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Low nitrogen leaching losses following a high rate of dairy slurry and urea application to pasture on a volcanic soil in Southern Chile
Agriculture, Ecosystems and Environment 160 (2012) 23–28
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Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee
Low nitrogen leaching losses following a high rate of dairy slurry and urea application to pasture on a volcanic soil in Southern Chile F. Salazar a,∗ , J. Martínez-Lagos a , M. Alfaro a , T. Misselbrook b a b
Agricultural Research Institute, Remehue Research Center, Box 24-0, Osorno, Chile Rothamsted Research, North Wyke, Okehampton, Devon EX20 2SB, United Kingdom
a r t i c l e
i n f o
Article history: Received 6 January 2011 Received in revised form 7 January 2012 Accepted 16 April 2012 Available online 29 May 2012 Keywords: Dairy slurry Urea Nitrogen losses Leaching Manure
a b s t r a c t Dairy slurry is an important plant nutrient source. However, mismanagement (e.g. high application rate) can lead to nutrient losses to the wider environment. There are few data on slurry management and its effect on nitrogen (N) losses specific to Southern Chile, although existing studies suggest that N leaching on volcanic Chilean soils might be expected to be low. The objective of this study was to evaluate the effect of heavy dairy slurry application on N leaching losses and compare it with an inorganic fertiliser on a volcanic soil of Southern Chile. A field experiment was carried out at the Agricultural Research Institute, Remehue Research Centre, on a volcanic soil of Southern Chile (40◦ 35 S, 73◦ 12 W) from March 2008 to March 2010. There were two N application treatments, with a target application rate of 400 kg N ha−1 yr−1 as either dairy slurry (S) or urea (U) split into four even applications over the year. Additionally, a control (C) treatment with no N addition was included. N leaching was measured using ceramic suction cups (3 per plot), with samples taken every 100 mm of drainage during the drainage season. Despite the high N rate and application time, N leaching losses were small with no significant differences between treatments in either year (P > 0.05). Concentrations of NO3 − –N for each sampling period never exceeded c. 5.5 mg L−1 and annual mean values were below 0.5 mg L−1 for all treatments. Cumulative N leaching losses were small at 1.4 and 1.2 kg ha−1 yr−1 (C), 2.8 and 4.2 kg ha−1 yr−1 (S) and 2.4 and 3.3 kg ha−1 yr−1 (U) for 2008 and 2009, respectively. We suggest that this could be explained mainly by the unique N retention properties of volcanic soils in Southern Chile and/or gaseous N losses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Dairy slurry is an important plant nutrient source on farms, supplying partial or total requirement for grass fertilisation. However, mismanagement, such as high application rate or inappropriate application time during the year, can lead to nutrient losses to the wider environment (Smith and Chambers, 1993). In dairy production systems one of the most important pathways of nitrogen (N) losses is leaching, for which greater losses have been reported from a grazed pasture than for a cut sward in New Zealand (Di and Cameron, 2002), and which may equal or exceed the range observed in arable production systems (Nissen and García, 1997; Salazar et al., 2005). Most of the pollution problems associated with the land spreading of livestock manures are due to inappropriate management practices (e.g. high application rates), applications at times of low crop demand or inadequately calibrated equipment. Losses of manure nutrients following application to the field are difficult to
∗ Corresponding author at: INIA-Remehue, Box 24-0, Osorno, Chile. Tel.: +56 64 334800. E-mail address: [email protected] (F. Salazar). 0167-8809/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2012.04.018
eliminate, but can be reduced by considering N requirements of the crops and the timing of manure application. Significant improvements can be made in these areas on most farms with proper manure storage facilities and sufficient land area on which to apply the manure (Pain, 2000). In most European countries, recommendations on manure application rates are based on the total N applied per year. For example, the Code of Good Agricultural Practice (Defra, 2009) applied in England recommends up to 250 kg N ha−1 yr−1 , although application rates are further restricted in Nitrate Vulnerable Zones according to the EC Nitrates Directive (91/676/EEC). In Chile there is no legislation to regulate slurry application on farms, and application rates can be as high as 300 m3 ha−1 yr−1 (Salazar et al., 2003). High manure application rates increase the risks of N losses through leaching, volatilisation and denitrification (e.g. Benoit, 1994; Chambers et al., 2000). In general, when comparing cattle slurry and inorganic fertiliser based on similar total N application rates, studies have shown lower N leaching losses with slurry (e.g. Di et al., 1998). This could be explained by the low input from manures of the available N forms, which can be taken up by plants or lost to the wider environment, mainly as nitrate. In recent years, pasture-based dairy production has intensified in Southern Chile, with increasing stocking rates and nutrient
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F. Salazar et al. / Agriculture, Ecosystems and Environment 160 (2012) 23–28
Table 1 Characterisation of dairy slurry used in the study and application rates for 2008 and 2009. Year
Date of application
Dry matter (%)a
N Kjeldahl (kg t−1 )a
N–NH4 (kg t−1 )a
Application rate (m3 ha−1 )
N applied (kg N)
2008
March 31st July 25th September 29th November 27th Average Total
4.6 4.8 4.1 4.1 4.4
1.5 1.4 1.6 1.8 1.5
0.5 0.4 0.6 0.7 0.6
80 80 60 60 70
117 108 94 108 107 427
2009
March 26th July 27th September 28th December 07th Average Total
4.7 4.8 5.2 1.7 4.9
1.8 1.9 1.2 1.3 1.6
0.7 0.7 0.3 0.4 0.5
70 50 90 65 69
127 93 110 47 94 377
a
N applied (kg NH4 + –N) 41 33 36 42 152 47 34 23 24 128
Presented data for each application date represent the mean of the 3 replicate samples.
application by purchased fertilisers and cattle slurry (Alfaro et al., 2006). Surveys on manure management have shown that farmers use a high rate of manure application (up to 300 m3 ha−1 yr−1 ) distributed in different seasons throughout the year (Salazar et al., 2003), with a potential risk for ground water pollution due to leaching during winter (Olson et al., 2009). The South of Chile has suitable soil and climatic conditions for cattle production. Consequently, 56% of the national cattle herd is concentrated in this maritime temperate climatic region, grazed on natural and improved pastures on volcanic soils. These cattle produce 80% of the country’s milk and 50% of the meat (ODEPA, 2007; Anrique, 1999). The volcanic soils are characterised by low nutrient availability, high phosphorus fixation capacity, high organic matter (OM) content, and pH-dependent cation exchange capacity (Escudey et al., 2001). Recent studies of forest volcanic soils of Southern Chile showed that they have very specialised microbial and abiotic retention processes which can reduce the risk of N leaching, despite the high N turnover rates observed (Huygens et al., 2008, 2010). The abiotic processes include dissimilatory nitrate reduction to ammonium (DNRA), which can be responsible for the consumption of more than 99% of the NO3 available in soil solution, and physical adsorption of NH4 into clay lattices (Huygens et al., 2007). The former process has been suggested as a widespread N retention mechanism in ecosystems that are N limited and receive high rainfall (Huygens et al., 2007), such as those of temperate pastures of southern Chile. In Chile there are few studies published relating to N leaching losses from grassland. Alfaro et al. (2006) reported losses from pasture grazed by beef cattle ranging from 3 to 70 kg N ha−1 yr−1 , according to the stocking rates and grazing strategies used, and ˜ et al. (2010) reported N leaching losses varying between 33 Nunez and 59 kg N ha−1 yr−1 from pastures grazed by non-lactating dairy cows. Also, nitrate leaching losses up to 67 kg N ha−1 yr−1 have been reported in a lysimeter study with dairy slurry application equivalent to 150 kg N ha−1 (Alfaro et al., 2006). Under cutting regimes, a study using the equivalent to 400 kg N ha−1 yr−1 as Sodium Nitrate applied in one dressing early in autumn showed very low N leaching losses, which were below 8% of the applied N (Salazar et al., 2010). The objective of the current study was to evaluate the effect of high rates of dairy slurry application on N leaching losses and compare this with leaching losses from an equivalent N application as an inorganic fertiliser on a volcanic soil. 2. Material and methods A field experiment was carried out from March 2008 to March 2010 at the Agricultural Research Institute, Remehue Research Center (40◦ 35 S, 73◦ 12 W) in Osorno-Chile. The soil is an Andisol
of the Osorno soil series; Typic Hapludands (CIREN, 2003). The Osorno soil series is a young soil of deep to moderately deep profiles originating from modern volcanic ashes deposited on fluvioglacial substrates with a moderate water permeability and good drainage, silty loam texture, slightly plastic, slightly sticky with many fine and medium roots and many fine pores (CIREN, 2003). At the experimental site the soil has more than 1 m depth and high organic matter content (19%). According to the meteorological station at the site, the 33 years average rainfall for the area is 1270 mm yr−1 , the evaporation is 868 mm yr−1 , the drainage 401 mm yr−1 and the mean ambient temperature is 11.3 ◦ C (5.8–16.8 ◦ C). The sward was a 10 years old perennial ryegrass (Lolium perenne). At the start of the study and the following year, the experimental site was sprayed with Picloram and Dichrolophenoxiacetic acid (Tordon 24% SL Dow AgroSciences, and DM 6 67% SL Dow AgroSciences) in order to eliminate clover and other legumes in the sward to ensure no N input through fixation in this experiment. There were two experimental treatments, with a target application rate of 400 kg N ha−1 yr−1 as either dairy slurry (S) or urea (U) split in four even applications during the year: March, July, September and November. Additionally, a control (C) treatment with no N addition was included. The experiment was set up in a randomised block design consisting of 3 blocks with 1 replicate plot per block, each measuring area of 9 m2 . Urea fertiliser was applied by hand and dairy slurry was applied using watering cans fitted with a small splash plate, which allowed an even distribution of slurry. A baseline fertilisation with P, K and Mg but no N, was applied for all treatments. The dairy slurry was obtained directly from the slurry storage at the INIA-Remehue farm, before each application date, stored in a slurry tank and sampled for analysis. Slurry samples were collected 2 weeks prior to application, in order to determine the application rates to use according to the different N contents of manures. During application, separate samples for each replicate (3) of the different treatments were collected and analysed to determine the actual rate applied. Characteristics of the manures used in the experiment (at application) are shown in Table 1. Dry matter (DM) contents were determined by drying subsamples of the slurries at 65 ◦ C for 36 h. Inorganic N was extracted by shaking 6 g of fresh dairy slurry with 100 ml of 2 M KCl for 1 h (Keeney and Nelson, 1982). The suspension was then filtered (Whatman N◦ 5) and the filtrate stored <4 ◦ C until analysis of NH4 + –N. Soluble N (ammonium) was determined by direct distillation and titrimetric method (Gerhard model Vapodest 12) revised by Sadzawka and Carrasco (1985) and Sadzawka (1990,1985). Total N was determined using 10 g of dairy slurry by Kjeldahl digestion (Gerhardt model Vapodest 5) according to the methodology described by AOAC (1990).
F. Salazar et al. / Agriculture, Ecosystems and Environment 160 (2012) 23–28
25
400 350
Water flux (mm.)
300 250 200 150 100 50 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Oct
Nov
Dec
Month Rainfall 2008
Evaporation 2008
400 350
Water flux (mm.)
300 250 200 150 100 50 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Month Rainfall 2009
Evaporation 2009
Fig. 1. Rainfall and evaporation data for 2008 (a) and 2009 (b), from the metereological station located at INIA-Remehue Research Centre, Osorno, Chile.
The plots were cut six times each year using a plot-harvesting machine with a reciprocating cutter bar, leaving a sward height of c. 5 cm. The harvester cut a strip of 2.7 m2 each from the centre of each plot for yield assessment. The whole sample collected was weighed in the field. Sub-samples of c. 300 g were taken at each harvest for DM determinations by drying at 65 ◦ C for 36 h. Dried samples were ground in a hammer mill to pass a 1 mm sieve and sub-samples were collected in vials and stored in a dry place prior to analysis for total N by Kjeldahl (AOAC, 1990). Nitrogen uptake was calculated as the product of DM production and N concentration in harvested forage. Apparent N Recovery (ANR) was calculated considering the control plots for each rotation, where ANR =
(Ntreatment − Ncontrol ) Napplied
Lord and Shepherd (1993) as the difference between rainfall and evaporation. Leachate samples were frozen until analysis for inorganic N (N–NO3 − and N–NH4 + ). Nitrate was determined by reduction to nitrite with hydrazine, diazotisation with sulphanilamide and coupling with N-1-naphthylethylenediamide dihydrochloride, and ammonium was determined through the indophenol methodology. Analysis was carried out on automated sample analyser (SKALAR, SA 4000, Breda, The Netherlands). Total N losses were calculated as the product of drainage and N concentration in the respective samples. Total N losses for the experimental period were calculated as the sum of N losses by leaching. Analysis of variance (ANOVA) was used (Genstat 7.1) to compare nitrate and ammonium concentrations, leaching losses and overall N losses between the treatments tested. 3. Results and discussion
Leaching losses at 60 cm depth were estimated using ceramic cups (Webster et al., 1993), with three cups per plot (n = 9 per treatment) installed at an angle of 30◦ to the vertical. A mixture of soil and water was introduced around the ceramic cup and pipe to ensure a good contact between the soil and the cup, and preventing the preferential flow of water down the tube. Samples were collected every 100 mm of drainage by applying a suction of 0.7 bar to the cups. Drainage for the period was calculated according to
3.1. Rainfall, evaporation and drainage Month rainfall, evaporation and drainage data for 2008 and 2009 for the INIA-Remehue meteorological station are presented in Fig. 1. Rainfall for both years was similar to the 33-year average (1270 mm), whereas drainage was equivalent to 574 mm (2008) and 686 mm (2009), and 676 mm (7 year average). Evaporation was
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F. Salazar et al. / Agriculture, Ecosystems and Environment 160 (2012) 23–28
Table 2 Average N concentration in leachates (mg L−1 ) and N losses (kg N ha−1 ) for different treatments, 2008 and 2009 (±SEM). No differences among treatments (P > 0.05) for 2008 and 2009. Average leaching concentrations (mg L−1 ) per year
Control
Soil fertilisation treatments Dairy slurry
Urea
2008 2009
0.1 ± 0.03 0.1 ± 0.01
0.1 ± 0.04 0.2 ± 0.08
0.05 ± 0.01 0.1 ± 0.03
2008 2009
0.1 ± 0.06 0.1 ± 0.06
0.4 ± 0.17 0.5 ± 0.17
0.4 ± 0.06 0.4 ± 0.24
2008 2009
0.4 ± 0.15 0.7 ± 0.09
0.7 ± 0.19 1.3 ± 0.62
0.3 ± 0.07 1.0 ± 0.20
N–NO3 −
2008 2009
1.0 ± 0.30 0.5 ± 0.24
2.1 ± 0.61 2.9 ± 1.13
2.1 ± 0.07 2.3 ± 1.38
N–NH4 + + N–NO3 −
2008 2009
1.4 ± 0.45 1.2 ± 0.33
2.8 ± 0.80 4.2 ± 1.75
2.4 ± 0.14 3.3 ± 1.58
+
N–NO3 −
N–NH4
Total N losses (kg ha−1 ) per year N–NH4 +
c. 140 mm higher in 2008 than the 33-year average, which could explain the lower drainage observed in 2008 compared to 2009. In Osorno, Southern Chile, 84% of the total average annual rainfall occurs between March and April, and 38% of the evaporation takes place in this period. Therefore, drainage occurs mainly during these months. In this region of the country rainfall could be from 800 mm to 3000 mm per year, therefore leaching is a potentially important pathway for N losses. 3.2. Dairy slurry application Dairy slurry used in this study was typical of slurries produced in the South of Chile, which are characterised by the high contribution of clean and dirty water into the slurry tank and therefore have relatively low DM and nutrients contents, with typical values reported by Salazar et al. (2003) of 3.9% DM, 2.0 kg total N L−1 and 0.65 kg N–NH4 + L−1 (fresh weight basis). Rates of manure application expressed as total N and NH4 + –N applied per hectare for 2008 and 2009 are shown in Table 1. Despite the normal variability within the year, slurry application rates were close to the target rate. The difference observed between target and actual rate could be due in part to small variations in the N contents prior to and at application. Such variations have been noted before in studies carried out in UK involving manures (e.g. Richards et al., 1999).
period when most of the drainage was concentrated (Fig. 1), losses are still very low. For the dairy slurry treatment, this may be partly explained by the fact that only c. 35% of the applied N was present as available N, reducing the potential for direct leaching losses after application. These leaching losses are lower than those reported by Di et al. (1998) in New Zealand, who applied the same total N rate as dairy effluent, but as a single application only rather than a split dressing strategy. Further lysimeter experiments in New Zealand using dairy effluents (200 kg N ha−1 ) have shown higher leaching losses occurring in autumn compared with spring applications (Di et al., 1999), in agreement with results of our study. Di et al. (1998) in a lysimeter experiment comparing a slurry with low dry matter content (<2% DM) and inorganic fertiliser applications (400 kg total N ha−1 yr−1 ) over a ryegrass and clover mixture, found lower leaching losses with slurry (8–25 kg NO3 − –N ha−1 yr−1 ) compared with NH4 Cl (28–48 kg NO3 − –N ha−1 yr−1 ). However, it is important to take into
3.3. Nitrogen uptake and efficiency Nitrogen uptakes were equivalent to 175, 290 and 358 kg N ha−1 for 2008–2009 and 188, 369 and 505 kg N ha−1 yr−1 for 2009–2010 for control, slurry and urea, respectively. The ANR values were 18% and 28% for 2008–2009 and 31% and 47% for 2009–2010 for slurry and urea, respectively. The ANR estimated in the present study are similar to the higher values reported for spring application of dairy slurry (9–31%) by Pain et al. (1986). Higher ANR values have been reported where slurry has been injected to the soil, which reduce N losses due to NH3 volatilisation (e.g. Misselbrook et al., 1996). 4. N leaching Despite the high N rate and time of application, losses due to leaching were small (Table 2) with no significant differences between fertiliser, slurry and control treatments in either year (P > 0.05). Cumulative net N losses (i.e. after subtracting the values for the control treatment) due to N leaching were less than 1% of the applied N for slurry and urea applications for both years. Even considering that only half of the annual N was applied during the
Fig. 2. Average concentration of NO3 − –N on leachate samples for the different treatments and sampling dates of 2008 (a) and 2009 (b).
F. Salazar et al. / Agriculture, Ecosystems and Environment 160 (2012) 23–28
account that in their experiment, N was applied as one application whereas in the present study it was split in four even doses. Average concentration of NO3 − –N in leachate samples for the different treatments and sampling dates per year are show in Fig. 2. There was no clear pattern of NO3 − –N concentration in leachate, with higher values observed at the start of 2008 and the end of 2009, respectively. The average concentration values for the different sampling dates never exceeded c. 5.5 mg L−1 during the two years of evaluation, and annual mean values of NO3 − –N concentrations were below 0.5 mg L−1 for all the treatments, and far below the EC limit for drinking water of 11.3 mg L−1 (EC, 1991). Most of the leached N was in the NO3 − form (43–9%), which is similar to previous studies elsewhere (e.g. Ledgard et al., 1999). Low N losses through leaching might be explained by soil processes leading to immobilisation of the N being applied as slurry or fertiliser. Recent studies of a forest volcanic soil of Southern Chile, similar to soil use in the present study, have shown very specialised microbial and abiotic retention processes occurring in this soil, which reduces the risk of N leaching despite the high N turnover rates (Huygens et al., 2008). Studies in these ecosystems indicated very high gross NH4 + production fluxes, but also a suppression of autotrophic nitrification as a result of strong competition for available NH4 + by DNRA and NH4 + assimilating heterotrophic microorganisms or NH4 adsorption into clay layers (Huygens et al., 2007). As a result, inorganic N losses via leaching are negligible in these forest ecosystems. Such low losses for these soils are also confirmed by results from a study on a permanent grass for cutting, where N leaching losses from a very high autumn fertiliser application (400 kg ha−1 yr−1 ) were only equivalent to 8% of the applied N (Salazar et al., 2010). In this experiment N, was applied in excess just prior to the winter period, with the aim of providing a high N soil solution concentration to induce N leaching losses for experimental purposes. Average N application rate in dairy farms in Chile varies between 80 and 250 kg N ha−1 yr−1 while in beef cattle production systems this amount ranges between 30 and 120 kg N ha−1 yr−1 . The results of this study, in combination with others mentioned above, suggest that the risk of N leaching is low in volcanic soils of Southern Chile. However, gaseous losses and nutrient runoff could be important pathways depending on manure management practices, therefore a nutrient balance and crop requirements approach should be used to avoid the risk of pollution to the wider environment. A general recommendation is to adjust rates according to the expected yields of crops and grass, taking into accounts the soil nutrient levels, previous cropping and N use and manure applications (e.g. Chambers et al., 2000). 5. Conclusions Leaching losses from high rates of dairy slurry and urea application to permanent pasture on a volcanic soil were very low (<1% of applied total N) for both experimental years, in agreement with previous studies in Southern Chile using inorganic fertilisers. This resulted in relatively high values for Apparent Nitrogen Recovery by the grass sward (up to 47%). We suggest that low N leaching losses could be explained mainly by the unique N retention properties of volcanic soils in Southern Chile and/or gaseous N losses. The results of this study, in combination with others mentioned above, suggest that the risk of N leaching is low in volcanic soils of Southern Chile. Acknowledgment This research was funded by the Scientific and Technological Research Council (FONDECYT), project 1080368.
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Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee
Low nitrogen leaching losses following a high rate of dairy slurry and urea application to pasture on a volcanic soil in Southern Chile F. Salazar a,∗ , J. Martínez-Lagos a , M. Alfaro a , T. Misselbrook b a b
Agricultural Research Institute, Remehue Research Center, Box 24-0, Osorno, Chile Rothamsted Research, North Wyke, Okehampton, Devon EX20 2SB, United Kingdom
a r t i c l e
i n f o
Article history: Received 6 January 2011 Received in revised form 7 January 2012 Accepted 16 April 2012 Available online 29 May 2012 Keywords: Dairy slurry Urea Nitrogen losses Leaching Manure
a b s t r a c t Dairy slurry is an important plant nutrient source. However, mismanagement (e.g. high application rate) can lead to nutrient losses to the wider environment. There are few data on slurry management and its effect on nitrogen (N) losses specific to Southern Chile, although existing studies suggest that N leaching on volcanic Chilean soils might be expected to be low. The objective of this study was to evaluate the effect of heavy dairy slurry application on N leaching losses and compare it with an inorganic fertiliser on a volcanic soil of Southern Chile. A field experiment was carried out at the Agricultural Research Institute, Remehue Research Centre, on a volcanic soil of Southern Chile (40◦ 35 S, 73◦ 12 W) from March 2008 to March 2010. There were two N application treatments, with a target application rate of 400 kg N ha−1 yr−1 as either dairy slurry (S) or urea (U) split into four even applications over the year. Additionally, a control (C) treatment with no N addition was included. N leaching was measured using ceramic suction cups (3 per plot), with samples taken every 100 mm of drainage during the drainage season. Despite the high N rate and application time, N leaching losses were small with no significant differences between treatments in either year (P > 0.05). Concentrations of NO3 − –N for each sampling period never exceeded c. 5.5 mg L−1 and annual mean values were below 0.5 mg L−1 for all treatments. Cumulative N leaching losses were small at 1.4 and 1.2 kg ha−1 yr−1 (C), 2.8 and 4.2 kg ha−1 yr−1 (S) and 2.4 and 3.3 kg ha−1 yr−1 (U) for 2008 and 2009, respectively. We suggest that this could be explained mainly by the unique N retention properties of volcanic soils in Southern Chile and/or gaseous N losses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Dairy slurry is an important plant nutrient source on farms, supplying partial or total requirement for grass fertilisation. However, mismanagement, such as high application rate or inappropriate application time during the year, can lead to nutrient losses to the wider environment (Smith and Chambers, 1993). In dairy production systems one of the most important pathways of nitrogen (N) losses is leaching, for which greater losses have been reported from a grazed pasture than for a cut sward in New Zealand (Di and Cameron, 2002), and which may equal or exceed the range observed in arable production systems (Nissen and García, 1997; Salazar et al., 2005). Most of the pollution problems associated with the land spreading of livestock manures are due to inappropriate management practices (e.g. high application rates), applications at times of low crop demand or inadequately calibrated equipment. Losses of manure nutrients following application to the field are difficult to
∗ Corresponding author at: INIA-Remehue, Box 24-0, Osorno, Chile. Tel.: +56 64 334800. E-mail address: [email protected] (F. Salazar). 0167-8809/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2012.04.018
eliminate, but can be reduced by considering N requirements of the crops and the timing of manure application. Significant improvements can be made in these areas on most farms with proper manure storage facilities and sufficient land area on which to apply the manure (Pain, 2000). In most European countries, recommendations on manure application rates are based on the total N applied per year. For example, the Code of Good Agricultural Practice (Defra, 2009) applied in England recommends up to 250 kg N ha−1 yr−1 , although application rates are further restricted in Nitrate Vulnerable Zones according to the EC Nitrates Directive (91/676/EEC). In Chile there is no legislation to regulate slurry application on farms, and application rates can be as high as 300 m3 ha−1 yr−1 (Salazar et al., 2003). High manure application rates increase the risks of N losses through leaching, volatilisation and denitrification (e.g. Benoit, 1994; Chambers et al., 2000). In general, when comparing cattle slurry and inorganic fertiliser based on similar total N application rates, studies have shown lower N leaching losses with slurry (e.g. Di et al., 1998). This could be explained by the low input from manures of the available N forms, which can be taken up by plants or lost to the wider environment, mainly as nitrate. In recent years, pasture-based dairy production has intensified in Southern Chile, with increasing stocking rates and nutrient
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Table 1 Characterisation of dairy slurry used in the study and application rates for 2008 and 2009. Year
Date of application
Dry matter (%)a
N Kjeldahl (kg t−1 )a
N–NH4 (kg t−1 )a
Application rate (m3 ha−1 )
N applied (kg N)
2008
March 31st July 25th September 29th November 27th Average Total
4.6 4.8 4.1 4.1 4.4
1.5 1.4 1.6 1.8 1.5
0.5 0.4 0.6 0.7 0.6
80 80 60 60 70
117 108 94 108 107 427
2009
March 26th July 27th September 28th December 07th Average Total
4.7 4.8 5.2 1.7 4.9
1.8 1.9 1.2 1.3 1.6
0.7 0.7 0.3 0.4 0.5
70 50 90 65 69
127 93 110 47 94 377
a
N applied (kg NH4 + –N) 41 33 36 42 152 47 34 23 24 128
Presented data for each application date represent the mean of the 3 replicate samples.
application by purchased fertilisers and cattle slurry (Alfaro et al., 2006). Surveys on manure management have shown that farmers use a high rate of manure application (up to 300 m3 ha−1 yr−1 ) distributed in different seasons throughout the year (Salazar et al., 2003), with a potential risk for ground water pollution due to leaching during winter (Olson et al., 2009). The South of Chile has suitable soil and climatic conditions for cattle production. Consequently, 56% of the national cattle herd is concentrated in this maritime temperate climatic region, grazed on natural and improved pastures on volcanic soils. These cattle produce 80% of the country’s milk and 50% of the meat (ODEPA, 2007; Anrique, 1999). The volcanic soils are characterised by low nutrient availability, high phosphorus fixation capacity, high organic matter (OM) content, and pH-dependent cation exchange capacity (Escudey et al., 2001). Recent studies of forest volcanic soils of Southern Chile showed that they have very specialised microbial and abiotic retention processes which can reduce the risk of N leaching, despite the high N turnover rates observed (Huygens et al., 2008, 2010). The abiotic processes include dissimilatory nitrate reduction to ammonium (DNRA), which can be responsible for the consumption of more than 99% of the NO3 available in soil solution, and physical adsorption of NH4 into clay lattices (Huygens et al., 2007). The former process has been suggested as a widespread N retention mechanism in ecosystems that are N limited and receive high rainfall (Huygens et al., 2007), such as those of temperate pastures of southern Chile. In Chile there are few studies published relating to N leaching losses from grassland. Alfaro et al. (2006) reported losses from pasture grazed by beef cattle ranging from 3 to 70 kg N ha−1 yr−1 , according to the stocking rates and grazing strategies used, and ˜ et al. (2010) reported N leaching losses varying between 33 Nunez and 59 kg N ha−1 yr−1 from pastures grazed by non-lactating dairy cows. Also, nitrate leaching losses up to 67 kg N ha−1 yr−1 have been reported in a lysimeter study with dairy slurry application equivalent to 150 kg N ha−1 (Alfaro et al., 2006). Under cutting regimes, a study using the equivalent to 400 kg N ha−1 yr−1 as Sodium Nitrate applied in one dressing early in autumn showed very low N leaching losses, which were below 8% of the applied N (Salazar et al., 2010). The objective of the current study was to evaluate the effect of high rates of dairy slurry application on N leaching losses and compare this with leaching losses from an equivalent N application as an inorganic fertiliser on a volcanic soil. 2. Material and methods A field experiment was carried out from March 2008 to March 2010 at the Agricultural Research Institute, Remehue Research Center (40◦ 35 S, 73◦ 12 W) in Osorno-Chile. The soil is an Andisol
of the Osorno soil series; Typic Hapludands (CIREN, 2003). The Osorno soil series is a young soil of deep to moderately deep profiles originating from modern volcanic ashes deposited on fluvioglacial substrates with a moderate water permeability and good drainage, silty loam texture, slightly plastic, slightly sticky with many fine and medium roots and many fine pores (CIREN, 2003). At the experimental site the soil has more than 1 m depth and high organic matter content (19%). According to the meteorological station at the site, the 33 years average rainfall for the area is 1270 mm yr−1 , the evaporation is 868 mm yr−1 , the drainage 401 mm yr−1 and the mean ambient temperature is 11.3 ◦ C (5.8–16.8 ◦ C). The sward was a 10 years old perennial ryegrass (Lolium perenne). At the start of the study and the following year, the experimental site was sprayed with Picloram and Dichrolophenoxiacetic acid (Tordon 24% SL Dow AgroSciences, and DM 6 67% SL Dow AgroSciences) in order to eliminate clover and other legumes in the sward to ensure no N input through fixation in this experiment. There were two experimental treatments, with a target application rate of 400 kg N ha−1 yr−1 as either dairy slurry (S) or urea (U) split in four even applications during the year: March, July, September and November. Additionally, a control (C) treatment with no N addition was included. The experiment was set up in a randomised block design consisting of 3 blocks with 1 replicate plot per block, each measuring area of 9 m2 . Urea fertiliser was applied by hand and dairy slurry was applied using watering cans fitted with a small splash plate, which allowed an even distribution of slurry. A baseline fertilisation with P, K and Mg but no N, was applied for all treatments. The dairy slurry was obtained directly from the slurry storage at the INIA-Remehue farm, before each application date, stored in a slurry tank and sampled for analysis. Slurry samples were collected 2 weeks prior to application, in order to determine the application rates to use according to the different N contents of manures. During application, separate samples for each replicate (3) of the different treatments were collected and analysed to determine the actual rate applied. Characteristics of the manures used in the experiment (at application) are shown in Table 1. Dry matter (DM) contents were determined by drying subsamples of the slurries at 65 ◦ C for 36 h. Inorganic N was extracted by shaking 6 g of fresh dairy slurry with 100 ml of 2 M KCl for 1 h (Keeney and Nelson, 1982). The suspension was then filtered (Whatman N◦ 5) and the filtrate stored <4 ◦ C until analysis of NH4 + –N. Soluble N (ammonium) was determined by direct distillation and titrimetric method (Gerhard model Vapodest 12) revised by Sadzawka and Carrasco (1985) and Sadzawka (1990,1985). Total N was determined using 10 g of dairy slurry by Kjeldahl digestion (Gerhardt model Vapodest 5) according to the methodology described by AOAC (1990).
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25
400 350
Water flux (mm.)
300 250 200 150 100 50 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Oct
Nov
Dec
Month Rainfall 2008
Evaporation 2008
400 350
Water flux (mm.)
300 250 200 150 100 50 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Month Rainfall 2009
Evaporation 2009
Fig. 1. Rainfall and evaporation data for 2008 (a) and 2009 (b), from the metereological station located at INIA-Remehue Research Centre, Osorno, Chile.
The plots were cut six times each year using a plot-harvesting machine with a reciprocating cutter bar, leaving a sward height of c. 5 cm. The harvester cut a strip of 2.7 m2 each from the centre of each plot for yield assessment. The whole sample collected was weighed in the field. Sub-samples of c. 300 g were taken at each harvest for DM determinations by drying at 65 ◦ C for 36 h. Dried samples were ground in a hammer mill to pass a 1 mm sieve and sub-samples were collected in vials and stored in a dry place prior to analysis for total N by Kjeldahl (AOAC, 1990). Nitrogen uptake was calculated as the product of DM production and N concentration in harvested forage. Apparent N Recovery (ANR) was calculated considering the control plots for each rotation, where ANR =
(Ntreatment − Ncontrol ) Napplied
Lord and Shepherd (1993) as the difference between rainfall and evaporation. Leachate samples were frozen until analysis for inorganic N (N–NO3 − and N–NH4 + ). Nitrate was determined by reduction to nitrite with hydrazine, diazotisation with sulphanilamide and coupling with N-1-naphthylethylenediamide dihydrochloride, and ammonium was determined through the indophenol methodology. Analysis was carried out on automated sample analyser (SKALAR, SA 4000, Breda, The Netherlands). Total N losses were calculated as the product of drainage and N concentration in the respective samples. Total N losses for the experimental period were calculated as the sum of N losses by leaching. Analysis of variance (ANOVA) was used (Genstat 7.1) to compare nitrate and ammonium concentrations, leaching losses and overall N losses between the treatments tested. 3. Results and discussion
Leaching losses at 60 cm depth were estimated using ceramic cups (Webster et al., 1993), with three cups per plot (n = 9 per treatment) installed at an angle of 30◦ to the vertical. A mixture of soil and water was introduced around the ceramic cup and pipe to ensure a good contact between the soil and the cup, and preventing the preferential flow of water down the tube. Samples were collected every 100 mm of drainage by applying a suction of 0.7 bar to the cups. Drainage for the period was calculated according to
3.1. Rainfall, evaporation and drainage Month rainfall, evaporation and drainage data for 2008 and 2009 for the INIA-Remehue meteorological station are presented in Fig. 1. Rainfall for both years was similar to the 33-year average (1270 mm), whereas drainage was equivalent to 574 mm (2008) and 686 mm (2009), and 676 mm (7 year average). Evaporation was
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Table 2 Average N concentration in leachates (mg L−1 ) and N losses (kg N ha−1 ) for different treatments, 2008 and 2009 (±SEM). No differences among treatments (P > 0.05) for 2008 and 2009. Average leaching concentrations (mg L−1 ) per year
Control
Soil fertilisation treatments Dairy slurry
Urea
2008 2009
0.1 ± 0.03 0.1 ± 0.01
0.1 ± 0.04 0.2 ± 0.08
0.05 ± 0.01 0.1 ± 0.03
2008 2009
0.1 ± 0.06 0.1 ± 0.06
0.4 ± 0.17 0.5 ± 0.17
0.4 ± 0.06 0.4 ± 0.24
2008 2009
0.4 ± 0.15 0.7 ± 0.09
0.7 ± 0.19 1.3 ± 0.62
0.3 ± 0.07 1.0 ± 0.20
N–NO3 −
2008 2009
1.0 ± 0.30 0.5 ± 0.24
2.1 ± 0.61 2.9 ± 1.13
2.1 ± 0.07 2.3 ± 1.38
N–NH4 + + N–NO3 −
2008 2009
1.4 ± 0.45 1.2 ± 0.33
2.8 ± 0.80 4.2 ± 1.75
2.4 ± 0.14 3.3 ± 1.58
+
N–NO3 −
N–NH4
Total N losses (kg ha−1 ) per year N–NH4 +
c. 140 mm higher in 2008 than the 33-year average, which could explain the lower drainage observed in 2008 compared to 2009. In Osorno, Southern Chile, 84% of the total average annual rainfall occurs between March and April, and 38% of the evaporation takes place in this period. Therefore, drainage occurs mainly during these months. In this region of the country rainfall could be from 800 mm to 3000 mm per year, therefore leaching is a potentially important pathway for N losses. 3.2. Dairy slurry application Dairy slurry used in this study was typical of slurries produced in the South of Chile, which are characterised by the high contribution of clean and dirty water into the slurry tank and therefore have relatively low DM and nutrients contents, with typical values reported by Salazar et al. (2003) of 3.9% DM, 2.0 kg total N L−1 and 0.65 kg N–NH4 + L−1 (fresh weight basis). Rates of manure application expressed as total N and NH4 + –N applied per hectare for 2008 and 2009 are shown in Table 1. Despite the normal variability within the year, slurry application rates were close to the target rate. The difference observed between target and actual rate could be due in part to small variations in the N contents prior to and at application. Such variations have been noted before in studies carried out in UK involving manures (e.g. Richards et al., 1999).
period when most of the drainage was concentrated (Fig. 1), losses are still very low. For the dairy slurry treatment, this may be partly explained by the fact that only c. 35% of the applied N was present as available N, reducing the potential for direct leaching losses after application. These leaching losses are lower than those reported by Di et al. (1998) in New Zealand, who applied the same total N rate as dairy effluent, but as a single application only rather than a split dressing strategy. Further lysimeter experiments in New Zealand using dairy effluents (200 kg N ha−1 ) have shown higher leaching losses occurring in autumn compared with spring applications (Di et al., 1999), in agreement with results of our study. Di et al. (1998) in a lysimeter experiment comparing a slurry with low dry matter content (<2% DM) and inorganic fertiliser applications (400 kg total N ha−1 yr−1 ) over a ryegrass and clover mixture, found lower leaching losses with slurry (8–25 kg NO3 − –N ha−1 yr−1 ) compared with NH4 Cl (28–48 kg NO3 − –N ha−1 yr−1 ). However, it is important to take into
3.3. Nitrogen uptake and efficiency Nitrogen uptakes were equivalent to 175, 290 and 358 kg N ha−1 for 2008–2009 and 188, 369 and 505 kg N ha−1 yr−1 for 2009–2010 for control, slurry and urea, respectively. The ANR values were 18% and 28% for 2008–2009 and 31% and 47% for 2009–2010 for slurry and urea, respectively. The ANR estimated in the present study are similar to the higher values reported for spring application of dairy slurry (9–31%) by Pain et al. (1986). Higher ANR values have been reported where slurry has been injected to the soil, which reduce N losses due to NH3 volatilisation (e.g. Misselbrook et al., 1996). 4. N leaching Despite the high N rate and time of application, losses due to leaching were small (Table 2) with no significant differences between fertiliser, slurry and control treatments in either year (P > 0.05). Cumulative net N losses (i.e. after subtracting the values for the control treatment) due to N leaching were less than 1% of the applied N for slurry and urea applications for both years. Even considering that only half of the annual N was applied during the
Fig. 2. Average concentration of NO3 − –N on leachate samples for the different treatments and sampling dates of 2008 (a) and 2009 (b).
F. Salazar et al. / Agriculture, Ecosystems and Environment 160 (2012) 23–28
account that in their experiment, N was applied as one application whereas in the present study it was split in four even doses. Average concentration of NO3 − –N in leachate samples for the different treatments and sampling dates per year are show in Fig. 2. There was no clear pattern of NO3 − –N concentration in leachate, with higher values observed at the start of 2008 and the end of 2009, respectively. The average concentration values for the different sampling dates never exceeded c. 5.5 mg L−1 during the two years of evaluation, and annual mean values of NO3 − –N concentrations were below 0.5 mg L−1 for all the treatments, and far below the EC limit for drinking water of 11.3 mg L−1 (EC, 1991). Most of the leached N was in the NO3 − form (43–9%), which is similar to previous studies elsewhere (e.g. Ledgard et al., 1999). Low N losses through leaching might be explained by soil processes leading to immobilisation of the N being applied as slurry or fertiliser. Recent studies of a forest volcanic soil of Southern Chile, similar to soil use in the present study, have shown very specialised microbial and abiotic retention processes occurring in this soil, which reduces the risk of N leaching despite the high N turnover rates (Huygens et al., 2008). Studies in these ecosystems indicated very high gross NH4 + production fluxes, but also a suppression of autotrophic nitrification as a result of strong competition for available NH4 + by DNRA and NH4 + assimilating heterotrophic microorganisms or NH4 adsorption into clay layers (Huygens et al., 2007). As a result, inorganic N losses via leaching are negligible in these forest ecosystems. Such low losses for these soils are also confirmed by results from a study on a permanent grass for cutting, where N leaching losses from a very high autumn fertiliser application (400 kg ha−1 yr−1 ) were only equivalent to 8% of the applied N (Salazar et al., 2010). In this experiment N, was applied in excess just prior to the winter period, with the aim of providing a high N soil solution concentration to induce N leaching losses for experimental purposes. Average N application rate in dairy farms in Chile varies between 80 and 250 kg N ha−1 yr−1 while in beef cattle production systems this amount ranges between 30 and 120 kg N ha−1 yr−1 . The results of this study, in combination with others mentioned above, suggest that the risk of N leaching is low in volcanic soils of Southern Chile. However, gaseous losses and nutrient runoff could be important pathways depending on manure management practices, therefore a nutrient balance and crop requirements approach should be used to avoid the risk of pollution to the wider environment. A general recommendation is to adjust rates according to the expected yields of crops and grass, taking into accounts the soil nutrient levels, previous cropping and N use and manure applications (e.g. Chambers et al., 2000). 5. Conclusions Leaching losses from high rates of dairy slurry and urea application to permanent pasture on a volcanic soil were very low (<1% of applied total N) for both experimental years, in agreement with previous studies in Southern Chile using inorganic fertilisers. This resulted in relatively high values for Apparent Nitrogen Recovery by the grass sward (up to 47%). We suggest that low N leaching losses could be explained mainly by the unique N retention properties of volcanic soils in Southern Chile and/or gaseous N losses. The results of this study, in combination with others mentioned above, suggest that the risk of N leaching is low in volcanic soils of Southern Chile. Acknowledgment This research was funded by the Scientific and Technological Research Council (FONDECYT), project 1080368.
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