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Influence of puddling procedures on the quality of rice paddy drainage water
Agricultural Water Management 96 (2009) 1052–1058
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Short communication
Influence of puddling procedures on the quality of rice paddy drainage water Hiroaki Somura *, Ikuo Takeda, Yasushi Mori Faculty of Life and Environmental Science, Shimane University, Matsue 690-8504, Japan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 June 2008 Accepted 15 December 2008
Drainage water quality in rice paddies was strongly influenced by the puddling of soil in the paddy fields by tractors and in response to opening of drainage gates. The concentrations of contaminants in drainage water increased rapidly when the puddling process began and were maintained at high concentrations throughout the puddling period. Moreover, the high concentrations did not decrease immediately after the puddling procedures ceased. Additionally, the ratio of dissolved nitrogen and phosphorous to total nitrogen and total phosphorous increased daily during the last half of the puddling period, due to discharge of chemical fertilizers with the drainage water. Also, the loads of particulate nitrogen and phosphorus discharged during the puddling period were larger than the loads discharge during irrigation. The discharge from paddy fields during puddling also increased the total annual contaminant load. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Drainage water Load discharge Puddling and transplanting period
1. Introduction The efflux of nitrogen (N) and phosphorous (P) from agricultural lands is believed to be a major contributor to the accelerated eutrophication of rivers and reservoirs worldwide (Kim et al., 2006). Agricultural lands are non-point sources of pollution, which contribute more pollutant load to many closed water areas than point sources (Takeda and Fukushima, 2006). However, it is difficult to evaluate the overall impact of agricultural farming activities such as irrigation and fertilizer application in a drainage basin. This is partially due to farmers cultivating many varieties of crops during the irrigation period, and to differences in their farming techniques. This is especially true in rice fields, which use a large amount of water that is ultimately drained into surrounding aquatic systems. Rice fields account for a large portion of agricultural land in Japan and other East Asian countries (Tabuchi and Hasegawa, 1995). As a result, gaining a thorough understanding of the relationship between farming activities during the crop cultivation period and variations in water quality may facilitate improvement of the quality of aquatic systems located near rice fields. Rice paddy fields accounted for approximately 54% of all farmland in Japan in 2005 (MAFF, 2005). Because paddy fields typically lie along rivers, they can have a major impact on water quality. In addition, the growing season of rice generally extends from May to October, which coincides with the hydrologically active period of most bodies of water.
* Corresponding author. Tel.: +81 852 32 6552; fax: +81 852 32 6552. E-mail address: [email protected] (H. Somura). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.12.005
Paddy fields can be managed in ways that enhance soil conservation, ground water recharge and denitrification, while contributing to food production (Mizutani, 1999). Furthermore, paddy fields can decrease the nitrogen load to the aquatic environment via increased denitrification under ponding conditions (Tabuchi and Kuroda, 1991; Yamaoka et al., 2003). Moreover, the volcanic ash soil that is present in many paddy fields in Japan readily adsorbs phosphorous (Shiratani et al., 2003; Takeda and Fukushima, 2004). However, even though rice paddy fields tend to purify water during the crop season, a large volume of drainage water with a high concentration of suspended solids (SS) is discharged during puddling and transplanting. Puddling is a common practice in rice cultivation for the following reasons (Adachi and Sakaki, 1999; Kaneki, 2003): (1) it softens the soil in the plow layer, thereby facilitating transplanting or direct seeding, (2) it creates a level soil surface, which helps ensure a uniform depth of flood water for adequate water management, (3) it reduces the incidence of weeds, (4) it mixes fertilizer and soil in the plow layer, and (5) it reduces the percolation rate. In this study, we examine the relationship between puddling procedures and changes in the quality of drainage water from paddy fields to determine the impact of paddy drainage water on the quality of aquatic systems located downstream. 2. Study area The study area is in the southeastern portion of Matsue City in Shimane Prefecture, Japan (Fig. 1). The cultivated area is approximately 115,000 m2. Irrigation water is supplied to paddy fields from the Hakuta River via a non-pressurized pipeline. The
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
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Fig. 1. Location of the study area and drainage system.
entire paddy system, which was constructed during a farmland consolidation program at the end of 2003, comprises 13 paddy fields with underground drainage systems that were installed following the harvest of rice in 2005. The underground drainage systems comprise vitrified-clay pipes that guide water from the paddy fields to a common drainage ditch. The water then flows through the drainage ditch and is finally discharged to the Yoshida River, which is located downstream of the paddy fields.
activities such as puddling, transplanting and gate operation of surface drains were monitored visually at each paddy field and evaluated via interviews with farmers during that time. Based on the results of the field investigation, the irrigation periods were set from 27 May to 8 October in 2005 and from 29 May to 9 October in 2006, while the non-irrigation periods were set from 12 April to 26 May in 2005, from 9 October to 28 May in 2006 and from 10
3. Methodology
Table 1 Date and time of the investigations conducted during the puddling period in 2006.
A field investigation was conducted from April 2005 to December 2006 to evaluate water quality. Water samples were collected approximately once each week during the irrigation period and twice each week during the non-irrigation period. In addition, the water was collected almost every hour from early in the morning to late at night during the puddling and transplanting period from 29 May to 3 June in 2006 (Table 1). Moreover, farming
Date
Investigation hours
29 May 30 May 31 May 1 June 2 June 3 June
9:00–21:00 5:00–21:00 6:00–21:00 6:00–20:00 6:00–21:00 3:00, 6:00, 9:00, 18:00
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October to 31 December in 2006. The puddling and transplanting periods were set from 27 May to 3 June in 2005 and from 29 May to 3 June in 2006. In this paper, the puddling and transplanting period is referred to as the puddling period, and the growing season refers to the portion of the irrigation period excluding the puddling period. It should be noted that field No. 1 was not cultivated in 2006. Moreover, no agricultural activities were conducted during the non-irrigation period in the study area. A water level sensor (DIK-610A, Daiki Rika Kogyo Co., Ltd., Saitama, Japan) was installed in the common drainage ditch. In addition, the flow velocity (VR-201 and VRT-200-20N, Kenek Co., Ltd., Tokyo, Japan) and the cross-sectional area of the flow were measured during the field investigation. The discharge from the drainage ditch was then calculated using a calibrated water leveldischarge curve. The pollutant loads were calculated by multiplying the estimated amount of drainage water by the corresponding concentrations of measured pollutants. Samples for water quality were collected using a bucket and then immediately transported to the laboratory for analysis. Upon arrival in the laboratory, the water samples were filtered using glass fiber-filters (Advantec GS-25) to separate the particles and dissolved substances. The filtered water was then stored in a refrigerator at 4 8C until further analysis, whereas the separated particles were dried and weighed to determine the concentration of suspended solids. The total organic carbon (TOC) concentration was determined using a total organic carbon analyzer (TOC-VCSN, Shimadzu Co., Ltd., Kyoto, Japan). The ammonia (NH4) concentration was determined using the indophenol method (Sagi, 1966). The nitrite (NO2) concentration was determined using the naphthyl ethylene method in accordance with the Japanese Industrial Standard (JIS) K 0102 (Namiki, 1993). The nitrate (NO3) concentration was determined by ion chromatography (PIA1000, Shimadzu Co., Ltd., Kyoto, Japan). The total nitrogen (TN) concentration was determined using the ultraviolet spectrophotometry method with potassium peroxydisulfate (JIS K 0102). The phosphate (PO4) concentration was determined using the molybdenum blue method (JIS K 0102). The total phosphorus (TP) concentration was determined using the molybdenum blue method with potassium peroxydisulfate (JIS K 0102). Particulate nitrogen (PN) and particulate phosphorus (PP) were calculated by subtracting the filtered concentrations from the total concentrations.
Table 2 Average concentrations (mg L
Irrigation period (Puddling) (Growing season) (July) (August) Non-irrigation period
1
) of drainage water in 2005 and 2006.
Suspended solids
Total nitrogen
Total phosphorus
Total organic carbon
26.8 296.2 11.1 11.3 8.1 21.2
1.79 6.27 1.37 1.23 1.18 2.56
0.15 1.13 0.09 0.09 0.08 0.13
3.45 10.79 2.95 2.95 2.05 4.55
sedimentation (Tomas et al., 2003; Braskerud, 2002). Alternatively, the decreased concentrations may have occurred due to a dilution effect induced by an influx of irrigation water from the Hakuta
4. Results and discussion 4.1. Variation in the concentrations of pollutants in drainage water The average contaminant concentrations during the nonirrigation period were relatively high. Specifically, concentrations of 21.2 mg L 1 SS, 2.56 mg L 1 TN, 0.13 mg L 1 TP, and 4.55 mg L 1 TOC were observed during this period (Table 2). Because no agricultural activities were conducted in this area during the nonirrigation period, it is believed that residual nutrients in the soil were leached by rainwater and subsequently flowed into the drainage ditch. During the irrigation periods, the average concentrations of SS, TN, TP and TOC were 26.8 mg L 1, 1.79 mg L 1, 0.15 mg L 1, and 3.45 mg L 1, respectively, which represent a decrease for several compounds such as TN and TOC, when compared with the non-irrigation period (Table 2). The concentrations of the pollutants evaluated in this study generally were lower during the irrigation periods in July and August than at the beginning and end of the growing season (Fig. 2). This might be due to the retention time of water in the paddy fields during the growing season, resulting in the induction of a purification mechanism similar to those present in natural and artificial wetlands, such as denitrification, plant uptake or
Fig. 2. Drainage water quality concentrations of SS, TN, TP and TOC from April 2005 to December 2006.
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
River and rough management of the drainage gate. In general, irrigation water flows into the paddy fields and is then pooled in the fields, after which it is discharged to a drainage ditch. However, field investigation revealed that irrigation water from the river also flowed directly into the common drainage ditch through the drain pipe before flowing into the paddy fields, due to the drainage gate being fully open. The average concentrations of SS, TN, TP and TOC in the river water in 2005 and 2006 were 6.1 mg L 1, 0.50 mg L 1, 0.05 mg L 1, and 1.13 mg L 1, respectively, which are low enough to enable river water to dilute drainage water from the paddy fields. The dilution ratio of the drainage water by the irrigation water that is drained directly through the drain pipe is very absorbing. However, because it is difficult to measure the amount of irrigation water drained directly through each drain pipe in each paddy field, the effect of this water on the concentration of pollutants is unknown. The water concentrations of these contaminants increased significantly during the puddling periods, as indicated by average concentrations of 296.2 mg L 1 SS, 6.27 mg L 1 TN, 1.13 mg L 1 TP, and 10.79 mg L 1 TOC. This finding is similar to the results of several studies of water quality indicators in drainage water from paddy fields in Japan (Kondoh et al., 1992). 4.2. Farming activities and water quality during puddling in 2006 In the field investigation conducted in 2005, a large amount of drainage water was observed during the puddling period. The increased level of drainage water released during this period was believed to have a high impact on downstream water quality. Therefore, water quality was extensively evaluated during the puddling period in 2006 to determine if a relationship existed
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between farming activities and variations in water quality. Prior to the puddling process, a large amount of water was pooled in the paddy fields and then simultaneously released to the common drainage ditch to adjust the depth of water in the paddy fields in preparation of the puddling process (Fig. 3). In most cases, a large amount of water with a high soil concentration was released through the surface drain when the puddling process was conducted using a tractor. This surface drain water was gathered by the drainage pipeline and subsequently discharged through a drainage ditch to the Yoshida River (Plate 1). In 2006, the puddling and transplanting processes lasted for 6 days. During that period, the average concentrations of SS, TN, TP and TOC in the drainage water were 330.7 mg L 1, 7.27 mg L 1, 1.53 mg L 1, and 13.80 mg L 1, respectively. In addition, the maximum concentrations of SS, TN, TP and TOC during this period were 3020 mg L 1, 36.17 mg L 1, 12.32 mg L 1, and 83.22 mg L 1. The correlation coefficients between SS and TN, TP, and TOC in the drainage water were 0.911, 0.897 and 0.915. These findings confirm that the concentrations of drainage water increased rapidly when the puddling processes began, and that high concentrations were maintained during the farming activities. Moreover, the high concentrations did not decrease following completion of the daily activities, which indicates that drainage water contains high concentrations of these compounds throughout the puddling period. However, a review of the history of farming activities and drainage water at paddy field No. 12 revealed that no water was released from that paddy field via the surface drain during the puddling processes. According to the farmer in charge of that field, there is an optimal water depth for puddling at which it is not necessary to drain the water during the puddling process, but that depth is uncertain.
Fig. 3. Changes in water quality in response to puddling processes conducted using a tractor and drainage gate operation on each paddy field.
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H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
Plate 1. Drainage water and puddling processes.
The composition ratios of TN and TP in the drainage water during the puddling period are shown in Fig. 4. Specifically, the discharge ratios of dissolved nitrogen (NH4–N, NO2–N, and NO3–N) to TN were small from 29 May to 31 May, as evidenced by an average of 2.9% NH4–N, 0.2% NO2–N, and 2.1% NO3–N being detected in the TN during this period. However, the ratio of the dissolved nitrogen to TN began increasing daily from 1 June, with maximum ratios of 40.8% NH4–N, 12.5% NO2–N, and 29.7% NO3–N observed on 3 June. In addition, the concentration of PO4–P also tended to increase from 1 June. This was demonstrated by an average ratio of 3.6% PO4–P to TP observed from 29 May to 31 May and then increasing by 15.5% on 3 June.
In the target paddy fields, rice transplanting began on 31 May and was completed on 3 June. During this period, farmers attempted to manage and decrease the volume of water discharged through the surface drain to increase the efficiency of the chemical fertilizer, as several types of fertilizer were applied simultaneously during transplanting. However, based on the date at which rice transplanting began (31 May) and the increase in the dissolved nutrients observed in the drainage water, it is likely that some of these fertilizers were discharged via surface water drainage. In addition, it has been reported that the concentrations of N and P in drainage water increase during puddling and transplanting, and also when fertilizer is applied (Takeda et al., 1991; Feng et al., 2004). Our results suggest that a similar situation occurred in the fields we studied. 4.3. Load discharge during puddling in 2006 To evaluate the impact of water drained during the puddling period on the downstream water environment, the average daily loads of drainage water during puddling, the growing season, and the non-irrigation period were determined (Fig. 5). A higher load of contaminants was discharged downstream during the puddling period than during the growing season and the non-irrigation period. Suspended solids increased almost 50-fold during the puddling period when compared with the other periods. Similar trends were observed for other constituents, although the increases were somewhat smaller than the increase in suspended solids.
Fig. 4. Composition ratios of TN and TP in drainage water during the puddling and transplanting period.
Fig. 5. Daily load discharges of SS, TN, TP and TOC from the paddy field area.
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
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Table 3 Annual pollutant discharge loads (kg) in 2006 and the ratios (%) of the load discharge during the puddling period to the discharge during the irrigation period and the annual discharge. Suspended solids Puddling
Total nitrogen
Ammonium nitrogen
Nitrite nitrogen
Nitrate nitrogen
Particulate nitrogen
Total phosphorus
Phosphate phosphorus
Particulate phosphorus
Total organic carbon
5/29 5/30 5/31 6/1 6/2 6/3
1479.3 1301.9 1016.3 549.8 242.1 25.2
26.7 19.2 19.7 14.5 8.3 3.4
0.73 0.55 0.58 0.74 0.81 1.38
0.073 0.028 0.018 0.028 0.011 0.422
1.01 0.37 0.12 0.63 0.61 1.00
24.92 18.27 18.98 13.06 6.87 0.58
6.9 5.1 5.0 2.3 1.4 0.2
0.43 0.14 0.09 0.20 0.13 0.03
6.4 5.0 5.0 2.1 1.3 0.2
47.5 39.0 41.5 28.4 13.9 4.3
Total
4614.6
91.8
4.79
0.581
3.75
82.67
21.0
1.03
20.0
174.7
2213.9 3712.5 43.8
325.6 590.5 9.1
160.3 251.3 1.1
25.6 3.2 2.0
83.7 118.3 1.8
56.0 222.8 22.9
29.8 29.3 26.2
13.7 3.4 5.7
16.1 25.9 32.2
1040.6 1121.6 7.5
67.6
22.0
2.9
2.2
4.3
59.6
41.3
7.0
55.3
14.4
Growing season 6/4 to 10/9 Non-irrigation period Ratio of puddling discharge vs. annual discharge Ratio of puddling discharge vs. irrigation period discharge
The ratios of loads discharged during the puddling period to the annual discharged loads were 43.8% for SS, 9.1% for TN, 22.9% for PN, 26.2% for TP, and 32.2% for PP (Table 3). According to a study conducted by Kondoh et al. (1993) in Niigata Prefecture, the average ratios of the TN and TP loads during the puddling periods to the overall TN and TP loads during the irrigation periods (puddling and growing periods) were 24.8% and 22.0%, respectively. In our study area, the TN and TP loads during the puddling period were 22.0% and 41.3% of the total loads observed during the irrigation period, respectively. When the results of the present study were compared with those of a study conducted by Kondoh et al., the ratio of TN discharged during the puddling period to that of TN discharged during the irrigation period was similar, even though the TP load was almost twice as high in the present study. Moreover, the load of dissolved substances during the puddling period was not dominant against the load discharge during the irrigation period (less than 10%). This finding indicates that the load discharge of particulate substances such as PN and PP during the puddling period has a greater impact on the downstream water environment than that of dissolved contaminants, as evidenced by the discharge percentages of PN and PP being approximately 60% and 55% of those observed during the irrigation period, respectively. 5. Conclusions This study focused on changes in the concentration of contaminants in drainage water from paddy fields over approximately 2 years, while paying particular attention to the relationship between farming activities during the puddling period and the quality of paddy drainage water in 2006. This study revealed several interesting aspects, which are as follows: 1. The drainage water quality at the sampling point was altered in response to puddling processes conducted using a tractor and by operation of the drainage gate. 2. Not all paddy fields released drainage water via the surface drain during the puddling process (for example, paddy field No. 12). Hence it is not always necessary to release water during puddling. 3. The criteria for determining the optimal water depth for the puddling process, which does not require discharge of the water via a surface drain, have not yet been established. If the optimal water depth were found for puddling and the amount of water drained during that time were decreased (such as in paddy field No. 12), contaminant load discharges would
decrease greatly. Additionally, determining the optimal depth for puddling would allow the amount of nutrient salts applied by chemical fertilizer to be decreased because the nutrient salt runoff via surface drainage would decrease. Taken together, these findings indicate that developing methods to optimize the water depth in paddy fields during the puddling process can reduce costs while improving and protecting the downstream environment of nearby bodies of water. Acknowledgments The authors would like to express our gratitude to the farming union in the study area for their cooperation. Additionally, the authors also gratefully acknowledge the support of Mr. Ken-ichi Sawata and Mr. Hidenori Takubo during the course of this study. Finally, this study was partially supported by a grant from the Shimane University Priority Research Project and a Grant-in-Aid for Scientific Research ‘‘KAKENHI’’ (#16380221) from the Japan Society for the Promotion of Science (JSPS). References Adachi, K., Sakaki, C., 1999. Percolation and seepage. In: Mizutani, M., Hasegawa, S., Koga, K., Goto, A., Murty, V.V.N. (Eds.), Advanced Paddy Field Engineering. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, p. 388 pp. Braskerud, B.C., 2002. Factors affecting nitrogen retention in small constructed wetlands treating agricultural non-point source pollution. Ecological Engineering 18, 351–370. Feng, Y.W., Yohinaga, I., Shiratani, E., Hitomi, T., Hasebe, H., 2004. Characteristics and behavior of nutrients in a paddy field area equipped with a recycling irrigation system. Agricultural Water Management 68, 47–60, doi:10.1016/ j.agwat.2004.02.012. Kaneki, R., 2003. Reduction of effluent nitrogen and phosphorus from paddy fields. Paddy and Water Environment 1, 133–138, doi:10.1007/s10333-003-0020-5. Kim, J.S., Oh, S.Y., Oh, K.Y., 2006. Nutrient runoff from a Korean rice paddy watershed during multiple storm events in the growing season. Journal of Hydrology 327, 128–139, doi:10.1016/j.jhydrol.2005.11.062. Kondoh, T., Misawa, S., Toyota, M., 1992. Characteristics of effluent loads of nutrient salts (N, P) from paddy fields located in the alluvial and lower area in Hokuriku District – research study on nutrient load in the low plain areas of Niigata. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 159, 17–27 (in Japanese with English abstract). Kondoh, T., Misawa, S., Toyota, M., 1993. Characteristics of effluents of nitrogen and phosphorous in paddy fields during the paddling and transplanting season. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 164, 147–155 (in Japanese with English abstract). MAFF, 2005. Abstract of statistics on agriculture forestry and fisheries in Japan. http://www.maff.go.jp/toukei/abstract/index.htm. Mizutani, M., 1999. Development of paddy field engineering in Japan. In: Mizutani, M., Hasegawa, S., Koga, K., Goto, A., Murty, V.V.N. (Eds.), Advanced Paddy Field Engineering. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, p. 388 pp. Namiki, H. (Ed.), 1993. Analytical Method of Water Quality for Industrial Wastewater (JIS K 0102). Japan Standard Association, Tokyo (in Japanese).
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Sagi, T., 1966. Determination of ammonia in sea water by the indophenol method and its application to the coastal and off-shore waters. Limnology and Oceanography 13, 440–447. Shiratani, E., Shiofuku, T., Kubota, T., Yoshinaga, I., Hasebe, H., 2003. Estimation of nutrient elution and removal on sediment surface of clayey canal based on hydraulic model experiments. Japan Agricultural Research Quarterly 36 (4), 195–200. Tabuchi, T., Kuroda, H., 1991. Nitrogen outflow diagram in a small agricultural area having uplands and lowlands – research on outflow load from an agricultural area without a point source (III). Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 154, 65–72 (in Japanese with English abstract). Tabuchi, T., Hasegawa, S. (Eds.), 1995. Paddy Fields in the World. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, 353 pp. Takeda, I., Kunimatsu, T., Kobayashi, S., Maruyama, T., 1991. Pollutants balance of a paddy field area and its loadings in the water system – studies on pollution
loadings from a paddy field area (II). Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 153, 63–72 (in Japanese with English abstract). Takeda, I., Fukushima, A., 2004. Phosphorus purification in a paddy field watershed using a circular irrigation system and the role of iron compounds. Water Research 38, 4065–4074, doi:10.1016/j.watres.2004.08.003. Takeda, I., Fukushima, A., 2006. Long-term changes in pollutant load outflows and purification function in a paddy field watershed using a circular irrigation system. Water Research 40, 569–578, doi:10.1016/j.watres.2005.08.034. Tomas, E.J., Whigham, E.D., Hofmockel, K.H., Pittek, M.A., 2003. Nutrient and sediment removal by restored wetland receiving agricultural runoff. Journal of Environmental Quality 32, 1534–1547. Yamaoka, M., Shinogi, Y., Abenney-Mickson, S., Saito, T., 2003. Estimation of nitrate removal potential for upland soil. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 225, 43–53 (in Japanese with English abstract).
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Short communication
Influence of puddling procedures on the quality of rice paddy drainage water Hiroaki Somura *, Ikuo Takeda, Yasushi Mori Faculty of Life and Environmental Science, Shimane University, Matsue 690-8504, Japan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 June 2008 Accepted 15 December 2008
Drainage water quality in rice paddies was strongly influenced by the puddling of soil in the paddy fields by tractors and in response to opening of drainage gates. The concentrations of contaminants in drainage water increased rapidly when the puddling process began and were maintained at high concentrations throughout the puddling period. Moreover, the high concentrations did not decrease immediately after the puddling procedures ceased. Additionally, the ratio of dissolved nitrogen and phosphorous to total nitrogen and total phosphorous increased daily during the last half of the puddling period, due to discharge of chemical fertilizers with the drainage water. Also, the loads of particulate nitrogen and phosphorus discharged during the puddling period were larger than the loads discharge during irrigation. The discharge from paddy fields during puddling also increased the total annual contaminant load. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Drainage water Load discharge Puddling and transplanting period
1. Introduction The efflux of nitrogen (N) and phosphorous (P) from agricultural lands is believed to be a major contributor to the accelerated eutrophication of rivers and reservoirs worldwide (Kim et al., 2006). Agricultural lands are non-point sources of pollution, which contribute more pollutant load to many closed water areas than point sources (Takeda and Fukushima, 2006). However, it is difficult to evaluate the overall impact of agricultural farming activities such as irrigation and fertilizer application in a drainage basin. This is partially due to farmers cultivating many varieties of crops during the irrigation period, and to differences in their farming techniques. This is especially true in rice fields, which use a large amount of water that is ultimately drained into surrounding aquatic systems. Rice fields account for a large portion of agricultural land in Japan and other East Asian countries (Tabuchi and Hasegawa, 1995). As a result, gaining a thorough understanding of the relationship between farming activities during the crop cultivation period and variations in water quality may facilitate improvement of the quality of aquatic systems located near rice fields. Rice paddy fields accounted for approximately 54% of all farmland in Japan in 2005 (MAFF, 2005). Because paddy fields typically lie along rivers, they can have a major impact on water quality. In addition, the growing season of rice generally extends from May to October, which coincides with the hydrologically active period of most bodies of water.
* Corresponding author. Tel.: +81 852 32 6552; fax: +81 852 32 6552. E-mail address: [email protected] (H. Somura). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.12.005
Paddy fields can be managed in ways that enhance soil conservation, ground water recharge and denitrification, while contributing to food production (Mizutani, 1999). Furthermore, paddy fields can decrease the nitrogen load to the aquatic environment via increased denitrification under ponding conditions (Tabuchi and Kuroda, 1991; Yamaoka et al., 2003). Moreover, the volcanic ash soil that is present in many paddy fields in Japan readily adsorbs phosphorous (Shiratani et al., 2003; Takeda and Fukushima, 2004). However, even though rice paddy fields tend to purify water during the crop season, a large volume of drainage water with a high concentration of suspended solids (SS) is discharged during puddling and transplanting. Puddling is a common practice in rice cultivation for the following reasons (Adachi and Sakaki, 1999; Kaneki, 2003): (1) it softens the soil in the plow layer, thereby facilitating transplanting or direct seeding, (2) it creates a level soil surface, which helps ensure a uniform depth of flood water for adequate water management, (3) it reduces the incidence of weeds, (4) it mixes fertilizer and soil in the plow layer, and (5) it reduces the percolation rate. In this study, we examine the relationship between puddling procedures and changes in the quality of drainage water from paddy fields to determine the impact of paddy drainage water on the quality of aquatic systems located downstream. 2. Study area The study area is in the southeastern portion of Matsue City in Shimane Prefecture, Japan (Fig. 1). The cultivated area is approximately 115,000 m2. Irrigation water is supplied to paddy fields from the Hakuta River via a non-pressurized pipeline. The
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
1053
Fig. 1. Location of the study area and drainage system.
entire paddy system, which was constructed during a farmland consolidation program at the end of 2003, comprises 13 paddy fields with underground drainage systems that were installed following the harvest of rice in 2005. The underground drainage systems comprise vitrified-clay pipes that guide water from the paddy fields to a common drainage ditch. The water then flows through the drainage ditch and is finally discharged to the Yoshida River, which is located downstream of the paddy fields.
activities such as puddling, transplanting and gate operation of surface drains were monitored visually at each paddy field and evaluated via interviews with farmers during that time. Based on the results of the field investigation, the irrigation periods were set from 27 May to 8 October in 2005 and from 29 May to 9 October in 2006, while the non-irrigation periods were set from 12 April to 26 May in 2005, from 9 October to 28 May in 2006 and from 10
3. Methodology
Table 1 Date and time of the investigations conducted during the puddling period in 2006.
A field investigation was conducted from April 2005 to December 2006 to evaluate water quality. Water samples were collected approximately once each week during the irrigation period and twice each week during the non-irrigation period. In addition, the water was collected almost every hour from early in the morning to late at night during the puddling and transplanting period from 29 May to 3 June in 2006 (Table 1). Moreover, farming
Date
Investigation hours
29 May 30 May 31 May 1 June 2 June 3 June
9:00–21:00 5:00–21:00 6:00–21:00 6:00–20:00 6:00–21:00 3:00, 6:00, 9:00, 18:00
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October to 31 December in 2006. The puddling and transplanting periods were set from 27 May to 3 June in 2005 and from 29 May to 3 June in 2006. In this paper, the puddling and transplanting period is referred to as the puddling period, and the growing season refers to the portion of the irrigation period excluding the puddling period. It should be noted that field No. 1 was not cultivated in 2006. Moreover, no agricultural activities were conducted during the non-irrigation period in the study area. A water level sensor (DIK-610A, Daiki Rika Kogyo Co., Ltd., Saitama, Japan) was installed in the common drainage ditch. In addition, the flow velocity (VR-201 and VRT-200-20N, Kenek Co., Ltd., Tokyo, Japan) and the cross-sectional area of the flow were measured during the field investigation. The discharge from the drainage ditch was then calculated using a calibrated water leveldischarge curve. The pollutant loads were calculated by multiplying the estimated amount of drainage water by the corresponding concentrations of measured pollutants. Samples for water quality were collected using a bucket and then immediately transported to the laboratory for analysis. Upon arrival in the laboratory, the water samples were filtered using glass fiber-filters (Advantec GS-25) to separate the particles and dissolved substances. The filtered water was then stored in a refrigerator at 4 8C until further analysis, whereas the separated particles were dried and weighed to determine the concentration of suspended solids. The total organic carbon (TOC) concentration was determined using a total organic carbon analyzer (TOC-VCSN, Shimadzu Co., Ltd., Kyoto, Japan). The ammonia (NH4) concentration was determined using the indophenol method (Sagi, 1966). The nitrite (NO2) concentration was determined using the naphthyl ethylene method in accordance with the Japanese Industrial Standard (JIS) K 0102 (Namiki, 1993). The nitrate (NO3) concentration was determined by ion chromatography (PIA1000, Shimadzu Co., Ltd., Kyoto, Japan). The total nitrogen (TN) concentration was determined using the ultraviolet spectrophotometry method with potassium peroxydisulfate (JIS K 0102). The phosphate (PO4) concentration was determined using the molybdenum blue method (JIS K 0102). The total phosphorus (TP) concentration was determined using the molybdenum blue method with potassium peroxydisulfate (JIS K 0102). Particulate nitrogen (PN) and particulate phosphorus (PP) were calculated by subtracting the filtered concentrations from the total concentrations.
Table 2 Average concentrations (mg L
Irrigation period (Puddling) (Growing season) (July) (August) Non-irrigation period
1
) of drainage water in 2005 and 2006.
Suspended solids
Total nitrogen
Total phosphorus
Total organic carbon
26.8 296.2 11.1 11.3 8.1 21.2
1.79 6.27 1.37 1.23 1.18 2.56
0.15 1.13 0.09 0.09 0.08 0.13
3.45 10.79 2.95 2.95 2.05 4.55
sedimentation (Tomas et al., 2003; Braskerud, 2002). Alternatively, the decreased concentrations may have occurred due to a dilution effect induced by an influx of irrigation water from the Hakuta
4. Results and discussion 4.1. Variation in the concentrations of pollutants in drainage water The average contaminant concentrations during the nonirrigation period were relatively high. Specifically, concentrations of 21.2 mg L 1 SS, 2.56 mg L 1 TN, 0.13 mg L 1 TP, and 4.55 mg L 1 TOC were observed during this period (Table 2). Because no agricultural activities were conducted in this area during the nonirrigation period, it is believed that residual nutrients in the soil were leached by rainwater and subsequently flowed into the drainage ditch. During the irrigation periods, the average concentrations of SS, TN, TP and TOC were 26.8 mg L 1, 1.79 mg L 1, 0.15 mg L 1, and 3.45 mg L 1, respectively, which represent a decrease for several compounds such as TN and TOC, when compared with the non-irrigation period (Table 2). The concentrations of the pollutants evaluated in this study generally were lower during the irrigation periods in July and August than at the beginning and end of the growing season (Fig. 2). This might be due to the retention time of water in the paddy fields during the growing season, resulting in the induction of a purification mechanism similar to those present in natural and artificial wetlands, such as denitrification, plant uptake or
Fig. 2. Drainage water quality concentrations of SS, TN, TP and TOC from April 2005 to December 2006.
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
River and rough management of the drainage gate. In general, irrigation water flows into the paddy fields and is then pooled in the fields, after which it is discharged to a drainage ditch. However, field investigation revealed that irrigation water from the river also flowed directly into the common drainage ditch through the drain pipe before flowing into the paddy fields, due to the drainage gate being fully open. The average concentrations of SS, TN, TP and TOC in the river water in 2005 and 2006 were 6.1 mg L 1, 0.50 mg L 1, 0.05 mg L 1, and 1.13 mg L 1, respectively, which are low enough to enable river water to dilute drainage water from the paddy fields. The dilution ratio of the drainage water by the irrigation water that is drained directly through the drain pipe is very absorbing. However, because it is difficult to measure the amount of irrigation water drained directly through each drain pipe in each paddy field, the effect of this water on the concentration of pollutants is unknown. The water concentrations of these contaminants increased significantly during the puddling periods, as indicated by average concentrations of 296.2 mg L 1 SS, 6.27 mg L 1 TN, 1.13 mg L 1 TP, and 10.79 mg L 1 TOC. This finding is similar to the results of several studies of water quality indicators in drainage water from paddy fields in Japan (Kondoh et al., 1992). 4.2. Farming activities and water quality during puddling in 2006 In the field investigation conducted in 2005, a large amount of drainage water was observed during the puddling period. The increased level of drainage water released during this period was believed to have a high impact on downstream water quality. Therefore, water quality was extensively evaluated during the puddling period in 2006 to determine if a relationship existed
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between farming activities and variations in water quality. Prior to the puddling process, a large amount of water was pooled in the paddy fields and then simultaneously released to the common drainage ditch to adjust the depth of water in the paddy fields in preparation of the puddling process (Fig. 3). In most cases, a large amount of water with a high soil concentration was released through the surface drain when the puddling process was conducted using a tractor. This surface drain water was gathered by the drainage pipeline and subsequently discharged through a drainage ditch to the Yoshida River (Plate 1). In 2006, the puddling and transplanting processes lasted for 6 days. During that period, the average concentrations of SS, TN, TP and TOC in the drainage water were 330.7 mg L 1, 7.27 mg L 1, 1.53 mg L 1, and 13.80 mg L 1, respectively. In addition, the maximum concentrations of SS, TN, TP and TOC during this period were 3020 mg L 1, 36.17 mg L 1, 12.32 mg L 1, and 83.22 mg L 1. The correlation coefficients between SS and TN, TP, and TOC in the drainage water were 0.911, 0.897 and 0.915. These findings confirm that the concentrations of drainage water increased rapidly when the puddling processes began, and that high concentrations were maintained during the farming activities. Moreover, the high concentrations did not decrease following completion of the daily activities, which indicates that drainage water contains high concentrations of these compounds throughout the puddling period. However, a review of the history of farming activities and drainage water at paddy field No. 12 revealed that no water was released from that paddy field via the surface drain during the puddling processes. According to the farmer in charge of that field, there is an optimal water depth for puddling at which it is not necessary to drain the water during the puddling process, but that depth is uncertain.
Fig. 3. Changes in water quality in response to puddling processes conducted using a tractor and drainage gate operation on each paddy field.
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Plate 1. Drainage water and puddling processes.
The composition ratios of TN and TP in the drainage water during the puddling period are shown in Fig. 4. Specifically, the discharge ratios of dissolved nitrogen (NH4–N, NO2–N, and NO3–N) to TN were small from 29 May to 31 May, as evidenced by an average of 2.9% NH4–N, 0.2% NO2–N, and 2.1% NO3–N being detected in the TN during this period. However, the ratio of the dissolved nitrogen to TN began increasing daily from 1 June, with maximum ratios of 40.8% NH4–N, 12.5% NO2–N, and 29.7% NO3–N observed on 3 June. In addition, the concentration of PO4–P also tended to increase from 1 June. This was demonstrated by an average ratio of 3.6% PO4–P to TP observed from 29 May to 31 May and then increasing by 15.5% on 3 June.
In the target paddy fields, rice transplanting began on 31 May and was completed on 3 June. During this period, farmers attempted to manage and decrease the volume of water discharged through the surface drain to increase the efficiency of the chemical fertilizer, as several types of fertilizer were applied simultaneously during transplanting. However, based on the date at which rice transplanting began (31 May) and the increase in the dissolved nutrients observed in the drainage water, it is likely that some of these fertilizers were discharged via surface water drainage. In addition, it has been reported that the concentrations of N and P in drainage water increase during puddling and transplanting, and also when fertilizer is applied (Takeda et al., 1991; Feng et al., 2004). Our results suggest that a similar situation occurred in the fields we studied. 4.3. Load discharge during puddling in 2006 To evaluate the impact of water drained during the puddling period on the downstream water environment, the average daily loads of drainage water during puddling, the growing season, and the non-irrigation period were determined (Fig. 5). A higher load of contaminants was discharged downstream during the puddling period than during the growing season and the non-irrigation period. Suspended solids increased almost 50-fold during the puddling period when compared with the other periods. Similar trends were observed for other constituents, although the increases were somewhat smaller than the increase in suspended solids.
Fig. 4. Composition ratios of TN and TP in drainage water during the puddling and transplanting period.
Fig. 5. Daily load discharges of SS, TN, TP and TOC from the paddy field area.
H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
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Table 3 Annual pollutant discharge loads (kg) in 2006 and the ratios (%) of the load discharge during the puddling period to the discharge during the irrigation period and the annual discharge. Suspended solids Puddling
Total nitrogen
Ammonium nitrogen
Nitrite nitrogen
Nitrate nitrogen
Particulate nitrogen
Total phosphorus
Phosphate phosphorus
Particulate phosphorus
Total organic carbon
5/29 5/30 5/31 6/1 6/2 6/3
1479.3 1301.9 1016.3 549.8 242.1 25.2
26.7 19.2 19.7 14.5 8.3 3.4
0.73 0.55 0.58 0.74 0.81 1.38
0.073 0.028 0.018 0.028 0.011 0.422
1.01 0.37 0.12 0.63 0.61 1.00
24.92 18.27 18.98 13.06 6.87 0.58
6.9 5.1 5.0 2.3 1.4 0.2
0.43 0.14 0.09 0.20 0.13 0.03
6.4 5.0 5.0 2.1 1.3 0.2
47.5 39.0 41.5 28.4 13.9 4.3
Total
4614.6
91.8
4.79
0.581
3.75
82.67
21.0
1.03
20.0
174.7
2213.9 3712.5 43.8
325.6 590.5 9.1
160.3 251.3 1.1
25.6 3.2 2.0
83.7 118.3 1.8
56.0 222.8 22.9
29.8 29.3 26.2
13.7 3.4 5.7
16.1 25.9 32.2
1040.6 1121.6 7.5
67.6
22.0
2.9
2.2
4.3
59.6
41.3
7.0
55.3
14.4
Growing season 6/4 to 10/9 Non-irrigation period Ratio of puddling discharge vs. annual discharge Ratio of puddling discharge vs. irrigation period discharge
The ratios of loads discharged during the puddling period to the annual discharged loads were 43.8% for SS, 9.1% for TN, 22.9% for PN, 26.2% for TP, and 32.2% for PP (Table 3). According to a study conducted by Kondoh et al. (1993) in Niigata Prefecture, the average ratios of the TN and TP loads during the puddling periods to the overall TN and TP loads during the irrigation periods (puddling and growing periods) were 24.8% and 22.0%, respectively. In our study area, the TN and TP loads during the puddling period were 22.0% and 41.3% of the total loads observed during the irrigation period, respectively. When the results of the present study were compared with those of a study conducted by Kondoh et al., the ratio of TN discharged during the puddling period to that of TN discharged during the irrigation period was similar, even though the TP load was almost twice as high in the present study. Moreover, the load of dissolved substances during the puddling period was not dominant against the load discharge during the irrigation period (less than 10%). This finding indicates that the load discharge of particulate substances such as PN and PP during the puddling period has a greater impact on the downstream water environment than that of dissolved contaminants, as evidenced by the discharge percentages of PN and PP being approximately 60% and 55% of those observed during the irrigation period, respectively. 5. Conclusions This study focused on changes in the concentration of contaminants in drainage water from paddy fields over approximately 2 years, while paying particular attention to the relationship between farming activities during the puddling period and the quality of paddy drainage water in 2006. This study revealed several interesting aspects, which are as follows: 1. The drainage water quality at the sampling point was altered in response to puddling processes conducted using a tractor and by operation of the drainage gate. 2. Not all paddy fields released drainage water via the surface drain during the puddling process (for example, paddy field No. 12). Hence it is not always necessary to release water during puddling. 3. The criteria for determining the optimal water depth for the puddling process, which does not require discharge of the water via a surface drain, have not yet been established. If the optimal water depth were found for puddling and the amount of water drained during that time were decreased (such as in paddy field No. 12), contaminant load discharges would
decrease greatly. Additionally, determining the optimal depth for puddling would allow the amount of nutrient salts applied by chemical fertilizer to be decreased because the nutrient salt runoff via surface drainage would decrease. Taken together, these findings indicate that developing methods to optimize the water depth in paddy fields during the puddling process can reduce costs while improving and protecting the downstream environment of nearby bodies of water. Acknowledgments The authors would like to express our gratitude to the farming union in the study area for their cooperation. Additionally, the authors also gratefully acknowledge the support of Mr. Ken-ichi Sawata and Mr. Hidenori Takubo during the course of this study. Finally, this study was partially supported by a grant from the Shimane University Priority Research Project and a Grant-in-Aid for Scientific Research ‘‘KAKENHI’’ (#16380221) from the Japan Society for the Promotion of Science (JSPS). References Adachi, K., Sakaki, C., 1999. Percolation and seepage. In: Mizutani, M., Hasegawa, S., Koga, K., Goto, A., Murty, V.V.N. (Eds.), Advanced Paddy Field Engineering. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, p. 388 pp. Braskerud, B.C., 2002. Factors affecting nitrogen retention in small constructed wetlands treating agricultural non-point source pollution. Ecological Engineering 18, 351–370. Feng, Y.W., Yohinaga, I., Shiratani, E., Hitomi, T., Hasebe, H., 2004. Characteristics and behavior of nutrients in a paddy field area equipped with a recycling irrigation system. Agricultural Water Management 68, 47–60, doi:10.1016/ j.agwat.2004.02.012. Kaneki, R., 2003. Reduction of effluent nitrogen and phosphorus from paddy fields. Paddy and Water Environment 1, 133–138, doi:10.1007/s10333-003-0020-5. Kim, J.S., Oh, S.Y., Oh, K.Y., 2006. Nutrient runoff from a Korean rice paddy watershed during multiple storm events in the growing season. Journal of Hydrology 327, 128–139, doi:10.1016/j.jhydrol.2005.11.062. Kondoh, T., Misawa, S., Toyota, M., 1992. Characteristics of effluent loads of nutrient salts (N, P) from paddy fields located in the alluvial and lower area in Hokuriku District – research study on nutrient load in the low plain areas of Niigata. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 159, 17–27 (in Japanese with English abstract). Kondoh, T., Misawa, S., Toyota, M., 1993. Characteristics of effluents of nitrogen and phosphorous in paddy fields during the paddling and transplanting season. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 164, 147–155 (in Japanese with English abstract). MAFF, 2005. Abstract of statistics on agriculture forestry and fisheries in Japan. http://www.maff.go.jp/toukei/abstract/index.htm. Mizutani, M., 1999. Development of paddy field engineering in Japan. In: Mizutani, M., Hasegawa, S., Koga, K., Goto, A., Murty, V.V.N. (Eds.), Advanced Paddy Field Engineering. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, p. 388 pp. Namiki, H. (Ed.), 1993. Analytical Method of Water Quality for Industrial Wastewater (JIS K 0102). Japan Standard Association, Tokyo (in Japanese).
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H. Somura et al. / Agricultural Water Management 96 (2009) 1052–1058
Sagi, T., 1966. Determination of ammonia in sea water by the indophenol method and its application to the coastal and off-shore waters. Limnology and Oceanography 13, 440–447. Shiratani, E., Shiofuku, T., Kubota, T., Yoshinaga, I., Hasebe, H., 2003. Estimation of nutrient elution and removal on sediment surface of clayey canal based on hydraulic model experiments. Japan Agricultural Research Quarterly 36 (4), 195–200. Tabuchi, T., Kuroda, H., 1991. Nitrogen outflow diagram in a small agricultural area having uplands and lowlands – research on outflow load from an agricultural area without a point source (III). Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 154, 65–72 (in Japanese with English abstract). Tabuchi, T., Hasegawa, S. (Eds.), 1995. Paddy Fields in the World. The Japanese Society of Irrigation, Drainage and Reclamation Engineering, Tokyo, 353 pp. Takeda, I., Kunimatsu, T., Kobayashi, S., Maruyama, T., 1991. Pollutants balance of a paddy field area and its loadings in the water system – studies on pollution
loadings from a paddy field area (II). Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 153, 63–72 (in Japanese with English abstract). Takeda, I., Fukushima, A., 2004. Phosphorus purification in a paddy field watershed using a circular irrigation system and the role of iron compounds. Water Research 38, 4065–4074, doi:10.1016/j.watres.2004.08.003. Takeda, I., Fukushima, A., 2006. Long-term changes in pollutant load outflows and purification function in a paddy field watershed using a circular irrigation system. Water Research 40, 569–578, doi:10.1016/j.watres.2005.08.034. Tomas, E.J., Whigham, E.D., Hofmockel, K.H., Pittek, M.A., 2003. Nutrient and sediment removal by restored wetland receiving agricultural runoff. Journal of Environmental Quality 32, 1534–1547. Yamaoka, M., Shinogi, Y., Abenney-Mickson, S., Saito, T., 2003. Estimation of nitrate removal potential for upland soil. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation Engineering 225, 43–53 (in Japanese with English abstract).