reducing nitrate losses from simulated grazing on ...

Samuel J. Dennis (Corresponding author; e-mail: samuel.dennis@agre search.co.nz), Keith C. Cameron, Hong J. Di and Jim L. Moir, Centre for Soil & Environmental Research, Lincoln University, Canterbury, New Zealand; Vincent Staples, Pat Sills and Karl G. Richards, Environment Research Centre, Teagasc, Johnstown Castle, Co., Wexford, Ireland. Cite as follows: Dennis, S.J., Cameron, K.C., Di, H.J., Moir, J.L., Staples, V., Sills, P. and Richards, K.G. 2012 Reducing nitrate losses from simulated grazing on grassland lysimeters in Ireland using a nitrification inhibitor (dicyandiamide). Biology and Environment: Proceedings of the Royal Irish Academy 112B. DOI: 10.3318/ BIOE.2011.24.

Received 18 March 2011. Accepted 24 May 2011. Published 22 March 2012.

REDUCING NITRATE LOSSES FROM SIMULATED GRAZING ON GRASSLAND LYSIMETERS IN IRELAND USING A NITRIFICATION INHIBITOR (DICYANDIAMIDE) Samuel J. Dennis, Keith C. Cameron, Hong J. Di, Jim L. Moir, Vincent Staples, Pat Sills and Karl G. Richards ABSTRACT Nitrate (NO 3 ) pollution of water is a serious environmental problem, as NO3 can contribute to the eutrophication of surface waters, and high levels may cause methaemoglobinaemia in formula-fed infants. Grassland agriculture is a major source of diffuse NO 3 pollution, with much of this NO3 originating from urine deposited by grazing animals. The research objective was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in reducing NO 3 leaching under Irish dairy farming conditions. Urine was applied in autumn to undisturbed monolith lysimeters to replicate an average cattle urination (2l of 8.6g N l 1 urine), or 344kg N ha1 equivalent. Nitrogen (N) fertiliser was applied at 141kg ha1 and 291kg ha 1. DCD was applied in autumn and spring. The total annual NO 3 N losses from urine patches on three soils ranged from 16kg to 1. Peak concentrations on the non-urine treatments did not exceed 6.1mg N ha 204kg NO 3 1 1 , but reached 17.1148.6mg NO when urine was applied. DCD reduced NO 3 N l 3 N l the total NO3 N losses from urine treatments on the lighter soils by 38%42%, and reduced peak NO 3 N concentrations by over 50%. This trial has shown that DCD has the potential to significantly reduce NO 3 leaching losses from grazed grassland in Ireland.

INTRODUCTION Nitrate (NO 3 ) pollution of water is being increasingly recognised as a serious environmental problem around the world. Nitrate contributes to the eutrophication of surface waters and marine environments (Stark and Richards 2008). There have been conflicting reports on the effect of nitrate in drinking water. Traditionally, high levels of nitrate in drinking water have been associated with methaemoglobinaemia in formula-fed infants (World Health Organization 2006) and a range of other medical conditions such as non-Hodgkins lymphoma and Parkinson’s disease (Ward et al. 1996). More recent research has shown that under acidic conditions, in the stomach, nitrous acid (HNO2) and nitric oxide (NO) can be formed. These two products have strong antimicrobial properties that help control air tract inflammations (L’Hirondel and L’Hirondel 2002), viral infections (Colosanti et al. 1999) and fungal infections (Addiscott and Benjamin 2004). Although there is dispute in relation to the health effects of nitrate in drinking water, it is necessary to reduce nitrate

DOI: 10.3318/BIOE.2011.24. BIOLOGY AND ENVIRONMENT: PROCEEDINGS

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loss in water to reduce eutrophication of sensitive water bodies (Stark and Richards 2008) and, potentially, to reduce indirect NO emissions as well (Reay et al. 2009). Grassland agriculture is a major source of nitrate entering into ground and surface waters. Urine patches deposited by grazing animals apply a high rate of nitrogen (up to 1000kg N ha1) at one point in time to a small area of soil (Haynes and Williams 1993). This nitrogen is mainly in the form of urea, which under warm aerobic conditions is rapidly mineralised to ammonium (NH 4 ) and nitrified to form nitrate (NO 3 ): As an anion, NO3 is not strongly held in the soil and leaches readily from the soil profile. European farmers are having to deal with increasing levels of environmental regulation as a result of European Union legislation, such as the Nitrates and Water Framework Directives. These regulations have added considerably to the measures that farmers must adhere to improve water quality (Richards et al. 2009). There are limited data available for quantifying nitrate loss from grazed

ROYAL IRISH ACADEMY, VOL. 112B (2012).

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ROYAL IRISH ACADEMY

1

BIOLOGY

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grassland systems in Ireland. In a four-year soil solution sampling study, Ryan et al. (2006) concluded that dirty water irrigation and grazed-only pastures had significantly higher nitrate leaching than silage systems. Most published data to date on nitrate losses from grassland in Ireland have involved soil sampling (Humphreys et al. 2008), soil solution sampling with suction cups (Ryan et al. 2006) or groundwater sampling (Fenton et al. 2009). These methods do not allow direct measurements of nitrate losses but only measure nitrate concentrations at a particular point in time. Lysimeters allow direct measurement of both drainage volumes and nutrient losses, and offered an improved method for quantifying nitrate leaching losses for this study. Dicyandiamide (DCD) inhibits nitrification by soil bacteria (Di et al. 2009), and has been shown to reduce NO 3 losses from autumn-deposited simulated urine patches in New Zealand by 45%83% (Di and Cameron 2002; 2004b; 2005; 2007; Menneer et al. 2008; Singh et al. 2009; Sprosen et al. 2009), and from grazed grassland and forage crops (Monaghan et al. 2009; Smith et al. 2008). At the same time, it has been shown to reduce N2O emissions (Di and Cameron 2003; 2006; 2008; Di et al. 2007; Smith et al. 2008; Singh et al. 2009; Sprosen et al. 2009), reduce the leaching of nutrient cations (Di and Cameron 2004a; 2005) and increase pasture production by as much as 33% (Di and Cameron 2002; 2004b; 2007; Smith et al. 2005; Moir et al. 2007; Sprosen et al. 2009). However, the aforementioned research has been conducted only in New Zealand and it is unclear whether these results are applicable to different soil and climatic conditions of Irish farmland. Although DCD has been shown to reduce N2O losses from ungrazed grassland in the UK (Pain et al. 1994; McTaggart et al. 1997; Dobbie and Smith 2003), and some of the New Zealand results are from Southland (which is similar climatically to Ireland), there is a need to determine whether DCD can reduce NO 3 losses from grazed grassland under the high drainage conditions of Ireland. This experiment was designed firstly to measure the actual losses of NO 3 under simulated dairy grazing in Irish climatic conditions and secondly to determine the effectiveness of DCD in reducing NO 3 losses from grazed grassland in Ireland.

MATERIALS AND METHODS A field lysimeter facility was established in 2003 to provide directly measured data on nitrate losses from Irish pasture. Seventy-two undisturbed perennial ryegrass (variety Gilford) monolith lysimeters (0.8m diameter, 1m deep) were collected following 2

ENVIRONMENT the method of Cameron et al. (1992), representing three soil classes used for dairy farming in Ireland: Clonakilty (well drained, WRB: Haplic Podzol (Anthric) (IUSS Working Group WRB 2006)), Elton (moderately drained, WRB: Cutanic Luvisol (Siltic)) and Rathangan (poorly drained, WRB: Luvic Stagnosol (Eutric, Siltic)). Selected soil properties were determined using standard methods (Byrne 1979) and are presented in Table 1. The lysimeters were transported to the Teagasc Johnstown Castle Research Centre in County Wexford and installed in a randomised complete block design (seven treatments, three soils and three blocks). A 25mm thick layer of soil was removed from the base of each core and replaced with gravel. Cores were gravity drained, with leachate piped from the lysimeter base to 20l low density polyethylene (LDPE) containers. Treatments are outlined in Table 2. Urine was collected from dairy cows and standardised by the addition of urea to 8.6g N l1 (literature average from Doak 1952; Whitehead 1970; Safley et al. 1984; Betteridge et al. 1986; Bristow et al. 1992; Stout et al. 1997; Whitehead 2000; Bohane 2003; Misselbrook et al. 2005; Olsson 2005). Two litres of urine (literature average from Doak 1952; Davies et al. 1962; Whitehead 1970; Robertson 1972; Nguyen and Goh 1994) were applied to the centre of each lysimeter using a measuring cylinder, simulating a cattle urination, on 8 November 2007. Assuming the urine spread to cover an 0.33m2 area (literature average from Doak 1952; Williams et al. 1990; Nguyen and Goh 1994; Williams and Haynes 1994), the leaching loss from these lysimeters represents that from an 0.5m2 area of soil containing an 0.33m2, 521kg N ha1 urine patch. The mean application rate over the entire lysimeter surface was 344kg N ha 1. Dicyandiamide (DCD) was applied at 10kg ha 1, in solution, to replicate previous work in New Zealand (Di and Cameron 2007). Fifty millilitres of solution were applied to the surface of each lysimeter using a fine mist spray bottle, close to the ground surface to minimise the potential for spray drift. DCD was applied once immediately following urine application, and again on 11 March 2008, resulting in a total application of 20kg DCD ha1 year1, in line with the recommended commercial use in New Zealand (Di and Cameron 2007). Fertiliser was applied at two rates: 141kg N ha1 year 1 and 291kg N ha1 year 1 (Table 2), as five (141) or seven (291) separate applications throughout the year. Urea was the form of fertiliser applied in the first two applications, with calcium ammonium nitrate (CAN) being the form that was applied for the remainder of the year, to simulate normal recommended Irish fertilisation practice.

*

Selected soil properties for lysimeter soils, analysed using standard methods (Byrne 1979). Depth (cm)

Sand (%)

Silt (%)

Clay (%)

Total C (%)

Organic C (%)

Total N (%)

C/N (ratio)

P (mg l1)

K (mg l1)

Clonakilty

A1 A2 B C

030 3050 5060 60

46.0 40.7 42.8 46.5

25.4 37.8 43.2 37.3

12.3 11.8 7.5 5.1

2.4 1.4 0.7 0.2

2.3 1.3 0.7 0.2

0.2 0.1 0.1 0.0

10.5 13.6 13.8 9.9

2.2 0.3 0.3 0.8

25.7 11.5 11.0 11.0

Elton

A1 A2 B C

020 2040 4060 60

39.9 43.5 39.2 25.2

27.6 23.9 26.8 21.8

19.7 24.1 26.6 17.1

4.0 1.3 0.9 2.8

3.8 1.2 0.9 0.5

0.4 0.1 0.1 0.0

10.1 8.7 8.7 102.7

2.3 0.6 0.8 0.4

57.5 22.0 13.5 12.0

Rathangan

A B C

020 2040 40

25.2 28.7 33.4

35.1 26.3 34.9

25.8 37.8 23.7

3.5 0.6 0.2

3.5 0.5 0.1

0.3 0.1 0.0

11.7 8.9 5.4

3.2 0.1 0.2

25.0 23.0 16.7

NITRATE LOSSES FROM SIMULATED GRAZING

Soil (Horizon)

Site

REDUCING

Table 1

3

BIOLOGY Table 2

*

ENVIRONMENT

Details of fertiliser, urine and DCD rates used in the treatment structure.

Treatment Control Low fertiliser (Fert low) High fertiliser (Fert high) Urine plus low fertiliser (Urine FL) Urine plus high fertiliser (Urine FH) Urine, low fertiliser plus DCD (U FL DCD) Urine, high fertiliser plus DCD (U FH DCD) a

AND

Fertiliser (kg N ha1 year1)

Urine (kg N ha 1 year1)

141 291 141

344

291

344

141

344

20

15.2a

291

344

20

15.2a

DCD rate (kg DCD ha1 year 1)

DCD (kg N ha1 year 1)

DCD is 76% N and the annual application rate of 20kg DCD ha 1 year1 equates to 15.2kg N ha 1.

Leachate was sampled after approximately every 20mm of drainage for a twelve-month period, and leachate NO 3 N and chloride were determined using standard methods (Askew and Smith 2005a; 2005b) within 48 hours of sampling. Herbage was cut on a 30-day rotation, simulating grazing over a nine-month grazing season; dry matter (DM) and nitrogen content were determined using standard methods (Byrne 1979). Data were statistically analysed using ANOVA and orthogonal contrasts in R (R Development Core Team 2008). The NO 3 N to Cl ratio was used as an indicator of denitrification (Gambrell et al. 1975). Both N and Clare present in large quantities in urine. The Clanion is presumed to be transported similarly to NO 3 in soil and primarily lost via leaching. Nitrogen can be leached but also removed by biological processes, such as denitrification, that do not affect Cl . If denitrification is occurring in a soil, the concentration of Cl in drainage water will not be affected, but NO 3 will reduce, lowering the ratio of NO 3 N to Cl . This does not give a direct measure of the quantity of nitrate removed by denitrification, as nitrogen can be removed from the soil by a number of mechanisms, but it is used here to give an indication of the relative difference in denitrification between soil types.

RESULTS LEACHATE

The total rainfall in the twelve months following urine application was 1233mm. The total potential evapotranspiration [calculated using the simplified 4

Penman equation of Valiantzas (2006), equation 38)] was 524mm. The NO 3 N concentration versus cumulative drainage (mm) for the Elton soil is illustrated in Fig. 1, and a similar breakthrough curve was observed for the Clonakilty soil. Peak NO 3 N concentrations were recorded at 250300mm of drainage and concentrations had returned to background levels by around 500mm of drainage. The mean total drainage from the Clonakilty, Elton and Rathangan soils was 677mm, 622mm and 374mm, respectively. The peak concentrations attained by each treatment are shown in Table 3. The peak concentration from the Clonakilty and Elton soils was higher than the Rathangan (PB0.001), but there was no difference between the Clonakilty and Elton soils (P 0.05). There was a significant soil by treatment interaction (P B0.05), with the highest peak concentration occurring from the urine plus low fertiliser (urine FL) treatment on the Elton soil. Multiple applications of fertiliser alone (i.e. no urine) caused no change in peak N concentration from that in the control on any soil (P0.05), but urine application increased peak concentrations on all three soils (PB0.001). The effect of fertiliser was inconsistent, with peak NO 3 N concentration from the urine plus high fertiliser (urine FH) treatment being higher than that from the urine FL treatment on the Clonakilty soil (P B0.001), but lower on the Elton (P B0.01). The application of DCD reduced the mean peak NO 3 N concentration from urine by 50% and 52% on the Clonakilty and Elton soils, respectively (P B0.001), but had no significant effect on the Rathangan (P 0.05). Table 4 presents the mean annual NO 3 N concentrations in the leachate from each soil. Mean

REDUCING 180


A

150 Control Fert Low Urine FL U FL DCD

−

Nitrate concentration in drainage (mg NO3 −N L−1)

120 90 60 30 0 180

B

150 Control Fert High Urine FH U FH DCD

120 90 60 30 0 0

100

200 300 400 500 Drainage (mm)

600

*

Fig. 1 Nitrate concentration versus drainage for the Elton soil (91 SEM): (A) low fertiliser and (B) high fertiliser.

however, the apparent reductions on the Clonakilty and Rathangan were not significant (P 0.05). There was no difference between total NO 3 N losses from the Clonakilty and Elton soils (Fig. 2), but these two soils had higher NO 3 N losses than the Rathangan soil (PB 0.001). There was a significant soil by treatment interaction (P B0.05). There was no difference in total NO 3 N loss between the control and fertiliser only treatments on any soil (P0.05), but NO 3 N loss increased from that in the non-urine treatments (Control, Fert Low and Fert High) when urine was applied to any soil (P B0.001). The effect of fertiliser was again inconsistent, as there were higher NO 3 N losses from Urine FH than Urine FL on the Clonakilty soil (P B0.001), but the opposite effect occurred on the Elton soil (PB 0.01). DCD significantly reduced total N losses by 42% and 38% on the Clonakilty and Elton soils, respectively (P B0.001), but had no significant effect on the Rathangan (P0.05). The mean annual NO 3 N to Cl ratio in leachate was 0.73, 0.81 and 0.20 for the Clonakilty, Elton and Rathangan soils, respectively. There was no difference between the Clonakilty and Elton, but the ratio from the heavier Rathangan soil was lower than that from the lighter soils (PB0.001).

HERBAGE

concentrations were lower on the Rathangan soil than the Clonakilty and Elton (P B0.01), which had no difference in mean concentrations between them (P 0.05). Leachate NO 3 N concentrations from the control and fertiliser only treatments were all below the EU maximum admissible concentration (MAC) 1 of 11.3mg NO (Table 4), with mean 3 N l concentrations increasing with the application of urine on each soil (P B0.001) to above the MAC in every case except on the Rathangan with high fertiliser. DCD reduced mean NO 3 N concentrations on the Elton soil by 46% (PB0.001); Table 3

*

Total DM yield ranged from 2.46 tonnes ha 1 (Rathangan, Control) to 10.81 tonnes ha 1 (Elton, Urine FH, Fig. 3). Total yield from the Rathangan soil was lower than that from the lighter soils (PB 0.001), and yield from the Elton soil was higher than that from the Clonakilty soil (PB0.05). Dry matter (DM) yield from urine treatments was higher than that from the control or fertiliser alone treatments (PB0.001). Yield increased from the control with the addition of fertiliser (PB 0.001), and the high fertiliser treatment produced more herbage than the low fertiliser treatment whether no urine (P B0.05), urine (P B0.001) or

1 Peak nitrate N concentration in the leachate (mg NO ): Parenthetical values 3 N l are identified as SEM value in Tables 3 5.

Treatment Control Fert low Fert high Urine FL Urine FH U FL DCD U FH DCD

Clonakilty (SEM) 1.4 1.9 2.8 92.8 144.2 57.0 62.5

(1.4) (1.6) (2.3) (43.6) (2.9) (2.7) (6.3)

Elton (SEM) 6.1 0.6 2.9 148.6 142.6 61.0 78.1

(6.0) (0.6) (2.6) (18.8) (2.2) (9.6) (28.1)

Rathangan (SEM) 0.7 1.0 1.7 59.9 17.1 3.5 3.6

(0.6) (0.9) (0.9) (49.4) (10.1) (2.1) (1.6) 5

BIOLOGY Table 4

*

AND

ENVIRONMENT

1 Mean annual nitrate N concentration in the leachate (mg NO ): Parenthetical 3 N l values are identified as SEM value in Tables 3 5.

Treatment

Clonakilty (SEM)

Control Fert low Fert high Urine FL Urine FH U FL DCD U FH DCD

0.2 0.6 0.5 13.2 28.1 12.4 13.0

Elton (SEM)

(0.2) (0.6) (0.4) (8.1) (1.0) (2.3) (1.8)

urine and DCD (PB0.05) were applied. There was a 1.3% increase in mean DM production across all three soils with DCD at the high fertiliser rate only (PB0.001). When each soil was considered separately, there was a 35% increase in herbage production with DCD at the low fertiliser rate (Urine FL and U FL DCD treatments) only on the Clonakilty soil (PB0.05). On the Elton soil, there was a decrease in herbage production with DCD at the high fertiliser rate only (Urine FH and U FH DCD treatments, PB0.01). DCD had no effect on herbage production from the Rathangan soil. Across all soils there was an increase in mean herbage N with the application of urine and an increase from the control with the application of fertiliser (P B0.001; Table 5), while the N content on the high fertiliser treatment was higher than the low both with and without the application of urine and DCD (P B0.01). Across all soils, there was an overall increase in mean herbage N with the application of DCD at the low fertiliser rate (Urine FL and U FL DCD treatments, PB0.05), but not at the high fertiliser rate (Urine FH and U FH DCD treatments, P0.05). When the soils were analysed individually, this increase at the low

1.7 0.1 0.4 28.1 27.0 12.9 17.0

(1.4) (0.1) (0.3) (1.5) (3.8) (0.8) (2.0)

0.2 0.1 0.2 14.0 5.4 1.7 1.9

(0.1) (0.1) (0.1) (10.3) (0.9) (1.0) (0.7)

fertiliser rate was only significant on the Clonakilty soil (P B0.01). The total N uptake by pasture (Fig. 4) ranged from 74kg N ha1 (Control, Rathangan) to 388kg N ha 1 (Urine FH, Elton) and, generally, followed a similar pattern for DM production (Fig. 3). Total N uptake was lowest from the Rathangan soil and highest from the Elton (PB0.001). Nitrogen uptake was lowest in the Control and increased with the application of fertiliser, with higher N uptake at the high fertiliser rate (P B 0.001). Nitrogen uptake with urine was higher than that from the control and fertiliser only treatments and was again higher at the high fertiliser rate whether with or without DCD (P B0.01). When averaged across all soils, DCD increased total N uptake at both the low (PB0.05) and high (P B0.001) fertiliser levels. When each soil was considered separately, DCD increased N uptake at the low fertiliser level on the Clonakilty soil (P B 0.01). There was an overall increase in N uptake across the two fertiliser levels on the Elton soil, which was nearly significant (P 0.0503). No 12

240 Control Fert Low Fert High Urine FL Urine FH U FL DCD U FH DCD

−

180

120

60

Control Fert Low Fert High Urine FL Urine FH U FL DCD U FH DCD

10 Herbage yield (t DM ha−1)

Nitrate loss (kg NO3 −N ha−1)

Rathangan (SEM)

8

6

4

2

0

*

Fig. 2

6

0 Clonakilty

Elton

Rathangan

Cumulative nitrate leaching losses (91 SEM).

Clonakilty

*

Fig. 3

Elton

Total annual DM yield (91 SEM).

Rathangan

REDUCING Table 5

*


Mean herbage dry matter N concentration (percent). Parenthetical values are identified as SEM value in Tables 3 5.

Treatment

Clonakilty (SEM)

Control Fert low Fert high Urine FL Urine FH U FL DCD U FH DCD

2.79 3.19 3.64 2.99 3.23 3.31 3.38

(0.10) (0.17) (0.03) (0.08) (0.09) (0.11) (0.09)

effect of DCD on N uptake was observed on the Rathangan soil.

DISCUSSION LEACHATE

Although the 1233mm total precipitation was comparable to that in previous work on irrigated dairy pasture in New Zealand (e.g. Di and Cameron 2002; 2004b), total drainage was approximately double that observed in New Zealand. This was primarily due to Ireland’s relatively low evapotranspiration rate (Schulte et al. 2006) compared to New Zealand. Peak nitrate concentration was observed at 250300mm drainage, or just under one pore volume (370mm for the Rathangan and Elton soils, see Kramers et al. (2012)). This is comparable to the peaks at around 250mm observed in New Zealand (Di and Cameron 2004b; 2005). This would suggest that although the total annual drainage is different to that in New Zealand, the NO 3 leaching mechanisms through the soils are similar

Herbage nitrogen (kg N ha−1)

450 Control Fert Low Fert High Urine FL Urine FH U FL DCD U FH DCD

360

270

180

90

0

*

Fig. 4

Clonakilty

Elton

Total N in herbage (91 SEM).

Rathangan

Elton (SEM) 2.86 3.21 3.86 3.19 3.65 3.39 3.57

(0.16) (0.15) (0.06) (0.01) (0.11) (0.17) (0.10)

Rathangan (SEM) 2.87 2.95 3.74 3.08 3.61 3.30 3.96

(0.32) (0.11) (0.06) (0.02) (0.07) (0.08) (0.08)

and that it is reasonable to compare these results directly with those obtained in New Zealand. With a 344kg N ha1 urine application, 114 1 204kg NO was leached from the 3 N ha Clonakilty and Elton soils, which is considerably 1 higher than the 60kg NO recorded by 3 N ha Di and Cameron (2007) with 300kg urine N ha 1, or the 40kg total N loss observed by Fraser et al. (1994) with 500kg urine N ha1. The higher N losses in this experiment may have been due in part to the seasonal drainage pattern. Because the total drainage volume was higher than that in New Zealand, the peak nitrogen concentration occurred sooner (on a temporal basis) after the application of urine, that is, in the middle of winter. The peak concentration occurred in January for all urine treatments, which is the middle of winter. Drainage, however, continued for several months after this date. Most NO 3 was, therefore, lost from the soil before pasture growth rates increased in spring. In contrast, the peak NO 3 concentration in Di and Cameron (2004b) occurred in the latter half of the drainage period (i.e. spring). It is, therefore, likely that in the Di and Cameron (2004b) study more nitrogen was able to be taken up by spring pasture before being leached from the soil, and that this may help explain the lower leaching losses reported in these New Zealand studies. The total NO 3 N loss from the heavy 1 Rathangan soil was 1683kg NO 3 N ha 1 with 344kg urine N ha , lower than that from the lighter soils and comparable to the losses in the New Zealand trials quoted earlier. The lower losses on this soil may be in part due to a higher level of denitrification, as indicated by the low NO 3 N to Cl ratio in leachate from this soil (Gambrell et al. 1975), and the low ratios in groundwater under a similar soil type recorded by Fenton et al. (2009). The lower losses may also be related to the lower drainage volume from this soil, while slow infiltration of urine and urea on this heavy soil could also have enhanced ammonia losses. 7

BIOLOGY

AND

The drainage results from the lighter soils (i.e. the Clonakilty and Elton soils) are reasonably consistent with the measured rainfall and calculated evapotranspiration rates; however, the total drainage from the Rathangan soil was 250300mm lower than that from these soils. This could be due in part to slower infiltration and greater water storage in this heavy soil, which would have maintained moist conditions and occasional ponding on the soil surface, allowing more evaporation of water than that occurred from the lighter soils. However, the total evaporation expected from open water at this site (Valiantzas 2006, equation 31), representing the maximum evaporative loss was water ponding on the surface all year, was 635mm, or 111mm higher than the predicted evapotranspiration. Ponding may, therefore, account for up to 100mm of additional evaporation but is unlikely to account for the entire difference in losses. Overflow from these lysimeters is considered unlikely as it was never observed during the experiment, but cannot be entirely discounted. Some moisture may also have been carried over to the following drainage season. However, as the majority of the results from the Rathangan soil were not significant, this discrepancy does not affect the conclusions. Dicyandiamide (DCD) reduced the total NO 3 loss from the 344kg urine N ha 1 treatments by 38%42% on the lighter soils. This reduction in loss was not as large as has been total NO 3 observed in New Zealand, where reductions of up to 83% have been observed with 300kg urine N ha 1 (Di and Cameron 2007), and 45%76% with higher rates of urine (Di and Cameron 2002; 2004b; 2005; 2007; Menneer et al. 2008). Nevertheless, it is important to recognise that an approximately 40% reduction in NO 3 leaching loss shows DCD to be a promising tool to mitigate leaching losses from temperate European grassland soils. Peak nitrate concentrations occurred in January, long before the second DCD application (in March). By March, most nitrate had already been lost, so the second DCD application would have limited effect. By contrast, as well as more nitrate being able to be taken up by spring pasture in New Zealand, there may be more N still in the soil for the spring DCD application to work on. It may be necessary to consider a mid-winter DCD application under higher drainage conditions such as in Ireland, to combat the high drainage rate and achieve comparable reductions in N loss to those observed in New Zealand. Alternatively, to avoid driving on wet soils, a higher DCD application rate could be used in autumn. The peak NO 3 N concentrations in leachates draining from lysimeters in this study were well below the EU MAC for drinking water 1 in the control (MAC) of 11.3mg NO 3 N l 8

ENVIRONMENT and fertiliser only treatments, but the urine treatments greatly exceeded the MAC (Table 3). The mean NO 3 N concentrations from the urine treatments were also above the MAC (Table 4), except for the Rathangan urine plus high fertiliser treatment. Dicyandiamide (DCD) halved the peak drainage NO 3 N concentrations from the light soils (Table 3), but maintained high N concentrations for slightly longer than when DCD was not applied (Fig. 1), consistent with the observations of Singh et al. (2009) at a similar rate of urine N. DCD reduced mean concentrations as well; however, the concentrations from the Clonakilty and Elton soils were still greater than the MAC (Table 4). However, as they were not far above the MAC (12.3 1 ), and the mean concentra17.0mg NO 3 N l tions from non-urine treatments were well below the MAC, it is likely that overall the mean concentrations leaving a grazed grassland (consisting mainly of non-urine areas) would be below the MAC where DCD was applied, consistent with field-scale measurements by other researchers (Monaghan et al. 2009). Despite the higher total N losses in this experiment (cf. New Zealand data), the mean annual concentrations observed were similar to 1 obconcentrations of 2025mg NO 3 N l served with a urine application in New Zealand (Di and Cameron 2002; 2004b).

HERBAGE

The mean DM yield from this experiment (Fig. 3) was lower than generally recorded in the literature. For example, Hopkins et al. (1990) and Laidlaw (1984) recorded 4.3 and 7.3t DM ha1, respectively, from control plots in the UK, and 6.99.1t DM ha1 at similar fertiliser rates to those used in this experiment, which only yielded 3.1 and 5.8t DM ha1 from the control and fertiliser plots. This low pasture yield was at least partly due to weed ingress on these lysimeters, reducing ryegrass cover, an ongoing problem throughout the experiment. As the yield was so low, the N uptake may not have been optimised, and it may be reasonable to expect higher DM yields and N uptake in the field. Dicyandiamide (DCD) increased N uptake by pasture, especially at the low fertiliser level. DCD also increased the annual mean herbage N% on the low fertiliser level (Table 5), and increased the annual N off-take by pasture at both fertiliser levels (Fig. 4). Although DCD consistently increased N uptake, increases in DM production were less consistent. There was a mean increase in DM production of 1.3% with DCD across all three soils

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at the high fertiliser rate, and an increase of 35% at the low fertiliser rate on the Clonakilty soil only (Fig. 3). These individual increases were promising, however consistent increases in DM production as have been observed in New Zealand (Di and Cameron 2002; 2004b; 2007; Moir et al. 2007) were not seen in this experiment. Further research into the effect of DCD on pasture production in Ireland is needed, and this could include investigating different DCD application regimes that may be more suited to the high drainage environment (such as more frequent DCD applications or higher application rates). Direct measurements of N2O and NH3 losses with and without DCD in Ireland would also be of value. The concentration of N in herbage from the high fertiliser rate with no urine exceeded 3.5% N (Table 5). As pasture had a low growth rate over the winter months after urine was applied, and thus a low requirement for N, this concentration is likely to have been already in excess of the requirements of the pasture. Luxury uptake of N occurred when DCD was applied, with herbage N content increasing with DCD, but there was little scope for this increased N to result in greater DM production, as production was most likely limited by temperature rather than N. The fact that the nitrogen was so plentiful at the fertiliser N application rates used in this experiment suggests that it may be possible to reduce fertiliser N application rates when DCD is used while maintaining pasture production. This could reduce costs for farmers. However, this experiment did not investigate the effect of DCD on the inter-urine area, which makes up the majority of the pasture, so further research is needed to confirm whether DCD can be used in this way. CONCLUSIONS Autumn urine application resulted in considerably higher NO 3 N leaching losses than fertiliser alone. Although the drainage volume in this study was high compared to that in New Zealand, mean concentrations were similar but NO 3 N loads leached were higher. The environmental implications of this will be different depending on whether the NO 3 N loads or concentrations are the most important. In terms of drinking water, it is the concentration that is important, and NO 3 N concentrations from most of the paddock area (the non-urine area) were well below the MAC. When DCD was applied, only the mean concentration from urine patches on lighter soils exceeded the MAC, and not by a large amount. However, if eutrophication is the issue being considered the total loads may be more important than the

concentration, and the loss measured in this study may be a greater concern. Dicyandiamide (DCD) reduced total NO 3 N losses from urine patches by up to c. 42% on the lighter soils. This is a considerable reduction, showing DCD to have high potential for reducing NO 3 losses from Irish grassland. ACKNOWLEDGEMENTS This project was funded by Teagasc through the Walsh Fellowship Scheme.

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