial and fungal community in the paddy soil. The community composition and abundance of bacteria or fungi in the paddy soil were assessed at different growth stages of rice by denaturing gradient gel electrophoresis and real-time polymerase chain reaction based on 16S rRNA gene or SSU rRNA gene in the 4th year after the experimental establishment. The composition of bacterial or fungal community changed during rice growth, while no significant differences were observed between the fields cultivated with GM1 and CK1, or between the fields cultivated with GM2 and CK2 in either bacterial or fungal community composition. The copy numbers of bacterial 16S rRNA gene in the soils with CK1, CK2, GM1 and GM2 ranged from 5.64 × 1011 to 6.89 × 1011 copies g−1 dry soil at rice growth stages, and those of fungal SSU rRNA gene from 5.24 × 108 to 8.68 × 108 copies g−1 dry soil. There were no marked differences in the copies of bacterial 16S rRNA gene or fungal SSU rRNA gene between CK1 and GM1 or between CK2 and GM2 at any growth stage of rice. Planting cry1Ac/cpti transgenic rice had no significant effect on composition and abundance of bacterial and fungal community in paddy soil during the rice growing season at least in the short term.

Effect of elevated carbon dioxide and temperature on phosphorus uptake in tropical flooded rice (Oryza sativa L.)

A field experiment was carried out to assess the impact of elevated carbon dioxide (CO2) and temperature on phosphorous (P) nutrition in relation to organic acids exudation, soil microbial biomass P (MBP) and phosphatase activities in tropical flooded rice. Rice (cv. Naveen) was grown under chambered control (CC), elevated CO2 (EC, 550μmolmol−1) and elevated CO2+elevated temperature (ECT, 550μmolmol−1 and 2°C more than CC) in a tropical flooded soil under open top chambers (OTCs) along with unchambered control (UC) for three years. Root exudates were analyzed at different growth stages of rice followed by organic acids determination. Rhizospheric soil was used for analysis of soil phosphatase, MBP and available P. The total organic carbon (TOC) in root exudates was increased by 27.5% and 30.2% under EC and ECT, respectively over CC. Four different types of organic acids viz. acetic acid (AA), tartaric acid (TA), malic acid (MA) and citric acid (CA) were identified and quantified as dominant in root exudates, concentration of these was in the order of TA>MA>AA>CA. The TA, MA, AA and CA content were increased by 34.4, 31.1, 38.7 and 58.3% under ECT compared to that of UC over the period of 3 years. The P uptake in shoot, root and grain under elevated CO2 increased significantly by 29, 28 and 22%, respectively than CC. Soil MBP, acid and alkaline phosphatase activity was significantly higher under elevated CO2 by 35.1%, 27 and 36%, respectively, compared to the CC. Significant positive relationship exists among the organic acid exudation, MBP, phosphatase activities and P uptake by rice. The enhanced organic acid in root exudates coupled with higher soil phosphatase activities under elevated CO2 resulted in increased rate of soil P solubilization leading to higher plant P uptake.

Diversity of the bacterial community in the rice rhizosphere managed under conventional and no-tillage practices

Bacterial diversity in the rice rhizosphere at different rice growth stages, managed under conventional and no-tillage practices, was explored using a culture-based approach. Actinobacteria are among the bacterial phyla abundant in the rice rhizosphere. Their diversity was further examined by constructing metagenomic libraries based on the 16S rRNA gene, using actinobacterial- and streptomycete-specific polymerase chain reaction (PCR) primers. The study included 132 culturable strains and 125 clones from the 16S rRNA gene libraries. In conventional tillage, there were 38% Proteobacteria, 22% Actinobacteria, 33% Firmicutes, 5% Bacteroidetes, and 2% Acidobacteria, whereas with no-tillage management there were 63% Proteobacteria, 24% Actinobacteria, 6% Firmicutes, and 8% Bacteroidetes as estimated using the culture-dependent method during the four stages of rice cultivation. Principal coordinates analysis was used to cluster the bacterial communities along axes of maximal variance. The different growth stages of rice appeared to influence the rhizosphere bacterial profile for both cultivation practices. Novel clones with low similarities (89-97%) to Actinobacteria and Streptomyces were retrieved from both rice fields by screening the 16S rRNA gene libraries using actinobacterial- and streptomycete-specific primers. By comparing the actinobacterial community retrieved by culture-dependent and molecular methods, it was clear that a more comprehensive assessment of microbial diversity in the rice rhizosphere can be obtained using a combination of both techniques than by using either method alone. We also succeeded in culturing a number of bacteria that were previously described as unculturable. These were in a phylogenetically deep lineage when compared with related cultivable genera.

Phosphine in paddy fields and the effects of environmental factors

Ambient levels of phosphine (PH3) in the air, phosphine emission fluxes from paddy fields and rice plants, and the distribution of matrix-bound phosphine (MBP) in paddy soils were investigated throughout the growing stages of rice. The relationships between MBP and environmental factors were analyzed to identify the principal factors determining the distribution of MBP. The phosphine ambient levels ranged from 2.368±0.6060 ng m(-3) to 24.83±6.529 ng m(-3) and averaged 14.25±4.547 ng m(-3). The highest phosphine emission flux was 22.54±3.897 ng (m(2)h)(-1), the lowest flux was 7.64±4.83 ng (m(2)h)(-1), and the average flux was 14.17±4.977 ng (m(2)h)(-1). Rice plants transport a significant portion of the phosphine emitted from the paddy fields. The highest contribution rate of rice plants to the phosphine emission fluxes reached 73.73% and the average contribution was 43.00%. The average MBP content of 111.6 ng kg(-1)fluctuated significantly in different stages of rice growth and initially increased then decreased with increasing depth. The peak MBP content in each growth stage occurred approximately 10 cm under the surface of paddy soils. Pearson correlation analyses and stepwise multiple regression analysis showed that soil temperature (Ts), acid phosphatase (ACP) and total phosphorus (TP) were the principal environmental factors, with correlative rankings of Ts>ACP>TP.

Split application of vermicompost to rice (Oryza sativa L.): its effect on productivity, yield components, and N dynamics

Organic agriculture is gaining a gradual momentum across the world for improving nutritional quality of food, restoring soil health, generating rural economy, and creating better environmental conditions. Organic agriculture can foster sustainability in subhumid tropical soils low in organic carbon. Nutrient use efficiency of basal soil application of vermicompost is very low. Thus, this study was aimed to test whether nitrogen use efficiency (NUE) and crop yield can be enhanced by split application of vermicompost. There is no published information on split application of vermicompost (VC) in rainfed rice. An experiment with rice (cv. Pankaj) was conducted on loam soil in Giridih, India, during 2008 and 2009. Vermicompost, a rich source of readily available nutrients, has high microbial activity and contains growth hormones. Study comprises one of three split applications of vermicompost at different growth stages of rice (i.e., maximum tillering, panicle initiation, and flower). Split application of vermicompost resulted higher yield parameters such as panicles (294 m−2), filled grains per panicle (138), and total spikelets per panicle (142), grain yield (3.91 t ha−1), and NUE, but only if vermicompost was applied at two or three doses. Higher availability of nitrogen (N) in soil with split applications coincides with higher NUE, and thus, split application not promoted N losses. Split application of vermicompost enhances the sustainability of rice cropping system.

Impacts of climate change on irrigation water requirements for rice–wheat cultivation in Bagmati River Basin, Nepal

This study highlights the spatial and temporal impacts of climate change on rice–wheat cropping systems, focusing on irrigation water requirement (IWR) in the Bagmati River Basin of Nepal. The outputs from a general circulation model (HadCM3) for two selected scenarios (A2 and B2) of IPCC and for three time periods (2020s, 2050s, and 2080s) have been downscaled and compared to a baseline climatology. CROPWAT 8.0 model is used to estimate the water requirements. IWRs show different trends in different physiographic regions and different growth stages of rice and wheat. A decreasing trend of IWRs in the Mid Hills and the High Hills indicates that farmer-based small irrigation schemes are sufficient to meet the requirements. However, in the Terai region, where there is an increasing trend in IWRs, the deficit volume of water needs to be supplied from potential large-scale irrigation schemes.

Analysis of Precipitation Concentration in Gaoyou Irrigation District: Implications for Increasing Effective Rainfall

The humid region in south China has abundant rainfall. In order to make effective use of rainfall and save irrigation water, we collected the historical precipitation data of Gaoyou Irrigation District for the past fifty years and used the Geordie Coefficient model of precipitation time evenness index to calculate the precipitation concentration index in different growth stages of rice. The results showed that the precipitation concentration index was low in the early stages of rice; while it gradually increased in the later stages. The precipitation concentration index reached the minimum during the jointing-booting stage and the peak the maturing stage. There were also deceasing trends in precipitation concentration for the early stages. Therefore, it is possible to make better use of rainfall in the early stages of rice growth and save irrigation water. It is necessary to investigate accuracy of rainfall forecasts in future studies.

Influencing Factors on Rice Sheath Blight Epidemics in Integrated Rice-Duck System

Sheath blight, a disease caused by the fungus Rhizoctonia solani Kuhn (anamorph), has been the most economically significant disease of rice. It was frequently reported that the disease was well-controlled in integrated rice-duck system without the employment of fungicides. However, the effecting factors behind this phenomenon were rarely reported. In this research, experiment was carried out between two treatments, rice combined with ducks (RD) and conventional rice field without ducks rearing (CK) in early season rice paddy, to investigate the variations of sclerotia in floodwater and on rice plant, microclimate 10 cm above the waterline in rice paddy and activity of protective enzymes in rice plants. The results showed that the floating sclerotia in floodwater in RD was 86-91% lower than that in CK, and adhering sclerotia in rice plant in RD was 67-78% lower than that in CK. The relative humidity tested significantly lower and light intensity tested significantly higher in RD. The temperature in the early rice growth stages in RD was slightly lower than that in CK, but it was significantly higher (32.3–36.5°C) in the middle stage rice growth stages. The polyphenoloxidase (PPO) activity in RD were lower than that in CK, but the enhanced activity of phenylalanine ammonia-lyase (PAL), peroxidase (POD) and Chitinase was observed in different stages of rice growth in RD, especially the Chitinase which showed higher activity in all investigating days.