Quantitative risk assessment for reclaimed wastewater irrigation on paddy rice field in Korea

Water shortage has become an important issue for Korean agriculture. Korea suffers from a limited agricultural water supply, and wastewater reuse has been recommended as an alternative solution. This study examined the concentrations of toxic heavy metals and Escherichia coli in a paddy rice field irrigated with reclaimed wastewater to evaluate the risk to farmers. Most epidemiological studies have been based on upland fields, and therefore may not be directly applicable to paddy fields. In this study, a Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion. The risk value increased significantly after irrigation and precipitation. The results of the microbial risk assessment showed that risk values of groundwater and reclaimed wastewater irrigation were lower than the values of effluent directly from wastewater treatment plants. The monitoring results of heavy metals for each irrigated paddy fields did not show specific tendency. A risk assessment for toxic heavy metals was performed according to various exposure pathways; however, the results of the carcinogenic and noncarcinogenic risk estimation showed that the risk from reclaimed wastewater-irrigated paddy fields was the lowest.     

Integrated nutrient management for environmental-friendly rice production in salt-affected rice paddy fields of Saemangeum reclaimed land of South Korea

This study was conducted in an attempt to determine the proper nitrogen and phosphorus application levels, nitrogen split application ratio, and application method for environmental-friendly rice production in a salt-affected rice paddy field, which was located in the Saemangeum reclaimed tidal belt on the western coast of South Korea, between April 1, 2003 and October 10, 2004. All treatments were replicated three times in a randomized block design (5 m × 4 m plot) with 11 treatments (total 33 plots). We designed three treatments for the evaluation of reasonable application levels of nitrogen and phosphorus fertilizers (A1–A3); five treatments to evaluate the nitrogen split application system (T1–T5); and three treatments to determine the proper application for chemical fertilizer (M1–M3). There was no significant difference of amylose and protein content among the application levels, application methods, and nitrogen split application ratios (P < 0.05). No significant differences in grain yield and yield components of rice were observed among the different application levels, application methods, and nitrogen split application ratios (P < 0.05). In order to save labor in agricultural households, preserve or enhance the grain quality of rice, and reduce nutrient losses, we determined that the optimum application level of nitrogen fertilizer was 140 kg ha⁻¹; the application split ratio of nitrogen fertilizer at four different periods was 40% for basal fertilization, 20% for maximum tilling stage, 30% for the panicle formation stage, and 10% for the booting stage; and the best application methods were deep layer application and whole layer application.     

Surface and subsurface losses of N and P from salt-affected rice paddy fields of Saemangeum reclaimed land in South Korea

The present study was carried out to evaluate nutrient losses that occur during the course of agricultural activity from rice paddy fields of reclaimed tidal flat. For this study, we chose a salt-affected rice paddy field located in the Saemangeum reclaimed tidal area, which is located on the western South Korean coasts. The plot size was 1,000 m² (40 m × 25 m) with three replicates. The soil belonged to the Gwanghwal series, i.e., it was of the coarse silty, mixed, mesic type of Typic Haplaquents (saline alluvial soil). The input quantities of nitrogen and phosphorus (as chemical fertilizer) into the experimental rice paddy field were 200 kg N ha⁻¹ and 51 kg P₂O₅ ha⁻¹ per annum, and the respective input quantities of each due to precipitation were 9.3–12.9 kg N ha⁻¹ and 0.4–0.7 kg P ha⁻¹ per annum. In terms of irrigation water, these input quantities were 4.5–8.2 kg N ha⁻¹ and 0.3–0.9 kg P ha⁻¹ per annum, respectively. Losses of these nutrients due to surface runoff were 22.5–38.1 kg N ha⁻¹ and 0.7–2.2 kg P ha⁻¹ for the year 2003, and 26.8–29.6 kg N ha⁻¹ and 1.6–1.9 kg P ha⁻¹ for the year 2004, respectively. Losses of these nutrients due to subsurface infiltration during the irrigation period were 0.44–0.67 kg N ha⁻¹ and 0.03–0.04 kg P ha⁻¹ for the year 2003, and 0.15–0.16 kg N ha⁻¹ and 0.05–0.06 kg P ha⁻¹ for 2004. When losses of nitrogen and phosphorus were compared to the amount of nutrients supplied by chemical fertilizers, it was found that 11.3–19.1% of nitrogen and 0.5–1.7% of phosphorus were lost via surface runoff, whereas subsurface losses accounted to 0.2–0.8% for nitrogen and only 0.02–0.04% for phosphorus during the 2-year study period.     

National risk assessment of irrigation on farmland near wastewater treatment plants in Korea

There are more than 130 agricultural water sources that are located near wastewater treatment plants (WWTPS) in Korea. The majority of the stream flow in these farmlands is dependent on effluent from the WWTPS during the dry season. This explains the indirect or direct reuse of effluent from WWTPs. Most of the farm workers use the effluent without any additional treatment because they have a lack of knowledge regarding water reuse. In addition, insufficient consideration is given to health and hygiene safety. This study reviewed the safety issues in these farmlands. A total of 53 farmlands located near WWTPs were investigated to determine if farm workers used effluent as irrigation water on their paddy rice fields. Total coliform, fecal coliform, Escherichia coli (E. coli), and the concentration of some heavy metals in paddy water and soils were measured. Quantitative microbial and toxic risk assessment methods were used to review the safety of wastewater irrigation. E. coli concentrations were used to estimate the microbial risk of enteric disease in the paddy fields. The microbial risk was 5.9 × 10^?4, which did not satisfy the minimum safety standards. Carcinogenic risk was 3.99 × 10^?5 and non-carcinogenic risk was 6.34 × 10^?1. These values were too high to be considered safe, even though the measurements of E. coli and some toxic metals were of short duration.     

A combined technique of floodplain storage and reservoir irrigation for paddy rice cultivation

This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety, soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is examined.     

Modeling risk analysis for rice production due to agro-climate change and uncertainty in irrigation water

Paddy and Water Environment - This study proposes a risk analysis model for quantifying the insufficient risk of rice production due to the climate change and variation in irrigation water and...     

Analysis of sample size for variables related to plant,soil, and soil microbial respiration in a paddy rice field

Pre-samplings for sample size determination are strongly recommended to assure the reliability of collected data. However, there is a certain dearth of references about sample size determination in field experiments. Seldom if ever, differences in sample size were identified under different management conditions, plant traits, varieties grown and crop age. In order to analyze any differences in sample size for some of the variables measurable in rice field experiments, the visual jackknife method was applied to pre-samples collected in a paddy rice field in Northern Italy, where a management typical for European rice was conducted. Sample sizes for 14 variables describing plant features (plant density, spikelet sterility, biomass, carbon and nitrogen concentration for the different plant organs and for the whole plant) and for 12 variables describing physical and chemical soil features (texture, pH, water holding capacity, soil organic matter, total carbon and nitrogen concentration, mineral nitrogen concentration) and soil microbial activity were estimated. The elementary units of observation were a 3-plant sample and an aggregate sample of four 125 cm³ sub-samples respectively for plant- and soil-related variables. Sample sizes ranged between 15 and 27 for plant-related variables and between 5 and 6 for soil variables. Relating to plant features, remarkable differences in sample size were observed in carbon concentration values of different plant organs, probably due to maintenance respiration. Homogeneity among sample sizes for soil variables could be explained by the capability of aggregate samples in capturing a big part of the total variance. This study underlines importance of carrying out pre-samplings aiming at sample size determination for different variables describing the cropping system.     

The assessment of rill irrigation and perforated pipes for Lowland paddy rice under the system of rice intensification (SRI)

Paddy and Water Environment - Irrigated paddy rice needs new strategies and tools to improve water use efficiency and productivity by applying just enough to sustain production with huge savings on...     

A preliminary investigation for Cu distribution in paddy soil and rice plants in contaminated paddy fields

Paddy and Water Environment - The soil sample of a paddy field was found to be contaminated by copper (Cu). The application of wastewater as the nitrogen fertilizer was identified as the cause in...     

Effects of irrigation method and rice straw incorporation on CH4 emissions of paddy fields in Northeast China

Paddy and Water Environment - Irrigation methods and rice straw incorporation (RSI) are two major factors influencing CH4 emissions from paddy fields. However, their effects have never been studied...     

Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan’s average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T_2 cm, T_3 cm, T_4 cm and T_5 cm) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m³) was achieved in T_5 cm and the lowest in T_2 cm (1.62 kg/m³). The highest total water productivity, (0.75 kg/m³) and irrigation water productivity (1.40 kg/m³) was achieved in T_2 cm. The total amount of water saved in T_4 cm, T_3 cm and T_2 cm was 20, 40, and 60%, respectively. Weekly application of T_4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T_5 cm. Thus, we assert that the weekly application of T_4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.     

A novel method for controlling rice blast disease using fan-forced wind on paddy fields

Rice blast disease is one of the obstacles of rice production not only in Japan but throughout rice producing countries. The effects of fan-forced wind on the incidence of rice blast disease were studied in two successive seasons. Electric fans (5 KW, 110-cm blade diameter) set on the ridge of paddy fields at a height 5 m from the ground level were used to artificially generate wind. In season 1, the fan operated twice daily for 30 min periods at 11:00 pm and 4:00 am from June 15 to September 1. The blocks of the paddy fields were divided into 6 zones according to wind speed and distance from the fan. The wind speed ranged from 2.0 to >7.3 m/s. The incidence of both rice leaf and panicle blast was significantly lower in the zones receiving wind between 2.6 and 7.3 m/s; however, the zone that received a velocity >7.3 m/s was severely affected by leaf and panicle blast. The zone that received the a wind speed of 2.6 m/s or lower exhibited an inefficient reduction of leaf and panicle blast disease, but it was better than in the control fields. In season 2, a wind-forced fan was applied from June 16 to September 9, with the velocity adjusted between ca. 3.0 and 6.0 m/s. The incidence and severity of leaf and panicle blasts (chuff, rachis-branch and neck blast) were efficiently reduced in the wind-treated fields. Fan-forced wind was more effective than the application of conventional chemical fungicides for controlling rice blast disease. These data demonstrate the potential of fan-forced wind for controlling rice blast disease.     

High yield and nutritional quality of rice for animal feed achieved by continuous irrigation with treated municipal wastewater

Paddy and Water Environment - Two consecutive pilot-scale experiments were conducted to investigate the potential reuse of treated municipal wastewater (TWW) as an irrigation source for cultivating...     

Experimental study on radiation utilization efficiency and soil temperature in paddy field with different irrigation methods in Northeast China

Paddy and Water Environment - In order to investigate the radiation utilization efficiency and soil temperature with different irrigation methods in cold region and black glebe, northeast, China,...     

Water quality monitoring and multivariate statistical analysis for rural streams in South Korea

South Korea is located in the Asian monsoon region, and paddy rice farming is one of the important agricultural activities, which may contribute to the non-point source pollution of inland water bodies along with rainfall runoff. The status of water quality in rural streams located throughout South Korea was examined in this study by water quality monitoring and statistical analysis. Totally six surveys were conducted in 2003 and 2005 to monitor 300 streams located in rural subwatersheds; these streams are affected by agricultural activities and water supply for agricultural practices. The monitoring was performed at the terminal point of each subwatershed. In each study year, the streams were monitored in the three hydrological periods (April, July, and October) to observe differences in the impacts of agricultural activity and rainfall pattern. During the surveys, 15 water quality parameters were measured and interpreted using multivariate statistical methods including factor analysis and cluster analysis. Results show that the water quality of the rural streams monitored in this study appeared to meet the Korean water quality criteria for agricultural use, which are 8.0 and 100 mg/L for biochemical oxygen demand and suspended solids, respectively. In terms of organic contamination and suspended solids, the best stream water quality was observed in October compared to other periods. This can be attributed to the fact that October follows the rice-harvesting period and has low rainfall; thus the streams are probably less affected by agricultural activities and surface runoff. The three hydrological periods did not show much variation in the nitrogen and phosphorus parameters related to stream water nutrient conditions. Factor analysis indicates that the first five factors for April explained about 67% of the total sample variance. In July, the first four factors explained about 60% of the total variance, while the first four factors for October explained about 65%. Cluster analysis reveals that the streams could be divided into four groups in April and October and five groups in July. The box-and-whisker plots of the physicochemical variables indicate that Group A had the best water quality among the groups. This study demonstrates that the rural stream water quality of South Korea in the Asian monsoon region can be greatly affected by agricultural activities such as paddy rice farming and rainfall patterns.     

Future potential impacts of climate change on agricultural watershed hydrology and the adaptation strategy of paddy rice irrigation reservoir by release control

This study is to assess the climate change impact on the temporal variation of paddy rice irrigation reservoir water level from the future evaluated watershed inflow, and to suggest an adaptation method of the future reservoir water level management for stable water supply of paddy irrigation demands. A 366.5 km² watershed including two irrigation reservoirs located in the upper middle part of South Korea was adopted. For the future evaluation, the SLURP model was set up using 9 years daily reservoir water level and streamflow records at the watershed outlet. The average Nash-Sutcliffe model efficiencies for calibration and validation were 0.69 and 0.65, respectively. For the future climate condition, the NIES MIROC3.2 hires data by SRES A1B and B1 scenarios of the IPCC was adopted. The future data were downscaled by applying Change Factor statistical method through bias-correction using 30 years past weather data. The results of future impact showed that the future reservoir storages of autumn and winter season after completion of irrigation period decreased for 2080s A1B scenario. Considering the future decrease of summer and autumn reservoir inflows, the reservoir operation has to be more conservative for preparing the water supply of paddy irrigation, and there should be a more prudent decision making for the reservoir release by storm events. Therefore, as the future adaptation strategy, the control of reservoir release by decreasing in August and September could secure the reservoir water level in autumn and winter season by reaching the water level to almost 100% like the present reservoir water level management.     

A comparative analysis of two paddy irrigation schemes under contrasting water management of participatory and top-down systems in Uganda

Paddy and Water Environment - This research focused on two large-scale paddy irrigation schemes of Doho (1000&nbsp;ha) and Lwoba (700&nbsp;ha) in Uganda for a comparative analysis of major...     

稻田油菜机械直播高产栽培技术研究初报

以湘杂油5号为材料,用小型耕整机牵引"署华MLB-100型多功能播种机"进行稻田直播油菜试验.结果表明,用机械直播栽培油菜具有减轻劳动强度、降低生产成本、提高经济效益等优点.其高产栽培关键措施是:前作水稻开好丰产沟,适时播种,播种量3.75～4.5kg/hm2;精心操作,不漏播;利用直播机集中施足基肥,及时追肥,促冬发;化学除草;施用硼肥.