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Water, Air, and Soil Pollution: Focus (2005) 5: 165–173 DOI: 10.1007/s11267-005-7411-0

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Springer 2005

REGIONAL ASSESSMENT OF NUTRIENT AND PESTICIDE LEACHING IN THE VEGETABLE PRODUCTION AREA OF RATTAPHUM CATCHMENT, THAILAND W. CHATUPOTE∗ and N. PANAPITUKKUL Faculty of Natural Resources, Prince of Songkhla University, Hat Yai, Thailand (∗ author for correspondence, e-mail: [email protected]; phone: +66 74 286 175; fax: +66 74 212 823)

Abstract. Regional groundwater vulnerability maps to indicate the impact of leaching of chemicals under different management scenarios were prepared for the Rattaphum Catchment using several leaching models and GIS techniques. The Attenuation Factor (AF) model was used to simulate the leaching potential of several pesticides for selected soils in the catchment under different rates of recharge from irrigation. The LEACHN model was used to simulate the NO− 3 leaching potential and LEACHP was used to simulate leaching potential of metolachlor under different management scenarios. The results showed that only a small number of pesticides have the potential to contaminate the shallow groundwater. However, the risk of contamination with nutrients is much higher due to the mobility and conservative nature of the NO− 3 . The LEACHP results indicated that the intensive use of agrochemicals in the vegetable growing area, especially during the rainy season when the groundwater is near the surface, increases the risk of pesticide contamination. The results of upscaling from the farm to the catchment scale using soil maps and GIS techniques under various management scenarios and chemical application rates showed that the most effective strategy to reduce chemical leaching is by reducing pesticide application rates and optimizing the application of irrigation water. The identification of potential high risk farms by ranking soils and agricultural practices could be used to formulate management practices that reduce pesticide contamination of the surface and ground water resources in the area. Keywords: GIS, leaching models, pesticides, surface and groundwater contamination, upscaling

1. Introduction This study was conducted in the vegetable growing areas of Rattaphum Catchment, Songkhla Lake Basin (SLB) (Songkhla Lake Basin, 1985). The main groups of agricultural agro-ecosystems consist of rubber, fruits, rice and vegetables (Kamnalrut et al., 2001). Of the total cultivated area, paddy rice occupies about 50%, rubber about 40% and the intensive agriculture (fruits, vegetables and field crops) about 10%. However, the economic return per unit land area is higher from the intensive agriculture. The main vegetables grown are: cauliflower, kale, onion, petasi, lettuce, eggplant and chilli. It is estimated that the fruit and vegetable industry in the Rattaphum watershed region is worth about 30 million dollars per year and engages a workforce of about 35,000 (Department of Agriculture, 2000). The vegetable production systems in the Rattaphum Catchment consist of intensive commercial farms and home garden vegetable farms. The intensive commercial

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W. CHATUPOTE AND N. PANAPITUKKUL

farms are mainly located in the flood plain with medium to clay soils, while the home gardens are mainly on the old sand dunes with light textured soils near Songkhla Lake. In commercial vegetable areas, at least four high market-demand vegetable crops (chaisim, Chinese cabbage and kale) are grown annually. In the home garden vegetable area, two to three crops are grown annually (shallot, cauliflower, chaisim, lettuce and others). In both areas, the vegetable cropping season is between January and September. No cropping takes place between October and December due to the rainy season (Kamnalrut et al., 2001). The application of inorganic fertilisers and chicken manure in the Rattaphum Catchment is high (550 kg/ha N, 230 kg/ha P and 150 kg/ha K) (Kamnalrut et al., 2001). A wide variety of insecticides and fungicides are also used. The most commonly used insecticides include carbosulfan, cabaryl, methamidophos, prothiophos, fenvalerate, permethrin and teflubenzuron, while the most common fungicides include benomyl, mancozeb, diuron, captafol, chlorothalonil and copper oxychloride (Pipithsagchan et al., 1994, 2001; Pipithsagchan and Choto, 1999). Irrigation is essential to supplement natural precipitation, especially during the dry season. Irrigation water is mainly from shallow groundwater wells, and during rainless periods is applied almost daily and sometimes even twice a day (Kamnalrut et al., 1999). The frequent and high use of fertilisers and pesticides, intensive irrigation on light and medium textured soils combined with a shallow water table helps create a favourable environment for the excessive leaching of nutrients and pesticides into the subsurface environment. The objectives of this study were to assess nutrient and pesticide leaching at the farm scale level and extrapolate the results to the catchment level using GIS techniques.

2. Materials and Methods The major soil types in the vegetable areas were sampled and analysed to determine their physical characteristics and other parameters needed for the modelling (Panapitukkul et al., this issue). The location of each vegetable farm was referenced by GPS. Information on factors affecting the upscaling and identification of high risk location areas was collected by field surveys, and interviews with both commercial and home garden producers were conducted. The data collected included information on the cropping calendar, irrigation practices and rates of chemical and pesticide application. Several leaching models (Hornsby Index, Attenuation Factor (AF), LEACHP and LEACHN) were used in the study and are briefly described here. 2.1. H ORNSBY INDEX The tendency of a pesticide to move with water through soils is influenced by its chemistry; this is referred to as leaching potential. The Hornsby Index (HI) is a

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relative indication of the leaching ability of a pesticide (Hornsby, 1992). It combines the sorption characteristics of the soil with the half-life of a pesticide to define a leaching index for that pesticide. Hornsby Index =

K oc T1/2

× 10

where Koc is organic carbon sorption coefficient and T1/2 is pesticide half life. The smaller the index, the greater the possibility of the pesticide leaching to the groundwater (Hornsby, 1992). A pesticide with an index of ≤10 or Koc of ≤100 would have a high leaching potential. If the index is ≥2000, the pesticide would have a low leaching potential. Pesticides that do not meet these criteria are considered to have intermediate leaching potential (Nofziger et al., 1982). 2.2. A TTENUATION FACTOR (AF) A ratio of half-life (T1/2 ) to the organic-carbon normalised sorption coefficient (Koc ) of a pesticide can serve as a simple index of its leaching potential; these two parameters can be used to group the pesticides in terms of their relative potential for groundwater contamination (Rao and Alley, 1993). 2.3. LEACHP

AND

LEACHN

LEACHP and LEACHN are mechanistically-based models of water and solute movement that make it more suitable than the capacity type models for simulating landuse impacts on leaching (Hutson and Wagenet, 1992). They use the numerical solution of the Richards equation to simulate the water flow and convection– dispersion equation to estimate pesticide and nutrient movement. The soil data required include: clay, silt, organic carbon, water retention properties, bulk density and hydraulic conductivity; crop, chemistry and infiltration data are also required.

3. Results and Discussion 3.1. LEACHING P OTENTIAL The Hornsby Index was used to find the properties and leaching potentials of commonly used pesticides in the Rattaphum Catchment (Table I). The results indicated that most of the pesticides had intermediate leaching potential. Paraquat, profenofos, permethrin and cypermethrin had low leaching potentials, and carbofuran, metolachlor, carbendazim and methamidophos had high leaching potential. However, the risk of their leaching to the groundwater may be

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TABLE I Leaching potential of the most commonly used pesticides in Rattaphum Catchment Pesticide Carbofuran (3) Methamidophos (2)

Half-life (T1/2 ) days

Soil sorption (Koc )

HI (Koc /T1/2 ) × 10

Leaching potential

50 6

22 5

4 8

Metolachlor (7) Carbendazim (8) Alachlor (5) Mevinphos (4) Glyphosate (9) Mancozeb (10)

200 120 15 3 47 70

90 400 170 44 1105 2000

22 33 113 146 235 285

High High Intermediate Intermediate Intermediate Intermediate

Captan (6) Fenvalerate (13)

3 35

200 5300

666 1514

Intermediate Intermediate

Chlorothalonil (16) Endosulfan (1) Carbaryl (12)

30 50 10

1380 12,400 300

460 2480 300

Intermediate Intermediate Intermediate

8 1000

2000 1,000,000

2500 10,000

Low Low

30

100,000

33,333

Low

Profenofos (11) Paraquat (15) Cypermethrin (14)

High High

low because of their relatively short half-life. This will not be the case in the areas with shallow groundwater and intensive irrigation. The AF model was also used to screen the highly leachable pesticides used in Rattaphum Catchment. Five soil types were used. For each soil, the pesticides lying on the right side of a specific soil line have relatively low groundwater contamination potential, because they have sufficiently long residence time and/or short half life (Rao and Alley, 1993). Pesticides that lie above the line have relatively higher contamination potential, because they degrade slowly and/or leach rapidly. The results show that all the pesticides are filtered through the soils due to the high organic carbon content (Figure 1). For upscaling to the catchment scale, the AF model was also used in conjunction with soil maps of the Rattaphum Catchment to study the vulnerability of the most commonly used pesticide at the regional scale. The fractions of the applied pesticide mass that are likely to leach past the chosen reference depth of 800 mm are shown in Figure 2 which displays the regional risk of a pesticide (metolachlor) for three soils from the project area under three different recharge rates of 10, 30 and 60 mm per day. As expected, the results showed that the AF index rose with increased recharge rate. The maps also show the effect of different soils on the AF index. The most


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Figure 1. Soil type control on pesticide attenuation. The results show that all the pesticides are filtered through the three soils from sites BP1, BP4 and BP8 due to the high organic carbon content (see Table I for number of pesticide).

Figure 2. AF index of metolachlor at 800 mm depth and recharge rates of: 10 mm; 30 mm; and 60 mm/day (left to right).

vulnerable soils are the Kleang and Ban Thon series, which are relatively well drained soils in the western parts of the catchment. The least vulnerable ones are Visai Complex and Bang Klam soils due to the relatively low hydraulic conductivity and higher organic carbon content in the top 150 mm of the soil. 3.2. L EACHING OF N UTRIENTS AND GIS TECHNIQUES

AND

PESTICIDES U SING LEACHP, LEACHN

LEACHP was used to simulate the leaching of metolachlor in the vegetable production areas. Simulations were carried out to determine the impact of various management scenarios on leaching of the pesticides. Four management scenarios were simulated: (1) existing farming practices with normal rate of irrigation; (2) fifty

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Figure 3. Metolachlor leaching below 800 mm for LEACHP Scenarios 1 and 4 with the eastern area of vegetable showing the highest leaching potential (left to right).

percent reduction from existing practices; (3) double the organic carbon content of the top 200 mm of the soil; and (4) reduce irrigation water by half and double the organic carbon content in the top 200 mm of soil. The amount of pesticide applied in all four scenarios was 100 mg/m2 . The results were upscaled to the catchment using GIS techniques (Figure 3). Applying Scenario 1, the pesticide leaching below the 800 mm layer for the Kleang and Ban Thon soils was at the rate of 40–50 and 50–60 mg/m2 respectively. This was due mainly to the low organic carbon of the Kleang soil and well drained sandy texture of Ban Thon soil. In most of the poorly drained paddy soils the pesticide leaching below the 800 mm depth ranged from 25 to 30 mg/m2 . Reducing the amount of pesticide application to half or doubling the organic carbon content resulted in a reduction of the chemical flux by half in all soils (Scenarios 2 and 3 respectively). This is due to an increase in the filtration capacity of the pesticide in the top soils and allowing for more time to degrade. A combination of halving of irrigation water and doubling the organic carbon content in the top 200 mm of soil (Scenario 4), significantly decreased the amount of pesticide flux in all soils and was a better management option for reducing the leaching of chemicals. LEACHN model was used to simulate the leaching of nitrogen fertilisers applied to both commercial and home garden vegetable production areas. In those areas, nitrogen fertilisers (inorganic N and chicken manure) are applied at the rates of 130 and 250 kg N/ha respectively. Modelling results showed that the commercial vegetable areas and the light textured soils in the home garden areas had relatively high N leaching past 800 mm depth, due mainly to high N application rate, intensive rain and irrigation (Figure 4). 3.3. I DENTIFICATION

OF

H IGH C HEMICAL R ISK FARMS

Data required for the identification of high chemical risk areas included farm vegetable locations, soil types (Panapitukkul and Chatupote (this issue)) and pesticide


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Figure 4. NO− 3 leaching showing high leaching in the vegetable area.

usage. These were collected using GPS and questionnaires, respectively. The attributes used in ranking areas in terms of risk were: leaching potential for each soil, rates of chemical application, cultural practices, soil texture/drainage classes, depth to water table, soil texture/clay content, organic matter (OM) content and acreage of vegetable fields. The score and weighting results for each attribute were grouped into the risk potential classes (Figure 5). The results showed that the high risk locations were mainly located in the commercial vegetable areas with high chemical

Figure 5. The location of low to high risk areas in the vegetable growing region of the Rattaphum Catchment.

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(pesticides and nitrate) application rates and the excessive use of irrigation water during the intensive vegetable production period. The problem was compounded by the development of shallow ground water levels at the end of the rainy season.

4. Conclusions Application of leaching models to determine the potential for pesticide and nutrient leaching in vegetable growing areas of the Rattaphum Catchment indicated that only a small number of pesticides were likely to cause groundwater contamination. The risk of NO− 3 contamination was much higher due to its mobility and conservative nature. The AF and LEACHP models indicated that the vulnerability to chemical leaching was dependent on the amount of chemical application and irrigation water. The results of upscaling to the catchment using soils subject to different management scenarios and different rates of chemical application indicated that the most effective approach to reduce chemical leaching was to limit application rates and optimise the amount of irrigation water used. The identification of potential high risk farms by ranking soils and agricultural practices could be used to formulate the most appropriate management practices that would result in a reduction of pesticide contamination/leaching to the surface and ground water resources of the Rattaphum Catchment.

References Hutson, J. L. and Wagenet, R. J.: 1992, LEACHM, Leaching Estimation and Chemistry Model, Version 3, Cornell Univeristy, New York. Hornsby, A. G.: 1992, ‘Site-specific pesticide recommendations: The final step in environmental impact prevention’, Weed Tech. 6, 736–742. Department of Agriculture: 2000, Annual Report, Ministry of Agriculture and Co-operatives, Bangkok, Thailand. Kamnalrut, A., Choto, S. and Pipithsangcha, S.: 1999, ‘Management practices in the agrosystems in Rattaphum watershed area’, in Proceedings of an International Workshop on Agrochemical Pollution of Water Resources Under Tropical Intensive Agricultural Systems, Songkhla, Thailand, 3–7 May. Kamnalrut, A., Choto, S. and Pipithsangchan, S.: 2001, ‘Management practices in the agrosystems of Rataphum watershed area’, in Proceedings of an International Workshop on Agrochemical Pollution of Water Resources Under Tropical Intensive Agricultural Systems, Hat Yai, Thailand, 3–7 May. Nofziger, D. L., Chen, J. S., Wu, J., Ma, F. and Hornsby, A. G.: 1982, ‘CMLS98B: The chemical movement in layered soils. Model for batch processing’, Division of Agricultural Sciences and Natural Resources, Oklahoma State University. Panapitukkul, N., Pengnoo, N., Siriwong, C. and Chatupote, W.: 2005, ‘Hydrogeomorphological controls on groundwater quality in the Rattaphum Catchment (Songkhla Lake Basin), Thailand’, Water Air Soil Pollut., this issue.


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Panapitukkul, N. and Chatupote, W.: 2005. Variability of Flow and Solutes in the Rattaphum Catchment (Songkhla Lake Basin), Thailand (this issue). Pipithsagchan, S., Kanatharana, P., Siriwong, C., Kammalrat, A. and Chatupote, W.: 1994, ‘Impact of the use of agrochemicals on water resources in southern Thailand’, ACIAR Proceeding No 61, Agricultural Impact on Groundwater Quality, Canberra, Australia, pp. 71–76. Pipithsangchan, S. and Choto, S.: 1999, ‘The use and abuse of pesticides in the agrosystems of Rataphum Watershed Study Area, Thailand’, in Proceedings of an International Workshop on Agrochemical Pollution of Water Resources Under Tropical Intensive Agricultural Systems, Hat Yai, Thailand, 3–7 May. Pipithsangchan, S., Sritungnan, S. and Choto, S.: 2001, ‘On-farm comparisons between bioinsecticides and synthetic insecticides in vegetable production’, in Proceedings of a Conference, Hat Yai, Thailand, 16–18 February 2000. Rao, P. S. C. and Alley, W. M.: 1993, ‘Pesticides’, in W. M. Alley (ed), Regional Groundwater Quality, VNR, New York, pp. 345–382. Songkhla Lake Basin Planning Study: 1985, Main Report, John Taylor & Sons.