Accumulation of Heavy Metals in Maga-Pouss Rice Fields (Far-North Region, Cameroon) and Transfer to Rice Grains

Monitoring of heavy metals contamination of agricultural products and their transfer and bioaccumulation in crops like rice has become a hot topic worldwide over the last two decades. The present study was carried out to determine the accumulation of heavy metals in rice fields and their transfer to rice grains. Soil, irrigation water and rice grains samples were gathered in Maga-Pouss, Far-North, Cameroon. Concentrations of six heavy metals (lead, cadmium, zinc, copper, iron and mercury) were evaluated by Atomic Absorption Spectrophotometer (AAS). Mercury was not detected in this study. Average concentrations of metals were in this order (in mg/kg): Fe (188.60 ± 97.06) > Pb (63.63 ± 7.11) > Cd (2.59 ± 0.29) > Zn (1.10 ± 1.05) > Cu (0.80 ± 0.73) in water and Pb (105.50 ± 31.11) > Fe (105.50 ± 31.11) > Cu (45.93 ± 14.39) > Zn (22.52 ± 6.40) > Cd (3.15 ± 0.49) in soil. Water in Maga-Pouss rice fields appears to be more harmful than the soil, notably for lead, cadmium and copper. In rice grains, heavy metals were found in this order (mg/kg): Fe (188.01 ± 82.62) > Cu (27.20 ± 0.00) > Zn (23.61 ± 12.42) > Pb (19.50 ± 19.91) > Cd (2.02 ± 1.05). The mean bioconcentration factor (BCF) of metals from soil to rice grains was in the following order: Fe (2.60) > Zn (1.05) > Cd (0.64) > Cu (0.59) > Pb (0.18). From water to rice grains, the order is: Cu (37.26) > Zn (22.49) > Cd (6.97) > Pb (2.74) > Fe (1.94). Rice field pH and electrical conductivity favored the uptake of lead, copper and cadmium by rice grains. The findings of this study will be good documentation for risk assessment, and decision-making by environmental managers in this region.

The Effect of Three New Fungicides against Rice Sheath Blight in Field Experiment

[Objective] The aim was to study the effect of three new fungicides against rice sheath blight in field experiment. [Methods] The experiment set up 7 treatments with three times of repetition and designed by random grouping. By using 5 sampling points in each plot, and investigating continuous 4 holes of each point, total plants, diseased plants and disease degrees were recorded. Then disease index and control efficiency were calculated, and variance analysis was carried out. [Results] 300 or 450 ml/hm^2 azoxystrobin ＋ difenoconazole 325 g/L SC had better control efficiency to rice sheath blight and had no phytotoxicity effect, we should use it at the initial disease stage and continuously spray 2-3 times. [Conclusion] The experiment provided a theoretical basis for controlling rice sheath blight using fungicides.

Estimate of CH_4 Emissions from Year-Round Flooded Rice Fields During Rice Growing Season in China

A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4 emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season. CH4 emission factors were used to estimate the CH4 emissions from year-round flooded rice fields during the rice-growing season in China. The CH4 emissions for the year-round flooded rice fields in China for the rice growing season over a total area of 2.66 Mha were estimated to be 2.44 Tg CH…

Nitrogen Losses from Flooded Rice Field

A field microplot experiment was conducted during the tillering stage of paddy rice to investigate nitrogen(N) Iosses from flooded rice fields following fertilizer application. After application of ammonium bicarbonate,most of nitrogen in the floodwater was present as NH4-N and its concentration varied widely with time.Concentrations of both NO3-N and NO2-N in the floodwater were low due to the weakened nitrification.Under flooded anaerobic reducing conditions, soil solution concentrations of NO3-N and NH4-N were nothigh, ranging from 0.6 mg L-1 to 4.8 mg L-1, and decreased with soil depth. However, the groundwater wasstill contaminated with NO3-N and NH4-N. Rainfall simulation tests showed that the N losses via runoff inrice fields were closely related to the time intervals between fertilizer applications and rainfall events. Whena large rain fell for a short period after fertilizer application, the N losses via runoff could be large, whichcould have a considerable effect on surface water quality. Both irrigation and N fertilizer application mustbe controlled and managed with great care to minimize N losses via runoff from agricultural land.

Phosphorus Concentration and Forms in Surface and Subsurface Drainage Water from Wetland Rice Fields in the Shaoxing Plain

Phosphorus (P) is the limiting factor for eutrophication in most freshwater ecosystems. In China, Ptransported from intensively cultivated land has been reported as an important source of P in surface waters.In this study, we investigated P concentration and forms in surface and subsurface drainage from wetland ricefields in the Shaoxing plain, Zhejiang Province, China. From selected rice fields, surface drainage sampleswere collected at rice-growing, non-growing and fertilization periods, and subsurface drainage samples atdrought and rewetting (irrigation or precipitation after 5～10 d drought period in the surface soils) and wet(drainage under long-term wet soil condition) periods. Water samples were characterized for their totalreactive P (TRP), dissolved reactive P (DRP) and particulate reactive P (PRP). Concentrations of the TRPand DRP in the surface drainage ranged from 0.08 to 1.50 and 0.06 to 1.27 mg L-1, respectively. The TRPand DRP were dependent on field operation activities, and decreased in the order of fertilization period ＞rice-growing period ＞ non-growing period. Phosphorus concentration of runoff receiving P fertilizer can bean environmental concern. The PRP concentration in the surface drainage, ranging from 0.01 to 0.57 mgL-1, accounted for 8%～78% of the TRP. Concentration of the TRP in the subsurface drainage was from0.026 to 0.090 mg L-1, consisting of 29%～90 % of the DRP and 10%～71% of the PRP. In the droughtand rewetting period, the PRP accounted for, on average, 63% of the TRP, much higher than in the wetperiod (23%), suggesting that there was transport of P in preferential flow during drainage events after ashort-term drought period in the surface soils. Therefore, P losses in particulate form may be importantin the subsurface drainage from rice fields when surface soils form cracks and favor rapid flow downwardthrough the soil profiles, suggesting the important role of water-dispersible colloid particles in mediating andco-transporting P in the subsurface drainage of rice fields.

Field effect of Cnaphalocrocis medinalis granulovirus (CnmeGV) on the pest of rice leaffolder

Rice leaffolder,Cnaphalocrocis medinalis(Guenée),has become a major pest throughout the rice cultivating areas of China and caused severe damage to rice production.Cnaphalocrocis medinalis granulovirus(CnmeGV),a naturally occurring baculovirus,is revealed as a potential microbial agent for the pest control.Field applications of CnmeGV were conducted against rice leaffolder larvae in rice paddies.CnmeGV infected the larvae not only in the current generation but also in the successive generation,resulting in a sustained infection in the larva population for at least 48 days.Under diferent concentrations of CnmeGV(7.5×1011 and 1.125×1012 occlusion body(OB)ha-1)at 30 days after spraying,larval population reduced up to 76.32%and rice leaf rolled rate kept in 15.42%.Simultaneously,CnmeGV had no impact on arthropod predators of C.medinalis,with abundances ranging from 2.39 to 3.79 per ten hills.These results revealed that CnmeGV is suitable as a bio-pesticide for rice leaffolder management in rice paddies.

N_2O Emission from Paddy Field under Different Rice Planting Modes

Measurements of N2O emissions from conventional rice cultivation （CRC）, CRC with straw mulching, system of rice intensification （SRI） and SRI with plastic film mulching were conducted through static chamber/gas-chromatography techniques. The results show that daily fluctuation of N2O emissions in jointing stage are much higher than in others. A type peak of N2O seasonal emission presented between jointing and bearing stages companying with high daily average temperature and low precipitation. Biomass and leaf stomatal conductance were observed. Total quantities of N2O emission were budgeted. The results showed that after jointing stage the average N2O emission flux of SRI with plastic film mulching increased significantly than CRC with straw mulching and SRI, the leaf stomatal conductance of those showed the same trend （p〈 0.05）. Yield and total quantity of N20 emission in CRC with straw mulching enhanced 13. 7% and 10.7% compared with those of CRC, respectively. The total quantity of N20 emissions reduced 3. 6% in SRI with plastic film mulching compared with CRC, however, the yield increase of that was not significant.

Model for Methane Emission from Rice Fields and Its Application in Southern China

A process model has been developed. The model has been used to calculate the methane emission from rice fields. The influence of climate conditions, field water management, organic fertilizers and soil types on methane emission from rice fields are considered. There are three major segments which are highly interactive in nature in the model:rice growth, decomposition of soil organic matter and methane production, transport efficiency and methane emission rate. Explicit equations for modeling each segment mentioned above are given. The main results of the model are: 1. The seasonal variation of methane emission of the model output agrees with that of field experiments. The deviation of seasonal average methane emission rate between modeled value and experimental data is about 10%. 2. In the whole rice growing period, model output is similar to experimental data in the seasonal variation of transport ability of rice plant. 3. Soil organic matter content and soil physics and chemistry are major factors that determine the total season average emission rate, while soil temperature controls the temporal variation of methane emission from rice fields.

Control Efficiency and Crop Safety of 20% Cyhalofop-butyl WP on Grass Weeds in Direct Seeded Rice Fields

The purpose was to define the control efficiency and safety of 20% cy- halofop-butyl WP on grass weeds in direct seeded rice fields, in order to provide the basis for chemical weeding. This study measured Leptochloa chinensis（L.） Nees, Echinoch/oa crusgalli （L.） Beauv and other gramineous weed control efficiency with four concentrations of 20% cyhalofop-dutyl WP and 100 g/L cyhalofop-dutyl EC in direct seeded rice fields, and analyzed the yield-increasing effect and safety of rice. The results showed that 20% cyhalofop-butyl WP had a good control efficiency on grass weeds such as Leptochloa chinensis（L.） Nees, Echinoch/oa crusgalli（L.） Beauv and other grasses. The effective dosage of 90-150 g/hm2 was over 90.7% on Lep- foch/oa chinensis（L.） Nees and the comprehensive control effect of the grass weeds was above 86.7%, which was basically consistent with 100 g/L cyhalofop-dutyl EC. Furthermore, 20% cyhalofop-dutyl WP was high security for direct seeded rice fields. The yield of rice was increased by 10.18%-11.22% after spraying herbicide. There- fore, 20% of cyhalofop-dutyl WP can be used as a special herbicide for controlling Leptochloa chinensis（L.） Beauv in direct seeded rice fields, and has a good applica- tion prospect.

Greenhouse Gas Emissions from Northeast China Rice Fields in Fallow Season

CH4, N2O and CO2 emissions from northeast Chinese rice fields were measured in the fallow season （November to March） to investigate the effects of freezing-thawing on the emissions. Both CH4 emission from and atmospheric CH4 oxidation by the soil occurred, but the flux was small. During the fallow season, rice fields acted as a minor source of atmospheric CH4, which accounted for about 1% of the CH4 emission during the rice growing period. The field was also a substantial source of atmospheric N20, which ranged between 40 to 77 mg m-2 and eu=counted for 40%-50% of the annual N20 emission. The largest N20 flux was observed in the thawing period during the fallow season. Laboratory incubation tests showed that the largest N20 flux came from the release of N20 trapped in frozen soil. Tillage and rice straw application （either mulched on the soil surface or incorporated in the soil） stimulated the CH4 and CO2 emissions during the fallow season, but only straw application stimulated N2O emission substantially.

Field identification of morphological and physiological traits in two special mutants with strong tolerance and high sensitivity to drought stress in upland rice(Oryza sativa L.)

The two mutants idr1-1 and 297-28, which were obtained from the radiation mutation of HD297 and IAPAR9, were used as experimental materials in this study for a 2-year(2012 and 2013) experiment about field drought resistance identification in Beijing, China. Key agronomic traits and water-related physiological indexes were observed and measured, including the leaf anti-dead level(LADL), days to heading, plant height, setting percentage, aboveground biomass, leaf water potential(LWP), net photosynthetic rate(Pn) and transpiration rate. The results showed that the mutant idr1-1 that was under drought stress(DS) conditions for 2 years had the highest LADL grades(1.3 and 2.0) among all the materials, and they were 2–3 grades stronger than the wild-type IAPAR9 with an average that was 21.4% higher for the setting percentage than the wild type. Compared with the IAPAR9 for the 2-year average delay in the days to heading and the reduction rates in the plant height, setting percentage, and aboveground biomass under DS compared with the well-watered(WW) treatment, idr1-1 showed 3.2% less delay and 19.1, 16.4, and 6.1% less reduction, respectively. The idr1-1 in the LWP always exhibited the highest performance among all the materials. The Pn of idr1-1 under severe and mild DS comparing with that under WW was slightly decreased and even slightly increased, respectively, leading to an average reduction rate of only 0.92%, which was 26.93% less than that of IAPAR9. Under the severe DS, idr1-1 still showed the highest value of 16.88 μmol CO2 m–2 s–1 among all the materials and was significantly higher than that of IAPAR9(11.66 μmol CO2 m–2 s–1). Furthermore, only idr1-1 had the increased and the highest transpiration rate values(7.6 and 6.04 mmol H2 O m–2 s–1) under both mild and severe DS compared with the values under WW, when the transpiration rate of all the other materials significantly decreased. By contrast, the 297-28 in terms of the LADL grade under DS was the lowest(7.0), and it was four grades weaker than its wildtype HD297 and even one grade weaker than the drought-sensitive paddy rice SN265. For the 2-year average reduction rates in aboveground biomass and plant heights under DS compared with those under the WW, 297-28 was 31.6 and 31.8% higher than HD297, respectively. Meanwhile, 297-28 showed the worst performance for the LWP, Pn, and transpiration rate. These results suggest that idr1-1 might be a superior drought tolerant mutant of upland rice found in China. It has a strong ability to maintain and even enhance leaf transpiration while maintaining a high plant water potential under DS, thus supporting a high Pn and alleviating the delay in agronomic trait development and yield loss effectively. 297-28 is a much more highly drought-sensitive mutant that is even more sensitive than paddy rice varieties. The two mutants could be used as drought tolerance controls for rice germplasm identification and the drought resistant mechanism studies in the future. idr1-1 is also suitable for breeding drought-tolerant and lodging-resistant high-yield rice varieties.

Effects of nitrogen application rate and hill density on rice yield and nitrogen utilization in sodic saline–alkaline paddy fields

Soil salinity and alkalinity can inhibit crop growth and reduce yield,and this has become a global environmental concern.Combined changes in nitrogen (N) application and hill density can improve rice yields in sodic saline–alkaline paddy fields and protect the environment.We investigated the interactive effects of N application rate and hill density on rice yield and N accumulation,translocation and utilization in two field experiments during 2018 and 2019 in sodic saline–alkaline paddy fields.Five N application rates (0 (control),90,120,150,and 180 kg N ha^(-1) (N0–N4),respectively) and three hill densities(achieved by altering the distance between hills,in rows spaced 30 cm apart:16.5 cm (D1),13.3 cm (D2) and 10 cm (D3))were utilized in a split-plot design with three replicates.Nitrogen application rate and hill density significantly affected grain yield.The mathematical model of quadratic saturated D-optimal design showed that with an N application rate in the range of 0–180 kg N ha^(-1),the highest yield was obtained at 142.61 kg N ha^(-1) which matched with a planting density of 33.3×10^(4) ha^(-1).Higher grain yield was mainly attributed to the increase in panicles m^(–2).Nitrogen application rate and hill density significantly affected N accumulation in the aboveground parts of rice plants and showed a highly significant positive correlation with grain yield at maturity.From full heading to maturity,the average N loss rate of the aboveground parts of rice plants in N4 was 70.21% higher than that of N3.This is one of the reasons why the yield of N4 treatment is lower than that of the N3 treatment.Nitrogen accumulation rates in the aboveground parts under treatment N3 (150 kg N ha^(-1)) were 81.68 and 106.07% higher in 2018 and 2019,respectively,than those in the control.The N translocation and N translocation contribution rates increased with the increase in the N application rate and hill density,whereas N productivity of dry matter and grain first increased and then decreased with the increase in N application rate and hill density.Agronomic N-use efficiency decreased with an increase in N application rate,whereas hill density did not significantly affect it.Nitrogen productivity of dry matter and grain,and agronomic N-use efficiency,were negatively correlated with grain yield.Thus,rice yield in sodic saline–alkaline paddy fields can be improved by combined changes in the N application rate and hill density to promote aboveground N accumulation.Our study provides novel evidence regarding optimal N application rates and hill densities for sodic saline–alkaline rice paddies.

ESTIMATE OF METHANE EMISSIONS FROM RICE FIELDS IN CHINA BY CLIMATE-BASED NET PRIMARY PRODUCTIVITY

Rice fields provide food for over half of the world population but are also an important source of atmospheric CH(4). Using the climate-based GIS empirical model and the meteorological data collected from 600 meteorological stations in China, with county as the basic unit, the net primary productivity (NPP) of rice fields in China in 1990, 1995, 1998, and 2000 were estimated to be in the range from 202.19x10(12)g C in 1990 to 163.46x10(12)g C in 2000. From the measured data of the factors affecting CH(4) emission and NPP, the conversion ratio of the NPP into CH(4) emission for the rice fields of China was determined to be 1.8%. Using this ratio and estimated NPP, the CH(4) emissions from rice fields of China in 1990, 1995, 1998, and 2000 were estimated to be 7.24x10(12), 6.31x10(12), 6.77x10(12) and 5.85x10(12)g CH(4), respectively.

Field Efficacy Trial and Optimum Control Period of Rice False Smut(Ustilaginoidea virens) in Single Cropping Middle-late Rice

[Objective]The paper was to study optimum chemical agents and control periods against rice false smut( Ustilaginoidea virens) in single cropping middle-late rice. [Method]Taking chemical agents( triadimefon,armure,Jinggangmycin) as main treatments and spraying periods( within 7 d before initial heading stage,within 7 d before initial heading stage + initial heading stage,initial heading stage) as assisted treatments,the field efficacy trial and optimum control period of U. virens in single cropping middle-late rice were studied using Huanghuazhan and Jinnongsimiao as experimental materials in 2013. [Result] Three chemical agents,triadimefon,armure,Jinggangmycin,extremely reduced diseased panicle rate and disease index of U. virens,but there was no significant difference among three chemical agents. Spraying period did not have significant impact on diseased panicle rate and disease index of U. virens,whereas spraying within7 d before initial heading stage and during initial heading stage had relatively good control effect. Yield increased significantly after application of three chemical agents,and armure led to greater increase. The reason for yield increase was that seed setting rate was significantly increased,and the number of filled grains per panicle was significantly increased. Although spraying period influenced yield,the difference was not significant. [Conclusion] Triadimefon,armure and Jinggangmycin had good control effects against U. virens in single cropping middle-late rice,of which armure had better control effects. Spraying chemical agents increased seed setting rate,and further increased the number of filled grains per panicle and yield. Spraying within 7 d before initial heading stage and during initial heading stage had relatively better control effect against U. virens.

Methane emission in a rice field of Thailand

In this study, emission of methane have been measured in a Thai rice field. Clear patterns of diurnal variations of methane emission have been observed and were found to follow the diurnal variation of the soil temperature. A detailed explanation was given for explaining the occurrence of a methane emission peak at night.The effects of urea fertilization and field draining on methane emissions were discussed. Methane emission from Thai rice fields is estimated to be 3. 32 Tg CH_4(2. 49 Tg CH_4-C) each year , contributing about 3. 4% to global methane budget due to rice cultivation.

Assessment of rice fields by GIS／GPS-supported classification of MODIS data

The new Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite image offers a large choice of opportunities for operational applications. The 1-km Advanced Very High Resolution Radiometer (AVHRR) image is not suitable for retrieval of field level parameter and Landsat data are not frequent enough for monitoring changes in crop parameters during the critical crop growth periods.A methodology to map areas of paddy fields using MODIS,geographic information system (GIS) and global position system (GPS) is introduced in this paper. Training samples are selected and located with the help of GPS to provide maximal accuracy.A concept of assessing areas of potential cultivation of rice is suggested by means of GIS integration. By integration of MODIS with GIS and GPS technologies the actual areas of rice fields in 2002 have been mapped. The classification accuracy was 95.7% percent compared with the statistical data of the Agricultural Bureau of Zhejiang Province.

Production Benefits of Double-Cropping Rice Under Optimized Application of Nitrogen and Potassium Fertilizers Combined with Chinese Milk Vetch and Straw Co-Returning to Fields

In order to explore the technology and effects of reducing nitrogen and potassium fertilizer applications in double-cropping rice,a field plot experiment was conducted to study the effects of optimized application of nitrogen and potassium fertilizers combined with returning Chinese milk vetch and straw to fields on yield,fertilizer utilization efficiency,net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO_(2) concentration(Ci),chlorophyll content(SPAD value)and soil physical and chemical properties in late rice harvest period.The results showed that the optimized application of nitrogen and potassium fertilizers combined with the integrated technology of Chinese milk vetch and straw co-returning to the field could enhance the photosynthetic efficiency of double-cropping rice,increase rice yield,and enhance soil biological activity,especially T4 treatment involving the returning of Chinese milk vetch and straw to the field instead of 30%nitrogen fertilizer achieved the highest rice yield,fertilizer use efficiency,net photosynthetic rate and soil biological activity.Compared with the conventional fertilization treatment T2,the total rice yield of T4 treatment increased by 4.1%,among which the early rice and late rice increased by 6.3%and 2.4%,respectively;Pn,Gs and SPAD values of flag leaves at full heading stage significantly increased,and the contents of soil active organic carbon,alkali hydrolyzed nitrogen,available phosphorus and readily available potassium significantly increased.

Effects of Winter Planting Milk Vetch on Yield and PartialProductivity of Nitrogen Fertilizer of Machine-transplantedDouble-cropping Rice under Straw Returning to the Field

From 2017 to 2018,the effects of winter planting of milk vetch on yield and partial productivity of nitrogen fertilizer of machine-transplanted double-cropping rice under straw returning were studied in Ningxiang city,Hunan Province.The results showed that the dry matter accumulation,effective panicle,yield and partial productivity of nitrogen fertilizer in the stem,leaf,panicle and aboveground parts of early and late rice treated with winter planting milk vetch and straw returning were signi ficantly higher than those treated with straw returning only.Among them,the effective panicles of early and late rice increased by 2.58%,3.18%(2017)and 5.22%,6.32%(2018),respectively.Yield increased by 11.85%,10.07%(2017)and 12.42%,10.92%(2018),annual partial productivity of nitrogen fertilizer increased by 10.90%(2017)and 11.66%(2018),respectively.In conclusion,winter planting milk vetch under straw returning is beneficial to increase dry matter accumulation,rice yield and partial productivity of nitrogen fertilizer in mechanized double cropping rice.

Study of Dynamics of Floodwater Nitrogen and Regulation of Its Runoff Loss in Paddy Field-Based Two-Cropping Rice with Urea and Controlled Release Nitrogen Fertilizer Application

The article deals with the effects of urea and controlled release nitrogen fertilizer （CRNF） on dynamics of pH, electronic conductivity （EC）, total nitrogen （TN）, NH4^＋-N and NO3 -N in floodwater, and the regulation of runoff TN loss from paddy field-based two-cropping rice in Dongting Lake, China, and probes the best fertilization management for controlling N loss. Studies were conducted through modeling alluvial sandy loamy paddy soil （ASP） and purple calcareous clayey paddy soil （PCP） using lysimeter, following the sequence of the soil profiles identified by investigating soil profile. After application of urea in paddy field-based two-cropping rice, TN and NHa＋-N concentrations in floodwater reached peak on the 1st and the 3rd day, respectively, and then decreased rapidly over time; all the floodwater NO3--N concentrations were very low; the pH of floodwater gradually rose in case of early rice within 15 d （late rice within 3 d） after application of urea, and EC remained consistent with the dynamics of NH4^＋-N. The applied CRNF, especially 70% CRNF, led to significantly lower floodwater TN and NH4^＋ concentrations, pH, and EC values compared with urea within 15 d after application. The monitoring result for N loss due to natural rainfall runoff indicated that the amount of TN lost in runoff from paddy field- based two-cropping rice with urea application in Dongting Lake area was 7.47 kg ha^-1, which accounted for 2.49% of urea- N applied, and that with CRNF and 70% CRNF application decreased 24.5 and 27.2% compared with urea application, respectively. The two runoff events, which occurred within 20 d after application, contributed significantly to TN loss from paddy field. TN loss due to the two runoffs in urea, CRNF, and 70% CRNF treatments accounted for 72, 70, and 58% of the total TN loss due to runoff over the whole rice growth season, respectively. And the TN loss in these two CRNF treatments due to the first run-off event at the 10th day after application to early rice decreased 44.9 and 44.2% compared with urea, respectively. In conclusion, the 15-d period after application of urea was the critical time during which N loss occurred due to high floodwater N concentrations. But CRNF decreased N concentrations greatly in floodwater and runoff water during this period. As a result, it obviously reduced TN loss in runoff over the whole rice growth season.

Research on Greenhouse Gases Emission in Rice Fields at County Level

[ Objective] The study aimed to analyze greenhouse gases emission in rice fields at county level. [ Method] Based on GIS platform of soil system and greenhouse gas emission model, CH4 and N20 emission in rice fields of Chaohu City during 1990 -2009 were studied by using rice yield, fertilizer, climate and other data. [ Result] From 1990 to 2009, annual emission of CH4 emission in rice fields of Chaohu City varied from 6.47 to 11.67 Gg, and rice area, yield and the rate of straw returning to fields were the main factors influencing CH4 emission. For instance, when the rate of straw returning to fields rose to 30% and 45% respectively, CH4 emission increased by 14.4% and 27.4% separately. Annual emission of N20 in rice fields of Chaohu City from 1990 to 2009 was 0.119 -0.217 Gg. N20 emission rose slowly during 1990 -1998, then it enhanced fast and greatly as the rapid increase of chemical fertilizer and manure in their application after 1998; it reached the maximum value in 2000, then showed a decreasing trend after 2000. Thus, controlling nitrogen input and improving the utilization rate of nitrogenous fertilizer were the fundamental ways to decrease N20 emission in rice fields. [ Conclusion] The research could provide scientific references for the establishment of measures to reduce greenhouse gases emission in rice fields.