Effect of N-fertilizer application on return flow water quality from a terraced paddy field in Northern Taiwan

Intensive use of chemical fertilizer for crops may be responsible for nitrogen and phosphate accumulation in both groundwater and surface waters. The return flow polluted by nutrients not only results in the limitation of water reuse goals but also creates many environmental problems, including algal blooms and eutrophication in neighboring water bodies, posing potential hazards to human health. This study is to evaluate the N-fertilizer application of terraced paddy fields impacting return flow water quality. Water quality monitoring continued for two crop-periods around subject to different water bodies, including the irrigation water, drainage water at the outlet of experimental terraced paddy field, and shallow groundwater were conducted in an experimental paddy field located at Hsin-chu County, Northern Taiwan. The analyzed results indicate that obviously increasing of ammonium-N (NH₄ ⁺-N) and nitrate-N (NO₃ ^?-N) concentrations in the surface drainage water and ground water just occurred during the stage of basal fertilizer application, and then reduced to relatively low concentrations (<0.1 mg/l and <3 mg/l, respectively) in the remaining period of cultivation. The experimental results demonstrate the potential pollution load of nitrogen can be reduced by proper drainage water control and fertilizer application practices.     

Effect on water quality in irrigation reservoir due to application reduction of nitrogen fertilizer

Until 1997, tea farmers in the Makinohara district of Shizuoka Prefecture, Japan, applied around 1.2 ton/ha of nitrogen fertilizer per year to their tea fields. In general, uptake amount of nitrogen by tea plants is around 300–350 kg/ha. Then some part of the remainder of nitrogen fertilizer leach into ground water and flow out into the river. The other part of remainder of nitrogen fertilizer is accumulated in the soil layer. Following a recommendation by the local government, this amount was then gradually decreased to 660 kg/ha in 1999 and 540 kg/ha in 2000. Although nitrate nitrogen concentrations in local ground and river water have decreased, they remain high today. The river water runs off from a watershed in the Makinohara area and enters a small irrigation reservoir called Tanno Reservoir, where it has caused deterioration of the water quality, that is, acidification of the reservoir. In Japan, environmental standard for nitrate nitrogen is 10 mg/L in public water body and ground water. Here, the author developed the Water Quality Tank Model, and applied this model to investigate the nitrate nitrogen concentrations in the rivers and an irrigation reservoir called Tanno. The author applies these findings to demonstrate that nitrogen concentrations continue to remain high due to nitrogen accumulation in the soil layer, and that the amount accumulated would be reduced by a reduction in application. The simulation results demonstrate a small decrease in accumulation in the soil layer, and thus that the present high nitrate nitrogen concentrations will continue in ground, river and reservoir water will decrease only gradually.     

Relative efficiency of vermicompost as direct application manure in pisciculture

Wide variation (>10.28 times) of fish yield (Cyprinus carpio Linnaeus, 1758) was obtained in a trial arranged in concrete cisterns (100 l) receiving compost (T-2), Diammonium phosphate (=DAP) (T-3) and vermicompost (T-4) as direct application fertilizer and manure in those systems. Significant (P < 0.005) differences were observed in diversity and abundance of plankton in response to manure application among treatments. Highest phyto- and zooplankton population was found in the cistern treated with vermicompost followed by DAP, compost and control. In all the treatments dry weight and population of both phyto- and zooplankton population were significantly (P < 0.005) higher than control. The highest production of fish was obtained in the cisterns treated with vermicompost (3,970.56 kg ha⁻¹ 90 day⁻¹), followed by diammonium phosphate (3,080.45 kg ha⁻¹ 90 day⁻¹), compost (1,952.64 kg ha⁻¹ 90 day⁻¹) and the lowest in the control (385.92 kg ha⁻¹ 90 day⁻¹). Vermicompost might be cost-effective manure in carp culture, replacing the expensive chemical fertilizer diammonium phosphate.     

水稻田表水磷素的动态特征及其潜在环境效应的研究

通过独立排灌式磷肥大田试验探讨了水稻田表水磷素的动态特征及其潜在的环境效应。研究发现, 施入磷肥增加了田表水磷素水平, 首次水样总磷水平为0.201～ 1.301 mg/kg, 溶解磷水平为0.058～ 0.926 mg/kg; 在等量施磷的条件下, 与单施无机磷肥比较, 有机无机磷配施能显著地提高田表水磷素水平; 在首次采样的一周之内, 两者总磷水平相差达3.85～1.89 倍, 但随着时间的推移, 因施磷结构的不同导致田表水磷素水平的差异逐渐缩小并趋于一致。任一次田间排水都存在诱发附近水域水体富营养化的可能。从减少磷素流失的角度出发, 在施磷灌水后约一周之内或田间耘田时, 田间排水磷素流失潜能增大, 另外, 还要避免在雨水集中的季节施用磷肥。     

不同施氮方式对玉米田土壤无机氮动态变化的影响

研究不同施氮方式对玉米田土壤水分动态变化和土壤无机氮变化特征的影响。结果表明,玉米生育期不同施氮方式下,0~100 cm土壤水分变化趋势相似,非雨季0~20 cm土壤含水量施肥处理比不施肥(CK)低2~4个百分点,雨季由于降雨的补给各处理各层土壤水分无明显变化。施氮显著增加了0~100 cm土层无机氮含量。习惯施肥处理土壤硝态氮含量受降雨影响较大,表现出向土壤深层迁移的趋势;缓控释肥、优化施肥和优化施肥+秸秆还田处理可降低土壤硝态氮的残留。0~40 cm土壤铵态氮含量受基肥和追肥影响较大,41~100 cm土壤铵态氮含量为3~5 mg/kg,变化幅度较小,趋于稳定。合理的氮肥用量及施氮方式,可有效减少土壤硝态氮的残留,减轻浅层地下水硝态氮污染的风险。     

鱼塘种稻对养殖水体营养物质的去除作用研究

以黄颡鱼精养塘为例,探索鱼塘种植高秆型水稻对精养池塘水体氮磷养分等水质指标的修复作用。结果表明,在水稻生长期,种稻黄颡鱼精养塘水体氮、磷养分含量显著低于单养鱼池塘。在水稻收获期,单养鱼塘水体总氮(TN)和总磷(TP)含量高达11.98mg/L和0.52mg/L,超过了《淡水池塘养殖水排放要求》标准;而种稻鱼塘水体中TN、TP含量则仅为0.49mg/L和0.08mg/L,达到《淡水池塘养殖水排放要求》一级排放标准。种稻鱼塘水体中TN、NH4+-N、NO3--N、TP和PO43--P含量比不种稻单养鱼塘分别降低95.95%、98.09%、98.07%、84.47%和64.57%。种稻鱼塘COD含量和pH值低于单养鱼塘。可见,种稻能有效降低水体养分含量,改善养殖水体水质。     

Nitrogen loss and its health risk in paddy fields under different drainage managements

Subsurface drainage is a prerequisite for year-round crop production in a large area of northern Iran^, s paddy fields. Minimizing environmental and health issues related to nitrogen (N) losses through subsurface drainage systems provides suitable condition for sustainable agriculture in these fields. A field study was conducted to evaluate nitrogen loss and its health risk in the conventional and subsurface-drained paddy fields. Ammonium, nitrate, and total N concentrations of subsurface drainage effluents, surface runoff, and leachates were monitored during three successive rice-canola-rice growing seasons from July 2011 to August 2012. Different components of N balance and health risk of nitrate leaching to groundwater were also investigated. Ammonium in drainage effluents collected during the experimental period ranged from approximately zero to 1.72 mg L^?1, while nitrate fluctuated from 0.5 to 28.6 mg L^?1. Average nitrate concentration in leachates of subsurface-drained area was 7.7–81.4 % higher than that in subsurface drainage effluents, while it was 126.8 % higher than that in surface runoff for the conventional field. Subsurface drainage provided a better utilization of soil N through providing winter cropping and reduced the potential for non-carcinogenic risks of nitrate leaching to groundwater. The results are encouraging for producers engaged in rice-canola production in the study area with respect to the environment and human health quality.     

Factors determining the leaching of nitrogen from soil,including some aspects of maintenance of water quality

N leaching from the topsoil, which occurs both by vertical percolation and runoff, is becoming increasingly important, not only from the point of view of crop production but also in the maintenance of water quality. N runoff from sloping fields has not yet been investigated extensively, but lysimeter studies have provided us with comprehensive data on vertical percolation of this nutrient. Numerous investigations throughout Europe have determined the most important factors concerned with N leaching from the topsoil and their relationship to water quality. The results may be summarized as follows: The amount and distribution of rainfall have a considerable effect on translocation of N from the topsoil. To exactly what extent is determined by the amount of water leached, which in turn depends to a large degree on the growth of the plant. Therefore the vegetative cover, as a result of its water utilization (mainly by transpiration) and its nutrient uptake, is often the most important factor in N leaching. This is borne out by the fact that by far the greatest leaching occurs in uncropped land (fallow) and during the part of the year where little growth occurs. Under crops with a limited root system and low transpiration, such as vines, leaching will also be higher than under a profuse plant cover (e.g. grassland). The main effect of the soil itself depends on its own N reserves and their mineralization rate. The amount of naturally occurring N in a mineral soil can vary between 600 and 12,000 kg/ha. Of this, approximately 10 – 250 kg/ha is given off anually under European climatic conditions. Thus as well as the factors already mentioned, the soil's N reserves also play an important part in the extent of N leaching. The vast majority of lysimeter studies carried out in Europe prove that the addition of N in mineral fertilizers has comparatively little influence on the amount of N leached out. An important point about N fertilizers is that they are applied when needed by the plant, which of course cannot occur in nature with the N from mineralization of the soil reserves. According to the data on hand, less than 5% of the N added in the form of mineral fertilizers will be leached out. Although excessive rates of N in lysimeter trials led to increased translocation into the subsoil, it was also proved that as a result of increased plant growth, N leaching losses were lower in a plot fertilized with N than in the PK control. Since N is leached out almost exclusively in the form of nitrate, and since the ammonium added as fertilizer is converted relatively quickly to nitrate, there is little difference in the leaching losses following application of the various types of N used today. The time of application, however, can be a determining factor. Gaseous N losses, in particular as a result of denitrification, can also affect N leaching indirectly. Discussion of N leaching leads inevitably to the question of water quality maintenance and what part N leached from soil plays in the eutrophication of surface waters and the nitrate content of ground water. The effect of agricultural land on the nitrate content of ground water depends on the cropping system: Vines, for instance, do not have a very extensive root system, and there are high leaching losses from the soil of vineyards. Under permanent grassland, on the other hand, the lowest losses have been recorded. In crops with a limited root system it is theoretically impossible to avoid an increase in the nitrate level of the ground water following high N application rates. This is however only a theory, and has not yet been fully investigated. In relation to agriculture as a whole these cases are to be regarded as exceptions, and they could possibly be improved by new agricultural techniques. As far as eutrophication is concerned, N leaching and the factors that affect it are of minor importance, since nitrogen, in contrast to phosphate, is already present in surface water at a concentration high enough to cause eutrophication. To sum up, it may be said that high rates of N are applied in intensive agriculture, but they do not usually lead to an increased N content in ground water and surface water. The reason for this is that the additional N promotes plant growth, which results in a greater nutrient uptake, and rationalization of agricultural methods on economic grounds ensures an adequate utilization of nutrients by applying rates commensurate with and timed according to the crop's need.     

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.     

Pesticide discharge and water management in a paddy catchment in Japan

Concentrations of several pesticides were monitored in a paddy block and in the Kose river, which drains a paddy catchment in Fukuoka prefecture, Japan. Detailed water management in the block was also monitored to evaluate its effect on the pesticide contamination. The concentrations of applied pesticides in both block irrigation channel and drainage canal increased to tens of μg/L shortly after their applications. The increase in pesticide concentrations was well correlated with the open of irrigation and drainage gates in the pesticide-applied paddy plots only 1–3 days after pesticide application. High concentration of other pesticides, mainly herbicides, was also observed in the inflow irrigation and drainage waters, confirming the popularity of early irrigation and drainage after pesticide application in the area. The requirement of holding water after pesticide application (as a best management practice) issued by the authority was thus not properly followed. In a larger scale of the paddy catchment, the concentration of pesticides also increased significantly to several μg/L in the water of the Kose river shortly after the start of the pesticide application period either in downstream or mid–upstream areas, confirming the effect of current water management to the water quality. More extension and enforcement on water management should be done in order to control pesticide pollution from rice cultivation in Japan.     

两种灌水条件下4种氮源对小麦籽粒淀粉含量及其特性的影响

为明确不同水分条件下氮源类型对小麦籽粒淀粉含量及其特性的影响,以郑麦366(强筋)和百农207(中筋)两个小麦品种为试验材料,分别在全生育期不灌水和灌拔节期+抽穗期2水条件下,研究了4种氮源(硝酸钙、硝酸铵钙、尿素和氯化铵)对小麦籽粒淀粉含量及其特性的影响。结果表明,灌2水条件下,小麦籽粒总淀粉含量、淀粉糊化特性及小淀粉粒占比均高于不灌水处理。灌水和氮源类型对淀粉含量、糊化特性及淀粉粒度分布有交互作用。在不灌水条件下,施用尿素籽粒淀粉含量和支链淀粉含量较高。在灌2水条件下,百农207以硝酸钙处理的淀粉峰值粘度、小淀粉粒表面积和体积占比最高;而郑麦366淀粉峰值粘度和小淀粉粒数量则分别以施用硝酸钙和硝酸铵钙最高。郑麦366在两种水分条件下均以施用硝酸铵钙淀粉失水率最低。品种对水分和氮肥类型的响应存在差异,总体而言,灌2水条件下,施用硝酸钙有利于淀粉糊化特性的改善;不灌水条件下,施用尿素有利于淀粉含量和支/直比提高。     

Nitrogen and phosphorus leaching losses from paddy fields with different water and nitrogen managements

While many water-saving rice production techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study aims to assess nitrogen (N) and phosphorus (P) leaching losses under real conditions in different water and N managements. Two water and three N treatments are conducted in the Taihu Lake region of China. Results show that the total N leaching losses during the rice season under flooding irrigation (FI) are 12.4, 9.31, and 7.17 kg ha⁻¹ for farmers’ fertilization practices (FFP), site-specific N management (SSNM), and controlled-release nitrogen fertilizer management (CRN), respectively. Under controlled irrigation (CI), the respective losses were 7.40, 5.86, and 3.79 kg ha⁻¹ for the same management methods. The total P leaching losses during the rice season under FI were 0.939, 0.927, and 0.353 kg ha⁻¹ for FFP, SSNM, and CRN, respectively. Under CI, the losses were 0.424, 0.433, and 0.279 kg ha⁻¹, respectively, for the same management methods. Ammonium and nitrate N accounted for 42.2–65.5% and 11.8–14.7% of the total nitrogen leaching losses under different water and N management methods, respectively. Due to significant decrease of volumes of percolation water and nitrogen and phosphorus concentrations in percolation water, N and P leaching losses were reduced in the CI treatment compared to the FI treatment under the same N management. The reduction of N input and application of controlled-release nitrogen fertilizer can reduce N and P leaching losses from paddy fields.     

Decreasing input–output balance by reducing chemical fertilizer input without yield loss in intensive cropping system in the Coastal Area of southeast Lake Dianchi,Yunnan Province,China

Overuse of chemical fertilizer and/or manure in agriculture is a principal factor in water eutrophication in China. Our previous study indicated that reducing chemical fertilizer input effectively decreased the soil nitrogen, phosphorus, and potassium in an intensive vegetable cropping system in the coastal area of southeast Lake Dianchi, China. This study aimed to decrease the input–output balance, namely the nutrient balance between input of fertilizer and output through vegetable harvesting, by reducing chemical fertilizer application without yield loss. A pot experiment was performed using chemical fertilizer with different amounts of N, P, and K on soils from six vegetable fields’ representative of the study area. High nitrate concentration in soils 2, 3, and 6 resulted in high N absorption from soil, and low N absorption from chemical fertilizer. Moreover, the responses of dry matter production to N absorbed from chemical fertilizer were less sensitive in soils 2, 3, and 6 than those in the other soils. Accordingly, reducing N input of chemical fertilizer did not decrease total N absorption or dry matter production, which should be the reason why reducing N input of chemical fertilizer did not reduce dry matter production in soils 2, 3, and 6. In the cases of soils 1, 4, and 5, reducing N input of chemical fertilizer reduced dry matter production, owing to lower levels of soil nitrate. This study should be helpful for reducing nutrient surplus from chemical fertilizer in the coastal area of southeast Lake Dianchi and other eutrophic agricultural areas in China.     

Long-term changes in nitrogen loads of a stream in the vicinity of an earthen waste storage pond

It is not sufficiently known for how long earthen waste storage ponds that are no more in use continue to affect surface water quality. In 2006, we carried out an investigation on the water quality and hydrology at the outlet of a small agricultural catchment area (area A) by estimating the in-stream nitrogen loads and nitrogen inputs. In this area, swine waste had been retained in an earthen waste storage pond, which was not in use since 1990. Similar investigations were conducted at the same location in 1992 and 2002, and the results of all these three studies were compared. The average nitrate nitrogen (NO₃-N) concentrations were 26, 4.9, and 4.0 mg L⁻¹ in 1992, 2002, and 2006, respectively. Despite 76% of the land use of area A being forest, the average NO₃-N concentration was relatively high, indicating that effluents from the earthen waste storage pond continued to affect surface water quality in 2006. The ranges of in-stream nitrogen loads derived from the earthen waste storage pond were estimated to be 154 to 207, −14 to 39, and 14 to 74 kg ha⁻¹ for 1992, 2002, and 2006, respectively. The results suggested that although the effects of effluents from the earthen waste storage pond on water quality decreased over 14 years, they still continued in 2006.     

Efficient shoot regeneration from direct apical meristem tissue to produce virus-free purple passion fruit plants

Purple passion fruit is an important fresh table fruit. At present, the production of passion fruit is decreasing because of the spread of viral diseases throughout the planting area. The aim of this research was to propagate virus-free plants using a tissue culture technique involving the apical meristem of purple passion fruit. Shoot tips were excised to a length of 2 mm and the shoots were regenerated by culturing on Murashige and Skoog medium supplemented with different concentrations of benzyladenine (BA) (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mg/l) and 1-naphthaleneacetic acid (NAA) (0.2, 0.5, 1.0, 1.5 and 2.0 mg/l). Root formation was promoted using different concentrations of indole-3-butyric acid (IBA) (0.0, 0.2, 0.4, 0.6, 0.8 and 1.2 mg/l). A greater number of shoots were produced with BA concentrations of 1.0 and 1.5 mg/l than with any other BA concentrations tested (less than 1.0 mg/l or greater than 1.5 mg/l). However, when NAA at any concentration was included in the medium, no shoots were produced in culture. The cultures including 1.0 mg/l and 1.5 mg/l BA were then subcultured four times every two weeks. Initially, the tissue cultured in the 1.5 mg/l BA medium grew faster than that cultured in the 1.0 mg/l BA medium. The tissue cultured with 1.5 mg/l BA generated many short shoots, whereas the tissue cultured with 1.0 mg/l BA, generated long shoots that could be subcultured into individual plants. These regenerated shoots were assayed for the presence of the passion fruit woodiness virus using ELISA or a test strip kit; only virus-free shoots were used for further propagation. Root formation was very good in IBA concentrations of 0.4 and 0.6 mg/l. Thus, virus-free plants could be successfully regenerated directly from the apical meristem.     

不同种类磷肥对果蔗的有效性研究

通过室内盆栽试验,以不施磷作为对照,分别选用钙镁磷肥、聚磷酸铵和磷酸一铵进行施磷处理,研究施用不同类型磷肥对黑皮果蔗生物量、根系形态及磷吸收特性的影响。结果显示,施磷处理能够显著促进果蔗生长,与未施磷处理的相比较,钙镁磷肥、聚磷酸铵和磷酸一铵处理的果蔗地上部生物量分别增加了67.00%、58.38%、50.65%。在同一施磷水平下,钙镁磷肥处理的果蔗生物量显著高于聚磷酸铵和磷酸一铵处理。在不同类型磷肥处理下,果蔗的根系形态特征有显著差异。钙镁磷肥处理的果蔗根系总根长和总根系表面积均比其他两种磷肥处理有显著增加;钙镁磷肥和聚磷酸铵处理的果蔗根平均直径和根总体积之间无显著差异。不同类型磷肥处理下,果蔗地上部和根系的磷含量无显著差异;但钙镁磷肥处理的果蔗磷积累量显著高于磷酸一铵处理。     

Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications

In California’s water-seeded rice systems, algal/cyanobacterial biomass can be a problem during rice establishment and can lead to yield reductions. Laboratory, enclosure, and field-scale experiments were established to evaluate the effects of fertilizer P management on algal/cyanobacterial growth. Two field-scale experiments evaluated the response of algal/cyanobacterial growth to three P management strategies: conventional surface applied, incorporated into the soil, and delaying P applications by 30 days. Results from these experiments indicated rice fields that received conventional surface-applied P fertilizer had 4–8 times more algal/cyanobacterial biomass and 3–11 times higher concentrations of soluble reactive phosphate (SRP) than those in which P fertilizer was incorporated or delayed. Laboratory experiments evaluated the ability of field water to support growth of Nostoc spongiaeforme. Results indicate that water from the incorporated or delayed P application fields was P limited for N. spongiaeforme growth. Water from the surface-applied fields was not P limited. Enclosure experiments evaluated the effects of delayed P applications on algal/cyanobacterial biomass and rice yields. Algal/cyanobacterial cover and biomass increased in enclosures which received added P. Soluble reactive phosphate concentrations were also significantly greater in these enclosures. Delaying the application by up to 28 days did not reduce rice yields in the enclosures. One management implication is that reducing SRP concentrations early in the season in rice field water will result in reduced algal/cyanobacterial biomass. Strategies to reduce water SRP include incorporating fertilizer P or delaying the P application by up to 30 days.     

Soil chemical properties,plant species composition,herbage quality,production and nutrient uptake of an alluvial meadow after 45 years of N,P and K application

Little is known about the long-term effects of mineral N, P and K application on the nutritional status of mown alluvial grasslands. We asked how long-term fertilizer application affected soil chemical properties, plant species composition, herbage production, nutrient concentrations in soils and plants and balance of nutrients. Six treatments (control, PK, N50PK, N100PK, N150PK and N200PK) were investigated at the Černíkovice Experiment (Czech Republic) established in 1966 on an Alopecurus pratensis meadow, using annual application rates of 50, 100, 150 and 200 kg N, 40 kg P and 100 kg K ha⁻¹. Data were collected and analysed for 2007, 2008 and 2009. Although fertilizers had been applied over 45 years, differences in soil chemical properties between fertilization treatments were small. The legumes Lathyrus pratensis and Trifolium repens responded highly positively to PK application, and tall grasses, A. pratensis in particular, to NPK application. Herbage quality was high in terms of content of major nutrients, and its chemical properties varied considerably between treatments, cuts and years. Mean annual herbage yield ranged from 6·1 in the control to 9·7 t ha⁻¹ in the N200PK treatment. Herbage production was N-limited in 2007 and 2009, but not in 2008. Seasonal N agronomical efficiency ranged from 4·2 to 22·9 kg of DM herbage per kg of applied N. The herbage N:P and N:K ratios did not reflect the actual response of herbage production to N application. A negative balance between N applied and N removed in harvested herbage was recorded in all treatments. We concluded that in highly productive alluvial grasslands, mineral-rich soils can respond weakly to N, P and K application, fertilizer application modifies plant species composition and herbage production is not N-limited in all years. Nutrient ratios must be interpreted with caution for the estimation of nutrient limitation.     

Fluctuation of NO3-N in groundwater of the reservoir of the Sunagawa Subsurface Dam, Miyako Island, Japan

The Japanese government started to construct two subsurface dams on Miyako Island in 1988, and the project was completed in 2001. Before the construction of the dams, the NO₃-N concentration of groundwater on the island was about 10 mg/l, the upper limit for drinking water in Japan, owing to the application of fertilizer to sugarcane fields. Predicting the effect of these subsurface dams on the groundwater environment was difficult because they were probably the first mega-subsurface dams in the world. We measured the NO₃-N concentration in the groundwater at observation wells before and after construction of the Sunagawa Dam and after the groundwater began to be used. We also measured the NO₃-N concentration monthly at a typical observation well in the catchment over a period 14 years to evaluate the environmental impact of construction of the dam. The highest NO₃-N concentrations were downstream before completion of the subsurface dam, and a high NO₃-N concentration zone remained around the cut-off wall after its completion, but this high-concentration zone disappeared and the distribution of NO₃-N became uniform after pumping of the groundwater began. Overall, the NO₃-N concentration decreased gradually. These results show that the groundwater quality did not deteriorate as a result of the construction of the Sunagawa Subsurface Dam.     

尿素及磷酸二铵对黑土区甜菜生长发育的影响

选用生产上广泛应用的尿素、磷酸二铵为试材,探讨肥料对黑土区甜菜株高、出叶速度、叶面积、根重、含糖率、净光合生产率的影响,为指导合理施肥提供理论依据。试验结果表明,尿素对甜菜株高、叶片数、叶面积、根重等影响较大,磷酸二铵对其影响较小;尿素对根产量的增产作用约是磷酸二铵的2 倍;尿素、磷酸二铵配合施用效果最好。