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Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater
Agricultural Water Management 97 (2010) 271–276
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Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater Rafael Marques Pereira Leal a,b,*, Lilian Pittol Firme b, Uwe Herpin b, Adriel Ferreira da Fonseca c, Ce´lia Regina Montes b,d, Carlos Tadeu dos Santos Dias e, Adolpho Jose´ Melfi b,f a
Laborato´rio de Ecotoxicologia, Centro de Energia Nuclear na Agricultura – CENA/USP, P.O. Box 96, 13400-970, Piracicaba (SP), Brazil Nu´cleo de Pesquisa em Geoquı´mica e Geofı´sica da Litosfera (NUPEGEL), Universidade de Sa˜o Paulo (USP), P.O. Box 09, 13418-900, Piracicaba (SP), Brazil Departamento de Cieˆncia do Solo e Engenharia Agrı´cola (DESOLO), Universidade Estadual de Ponta Grossa (UEPG), 84030-900, Ponta Grossa (PR), Brazil d Laborato´rio de Ana´lise Ambiental e Geoprocessamento, Centro de Energia Nuclear na Agricultura (CENA), USP, 13400-970, Piracicaba (SP), Brazil e Departamento de Cieˆncias Exatas, Escola Superior de Agricultura Luiz de Queiroz (ESALQ), USP, 13418-900, Piracicaba (SP), Brazil f Departamento de Cieˆncia do Solo, Escola Superior de Agricultura Luiz de Queiroz (ESALQ), USP, 13418-900, Piracicaba (SP), Brazil b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 March 2009 Received in revised form 20 September 2009 Accepted 23 September 2009
Carbon (C) and nitrogen (N) dynamics in agro-systems can be altered as a consequence of treated sewage effluent (TSE) irrigation. The present study evaluated the effects of TSE irrigation over 16 months on N concentrations in sugarcane (leaves, stalks and juice), total soil carbon (TC), total soil nitrogen (TN), NO3-N in soil and nitrate (NO3) and dissolved organic carbon (DOC) in soil solution. The soil was classified as an Oxisol and samplings were carried out during the first productive crop cycle, from February 2005 (before planting) to September 2006 (after sugarcane harvest and 16 months of TSE irrigation). The experiment was arranged in a complete block design with five treatments and four replicates. Irrigated plots received 50% of the recommended mineral N fertilization and 100% (T100), 125% (T125), 150% (T150) and 200% (T200) of crop water demand. No mineral N and irrigation were applied to the control plots. TSE irrigation enhanced sugarcane yield but resulted in total-N inputs (804– 1622 kg N ha1) greater than exported N (463–597 kg N ha1). Hence, throughout the irrigation period, high NO3 concentrations (up to 388 mg L1 at T200) and DOC (up to 142 mg L1 at T100) were measured in soil solution below the root zone, indicating the potential of groundwater contamination. TSE irrigation did not change soil TC and TN. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Wastewater irrigation Water reuse Saccharum spp. Nitrate Dissolved organic carbon Tropical soil
1. Introduction Treated sewage effluent (TSE) is increasingly used as a source of water and nutrients (mainly nitrogen) in crop production in Brazil (da Fonseca et al., 2007a). However, the country lacks a long-term tradition on the agricultural use of such residues, so that national legal regulations and general guidelines for its sustainable application are still in development. For these reasons, scientific experimentation concerning the major implications of effluent irrigation under the local tropical conditions is highly required, in order that TSE may be used as part of a rational and sustainable agricultural planning. Carbon (C) and nitrogen (N) cycling in agro-systems can be altered by TSE irrigation, mainly in the long-term (da Fonseca et al.,
* Corresponding author at: Laborato´rio de Ecotoxicologia, Centro de Energia Nuclear na Agricultura – CENA/USP, P.O. Box 96, 13400-970, Piracicaba (SP), Brazil. Tel.: +55 19 34294764; fax: +55 19 34294764. E-mail address: fi[email protected] (R.M.P. Leal). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.09.018
2007a). Several studies have shown increased total carbon (TC) and total nitrogen (TN) contents in the soil due to C and N input by TSE irrigation (Friedel et al., 2000; Ramirez-Fuentes et al., 2002). Other studies have found decreased contents of soil TC and TN (Speir et al., 1999; Snow et al., 1999), mainly attributed to enhanced mineralization and nitrification processes under effluent irrigation (da Fonseca et al., 2007a). Of greater concern, increasing concentrations of nitrate (NO3) in soil solution due to TSE irrigation have often been reported (Polglase et al., 1995; Smith and Bond, 1999), representing one of the main challenges for the sustainable land application of effluents (Bond, 1998; da Fonseca et al., 2007a). Also increases in dissolved organic carbon (DOC) in soil solution were reported after effluent irrigation (Bhandral et al., 2007; Gloaguen et al., 2007). The DOC fraction represents an important indicator of soil quality (Silveira, 2005) and may play an important role as a carrier of metals and pollutants in the soil profile due to its high mobility (Ciglasch et al., 2004). Sugarcane (Saccharum spp.) may represent an attractive crop for TSE irrigation in Brazil, because of the following characteristics:
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(i) predominance of non-irrigated plantations with large potential for the adoption of irrigation practices; (ii) high demand of N (one of the main nutrient in TSE); (iii) perennial crop fitted to full mechanization, without direct contact to farm workers; (iv) major commodity for ethanol production in Brazil. These characteristics may result in agronomic, economic and environmental benefits, however, detailed studies on TSE irrigation in sugarcane agrosystems are lacking. The purpose of this study was to evaluate the effects of short term TSE irrigation (16 months) on N uptake by sugarcane, N and C accumulation in soil and NO3 and DOC leaching. 2. Materials and methods The experimental area is situated near the city of Lins, State of Sa˜o Paulo (longitude: 498500 W; latitude: 228210 S; average altitude of 440 m), Brazil, adjacent to the municipal wastewater treatment plant (stabilization ponds system). Mean annual temperature is 23 8C and precipitation was 1292 mm during the experimental period (16 months). Monthly rainfall and the amounts of TSE applied as irrigation throughout the experiment are presented in Fig. 1. The soil was classified as Typic Haplustox (Soil Survey Staff, 1999), sandy clay loam. The soil mineralogy of the area is dominated by quartz and kaolinite, and subordinately by hematite, magnetite and/or maghemite. The dominance of these minerals, commonly occurring in highly weathered and acid tropical soils, results in low cation exchange capacity (CEC) (Table 1). The chemical and physical soil characteristics found at the beginning of the experiment (Table 1) are usual for most Brazilian agro-systems cropped with sugarcane. Available calcium (Ca), magnesium (Mg), potassium (K) and phosphorus (P) were found in adequate concentrations for sugarcane growth due to previous liming and addition of mineral fertilizers at the beginning of the experiment. Sugarcane was planted in March 2005 with a distance of 1.4 m between the rows. TSE irrigation was carried out from May 2005 till August 2006 (16 months). After this period irrigation was stopped because sugarcane needs water stress before harvest in order to concentrate sugar. Plants were irrigated when Cm were less than 40 kPa. Harvest took place at the end of September 2006. Concerning mineral fertilizer application, all experimental plots received 15 kg ha1 of N (ammonium nitrate, 50% of recommended mineral N), except the control plot; 52 kg ha1 of P (simple superphosphate), and 66 kg ha1 of K (potassium chloride), distributed manually to the furrows during planting.
Fig. 1. Monthly amounts of applied water (rainfall and wastewater irrigation) during the experimental period. Month 1 corresponds to May 2005 and month 16 to August 2006. T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
Detailed information about irrigation and crop management are available in a previous work (Leal et al., 2009). The experiment was arranged in a complete block design, with five treatments and four replications. The treatments consisted of: (i) control, without TSE irrigation and N fertilization; (ii) T100, T125, T150 and T200, with TSE irrigation supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand, respectively. Total plot size was 280 m2 (40 m 7 m) with a useful area of 126 m2. The effects of effluent irrigation on carbon and nitrogen dynamics were evaluated by considering two application scenarios: (i) land application of TSE rates higher than 100% of crop water requirement (T125, T150 and T200) as a TSE disposal alternative, and (ii) TSE application according to crop water requirement (T100) to enhance agricultural production through the provision of water and nutrients. Data about TSE constituents were taken from a previous detailed effluent characterization (da Fonseca et al., 2007b) because TSE quality has not changed considerably during the last five years (Leal et al., 2009). In average, TSE is characterized by: pH of 7.7; total-N concentration of 31.9 mg L1; 22.4 mg L1 of NH4+N (predominant N form); 0.6 mg L1 of NO3-N; 65.28 mg L1 of dissolved organic carbon (DOC); 301 mg L1 of bicarbonate (HCO3); 146 mg L1 of Na and a sodium adsorption ratio (SAR) of 11.9 (mmol L1)0.5. The total-C and total-N inputs to the soil–plant system via TSE irrigation (16 months) were calculated for each treatment. As a result, 4500, 5690, 6830 and 8430 kg ha1 of total-C and 800, 1020,
Table 1 Chemical and physical soil properties at the beginning of the experiment (March 2005). Layer (m)
pH
H + Al (mmolc kg1)
Al (mmolc kg1)
Ca (mmolc kg1)
Mg (mmolc kg1)
K (mmolc kg1)
Na (mmolc kg1)
CECa (mmolc kg1)
P (mg kg1)
TCb (g kg1)
TNc (g kg1)
0–0.1 0.1–0.2 0.2–0.4 0.4–0.6
5.1 5.2 4.9 4.6
15.4 15.0 15.9 21.8
0.9 0.8 1.8 4.0
12.7 13.2 10.2 6.2
3.5 3.6 3.6 2.3
3.0 2.4 1.8 1.2
0.7 1.5 2.5 2.8
35.4 35.6 34.0 34.3
17.3 15.5 4.1 1.0
6.0 6.4 5.1 4.1
0.5 0.5 0.4 0.3
Layer (m)
BSd (%)
ESPe (%)
B (mg kg1)
Cu (mg kg1)
Fe (mg kg1)
Mn (mg kg1)
Zn (mg kg1)
ECf (dS m1)
Sand (g kg1)
Silt (g kg1)
Clay (g kg1)
0–0.1 0.1–0.2 0.2–0.4 0.4–0.6
56.3 57.9 53.3 36.5
2.1 4.1 7.4 8.1
0.6 0.6 0.6 0.4
0.5 0.7 0.3 0.5
21.5 20.9 15.5 10.4
3.0 2.7 1.7 1.2
1.2 1.5 0.3 0.2
0.7 0.4 0.2 0.2
774 775 732 707
90 78 75 65
135 147 192 227
a b c d e f
Cation exchange capacity at pH 7.0 ! CEC = Ca + Mg + K + Na + H + Al. TC = total carbon. TN = total nitrogen. Base saturation ! BS = (Ca + Mg + K + Na) 100/CEC. Exchangeable sodium percentage ! ESP = Na 100/CEC. EC = electrical conductivity.
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1220 and 1620 kg ha1 of total-N were added to the soil at T100, T125, T150 and T200, respectively. Taking into account that the TSE applied presents a Na/total-N ratio of about five (da Fonseca et al., 2007b), its application also added high amounts of Na to the soil system, representing a major risk of sodification (Leal et al., 2009). Soil sampling for TC and TN was carried out in February 2005 (before planting) and in September 2006 (after sugarcane harvest and 16 months of irrigation). At each plot, twelve subsamples were randomly collected at the 0–0.1, 0.1–0.2 m soil layers to compound composite samples. At the 0.2–0.4 and 0.4–0.6 m soil layers six subsamples were taken to form composite samples. Soil samples were air-dried, sieved at 0.15 mm and soil TC and TN were determined by dry combustion (Nelson and Sommers, 1996). For initial soil chemical characterization (Table 1), sieved (2 mm) soil samples were analyzed according to standard procedures: (i) Embrapa (1999) for P, Ca, Mg, K, Al, and Na, and (ii) Van Raij et al. (2001) for pH, H + Al, B, Cu, Fe, Mn and Zn. Soil solution electrical conductivity (EC) was obtained using saturation extracts, according to Van Raij et al. (2001). Nine months after planting (December 2005), sugarcane was in the stage of maximum vegetative growth. At that time, 25 leaves were randomly sampled within each plot for mineral nutrition analysis. The samples were rinsed in distilled water, oven dried at 60 8C, ground in a Wiley type mill, passed through a 0.85 mm sieve and stored in capped vials. For N analyses the samples were submitted to sulphuric acid digestion and determined by the semimicro-Kjeldahl procedure proposed by Malavolta et al. (1997). In September 2006 (date of harvest), ten stalks per plot were randomly sampled for N analyses. The procedures used for stalks N analyses were similar to those described for the leaves. Juice extracted from stalk samples were kept frozen prior to N analysis and subsequently evaluated according to the same analytical procedures as mentioned above. For soil inorganic N determination, fresh soil samples (10 g) from the sampling campaign in September 2006 were immediately extracted in 50 mL of 2 M KCl, according to Piccolo et al. (1994). After 24 h, the extracts were centrifuged and colorimetrically analysed using an automated flow injection system (Ruzicka and Hansen, 1981). For the estimation of mineral N stocks in the 0– 0.60 m soil layer at the end of the experimental period (Table 3), an average soil density of 1.5 kg dm3 was employed. Nitrate and DOC concentrations in soil solution were monitored every 2 months, from May 2005 (start of the irrigation period) to June 2006 (approximately 45 days before irrigation was stopped). The samples were obtained using porous ceramic cups installed at soil depths of 1–3 m. Samples were collected after applying a tension of 50 kPa for 8 days to obtain a minimum amount of soil solution required for analysis (Surita et al., 2007). Subsequently the samples were filtered through a 0.22 mm pore diameter estercellulose membrane and frozen prior to NO3 determination. Nitrate analyses were carried out with liquid chromatography (Dionex 500). Only mineral N in form of NO3 was quantified, because Gloaguen et al. (2007) found in effluent generated in the same treatment plant a mean [NO3]/[NH4+] ratio of 0.05 toward 396 in the soil solution due to fast nitrification of effluent-N in the soil (da Fonseca et al., 2007c). For DOC analyses, an aliquot of soil solution was filtered through a fiber glass filter (0.7 mm) and preserved with 30 mmol L1 mercuric chloride solution (HgCl2). Determinations were carried out using a Shimadzu TOC-5000 Analyzer. At the control plots without TSE application, no sufficient volume of soil solution for NO3 and DOC determinations could be obtained during the sampled period. Soil and plant data were submitted to analysis of variance. The analysis presented a homogeneous variance, a necessary condition to carry out univariate statistical analysis for a complete block design, considering time (sampling date) as subplot. The variables
273
which showed significant F test (P < 0.05) were submitted to multiple comparisons by Tukey’s test adjusted for descriptive level (a = 0.05). Mean comparisons of NO3 and DOC values of soil solution were made with transformed data (square root transformation for NO3 values and logarithmic transformation for DOC values). However, all given means are original values. All statistical analyses were carried out using the SAS system, version 8.02 (SAS System, 1999). 3. Results and discussion 3.1. Nitrogen contents in plants and sugarcane yield There were no differences between N concentrations in sugarcane leaves at the irrigated treatments (17.1–18.2 g kg1) compared to the control (19.7 g kg1). At the irrigated plots, N concentrations in leaves were close to the lower range limit of adequate values (18–25 g N kg1 leaves) proposed by Van Raij et al. (1996). Nitrogen concentrations in sugarcane juice (8.4– 11.7 g L1) and stalks (7.2–8.6 g kg1) were also not influenced by the treatments. However, the accumulated N in stalks (2.30– 2.60 kg N per Mg of fresh stalks1) was considerably higher than the reference range (0.90–1.32 kg N per Mg of fresh stalks1) (Dematteˆ, 2005). Although N concentration in leaves were close to the lower range limit of adequate values, the high accumulated N in stalks and the high sugarcane yields suggest adequate conditions for crop development. All TSE irrigated plots (T100 = 247 Mg ha1; T150 = 233 Mg ha1; T200 = 232 Mg ha1), except T125 (199 Mg ha1), showed significant higher yields than the control (153 Mg ha1), probably due to the water supplied by TSE irrigation. However, despite increasing irrigation rates, similar (T150 and T200) or lower (T125) yields were found compared to T100. This indicates no positive effect of higher TSE irrigation rates (T125–T200) on sugarcane yield and is important to be considered for an adequate and sustainable land application of TSE. Sugarcane extracted significant amounts of N from the soil, from 345 kg ha1 at the control to a maximum of 597 kg ha1 (T200), with no differences between irrigated treatments (463–597 kg ha1). However, the accumulated N in stalks was not sufficient to counterbalance the large N input via TSE irrigation, resulting in a low N recovery (maximum of 23%, given as the ratio between N in stalks and total N applied). Effluent induced N overfertilization may negatively affect the ability of the crop to resist disease and also to synthesize important compounds related to crop natural defenses (Hamilton et al., 2007), representing a relevant aspect to be considered in TSE irrigation management. Different from the following productive cycles, the first sugarcane cycle is known to be not responsive to N fertilization, because the required N can be obtained by alternative sources such as biological fixation of atmospheric N and through the utilization of N reserves stored in the seedpiece (Carneiro et al., 1995). Therefore, it is suggested that mineral N application in the first crop cycle can be avoided because the effluent may entirely supply the required N. The high yields at the irrigated treatments, where 50% of the recommended mineral N fertilization was applied, also support this statement. Effluent irrigation schemes should be designed in such a way that the cover crop can completely utilize the applied N in order to prevent N leaching and N discharge to water systems fostering eutrophication processes (Bond, 1998; Barton et al., 2005). Barton et al. (2005) pointed out that, although denitrification, volatilization and soil storage are alternative pathways for wastewater applied N, these processes are often variable and more difficult to predict and to control than plant uptake. Gloaguen et al. (2007) also emphasized the relevance to optimize plant N uptake for the sustainability of TSE irrigation under tropical conditions.
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Table 2 Total carbon and nitrogen (g kg1) concentrations in soil after application of different treated sewage effluent (TSE) irrigation rates (T100, T125, T150 and T200). Treatmentsa
Time after the beginning of irrigation (month) 0
16
0
Carbon
16
Nitrogen
0–0.1 m layer (CVb = 9.1%) Control T100 T125 T150 T200
6.10 5.82 6.62 5.75 6.00
aAc aA aA aA aA
6.40 6.62 6.25 6.02 5.90
aA aA aA aA aA
0–0.1 m layer (CV = 8.6%) 0.52 aA 0.52 aA 0.55 aA 0.50 aA 0.52 aA
0.52 0.42 0.55 0.47 0.47
aAB aB aA aAB aAB
0.1–0.2 m layer (CV = 10.6%) Control T100 T125 T150 T200
6.22 6.37 7.10 5.77 6.50
aA aA aA aA aA
6.00 6.02 6.25 6.12 5.80
aA aA aA aA aA
0.1–0.2 m layer (CV = 13.6%) 0.57 aA 0.52 aA 0.60 aA 0.52 aA 0.55 aA
0.57 0.55 0.55 0.60 0.52
aA aA aA aA aA
0.2–0.4 m layer (CV = 10.2%) Control T100 T125 T150 T200
5.05 5.15 5.22 4.97 5.22
aA aA aA aA aA
5.12 5.10 5.52 5.72 4.77
aA aA aA aA aA
0.2–0.4 m layer (CV = 12.8%) 0.45 aA 0.42 aA 0.47 aA 0.42 bA 0.42 aA
0.45 0.42 0.52 0.60 0.47
aAB aB aAB aA aAB
0.4–0.6 m layer (CV = 8.5%) Control T100 T125 T150 T200
4.07 4.25 4.17 4.10 4.10
aA aA aA aA aA
4.02 4.20 4.12 4.37 4.20
aA aA aA aA aA
0.4–0.6 m layer (CV = 17.4%) 0.35 aA 0.32 aA 0.37 aA 0.35 aA 0.35 aA
0.32 0.37 0.42 0.37 0.42
aA aA aA aA aA
a Treatments: control (without TSE irrigation and mineral N fertilization) and T100, T125, T150 and T200 corresponding to TSE irrigation supplying 100, 125, 150 and 200% of the crop water demand, respectively. b CV = coefficient of variation. c Means followed by same small letters in the same row (different sampling data) and same capital letters in the same column (different treatments) do not differ by adjusted Tukey’s test (a = 0.05).
3.2. Total carbon (TC) and total nitrogen (TN) in soil Effluent irrigation showed no effects on soil TC (Table 2) and negligible effects on soil TN contents (Table 2), which may be referred to the short term experimental period. da Fonseca (2005) found significant decreases in soil TC and TN concentrations after 18 months of effluent irrigation of Tifton 85 bermudagrass, and attributed it to the mineralization of native organic matter due to a high N (through mineral fertilization and effluent irrigation) input, a process known as ‘‘the priming effect’’. Generally, changes in soil TC and TN contents were mainly found after effluent irrigation in long-term studies (da Fonseca et al., 2007a), showing both increases (Friedel et al., 2000; RamirezFuentes et al., 2002) and decreases (Polglase et al., 1995; Falkiner and Smith, 1997). The increases in soil TC and TN were related to the significant input of N and C via effluent irrigation over time. On the other hand, decreases in soil TC and TN were mainly referred to the occurrence of permanent moist soil conditions due to irrigation and the low C/N ratio of the effluent. These factors might stimulate microbial activity enhancing soil organic matter mineralization (da Fonseca et al., 2007a). Moreover, prolonged TSE irrigation may increase pollutants (heavy metals) concentrations in soil (Friedel et al., 2000). In the long-term, this accumulation may provoke detrimental effects on soil microbial communities, affecting negatively C, N, P and sulphur (S) cycling processes (Kandeler et al., 1996). 3.3. Nitrate (NO3) in soil and in soil solution Although the additions of effluent-N varied about 800 kg ha1 at the irrigated treatments (T100–T200), inorganic soil N (NO3-N) concentrations were similar at the end of the experiment (Table 3).
However, nitrate concentrations at the irrigated treatments (minimum of 3.5 mg kg1 and maximum of 12.1 mg kg1) were high in comparison to the control (maximum of 3 mg kg1) (Table 3). The higher levels of soil inorganic N stocks at the irrigated treatments compared to the control (Table 3) evidences the potential of N losses due to the low chemical affinity of nitrate anions to net negatively charged soil particles. Although soil inorganic N were only determined at the end of the experiment, higher nitrate levels in the irrigated soils are coherent with the high concentrations (>100 mg L1) of the leached NO3 fraction measured between 1 and 3 m depth at T100–T200 over the experimental period (Fig. 2 and Table 3). Although N recovery was not affected by effluent irrigation, the lost N, considered as the difference between total N input and N recovered at each treatment, was much higher at T200 (1383 kg) compared to T100 (626 kg), indicating a higher potential of N leaching at T200. Coherently, the leached NO3 was higher at T200 than at T100 (Table 3). At other depths, the concentrations of leached NO3 were similar at all irrigated treatments. Although chemically poor, Oxisols have generally good physical properties (porosity and permeability) and a very stable soil structure because of strong micro-aggregation (Driessen et al., 2001), which may favor N leaching throughout the soil profile. Because more than 50% of sugarcane roots are found in the 0–0.4 m layer (Faroni, 2004), we expect that NO3 at 1 m depth has already passed through the root zone and unless further denitrification takes place it can reach and impact the groundwater table. Although major concerns about groundwater nitrate contamination are present, higher mineral N stocks in the soil (Table 3) may represent an important nitrogen reservoir for crop nutrition in the following productive cycles, which may partially reduce
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Table 3 Mean soil inorganic N concentrations (mg NO3-N kg1 dry soil), nitrate (NO3) and dissolved organic carbon (DOC) concentrations in soil solution and mineral N stocks (kg ha1) of a tropical agro-system cropped with sugarcane after application of different treated sewage effluent (TSE) irrigation rates (T100, T125, T150 and T200). Depth (m)
Treatmentsa T100
T125
T150
T200
Control
183.1 a 207.8 ab 235.3 a
193.6 a 204.2 ab 192.1 a
264.6 a 228.3 a 270.2 a
– – –
Dissolved organic carbon (mg L1) in soil solution 1 110.4 a 2 83.5 a 3 111.0 a
78.3 a 90.1 a 72.0 a
99.3 a 84.8 a 76.4 a
26.5 b 24.8 b 31.9 b
– – –
Nitrate concentrations in soil (mg NO3-N kg1 dry soil) 0–0.1 4.54 AB 0.1–0.2 5.51 AB 0.2–0.4 10.68 A 0.4–0.6 5.21 A
6.21 AB 8.09 A 12.05 A 4.90 A
7.95 7.86 9.82 4.42
6.99 7.18 9.00 3.45
1.91 2.99 1.07 1.75
Mineral N stock (kg ha1) 0–0.6
72.30
66.43
Nitrate concentrations (mg L1) 1 2 3
in soil solution 177.8 ab 111.6 b 183.0 a
62.74
A A A AB
AB AB A AB
58.60
B B B B
15.81
a
Treatments: T100, T125, T150 and T200 corresponding to TSE irrigation supplying 100, 125, 150 and 200% of the crop water demand, respectively. Control: without TSE irrigation and mineral N fertilization. b Means followed by same small letters in the same row (different treatments) do not differ by adjusted. Tukey’s test (a = 0.05).
mineral N fertilization additions. Our results suggest further approaches to evaluate effluent irrigation by supplying, e.g. different percentages of sugarcane N requirements via effluent which would provide more information about the potential of effluent irrigation to replace mineral N fertilization in sugarcane agriculture. Nitrate leaching after wastewater irrigation have often been reported (Polglase et al., 1995; Speir et al., 1999). For example, after two cycles of maize and sunflower irrigated with TSE, nitrate leached up to a depth of 2 m, however, NO3 concentrations below 1 m did not exceed 35 mg L1 (Gloaguen et al., 2007). The high concentrations of NO3 found in the present study indicate the importance of an adequate irrigation management to avoid N losses in soil. Concerns related to excessive levels of NO3 in soil solution have been stated due to its potential adverse effects on human health (when water is used for human consumption) and on the
Fig. 2. Temporal evolution of nitrate concentrations (6 n 9) (mean of depths 100, 200 and 300 cm, standard deviation) of soil solution in a tropical agro-system cropped with sugarcane and irrigated with treated sewage effluent (TSE). T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
ecological balance (when N-rich wastewater reaches surface waterbodies) (Bond, 1998; da Fonseca et al., 2007a). According to Bond (1998), although NO3 leaching from effluent irrigated areas is almost inevitably, the extent of possible negative effects depends on a range of factors such as: (i) depth of the watertable; (ii) quality of groundwater prior to effluent irrigation; (iii) extent of dilution of NO3 in the groundwater; (iv) size of the effluent irrigated areas; (v) proximity of the effluent irrigation site to discharge zones and water supply wells. 3.4. Dissolved organic carbon (DOC) in soil solution Considerable amounts of DOC in soil solution were measured between 1 and 3 m depth throughout the experimental period (Fig. 3 and Table 3). With exception of T200 (26.5–31.9 mg L1) DOC concentrations were very similar (72–111 mg L1) between the other irrigated plots and remained high over time (Table 3). The measured DOC concentrations were much higher than the concentration ranges for other Brazilian tropical soils for which average values of 5 mg L1 (Lilienfein et al., 2001) and <15 mg L1 (Ciglasch et al., 2004) were reported. However, our values are consistent with data from Gloaguen et al. (2007), who reported for a two years experiment on maize and sunflower irrigated with the
Fig. 3. Temporal evolution of dissolved organic carbon (DOC) concentrations (5 n 9) (mean of depths 100, 200 and 300 cm) of soil solution in a tropical agrosystem cropped with sugarcane and irrigated with treated sewage effluent (TSE). T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
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same TSE in the same area DOC concentrations from 7 to 131 mg L1. High DOC concentrations in soil solution may reach groundwater, where it may interact with organic and inorganic contaminants, fuel denitrification, leading also to potential problems for potable water treatment (Chomycia et al., 2008). DOC concentrations in the soil solution are closely related to land management and microbial activity (Silveira, 2005). The high DOC values found in the present study may be attributed to the degradation of the added organic matter via effluent and to the organic components originated from higher microbial activity under irrigation conditions (Gloaguen et al., 2007). Due to its high mobility, the DOC fraction may play an important role as a carrier of metals and pollutants throughout the soil profile (Ciglasch et al., 2004). Moreover, DOC may enhance leaching of N, P and S, because these nutrients are also part of the chemical structure of dissolved organic matter (Ciglasch et al., 2004). 4. Conclusions Although sugarcane extracted high amounts of N from soil, the quantities were insufficient to balance the large N input via effluent irrigation leading to nitrate leaching into the deeper soil layers. Also high concentrations of DOC in soil solution were identified. The supply of C and N by effluent irrigation had not affected soil total-C and total N concentrations possibly because of the short term experimental period. On the other hand, soil NO3 concentrations were higher at the irrigated treatments compared to the control at the end of the experiment. Treated sewage effluent irrigation according to crop water requirement (T100) caused an excessive nitrogen input compared to the plant demand. The results indicated that crop full water supply by TSE irrigation should be avoided in the first crop cycle where sugarcane response to N fertilization is less pronounced than in the following cycles. Moreover, mineral N application can be avoided due to the N additions by effluent. Adequate plant selection combined with adapted irrigation management strategies are of future concern for an optimal and sustainable sugarcane production under effluent irrigation systems. Acknowledgements To FAPESP, CNPq and SABESP for financial support as well as to SABESP and the agroindustry EQUIPAV for logistic support. We also thank two anonymous reviewers for their meaningful contribution to the paper. References Barton, L., Schipper, L.A., Barkle, G.F., McLeod, M., Speir, T.W., Taylor, M.D., McGill, A.C., Van Schaik, A.P., Fitzgerald, N.B., Pandey, S.P., 2005. Land application of domestic effluent onto four soil types: plant uptake and nutrient leaching. J. Environ. Qual. 34, 635–643. Bhandral, R., Bolan, N.S., Saggar, S., Hedley, M.J., 2007. Nitrogen transformation and nitrous oxide emissions from various types of farm effluents. Nutr. Cycl. Agroecosyst. 79, 193–208. Bond, W.J., 1998. Effluent irrigation—an environmental challenge for soil science. Aust. J. Soil Res. 36, 543–555. Carneiro, A.E.V., Trivelin, P.C.O., Victoria, R.L., 1995. Utilizac¸a˜o da reserva orgaˆnica e de nitrogeˆnio do tolete de plantio (colmo-semente) no desenvolvimento da cana-planta. Sci. Agric. 52, 199–209. Chomycia, J.C., Hernes, P.J., Harter, T., 2008. Land management impacts on dairyderived dissolved organic carbon in ground water. J. Environ. Qual. 37, 333–343. Ciglasch, H., Lilienfein, J., Kaiser, K., Wilcke, W., 2004. Dissolved organic matter under native Cerrado and Pinus caribaea plantations in the Brazilian savanna. Biogeochemistry 67, 157–182.
da Fonseca, A.F., 2005. Viabilidade agronoˆmico-ambiental da disposic¸a˜o de efluente de esgoto tratado em um sistema solo-pastagem. PhD Thesis. Universidade de Sa˜o Paulo – Escola Superior de Agricultura Luiz de Queiroz. da Fonseca, A.F., Herpin, U., Paula, A.M., Victoria, R.L., Melfi, A.J., 2007a. Agricultural use of treated sewage effluents: agronomic and environmental implications and perspectives for Brazil. Sci. Agric. 64, 194–209. da Fonseca, A.F., Melfi, A.J., Monteiro, F.A., Montes, C.R., Almeida, V.V., Herpin, U., 2007b. Treated sewage effluent as a source of water and nitrogen for Tifton 85 bermudagrass. Agric. Water Manage. 87, 328–336. da Fonseca, A.F., Herpin, U., Dias, C.T.S., Melfi, A.J., 2007c. Nitrogen forms, pH and total carbon in a soil incubated with treated sewage effluent. Braz. Arch. Biol. Technol. 50, 743–752. Driessen, P., Deckers, J., Spaargaren, O., Nachtergaele, F., 2001. Lecture notes on the major soils of the world. Food Agric. Org. U.N.. Falkiner, R.A., Smith, C.J., 1997. Changes in soil chemistry in effluent-irrigated Pinus radiata and Eucalyptus grandis. Aust. J. Soil Res. 35, 131–147. Dematteˆ, J.L.I., 2005. Recuperac¸a˜o e manutenc¸a˜o da fertilidade dos solos. Inform. Agron. 111, 1–24. Embrapa (Empresa Brasileira de Pesquisa Agropecua´ria), 1999. Manual de ana´lises quı´micas de solos plantas e fertilizantes. Embrapa - Comunicac¸a˜o para Transfereˆncia de Tecnologia, Brası´lia, Brazil. Faroni, C.E., 2004. Sistema radicular de cana-de-ac¸u´car e identificac¸a˜o de raı´zes metabolicamente ativas. MSc Dissertation. Universidade de Sa˜o Paulo – Escola Superior de Agricultura Luiz de Queiroz. Friedel, J.K., Langer, T., Siebe, C., Stahr, K., 2000. Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico. Biol. Fertil. Soils 31, 414–421. Gloaguen, T.V., Forti, M.C., Lucas, Y., Montes, C.R., Gonc¸alves, R.A.B., Herpin, U., Melfi, A.J., 2007. Soil solution chemistry of a Brazilian Oxisol irrigated with treated sewage effluent. Agric. Water Manage. 88, 119–131. Hamilton, A.J., Stagnitti, F., Xiong, X., Kreidl, S.L., Benke, K.K., Maher, P., 2007. Wastewater irrigation: the state of play. Vadose Zone J. 6, 823–840. Kandeler, E., Kampichler, C., Horak, O., 1996. Influence of heavy metals on the functional diversity of soil microbial communities. Biol. Fertil. Soils 23, 299– 306. Leal, R.M.P., Herpin, U., da Fonseca, A.F., Firme, L.P., Montes, C.R., Melfi, A.J., 2009. Sodicity and salinity in a Brazilian Oxisol cultivated with sugarcane irrigated with wastewater. Agric. Water Manage. 96, 307–316. Lilienfein, J., Wilcke, W., Thomas, R., Vilela, L., Lima, S.C., Zech, W., 2001. Effects of Pinus caribaea forests on the C, N, P, and S status of Brazilian savanna Oxisols. For. Ecol. Manage. 147, 171–182. Malavolta, E., Vitti, G.C., Oliveira, S.A., 1997. Avaliac¸a˜o do estado nutricional das plantas: princı´pios e aplicac¸o˜es, 2nd ed. Potafos, Piracicaba Brazil. Nelson, D.W., Sommers, L.E., 1996. Total carbon, organic carbon, and organic matter. In: Sparks, D.L. (Ed.), Methods of Soil Analysis: Chemical Methods. SSSA/ASA, Madison, pt. 3, pp. 961–1010. Piccolo, M.C., Neill, C., Cerri, C.C., 1994. Net mineralization and net nitrification along a tropical forest-to-pasture chronossequence. Plant Soil 162, 61–71. Polglase, P.J., Tomkins, L.G., Stewart, L.G., Falkiner, R.A., 1995. Mineralization and leaching of nitrogen in an effluent-irrigated pine plantation. J. Environ. Qual. 24, 911–920. Ramirez-Fuentes, E., Lucho-Constantino, C., Escamilla-Silva, E., Dendooven, L., 2002. Characteristics, and carbon and nitrogen dynamics in soil irrigated with wastewater for different lengths on time. Bioresour. Technol. 85, 79–187. Ruzicka, J., Hansen, E.H., 1981. Flow Injection Analyses. Wiley, New York. SAS System, 1999. SAS Institute Inc. Release 8.02. The SAS Institute, Cary, NC. Silveira, M.L.A., 2005. Dissolved organic carbon and bioavailability of N and P as indicators of soil quality. Sci. Agric. 62, 502–508. Smith, C.J., Bond, W.J., 1999. Losses of nitrogen from an effluent-irrigated plantation. Aust. J. Soil Res. 37, 371–389. Snow, V.O., Smith, C.J., Polglase, P.J., Probert, M.E., 1999. Nitrogen dynamics in a eucalypt plantation irrigated with sewage effluent or bore water. Aust. J. Soil Res. 37, 527–544. Soil Survey Staff, 1999. Soil taxonomy. In: Agriculture Handbook #436, 2nd ed. USDA-NRCS, Washington, DC. Speir, T.W., Van Schaik, A.P., Kettles, H.A., Vicent, K.W., Campbell, D.J., 1999. Soil and stream-water impacts of sewage effluent irrigation onto steeply sloping land. J. Environ. Qual. 28, 1105–1114. Surita, C.A., Montes, C.R., Gomes, T.M., Melfi, A.J., 2007. Nitrato em soluc¸a˜o do solo em a´rea de aplicac¸a˜o de a´guas residua´rias cultivada com cana-de-ac¸u´car: experimento em campo, Lins (SP). In: Proceedings of the XXI Brazilian Symposium on Water Resources, Sa˜o Paulo, SP, Brazil, 25–29 November 2007. Van Raij, B., Cantarella, H., Quaggio, J.A., Furlani, A.M.C. (Eds.), 1996. Recomendac¸o˜es de adubac¸a˜o e calagem para o Estado de Sa˜o Paulo, 2nd ed. Boletim Te´cnico #100. Instituto Agronoˆmico, Campinas, Brazil. Van Raij, B., Andrade, J.C., Cantarella, H., Quaggio, J.A. (Eds.), 2001. Ana´lise quı´mica para avaliac¸a˜o da fertilidade de solos tropicais. Instituto Agronoˆmico, Campinas, Brazil.
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Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater Rafael Marques Pereira Leal a,b,*, Lilian Pittol Firme b, Uwe Herpin b, Adriel Ferreira da Fonseca c, Ce´lia Regina Montes b,d, Carlos Tadeu dos Santos Dias e, Adolpho Jose´ Melfi b,f a
Laborato´rio de Ecotoxicologia, Centro de Energia Nuclear na Agricultura – CENA/USP, P.O. Box 96, 13400-970, Piracicaba (SP), Brazil Nu´cleo de Pesquisa em Geoquı´mica e Geofı´sica da Litosfera (NUPEGEL), Universidade de Sa˜o Paulo (USP), P.O. Box 09, 13418-900, Piracicaba (SP), Brazil Departamento de Cieˆncia do Solo e Engenharia Agrı´cola (DESOLO), Universidade Estadual de Ponta Grossa (UEPG), 84030-900, Ponta Grossa (PR), Brazil d Laborato´rio de Ana´lise Ambiental e Geoprocessamento, Centro de Energia Nuclear na Agricultura (CENA), USP, 13400-970, Piracicaba (SP), Brazil e Departamento de Cieˆncias Exatas, Escola Superior de Agricultura Luiz de Queiroz (ESALQ), USP, 13418-900, Piracicaba (SP), Brazil f Departamento de Cieˆncia do Solo, Escola Superior de Agricultura Luiz de Queiroz (ESALQ), USP, 13418-900, Piracicaba (SP), Brazil b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 March 2009 Received in revised form 20 September 2009 Accepted 23 September 2009
Carbon (C) and nitrogen (N) dynamics in agro-systems can be altered as a consequence of treated sewage effluent (TSE) irrigation. The present study evaluated the effects of TSE irrigation over 16 months on N concentrations in sugarcane (leaves, stalks and juice), total soil carbon (TC), total soil nitrogen (TN), NO3-N in soil and nitrate (NO3) and dissolved organic carbon (DOC) in soil solution. The soil was classified as an Oxisol and samplings were carried out during the first productive crop cycle, from February 2005 (before planting) to September 2006 (after sugarcane harvest and 16 months of TSE irrigation). The experiment was arranged in a complete block design with five treatments and four replicates. Irrigated plots received 50% of the recommended mineral N fertilization and 100% (T100), 125% (T125), 150% (T150) and 200% (T200) of crop water demand. No mineral N and irrigation were applied to the control plots. TSE irrigation enhanced sugarcane yield but resulted in total-N inputs (804– 1622 kg N ha1) greater than exported N (463–597 kg N ha1). Hence, throughout the irrigation period, high NO3 concentrations (up to 388 mg L1 at T200) and DOC (up to 142 mg L1 at T100) were measured in soil solution below the root zone, indicating the potential of groundwater contamination. TSE irrigation did not change soil TC and TN. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Wastewater irrigation Water reuse Saccharum spp. Nitrate Dissolved organic carbon Tropical soil
1. Introduction Treated sewage effluent (TSE) is increasingly used as a source of water and nutrients (mainly nitrogen) in crop production in Brazil (da Fonseca et al., 2007a). However, the country lacks a long-term tradition on the agricultural use of such residues, so that national legal regulations and general guidelines for its sustainable application are still in development. For these reasons, scientific experimentation concerning the major implications of effluent irrigation under the local tropical conditions is highly required, in order that TSE may be used as part of a rational and sustainable agricultural planning. Carbon (C) and nitrogen (N) cycling in agro-systems can be altered by TSE irrigation, mainly in the long-term (da Fonseca et al.,
* Corresponding author at: Laborato´rio de Ecotoxicologia, Centro de Energia Nuclear na Agricultura – CENA/USP, P.O. Box 96, 13400-970, Piracicaba (SP), Brazil. Tel.: +55 19 34294764; fax: +55 19 34294764. E-mail address: fi[email protected] (R.M.P. Leal). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.09.018
2007a). Several studies have shown increased total carbon (TC) and total nitrogen (TN) contents in the soil due to C and N input by TSE irrigation (Friedel et al., 2000; Ramirez-Fuentes et al., 2002). Other studies have found decreased contents of soil TC and TN (Speir et al., 1999; Snow et al., 1999), mainly attributed to enhanced mineralization and nitrification processes under effluent irrigation (da Fonseca et al., 2007a). Of greater concern, increasing concentrations of nitrate (NO3) in soil solution due to TSE irrigation have often been reported (Polglase et al., 1995; Smith and Bond, 1999), representing one of the main challenges for the sustainable land application of effluents (Bond, 1998; da Fonseca et al., 2007a). Also increases in dissolved organic carbon (DOC) in soil solution were reported after effluent irrigation (Bhandral et al., 2007; Gloaguen et al., 2007). The DOC fraction represents an important indicator of soil quality (Silveira, 2005) and may play an important role as a carrier of metals and pollutants in the soil profile due to its high mobility (Ciglasch et al., 2004). Sugarcane (Saccharum spp.) may represent an attractive crop for TSE irrigation in Brazil, because of the following characteristics:
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(i) predominance of non-irrigated plantations with large potential for the adoption of irrigation practices; (ii) high demand of N (one of the main nutrient in TSE); (iii) perennial crop fitted to full mechanization, without direct contact to farm workers; (iv) major commodity for ethanol production in Brazil. These characteristics may result in agronomic, economic and environmental benefits, however, detailed studies on TSE irrigation in sugarcane agrosystems are lacking. The purpose of this study was to evaluate the effects of short term TSE irrigation (16 months) on N uptake by sugarcane, N and C accumulation in soil and NO3 and DOC leaching. 2. Materials and methods The experimental area is situated near the city of Lins, State of Sa˜o Paulo (longitude: 498500 W; latitude: 228210 S; average altitude of 440 m), Brazil, adjacent to the municipal wastewater treatment plant (stabilization ponds system). Mean annual temperature is 23 8C and precipitation was 1292 mm during the experimental period (16 months). Monthly rainfall and the amounts of TSE applied as irrigation throughout the experiment are presented in Fig. 1. The soil was classified as Typic Haplustox (Soil Survey Staff, 1999), sandy clay loam. The soil mineralogy of the area is dominated by quartz and kaolinite, and subordinately by hematite, magnetite and/or maghemite. The dominance of these minerals, commonly occurring in highly weathered and acid tropical soils, results in low cation exchange capacity (CEC) (Table 1). The chemical and physical soil characteristics found at the beginning of the experiment (Table 1) are usual for most Brazilian agro-systems cropped with sugarcane. Available calcium (Ca), magnesium (Mg), potassium (K) and phosphorus (P) were found in adequate concentrations for sugarcane growth due to previous liming and addition of mineral fertilizers at the beginning of the experiment. Sugarcane was planted in March 2005 with a distance of 1.4 m between the rows. TSE irrigation was carried out from May 2005 till August 2006 (16 months). After this period irrigation was stopped because sugarcane needs water stress before harvest in order to concentrate sugar. Plants were irrigated when Cm were less than 40 kPa. Harvest took place at the end of September 2006. Concerning mineral fertilizer application, all experimental plots received 15 kg ha1 of N (ammonium nitrate, 50% of recommended mineral N), except the control plot; 52 kg ha1 of P (simple superphosphate), and 66 kg ha1 of K (potassium chloride), distributed manually to the furrows during planting.
Fig. 1. Monthly amounts of applied water (rainfall and wastewater irrigation) during the experimental period. Month 1 corresponds to May 2005 and month 16 to August 2006. T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
Detailed information about irrigation and crop management are available in a previous work (Leal et al., 2009). The experiment was arranged in a complete block design, with five treatments and four replications. The treatments consisted of: (i) control, without TSE irrigation and N fertilization; (ii) T100, T125, T150 and T200, with TSE irrigation supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand, respectively. Total plot size was 280 m2 (40 m 7 m) with a useful area of 126 m2. The effects of effluent irrigation on carbon and nitrogen dynamics were evaluated by considering two application scenarios: (i) land application of TSE rates higher than 100% of crop water requirement (T125, T150 and T200) as a TSE disposal alternative, and (ii) TSE application according to crop water requirement (T100) to enhance agricultural production through the provision of water and nutrients. Data about TSE constituents were taken from a previous detailed effluent characterization (da Fonseca et al., 2007b) because TSE quality has not changed considerably during the last five years (Leal et al., 2009). In average, TSE is characterized by: pH of 7.7; total-N concentration of 31.9 mg L1; 22.4 mg L1 of NH4+N (predominant N form); 0.6 mg L1 of NO3-N; 65.28 mg L1 of dissolved organic carbon (DOC); 301 mg L1 of bicarbonate (HCO3); 146 mg L1 of Na and a sodium adsorption ratio (SAR) of 11.9 (mmol L1)0.5. The total-C and total-N inputs to the soil–plant system via TSE irrigation (16 months) were calculated for each treatment. As a result, 4500, 5690, 6830 and 8430 kg ha1 of total-C and 800, 1020,
Table 1 Chemical and physical soil properties at the beginning of the experiment (March 2005). Layer (m)
pH
H + Al (mmolc kg1)
Al (mmolc kg1)
Ca (mmolc kg1)
Mg (mmolc kg1)
K (mmolc kg1)
Na (mmolc kg1)
CECa (mmolc kg1)
P (mg kg1)
TCb (g kg1)
TNc (g kg1)
0–0.1 0.1–0.2 0.2–0.4 0.4–0.6
5.1 5.2 4.9 4.6
15.4 15.0 15.9 21.8
0.9 0.8 1.8 4.0
12.7 13.2 10.2 6.2
3.5 3.6 3.6 2.3
3.0 2.4 1.8 1.2
0.7 1.5 2.5 2.8
35.4 35.6 34.0 34.3
17.3 15.5 4.1 1.0
6.0 6.4 5.1 4.1
0.5 0.5 0.4 0.3
Layer (m)
BSd (%)
ESPe (%)
B (mg kg1)
Cu (mg kg1)
Fe (mg kg1)
Mn (mg kg1)
Zn (mg kg1)
ECf (dS m1)
Sand (g kg1)
Silt (g kg1)
Clay (g kg1)
0–0.1 0.1–0.2 0.2–0.4 0.4–0.6
56.3 57.9 53.3 36.5
2.1 4.1 7.4 8.1
0.6 0.6 0.6 0.4
0.5 0.7 0.3 0.5
21.5 20.9 15.5 10.4
3.0 2.7 1.7 1.2
1.2 1.5 0.3 0.2
0.7 0.4 0.2 0.2
774 775 732 707
90 78 75 65
135 147 192 227
a b c d e f
Cation exchange capacity at pH 7.0 ! CEC = Ca + Mg + K + Na + H + Al. TC = total carbon. TN = total nitrogen. Base saturation ! BS = (Ca + Mg + K + Na) 100/CEC. Exchangeable sodium percentage ! ESP = Na 100/CEC. EC = electrical conductivity.
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1220 and 1620 kg ha1 of total-N were added to the soil at T100, T125, T150 and T200, respectively. Taking into account that the TSE applied presents a Na/total-N ratio of about five (da Fonseca et al., 2007b), its application also added high amounts of Na to the soil system, representing a major risk of sodification (Leal et al., 2009). Soil sampling for TC and TN was carried out in February 2005 (before planting) and in September 2006 (after sugarcane harvest and 16 months of irrigation). At each plot, twelve subsamples were randomly collected at the 0–0.1, 0.1–0.2 m soil layers to compound composite samples. At the 0.2–0.4 and 0.4–0.6 m soil layers six subsamples were taken to form composite samples. Soil samples were air-dried, sieved at 0.15 mm and soil TC and TN were determined by dry combustion (Nelson and Sommers, 1996). For initial soil chemical characterization (Table 1), sieved (2 mm) soil samples were analyzed according to standard procedures: (i) Embrapa (1999) for P, Ca, Mg, K, Al, and Na, and (ii) Van Raij et al. (2001) for pH, H + Al, B, Cu, Fe, Mn and Zn. Soil solution electrical conductivity (EC) was obtained using saturation extracts, according to Van Raij et al. (2001). Nine months after planting (December 2005), sugarcane was in the stage of maximum vegetative growth. At that time, 25 leaves were randomly sampled within each plot for mineral nutrition analysis. The samples were rinsed in distilled water, oven dried at 60 8C, ground in a Wiley type mill, passed through a 0.85 mm sieve and stored in capped vials. For N analyses the samples were submitted to sulphuric acid digestion and determined by the semimicro-Kjeldahl procedure proposed by Malavolta et al. (1997). In September 2006 (date of harvest), ten stalks per plot were randomly sampled for N analyses. The procedures used for stalks N analyses were similar to those described for the leaves. Juice extracted from stalk samples were kept frozen prior to N analysis and subsequently evaluated according to the same analytical procedures as mentioned above. For soil inorganic N determination, fresh soil samples (10 g) from the sampling campaign in September 2006 were immediately extracted in 50 mL of 2 M KCl, according to Piccolo et al. (1994). After 24 h, the extracts were centrifuged and colorimetrically analysed using an automated flow injection system (Ruzicka and Hansen, 1981). For the estimation of mineral N stocks in the 0– 0.60 m soil layer at the end of the experimental period (Table 3), an average soil density of 1.5 kg dm3 was employed. Nitrate and DOC concentrations in soil solution were monitored every 2 months, from May 2005 (start of the irrigation period) to June 2006 (approximately 45 days before irrigation was stopped). The samples were obtained using porous ceramic cups installed at soil depths of 1–3 m. Samples were collected after applying a tension of 50 kPa for 8 days to obtain a minimum amount of soil solution required for analysis (Surita et al., 2007). Subsequently the samples were filtered through a 0.22 mm pore diameter estercellulose membrane and frozen prior to NO3 determination. Nitrate analyses were carried out with liquid chromatography (Dionex 500). Only mineral N in form of NO3 was quantified, because Gloaguen et al. (2007) found in effluent generated in the same treatment plant a mean [NO3]/[NH4+] ratio of 0.05 toward 396 in the soil solution due to fast nitrification of effluent-N in the soil (da Fonseca et al., 2007c). For DOC analyses, an aliquot of soil solution was filtered through a fiber glass filter (0.7 mm) and preserved with 30 mmol L1 mercuric chloride solution (HgCl2). Determinations were carried out using a Shimadzu TOC-5000 Analyzer. At the control plots without TSE application, no sufficient volume of soil solution for NO3 and DOC determinations could be obtained during the sampled period. Soil and plant data were submitted to analysis of variance. The analysis presented a homogeneous variance, a necessary condition to carry out univariate statistical analysis for a complete block design, considering time (sampling date) as subplot. The variables
273
which showed significant F test (P < 0.05) were submitted to multiple comparisons by Tukey’s test adjusted for descriptive level (a = 0.05). Mean comparisons of NO3 and DOC values of soil solution were made with transformed data (square root transformation for NO3 values and logarithmic transformation for DOC values). However, all given means are original values. All statistical analyses were carried out using the SAS system, version 8.02 (SAS System, 1999). 3. Results and discussion 3.1. Nitrogen contents in plants and sugarcane yield There were no differences between N concentrations in sugarcane leaves at the irrigated treatments (17.1–18.2 g kg1) compared to the control (19.7 g kg1). At the irrigated plots, N concentrations in leaves were close to the lower range limit of adequate values (18–25 g N kg1 leaves) proposed by Van Raij et al. (1996). Nitrogen concentrations in sugarcane juice (8.4– 11.7 g L1) and stalks (7.2–8.6 g kg1) were also not influenced by the treatments. However, the accumulated N in stalks (2.30– 2.60 kg N per Mg of fresh stalks1) was considerably higher than the reference range (0.90–1.32 kg N per Mg of fresh stalks1) (Dematteˆ, 2005). Although N concentration in leaves were close to the lower range limit of adequate values, the high accumulated N in stalks and the high sugarcane yields suggest adequate conditions for crop development. All TSE irrigated plots (T100 = 247 Mg ha1; T150 = 233 Mg ha1; T200 = 232 Mg ha1), except T125 (199 Mg ha1), showed significant higher yields than the control (153 Mg ha1), probably due to the water supplied by TSE irrigation. However, despite increasing irrigation rates, similar (T150 and T200) or lower (T125) yields were found compared to T100. This indicates no positive effect of higher TSE irrigation rates (T125–T200) on sugarcane yield and is important to be considered for an adequate and sustainable land application of TSE. Sugarcane extracted significant amounts of N from the soil, from 345 kg ha1 at the control to a maximum of 597 kg ha1 (T200), with no differences between irrigated treatments (463–597 kg ha1). However, the accumulated N in stalks was not sufficient to counterbalance the large N input via TSE irrigation, resulting in a low N recovery (maximum of 23%, given as the ratio between N in stalks and total N applied). Effluent induced N overfertilization may negatively affect the ability of the crop to resist disease and also to synthesize important compounds related to crop natural defenses (Hamilton et al., 2007), representing a relevant aspect to be considered in TSE irrigation management. Different from the following productive cycles, the first sugarcane cycle is known to be not responsive to N fertilization, because the required N can be obtained by alternative sources such as biological fixation of atmospheric N and through the utilization of N reserves stored in the seedpiece (Carneiro et al., 1995). Therefore, it is suggested that mineral N application in the first crop cycle can be avoided because the effluent may entirely supply the required N. The high yields at the irrigated treatments, where 50% of the recommended mineral N fertilization was applied, also support this statement. Effluent irrigation schemes should be designed in such a way that the cover crop can completely utilize the applied N in order to prevent N leaching and N discharge to water systems fostering eutrophication processes (Bond, 1998; Barton et al., 2005). Barton et al. (2005) pointed out that, although denitrification, volatilization and soil storage are alternative pathways for wastewater applied N, these processes are often variable and more difficult to predict and to control than plant uptake. Gloaguen et al. (2007) also emphasized the relevance to optimize plant N uptake for the sustainability of TSE irrigation under tropical conditions.
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Table 2 Total carbon and nitrogen (g kg1) concentrations in soil after application of different treated sewage effluent (TSE) irrigation rates (T100, T125, T150 and T200). Treatmentsa
Time after the beginning of irrigation (month) 0
16
0
Carbon
16
Nitrogen
0–0.1 m layer (CVb = 9.1%) Control T100 T125 T150 T200
6.10 5.82 6.62 5.75 6.00
aAc aA aA aA aA
6.40 6.62 6.25 6.02 5.90
aA aA aA aA aA
0–0.1 m layer (CV = 8.6%) 0.52 aA 0.52 aA 0.55 aA 0.50 aA 0.52 aA
0.52 0.42 0.55 0.47 0.47
aAB aB aA aAB aAB
0.1–0.2 m layer (CV = 10.6%) Control T100 T125 T150 T200
6.22 6.37 7.10 5.77 6.50
aA aA aA aA aA
6.00 6.02 6.25 6.12 5.80
aA aA aA aA aA
0.1–0.2 m layer (CV = 13.6%) 0.57 aA 0.52 aA 0.60 aA 0.52 aA 0.55 aA
0.57 0.55 0.55 0.60 0.52
aA aA aA aA aA
0.2–0.4 m layer (CV = 10.2%) Control T100 T125 T150 T200
5.05 5.15 5.22 4.97 5.22
aA aA aA aA aA
5.12 5.10 5.52 5.72 4.77
aA aA aA aA aA
0.2–0.4 m layer (CV = 12.8%) 0.45 aA 0.42 aA 0.47 aA 0.42 bA 0.42 aA
0.45 0.42 0.52 0.60 0.47
aAB aB aAB aA aAB
0.4–0.6 m layer (CV = 8.5%) Control T100 T125 T150 T200
4.07 4.25 4.17 4.10 4.10
aA aA aA aA aA
4.02 4.20 4.12 4.37 4.20
aA aA aA aA aA
0.4–0.6 m layer (CV = 17.4%) 0.35 aA 0.32 aA 0.37 aA 0.35 aA 0.35 aA
0.32 0.37 0.42 0.37 0.42
aA aA aA aA aA
a Treatments: control (without TSE irrigation and mineral N fertilization) and T100, T125, T150 and T200 corresponding to TSE irrigation supplying 100, 125, 150 and 200% of the crop water demand, respectively. b CV = coefficient of variation. c Means followed by same small letters in the same row (different sampling data) and same capital letters in the same column (different treatments) do not differ by adjusted Tukey’s test (a = 0.05).
3.2. Total carbon (TC) and total nitrogen (TN) in soil Effluent irrigation showed no effects on soil TC (Table 2) and negligible effects on soil TN contents (Table 2), which may be referred to the short term experimental period. da Fonseca (2005) found significant decreases in soil TC and TN concentrations after 18 months of effluent irrigation of Tifton 85 bermudagrass, and attributed it to the mineralization of native organic matter due to a high N (through mineral fertilization and effluent irrigation) input, a process known as ‘‘the priming effect’’. Generally, changes in soil TC and TN contents were mainly found after effluent irrigation in long-term studies (da Fonseca et al., 2007a), showing both increases (Friedel et al., 2000; RamirezFuentes et al., 2002) and decreases (Polglase et al., 1995; Falkiner and Smith, 1997). The increases in soil TC and TN were related to the significant input of N and C via effluent irrigation over time. On the other hand, decreases in soil TC and TN were mainly referred to the occurrence of permanent moist soil conditions due to irrigation and the low C/N ratio of the effluent. These factors might stimulate microbial activity enhancing soil organic matter mineralization (da Fonseca et al., 2007a). Moreover, prolonged TSE irrigation may increase pollutants (heavy metals) concentrations in soil (Friedel et al., 2000). In the long-term, this accumulation may provoke detrimental effects on soil microbial communities, affecting negatively C, N, P and sulphur (S) cycling processes (Kandeler et al., 1996). 3.3. Nitrate (NO3) in soil and in soil solution Although the additions of effluent-N varied about 800 kg ha1 at the irrigated treatments (T100–T200), inorganic soil N (NO3-N) concentrations were similar at the end of the experiment (Table 3).
However, nitrate concentrations at the irrigated treatments (minimum of 3.5 mg kg1 and maximum of 12.1 mg kg1) were high in comparison to the control (maximum of 3 mg kg1) (Table 3). The higher levels of soil inorganic N stocks at the irrigated treatments compared to the control (Table 3) evidences the potential of N losses due to the low chemical affinity of nitrate anions to net negatively charged soil particles. Although soil inorganic N were only determined at the end of the experiment, higher nitrate levels in the irrigated soils are coherent with the high concentrations (>100 mg L1) of the leached NO3 fraction measured between 1 and 3 m depth at T100–T200 over the experimental period (Fig. 2 and Table 3). Although N recovery was not affected by effluent irrigation, the lost N, considered as the difference between total N input and N recovered at each treatment, was much higher at T200 (1383 kg) compared to T100 (626 kg), indicating a higher potential of N leaching at T200. Coherently, the leached NO3 was higher at T200 than at T100 (Table 3). At other depths, the concentrations of leached NO3 were similar at all irrigated treatments. Although chemically poor, Oxisols have generally good physical properties (porosity and permeability) and a very stable soil structure because of strong micro-aggregation (Driessen et al., 2001), which may favor N leaching throughout the soil profile. Because more than 50% of sugarcane roots are found in the 0–0.4 m layer (Faroni, 2004), we expect that NO3 at 1 m depth has already passed through the root zone and unless further denitrification takes place it can reach and impact the groundwater table. Although major concerns about groundwater nitrate contamination are present, higher mineral N stocks in the soil (Table 3) may represent an important nitrogen reservoir for crop nutrition in the following productive cycles, which may partially reduce
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275
Table 3 Mean soil inorganic N concentrations (mg NO3-N kg1 dry soil), nitrate (NO3) and dissolved organic carbon (DOC) concentrations in soil solution and mineral N stocks (kg ha1) of a tropical agro-system cropped with sugarcane after application of different treated sewage effluent (TSE) irrigation rates (T100, T125, T150 and T200). Depth (m)
Treatmentsa T100
T125
T150
T200
Control
183.1 a 207.8 ab 235.3 a
193.6 a 204.2 ab 192.1 a
264.6 a 228.3 a 270.2 a
– – –
Dissolved organic carbon (mg L1) in soil solution 1 110.4 a 2 83.5 a 3 111.0 a
78.3 a 90.1 a 72.0 a
99.3 a 84.8 a 76.4 a
26.5 b 24.8 b 31.9 b
– – –
Nitrate concentrations in soil (mg NO3-N kg1 dry soil) 0–0.1 4.54 AB 0.1–0.2 5.51 AB 0.2–0.4 10.68 A 0.4–0.6 5.21 A
6.21 AB 8.09 A 12.05 A 4.90 A
7.95 7.86 9.82 4.42
6.99 7.18 9.00 3.45
1.91 2.99 1.07 1.75
Mineral N stock (kg ha1) 0–0.6
72.30
66.43
Nitrate concentrations (mg L1) 1 2 3
in soil solution 177.8 ab 111.6 b 183.0 a
62.74
A A A AB
AB AB A AB
58.60
B B B B
15.81
a
Treatments: T100, T125, T150 and T200 corresponding to TSE irrigation supplying 100, 125, 150 and 200% of the crop water demand, respectively. Control: without TSE irrigation and mineral N fertilization. b Means followed by same small letters in the same row (different treatments) do not differ by adjusted. Tukey’s test (a = 0.05).
mineral N fertilization additions. Our results suggest further approaches to evaluate effluent irrigation by supplying, e.g. different percentages of sugarcane N requirements via effluent which would provide more information about the potential of effluent irrigation to replace mineral N fertilization in sugarcane agriculture. Nitrate leaching after wastewater irrigation have often been reported (Polglase et al., 1995; Speir et al., 1999). For example, after two cycles of maize and sunflower irrigated with TSE, nitrate leached up to a depth of 2 m, however, NO3 concentrations below 1 m did not exceed 35 mg L1 (Gloaguen et al., 2007). The high concentrations of NO3 found in the present study indicate the importance of an adequate irrigation management to avoid N losses in soil. Concerns related to excessive levels of NO3 in soil solution have been stated due to its potential adverse effects on human health (when water is used for human consumption) and on the
Fig. 2. Temporal evolution of nitrate concentrations (6 n 9) (mean of depths 100, 200 and 300 cm, standard deviation) of soil solution in a tropical agro-system cropped with sugarcane and irrigated with treated sewage effluent (TSE). T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
ecological balance (when N-rich wastewater reaches surface waterbodies) (Bond, 1998; da Fonseca et al., 2007a). According to Bond (1998), although NO3 leaching from effluent irrigated areas is almost inevitably, the extent of possible negative effects depends on a range of factors such as: (i) depth of the watertable; (ii) quality of groundwater prior to effluent irrigation; (iii) extent of dilution of NO3 in the groundwater; (iv) size of the effluent irrigated areas; (v) proximity of the effluent irrigation site to discharge zones and water supply wells. 3.4. Dissolved organic carbon (DOC) in soil solution Considerable amounts of DOC in soil solution were measured between 1 and 3 m depth throughout the experimental period (Fig. 3 and Table 3). With exception of T200 (26.5–31.9 mg L1) DOC concentrations were very similar (72–111 mg L1) between the other irrigated plots and remained high over time (Table 3). The measured DOC concentrations were much higher than the concentration ranges for other Brazilian tropical soils for which average values of 5 mg L1 (Lilienfein et al., 2001) and <15 mg L1 (Ciglasch et al., 2004) were reported. However, our values are consistent with data from Gloaguen et al. (2007), who reported for a two years experiment on maize and sunflower irrigated with the
Fig. 3. Temporal evolution of dissolved organic carbon (DOC) concentrations (5 n 9) (mean of depths 100, 200 and 300 cm) of soil solution in a tropical agrosystem cropped with sugarcane and irrigated with treated sewage effluent (TSE). T100, T125, T150 and T200: Treated sewage effluent irrigation (TSE) supplying 100% (0% surplus), 125% (25% surplus), 150% (50% surplus) and 200% (100% surplus) of crop water demand.
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same TSE in the same area DOC concentrations from 7 to 131 mg L1. High DOC concentrations in soil solution may reach groundwater, where it may interact with organic and inorganic contaminants, fuel denitrification, leading also to potential problems for potable water treatment (Chomycia et al., 2008). DOC concentrations in the soil solution are closely related to land management and microbial activity (Silveira, 2005). The high DOC values found in the present study may be attributed to the degradation of the added organic matter via effluent and to the organic components originated from higher microbial activity under irrigation conditions (Gloaguen et al., 2007). Due to its high mobility, the DOC fraction may play an important role as a carrier of metals and pollutants throughout the soil profile (Ciglasch et al., 2004). Moreover, DOC may enhance leaching of N, P and S, because these nutrients are also part of the chemical structure of dissolved organic matter (Ciglasch et al., 2004). 4. Conclusions Although sugarcane extracted high amounts of N from soil, the quantities were insufficient to balance the large N input via effluent irrigation leading to nitrate leaching into the deeper soil layers. Also high concentrations of DOC in soil solution were identified. The supply of C and N by effluent irrigation had not affected soil total-C and total N concentrations possibly because of the short term experimental period. On the other hand, soil NO3 concentrations were higher at the irrigated treatments compared to the control at the end of the experiment. Treated sewage effluent irrigation according to crop water requirement (T100) caused an excessive nitrogen input compared to the plant demand. The results indicated that crop full water supply by TSE irrigation should be avoided in the first crop cycle where sugarcane response to N fertilization is less pronounced than in the following cycles. Moreover, mineral N application can be avoided due to the N additions by effluent. Adequate plant selection combined with adapted irrigation management strategies are of future concern for an optimal and sustainable sugarcane production under effluent irrigation systems. Acknowledgements To FAPESP, CNPq and SABESP for financial support as well as to SABESP and the agroindustry EQUIPAV for logistic support. We also thank two anonymous reviewers for their meaningful contribution to the paper. References Barton, L., Schipper, L.A., Barkle, G.F., McLeod, M., Speir, T.W., Taylor, M.D., McGill, A.C., Van Schaik, A.P., Fitzgerald, N.B., Pandey, S.P., 2005. Land application of domestic effluent onto four soil types: plant uptake and nutrient leaching. J. Environ. Qual. 34, 635–643. Bhandral, R., Bolan, N.S., Saggar, S., Hedley, M.J., 2007. Nitrogen transformation and nitrous oxide emissions from various types of farm effluents. Nutr. Cycl. Agroecosyst. 79, 193–208. Bond, W.J., 1998. Effluent irrigation—an environmental challenge for soil science. Aust. J. Soil Res. 36, 543–555. Carneiro, A.E.V., Trivelin, P.C.O., Victoria, R.L., 1995. Utilizac¸a˜o da reserva orgaˆnica e de nitrogeˆnio do tolete de plantio (colmo-semente) no desenvolvimento da cana-planta. Sci. Agric. 52, 199–209. Chomycia, J.C., Hernes, P.J., Harter, T., 2008. Land management impacts on dairyderived dissolved organic carbon in ground water. J. Environ. Qual. 37, 333–343. Ciglasch, H., Lilienfein, J., Kaiser, K., Wilcke, W., 2004. Dissolved organic matter under native Cerrado and Pinus caribaea plantations in the Brazilian savanna. Biogeochemistry 67, 157–182.
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