Monitoring nutrient accumulation and leaching in plastic greenhouse cultivation

Agricultural Water Management 146 (2014) 11–23

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Monitoring nutrient accumulation and leaching in plastic greenhouse cultivation Eun-Mi Hong a , Jin-Yong Choi a,b,∗ , Won-Ho Nam c , Moon-Seong Kang a,b , Jeong-Ryeol Jang d a

Research Institute for Agriculture & Life Sciences, Seoul National University, Seoul, Republic of Korea Department of Rural Systems Engineering, Seoul National University, Seoul, Republic of Korea c School of Natural Resources, University of Nebraska-Lincoln, Lincoln, NE, USA d Department of Saemangeum Research, Rural Research Institute, Korea Rural Community Corporation, Ansan, Republic of Korea b

a r t i c l e

i n f o

Article history: Received 6 September 2013 Received in revised form 2 July 2014 Accepted 15 July 2014 Keywords: Fertigation Nutrient accumulation Nutrient leaching Plastic greenhouse cultivation

a b s t r a c t Plastic greenhouse cultivation is expanding in Korea due to increasing demand for value-added agricultural products. Potential pollutant accumulate in the root zone and may leach downward by irrigation water, causing soil and groundwater contamination. A nutrient management plan is needed to reduce the nutrient load from plastic greenhouse cultivation, although few studies have examined nutrient leaching and accumulation in the soil layers. In this study, soil, soil water, irrigation water, and weather conditions were monitored in the twice-a-year cultivation of cucumber and tomato in a plastic greenhouse for 2 years. Soil and soil water samples were analyzed every two weeks to investigate the level of nutrient accumulation and the nutrient leaching characteristics. Excessive fertilization caused nutrient accumulation in the root zone and the leaching of nutrients into the lower soil profile. The amount of phosphorus that accumulated on the soil particles of the root zone, however, did not significantly leach out with soil water movement. The electrical conductivity (EC) and NO3 –N of the soil water gradually increased from the root zone to the lower zone and the NO3 –N average concentration in the 150 cm soil layer was nearly equal to the maximum concentration of the fertigation water. The amount of percolation was 476.3 mm (56% of the irrigation water) in the cropping period for first cucumber cultivation (CP-C#1), 241.8 mm (53% of the irrigation water) in the cropping period for second cucumber cultivation (CP-C#2), 346.6 mm (42% of the irrigation water) in the cropping period for first tomato cultivation (CP-T#1), and 348.1 mm (51% of the irrigation water) which in the cropping period for second tomato cultivation (CPT#2). The total NO3 –N losses through leaching from the lower zone (60 to 150 cm soil layer) to deeper soil were 137.4 kg N ha−1 in the CP-C#1, 195.9 kg N ha−1 in the CP-C#2, 758.6 kg N ha−1 in the CP-T#1, and 54.7 N ha−1 in the CP-T#2. A significant amount of nutrients were not utilized for crop growth but instead leached in accordance with the movement of the soil water. The results of this study can serve as a baseline for the long-term monitoring of greenhouse nutrient loads and can be used in the design of new guidelines to reduce nutrient loads from plastic greenhouse cultivation. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Greenhouse cultivation has expanded due to the increasing demand for value-added agricultural products and the decreasing area of available agricultural land in Korea. According to the Agriculture, Forestry and Fisheries survey, the number of households with greenhouse farms was 10.2% of the total number of rural

∗ Corresponding author at: Seoul National University, Department of Rural Systems Engineering, Seoul 151742, Republic of Korea. Tel.: +82 2 880 4583; fax: +82 2 873 287. E-mail address: [email protected] (J.-Y. Choi). http://dx.doi.org/10.1016/j.agwat.2014.07.016 0378-3774/© 2014 Elsevier B.V. All rights reserved.

households in 2010 (KOSTAT, 2011). Approximately 60% of the new plastic greenhouses in Korea have been installed in paddy fields, where water for crop is typically obtained from irrigation or precipitation (Lee et al., 1998). Unlike in paddy field cultivation, precipitation is blocked in plastic greenhouse cultivation and water for crops can only be obtained through irrigation systems. Nutrients required for plant growth in plastic greenhouse systems are supplied by fertigation, which is a fertilization method that involves supplying nutrients in irrigation water because it is known to increase nutrient uptake by plants (Singandhupe et al., 2003; Mahajan and Singh, 2006; Liang et al., 2013). Plastic greenhouse farming occurs year-round, with more than two crop rotations per year. Because of the misconception that

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the application of large amounts of nutrient fertilizer results in high crop yields, it is general practice to apply a standard dose of fertilizer to a single crop once a year. For this reason, excess nutrients have been applied in greenhouses without consideration for the impact on the physical and chemical characteristics of the soil. If the amount of nutrients applied to the soil exceeds the amount needed by the crops, it can lead to soil pollution (Thompson et al., 2007; Min et al., 2012). During crop cultivation in plastic greenhouse, excess nutrients that are a potential source of nonpoint pollution accumulate in the soil. In long-term greenhouse cultivation, nutrient accumulation leads to higher soil salinity (Shi et al., 2009). Some nutrients that accumulate in the root zone may leach downward with the application of irrigation water, possibly causing soil and groundwater contamination (Kim et al., 2008). In a study by Ha et al. (1997), because of yearly increases in greenhouse cultivation, nitrate–nitrogen (NO3 –N) concentrations in the shallow groundwater near the greenhouse area had increased and in some cases the concentrations exceeded the groundwater quality standard for agricultural water (20 mg L−1 ). In addition, it was found that in Korea, 82.8% of the irrigation water in greenhouses was supplied by shallow groundwater (Lee et al., 1998). If contaminated or salinized groundwater is used for irrigation water, it can cause a cycle in which nutrients reaccumulate in the soil (Lee et al., 2008). A nutrient management plan is needed to reduce pollution loads from greenhouse cultivation. To minimize nutrient accumulation in the upper soil layer and the leaching of nutrients into lower soil layers and shallow groundwater, it is necessary to investigate soil nutrient concentrations and the processes of nutrient accumulation and leaching in the soil layers. In particular, nitrogen and phosphate are important nutrients not only for plant growth but also for soil and water pollution management in agricultural areas. Nitrogen is a mobile nutrient that is rapidly leached. When there is no supply of irrigation water, nitrogen leaching may be slow or nonexistent (Li et al., 2003; Shen et al., 2003; Ajdary et al., 2007; Yu et al., 2008). However, a combination of irrigation and high nitrogen use in plastic greenhouse cultivation results in the substantial loss of nitrogen through leaching and the consequent contamination of the groundwater by nitrogen, especially, NO3 –N (Li et al., 2003; Thompson et al., 2007; Wan et al., 2010). Phosphate on the other hand, is not easily leached with the movement of water from soil layers. Phosphate is strongly fixed to soil particles and is reactive with iron, calcium, and several other elements, so most phosphate forms tight bonds with soil and tends to accumulate rather than leach (Yang et al., 2011; Hu et al., 2012). Because there is little surface runoff in plastic greenhouses, phosphate accumulation in the soil can cause problems for soil management. In addition, an excessive concentration of phosphate in the soil particles interferes with the absorption of other ions in crops and can even leach into the lower soil layers along with the soil water (Peng et al., 2011). There are several studies that examine the status of soils in plastic greenhouses in Korea. These research projects (Kang and Hong, 2004; Lee et al., 2005; Lee et al., 2005; Lee et al., 2008, RDA, 2006) were all conducted in an area with a large proportion of plastic greenhouses, monitored the nutrients via the EC, and monitored the level of phosphorus pentoxide (P2 O5 ), NO3 –N, and total-nitrogen (T-N) in the surface only. The EC of the soil exceeded the levels suitable for crop production of the RDA (Rural Development Administration) (2.0 dS m−1 ) and sometimes even exceeded the standard of the U.S. Soil Salinity Laboratory Staff (4.0 dS m−1 ) (U.S. Salinity Laboratory Staff, 1954; Ha et al., 1997; RDA, 2006; Lee et al., 2008; Kim et al., 2008). Kang and Hong (2004) found a significant correlation between soil EC and NO3 –N. Lee et al. (2005) found that the ratio of the greenhouse area that could maintain the proper status of soil nutrients was 26.1% in EC and only 4.3% in P2 O5 . Castellanos et al. (2013) observed that greenhouse soil had sufficient quantities of nutrients even after

crop harvesting and that this phenomenon was particularly serious in plastic greenhouse systems in Korea. Unlike rice paddy or upland agriculture, in which pollutants leave the system through surface flow, pollutants in a greenhouse infiltrate into the soil and leach downward by water movement through soil pores. Therefore, it is important to understand the movement of contaminants not only along the surface of the soil but also from the surface to the subsoil. However, most studies have only focused on surface soil concentrations and the relationship between nutrient concentration in the surface soil layers and crop yield or groundwater quality in areas near plastic greenhouses (Lim et al., 2007; Kang and Hong, 2004). Nutrient monitoring studies of soil and soil water that include an analysis of soil depth, nutrient accumulation, and the process of nutrient leaching are lacking. Further plastic greenhouse studies are needed to understand the interactions among fertigation, water movement, nutrient cycling and the leaching process. This study aims to investigate soil nutrient concentrations and movement, especially phosphate accumulation and nitrogen leaching, under plastic greenhouse conditions. Nutrient leaching is related to soil moisture content, soil physical characteristics and the concentrations of available nutrients in soil and soil water (He et al., 2011; Castellanos et al., 2013). Therefore, in this study, to investigate the characteristics of nutrient accumulation and leaching in soil under plastic greenhouse cultivation, soil moisture content, irrigation, and climate conditions were monitored and fertigation water was collected at each fertigation event. Soil samples were collected before, during, and after cropping periods and soil water samples were collected to determine the fluctuations in soil nutrient concentrations as well as nutrient accumulation and leaching. Using the monitoring data and the results of the nutrient analyses, the volume of the percolated water in the root zone and the amount of nutrient loss in the soil layers were determined. 2. Materials and methods 2.1. Experimental site The field experiments were conducted in plastic greenhouses located in Namsa-Myeon, Cheoin-Gu, Yongin-Si, and Gyeonggi-Do, South Korea (E 37◦ 06 04 , N 127◦ 08 08 ). Fig. 1 shows a location map of the experimental sites. Although the study area was a rural area that has traditionally cultivated crops in rice paddies, the area has recently experienced an expansion in the greenhouse cultivation of vegetables and flowers. The 30-year average annual temperature in the study area is 11.4 ◦ C. The monthly high average air temperature is 25.6 ◦ C (August) and the low is −2.9 ◦ C (January). The 30-year average annual solar radiation is 18.7 MJ m−2 . The 30-year average annual precipitation is approximately 1312.2 mm and rainfall is mainly concentrated in the summer season from June to September. The soil type in the study area (RDA SIS, http://soil.rda.go.kr) is classified as the Seogcheon (SE) series (coarse loamy, mixed, nonacid, mesic Fluvaquentic Endoaquept). 2.2. Crop management At the experimental site (100 × 30 m), cucumber was cultivated two times during first year (2011) and tomato was cultivated two times during the second year (2012). Table 1 shows the cucumber and tomato crop management schedules for both years. In 2011, during the fallow period prior to planting (FP-C#1: fallowing period before first cucumber cultivation) from December 2 to December 23, 2010, the field was ploughed, the soil was bedded, and basal fertilizers were applied. In the second fallow period (FP-C#2: fallowing period before second cucumber cultivation) from June 20 to

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Fig. 1. Location map of the experimental sites.

August 2, 2011, basal fertilizers were applied but the field was not ploughed. The cucumber plants were transplanted on December 24, 2010 and August 3, 2011. The crops were harvested from February to June (CP-C#1: cropping period for first cucumber cultivation) and September to November (CP-C#2: cropping period for second cucumber cultivation). In 2012, during the fallow period prior to planting (FP-T#1: fallowing period before first tomato cultivation) from November 3 2011 to January 9, 2012, the field was ploughed, the soil was bedded and basal fertilizers were applied. In the

second fallow period (FP-T#2: fallowing period before second tomato cultivation) from June 30 to July 5, 2011, basal fertilizers were not applied and the field was not ploughed. The tomato plants were transplanted on January10, 2012 and July 6, 2012. The crops were harvested from February to June (CP-T#1: cropping period for first tomato cultivation) and September to November (CP-T#2: cropping period for second tomato cultivation). The field did not receive precipitation because it was covered by plastic. Drip irrigation systems were installed for irrigation and fertigation. In

Table 1 Dates of planting and harvesting and the annual sequence of cucumber and tomato crops. Crop planting periods1 2011

CP-C#1 (179 days) CP-C#2 (92 days)

2012

CP-T#1 (172 days) CP-T#2 (142 days)

1 2

Fallow period

Planting date

Final harvesting date

Irrigation times (including fertigation)

Dec. 2–Dec. 23, 2010 Jun. 21–Aug. 2, 2011 Nov. 3, 2011 –Jan. 9, 2012 Jun. 30– Jul. 5, 2012

Dec. 24, 2010

Jun. 20, 2011

Jan. (10)2 , Feb. (11), Mar. (16), Apr. (16), May (17), Jun. (11)

Aug. 3, 2011

Nov. 2, 2011

Aug. (13), Sep. (18), Oct. (17)

Jan. 10, 2012

Jun. 29, 2012

Jan. (6), Feb. (8), Mar. (12), Apr. (12), May (16), Jun. (9)

Jul. 6, 2012

Nov. 24, 2012

Jul. (7), Aug. (18), Sep. (18), Oct. (14), Nov. (1)

CP: cropping period, C: cucumber, T: tomato, #1: first cropping, #2: second cropping. (): Times.

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Table 2 Composition of the fertigation applications used in the experiment. Items

pH

T-N (mg L−1 )

T-P (mg L−1 )

NO3 –N (mg L−1 )

NH4 –N (mg L−1 )

EC (dS m−1 )

PO4 –P (mg L−1 )

Average Minimum–maximum

7.83 6.47–8.52

85.2 17.0–190.2

12.4 0.5–42.3

51.5 0.5–188.8

3.32 0.45–47.11

1.05 0.08–1.74

2.30 0.17–4.47

data, an Automatic Weather Station (AWS, WatchDog 2000 Series Weather Stations, Spectrum Technologies, Inc., Plainfield, IL) was installed in the center of the experimental site. Data for humidity (%), wind speed (m s−1 ), solar radiation (W m−2 ) and temperature (◦ C) were recorded every 15 min. Volumetric soil moisture content (%) was measured using a Frequency Domain Reflection (FDR) probe (EnviroSMART soil moisture probe, Sentek Pty. Ltd., Adelaide, Australia) at four depths (10, 30, 60, and 90 cm) and data were recorded every 15 min. To measure the volume of irrigation water over the experimental period, a flow meter was installed that collected data every 10 min. All hydrological data were recorded by a data logger and downloaded periodically.

Fig. 2. Nutrients and water flow processes in a plastic greenhouse.

this study, crop management and the frequency, volume and time of irrigation and fertigation followed local farming practices. From the time of planting until the last crop harvest date, fertigation events occurred every 2 or 3 days, although there were differences in the volume and nutrient concentrations of the applications. Table 1 shows the timing of the irrigation/fertigation events and Table 2 shows the average nutrient concentrations of the fertigation. Irrigation/fertigation water was applied for 2 or 3 h with an average volume of water per irrigation event of 20 m3 ha−1 . The average NO3 –N concentration of the fertigation applications was 51.5 mg L−1 , the average EC was 1.05 dS m−1 , and the average PO4 -P concentration was 2.30 mg L−1 . 2.3. Field monitoring, sampling and analyzing 2.3.1. Monitoring design Water and nutrient flows in a plastic greenhouse depend on the irrigation method, antecedent soil moisture and climate conditions, among other factors. Nutrients flow into the root zone through irrigation/fertigation. Some nutrients are taken up by plants, others accumulate in the root zone and the remaining nutrients are removed by leaching into lower soil layers as shown in Fig. 2. To monitor nutrient accumulation and leaching in this study, hydrological data were collected for soil moisture content, meteorological conditions, and irrigation events. Water quality data were collected for soil, soil water, and fertigation water. Fig. 3 shows a schematic of the monitoring design. 2.3.2. Hydrological monitoring The meteorological variables and soil moisture content were monitored in the plastic greenhouse. To collect meteorological

2.3.3. Soil and soil water data collection and analysis Soil and soil water samples were collected periodically. The soil samples were collected using an auger before, during and after crop cultivation at depths of 0–20, 20–40, 40–60, 60–80 and 80–100 cm with two replications per sampling. All soil samples were airdried and analyzed for soil texture and chemical characteristics. Table 3 shows the soil texture classification for the experimental site according to the United States Department of Agriculture (USDA) Soil Taxonomy. The soil in all soil layers was classified as a sandy loam, which is a texture with suitable physical characteristics for cucumber cultivation according to crop fertilizer application standards (RDA, 2006). To collect the soil water samples, soil water samplers (1900L, ENVCO, Auckland, New Zealand) consisting of suction cups with many pores were installed vertically into the soil at 30, 60, 90, and 150 cm depths prior to the experiment. For analyzing, the soil profile was divided into two zones as shown in Fig. 2: (1) the root zone (upper zone, from the surface to 60 cm in depth) and (2) the lower zone (60 to 150 cm in depth), and the monitored variables were sampled separately for each zone. Soil water was sampled biweekly during the periods of crop cultivation. The soil and soil water samples were analyzed at the Seoul National University National Instrumentation Center for Environmental Management (NICEM). The equipment and methods used in the analysis are shown in Table 4. To measure the accumulation of nutrients in the soil, the EC (EC1:5 methods, electrical conductivity of 1:5 soil to water extract) and the concentrations of NO3 –N, T-N, P2 O5 , and T-P were determined for each soil sample. To measure the nutrient leaching processes, the EC (ECw, electrical conductivity of the soil solution) and the concentrations of NO3 –N, T-N, and T-P were determined for the soil water samples. 2.4. Nutrient losses in the soil Nutrient leaching is related to the water flow. In order to investigate nutrient losses in the soil, the amount of water that percolated through the soil layers first needs to be determined. To estimate the Table 3 Soil physical characteristics at the experimental site prior to planting. Soil depth (cm)

Sand (%)

Silt (%)

Clay (%)

Soil texture

0–20 20–40 40–60 60–80 80–100

63.2 60.8 55.6 52.7 69.2

23.0 26.6 30.4 32.8 22.4

13.8 12.6 14.0 14.5 8.4

Sandy loam

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Fig. 3. Overview of the monitoring design at the experimental site.

volume of water that percolated out of the root zone (0–60 cm), the volume of percolated water was calculated as follows:

lower zone (60–150 cm) so it was assumed that NO3 –N was only lost by leaching.

DPt = SMt − SMt−1 +IRt − ET1

NO3 − Nleached =

SMt,i

(1)

SMCt,i × di = 100

SMt = ETo =



(2)

SMti

900 u − ea ) 0.408 (Rn − G) +  T + 273 2 (es

 +  (1 + 0.34u2 )



Lvolume (t) × CNO3 -N (t)

(3)

where Lvolume is the volume of drainage calculated using the soil moisture content, CNO3 -N is the NO3 –N concentration of the soil water (mg L−1 ), and t is the day of determination (Zhao et al., 2012).

(4)

3. Results and discussion

where SMC is the soil moisture content (%) and SM is the daily variation of volumetric soil moisture content (mm) calculated using the soil moisture monitoring data. The root zone was assumed to be from the surface to 60 cm depth within the soil layer as shown in Section 2.2.3. di is the soil depth (mm) at a soil layer of i cm. IR is the volume of irrigation water (mm) measured by the flow meter, DP is the volume of deep percolation (mm), t is the day of determination., ET is the evapotranspiration (mm) calculated by the FAO (Food and Agriculture Organization) Penman–Monteith equation (Eq. (4)),  is slope of saturated vapor pressure/temperature curve (kPa ◦ C−1 ), ␥ is psychometric constant (kPa ◦ C−1 ), U2 is wind speed at 2 m height (m s−1 ), Rn is total net radiation at the crop surface (MJ m−2 day), G is soil heat flux density (MJ/m2 day), T is mean daily air temperature at 2 m height (◦ C), es is saturation vapor pressure (kPa), and ea is actual vapor pressure (kPa). To determine the soil nutrient losses in the root zone and lower zone, leaching losses of NO3 –N were analyzed based on the soil moisture content and NO3 –N concentrations of the fertigation and soil water. The NO3 –N losses (NO3 –Nleached ) below the root zone were calculated by multiplying the concentration of soil water collected in the soil water sampler by the volumetric soil moisture content (Eq. (5)). Because soil water samples were collected every two weeks, these values were assumed to be the average concentrations during these days. There is little crop root activity in that

3.1. Nutrient accumulation in the plastic greenhouse soils Soil samples were collected and analyzed to determine the level of nutrient accumulation. Table 5 shows soil pH, EC, and nutrient (NO3 –N, NH4 –N, TN, P2 O5 , and TP) concentrations for each soil layer for two cucumber and two tomato crop rotations for two years. The average, minimum and maximum values for each variable tended to be the highest in the root zone (0–60 cm) and decreased with depth. The differences between the maximum and minimum values and the third and first quartile values were also higher in the root zone than in the lower soil zone. To compare nutrient accumulation in soils with different characteristics, the soil EC and P2 O5 and NO3 –N concentrations from early studies were also examined, as shown in Table 6. The results of the earlier studies suggest that a significant amount of nutrients accumulated in the soil caused by excessive fertilization (nutrient levels higher than the optimal value for crop absorption) during the cropping season. Although greenhouse cultivation has expanded, soil nutrient and salinity management techniques remain inadequate. The results of this study were similar to those of previous studies. According to the RDA (2006), average soil EC in greenhouse soils in Korea has slightly decreased from 3.7 to 2.9 dS m−1 since 1980. Nevertheless, most previous studies found EC values in surface soils (0–20 cm) that were higher than 2.0 dS m−1 (within the optimal

Table 4 Soil and soil water quality analysis methods. Analysis items

1 2

Analysis methods Soil1

Soil water2

NO3 –N (Nitrate–Nitrogen) T-N (Total Nitrogen)

EC meter (EC1:5, electrical conductivity of 1:5 soil to water extract) 2M-KCl extraction method Micro Kjeldahl method

P2 O5 (Phosphorus pentoxide) T-P (Total phosphorus)

Olsen P method Olsen P method

EC meter (ECw, electrical conductivity of the soil solution) ion chromatography method Reduction–Distillation Kjeldahl method – Absorption photometry method

EC (electrical conductivity)

(5)

Soil samples were analyzed in NICEM by the methods suggested in Sparks et al. (1996). Soil water samples were analyzed in NICEM by the methods suggested in MOE (2011).

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Table 5 Soil pH, EC (EC1:5), and nutrient concentrations during two cucumber and two tomato crop rotations. Soil layer (cm) 0–20 cm

20–40 cm

40–60 cm

60–80 cm

80–100 cm

1 2 3

Avg ± std Min–max2 1st Q–3rd Q3 Avg ± std Min–max 1st Q–3rd Q Avg ± std Min–max 1st Q–3rd Q Avg ± std Min–max 1st Q–3rd Q Avg ± std Min–max 1st Q–3rd Q 1

pH

EC (dS m−1 )

NO3 –N (mg kg−1 )

NH4 –N (mg kg−1 )

T-N (%)

T-P (mg kg−1 )

P2 O5 (mg kg−1 )

6.7 ± 0.3 6.1–7.2 6.6–6.9 6.9 ± 0.2 6.6–7.4 6.8–7.1 7.0 ± 0.3 6.3–7.4 6.9–7.2 6.6 ± 0.6 5.2–7.2 6.4–7.0 6.4 ± 0.5 5.3–7.2 6.4–6.6

4.0 ± 2.7 1.4–9.5 1.6–6.1 2.6 ± 1.8 1.1–6.7 1.2–4.1 2.5 ± 1.1 0.8–4.2 1.5–3.5 1.8 ± 0.8 0.7–3.6 1.2–2.2 1.7 ± 1.1 0.6–4.3 0.9–2.1

257.0 ± 148.9 64.3–475.3 110.8–394.5 212.3 ± 221.2 50.2–1014.2 92.9–243 123.5 ± 49.1 32.9–228.5 102.7–144.2 92.2 ± 35.6 14.1–160 74.5–107.6 86.7 ± 77.9 44.2–350.6 51–78

22.7 ± 25.6 ND–112.2 10.6–27.6 15.9 ± 12.3 ND–48.6 8.4–21.3 12.4 ± 8.7 ND–27.5 4.4–18 11.2 ± 11.2 ND–44.7 4.8–13.8 7.1 ± 8.4 ND–22.3 ND–10.2

0.3 ± 0.1 0.1–0.4 0.2–0.3 0.3 ± 0.1 0.2–0.4 0.2–0.3 0.2 ± 0.1 0.1–0.4 0.2–0.3 0.2 ± 0 0.1–0.2 0.1–0.2 0.1 ± 0 0.1–0.2 0.1–0.2

2,239 ± 1,016 310–4438 2,006–2,425 2,194 ± 849 1,040–4,084 1,888–2,184 1,978 ± 914 745–3,678 1,210–2,692 844 ± 438 380–1,856 486–981 629 ± 426 299–1,784 344–701

718 ± 276 213–1,388 533–881 641 ± 221 358–1,089 472–778 629 ± 351 162–1,398 358–950 248 ± 171 42–619 103–341 123 ± 160 13–484 20–191

Avg: average value, std: standard deviation value. Max: maximum value, min: minimum value. 1st Q: results from the first quartile of monitoring, 3rd Q: results from the third quartile of monitoring.

range of greenhouse cultivation). In this study, the average soil EC values were lower than 2.0 dS m−1 in the lower zone below the 60 cm soil layer (1.7–1.8 dS m−1 ), but in the root zone (0–60 cm), the EC ranged from 2.5 to 4.0 dS m−1 and the maximum EC in the surface was up to 9.5 dS m−1 , as shown in Table 5. Temporal variations of EC in the different soil layers are shown in Fig. 4(a). The average EC of the 0–20 cm soil layer found in the FP-C#1 was 3.5 dS m−1 , which was higher than the value of 2.0 dS m−1 . The average EC values for the CP-C#1 and the FP-C#2 were decreased but were increased after the CP-C#2. In 2012, the average EC of the 0–20 cm soil layer was increased up to 6.5 dS m−1 in CP-T#1, but after the last crop harvesting, the EC decreased below 2.0 dS m−1 after cropping periods (ACP). In the 20–60 cm soil layer, the EC of 2011 (cucumber crop) was similar or lower than 2.0 dS m−1 , but the EC for 2012 (tomato crop) was slightly increased. After the harvesting of the tomato, the EC was decreased to 1.6–1.8 dS m−1 . In the lower zone (below 60 cm), the EC was lower than 2.0 dS m−1 except in the FP-C#2, but even then the EC values were close to 2.0 dS m−1 . According to the fertigation data in Table 1, the fertigation levels were excessive in the last stage of cucumber cultivation. Even though a sufficient amount of nutrients had already been applied during the active crop growth period, farmers were likely to apply more fertilizer in the final month before finishing the harvest as they did in the active crop growth period. As a result, the nutrient levels in the soil

increased due to fertilization but the additional nutrients were not utilized for crop growth and instead accumulated in the root zone. This phenomenon was more apparent in 2012. P2 O5 is the nutrient most widely used to analyze the accumulation of nutrients on soil particles and in soil layers. According to the RDA (2006), as shown in Table 6, P2 O5 concentrations increased in the 2000s, with several studies reporting concentrations higher than 1500 mg kg−1 . P2 O5 concentrations in this study (123–718 mg kg−1 ) were lower on average than in the early studies. Nevertheless, P2 O5 concentrations in the root zone (0–60 cm) were higher than 500 mg kg−1 (the optimal value for greenhouse cultivation). Temporal variations of P2 O5 concentrations in the different soil layers are shown in Fig. 4(b). In the root zone from 0 to 60 cm, P2 O5 concentrations increased from 354.2 (FP-C#1) to 994.1 (FP-T#1) mg kg−1 at the 0–20 cm soil layer, from 365.6 (FP-C#1) to 939.8 (FP-T#1) mg kg−1 at the 20–40 cm soil layer, and from 227.9 (FP-C#1) to 842.7 (FP-T#1) mg kg−1 at the 40–60 cm soil layer. The P2 O5 concentrations in the FP-T#1 were double the concentrations found in the FP-C#1, and this difference was particularly striking in the 0–20 cm soil layer. Initially, P2 O5 concentrations in the root zone in the FP-C#1 were lower than 500 mg kg−1 (and within the optimal range for greenhouse cultivation of the cucumber crops). Vegetative growth ended at the end of May in 2011, yet a large amount of irrigation water and fertigation was applied to the soil

Table 6 Average soil EC (EC1:5) and P2 O5 and NO3 –N concentrations in plastic greenhouse soils from earlier studies.

1

References

Soil depth (cm)

EC (dS m−1 )

P2 O5 (mg kg−1 )

NO3 –N (mg kg−1 )

Remarks

Lee et al. (2008)

0–15

4.3

1,458

–

Lim et al. (2007)

0–20

2.6

2,420

183.6 (260.0)1

Lee et al. (2005)

–

3.0

1,084

–

Kang and Hong (2004)

0–20

2.8

810

182.5 (280.0)1

RDA (2006)

0–20

3.7 2.9 2.9 <2

945 943 966 400–500

– – – –

Average values during fallow period in Gyeongnam, Korea (n = 40) Average values of the research results in Chungbuk, Korea (n = 8) Average values with fertigation system in Gyeongnam, Korea (n = 23) 12 points average value of the research results 1980s 1990s 2000s The optimal range of greenhouse soil for crop cultivation

Upper limit for crop cultivation.

1980s Representative average value in plastic greenhouse of Korea

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Fig. 4. Temporal variations of EC and P2 O5 concentrations in the soil layers (FP: fallowing period, CP: cropping period, ACP: after cropping period, C: cucumber, T: tomato, #1: first cropping period, #2: second cropping period).

during the final stage of crop growth. In addition, there was a sufficient level of P2 O5 in the root zone in the FP-C#2 and FP-T#1, but basal fertilizer was still applied. Therefore, P2 O5 accumulation was found in the surface soil layer following the two crop rotations. However in FP-T#2, there was no basal fertilization, so the P2 O5 concentrations decreased to 525.0 mg kg−1 in the 0–20 cm soil layer and concentrations in the 20–60 cm soil layer were lower than the optimal value for greenhouse cultivation. Excess phosphorus may have accumulated in the root zone, and because phosphorus is immobile it does not readily leach and is held in the soil rather than moving into the soil water. Below the 60 cm soil layer, the average P2 O5 concentrations were below the optimal value for greenhouse cultivation and had low variations as shown in Table 5 and Fig. 4(b). According to the RDA, the recommended rate of NO3 –N fertilizer application depends on the EC condition of the soil. Unlike EC and P2 O5 concentration, however, there are no guidelines for NO3 –N use in the growth of crops in plastic greenhouse. According to Kang

and Hong (2004), the upper limit of soil NO3 –N concentration for crop cultivation was 280 mg kg−1 , while according to Lim et al. (2007), a NO3 –N concentration of 260 mg kg−1 in soil was judged to be permissive for non-fertilization cropping. In comparison with the previous studies, as shown in Table 6, the average NO3 –N concentration (257.0 mg kg−1 ) of the surface soil layer (0–20 cm) in this study was similar or somewhat higher than the average values reported in most previous studies, but was lower than the upper limit for crop cultivation reported by Kang and Hong (2004) and Lim et al. (2007). The average NO3 –N concentrations below the 40 cm soil layer were lower than the values reported by previous studies as well as the recommended upper limit for crop cultivation. Due to the basal fertilization, the initial NO3 –N concentration in the soil was higher in the 0–20 cm soil layer but decreased according to the crop growth. Some nutrients can be consumed by crops, but nitrogen is vulnerable to moisture content and can ionize in the soil water and be leached.

2.82 ± 1.4 (0.3–5.01) 7.56 ± 2.2 (3.39–11.03) 5.24 ± 3.01 (0.3–11.03) 0.7 ± 0.78 (0.09–3.35) 3.02 ± 1.19 (0.04–5.66) 1.93 ± 1.54 (0.04–5.66) 0.76 ± 0.83 (0.15–2.78) 1.9 ± 0.98 (0.01–5.56) 1.34 ± 1.07 (0.01–5.56) 0.96 ± 0.72 (0.21–3.3) 1.53 ± 1.39 (0.01–4.51) 1.27 ± 1.17 (0.01–4.51) 0.79 ± 2.95 (0–17) 0.74 ± 1.98 (0–9.27) 0.77 ± 2.55 (0–17) 0.37 ± 0.92 (0–4.67) 0.51 ± 1.74 (0–9.93) 0.44 ± 1.36 (0–9.93) 0.34 ± 0.96 (0–4.18) 0.41 ± 1.32 (0–7.24) 0.37 ± 1.15 (0–7.24) 0.02 ± 0.06 (0–0.27) 0.07 ± 0.14 (0–0.51) 0.04 ± 0.11 (0–0.51) 114.6 ± 53.2 (35.9–212) 407.0 ± 233.8 (140.1–947.3) 242.2 ± 215.6 (35.9–947.3) 99.7 ± 47.7 (15.1–193.4) 354.5 ± 99.9 (77.1–539.4) 219.1 ± 148.5 (15.1–539.4) 154.7 ± 81.4 (36.5–360.2) 319.0 ± 116.9 (8.6–663.1) 239.6 ± 130.4 (8.6–663.1) 178.4 ± 98.3 (2.1–369) 268.4 ± 197.8 (6.5–743.9) 226.8 ± 165.9 (2.1–743.9) 2.30 ± 0.74 (0.44–4.43) 5.17 ± 2.74 (2.01–12) 3.66 ± 2.43 (0.44–12) 2.42 ± 1.21 (0.14–6.36) 4.42 ± 2.09 (0.19–12.29) 3.36 ± 1.95 (0.14–12.29) 2.92 ± 1.46 (0.15–7.57) 4.07 ± 1.91 (0.2–11.75) 3.49 ± 1.8 (0.15–11.75) 2.81 ± 0.87 (0.15–4.12) 3.01 ± 1.97 (0.2–8.43) 2.91 ± 1.56 (0.15–8.43)

112.2 ± 55.8 (30.7–211.2) 397.7 ± 236.4 (111.6–947.3) 236.7 ± 214.9 (30.7–947.3) 98.3 ± 48.9 (15–193.3) 348.4 ± 100.6 (77.1–539.3) 215.5 ± 147 (15–539.3) 153.3 ± 82.3 (32–358.5) 324.2 ± 108.0 (163.6–663.1) 240.2 ± 128.7 (32–663.1) 177.8 ± 96.9 (18.8–368) 276.3 ± 198.2 (23.5–743.9) 230 ± 166.3 (18.8–743.9)

T-P (mg L−1 ) NH4 –N (mg L−1 ) NO3 –N (mg L−1 ) T-N (mg L−1 )

2

EC (dS m−1 )

Average ± standard deviation. (Minimum–maximum). 2

1

150

90

60

2011 (cucumber) 2012 (tomato) Total 2011 (cucumber) 2012 (tomato) Total 2011 (cucumber) 2012 (tomato) Total 2011 (cucumber) 2012 (tomato) Total 30

Soil layer (cm)

fore, the results of this study were compared with the guidelines for agricultural water quality from the USDA and the FAO. According to the USDA, irrigation water with an EC greater than 2.25 dS m−1 is difficult to use for agricultural purposes (U.S. Salinity Laboratory Staff, 1954). According to the FAO, an EC greater than 3.0 dS m−1 has adverse effects on crop growth (Ayers and Wescot, 1995). The average EC of the irrigation water used in this study (Table 2) was 1.05 dS m−1 (0.08–1.74 dS m−1 ), lower by two units than the above mentioned standards. In the soil water of the root zone (0–60 cm), however, the EC values were higher than 2.25 dS m−1 , and there were a significant amount of nutrients. The crops appear to have absorbed nutrients from the soil water, which was recharged by irrigation/fertigation. When compared with the results of the soil moisture content monitoring in Fig. 6, the soil moisture content in the 30 cm soil layer in the root zone during crop cultivation tended to be higher by 36.3% on average in cucumber during the cropping period and by 25.9% on average during the tomato cropping period. Furthermore, during the tomato cropping period, the soil moisture content in the root zone was subjected to sharp fluctuations. This result indicates that in addition to the increase in salinity that occurs in the root zone from irrigation/fertigation, the downward movement of soil water can result in an increase in the salinity of the lower soil zone. This result suggests that the nutrients that accumulated in the root zone were not taken up by the crops and instead were leached into the lower zone through the infiltration of water. In the case of phosphorus, it was found that a significant amount of phosphorus had accumulated on the soil particles in the root zone. The levels of phosphorus in the soil water (PO4 -P: 1.63–3.58 mg L−1 ) were not higher than or similar to the concentrations of phosphorus in the fertigation treatments (Table 2). Thus, from the perspective of pollutant management in plastic greenhouse cultivation systems, phosphorus can accumulate in the root zone but does not significantly leach out of the profile with the movement of soil water. In contrast, although only a small quantity of nitrogen accumulated in the root zone relative to phosphorus, the average nitrogen concentrations in the soil water were higher than 100 mg L−1 in most soil layers for two years. The results of the nitrogen analysis were similar to the EC analysis results, with NO3 –N comprising approximately 90% of the nitrogen concentration in the leachates (Min et al., 2012). The average NO3 –N concentrations during the two year period were similar in all soil layers (215.5–240.2 mg L−1 ). The average NO3 –N concentrations

Table 7 Average, standard deviation, minimum and maximum EC (ECw) and nutrient concentrations (PO4 –P, T-P, NO3 –N, NH4 –N, and T-N) of soil water in the greenhouse.

In a plastic greenhouse, even though rainfall is intercepted, soil moisture content tends to be high because of frequent irrigation/fertigation. Although soil water movement and drainage are slow, there is the possibility of nutrient accumulation and subsequent leaching into the lower soil layers or into the shallow groundwater. Table 7 shows the average nutrient concentrations in the soil water from each soil layer for two years (the two cucumber and two tomato crop rotations). EC is correlated with salinity. Excessive salinity in the root zone can inhibit plant growth. High salinity in irrigation water also causes nutrient absorption problems for crop roots. If the EC of the soil water is high, it can cause nutrient absorption problems, nutrient imbalance and growth inhibition. In addition, nutrients that are not taken up by plants can accumulate or be leached. The EC of the soil water in 2011 (cucumber) gradually increased from the 30 cm (2.30 dS m−1 ) to the 90 cm (2.92 dS m−1 ) soil layers. At the 150 cm soil layer, the EC (2.81 dS m−1 ) was higher than in the root zone (2.30–2.42 dS m−1 ). The EC in 2012 (tomato) decreased from the 30 cm (5.17 dS m−1 ) to the 150 cm (3.01 dS m−1 ) soil layer, but was higher than during the cucumber cropping period. There are no guidelines for the EC of soil water for greenhouse cultivation. There-

PO4 –P (mg L−1 )

3.2. Nutrient concentrations in the soil water

1.35 ± 0.67 (0.37–2.69) 5.29 ± 2.65 (0–9.08) 3.52 ± 2.81 (0–9.08) 0.47 ± 0.34 (0.09–1.87) 3.58 ± 1.62 (0.04–7) 2.16 ± 1.97 (0.04–7) 0.36 ± 0.24 (0.04–1.01) 2.92 ± 1.28 (0–4.97) 1.78 ± 1.6 (0–4.97) 0.76 ± 0.43 (0.1–1.75) 2.33 ± 1.58 (0.05–6.97) 1.63 ± 1.44 (0.05–6.97)

E.-M. Hong et al. / Agricultural Water Management 146 (2014) 11–23

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during cucumber cultivation were higher in the lower soil layers (60–150 cm, 143.6–172.3 mg L−1 ) than in the root zone (0–60 cm, 95.5–105.5 mg L−1 ). The average NO3 –N concentrations during tomato cultivation were the highest in the 30 cm soil layer and decreased with depth (276.3–397.7 mg L−1 ). The NO3 –N concentrations of the soil water in the root zone were higher than the average NO3 –N concentration of the irrigation water (51.5 mg L−1 ), as shown in Table 7. Furthermore, the NO3 –N concentration of the soil water in the 150 cm soil layer was on average 4.5 times higher (3.4 times in 2011 and 5.4 times in 2012) than the average NO3 –N of the fertigation water and higher than the maximum concentration in the irrigation water. The results of the monitoring showed higher values than reported by Min et al. (2012) and indicate significant NO3 –N accumulation. The monitoring results were also similar to the results of a study by Guimerà et al. (1995). In that study, the NO3 –N concentration in the soil water from 0 to 30 cm soil layer was 146–890 mg L−1 , and it was suggested that the accumulation and leaching of NO3 –N in the greenhouse soils were significant. The high NO3 –N concentrations in both the root zone and the lower layer in this study can be explained as follows. First, crop plantings occurred several times per year in the plastic greenhouse. Therefore, excess nutrients from the fertilizer may have accumulated in the root zone and resulted in high nutrient concentrations. Then, soil moisture content would increase after irrigation/fertigation, causing nutrients in the root zone to be leached into the lower soil zone. 3.3. NO3 –N leaching in the soil water from plastic greenhouse cultivation 3.3.1. Temporal variation of NO3 –N concentrations The EC and NO3 –N and T-N levels are the main factors that influence shallow groundwater contamination through leaching in greenhouse cultivation (Kim et al., 2008). In particular, excess NO3 –N leaching into groundwater can cause many problems in the exposed population, including cyanosis. Therefore, the NO3 –N concentrations in the soil water were specifically analyzed in this study (Kurunc et al., 2011). Fig. 5 shows the average, first and third quartile, and minimum and maximum NO3 –N concentrations for each crop rotation sequence. Fig. 6 is a time series of the NO3 –N concentrations in four soil layers (30, 60, 90, and 150 cm) and the soil moisture contents in four soil layers (10, 30, 60, and 90 cm). Nitrate leaching is strongly dependent on soil moisture content. When soils are near saturation, leaching occurs rapidly because NO3 –N is a mobile nutrient. Between irrigation events, nitrate leaching may be slow or nonexistent, but when irrigation occurs, there is a possibility that the nutrient will leach into the lower soil layers (Wang et al., 2007). Soil moisture content in the 10 and 30 cm soil layers increased following each irrigation/fertigation event throughout the growing season. When more water was applied than the plants needed, the soil drained rapidly and soil moisture contents increased even in the 60 and 90 cm layers. Excessive water percolation may also reduce nutrient retention and increase nutrient leaching. As shown in Fig. 5(a), the NO3 –N concentrations of the soil water in FP-C#1 ranged from 31.4 (30 cm depth) to 32.1 mg L−1 (90 cm depth). There appeared to be only small differences in concentrations among the soil layers. During the CP-C#1, however, the NO3 –N concentrations in the soil water increased compared to FPC#1, and average concentrations ranged from 73.4 mg L−1 (60 cm depth) to 183.7 mg L−1 (150 cm depth), which were considerably higher than the average NO3 –N concentrations (51.5 mg L−1 ) in the fertigation applied in the plastic greenhouse (Table 2). The explanation for this result is that the irrigation water tended to be applied in the form of fertigation even during the periods in which only

19

irrigation water was needed. Fertigation was applied more than 10 times per month in the CP-C#1. The average NO3 –N concentrations increased not only in the root zone where irrigation water had directly infiltrated, but also in the lower soil zone where soil water had percolated from the root zone. However, the time series of the NO3 –N concentrations shows a different pattern between the root zone and the lower soil zone. As shown in Fig. 6, the NO3 –N concentrations of the soil water in the root zone (30 and 60 cm soil layers) were higher and the differences were small in the early stages of crop growth during CP-C#1. However, the NO3 –N concentrations rapidly decreased during the last stages of cucumber growth in CP-C#1. In contrast, in the 90 and 150 cm soil layers, NO3 –N concentrations continuously increased in accordance with the stages of crop growth in CP-C#1. The NO3 –N concentrations at these lower depths increased steeply in the last stages of crop growth when the NO3 –N concentrations in the 10 cm soil layer were rapidly decreasing. The average and standard deviation for the NO3 –N concentration in the 150 cm soil layer were the highest of any of the soil layers, as shown in Figs. 5(a) and 6(b). These results can be explained as follows. Although the amount of soil water required for crop growth also decreased during this stage, irrigation water was continually applied at the same volumes as during the active growth period. Therefore, soil moisture content was maintained at a high level in the root zone (10 and 30 cm in depth), as shown in Fig. 6(a). Excess soil water in the root zone percolated to the lower soil layers following irrigation. Along with the percolating soil water, nutrients that had accumulated in the root zone leached to the lower zone. NO3 –N concentration in the FP-C#2 ranged from 126.3 (60 cm) to 280.4 mg L−1 (150 cm). These concentrations were higher than those in the CP-C#1. Following traditional farming practices, a basal fertilizer was applied to the root zone during the fallow period to improve cucumber growth in the next crop rotation even though a large amount of nutrients accumulated in the root zone, and the soil in the root zone was saturated in advance for planting seed. Consequently, dramatic increases in NO3 –N were seen in the 30 cm soil layer and also in the lower soil layers during the fallow period. As seen in Figs. 5(b) and 6, the NO3 –N concentrations were above 100 mg L−1 in the fallow period. In the CP-C#2, as shown in Fig. 5(c), the concentration of NO3 –N decreased rapidly compared to the middle stages of growth, as seen in the time series of NO3 –N at 30 cm of depth in Fig. 6(a). Although the average NO3 –N concentration for the 30 cm soil layer was smaller in the CP-C#2 than in the FP-C#2, the standard deviation and maximum value were slightly higher. In contrast, the NO3 –N concentrations at the 60 cm soil layer gradually increased and the increase in NO3 –N was greatest in the 90 cm soil layer. This was likely a result of the same process driving the NO3 –N accumulations at greater depths during the CP-C#1: nutrient accumulation in the root zone followed by leaching due to percolation from the root zone to the lower zone. The NO3 –N concentration in the 150 cm soil layer in the CP-C#2 was smaller than in the previous period. An examination of the time series data shows that the NO3 –N concentrations decreased over time at this depth. It is possible that the reduction in nutrient concentrations in the 150 cm soil layer was due to smaller amounts of nutrients leaching into the soil layer below 90 cm. However, it was expected that nutrients that were not taken up by crops would leach from the 150 cm layer to depths below 150 cm. Figs. 5(d)–(e) and 6(c)–(d) show the NO3 –N concentrations of the soil water during tomato cropping periods. As shown in Fig. 5(d), the average NO3 –N concentrations of the soil water in CP-T#1 ranged from 360.2 (60 cm depth) to 462.6 mg L−1 (30 cm depth) and were considerably higher than the average NO3 –N concentrations (51.5 mg L−1 ) in the fertigation applied in the plastic greenhouse. In addition, the NO3 –N concentration during

20

E.-M. Hong et al. / Agricultural Water Management 146 (2014) 11–23

Fig. 5. NO3 –N concentrations in the soil water for each crop rotations (avg: average, 1st Q: results from the first quartile of monitoring, 3rd Q: results from the third quartile of monitoring, max: maximum value, min: minimum value, FP: fallowing period, CP: after cropping period, C: cucumber, T: tomato, #1: first cropping period, #2: second cropping period).

the tomato cropping periods (2012) was higher than during the cucumber cropping periods. In particular, as shown in Figs. 5(d) and 6(c)–(d), the NO3 –N concentration in the early crop growth stage of CP-T#1 was the highest as compared to the other periods. Tomato crops consume a large amount of nitrogen, so the standard amount of fertilizer for tomato tends to be higher than that for cucumber. Though fertilization methods with low nutrient concentrations are more effective than applying higher concentrations of basal fertilizer, farmers tend to apply large amounts of basal fertilizer before cropping. Over-fertilization can result in the nutrients not consumed by crops leaching from the root zone to lower soil layers. The greatest differences in NO3 –N concentration were observed in the 30 cm soil layer between the first and third quartile, and between the minimum and maximum. However, the NO3 –N concentration decreased according to the time-series changes shown

in Fig. 6(c). Some nutrients in the soil water might be consumed by crops. However, as shown by the NO3 –N concentration of the soil water in the 60 cm soil layer in Fig. 6(c) and the soil moisture content of the 60 cm soil layer in Fig. 6(d), although the soil moisture content rapidly increased when irrigated and decreased after the gravitational movement of water, the soil moisture content remained consistently high and the NO3 –N concentration of the soil water was partially increased. This suggests that the amount of nutrient loads could be increased. The NO3 –N concentrations in the 90 and 150 cm soil layers continuously decreased, although the soil moisture content was maintained at a consistent level except during irrigation times. Some nutrients were possibly used for crop growth, but below the root zone, the decrease in nutrient levels was likely due to leaching and not extraction for crop growth.

E.-M. Hong et al. / Agricultural Water Management 146 (2014) 11–23

21

Fig. 6. Time series of NO3 –N concentrations and soil moisture content. (a) NO3 –N concentration (depth of 30 cm) and soil moisture content (depths of 10 and 30 cm): cucumber. (b) NO3 –N concentration (depths of 60, 90 and 120 cm) and soil moisture content (depths of 60 and 90 cm): cucumber. (c) NO3 –N concentration (depth of 30 cm) and soil moisture content (depths of 10 and 30 cm): tomato (d) NO3 –N concentration (depths of 60, 90 and 120 cm) and soil moisture content (depths of 60 and 90 cm): tomato.

The fallowing periods between CP-T#1 and CP-T#2 were shorter than the other fallowing periods and there was no use of basal fertilization. Unlike the cucumber cropping periods (2011), there were no further increases in nutrient concentration between CP-T#1 and CP-T#2. In the CP-T#2, the average NO3 –N concentrations of the soil water ranged from 65.4 mg L−1 (150 cm depth) to 330.8 mg L−1 (60 cm depth). The average NO3 –N concentration and the differences between the maximum and minimum and between the first and third quartile of all soil layers were smaller than in the CP-T#1, as shown in Fig. 5(e). The concentration of NO3 –N up to the 90 cm soil layer was stable, although the concentration in the 150 cm soil layer decreased according to the stages of growth, as seen in the time series of NO3 –N shown in Fig. 6(c) and (d). During CPT#2, when there was no basal fertilization and relatively short fertilization times, it was observed that there was no increase in nutrient concentration. However, due to long-term crop cultivation and over-fertilization in the past periods, large amounts of NO3 –N remained in the soil water at comparably higher levels than during the cucumber cultivation periods. Both the NO3 –N concentration in the 150 cm soil layer and the soil moisture content during CP-T#2 were lower as compared to the cucumber cropping periods. That meant that a significant amount of nutrients were either consumed by the crops or more likely leached into further soil depths. 3.3.2. NO3 –N losses from leaching in plastic greenhouse cultivation Plastic greenhouse cultivation practices tend to involve high volumes of irrigation and high frequency and nutrient levels in the fertigation. As a result, nitrate leaching is much greater in

greenhouse cultivation than in field crops (Sun et al., 2012). Many studies have shown that drip irrigation can reduce water inputs and optimize fertilizer inputs to significantly reduce nitrate leaching in the soil (Min et al., 2011; Sun et al., 2012). Nevertheless, there are no proper guidelines for irrigation and fertigation in plastic greenhouse systems. Fertilization and irrigation have continued to be applied at high levels and this practice appears to cause a significant amount of nutrient leaching. High nutrient concentrations in the soil water do not necessarily signify an excess of nutrients, but could indicate a potential risk of leaching. The amount of evapotranspiration, irrigation/fertigation, and percolation water were higher in the CP-C#1 and CP-T#1 than in the CP-C#2 and CP-T#2 as shown in Table 8. This is because the cropgrowing period in the CP-C#2 (92 days) and CP-T#2 (142 days) was shorter than in the CP-C#1 (179 days) and CP-T#1 (172 days). The amount of irrigation was 456.6 mm (CP-C#2) to 846.8 mm (CP-C#1) and the amount of evapotranspiration was 222.6 mm (CP-C#2) to 499.3 mm (CP-T#1). Using the water balance, the volume of percolated water was determined for four crop cultivation for two years. The amount of percolation was 476.3 mm in the CP-C#1 (56% of the irrigation water), 241.8 mm in the CP-C#2 (53% of the irrigation water), 346.6 mm in the CP-T#1 (42% of the irrigation water), and 348.1 mm which in the CP-T#2 (51% of the irrigation water). These processes of soil water percolation are mechanisms of leaching in the greenhouse. NO3 –N losses through leaching were estimated for the four cropping seasons as shown in Table 9. The total NO3 –N concentration in fertigation was 909.9 kg ha−1 in the CP-C#1, 501.7 kg ha−1 in the CP-C#2, 881.9 kg N ha−1 in the CP-T#1, and 447.8 kg N ha−1 in

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E.-M. Hong et al. / Agricultural Water Management 146 (2014) 11–23

Table 8 Total water balance during the cultivation period (two cucumber and two tomato crop rotations). Items

CP-C#2

CP-C#1

Irrigation Evapotranspiration Percolation

Amount (mm)

Fraction (%)

Amount (mm)

846.8 397.2 476.2

– 46.9 56.2

456.6 222.6 241.8

CP-T#1 Fraction (%) – 48.8 53.0

CP-T#2

Amount (mm)

Fraction (%)

Amount (mm)

817.1 499.3 346.6

– 61.1 42.4

678.4 349.6 348.1

Fraction (%) – 51.5 51.3

Table 9 Nitrate–nitrogen flow during the cultivation period (two cucumber and two tomato crop rotations). Items

Fertigation Leaching from root zone to lower zone Leaching from lower zone to deeper soil layer

CP-C#1

CP-C#2

Amount (kg N ha−1 )

Fraction (%)

Amount (kg N ha−1 )

909.6 293.2

– 32.2

501.7 143

137.4

15.1

195.9

CP-T#1

the CP-T#2. The NO3 –N losses through leaching from the root zone to the lower soil layers were 293.2 kg N ha−1 (1.6 kg N ha−1 day−1 ) in the CP-C#1, 143.0 kg N ha−1 (1.6 kg N ha−1 day−1 ) in the CPC#2, 788.6 kg N ha−1 (65.7 kg N ha−1 day−1 ) in the CP-T#1, and 107.0 kg N ha−1 (0.8 kg N ha−1 day−1 ) in the CP-T#2. Crops are unable to take up nitrate from deeper soil. As a result, the accumulation of nitrate in the lower soil layers is a serious concern because of the potential negative impacts on the environment. Previous studies have suggested that traditional fertilization and irrigation practices have led to large amounts of nitrate leaching and high residual nitrate concentrations in the soil in vegetable fields (Thompson et al., 2007; Song et al., 2009; Min et al., 2011; Sun et al., 2012). NO3 –N losses through leaching from the lower zone (60 to 150 cm soil layer) to deeper soil layer in this study were 137.4 kg N ha−1 (0.8 kg N ha−1 day−1 ) in the CP-C#1, 195.9 kg N ha−1 (2.1 kg N ha−1 day−1 ) in the CP-C#2, 758.6 kg N ha−1 (63.2 kg N ha−1 day−1 ) in the CP-T#1, and 54.7 kg N ha−1 (0.4 kg N ha−1 day−1 ) in the CP-T#2. Zhao et al. (2012) investigated the NO3 –N leachate from 90 cm soil depth under a greenhouse tomato–cucumber rotation system in Northern China. With conventional fertilization methods (811–1078 kg N ha−1 ), NO3 –N leachates ranged from 41.7 ± 13.4 kg N ha−1 to 75.3 ± 23.3 kg N ha−1 . Vazquez et al. (2006) investigated nitrate leaching during tomato cultivation with drip irrigation in Spain considering different irrigation scenarios. The amount of NO3 –N leachate ranged from 155 (fertigation applied 457 ± 41.4 N ha−1 ) to 421 (fertigation applied 334 ± 117.2 N ha−1 ) kg N ha−1 when the researches supplied 157–517 kg N ha−1 . Our results in CP-C#1 and CP-T#2 are in agreement with Zhao et al. (2012), but lower those reported by Vázquez et al. (2006). NO3 –N leaching losses in CP-C#2 from this experiment were higher than the results from Zhao et al. (2012), but in agreement with those of Vázquez et al. (2006). However the loss to leaching in CP-T#1 was higher than both previous studies. As mentioned in Sections 3.3.1 and 3.3.2, the NO3 –N concentration of the soil water and the soil moisture content below 90 cm soil depth were increased in CP-C#2 because of soil water recharging. As a result, a significant amount of soil nutrients accumulated in the soil and soil water. But unlike the nutrients in the root zone, the nutrients that accumulated in the lower zone were not utilized for crop growth. In addition, the crop growing period in the CP-C#2 was shorter. When a large amount of irrigation/fertigation were applied within a short period of time, significant amounts of nutrients were not utilized for crop growth but leached in

CP-T#2

Amount (kg N ha−1 )

Fraction (%)

Amount (kg N ha−1 )

– 28.5

881.9 788.6

– 89.4

447.8 107

– 23.9

39.0

758.6

86.0

54.7

12.2

Fraction (%)

Fraction (%)

accordance with the movement of soil water. Because of this effect, in addition to the basal fertilization in CP-T#1, the nutrient concentration in the early stages of crop growth was higher, and significant amounts of NO3 –N leached from the root zone in CP-T#1 compared to other cropping season. Most environmental factors, including weather conditions, irrigation, soil moisture content and even nutrients, can be controlled in a greenhouse. However, NO3 –N, which is one of the most important factors controlling crop growth, is difficult to retain in a soil layer because its movement depends on the mobility of soil water. When water percolates into lower soil profiles, nutrients are leached along with the soil water. Earlier studies as well as this current study have shown that nutrients such as NO3 –N can accumulate in excess. In particular, in this study, significant amounts of NO3 –N accumulated in the subsurface soils of the greenhouse. In addition, nutrients such as NO3 –N can leach into the lower soil layers and enter shallow groundwater, which has a higher elevation than confined groundwater (Tan et al., 2012). Some researchers have shown that reducing nitrogen fertilizer applications not only reduces nitrogen leaching but also increases crop yield and nitrogen use efficiency in greenhouse cultivation (Thompson et al., 2007; Sun et al., 2012). Therefore, to reduce nutrient accumulation in greenhouse soils and nutrient leaching into the lower soil layers and shallow groundwater, the continuous management of two factors is required. First, soil moisture must be controlled with irrigation. Second, soil management involves controlling nutrient concentrations for fertigation. Soil conditions should be accurately assessed before and during crop planting. In addition, the management of irrigation and fertigation volumes and timing is important. Future studies are necessary to make guideline for controlling irrigation and fertigation and to understand the relationships between soil water content and quality based on irrigation/fertigation scheduling scenarios. In addition, based on the modeling and monitoring result, hydrological analyses considering nutrient would allow for further analysis of the leaching processes and the movement of nutrients from lower soil layers to shallow groundwater. 4. Summary and conclusions In Korea’s agricultural areas, nutrients are discharged by various routes. Due to excessive fertilization, the excess of nutrients in the environment is becoming increasingly serious. The purpose of this study was to monitor and analyze subsurface nutrient concentrations and soil water movement at a greenhouse cultivation site. In

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a plastic greenhouse, cucumber and tomato were cultivated twice a year for two years by using a drip irrigation system and nutrients were applied by fertigation. The water quality of the soil water and irrigation water, the soil moisture content, and the weather conditions were monitored during the growing season. The EC and the concentrations of T-N, T-P, P2 O5 , and NO3 –N were determined using samples of soil and soil water. This study found that an overall high concentration of nutrients in the soil and soil water and a large amount of phosphorus accumulated in the soil particles of the root zone. The NO3 –N concentration and the EC of the soil water were high in the total soil layer, and some nutrient concentrations in the sub-soil layer were higher than those in the upper soil layer. The total NO3 –N losses through leaching from the lower zone (60 to 150 cm soil layer) to deeper soil were 137.4 kg N ha−1 in the CPC#1, 195.9 kg N ha−1 in the CP-C#2, 758.6 kg N ha−1 in the CP-T#1, and 54.7 N ha−1 in the CP-T#2. In this study, excessive fertilization caused nutrient accumulation in the root zone and nutrient leaching into the lower soil layers. It was recognized that if conventional management of greenhouse cultivation continued, there is a possibility of future groundwater pollution. The results of this study provide important information to motivate improvements in greenhouse farming practices guided by long-term monitoring. This study can inform guidelines for new farming practices that reduce the agricultural non-point pollution load and aid in the development of a model for analyzing agricultural non-point pollution from greenhouse cultivation. Acknowledgments This study was supported by funds provided to the Rural Research Institute of Korea Rural Community Corporation by the Ministry of Agriculture, Food and Rural Affairs as part of the project: “Development of Agricultural Non-Point Source Pollution Reduction Measures on the Saemangeum Watershed”. References Ajdary, K., Singh, D.K., Singh, A.K., Khanna, M., 2007. Modelling of nitrogen leaching from experimental onion field under drip fertigation. Agric. Water Manage. 89, 15–28. Ayers, R.S., Wescot, D.W., 1995. FAO Irrigation and Drainage Paper 29: Water Quality for Agriculture. FAO, Rome. Castellanos, M.T., Tarquis, A.M., Ribas, F., Cabello, M.J., Arce, A., Cartagena, M.C., 2013. Nitrogen fertigation: an integrated agronomic and environmental study. Agric. Water Manage. 120 (31), 46–55. Guimerà, J., Marfa, O., Candela, L., Serrano, L., 1995. Nitrate leaching and strawberry production under drip irrigation management. Agric. Ecosyst. Environ. 56, 121–135. Ha, H.S., Lee, Y.B., Sohn, B.K., Kang, U.G., 1997. Characteristics of soil electrical conductivity in plastic film house located in Southern Part of Korea. Korean J. Soil Sci. Fert. 30, 345–350 (in Korean with English abstract). He, B., Kanae, S., Oki, T., Hirabayashi, Y., Yamashiki, Y., Takara, K., 2011. Assessment of global nitrogen pollution in rivers using and integrated biogeochemical modeling framework. Water Res. 45, 2573–2586. Hu, Y.G., Song, Z.W., Lu, W.L., Poschenrieder, C., Schmidhalter, U., 2012. Current soil nutrient status of intensively managed greenhouses. Pedosphere 22 (6), 825–833. Kang, S.S., Hong, S.D., 2004. Estimation of optimum application rate of nitrogen fertilizer based on soil nitrate concentration for tomato cultivation in plastic film house. Korean J. Soil Sci. Fert. 37, 74–82 (in Korean with English abstract). Kim, J.H., Choi, C.M., Lee, J.S., Yun, S.G., Lee, J.T., Cho, K.R., Lim, S.J., Choi, S.C., Lee, G.J., Kwon, Y.G., Kyung, K.C., Uhm, M.J., Kim, H.K., Lee, Y.S., Kim, C.Y., Lee, S.T., Ryu, J.S., 2008. Characteristics of groundwater quality for agricultural irrigation in plastic film house using multivariate analysis. Korean J. Environ. Agric. 27 (1), 1–9 (in Korean with English abstract). Kurunc, A., Ersahin, S., Yetgin Uz, B., Sonmez, N.K., Uz, I., Kaman, H., Bacalan, G.E., Emekli, Y., 2011. Identification of nitrate leaching hot spots in a large area with contrasting soil texture and management. Agric. Water Manage. 98 (6), 1013–1019. Lee, N.H., Hwang, H.C., Nam, S.W., Hong, S.G., Jeon, W.J., 1998. A study on the utilization of irrigation water for greenhouse farming. J. Korean Soc. Rural Plann. 4 (2), 96–102 (in Korean with English abstract).

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