Rice Growth Period Research Articles

Development and evaluation of improved lines with broad-spectrum resistance to rice blast using nine resistance genes

BackgroundRice blast disease is a major restriction in rice production. That is usually managed using chemical pesticides, which are expensive in terms of cost and environment hazards. Use of blast-resistance genes to develop resistant varieties may therefore be a more economical and environmentally friendly method for effective control.ResultsIn this study, we improved the blast resistance of four sterile lines, Y58S, GuangZhan63S (GZ63), C815S and HD9802S, by introgression of 9 cloned broad-spectrum blast resistance genes Pi37, Pit, Pid3, Pigm, Pi36, Pi5, Pi54, Pikm and Pb1. Through molecular marker-assisted selection and backcross breeding, 31 single-gene derived lines and 20 double-gene combination lines were obtained. When infected naturally, single-gene lines with Pigm or Pid3 showed significantly enhanced resistance during whole growth period relative to their recurrent parent. Single-gene lines with Pi37, Pi5, Pit, Pi36, Pi54 or Pikm showed significantly enhanced resistance in some of the four backgrounds. No obviously enhanced resistance was observed in single-gene line with Pb1 for the whole growth period. Compared with recurrent parents, most of the double-gene lines showed improved resistance. Among these double-gene lines, lines with Pi37/Pid3, Pi5/Pi54, Pi54/Pid3 or Pigm/Pi37, exhibited significantly enhanced resistance and observable additive effects.ConclusionsTwo blast resistance genes, Pigm and Pid3, showed significantly enhanced resistance for the whole rice growth period, and six blast resistance genes Pi37, Pi5, Pit, Pi36, Pi54 or Pikm showed significantly enhanced resistance for some of the four backgrounds. Double-gene lines with Pi37/Pid3, Pi5/Pi54, Pi54/Pid3 and Pigm/Pi37 exhibited significantly enhanced resistance and observable additive effects. These lines could be used in rice hybrid and production.

Impact of warming climate, sowing date, and cultivar shift on rice phenology across China during 1981-2010.

Climate change would exert significantly impact on crop yield by altering crop growth and development processes. Therefore, to ensure food security, it is necessary to assess the response and adaptation of crop phenology to the natural (mainly climate change) and artificial (including sowing date (SD) change and cultivar shift) factors. In this study, using field data from 113 agro-meteorological experiment stations across China, along with the Agricultural Production System Simulator (APSIM) oryza model, we investigated the trends of rice phenology in relation to climate change and agronomic factors (i.e., SD change and cultivar shift) from 1981 to 2010. We found that flowering date (FD) and maturity date (MD) of single-rice were delayed by 0.3 and 1.4days10a-1, respectively, but FD and MD of double-rice were advanced by 0.7-0.8 and 0.2-1.1days10a-1, respectively. Climate change advanced FD and MD of rice at representative stations except FD of late-rice, and shortened length of rice growth period. SD change of rice mainly affected duration of vegetative growth phase (VGP, from SD to FD), but had no significant impact on duration of reproductive growth phase (RGP, from FD to MD). Cultivar shift delayed FD and MD of rice at all representative stations except late-rice at Lianhua. Moreover, cultivar shift prolonged the duration of rice RGP by 0.2-2.8days10a-1. Overall, the results suggested that rice phenology was adapting to ongoing climate change by SD change and adoption of cultivars with longer RGP. Therefore, crop phenological characteristics should be sufficiently taken into account to develop adaptation strategies in the future.

Effects of different manure nitrogen input ratio on rhizosphere soil microbial biomass carbon, nitrogen and microbial quotient in double-cropping rice field

To explore the characteristics of rhizosphere soil microorganisms in paddy fields with different manure nitrogen (N) input ratios at different growth stages of early and late rice in double-cropping rice system, a field experiment was conducted with five different treatments: 1) 100% N of chemical fertilizer (M1), 2) 30% N of organic matter and 70% N of chemical fertilizer (M2), 3) 50% N of organic matter and 50% N of chemical fertilizer (M3), 4) 100% N of organic matter (M4), and 5) no N fertilizer input as a control (M0). The rhizosphere soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial quotient (SQ) of the paddy fields were measured using the fumigation-extraction and chemical analysis methods. The results showed that the rhizosphere MBC, MBN, and SQ of the paddy fields at main different growth stages of early and late rice were increased by fertilization, which increased first and then decreased with the development of rice growth period, peaked at the heading stage, and reached the minimum value at the maturity stage. The effects of different fertilization treatments were in order of M4＞M3＞M2＞M1＞M0, with no significant difference among M2, M3 and M4, but being significantly higher than M0. Therefore, the application of organic matter, and combined application of chemical fertilizer with organic matter could significantly increase the rhizosphere MBC, MBN, and SQ of the paddy fields at early and late rice growth period, while chemical fertilizer alone had little effect.

Estimation of Net Primary Production of Rice Crop using CASA model in Nankana Sahib.

Estimation of Net Primary Production (NPP) is crucial for the supply of food/wood. Precise estimates of NPP are important for sustainable development. We used Light Use Efficiency (LUE) model to appraise various growth-related processes e.g., photosynthesis, respiration and transpiration, in the rice plant. The study site received 1213 actual sunshine hours in comparison to total possible sunshine hours which were 1595 during the complete Rice Growth Period (RGP). Water stress was estimated throughout the RGP which resulted in surplus of water in early growth stages (W=53) and deficiency in the final ripening stage with W=0.14. Careful results indicate that about 5128 kg/ha of wet biomass was generated during the complete RGP. We applied a harvest index of 0.50 to estimate the dry biomass that was 2564 kg/ha which is about (2.82 ton/ha). These estimates seem to be in exaggeration according to real time field estimates collected by Crop Reporting Service (CRS) department which were (1.83 ton/ha). To manage this exaggeration, we applied the Soil Suitability Constant (ħα) which resulted as 1.99 ton/ha in suitable zone, 1.21 ton/ha in less suitable, 1.76 ton/ha in moderately suitable and 0.73 ton/ha in not suitable zones. The average yield was estimated as 1.62 ton/ha. According to CRS department, the rice area in the study site was reported as 107000 ha and the net rice production was estimated as 1,73,340 tons in the study site. The LUE model is reliable to estimate NPP of rice crop which is useful for decision makers to determine the contribution of rice in Gross Domestic Product (GDP) at regional scales in term of surplus or shortfall.

Estimation of Water Stress on Rice Crop Using Ecological Parameters.

About half of world’s population intake rice as a staple food. As being water baby, rice need surplus of water to get targeted yield. Water scarcity has become a global issue therefore it has become a need to enhance the rice yield with reduced amount of water. In this research we used ecological parameters e.g., temperature, pressure, actual vapor pressure, sunshine hours and the extraterrestrial radiation to compute net radiations, ground and sensible heat fluxes on daily basis. Net shortwave radiations were observed as 23087 w/m2 in comparison to net longwave radiations which were 4387 w/m2 for the complete Rice Growth Period (RGP). The soil heat flux Go was observed as 3104 w/m2. Go was observed dependent upon the Leaf Area Index (LAI) with inverse relationship between them. Sensible heat flux (H) was measured as 1771 w/m2 throughout the RGP. H was observed dependent upon net radiations with a direct relationship between them. Rn, Go and H were used as input parameters to compute water stress which determines the excess of water in early growth stages of rice crop and water scarcity in the ripening stage. The flow of methodology is easily applicable at domestic level to determine water stress in rice fields.

Effect of Liming with Various Water Regimes on Both Immobilization of Cadmium and Improvement of Bacterial Communities in Contaminated Paddy: A Field Experiment.

Cadmium (Cd) in paddy soil is one of the most harmful potentially toxic elements threatening human health. In order to study the effect of lime combined with intermittent and flooding conditions on the soil pH, Cd availability and its accumulation in tissues at the tillering, filling and maturity stages of rice, as well as enzyme activity and the microbial community in contaminated soil, a field experiment was conducted. The results showed that liming under flooding conditions is a more suitable strategy for in situ remediation of Cd-contaminated paddy soil than intermittent conditions. The availability of Cd in soils was closely related to the duration of flooding. Liming was an effective way at reducing available Cd in flooding soil because it promotes the transformation of Cd in soil from acid-extractable to reducible fraction or residual fraction during the reproductive growth period of rice. Compared with control, after liming, the concentration of Cd in brown rice was reduced by 34.9% under intermittent condition while reduced by 55.8% under flooding condition. Meanwhile, phosphatase, urease, and invertase activities in soil increased by 116.7%, 61.4% and 28.8%, and 41.3%, 46.5% and 20.8%, respectively. The high urease activity in tested soils could be used to assess soil recovery with liming for the remediation of contaminated soil. Soil microbial diversity was determined by the activities of soil acid phosphatase, urease and available Cd by redundancy analysis (RDA). The results indicated that the problem of Cd-contaminated paddy soil could achieve risk control of agricultural planting by chemical treatment such as lime, combined with various water regimes.

Estimation of Dynamic Canopy Variables Using Hyperspectral Derived Vegetation Indices Under Varying N Rates at Diverse Phenological Stages of Rice.

Non-destructive and rapid estimation of canopy variables is imperative for predicting crop growth and managing nitrogen (N) application. Hyperspectral remote sensing can be used for timely and accurate estimation of canopy physical and chemical properties; however, discrepancies associated with soil and water backgrounds complicate the estimation of crop N status using canopy spectral reflectance (CSR). This study established the quantitative relationships between dynamic canopy nitrogen (CN) status indicators, leaf dry weight (LDW), leaf N concentration (LNC), leaf N accumulation (LNA), and CSR-derived new hyperspectral vegetation indices (HVIs), and to access the plausibility of using these relationships to make in-season estimations of CN variables at the elongation (EL), booting (BT), and heading (HD) stages of rice crop growth. Two-year multi-N rate field experiments were conducted in 2015 and 2016 in Hubei Province, China, using the rice cultivar Japonica. The results showed that the sensitive spectral regions were negatively correlated with CN variables in the visible (400–720 nm and 560–710 nm) regions, and positively correlated (r > 0.50, r > 0.60) with red and NIR (720–900 nm) regions. These sensitive regions are used to formulate the new (SR777/759, SR768/750) HVIs to predict CN variables at the EL, BT, and HD stages. The newly developed stepwise multiple linear regression (SMLR) models could efficiently estimate the dynamic LDW at the BT stage and LNC and LNA at the HD stage. The SMLR models performed accurately and robustly when used with a validation data set. The projected results offer a suitable approach for rapid and accurate estimation of canopy N-indices for the precise management of N application during the rice growth period.

Cadmium and arsenic accumulation during the rice growth period under in situ remediation

Rice (Oryza sativa L.) planted in cadmium (Cd)- and arsenic (As)-contaminated soil is considered the main source of dietary Cd and As intake for humans in Southeast Asia and thereby poses a threat to human health. Minimizing the transfer of these pollutants to rice grain is an urgent task for environmental researchers. The main objective of this study was to investigate the effects and the mechanisms of a combined amendment (hydroxyapatite + zeolite + biochar, HZB) on decreasing Cd and As accumulation in rice. In situ remediation and aqueous solution adsorption experiments were conducted. The results showed that after application of HZB, Cd and As concentrations of the exchangeable fraction and TCLP extraction in soil decreased with the growth of rice plants. Cd concentrations in rice tissues were decreased at the tillering, filling and maturing stages after in situ remediation, while As concentrations in rice tissues were decreased only at the maturing stage. When 8 kg·plot−1 (9000 kg ha−1) HZB was applied, concentrations of Cd and inorganic As in brown rice were decreased to 0.18 and 0.16 mg kg−1, respectively, lower than the levels permissible for grain in China, i.e., 0.2 mg kg−1. Application of HZB reduced Cd accumulation in rice tissues, and the suppression of Cd accumulation was significantly greater than that of As. Furthermore, HZB significantly increased rice grain yield. An aqueous solution adsorption experiment demonstrated that HZB could adsorb and covalently bind Cd and As (V) via -OH, -COOH, -Si-O-Si and CO32- groups to produce carboxylates, silicates and carbonates, thereby promoting in situ immobilization of Cd and As in soil solution.

The relationship between phosphine, methane, and ozone over paddy field in Guangzhou, China

Greenhouse effect has been attracting more and more attention in the world. Carbon dioxide (CO2) and methane (CH4) are the most important greenhouse gases. Phosphine (PH3) may have a potential greenhouse effect because it can react with hydroxyl radicals (·OH) in competition with other reducing gases. The aim of this study is to discover the relationship among PH3, ozone (O3) and CH4 in paddy fields and estimate the potential greenhouse effect of PH3 by field experiment. The results reveal that there was a significant negative correlation between O3 and PH3 (r = −0.494, p = 0.001, n = 42) during the whole period of rice growth. Similarly, CH4 was also negatively correlated with PH3, but not significant (r = −0.283, p = 0.069, n = 42). However, it was found that PH3 and CH4 corresponded to the reciprocal model. These results show that there was a certain competition relationship between PH3 and CH4. It was widely speculated that PH3 and CH4 were similar in the photochemical elimination process. ·OH could react with PH3, resulting in PH bond break. Then PH3 was oxidized to phosphate and other oxidation substances. Through Pearson correlation analysis and multiple stepwise linear regression analysis, light intensity was the principal factor affecting PH3 levels over the paddy field. The regression equation was [PH3] = -0.0003*[L] +20.025 (R2 = 0.243; F = 5.177; P < 0.01). These discoveries in this study have great reference values for the future investigation of greenhouse effect.

Irrigation scheduling of paddy rice using short-term weather forecast data

Better use of rainfall is an essential strategy to save irrigation water for paddy rice. Since unnecessary irrigation is usually applied to field without considering the possible rainfall after irrigation, weather forecast (e.g., rainfall) can be used to potentially save irrigation water. In this study, the rainfall event mainly focused on the total rainfall in consecutive 3 days within rice growth period rather than the daily rainfall. Based on that, three rain levels were redefined for irrigation decision-making. By incorporating the possible rain level of the first 3 days in weather forecast horizon, a new method based on simple decision rule was proposed and evaluated for irrigation scheduling of paddy rice over a wide range of climate conditions in China. The results indicated that, the occurrence probability of each rain level in next 3 days can be clearly recognized, and their forecasting performance was much better than that of daily rain events. Comparing to the conventional irrigation, the newly proposed irrigation scheduling method can further save irrigation water (about 0 − 100 mm) and reduce drainage (about 0 − 60 mm) without significant yield loss (< 1%). The results also showed that, the efficiency of water saving and drainage reduction had a certain correlation with the total rainfall and the daily rainfall distribution during rice growth period. Moreover, about 1 − 3 extra irrigations were needed in this new irrigation scheduling method due to great temp-spatial variation of rainfall distributions and imperfect weather forecasts. Nevertheless, the newly proposed irrigation scheduling method incorporated with weather forecast is suggested to apply in irrigation practice for its simplicity and effectiveness.

Impacts of Recent Temperatures Rise on Double-Rice Phenology Across Southern China

Rice phenology was determined by temperature and agronomic management. It was essential to quantify the interaction between warming temperatures and rice phenology to understand the impact of climate change in rice farming systems. Based on the quantitative analysis of data from double-cropping rice in the south of China in the last 20 years, we found that the average temperature of the whole growth periods of early rice and late rice increased by an average of 0.76 °C and 0.49 °C decade−1, respectively. The whole growth period (WGP) change trend of early rice decreased by 0.07 d decade−1, but the WGP of late rice increased 1.26 d decade−1. The vegetative growth period (VGP) and the reproductive growth period (RGP) of early rice and late rice were all shorted. Regression analysis showed that the VGP of early rice and late rice decreased by 2.99 days and 2.82 days, and the RGP decreased by 1.67 days and 1.81 days, respectively, as the mean air temperature increased by 1 °C during the corresponding stages. The WGPs of early rice and late rice decreased by 3.81 days and 5.31 days, respectively, with the mean air temperature increased by 1 °C during growth duration. According to our studies, the rising mean air temperature could lead to a shortening of the double-rice growth period. Therefore, we must adjust the planting pattern of the double-rice system to mitigate and adapt to future climate change.

Vegetation Height Estimate in Rice Fields Using Single Polarization TanDEM-X Science Phase Data

This study presents the retrieval of rice paddy height using single polarization (single-pol) interferometric SAR (InSAR) data by means of model-based height inversion without an external DEM. A total of eight TanDEM-X (TDX) scenes were used and the TDX images were; acquired using a large cross-track baseline configuration during the TDX Science Phase (June–August 2015). A single-pol inversion approach for a flooded rice field is proposed and evaluated over the Buan test site in South Korea. A novel approach is adopted for the estimation of the ground (i.e., water level) interferometric phase within a flooded rice paddy from TDX data acquired during a period of early rice growth. It is consequently possible to apply the model-based inversion algorithm to the single-pol InSAR data. Rice height maps during the rice growth cycle presented and validated by field measurements. The results demonstrated the high performance of the inversion with a correlation coefficient of 0.78 and an RMSE of 0.10 m. The proposed methodology will be useful to monitor rice plants and to predict a gross rice yield, along with dual and fully polarimetric interferometric SAR data.

Chemical Weed Control in Paddy Fields Inoculated with Azospirillum lipoferum

ABSTRACT: Herbicides, as a major part of weed control strategy in paddy fields, have different impact on growth and activity of soil-beneficial bacteria such as Azospirillum species. A field experiment was conducted at Sefid Rood Livestock and Agricultural Company, northern Iran, to investigate the possibility of chemical weed control in paddy fields inoculated with Azospirillum lipoferum. The experiment was designed in a factorial arrangement based on a randomized complete block with three replicates. The factors were Azospirillum application (inoculation with or without Azospirillum lipoferum) and weed management regime (butachlor application with supplementary hand-weeding, bensulfuron methyl application with supplementary hand-weeding, combination of butachlor and bensulfuron methyl application with supplementary hand-weeding, hand-weeding at 15, 30, and 45 days after transplanting, and no weeding [not weeded during the rice-growing period). The results showed that plants inoculated with A. lipoferum produced 19% higher grain yield compared to plants that were not inoculated. The highest grain yields were recorded for plots treated with butachlor with supplementary hand-weeding (4,512 kg ha-1) and for those treated with a combination of butachlor and bensulfuron methyl with supplementary hand-weeding (4500.5 kg ha-1). The lowest yield (3494.3 kg ha-1) was recorded for weedy plots. No significant interaction was detected between A. lipoferum application and weed management regime for grain yield, indicating that the herbicides had no adverse effect on the efficiency of A. lipoferum in promoting growth and grain yield of rice. There was no significant difference in the dry weights of weed between inoculated and non-inoculated plots. The dry weights of weed in hand-weeded and herbicide-treated plots were significantly lower than that of the weedy plot. In conclusion, the result of this experiment confirms the possibility of chemical weed control in paddy fields inoculated with A. lipoferum.

Phosphorus availability changes in acidic soils amended with biochar, fly ash, and lime determined by diffusive gradients in thin films (DGT) technique.

The lime, biochar, and fly ash are widely used to ameliorate acidic soils. The purpose of our pot experiment was to understand whether these soil amendments affected the availability of phosphorus in soils using diffusive gradients in thin films (DGT) technique. Three soil amendments, biochar (B), fly ash (F), and lime (L), were applied alone or combined to Ultisol and Alfisol at the rate of 40, 40, and 6g/kg, respectively. The DGT and chemical extraction techniques were used to quantify the soil available (phosphorus) P dynamic in the rice growth period. The addition of amendments can effectively increase the phosphorus content extracted by 0.01M KCl solution. The biochar amendment showed the best effect on increasing the contents of DGT-P and Olsen-P in the soil. Combined with the DGT-induced fluxes in sediments (DIFS) model, it was found that soil amendments mainly increased the adsorption rate (k) and desorption rate (k-1), and reduced soil reflect time (Tc) of phosphorus released to the pore water. The P contents accumulated in rice grains correlated more closely with the effective P concentration measured by DGT technique, compared with those with soil total P, pore water P, and Olsen-P. These results suggested that the DGT technique had significant advantage over conventional chemical extraction techniques when assessing the bioavailability of phosphorus to rice growth. Application of soil amendments increased the contents of Al-P and Ca-P of both Ultisol and Alfisol, and decreased the content of Fe-P in soils. The addition of amendments could change the affinity of Fe and phosphorus decreasing the phosphorus fixation in soils. The increase of available phosphorus in soil is mainly due to the change of pH value and the direct diffusion of phosphorus in the amendments (biochar and fly ash). In conclusion, soil amendment can affect the availability and adsorption ability of phosphorus in soil, and biochar has the best effect on the availability of soil phosphorus.

Precipitation concentration in Jiangsu province, southeast China and its indicating function on the fluctuation of rice yield

Based on the precipitation record and single-crop rice yield data at 52 meteorological stations in Jiangsu province, southeast China from 1961 to 2012, a total of 14 precipitation concentration indices (PCI) during rice-growing period (May–October) were calculated, and then, the relationship between PCI and rice yield was explored. Results showed that: (1) the higher precipitation concentration was observed in north Jiangsu, and total precipitation was mainly concentrated in the rainstorm events and July rainfalls. (2) Precipitation concentration was increasing in recent 50 years, which was embodied in the significant increasing trends of precipitation contribution of rainstorm events and August rainfalls occurred in south Jiangsu. (3) The correlation analysis between rice yield and 14 PCI indicated that the precipitation contribution of rainstorm events (CDP6) was more suitable for accessing the losses of rice yield caused by excessive rainfall. (4) During the study period, the losses of rice yield in south Jiangsu exceeded 2%, owing to the stronger increasing trend of CDP6.

Effect of Paddy Field Construction on Soil Nutrients of Rice at Different Growth Stages in Xi’an

In this paper, three typical soil types around the banks of the Grand Xi’an River are described. Lou soil, entisols and loessial soil were used as the research objects and the rice growing stages, including pre-treatment, tillering stage, jointing stage, heading stage and maturity stage, in paddy field construction were analyzed. The results showed that: In the field, the effects of Tillage in different types of soil layer ranging from 0 to 20 cm on soil nutrients are obvious, in which available phosphorus, nitrate nitrogen, ammonium nitrogen content decreased during the growth period and the content of available potassium in the overall appear to be rising. It was concluded that the jointing stage was the most prosperous period of rice growth, the potassium content in the region could meet the growth demand, and the amount of potassium fertilizer could be reduced in the coming year.

A positive response of rice rhizosphere to alternate moderate wetting and drying irrigation at grain filling stage

Paddy fields are drained and irrigated several times during the whole rice growth period. Although studies have acknowledged the sensitivity of flooding and drainage in rice rhizosphere, current knowledge regarding how moderate drying at grain filling stage affects ecological characteristics of rice rhizosphere is limited. A field experiment with two irrigation regimes [alternate moderate wetting and drying irrigation (AMWD) and continuous irrigation (CI)] was conducted to investigate the changes in soil physical and chemical properties and microbial communities. Results from this investigation demonstrated that soil pH under AMWD was decreased, while Eh was increased. Moreover, soil electrical conductivity increased and decreased with a decline in soil water potential, interestingly all studied variables quickly recovered after re-watering.The terminal restriction fragment length polymorphism (T-RFLP) analysis revealed that the diversity indices of bacterial communities were higher in drying phase as compared to the initial treatment of AMWD regime, but the evenness index decreased. Remarkably, AMWD process increased the proportion of aerobic bacteria, such as Azotobacter, nitrifying bacteria, phosphate and potassium solubilizing bacteria (which participate in the nutrient cycling). In addition, the increase of enzyme activity under AMWD regime promoted the release of nutrients, thereby enhancing the amounts of NO3−-N, available phosphorus (P) and potassium (K) in soils, which met rice nutrient demands at late grain filling stage. This led to a promotion in plant physiological activities and grain filling, and hence increased grain yield. From these results we infer that there was a positive response of rice rhizosphere to AMWD irrigation at grain filling stage, which laid the groundwork to set up a sound irrigation system in rice fields without reducing its yield.

Application of a Dielectric Measurement Technique for Calculating Water Loss from Two Texture-contrasting Soils Grown with Upland Rice

Most of the water loss from the soil profile occurred through the evapotranspiration process especially when the plant covers were under maximum growth periods. This study aimed to apply a technique of measuring a dielectric variable for calculating soil water content and crop water use in the coarse and medium textured soils grown with upland rice. A couple of wires were inserted into the soil repacked in a 10-kg polybag grown with upland rice, the electrical impedance representing the dielectric value was measured using an instrument called the impedance meter. The impedance values were converted into the soil water content using a nonlinear regression model of ? = a.ebZ where a and b were constants. Results showed that the proposed technique of measuring the electrical impedance has successfully been applied to calculate the soil water content and the water use by upland rice grown in loamy sand and sandy loam soils. Cumulative water loss from loamy sand was about 4 L plant-1 higher for the coarse loamy sand in the first 30 days of a measurement period, but about 10 L plant-1 higher for finer sandy loam on the 90th day of the rice growth period. Higher biomass of upland rice in the sandy loam soil could increase the evapotranspiration rates and be the main reason for higher water use in this soil.

Characteristics of Mercury Transformation in Soil and Accumulation in Rice Plants in an Acidic Purple Paddy Soil Area

A pot experiment was conducted to analyze the characteristics of mercury (Hg) accumulation during the rice growth period in acidic purple paddy soil. Results showed that the soil total Hg concentration was stable with time during the rice growth period, while methylmercury (MeHg) increased greatly. Therefore, the ratio of MeHg/THg was mainly affected by MeHg concentration. THg concentration in rice plant parts followed the trend:root > grain > stalk > leaf > husk at the mature grain stage, while MeHg concentration followed grain > root > stalk > leaf > husk. The average of MeHg/THg in rice (24.03%) far exceeded that in soil (3.05%), suggesting that rice plants have a strong affinity for MeHg accumulation. This conclusion was supported also by the great difference in average of bio-concentration factors between MeHg (8.16) and THg (2.31) or the transfer factor in the grain, which was more than 1. Moreover, the bio-concentration factor for grain was higher than that for roots, stalks, and leaves, suggesting MeHg was prone to accumulation in grain compared with other part of rice plants.

Regional changes of climate extremes and its effect on rice yield in Jiangsu province, southeast China

In this study, the regional variations of climate extremes and its possible impact on rice yield in Jiangsu province, southeast China were investigated. A total of 18 climate extremes indices (CEI) of rice-growing period (May–October) based on the daily climate records and rice yield data at 52 stations during 1961–2012 were calculated and analyzed. The main findings were as follows: (1) due to the remarked regional differences of climate extremes, Jiangsu could be divided into six climatic subregions: westernmost, northwest, north, southwest, south, and southeast corner; (2) trends of 18 indices in the six subregions using Mann–Kendall test indicated that Jiangsu was dominated by an obvious wetting and warming tendency, especially in the southern area; (3) correlation analysis between rice yield and CEI using first-difference and climate-induced yield method showed that the negative influences of precipitation extremes were more notable compared to temperature extremes; (4) P95 [precipitation due to very wet days (> 95th percentile)] should be selected as a key meteorological disasters indicator affecting rice yield in the northwest, north, southwest, and south Jiangsu; (5) the increase of P95 since 1990s was detected in most of Jiangsu, which would bring huge risks to rice growing.