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.

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.

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.

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.

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.

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.

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.

Notable effects on comprehensive techniques of man-made biosphere in rice fields

Studied by Mr. LIU Zhongzhu, ex Chairman of Fujian Academy of Agri Sciences, a combined technique of man—made biosphere in rice fields deserves notice. The research indicated that using man—made biosphere in rice fields can enrich soil, reduce the infects of diseases, insects and weeds, economize the use of pesticide and herbicide, decrease green house effect, and improve atmosphere. As tested, the yield for rice is usually 10500—12000 kg/ha, for fish is usually 2250—3250 kg/ha. Again, about 50%—60% fertilizer and 30%—50% pesticide can be saved. The net income increased $ 1,080—1,800 per ha.

The Program of Fish Culture in rice fields has been developed in Zhejiang Province

1996 is the first year for realizing the object of fish culture in 66,600 ha of rice field in Zhejiang Province. The provincial government has appropriated $ 24,000 per ha for starting capital. Starting from this year, counties with the tradition of fish culture in rice fields as Youngjia and Qingtian have put stress on popularizing the new technique of fish culture in ditches and puddles to raise the yield for per unit area. In areas of Central Zhejiang and North Zhejiang with hilly land and plain area with double—season rice, people have changed traditional fish varieties into special and excellent fish varieties.

Developing a two-decadal time-record of rice field maps using Landsat-derived multi-index image collections with a random forest classifier:A Google Earth Engine based approach

Historic maps showing the temporal distribution of rice fields are important for precision agriculture,irrigation optimisation,forecasting crop yields,land use management and formulating policies.However,mapping rice felds using traditional ground surveys is impractical when high cost,time and labour requirements are considered,and the availability of such detailed records is limited.Although satellite remote sensing appears to be a viable solution,conventional segmentation and classification methods with spectral bands are often unable to contrast the distinct characteristics between rice fields and other vegetation classes.To this end,we explored a novel,Google Earth Engine(GEE)based multiindex random forest(RF)classification approach to map rice fields over two decades.Landsat images from 2000 to 2020 of two Sri Lankan rice cultivation districts were extracted from GEE and a multi-index RF classification algorithm was applied to distinguish the rice fields.The results showed above 80%accuracy for both training and validation,when compared against high spatial resolution Google Earth imagery.In essence,multi-index sampling and RF together synergised the compelling classifcation accuracy by effectively capturing vegetation,water(ponding)and soil characteristics unique to the rice felds using a single-click approach.The maps developed in this study were further compared against the MODIS land cover type product(MCD12Q1)and the corresponding superior statistics on rice fields demonstrated the robustness of the proposed approach.Future work seeking effective index combinations is recommended,and this approach can potentially be extended to other crop analyses elsewhere.

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.

Factors Influencing Indigenous Rice Protection in the Yuanyang Terraced Rice Fields of China

Indigenous rice has maintained the survival of local people for more than a thousand years in the Yuanyang terraced rice fields of southern Yunnan, China. It is the foundation for long-term stable development of local agriculture and food security and its unique and irreplaceable characteristics give the terraces value. The status of indigenous rice resources is threatened by serious loss, so a better understanding of rice diversity and the factors that influence rice variety protection is conducive to policy. Here, we investigate the planting and conservation situation of indigenous rice, analyze factors impacting the protection and loss of traditional rice varieties, and construct an indigenous rice protection influence index system. Controllable factors which have special meaning to the maintenance and management of local rice are identified and corresponding strategies for the protection and maintenance of indigenous rice are discussed.

Development of specific chromosomal DNA pool for rice field eel and their application to gene mapping

The chromosomes 1, 3, 5, 6, 7,10 and 12 of rice field eel (Monopterus albus Zuiew) have been microdissected successfully from meiosis I diakinesis spreads by using glass microneedlc under an inverted microscope. And the DOP-PCR products of the single chromosome dotted on the nylon membrane as 'specific chromosomal DNA pool', have been hybridized with 6 probes to map these genes. The mapping results show that Zfa has been mapped to chromosome 1, rDNA to chromosomes 3 and 7, both Gh and Pdegγto chromosome 10, Hsl to chromosome 5 and Hox genes have been detected on chromosomes 1, 3, 6 and 10 meantime. It has initiatively been suggested that chromosome 10 of rice field eel might possess the commom conserved synteny to that on chromosome 17 of human, chromosome 11 of mouse, chromosome 12 of pig and chromosome 19 of bovine. And so chromosome 3 of rice field eel might also contain the commom conserved synteny to that on chromosome 2 of zebraf-ish. Our study is an attempt to establish a new and feasible

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.

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.

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.

Effects of Nitrogen Dosage on the Yield and Nitrogen Use Efficiency of Machine Transplanted Rice Using Dry Soil Preparation in Rice Paddy Field

[Objective] The aim was to analyze the effects of nitrogen dosage on the yield and nitrogen use efficiency of machine transplanted rice using the technology of dry soil preparation in rice paddy field. [Method] With conventional Japonica rice cultivar Shengdao 18 as the study material, the effect of nitrogen dosage on stem and tillers dynamics, yield components and nitrogen use efficiency were investigated using the technology of dry soil preparation in rice paddy field. [Result] The highest yield was 10 957.20 kg/hm^2 as the nitrogen application was 315.00 kg/hm^2. Meanwhile, the roughness ratio, grain-straw ratio and nitrogen use efficiency remained at a higher level. Low nitrogen application could not obtain high yield. In contrast, high nitrogen application quantity led to a significant decline in nitrogen use efficiency. [Conclusion] The study could provide a scientific basis for the further promotion of the technology of dry soil preparation in rice paddy field.