Rice Growth Period Research Articles

Differences in Cd Accumulation in Typical Soils Under the Double Rice System

Pot experiments were used to study the differences of Cd uptake and accumulation in double-cropping rice in typical soil types. To analyze the soil availability of Cd (DTPA-Cd) in soils and the Cd accumulation in double-cropping rice at different growth stages of the rice, we conducted pot experiments that selected the yellow clayey soil (paddy soil developed from plate shaley parent materials) and the granitic sandy soil (paddy soil developed from granitic parent materials). Exogenous Cd was added with gradients of 0, 0.5, 1.0, 2.0, 5.0, and 10.0 mg·kg-1. Results showed that, during the rice growth period, the available Cd in the yellow clayey soil was higher than that in the granitic sandy soil, and the difference was significant (P<0.01). This showed that the content of Cd in rice (roots, shoots, leaves, rice shells, and brown rice) increased along with the treatment level and with the extension of the rice growth period. The accumulation characteristics of Cd in rice grains and other tissues of rice indicated differences between two seasons and two soil types, that is, late rice was higher in Cd than was early rice, and reddish yellow clayey soil was higher in Cd than granitic sandy soil. Significant positive linear correlations were found between the effective contents of Cd in soils and those in rice tissues (roots, shoots, leaves, and brown rice). The prediction model of Cd in rice and the characteristic equation for rice accumulation of Cd were applied to calculate the critical values of Cd:0.98 mg·kg-1 for early rice and 0.83 mg·kg-1 for late rice in reddish yellow clayey soil, and 0.86 mg·kg-1 for early rice and 0.56 mg·kg-1 for late rice in granitic sandy soil. These threshold values are higher than the National Standards given in "farmland environmental quality evaluation standards for edible agricultural products (HJ 332-2006)." The soil security threshold values and the soil environmental capacities of the two different parent materials varied greatly; therefore, different environmental quality standards may be formulated and different measures may be needed to control Cd pollution in different parent materials.

夜间增温对稻田甲烷排放的影响及其高光谱估算

PDF HTML阅读 XML下载 导出引用 引用提醒 夜间增温对稻田甲烷排放的影响及其高光谱估算 DOI: 10.5846/stxb201707201304 作者: 作者单位: 南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室,南京信息工程大学气象灾害预报预警与评估协同创新中心/江苏省农业气象重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41375159）；江苏省自然科学基金项目（BK20131430） Methane emission in response to nighttime warming and its hyperspectral estimation in a paddy field Author: Affiliation: Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology,Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Jiangsu Key Laboratory of Agricultural Meteorology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:昼夜不对称增温是全球气候变化的主要特征之一，有关夜间增温对稻田甲烷（CH4）排放影响的报道尚不多见。通过田间模拟试验，研究了被动式夜间增温下水稻田CH4排放及高光谱的特征，并用高光谱数据对稻田甲烷排放进行定量模拟。田间试验设夜间增温（NW）和对照处理（CK），夜间增温即在整个水稻生育期的夜间（19：00-6：00）用铝箔反射膜覆盖水稻冠层。结果表明，夜间增温显著促进水稻拔节期和抽穗期-灌浆期CH4排放。水稻冠层近红外光谱反射率表现为，在分蘖期和拔节期时，NW>CK；而在抽穗-灌浆期和成熟期时，CK>NW。水稻冠层光谱反射率、一阶导数光谱及光谱特征值均与CH4排放通量显著相关，相关系数最大可达0.8（P < 0.01），其中以"蓝边面积"（SDb）构成的二次多项式模型模拟精度和检验精度综合最佳，决定系数R2分别为0.70和0.72。研究结果对稻田CH4排放通量遥感监测的可行性提供了理论依据和技术支持。 Abstract:Asymmetric diurnal warming is one of the main features of global climate change, but the effects of nighttime warming on CH4emission from paddy fields is unclear. A field experiment with rice was conducted at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China, to investigate the effects of passive nighttime warming on CH4 emission in a paddy field and rice canopy hyperspectral characteristics. CH4 emission flux was estimated with hyperspectral data. The tested rice was hybrid rice cv. Y Liangyou 3399. The tested paddy soil was classified as a Typic Stagnic Anthrosol. The experiment was designed with two levels of warming, i.e., nighttime warming(NW) and control(CK). NW was created by covering the rice canopy with an aluminum foil reflective film at night(19:00-6:00).CH4 emission was measured by the closed chamber method at one-week intervals during the rice-growing period. The results showed that NW significantly increased CH4 emission at the rice jointing and heading-grain filling stages. Compared to CK, NW increased the reflectance of the near-infrared spectrum on the canopy at the tillering and jointing stages, but decreased at the heading-grain filling and maturity stages. Positive correlations were observed in the relationships of CH4 emission with spectral reflectance and the first derivative and the characteristic value of the spectrum. After comparing correlation coefficients (R2) of the fitting models and prediction models, the quadratic polynomial model by 'Area of Blue Edge' (SDb) was found to be the best model(fitting model R2=0.70, prediction model R2=0.72) for estimating CH4 emission. The results of this study provide a theoretical basis for and demonstrate the feasibility of non-destructively monitoring of CH4 emission in paddy fields. 参考文献 相似文献 引证文献

Yield variation of rainfed rice as affected by field water availability and N fertilizer use in central Benin

Rice is mainly grown under rainfed conditions in West Africa. Unpredictable and variable rainfall, poor soil quality, and suboptimal crop management practices are the main determinants of low productivity. We assessed the effects of soil water availability and fertilizer application, and their interaction on the yield of rainfed rice in Glazoue, Department of Zou-Collines, central Benin between 2010 and 2013. On-farm fertilizer management trials and field surveys were conducted in 13–39 farmers’ fields per year. Field water conditions were visually assessed three times per week during the rice-growing season and flood and drought indices were calculated on the basis of number of days with ponded water and dry surface soil relative to the total number of days for the vegetative, the reproductive and whole rice-growing period. Variations in flood and drought indices were related to the sand content of the soil. While nitrogen was the most limiting nutrient, average response to N fertilizer application was low with an agronomic N use efficiency of only 7–9 kg grain per kg of N applied. Year-to-year variation in rainfall and spatial variation in field water status affected both rice yield and response to N fertilizer. Some 47% of the observed yield variation was explained by field water status and the amounts of N fertilizer applied, with rice response to N fertilizer being less when water was limited. We conclude that the prevailing blanket fertilizer recommendations are unlikely to contribute to yield increases in rainfed systems of West Africa. There is a need for field-specific recommendations that consider soil texture and the spatial–temporal dynamics of water availability.

Forage rice varieties Fukuhibiki and Tachisuzuka emit larger CH4 than edible rice Haenuki

ABSTRACTTo determine methane (CH4) emission differences between edible and forage rice cultivars, we conducted a pot experiment in Yamagata, Japan to grow edible rice Haenuki, and forage rice Fukuhibiki (for feed rice) and Tachisuzuka (for whole-crop silage (WCS) rice) under similar soil and meteorological conditions. The total amounts of N, P, and K fertilizers applied for Fukuhibiki and Tachisuzuka were 1.7, 1.3, and 1.3 times, respectively, higher than those of Haenuki. CH4 fluxes, and rice plant night respirations were measured once weekly or fortnightly. As per the results, for the whole growth period, shoot height, maximum and productive tiller numbers, and plant biomass were significantly different among the three rice varieties. The rice growth period for Haenuki and Fukuhibiki was 107 days after transplanting (DAT), while that for Tachisuzuka was 135 DAT. The highest peak of CH4 flux occurred around the heading stage for the three varieties. Consistently significant (P < 0.05) or obvious (P < 0.1) positive correlations between CH4 flux and night respiration among the varieties were observed from 9 weeks after rice transplanting to harvest, indicating that much of the CH4 flux was from newly produced root exudates and plant debris through plant photosynthesis. The cumulated CH4 emissions during the same growth period, 106 DAT, from Haenuki, Fukuhibiki, and Tachisuzuka were 55.36, 77.46, and 78.40 g C m−2, respectively. Additionally, Tachisuzuka emitted 25.11 g C m−2 more CH4 between 106–134 DAT. The final cumulated CH4 emissions from Fukuhibiki and Tachisuzuka were 39.9% and 87.0% higher than that from Haenuki, respectively, throughout their growth period.

Uptake of silver by brown rice and wheat in soils repeatedly amended with biosolids

There have been numerous studies simulating the behaviour and fate of silver (Ag) applied to soils in biosolids in recent decades but the results remain to be verified under actual farming conditions. Here, we report a study of the transfer of Ag along the biosolids-soil-crop pathway with repeated biosolid applications over a four-year period to three contrasting soil types under rice-wheat rotation cultivation. A systematic investigation of Ag concentrations in biosolids throughout China shows Ag concentrations ranging from 0.64 to 7.47mgkg−1 with a mean value of 3.58mgkg−1 and a median of 3.02mgkg−1 on a dry weight basis. Silver concentrations were significantly higher in industrial biosolids than in domestic or mixed flow biosolids. Biosolids application enhanced Ag accumulation in whole wheat. Silver concentrations in whole wheat increased to 20.8, 20.5 and 4.87μgkg−1 after four years of high-metal industrial biosolids application to an acid Typic Ali-Perudic Aragsol, a neutral Typic Hapli-Stagnic Anthrosol, and a calcareous Typic Carbonati-Perudic Ferrosol, respectively. Moreover, the Ag translocation factor also increased in wheat following biosolids application with values of 5.6, 3.1 and 1.4, respectively. However, Ag accumulation in rice was found only in the acid soil with no discernible increase (p>0.05) in the translocation factor. The seasonal redox cycle may contribute to this phenomenon. A seedling incubation experiment confirms the influence of soil water regime on Ag bioavailability with a higher Ag translocation factor during the wheat growing season than the rice growth period. Incorporating a fallow period during the wheat (winter crop) season might be a suitable strategy for repeated biosolids application.

In-season assessment of grain protein and amylose content in rice using critical nitrogen dilution curve

Abstract Effective nitrogen (N) management strategies ensure optimal N status in rice (Oryza sativa L.) plants for improving crop growth and grain quality with optimal N use efficiency. In-season plant N status affects rice grain quality. The critical N (Nc) dilution curves have been applied for predicting in-season nitrogen requirement (NR) and grain yield in rice, however, its application for estimating rice grain quality at harvest is yet to be tested. This research was endeavored to establish the quantitative relationships of protein content (PC) and amylose content (AC) with nitrogen nutrition index (NNI), accumulated nitrogen deficit (AND), and NR at various growth stages during vegetative growth period of rice and to validate these relationships in Japonica and Indica rice ecotypes. Five multi-locational field trials with five rice cultivars and varied N application rates were carried out in eastern China. The quantitative relationships of PC and AC with NNI, AND, and NR at various growth stages in both rice ecotypes were highly significant (for Japonica and Indica, R2 > 0.88 and 0.85 for PC, R2 > 0.85 and 0.81 for AC, respectively). The strongest relations were observed for both rice ecotypes at later vegetative growth stages and periods. The validation of the developed quantitative relationships with the independent dataset revealed a solid model performance, especially during later vegetative growth period (R2 > 0.90, root mean square error

Effects of controlled release blend bulk urea on soil nitrogen and soil enzyme activity in wheat and rice fields

A field experiment was conducted to investigate the effect of controlled-release fertilizer (CRF) combined with urea (UR) on the soil fertility and environment in wheat-rice rotation system. Changes in four forms of nitrogen (total nitrogen, ammonium nitrogen, nitrate nitrogen, and microbial biomass nitrogen) and in activities of three soil enzymes participating in nitrogen transformation (urease, protease, and nitrate reductase) were measured in seven fertilization treatments (no fertilization, routine fertilization, 10%CRF+90%UR, 20%CRF+80%UR, 40%CRF+60%UR, 80%CRF+20%UR, and 100%CRF). The results showed that soil total nitrogen was stable in the whole growth period of wheat and rice. There was no significant difference among the treatments of over 20% CRF in soil total nitrogen content of wheat and rice. The soil inorganic nitrogen content was increased dramatically in treatments of 40% or above CRF during the mid-late growing stages of wheat and rice. With the advance of the growth period, conventional fertilization significantly decreased soil microbial biomass nitrogen, but the treatments of 40% and above CRF increased the soil microbial biomass nitrogen significantly. The soil enzyme activities were increased with over 40% of CRF in the mid-late growing stage of wheat and rice. By increasing the CRF ratio, the soil protease activity and nitrate reductase activity were improved gradually, and peaked in 100% CRF. The treatments of above 20% CRF could decrease the urease activity in tillering stage of rice and delay the peak of ammonium nitrogen, which would benefit nitrogen loss reduction. The treatments of 40% and above CRF were beneficial to improving soil nitrogen supply and enhancing soil urease and protease activities, which could promote the effectiveness of nitrogen during the later growth stages of wheat and rice. The 100% CRF treatment improved the nitrate reductase activity significantly during the later stage of wheat and rice. Compared with the treatments of 40%-80% CRF, 100% CRF reduced the soil nitrate content of 20-40 cm soil layer in wheat significantly suggesting it could reduce the loss of nitrogen.

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.

Emission and distribution of phosphine in paddy fields and its relationship with greenhouse gases

Phosphine (PH3), as a gaseous phosphide, plays an important role in the phosphorus cycle in ecosystems. In this study, the emission and distribution of phosphine, carbon dioxide (CO2) and methane (CH4) in paddy fields were investigated to speculate the future potential impacts of enhanced greenhouse effect on phosphorus cycle involved in phosphine by the method of Pearson correlation analysis and multiple linear regression analysis. During the whole period of rice growth, there was a significant positive correlation between CO2 emission flux and PH3 emission flux (r=0.592, p=0.026, n=14). Similarly, a significant positive correlation of emission flux was also observed between CH4 and PH3 (r=0.563, p=0.036, n=14). The linear regression relationship was determined as [PH3]flux=0.007[CO2]flux+0.063[CH4]flux−4.638. No significant differences were observed for all values of matrix-bound phosphine (MBP), soil carbon dioxide (SCO2), and soil methane (SCH4) in paddy soils. However, there was a significant positive correlation between MBP and SCO2 at heading, flowering and ripening stage. The correlation coefficients were 0.909, 0.890 and 0.827, respectively. In vertical distribution, MBP had the analogical variation trend with SCO2 and SCH4. Through Pearson correlation analysis and multiple stepwise linear regression analysis, pH, redox potential (Eh), total phosphorus (TP) and acid phosphatase (ACP) were identified as the principal factors affecting MBP levels, with correlative rankings of Eh>pH>TP>ACP. The multiple stepwise regression model ([MBP]=0.456∗[ACP]+0.235∗[TP]−1.458∗[Eh]−36.547∗[pH]+352.298) was obtained. The findings in this study hold great reference values to the global biogeochemical cycling of phosphorus in the future.

Influence of water potential and soil type on conventional japonica super rice yield and soil enzyme activities

We carried out a pool culture experiment to determine the optimal water treatment depth in loam and clay soils during the late growth stage of super rice. Three controlled water depth treatments of 0–5, 0–10 and 0–15 cm below the soil surface were established using alternate wetting and drying irrigation, and the soil water potential (0 to –25 kPa) was measured at 5, 10 and 15 cm. A 2-cm water layer was used as the control. We measured soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield. The results showed that the 0–5-cm water depth treatment significantly increased root antioxidant enzyme activities in loam soil compared with the control, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield did not differ from those of the control. The 0–10- and 0–15-cm water depth treatments also increased root antioxidant enzyme activities, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield decreased. In clay soil, the soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and yield did not change with the 0–5-cm water treatment, whereas the 0–10- and 0–15-cm water treatments improved these parameters. Therefore, the appropriate depths for soil water during the late growth period of rice with a 0 to –25 kPa water potential were 5 cm in loam and 15 cm in clay soil.

Estimating FAPAR of Rice Growth Period Using Radiation Transfer Model Coupled with the WOFOST Model for Analyzing Heavy Metal Stress

Timely assessment of crop growth conditions under heavy metal pollution is of great significance for agricultural decision-making and estimation of crop productivity. The object of this study is to assess the effects of heavy metal stress on physiological functions of rice through the spatial-temporal analysis of the fraction of absorbed photosynthetically active radiation (FAPAR). The calculation of daily FAPAR is conducted based on a coupled model consisting of the leaf-canopy radiative transfer model and World Food Study Model (WOFOST). These two models are connected by leaf area index (LAI) and a fraction of diffused incoming solar radiation (SKYL) in the rice growth period. The input parameters of the coupled model are obtained from measured data and GF-1 images. Meanwhile, in order to improve accuracy of FAPAR, the crop growth model is optimized by data assimilation. The validation result shows that the correlation between the simulated FAPAR and the measured data is strong in the rice growth period, with the correlation coefficients being above 7.5 for two areas. The discrepancy of FAPAR between two areas of different stress levels is visualized by spatial-temporal analysis. FAPAR discrepancy starts to appear in the jointing-booting period and experiences a gradual rise, reaching its maximum in the heading-flowering stage. This study suggests that the coupled model, consisting of the leaf-canopy radiative transfer model and the WOFOST model, is able to accurately simulate daily FAPAR during crop growth period and FAPAR can be used as a potential indicator to reflect the impact of heavy metal stress on crop growth.

Effects of Different Water Managements and Soil Eh on Migration and Accumulation of Cd in Rice

A pot experiment was conducted to study the effects of four modes of water managements on soil Eh values,bioavailability of soil Cd,migration and accumulation of Cd in rice.These four modes of water managements were moistening throughout the entire period of rice growth (M),moistening before filling stage and flooding after filling stage (M-F),flooding before filling stage and moistening after filling stage (F-M),and flooding throughout the entire period of rice growth (F).The results indicated that the exchangeable contents of Cd increased firstly and then declined with the soil Eh values changing from negative to positive.Compared with M,the other three modes (M-F,F-M,and F) significantly reduced the contents of Cd in all rice tissues,including roots,stems,husks and brown rice.Meanwhile,Cd contents in brown rice due to the treatments of M-F and F were 0.19 mg·kg-1 and 0.10 mg·kg-1,respectively.These Cd contents were lower than the limits of 0.2 mg·kg-1 in national food safety standard (GB 2762-2012).Compared with M,the other three modes significantly decreased Cd accumulation amounts in the aboveground parts of rice and also decreased Cd translocation factors in rice.There were significant positive exponential relations between soil Eh values and Cd accumulation amounts in the aboveground parts of rice,Cd translocation factors in rice,or Cd contents in brown rice.The rice biomass due to M-F treatment reached the maximum among the four modes.It was worthy to be mentioned that although Weiyou 46 was considered a variety rice with high Cd accumulation,Cd content in rice brown of Weiyou 46 could be lower than 0.2 mg·kg-1 in the 5 mg·kg-1 of Cd contaminated soil through proper water managements.In summary,M-F treatment ensured high rice yield with low Cd contents in brown rice and could be recommended as the irrigation mode in rice production.Simultaneously,maintaining soil Eh value between -160--130 mV was also important after the filling stage.

English

Methane (CH4) is the most important greenhouse gas, which was produced from paddy fields. The CH4 production and emission were affected by methane–oxidizing bacteria (methanotrophs). Therefore, it is significant to investigate the effects of fertilizer applications on the change of soil methanotrophs, which affected CH4 emission. The objective of this paper was to describe changes of CH4 and diversity and composition of methanotrophs in paddy soil in relation to the application of crop residues, mineral fertilizer, and manure based on a long-term field experiment. In this study, static chamber-gas chromatography technique, real-time polymerase chain reaction (PCR) and Illumina high-throughput sequencing of the 16S rRNA gene, respectively, were used to analyze the CH4 emissions from paddy fields, soil methanotrophs abundance and community diversity from May to October 2014 under five fertilization treatments: mineral fertilizer (MF), rice residue and mineral fertilizer (RF), low manure rate and mineral fertilizer (LOM), and high manure rate and mineral fertilizer (HOM), as compared to without fertilizer input (CK). The results indicated that CH4 from fertilization treatments displayed different emission patterns during early and late rice growth period. HOM treatment had the highest CH4 emissions during early and late rice growth period with 5.074 and 6.099 g m-2, respectively. Some methanotrophs genera (Methylosinus, Crenothrix, Methylocaldum, Methylomicrobium and Methylomonas) were identified at the early and late rice main growth stages. The abundance and composition of soil methanotrophs were affected by long-term fertilization managements. The methanotrophs abundance was inhibited under MF treatment, while they were stimulated under RF, LOM and HOM treatments. The abundance and community composition of methanotrophs in paddy soil were affected by fertilizers of mineral, crop residues, and manure. It was concluded that application with organic and crop residues enhance the abundance and community composition of methanotrophs in double-cropping paddy fields in Southern China through a long-term fertilizer experiment. Keywords: CH4, long-term fertilization, methanotrophs diversity, methanotrophs composition, paddy field.

Remote Sensing based Methane Emission from Rice Fields in Tiruchirapalli District

Rice cultivation has been recognized as one of the major anthropogenic source for CH4 emissions. Methane emission from rice fields is a microbial mediated anaerobic activity, mainly favoured by the flooded condition. SAR-based operational mapping of rice crop across a diverse range of environments is possible with the increasing availability of multi-temporal SAR satellite data. Precise estimation of methane emission from rice fields at regional scale depends on accurate assessment of rice area and the corresponding time of flooding in those fields with IPCC emission factor. Start of Season (SoS) map was derived from satellite data showing rice emergence dates in Tiruchirapalli district recording 87 to 121 days of flooding during rice growth period. The rate of methane emission based on IPCC factor ranged from 37.4 to 45.74 kg/ha for a period of 87 to 121 days of flooding. The total methane emission from Tiruchirapalli district was 1.57Gg during Samba season 2015-16.

Research on Different Irrigation Water Effect on Soda Alkaline Soil and Horizontal Drainage Water Salinity-alkalinity

The effect of tube-well water and river water irrigation on soda alkaline soil and horizontal drainage water salinity-alkalinity was studied. Through soil column simulated experiment, the influence of the tube-well water and river water irrigation on soda alkaline soil and horizontal drainage water salinity-alkalinity was studied. The salinity indexes of surface drainage water in puddling period, the rules of salt ions change of surface drainage water, and the soil electrical conductivity changes in prime field period and the change of soil salinity indexes after a growing season were analyzed. The results showed that, there was no significant different of irrigationwater on salinity-alkalinity index for the first surface drainage water in puddling period. But the EC, Na+,Ca2++Mg2+ and total alkalinity of CK 1 was significant higher than CK 2 for the second drainage water. Irrigation water quality has not significant influence on the soil EC, but desulfurization gypsum could significantly reduce EC value of 0 to 10 cm soil layer. After one rice growth period, the T1 with pH and EC value was significantly less than T2 in 20-40 cm soil layer, but there no significant different on the top layer. Therefore, the tube-well water was choosing at the puddling period, so as to increase the surface flushing effect. With the corresponding, the river water was choosing at the prime field period to prevent soil secondary salinization.

Effect of rates and sources of nitrogen on rice yield, nitrogen efficiency, and methane emission from irrigated rice cultivation

ABSTRACTThe agronomic benefits of manure application to increase rice production have been recognized, but the impact on global change has always been a controversial topic. This study was designed to determine the separate and combined effects of cattle manure (CM) and nitrogen (N) fertilizer on rice yield, N efficiency, and methane (CH4) emissions from rice cultivation. A pot-scale experiment was conducted with four levels (0, 60, 120, and 180 kg ha−1) of N from urea and two levels (120 and 180 kg ha−1) of N from combination of urea and CM (Urea:CM = 60:60 and 60:120). Rice yield and physiological N efficiency were obtained using agronomic measurements. To determine the global warming potential (GWP) of each treatment, CH4 emissions were measured throughout the rice-growing period. Grain yield (GY) was not significantly different between the treatments of 120 and 180 kg ha−1 regardless of N source. However, both rates of CM treatments enhanced CH4 emission and differences in GWP were significant. In conclusion, urea applied at 120 kg N ha−1 was optimal for rice productivity and environmental impact (EI) despite CM played a crucial role in improving the N efficiency and total N in the soil after harvest.

Dynamic Mapping of Rice Growth Parameters Using HJ-1 CCD Time Series Data

The high temporal resolution (4-day) charge-coupled device (CCD) cameras onboard small environment and disaster monitoring and forecasting satellites (HJ-1A/B) with 30 m spatial resolution and large swath (700 km) have substantially increased the availability of regional clear sky optical remote sensing data. For the application of dynamic mapping of rice growth parameters, leaf area index (LAI) and aboveground biomass (AGB) were considered as plant growth indicators. The HJ-1 CCD-derived vegetation indices (VIs) showed robust relationships with rice growth parameters. Cumulative VIs showed strong performance for the estimation of total dry AGB. The cross-validation coefficient of determination ( R C V 2 ) was increased by using two machine learning methods, i.e., a back propagation neural network (BPNN) and a support vector machine (SVM) compared with traditional regression equations of LAI retrieval. The LAI inversion accuracy was further improved by dividing the rice growth period into before and after heading stages. This study demonstrated that continuous rice growth monitoring over time and space at field level can be implemented effectively with HJ-1 CCD 10-day composite data using a combination of proper VIs and regression models.

Dynamics of bacterial communities in rice field soils as affected by different long-term fertilization practices.

Fertilization and the response of the soil microbial community to the process significantly affect crop yield and the environment. In this study, the seasonal variation in the bacterial communities in rice field soil subjected to different fertilization treatments for more than 50 years was investigated using 16S rRNA sequencing. The simultaneous application of inorganic fertilizers and rice straw compost (CAPK) maintained the species richness of the bacterial communities at levels higher than that in the case of non-fertilization (NF) and application of inorganic fertilizers only (APK) in the initial period of rice growth. The seasonal variation in the bacterial community structure in the NF and APK plots showed cyclic behavior, suggesting that the effect of season was important; however, no such trend was observed in the CAPK plot. In the CAPK plot, the relative abundances of putative copiotrophs such as Bacteroidetes, Firmicutes, and Proteobacteria were higher and those of putative oligotrophs such as Acidobacteria and Plactomycetes were lower than those in the other plots. The relative abundances of organotrophs with respiratory metabolism, such as Actinobacteria, were lower and those of chemoautotrophs that oxidize reduced iron and sulfur compounds were higher in the CAPK plot, suggesting greater carbon storage in this plot. Increased methane emission and nitrogen deficiency, which were inferred from the higher abundances of Methylocystis and Bradyrhizobium in the CAPK plot, may be a negative effect of rice straw application; thus, a solution for these should be considered to increase the use of renewable resources in agricultural lands.

Influence of Different Seedling‐Nursing Methods on Methane and Nitrous Oxide Emissions in the Double Rice Cropping System of South China

Numerous studies on methane (CH4) and nitrous oxide (N2O) emissions during the rice growth period have focused on paddy fields, but CH4 and N2O emissions from rice seedling nurseries are poorly documented. This holds especially true for South China, where the double rice cropping system dominates. Here, we report CH4 and N2O emissions from three types of rice seedling nurseries in South China: Seedlings raised on wetland soil beds (WSB) with continuous flooding, seedlings raised on dry land soil beds (DSB), and seedlings raised in wet conditions with moist irrigation on plastic trays (WPT). Moreover, global warming potential (GWP) for all the three seedling nursing systems were estimated over a 100‐year horizon. The results show that the WSB method produced the highest CH4 with negligible N2O emissions. Among the three methods, the DSB plots emitted the highest N2O and thus the highest GWP. Relative to the WSB method, the WPT method significantly decreased total CH4 emissions by 45%, and the WPT method decreased GWPs by 28 and 68% compared to the WSB and DSB method, respectively. The GWP of CH4 and N2O of WSB, DSB, and WPT account 30, 68, and 22% of that for the whole transplanted early‐rice growing season for an equal unit area, indicating that GHGs from seedling stage were not negligible. Moreover, the WPT method produced the best rice seedlings. Therefore, utilizing WPT instead of conventional WSB is proposed as a best method for mitigating the GWPs of CH4 and N2O while growing healthy seedlings in rice nurseries in the double rice cropping system in South China.

Spatial variability of chlorophyll and nitrogen content of rice from hyperspectral imagery

Chlorophyll and nitrogen are the most essential parameters for paddy crop growth. Spectroradiometric measurements were collected at canopy level during critical growth period of rice. Chemical analysis was performed to quantify the total leaf content. By exploiting the ground based measurements, regression models were established for chlorophyll and nitrogen aimed indices with their corresponding crop growth variables. Vegetation index models were developed for mapping these parameters from Hyperion imagery in an agriculture system. It was inferred that the present Simple Ratio (SR) and Leaf Nitrogen Concentration (LNC) indices, which followed a linear and nonlinear relationship respectively, were completely different from published Tian et al. (2011). The nitrogen content varied widely from 1 to 4% and only 2 to 3% for paddy crop using present modified index models and Tian et al. (2011) respectively. The modified LNC index model performed better than the established Tian et al. (2011) model as far as estimated nitrogen content from Hyperion imagery was concerned. Furthermore, within the observed chlorophyll range obtained from the studied rice varieties grown in the rice agriculture system, the index models (LNC, OASVI, Gitelson, mSR and MTCI) performed well in the spatial distribution of rice chlorophyll content from Hyperion imagery. Spatial distribution of total chlorophyll content varied widely from 1.77 to 5.81mg/g (LNC), 3.0 to 13mg/g (OASVI), 0.5 to 10.43mg/g (Gitelson), 2.18 to 10.61mg/g (mSR) and 2.90 to 5.40mg/g (MTCI). The spatial information of these parameters will help in proper nutrient management, yield forecasting, and will serve as inputs for crop growth and forecasting models for a precision rice agriculture system.