Ammonia and nitrous oxide emissions following land application of high and low nitrogen pig manures to winter wheat at three growth stages

Agriculture, Ecosystems and Environment 140 (2011) 208–217

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Ammonia and nitrous oxide emissions following land application of high and low nitrogen pig manures to winter wheat at three growth stages G. Meade a , K. Pierce a , J.V. O’Doherty a , C. Mueller b , G. Lanigan c , T. Mc Cabe a,∗ a b c

School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Lyons Research Farm, Newcastle, Co. Dublin, Ireland School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland Teagasc, Johnstown Castle, Wexford, Co. Wexford, Ireland

a r t i c l e

i n f o

Article history: Received 28 April 2010 Received in revised form 7 December 2010 Accepted 8 December 2010 Available online 11 January 2011 Keywords: Pig manure Ammonia Nitrous oxide Crude protein Winter wheat

a b s t r a c t Nitrous oxide (N2 O) and ammonia (NH3 ) emissions from surface applied high (HN) and low (LN) nitrogen pig manures were measured under field conditions. Manures were band-spread to a winter wheat crop at three growth stages—mid-tillering, stem elongation and flag leaf emergence. The N2 O flux rates were measured using the static chamber technique while NH3 volatilisation was assessed using a micrometeorological mass balance technique with passive flux samplers. The N2 O emissions were episodic in nature with flux rates observed ranging from 2.8 to 31.5 g N2 O–N ha−1 day−1 (P < 0.001). Higher N2 O emissions generally occurred after rainfall events. Highest N2 O losses were observed from the HN treatment with LN manure use decreasing emissions by 18% (P < 0.03). The NH3 volatilisation rates were highest within 1 h of manure application with 95% of emissions occurring within 24 h (P < 0.001). Cumulative N loss was highest at mid-tillering as low crop canopy cover and increased wind-speeds enhanced NH3 loss (P < 0.001). Highest emissions were measured from the HN manure (P < 0.03). Total ammoniacal N loss ranged from 6 to 11%. Crop N uptake and grain yield were unaffected by application timing or manure type. Therefore, the use of LN manures decreased gaseous emissions of N2 O and NH3 without any adverse effects on crop performance. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Intensive animal production and subsequent land application of manure can result in losses of ammonia (NH3 ) and nitrous oxide (N2 O) to the atmosphere. Nitrous oxide is an important atmospheric trace gas contributing to both global warming and the depletion of the stratospheric ozone layer (Crutzen, 1981; Phillips et al., 2007). Ammonia is an acidifying gas that readily combines with nitrate and sulphate in acid cloud droplets (Asman et al., 1998) and returns to the soil as acidic depositions leading to terrestrial and aquatic eutrophication. Irish agriculture contributes to 25.6% of national greenhouse gas (GHG) emissions (EPA, 2009) and approximately 98% of NH3 emissions (Hyde et al., 2003; Mc Gettigan et al., 2009). Atmospheric N2 O concentration is currently 319 ppb, with a long lifetime of 114 years and a greenhouse gas rating 298 times that of carbon dioxide (IPCC, 2007) and contributes to a total of 6% of the global atmospheric GHG content (Dalal et al., 2003). Legislation at both EU and national levels, makes it increasingly important for farmers to make optimal use of manure nitrogen (N) in agricultural

∗ Corresponding author. Tel.: +353 1 6288355; fax: +353 1 7161103. E-mail address: [email protected] (T. Mc Cabe). 0167-8809/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2010.12.007

production systems (Søgaard et al., 2002) in order to prevent N emissions. Losses through NH3 volatilisation can account for up to 30% of manure N applied and thereby reduces N availability for crop production (ECETOC, 1994). On average 1% of the total N input is emitted from the soil surface as N2 O (IPCC, 1996). Ammonia and N2 O emissions from field-applied manure are affected by weather conditions; manure characteristics, soil conditions, crop cover and application technique (Sommer et al., 1991; Huijsmans et al., 2001; Søgaard et al., 2002) with application by band spreader considerably reducing emissions compared to traditional broadcast methods (Huijsmans et al., 2003). Misselbrook et al. (2002) concluded that changing from splash-plate to band spreader reduced emissions by approximately 26%. Research has shown that manure N content can be reduced by lowering dietary crude protein (CP) (Carpenter et al., 2004; Leek et al., 2005). However, field research on gaseous emissions from land application of these modified manures and their subsequent impact on crop N uptake and crop agronomy has been limited. Decreased dietary CP content can also lessen manure volume produced per animal due to lower water consumption, reduce manure total ammoniacal N (TAN) content (Portejoie et al., 2004) and consequently result in lower urinary N percentage (Van der Peet-Schwering et al., 1999; Carpenter et al., 2004), thus minimising potential N loss to the environment. Velthof et al. (2003) also

G. Meade et al. / Agriculture, Ecosystems and Environment 140 (2011) 208–217 Table 1 Dietary inclusion rates (g kg−1 ) of ingredients as fed for high and low crude protein experimental treatments.

Composition (g kg−1 ) Wheat Soya bean meal Soya oil Minerals and vitaminsb Lysine HCl Methionine Threonine Analysis (g kg−1 ) Dry matter Crude protein Ash Crude oil Neutral detergent fibre Acid detergent fibre Gross energy (MJ kg−1 ) Lysine Methionine and cysteine (% lysine) Threonine (% lysine) Tryptophan (% lysine)

High crude proteina

Low crude proteina

648.5 314.5 13.5 23.4 0 0 0

829.2 122.8 13.6 23.4 6.6 1.4 2.7

868.6 230.4 54.7 24.3 118.3 46.3 15.74 11.2 0.60 0.65 0.17

868.5 160.3 44.6 23.5 110.4 42.5 15.60 11.6 0.56 0.65 0.18

a High N (HN) manure produced from feeding high crude protein (HCP) diet. Low N (LN) manure produced from feeding low crude protein (LCP) diet. b The premix (Devenish Nutrition, Belfast, N. Ireland) provided vitamins and minerals (per kg diet) as follows: 4.2 mg retinol, 0.07 mg cholecalciferol, 80 mg dl-alpha tocopherol, 120 mg copper as copper sulphate, 100 ppm iron and ferrous sulphate, 100 ppm zinc as zinc oxide, 0.3 ppm selenium and sodium selenite, 25 ppm manganese as manganous oxide and 0.2 ppm iodine as calcium iodate on a calcium sulphate/calcium carbonate carrier.

reported higher methane (CH4 ) emissions from high N manures during storage due to the changing of both the type and content of proteins and polysaccharides in an animal diet. The objectives of the current experiment were (1) to evaluate high and low N pig manures as sources of ammonia and nitrous oxide emissions to the environment, while examining their effect on N nutrition and grain yield, (2) to investigate the effect of manure application timing on gaseous emissions and crop performance and (3) to assess the effect of sample timing on gaseous emissions of NH3 and N2 O.

2. Materials and methods 2.1. Manure production One hundred and seventy growing pigs (35 kg, std dev 3.1 kg) were randomly allocated to one of two dietary treatments and housed in a grower/finisher house with two separate manure storage tanks. Pigs on treatment one were offered a low CP diet (16%) to produce a low N manure (LN) while pigs on treatment two received a high CP diet (23%) to produce a high N manure (HN). Crude protein levels were manipulated by varying the wheat and soybean meal inclusion rates and the LN diet was supplemented with synthetic lysine, methionine and threonine to achieve the ideal protein status (Table 1). The ingredient composition and analysis of the two experimental diets are shown in Table 1. The diets were formulated to have identical digestible energy (13.7 MJ kg−1 ) and ileal digestible lysine (9.5 g kg−1 ) contents. The crude protein concentration of the diets was determined using the LECO FP 328 instrument (LECO Corporation, St. Joseph, MI, USA). Pigs were housed for approximately 84 days in order to produce sufficient manure quantities for field application. The manure produced was removed on three separate occasions during the trial period and land-spread onto a growing winter wheat crop.

200

30 year average

2008

180

Rainfall (mm)

Treatment

209

160 140 120 100 80 60 40 20 0

April

May

June

July

August

Fig. 1. Monthly average rainfall at Lyons for the 5-month trial period, 30-year average rainfall levels are also included.

2.2. Site description and field experimental details The research was conducted during the 2007/2008 cropping season, on a medium clay loam soil on a winter wheat (Triticum aestivum L.) crop cv. Alchemy, at UCD Lyons Research Farm, Newcastle, Co. Dublin, Ireland (53◦ 18 16N, −6◦ 31 35W). The soil at Lyons was classified as a medium to heavy clay, grey-brown podzolic soil. The annual average air temperature is 13.1 ◦ C with an annual rainfall of 711 mm. Rainfall for the 2008 growing season is shown in Fig. 1. Previous cropping consisted of a winter wheat—forage maize (Zea mays L.) rotation. The crop was sown in November 2007 by conventional methods. The experiment was designed as a 2 × 3 × 7 (9) factorial consisting of two manure types (HN vs. LN) and three spread dates corresponding with Zadoks decimal growth stage (G.S) 25—mid-tillering, G.S 31/32—stem elongation and G.S 37–39—flag leaf emergence (Zadok et al., 1974) and seven (ammonia) or nine (nitrous oxide) gaseous emission sample timings. Emissions of N2 O and NH3 were measured using a randomised complete block design with three replicates per manure treatment. The trial area measured 7.3 ha in total and was divided into 18 plots measuring 750 m2 (25 m × 30 m) with six plots used for each of the three manure spreading dates (SD). For each SD the plots were separated by a buffer zone of 40 m in a line perpendicular to the prevailing wind direction. An untreated control treatment was included to evaluate the benefits of manure application on crop N uptake and grain yield. Nitrogen fertiliser (100 kgN/ha) was applied at G.S 20 (early tillering—18th March) prior to manure application. An additional 80 kgN/ha was applied at G.S 35–37 (late stem extension—15th May). Nitrogen was applied as calcium ammonium nitrate (27% N) with all trial plots being treated uniformly. 2.3. Manure application Manure treatments were applied using an Abbey Machinery (Abbey Machinery Ltd., Nenagh, Co. Tipperary) band spread applicator with a working width of 6 m to the plot area at a rate of 30,000 l/ha. There was a 21-day interval between spreading date one (17th April) and two (7th May) and a 14-day interval between spreading date two and three (21st May). Representative manure samples (1–2 L) were collected from each manure load on each SD to determine manure pH, percentage dry matter (DM), N, phosphorus (P), potassium (K) and the total ammoniacal N (TAN) of each of the manures applied (Table 2). Samples were then analysed in duplicate. Manure DM content was determined following drying at 100 ◦ C for 72 h. 2.4. N2 O measurements The N2 O fluxes from the soil–wheat system were measured using the static chamber technique based on the method described

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Table 2 Results of laboratory analysis of pig manure treatments for dry matter content, total ammoniacal nitrogen, specific macro-nutrients (phosphorus, potassium) and macronutrient application rates following either high or low N manure usage. Variable

Dry matter (g kg−1 ) TAN content (g kg−1 )a TAN applied (kg−1 /30 m3 ha−1 ) TAN as a % of total N content Application rate (m3 ha−1 ) Nitrogen (g kg−1 ) Nitrogen (kg N ha−1 applied) Phosphorus (g kg−1 ) Phosphorus (kg P/ha applied) Potassium (g kg−1 ) Potassium (kg K ha−1 applied) a

Spread date 1

Spread date 2

Spread date 3

High N

Low N

High N

Low N

High N

Low N

12.5 2.88 86.32 77.14 30 3.73 111.90 0.41 12.3 2.58 77.4

22.8 2.22 66.6 68.52 30 3.24 97.20 0.49 14.7 1.45 43.5

22.1 3.18 95.55 72.72 30 4.38 131.40 0.43 12.9 2.11 63.3

24.8 2.37 71.19 67.22 30 3.53 105.9 0.51 15.3 1.71 51.3

19.8 2.77 82.99 71.85 30 3.85 115.5 0.43 12.9 1.67 50.1

23.2 2.44 73.27 68.99 30 3.54 106.2 0.35 10.5 1.86 55.8

TAN, total ammoniacal nitrogen (NH4 + + NH3 ) at time of application.

by Hutchinson and Mosier (1981). Chambers consisted of a stainless steel structure with three components, a base (0.41 m × 0.41 m), an extension (0.41 m × 0.41 m × 0.41 m) and a lid (Fig. 2) giving a total volume of 0.085 m3 above ground level. Soil emissions were measured pre-manure application to quantify baseline levels of emission from the soil. Post manure application emission measurements were taken at 1, 24, 48 and 196 h during the first week after manure application, then at 3–7-day intervals for a total of 28 days. Three chambers were placed randomly within each plot receiving manure giving a nested design for nitrous oxide measurement. Three samples were taken at each sampling time to measure the flux, one prior to lid application and the second and third at 15 min intervals after lid closure. Samples were taken in 60 ml syringes with a luer-lock Discofix® 3 way stopcock (B. Braun Medical, Germany) attached to prevent gaseous losses. The sample was taken by piercing the rubber septum in the chamber lid with a needle, the sample was drawn from the chamber with the syringe and the stopcock was immediately closed sealing the syringe. Joints between chamber components were sealed with water to prevent gas leakage during sampling. Gas samples were analysed on a Shimadzu Gas Chromatographer (GC-2014) which included an electron capture detector (ECD) for N2 O within 24 h to prevent loss or contamination in the syringe. The samples were automatically injected by an auto-sampler provided by LAL (Goettingen, Germany) and described in Loftfield et al. (1997). The peak areas were recorded with the Peaksimple software (SRI Inc., Silicon Valley, CA, USA). Cumulative N2 O losses were calculated from the average daily N2 O emissions multiplied by the measurement period in days, N2 O losses over the 28-day measurement period were then expressed as a percentage of both total manure N and total ammoniacal N applied. This allowed for comparison of the percentage total N loss from both the high and low N manures.

Fig. 3. Schematic of the micrometeorological method using passive flux samples for ammonia measurement in a field situation.

2.5. Ammonia (NH3 ) measurements The NH3 flux was measured using the micrometeorological mass balance technique with passive flux samplers (PFS) placed on a wind vane based on the method described by Misselbrook et al. (2002) and Leuning et al. (1985). A steel wind vane (3.3 m tall) supporting five PFS was placed in the centre of the plot area (Fig. 3). The PFS were placed at five heights on the mast (0.2 m, 0.4 m, 0.8 m, 1.5 m and 3.0 m) with an additional mast placed 300 m up-wind (south west) of the experimental plots to measure background NH3

Fig. 2. Schematic of the static chamber technique for nitrous oxide measurement in a field situation.

G. Meade et al. / Agriculture, Ecosystems and Environment 140 (2011) 208–217

concentrations on which PFS were placed at 1.5 m and 3.0 m. The PFS were sampled and replaced on seven occasions in the following seven-day measurement period (1, 3, 6, 24, 48, 96 and 168 h post application) to give continuous NH3 measurement for the duration of the trial. The PFS consisted of 7.62 cm poly-vinyl chloride (PVC) piping with an insert of stainless steel honeycomb which was coated in a 3% oxalic acid in acetone solution, a blank which was not exposed to the field was also prepared to measure the NH3 concentration during shuttle preparation. The sample was extracted by washing the insert with 50 ml of deionised water. The liquid sample was then subjected to alkaline hydrolysis with sodium dichloroisocyanurate where the NH3 reacted with hypochlorite ions to form monochloramine. The addition of sodium nitroprusside then allowed the monochloramine to react with salicylate ions to form a blue compound. The absorbance of the compound was then determined spectrometrically (660 nm) on a Kony Aquakem 600 (Thermo Scientific, Waltham, USA) and related to ammonia concentration by means of a calibration curve. 2.6. Crop nitrogen uptake (CNU), yield components and grain yield Crop nitrogen uptake was measured at 21–28-day intervals post manure application. Three 1 m length crop samples were taken to ground level from each plot, weighed and dried at 55 ◦ C for 3 days and then ground by a C&N hammermill (Christy & Norris, Suffolk, UK). The N content was analysed by combustion analysis with a LECO FP 328 (LECO Corporation, St. Joseph, MI, USA). Ears per m2 and consequently grains per m2 were also calculated. At maturity, whole crop samples were collected and separated into grain and straw fractions and the straw portion was analysed for N content. The trial was harvested on September 8th, 2008 using a Sampo Rosenlew plot combine. Plot yield was recorded, adjusted to 15% moisture content and grain N content was analysed. 2.7. Statistical analysis Data were checked for normality and homogeneity of variance by histograms, qq plots, and formal statistical tests as part of the PROC UNIVARIATE procedure of SAS (SAS, 2003). The data which was not normally distributed were transformed by raising the variable to the power of lambda. The appropriate lambda value was obtained by conducting a Box–Cox transformation analysis using the PROC TRANSREG procedure. Ammonia measurements were then analysed using repeated measures ANOVA (MIXED procedure), with terms for manure type, spread date and sample time and their interaction included in the model. An additional factor, chamber, was included in nitrous oxide analysis giving a nested design of chamber within replicate. The model was run under compound symmetry and the Tukey test was applied as appropriate to evaluate pair-wise comparisons between factor means. Grain yield, crop N uptake and quality components were analysed by ANOVA, using the PROC GLM procedure of SAS (SAS Institute, Cary, NC, 2003). All data in the tables are presented as least squares means (LSM) ±standard error of the mean (SEM). 3. Results 3.1. Nitrous oxide fluxes Nitrous oxide sampling commenced immediately pre-manure application and ceased 28 days later. Initially, pre-manure application N2 O emissions averaged 2.8 g N2 O–N ha−1 day−1 . Regardless of manure N treatments, N2 O evolution from the soil surface commenced soon after manure application on each of the three manure

211

Table 3 Manure treatment and manure spread date analysis of variance showing daily nitrous oxide emissions means. Treatment

Nitrous oxide (g N2 O–N ha−1 day−1 )

Standard error

Pr > F

HN LN Spread date 1 Spread date 2 Spread date 3

15.8a 12.9b 15.9a 11.8b 15.4a

1.3 1.3 1.5 1.4 1.5

0.03 0.02

Means with like superscript values are not significantly different (P < 0.05).

application dates. The HN treatment had higher average daily N2 O emissions compared to the LN treatment which amounted to an 18% decline in N2 O emissions (15.8 g N2 O–N ha−1 day−1 vs. 12.9 g N2 O–N ha−1 day−1 , P < 0.03). Nitrous oxide emissions were also affected by manure application date with SD 1 and 3 having higher total daily emissions than SD 2 (15.9 and 15.4 g N2 O–N ha−1 day−1 vs. 11.8 g N2 O–N ha−1 day−1 , P < 0.02) (Table 3). Nitrous oxide emissions on SD 3 were facilitated by higher rainfall levels, approximately double that of the 28-day period following SD 1 (Fig. 4). Gaseous N fluxes were highly affected by sampling time (P < 0.001, Table 4) with N2 O losses ranging from 10.1 g to 17.9 g N2 O–N ha−1 day−1 when averaged across all spread dates and manure treatments. However, a sample time by spread date interaction was evident (Fig. 4). The occurrence of maximum emissions generally occurred within 4 days of the initial N loading with the exception of SD 1 where the episodic nature of N2 O is evident with a peak in emissions observed 11 days post manure amendment, after a period of substantial rainfall. Spread date 3 had significantly higher N emissions than SD 2, which can be explained by higher initial N2 O losses (days 0–2) (Fig. 4). At SD 2 N2 O emissions were similar pre and post-manure application (2.8 g N2 O–N ha−1 day−1 vs. 3.0 g N2 O–N ha−1 day−1 ). However, after precipitation occurred (days 2–3) emissions increased by approximately 7-fold. Manure application combined with substantial rainfall (3.4 mm day 0; 7.6 mm day 1) in this 48-h period provided conditions conducive to N2 O emissions. Highest cumulative rainfall for the 28-day measurement period occurred at SD 3 (40.8 mm) while lowest rainfall totals were measured at SD 1 (20.53 mm). Despite these rainfall differences, N2 O losses were similar (15.9 g N2 O–N ha−1 day−1 vs. 15.4 g N2 O–N ha−1 day−1 ). However, the pattern of precipitation (Fig. 4) for these two spread dates was different with two substantial rainfall events (11 mm days 0–1; 15.8 mm days 4–6) at SD 3 while a more continuous pattern gave consistent soil moisture inputs at SD 1. During a period of low rainfall at Table 4 Sampling time analysis of variance means for nitrous oxide emissions when averaged across manure treatment and spread date. Sample time (Hrsa /days post application)

g N2 O ha−1 day−1

Pre-spread 3h 24 h 48 h 96 h 9–11 days 12–15 days 16–18 days 22–23 days 25–27 days Pr > F

2.8 10.4 16.8 15.0 17.8 17.5 14.0 10.1 14.1 13.5 0.04

a

Hours post-manure application.

G. Meade et al. / Agriculture, Ecosystems and Environment 140 (2011) 208–217

Rainfall (mm) g N2O-N/ha/day

40 35 30 25 20 15 10 5 0

SD 1

14 12 10 8 6 4

Rainfall (mm)

N2O (g N ha-1 day-1)

212

2 0 0

2

4

6

8

10 12 14 16 18 20 22 24 26

Rainfall (mm) g N2O-N/ha/day

40 35 30 25 20 15 10 5 0

SD 2

14 12 10 8 6 4

Rainfall (mm)

N2O (g N ha-1 day-1)

Days Post Manure Application

2 0 0

2

4

6

8

10 12 14 16 18 20 22 24 26

Rainfall (mm) g N2O-N/ha/day

40 35 30 25 20 15 10 5 0

SD 3

14 12 10 8 6 4

Rainfall (mm)

N2O (g N ha-1 day-1)

Days Post Manure Application

2 0 0

2

4

6

8

10

12

14

16

18

20

22

24

26

Days Post Manure Application Fig. 4. Nitrous oxide emissions (g N2 O–N ha−1 day−1 ) post pig manure application (sample time × spread date interaction, P < 0.001). Cumulative rainfall data (mm) for each one-day (24 h) period are also included.

SD 1 (days 12–22) emissions were low. However, precipitation occurred on days 22–23 and emissions rates increased 4-fold. This rainfall event-nitrous oxide emission relationship is evident at each spread date. Cumulative emissions for the 28-day measurement period totalled 441 g N2 O–N/ha for the HN treatments and 363 g N2 O–N ha−1 for the LN manure representing an 18% decline in N2 O emissions. Nitrous oxide losses as a percentage of total nitrogen applied (0.37%—HN; 0.35%—LN) and total ammoniacal nitrogen applied (0.50%—HN; 0.52%—LN) were similar for both manure treatments. Although untreated manure plots were included for grain yield and crop N uptake assessment, background N2 O soil emissions were not measured for the 28-day periods as only the high and low N manures were being directly compared.

3.2. Ammonia volatilisation Reducing manure N content by dietary manipulation decreased N loss by volatilisation with the LN manure having significantly lower NH3 emissions than the HN manure (6.0 kg NH3 –N ha−1 vs. 6.9 kg NH3 –N ha−1 , SEM 0.487; P < 0.04). The highest NH3 emission levels were recorded at spread date 1 (7.6 kg NH3 –N ha−1 ), while emissions at spread date 2 and 3 were significantly lower (5.9 and 5.9 kg NH3 –N ha−1 , P < 0.001, Table 5). The functional form of NH3 release was typically in terms of a Michaelis–Menten curve which was used successfully by Sommer and Ersboll (1994) to describe ammonia emissions. Ammonia emissions were affected by sampling time (P < 0.001; Fig. 5) with highest losses occurring 1-h post-manure application with T50% (time taken for 50% of

G. Meade et al. / Agriculture, Ecosystems and Environment 140 (2011) 208–217

213

Table 5 Daily ammonia emissions and the cumulative ammonia losses in kg N ha−1 during the seven-day trial period from pig manure treatments and the three spread dates. Treatment HN LN Spread 1 Spread 2 Spread 3

Treatment averages (kg N ha−1 day−1 )

Cumulative losses (kg N ha−1 )

Standard error

a

0.99 0.86b 1.09a 0.84b 0.85b

a

0.07 0.07 0.08 0.08 0.08

6.93 6.03b 7.67a 5.88b 5.95b

Pr > F 0.04 0.001

Means with like superscript values are not significantly different (P < 0.05).

3.5

Ammonia Emissions (kg N ha-1 hr-1)

3

6.16 kgN

A

2.5

B

2

B

1.5

0.32kgN

C

1

D 0.5

D

D

96

168

0

1

-0.5

3

6

24

48

Hours Post Manure Application Fig. 5. Cumulative ammonia emissions (kg N ha−1 ) at each sampling period for the 168-h (7 days) trial period post manure application. Values are averaged for manure type and spread date. Columns with like data labels are not statistically different (P < 0.001).

emissions) occurring at approximately 2 h post-manure application (113 min). On average 95% of NH3 emissions occurred within the first 24 h post manure application with losses ranging from 94 to 96% (Fig. 6). Ammonia release from the manure treatments reduced significantly (−1 kg NH3 –N ha−1 ) from 6 to 24 h with a further 50% decrease in losses from the 24 to 48 h sample timing. As shown in Fig. 6 initial losses in the 1–6 h period post manure application at SD 1 were significantly higher than at SD 2 and SD

3 (+1.7 kg NH3 –N ha−1 ) with increased prevailing wind-speeds and low crop canopy cover conducive to NH3 release (Table 6). The same trend was evident when T50% was calculated for each individual spread date (Fig. 6). High initial emissions at SD 1 resulted in T50% being reached at 97 min while T50% occurred at 110 min at SD 2 and 132 min at SD 3. By the final sampling time (+168 h), emissions were minimal accounting for only 0.04% of the average TAN applied.

Cumulative NH3 Loss (kgN

ha -1)

9 8 7 6 5 4 3 SD 1 - T50% = 1 hr 37 mins

SD 2 - T50% = 1 hr 50 mins

2 SD 3 - T50% = 2 hr 12mins

1 0 1

Hours Post Manure Application

Fig. 6. Ammonia emissions from land application of pig manure as affected by a spread date × sample time interaction. The graph shows a typical Michaelis–Menten structure. T50% represents the time taken for 50% of NH3 emissions to be lost.

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Table 6 Laboratory analysis results of manure N characteristics, NH3 emissions as measured in field and crop/weather data for the duration of the experiments. Percentage of the total N and TAN content emitted from the pig manure treatments were then calculated. Variable

TAN content (g kg−1 ) TAN applied (kg−1 /30 m3 ha−1 ) TAN as a % of total N content Nitrogen (kg N ha−1 applied) N loss as ammonia (kg N ha−1 ) % emission reduction low vs. High N lost as % of TAN Dry matter (%) Crop height (cm) Wind-speed (knots)a Air Temperature ( ◦ C)a Solar Radiation (j cm3 )a Rainfall (mm)a

Spread date 1

Spread date 2

Spread date 3

High N

Low N

High N

Low N

High N

Low N

2.88 86.32 77.14 111.90 8.14

2.22 66.6 68.52 97.20 7.11 12.65 10.68 2.28 10-20 13.8 6.6 112 0

3.18 95.55 72.72 131.40 6.32

2.37 71.19 67.22 105.9 5.43 14.08 7.63 2.48 30-40 8.6 16.6 117 0.3

2.77 82.99 71.85 115.5 6.30

2.44 73.27 68.99 106.2 5.59 11.27 7.63 2.32 50-60 7.8 11.8 86 11

9.43 1.25

6.61 2.21

7.59 1.98

TAN: total ammoniacal nitrogen. a Meteorological data quoted is the average data for the 48 h period immediately post manure application with the exception of rainfall (cumulative mm).

Average NH3 emissions as a percentage of TAN applied ranged from 6.61 to 10.68% depending on manure treatment and application date (Table 5). Higher NH3 losses as a percentage of TAN were observed at SD 1, while SD 2 and 3 were similar (10.0% vs. 7.1% vs. 7.6%; SEM 0.302; P < 0.04). Higher wind speeds and low crop cover (Table 6) facilitated NH3 emissions at SD 1, while no difference in NH3 loss as a percentage of TAN occurred between manure types (7.9%—HN vs. 8.6%—LN; SEM 0.246; P < 0.17). However, overall N losses on a per hectare basis were higher for the HN treatment (6.9 vs. 6.0 kg NH3 –N ha−1 , P < 0.03) due to higher initial manure N content. 3.3. Crop yield, yield components and crop nitrogen uptake Manure application significantly increased grain yield (+1.25 t ha−1 ) compared to the untreated control while similar grain yield was achieved from the HN and LN manures types (P < 0.001) (Table 7). The grain yield components, ears/m2 and grains/m2 , were positively affected by manure treatment (P < 0.001) with the HN manure increasing both ear and grain number per m2 compared to the LN treatment (P < 0.001). Early season N uptake (NU) evaluation (G.S 45) was unaffected by manure treatment (P < 0.1; Table 7). However, by mid to lateseason sampling (G.S 65—mid-flowering and G.S 85—soft dough), NU had increased with the HN (+27.7 kg N ha−1 ; +62.4 kg N ha−1 ) and LN (+37.2 kg N ha−1 ; +66.6 kg N ha−1 ) treatments being significantly higher than the untreated control (P < 0.0091; P < 0.001). At G.S 45, early manure application (G.S 25) resulted in SD 1 having higher NU compared to SD 2 and 3 (P < 0.005; Table 6). However, by G.S 85, SD 1 remained higher than SD 3 but was similar to SD 2 (P < 0.04) as a longer time period had elapsed between application and sampling allowing manure NU by the crop. End of season crop nitrogen uptake values (grain NU + straw NU) were similar for all application timings (P < 0.3). Manure treatments (HN vs. LN) were similar but significantly higher than the untreated control (P < 0.001). Consequently, similar N use efficiency (NUE) levels were achieved from both manure treatments (HN—44%; LN—46%). 4. Discussion Animal manures are a valuable resource providing both macroand micro-nutrients for crop production. However, application of these manures to arable land can act as a significant source of both NH3 and N2 O emissions causing potential harm to the environment and reducing the N available for crop uptake. The objective of this study was to quantify the effect of dietary CP reduction

on trace gaseous emissions of NH3 and N2 O and on the crop N uptake and grain yield following pig manure application as a N source to arable land. Previous studies have focussed largely on gaseous emissions from inorganic rather than organic amendments to the soil. It is now necessary to assess the organic N input to global greenhouse gas emissions in order to assess the total impact of the animal production process on climate change. Reduction of dietary crude protein content and subsequent supplementation of deficiencies with synthetic amino acids, have previously been shown to decrease manure N content (Gatel and Grosjean, 1992; Lenis and Jongbloed, 1999; Sorensen and Fernandez, 2003). In this experiment, dietary crude protein content of the HN and LN diets was reduced from 23% to 16%. Total manure N content subsequently declined by 14% and total ammoniacal N content by 20%. Similar trends were evident in experiments reported by Aarnink et al. (1993) who concluded that urinary N excretion can be reduced by improving N utilisation from pig feed, resulting in lower total ammoniacal N contents in manure. Previously Carpenter et al. (2004) concluded, from pig performance studies in Ireland, that reducing dietary crude protein content from >20% to 15% was optimal in terms of growth performance, feed conversion and carcass characteristics while N excretion was reduced compared to diets formulated with higher CP diets. Thus, the current study aims to evaluate to effect of dietary crude protein reduction on N loss following land application of high and low N pig manures to winter wheat at three key growth stages. 4.1. Effect of manure treatments and application date on N2 O emissions Manure application enhances denitrification driven by the increased supply of easily available N and carbon which promote anaerobic conditions and denitrification (Davidson, 1991; Whalen, 2000) with hydrological factors exerting the strongest control on N2 O emissions (Brumme et al., 1999). In this study N2 O emissions increased within 3 h of application from baseline levels of 2.8–10.4 g N2 O–N ha−1 day−1 (365%). Incidents of increased N2 O emissions immediately following pig manure application have previously been reported by Sharpe and Harper (2002) and Rochette et al. (2004). Significant increases in N2 O emissions were evident during SD 1 and SD 3 for the initial 72-h period post-manure application. The flux rates observed during the field experiments ranged from 2.8 to 31.5 g N2 O–N ha−1 day−1 . The range found was similar to previous studies; however, higher maximum values of up to 155 g N2 O–N ha−1 day−1 have been measured from arable land (Kaiser et al., 1998). In this current study, the reduced dietary crude

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Table 7 Mean grain yield, grain quality and crop nitrogen uptake data by manure treatment and manure spread date following analysis of variance calculations. HN −1

Grain yield (t ha ) Ears/m2 Grains/m2 N uptake 1 (kg N ha−1 ) N uptake 2 (kg N ha−1 ) N uptake 3 (kg N ha−1 ) Grain nitrogen (%) Crop N uptake (kg N ha−1 ) Grain N uptake (kg N ha−1 ) Straw N uptake (kg N ha−1 ) Manure N recovered (kg N ha−1 )

LN a

11.51 536a 25,881a 69.88a 131.83a 165.52a 1.66a 252.26a 165.37a 86.89a 38.69

Control a

11.50 471b 21,698b 69.62a 143.36a 169.76a 1.64ab 246.27a 163.24a 83.03a 32.70

Pr > F b

10.24 369c 17,058c 60.42a 106.14b 103.12b 1.59b 213.57b 141.05b 72.52b

<0.001 <0.001 <0.001 0.1 0.01 <0.001 0.04 <0.001 <0.001 0.003

Spread 1

Spread 2 a

10.98 483a 22,900a 76.69a 141.07a 157.14a 1.59a 234.58a 155.37a 79.20a

Spread 3 a

11.12 449a 20,979a 59.77b 110.08ab 145.95ab 1.62a 235.28a 156.22a 79.06a

Pr > F a

11.14 445a 20,758a 63.46b 130.18b 135.31b 1.63a 242.25a 158.07a 84.18a

0.5 0.1 0.2 0.005 0.03 0.04 0.8 0.4 0.7 0.3

**Means with like superscript values are not significantly different (P < 0.05). CNU: crop N uptake; HN: high N manure; LN: low N manure; Unt: untreated control; manure N recovered; CNU HN/LN: CNU control.

protein content resulted in a decline in gaseous emissions of N2 O of 18% after application of the LN manure. Total percentage N loss as N2 O over the 28 days measurement period was low, however, by the cessation of N2 O emission measurement loss rates had not returned levels evident prior to manure application (Table 4). Thus, measurement of N2 O emissions for a longer time period is justified similar to studies by Velthof et al. (2003) and Rochette et al. (2004) where sampling continued for 98 and 365 days respectively post manure application. Emissions levels of just 0.37% for the HN treatment and 0.35% for the LN. Previous studies have shown a wider range in emissions from N application of between 0.001% and 6.8% (Eichner, 1990; Kaiser et al., 1998). 4.2. Effect of manure treatments and application date on NH3 emissions The micrometeorological technique with passive flux samplers used in the current study is commonly used for NH3 measurement in field conditions (Pain et al., 1989; Sutton et al., 1995; Misselbrook et al., 2002). They are an appropriate method for determining short or long term NH3 fluxes in a field system as they do not disturb the soil, plant or micro-environmental processes. Ammonia emissions were monitored for a seven-day period as additional losses beyond this time are minimal for liquid manures (Chambers et al., 1997). In general, cumulative emissions were very low. However, when measured values were compared to outputs from the ALFAM database, Ammonia Losses from Fieldapplied Animal Manure (Søgaard et al., 2002), similar values were observed (R2 = 0.84). The low emissions may have been due to the low dry matter content of the slurry and relatively low soil moisture content. Subsequently, slurry infiltration into the soil was rapid. Previously, Sommer et al. (2006) demonstrated that a doubling of the infiltration rate of TAN away from the soil surface could half cumulative ammonia emissions. Following surface application of manure, cumulative losses were lower for the LN diet (6.0 kg NH3 –N ha−1 vs. 6.9 kg NH3 –N ha−1 ) as the corresponding manure contained on average less TAN at the end of the storage period (70.4 kg N/30 m3 vs. 88.3 kg N/30 m3 ). These findings are in agreement with Portejoie et al. (2004), Huijsmans et al. (2003) and Misselbrook et al. (1998), who reported increased NH3 losses from manures with higher TAN contents. Lowest NH3 emission reduction, due to manure treatment was observed at SD 3 when manure was applied to a more advanced crop. Highest TAN emissions were observed at SD 1 where a low canopy cover, increased wind speeds and moderate solar radiation increased potential NH3 diffusion. Volatilised NH3 is removed by the wind, lowering the NH3 concentration in the air above the manure, stimulating further NH3 loss (Freney et al., 1983) while advanced crops may shelter the manure surface from air movements reducing ammonia emission. In addition,

more advanced crops may absorb NH3 within the canopy microclimate which can further reduce emissions at later application dates (Whitehead and Lockyer, 1987; Sommer and Jensen, 1991). Sommer et al. (1997) reported reabsorption figures in the region of 25% of emitted NH3 . The NH3 volatilisation rate from applied manure decreased with time (P < 0.001). Ammonia losses were highest immediately after manure application with 87% of emissions observed in the first 6 h after application. Pain et al. (1989) and Moal et al. (1995) reported that 50% of emissions were reached in the first 12 h. Manure application at more advanced growth stages (SD 2/3) resulted in a 23% reduction in ammonia volatilisation, while changing manure type (HN to LN) and applying at a later date (SD 2/3) decreased emissions by 33%. Misselbrook et al. (2000) concluded that losses of approximately 15% of TAN when pig manures with a DM <4% were applied to agricultural lands, while Smith et al. (2000) reported losses of 16.3% of TAN when higher dry matter cattle manure was top-dressed to arable crops in spring. Cumulative NH3 volatilisation from surface applied manure in this study ranged from 6.6 to 10.6% of the TAN applied. Low manure DM content (<2.5%) gave increased infiltration capacity and when combined with a tall, dense winter wheat canopy lower emission rates occurred. Despite lower total N losses from the LN treatment, the range of losses as a percentage of TAN applied were similar for the LN and HN treatment (7.6–10.7%—LN; 6.6–9.4%—HN). Losses of TAN applied can vary greatly and Frost et al. (1990) reported that losses can range from 7 to 84% with soil and environmental conditions, manure type and crop developmental stage affecting losses (Jarvis and Pain, 1990; Sommer et al., 1997). Results reported in this study would suggest that low crop cover, high solar radiation and increased wind speeds will increase the magnitude of NH3 emissions while other studies have shown a positive relationship between higher air temperatures and increased NH3 emissions (Rodhe and Johansson, 1996; Braschkat et al., 1997). However, at SD 1 air temperatures (6.6 ◦ C) were lower than SD 2 (16.6 ◦ C) and SD 3 (11.8 ◦ C). 4.3. Effect of manure treatments and application date on grain yield and crop N uptake Manure application increased crop nitrogen uptake and grain yield in winter wheat compared to the no-manure control. Benefits of manure usage have previously been shown by Nicholson et al. (1999) and Seiling (2004) with later manure applications being utilised more efficiently than applications at the commencement of spring growth. In this experiment crop N uptake and grain yield were unaffected by manure spread date and manure type. Despite the LN manure containing less plant available TAN, the magnitude of the difference in crop N uptake was not large enough to cause significant grain yield effects (HN +5.99 kg N ha−1 ). A similar scenario

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was evident for manure spread date with crop N uptake varying by a maximum of only 7.67 kg N ha−1 . Manure N use efficiency (NUE) as a percentage of the TAN applied averaged 45%. This is lower than the mean figure (60%; range 30–90%) reported by Smith and Chambers (1992) when pig manure was applied to growing cereals in small plot experiments. Low NUE could be as a result of high summer rainfall increasing the level of N loss through nitrate leaching with rainfall levels in June, July and August 1.3, 2.2 and 2.5 times the 30 year average respectively. However, the manure NUE was similar to that found by Jackson and Smith (1997) who reported an average manure NUE of 40% (range 22–68%) when spring applied to autumn sown winter wheat. 5. Conclusions Dietary manipulation to reduce manure N content and consequently decrease NH3 and N2 O emission post manure application is a realistic practice for gaseous emission reduction. While LN manures contained less plant available TAN, there was no adverse effect on crop N uptake, grain yield or grain nitrogen percentage observed. A potential reduction in NH3 loss of c.33% and N2 O emissions of 18% can be achieved by low N manure use at advanced growth stages. External factors such as precipitation rates play a key role in N2 O loss to the atmosphere, while a number of crop and meteorological factors are important in NH3 loss. While there was reduced gaseous N loss from low N manures, the N utilisation by the winter wheat crop was still moderate (<50%). Further research on gaseous emissions of NH3 and N2 O during land spreading of animal manures is justified as results from this trial would indicate that there are possibilities to reduce these losses by dietary manipulation during animal production. Acknowledgements This work was supported by the Department of Agriculture, Fisheries and Food Research Stimulus Fund. The authors thank Ms. Simone Hepp, Mr. John Kelly and Mr. Con Dowdall for their technical assistance. References Aarnink, A.J.A., Hoeksma, P., van Ouwerkerk, E.N.J., 1993. Factors affecting ammonium concentration in slurry from fattening pigs. In: Verstegen, M.W.A., den Hartog, L.A., van Kempen, G.J.M., Metz, J.H.M. (Eds.), Proceedings of the Congress on Nitrogen Flow in Pig Production and Environmental Consequences. Purdoc, Wageningen, The Netherlands, pp. 413–420. Asman, W.A.H., Sutton, M.A., Schørring, J.K., 1998. Ammonia: emission, atmospheric transport and deposition. New Phytol. 139, 27–48. Braschkat, J., Mannheim, T., Marschner, H., 1997. Estimation of ammonia losses after liquid cattle manure application. J. Plant Nutr. Soil Sci. 160, 117–123. Brumme, R., Borken, W., Finke, S., 1999. Hierarchical control on nitrous oxide emission in forest ecosystems. Global Biogeochem. Cycles 13 (4), 1137–1148. Carpenter, D.A., O’Mara, F.P., O’Doherty, J.V., 2004. The effect of dietary crude protein content on growth performance, carcass composition and nitrogen excretion in entire grower-finisher pigs. Irish J. Agric. Food Res. 43, 227–236. Chambers, B., Smith, K., Van der Weerden, T., 1997. Ammonia emissions following landspreading of solid manures. In: Jarvis, S.C., Pain, B.F. (Eds.), Gaseous Emissions from Grasslands. CAB International, Wallingford, UK, pp. 275–280. Crutzen, P.J., 1981. Atmospheric chemical processes of the oxides of nitrogen, including nitrous oxide. In: Delwiche, C.C. (Ed.), Denitrification, Nitrification and Atmospheric Nitrous Oxide. Wiley, New York, pp. 17–44. Dalal, R.C., Wang, W., Robertson, G.P., Parton, W.J., Meyer, C.P., Raison, J.R., 2003. Emission sources of nitrous oxide from Australian agriculture and forest lands and mitigation options. In: National Carbon Accounting System Technical Report No. 35 ,. Australian Greenhouse Gas Office, Department of the Environment and Heritage, Australian Government, Canberra, Australia, p. 43. Davidson, E.A., 1991. Fluxes of nitrous oxide and nitric oxide from terrestrial ecosystem. In: Rogers, J.E., Whitman, W.B. (Eds.), Microbial Production and Consumption of Greenhouse Gases: Methane, Nitrogen oxides, and Halomethanes. American Society for Microbiology, Washington, DC, pp. 219–235. ECETOC, 1994. Ammonia emissions to air in Western Europe. In: ECETOC Technical Report No. 62 , Belgium.

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