Fertilization management of paddy fields in Piedmont (NW Italy) and its effects on the soil and water quality

The fertilization management of the rice crop in Piedmont was analyzed at a regional scale, and the agronomic and environmental sustainability of the actual fertilization strategy of rice was evaluated through the analysis of its effect on the soils and waters quality. On average, a total amount of 127 kg ha⁻¹ of N, 67 kg ha⁻¹ of P₂O₅ and 161 kg ha⁻¹ of K₂O were supplied to the rice crop. In most cases N and P fertilization was rather well balanced with crop removal. The N balance was in the range ±50 kg for 77% of the surface. The low concentration of N in the groundwater reflected the small N surplus. P fertilization resulted to be smaller than removal for 53% of the surface. Nevertheless, the soil extractable P was very high, probably because of former higher P inputs. This resulted in a high concentration in water courses and aquifers. The K fertilization was excessive (surplus >100 kg ha⁻¹) for 53% of the surface, but most soils showed a low K content. K is probably contributing to nutrient leaching to a great extent. The average soil organic matter (SOM) content of paddy fields was higher than that of normally-cultivated soils in Piedmont, and the C/N was higher, owing to the low mineralization rate in waterlogged conditions. The SOM content was in relation with the management of the crop residues, as the tradition of burning straw after harvest was still widespread on 65% of the paddy surface.     

Model development for surface drainage loading estimates from paddy rice fields

A field experiment was performed at two Korean research sites to evaluate water and nutrient behavior in paddy rice culture operations for 2 years. One site was irrigated with groundwater, whereas the other site was irrigated with surface water. Both sites received average annual rainfall of about 1,300 mm, and about 70–80% of it was concentrated during July–September coinciding with rice growing season. Although most of the nutrient outflow was attributed to plant uptake, nutrient loss by surface drainage was substantial. The simplified computer model, PADDIMOD, was developed to simulate water and nutrient behaviors in the paddy rice field. The model predicts daily ponded water depth, surface drainage, and nutrient concentrations. It was formulated with a few equations and simplified assumptions, but its application and a model fitness test indicated that the simulation results reasonably matched the observed data. It is a simple and practical planning model that could be used to evaluate nutrient loading from paddy rice fields alone or in combination with other complex watershed models. Further validation might be required for general application of the PADDIMOD to the simulation of paddy rice fields with various agricultural environments.     

Evaluation of N and P mass balance in paddy rice culture along Kahokugata Lake, Japan, to assess potential lake pollution

Kahokugata Lake, a closed lake, has been subject to eutrophication. This research was conducted to clarify the actual phenomena and evaluation of the discharges of N and P from paddy test fields in the lowlands into Kahokugata Lake. A comprehensive mass balance of N and P was obtained from 4 years of study. About N, the mean value of harvested unhulled rice (79.9 kg/ha) was greater than mean controlled release fertilizer inputs (56.7 kg/ha). Other inputs and outputs include N in atmospheric acid deposition (21.4 kg/ha) and N fixation–denitrification (9.2 kg/ha). The rice straw recycled after harvest was balanced by straw produced in the succeeding year. The runoff and percolation losses discharged into the lake was 11.3 kg/ha, (8.6% of total inputs). Since the rice harvested was consumed domestically, which taking out from the farmland and, therefore, nitrogen pollutant into the lake was becoming small, paddy rice at this site is considered an “anti-polluting, purifying or cleansing” crop. The P content in harvested rice (39.4 kg/ha) was balanced by fertilizer inputs (36.4 kg/ha). Previous studies examining inflow–outflow relationships without considering a comprehensive mass balance may lead to erroneous conclusions. Our findings indicate paddy rice in lowlands could be an environmentally friendly crop and can play an important role in reducing pollution of lakes, and therefore should be considered in land use planning.     

Potential conflicts for the reuse of rice husk in Thailand

This study aims to investigate the impact of rice-husk power generation on agricultural uses of rice husk and its ash. We conducted case studies at a rice-husk power plant and organic farming groups in northeast Thailand. The case study on a rice-husk power plant showed that rice husk was useful in generating electricity without consuming fossil fuel, while husk ash, the by-product, could be utilized as silicate supplement for farmland soils. The case study on organic farming groups indicated that rice husk was one of the indispensable materials in conducting organic farming with locally available resources. On the basis of these findings, an analytical study on possible husk uses in Thailand was conducted, in which three potential major uses of rice husk were considered: i.e. (1) fuel use inside rice mills followed by husk-ash reuse, (2) fuel use at power plants followed by husk-ash reuse, and (3) direct reuse of husk for compost production. The result indicated that there would be conflicting demands for rice husk among those uses in the future. Therefore, there needs to be a strategy for balancing husk uses among them.     

Nitrous oxide emission measurement with acetylene inhibition method in paddy fields under flood conditions

Nitrous oxide (N₂O) emission from flooded rice paddy fields was continuously measured by the closed chamber method at an experimental plot in Thailand for a whole cultivation period. To characterize the N₂O emission with regard to the denitrification N loss, the C₂H₂ inhibition method was applied. Flood water on the soil greatly suppressed the N₂O emission. The N₂O emission was mitigated considerably by even a thin film of the flood water. The overall average N₂O emissions under flood conditions for one crop season (83 days) at the control site and the C₂H₂ treated site were 10.3 and 11.8 μg N m⁻² h⁻¹, respectively. The N₂O emission from the C₂H₂ treated site was consistently higher than that from the control site and the N₂O emission from both sites followed the same diurnal and seasonal variation pattern, indicating the effect of denitrification inhibition by the supplied C₂H₂. The N₂O emission enhanced along with temperature increase when NO₃–N concentration in the soil water was above 0.4 mg N l⁻¹ and soil temperature was above 24°C, suggesting specific temperature influence over the emission. The increase in NO₃–N concentration and temperature in the soil affected only the N₂O emission while the difference in the emission at the C₂H₂ treated site and the control site was not so much affected. It was suggested that most of the actively produced N₂O under higher NO₃–N concentration and temperature would likely to quickly emit to the atmosphere rather than to undergo further reduction to N₂.     

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.     

Convective velocity of ponded water in the vegetated paddy lysimeter

Ponded water convection kinetics should be altered by growth stages of rice plants. We investigated the convective velocity of ponded water in a vegetated paddy field. The convective velocity was measured using the equipment through use of the principle of a hot-wire anemometer, and the temperature profile of the ponded water was measured using lysimeters with and without paddy rice vegetation. The maximum convective velocity in a vegetated plot was 0.7 mm s⁻¹, slower than the maximum velocity in an unvegetated plot, which was 1.6 mm s⁻¹. The convective velocity in a vegetated plot increased slightly when the temperature of the surface water was higher than that near the soil, between 09:00 and 17:00.     

Effect of slope on surface drainage in converted rice paddy

Due to the recent regulation of rice production in Japan, it has become necessary to convert rice paddy to other field crops production. To achieve this, drainage conditions, especially for surface drainage, must be improved. We propose the introduction of a slight slope to improve surface drainage, but the optimal slope must be determined in order to prevent soil erosion caused by excessive slope, as well as increased cost. In Japan, a 0.1% slope has recently come into widespread use and, therefore, the impact on surface drainage must be quantified. In this report, observations were carried out to quantify the impact of a 0.1% slope for converted rice paddy and the following results were obtained: (1) An approximate 0.1% slope enables improvement of 46% of the soil surface saturation area as compared to flat conditions about 10 h after inundation; and (2) Inundated water remains on a flat field, while it moves downward toward the end on a sloped field. These results give a basis for determining a slope on a rice paddy in terms of surface drainage improvement. However, the optimal slope should be decided from various perspectives including engineering, agronomy, and economics etc.     

Nutrient management for rainfed lowland rice in northeast Thailand

Average grain yields of rainfed lowland rice in northeast Thailand are the lowest in the region, and they barely changed in the past decade. Improved fertilizer management is one of the few options to enhance cropping system productivity but related results from previous studies were often disappointing and sometimes contradictory, possibly due to the large variability of soil and water resources. Therefore, the objectives of this study were to develop a site-specific nutrient management approach, and to propose a related decision tool for farmers. For this purpose, we conducted on-farm experiments in Kumpa-Oong Village, Roi Et Province, during the 2003–2005 cropping seasons. Tested fertilizer treatments were designed based on topographic field position. A comparison of soil characteristics between lower and upper fields revealed significantly higher soil fertility for lower fields (higher pH, TOC, TSN, CEC, clay, and silt content; lower sand content). Across seasons and treatments, grain yields were higher in the valley bottom (VB; 2.82 t ha⁻¹) than on upper and middle terraces (UMT; 1.68 t ha⁻¹). In all seasons, significant fertilizer treatment effects were detected only in UMT fields. But the comparison of treatment effects in individual fields and in both toposequence positions showed that the limited average fertilizer response was mainly caused by low or even negative responses in fields with a higher control yield, i.e., with higher indigenous nutrient supply. A missing or even negative fertilizer response occurred at lower control yields in UMT fields, most probably because attainable yields in these fields were lower as a result of limited water resources. Thus, site-specific fertilizer recommendations need to take toposequence and the field-specific indigenous nutrient supply into account. Based on these results, we proposed a decision tool that helps farmers to choose the most adequate fertilizer treatment for their fields, based on their knowledge of specific field characteristics. On-farm testing of the proposed decision tool is the next step to show whether this approach is acceptable to farmers and can contribute to higher resource-use efficiency and system productivity.     

Experimental study on the influence of percolation patterns on the removal of soluble elements in stratified alluvial-soil paddy fields for rice

The dynamics of substances in percolating water was investigated using paddy field models planted with rice and fertilized. Percolation patterns mimicking the plow layer and plow sole were set up in these models for closed system percolation. In one of these models, in which the groundwater level was kept high, the percolation pattern of the subsoil layer was set up as closed system percolation. In another model with a lower groundwater level, the percolation pattern of the portions above and below the groundwater level was set up as open and closed system percolation, respectively.The results show that the concentrations of nitrate nitrogen and nitrite nitrogen in percolating water were higher in the upper portion of the subsoil layer with open system percolation than in the plow layer and plow sole with closed system percolation, while these concentrations tended to be lower in the lower portion of the subsoil layer with closed system percolation than in the plow layer and plow sole. Iron and manganese concentrations in the subsoil layer were higher in the portion with closed system percolation than those in the portion with open system percolation. The concentrations of bases such as calcium tended to increase with the increase in iron concentrations in soil water.     

防御寒地水稻冷害的施肥技术研究现状

冷害是水稻减产的主要原因之一,也是全世界普遍关注的问题,尤其寒地稻作区,低温冷害频繁发生。本文简要介绍了测土配方施肥、控制氮肥的施入、增施磷肥、增施钾肥、施用有机肥和微肥对防御低温冷害的作用,并对今后寒地水稻冷害防御的施肥技术方面研究提出了一些建议。     

不同形态氮肥在稻田土壤中的变化规律及对烤烟生长和烟碱含量的影响

试验于2007年在湖南农业大学进行,以烤烟K326为试验材料,围绕稻烟复种土壤的特定条件。开展不同形态氮肥对烤烟生长及品质影响和氮肥在土壤中转化的研究。结果表明：在稻田土壤中硝态氮在整个烤烟大田生长期呈逐渐下降的趋势。施用100％.铵态氮肥的烤烟前中期的生长势较强,而硝态氮与铵态氮各50％的烤烟在收获时茎围、株高、叶面积最大,干物质积累量最大。单一施用硝态氮或铵态氮的烤烟,烟叶中烟碱含量较高,而硝态氮与铵态氮各为50％的烤烟烟叶中烟碱含量较低。采用硝态氮与铵态氮各占50％配比的烤烟对氮肥的利用率较高。     

Assessment of irrigation efficiencies and water productivity in paddy fields in the lower Mekong River Basin

Improving irrigation performance is a crucial issue for agriculture and irrigation development in the Lower Mekong River Basin to secure food production for people’s livelihoods. Irrigation efficiency is the most important indicator to determine the performance of an irrigation scheme. This study looks at water management practices and irrigation efficiency in three pilot sites in the Lower Mekong River Basin: the Numhoum scheme in Laos, the Huay Luang scheme in Thailand, and the Komping Pouy scheme in Cambodia. Irrigation efficiency and water productivity were analyzed using a water balance approach at the irrigation scheme level and results in the pilot areas show efficiencies that are definitely higher using this approach than by using the classical concept. Lower water productivity was observed at pilot schemes in areas of single cropping and higher productivity in areas where multiple agricultural activities were practiced. Strict and active water management is required to control and save water to meet agricultural demand and have sufficient water to expand cultivation areas while avoiding shortages. Promoting multiple uses of water for various agricultural activities in command area will increase water productivity.

Improvement of nitrogen management in rice paddy fields using chlorophyll meter (SPAD)

Optimum rate and timing application of nitrogen (N) fertilizer are most crucial in achieving high yield in irrigated lowland rice. In order to assess leaf N status, a semidwarf rice cultivar (Khazar) was grown with different N application treatments (0, 40, 80, and 120 kg N ha⁻¹ splited at transplanting, midtillering, and panicle initiation stages) in a sandy soil in Guilan Province, Iran, in 2003. The chlorophyll meter (SPAD 502) readings were recorded and leaf N concentrations were measured on the uppermost fully expanded leaf in rice plants at 10-day internals from 19 days after transplanting to grain maturity. Regression analysis showed that the SPAD readings predicted only 23% of changes in the leaf N concentration based on pooled data of leaf dry weight (N _dw) for all growth stages. However, adjusting the SPAD readings for specific leaf weight (SPAD/SLW) improved the estimation of N _dw, up to 88%. Specific leaf weight (SLW), SPAD readings, leaf area and weight as independent variables in a multiple regression analysis predicted 96% of the N _dw changes, while SPAD readings independently predicted about 80% of leaf N concentration changes on the basis of leaf area (N _a). It seems that chlorophyll meter provides a simple, rapid, and nondestructive method to estimate the leaf N concentration based on leaf area, and could be reliably exploited to predict the exact N fertilizer topdressing in rice.     

Modeling of water and nitrogen balance in the ponded water of rice fields

A water and nitrogen balance model for the surface ponded water compartment of rice fields was developed. The model estimates the daily ponded water depth and the daily losses and the uses of NH₄–N and NO₃–N in their transformation processes. The model was applied with data obtained from two rice fields during 2005 at Thessaloniki plain in northern Greece. Significant amounts of applied irrigation water were lost with the surface runoff and deep percolation to groundwater. The gaseous losses of nitrogen (volatilization and denitrification) and nitrogen uptake by algae were the main processes of nitrogen reduction in the ponded water of rice fields. The study showed that the system of a rice field is a natural system where an important amount of influent nitrogen applied by irrigation water can be reduced. These processes decrease the possibilities of water resources contamination.     

Effect of irrigation method and N-fertilizer management on rice yield, water productivity and nutrient-use efficiencies in typical lowland rice conditions in China

Alternate wetting and drying irrigation (AWD) has been reported to save water compared with continuous flooding (CF) in rice cultivation. However, the reported effects on yield varied greatly and detailed agro-hydrological characterization is often lacking so that generalizations are difficult to make. Furthermore, it is not known how AWD modifies nutrient use efficiencies and if it requires different N-fertilizer management compared with CF. This study quantified the agro-hydrological conditions of the commonly practiced AWD and compared the impact of AWD and CF irrigations at different N-fertilizer management regimes on rice growth and yield, water productivity, and fertilizer-use efficiencies in five crop seasons in 1999 and 2000 at two typical lowland rice sites in China (Jinhua, Zheijang Province and Tuanlin, Hubei Province), with shallow groundwater tables.Grain yields varied from 3.2 to 4.5 t ha^–1 with 0 kg N ha^–1 to 5.3–8.9 t ha^–1 with farmers N-rates (150 kg N ha^–1 in Jinhua and 180 in Tuanlin). In both sites, no significant water by nitrogen interaction on grain yields, biomass, water productivity, nutrient uptakes and N-use efficiency were observed. Yield and biomass did not significantly differ (P >0.05) between AWD and CF and among N timings. The productivity of irrigation water in AWD was about 5–35% higher than in CF, but differences were significant (P <0.05) only when the rainfall was low and evaporation was high. Increasing the number of splits to 4–6 times increase the total N uptake, but not total P-uptake, and total K-uptake compared with farmers practices of two splits. Apparent Nitrogen recovery (ANR) increased as the number of splits increased, but there was no significant difference in ANR between AWD and CF. During the drying cycles of AWD irrigation, the perched water table depths seldom went deeper than – 20 cm and the soil in the root zone remained moist most of the time. The results suggest that in typical irrigated lowlands in China, AWD can reduce water input without affecting rice yields and does not require N-fertilizer management differently from continuous flooding. The results can be applied to many other irrigated lowland rice areas in Asia which have a shallow groundwater table.     

东港市水田旅生稻防除技术研究

介绍了东港地区水田旅生稻的发生及危害状况,阐述了旅生稻现有种类及生育特点。同时,分析了旅生稻发生危害的原因,并提出了综合防治技术措施。     

盘锦市水稻生产面临的问题与解决途径的探讨

针对盘锦市水稻生产存在的品种单一,化肥、农药用量较多,灌溉水定额较高,生产效率、生产效益较低等问题,提出了加快品种更新速度、优化品种布局,加强肥水管理促进水稻健康生长,合理使用化学农药综合防治病虫害,大力推广水稻生产机械化,发展复合稻作等解决问题的有效途径。     

Recent irrigation practices in the Upper East Bank of the Chao Phraya Delta

This study aims to investigate recent practices on water allocation and cultivation in the Upper East Bank of the Chao Phraya Delta in Thailand, by using data collected by RID local offices, questionnaires, and analyses of satellite images. As a result, we have identified the advantage that upstream areas of irrigation canals have enjoyed, namely the preferential water allocation over the downstream areas. This advantage was strongly associated with the intensive cropping patterns of rice: the upstream areas were estimated to conduct almost continuous rice cultivation throughout a year. In addition, the intensive rice cultivation would partly be supported by water from private shallow wells, which were mostly concentrated in the upstream areas of main canals. Those shallow wells would be used at the beginning of the dry season and in drought years, when farmers could not expect water supply from irrigation canals. The result indicated that the conjunctive use of surface and ground water would be practiced in this region.     

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.