Effluent quality and ammonia emissions from out-wintering pads in England, Wales and Ireland

Agriculture, Ecosystems and Environment 160 (2012) 82–90

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Effluent quality and ammonia emissions from out-wintering pads in England, Wales and Ireland P.A. Dumont a,b,∗ , D.R. Chadwick a , T.H. Misselbrook a , J.S. Robinson b , K.A. Smith c , E. Sagoo c , V. Camp a , R. Murray a , P. French d , R.A. Hill e,f , A. Scott f a

Rothamsted Research North Wyke, Okehampton, Devon EX20 2SB, UK The University of Reading, Whiteknights, Reading, Berkshire RG6 6AH, UK c ADAS, Woodthorne, Wergs Road, Wolverhampton WV6 8TQ, UK d Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co., Cork, Ireland e Westlakes Scientific Consulting, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3LN, UK f Jacobs, Kelton House, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3HX, UK b

a r t i c l e

i n f o

Article history: Received 3 December 2010 Received in revised form 23 January 2012 Accepted 16 April 2012 Available online 3 May 2012 Keywords: Beef cattle Out-wintering pads Effluent quality Dirty water Woodchip bedding Ammonia emissions Animal production

a b s t r a c t Out-wintering pads offer a reduced cost system for wintering cattle, minimising damage to pasture, providing animal welfare and production benefits, and generate, potentially, a more manageable effluent and lower ammonia emissions. The objectives of the present study were (i) to contribute to improved understanding of the factors impacting on effluent quality, ammonia emissions and animal welfare via observations on four farm-based out-wintering pads (ComOWPs) in England, Wales and Ireland and more detailed studies undertaken on four experimental OWPs (ExpOWPs) constructed at Rothamsted Research North Wyke, Devon, England and (ii) to corroborate the effluent quality data from both the ComOWPs and the ExpOWPs, with findings in the literature. Woodchip size, feeding management and area allowance were the treatment factors applied on the ExpOWPs. These three factors were randomised across the four ExpOWPs, over four 6–7 week periods. Effluent quality from the ExpOWPs was sampled frequently in a flow proportional way and analysed for total N (TN); total P (TP); total solids (TS); ammoniumN (NH4 + -N); nitrate-N (NO3 − -N). Beef cattle were periodically weighed for determination of live weight gain (LWG). An approximate nitrogen balance was calculated as a means of understanding its partitioning and fate during and after the ExpOWPs use. Effluent quality from the ComOWPs was sampled frequently, also in a flow-proportional way, and analysed for TN, TP, TS, NH4 + -N, NO3 − -N, total K and COD. Effluent quality data from the ExpOWPs showed no significant differences (P > 0.05) between treatments, with average concentrations of 1095 mg l−1 , and 806 mg l−1 , for TN and NH4 + -N, respectively. Average effluent concentrations from the ComOWPs were 356 mg l−1 TN and 124 mg l−1 NH4 + -N. Ammonia emissions from the ExpOWPs showed no significant differences (P > 0.05) between the treatments, with average mean emission rates of 2.5 g m−2 d−1 NH3 -N, respectively. A positive correlation was established between NH3 N emission rate and wind speed. Emission rates from the ComOWPs ranged from 0.7 to 1.6 g m−2 d−1 NH3 N. Average daily LWG on the ExpOWPs was 1.33 kg steer−1 d−1 . The effluent from both the ComOWPs and ExpOWPs were more similar with dirty water and of consistently lower strength than beef cattle slurry, as supported by findings in the literature, and therefore, it is suggested to be subject to the regulatory requirements of dirty water rather than slurry. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Cattle production in the UK is based mainly on grassland (Politiek and Bakker, 1982; Lowman and Wright, 1995; HCC, 2007) allowing producers to utilise this abundant resource without

∗ Corresponding author at: Rothamsted Research North Wyke, Okehampton, Devon EX20 2SB, UK. Tel.: +44 01837883544. E-mail address: [email protected] (P.A. Dumont). 0167-8809/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2012.04.019

having to depend on manufactured feeds. During the winter period the animals are commonly housed indoors to achieve efficient feeding and nutrient management and to avoid pasture damage by cattle. However, the relatively high construction and maintenance costs of conventional housing and the labour involved in daily feeding and manure management make it a high-cost management system which has encouraged cattle producers to consider alternative low capital-operational facilities. As such, an increasingly common practice is to out-winter animals on a bed of woodchip over a lined and artificially drained area known as out-wintering

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Fig. 1. Schematic design of the ExpOWPs. O: ammonia emission masts measuring at 0.5, 1.0, 2.0 and 3.5 m heights: , ammonia emission masts measuring at 1.0 m height; , water troughs.

pads (OWPs) (NHFT, 2004; DAF, 2007; Chadwick, 2009). Commonly used for cattle and occasionally for sheep (TSAC, 2007), OWPs have shown positive animal health (Hickey et al., 2004; Boyle et al., 2008; O’Driscoll et al., 2009) and, also, production benefits (Hickey et al., 2002; Smith et al., 2006; Chadwick et al., 2009). Originally developed in New Zealand around 20 years ago (Dexcel, 2005), OWPs are widespread in the UK, with a recent estimate of c.600 in use (Smith et al., 2010). The satisfactory performance of an OWP, both environmentally and with regard to animal production, relies on good design and the implementation of good management practices (French and Hickey, 2003). Pad design, area allowance, woodchip size and rainfall are factors that may affect drainage volume and effluent quality (Edwards et al., 2003) and also ammonia (NH3 ) emissions (Misselbrook et al., 2010). Careful management of the effluent is required, to avoid pollution of nearby ground and surface water (CREH, 2005; Vinten et al., 2006). The quality of the effluent and the volume generated are of key importance; the former may influence how the effluent is managed before and during land spreading (Augustenborg et al., 2008), and the latter will determine the storage capacity required during the wintering period. The effluent from OWPs is currently classified as slurry (DEFRA, 2009). However, research has shown that the average effluent quality from OWPs is similar to typical dirty water rather than beef cattle slurry (Edwards et al., 2003; French and Hickey, 2003; Vinten et al., 2006; Augustenborg et al., 2008; McDonald et al., 2008; Chadwick et al., 2009; Chadwick, 2009; Dumont et al., 2010). Dirty water is classified by definition according to its source, not its nutrient content (DEFRA, 2009). Out-wintering pads may also provide lower potential for NH3 emissions when compared with indoor cattle housing as urine is likely to drain quickly into the woodchip matrix. Concerns regarding the damaging environmental effects of NH3 emissions have led to international legislation requiring signatory nations to reduce emissions to below target ceilings (Webb et al., 2005; Erisman et al., 2008). Emissions from cattle housing and concrete yards currently account for c.25% of total annual emissions from UK agriculture (Webb and Misselbrook, 2004) and few cost-effective mitigation strategies currently exist, so there is considerable interest in the use of OWPs for cattle from this perspective. The partitioning of nitrogen across the OWP is dependent upon controlling the inputs and managing the outputs, thus reducing losses. A nitrogen balance is a tool that has contributed towards the understanding of nitrogen fluxes (Oenema et al., 2003) at all scales of research, from greenhouse tomato experiments (He et al., 2007) to farm (Spears et al., 2003), country (Lord et al., 2002) or continental level (Oenema et al., 2009).

This paper corroborates the potential effect of OWPs management on effluent quality and ammonia emissions at a research site with four experimental OWPs and in preliminary data from four farm-scale OWPs across England, Wales and Ireland. 2. Materials and methods 2.1. Experimental out-wintering pads (ExpOWPs) 2.1.1. Site climate Between October and December 2008 four lined OWPs were constructed at Rowden Farm, Rothamsted Research North Wyke, South West Devon, England (50◦ 46 36 N, 3◦ 55 23 W) at an altitude of 163 m. Climatological data for the region, collected over the past 50 years, indicate that annual average rainfall is 1059 mm (predominantly from October to January) and annual average temperature is 9.7 ◦ C, with a summer average of 15 ◦ C and a winter average of 3.5 ◦ C (Stone, 2010). 2.1.2. Construction The top soil was removed and the surface was graded to a 3 degree slope, leaving the back of the pads in a higher position than the front. Then 30 cm of the clay soil was excavated to prepare the bedding area on top of which was placed a geo-textile membrane and then a plastic liner. Drainage pipes of 150 mm diameter were placed on top of the liner – in a U shape form – allowing the effluent to drain freely by gravity towards the exit located in one corner of each pad (Fig. 1). The effluent was directed through closed drainage pipes to tipping buckets located 30 m down slope, to record the volume of effluent leaving each pad (Fig. 2a). Above the liner and the drainage pipes was placed a 30 cm base layer of coarse (5–10 cm) woodchip material (on-site fresh felled chipped Douglas Fir round wood) equally for each pad, on top of which was placed another 20 cm of one of the four different woodchip sizes (Fig. 2b). Each pad comprised an area of 100 m2 (10 m × 10 m) of actual woodchip bed (bed area) plus 30 m2 (10 m × 3 m) of concrete feeding area; therefore, each pad offered a total space area of 130 m2 for the groups of cattle fed off-pad and 100 m2 for cattle groups fed on-pad. The pads were separated by a 3 m space (Fig. 1) and fenced using round wood, and metal feed barriers for the concrete area. A water trough was installed on one of outer sides of the bed area of each pad, to avoid any obstruction whilst scraping and collecting the slurry from the concrete feeding area. This area could be manually separated on each pad by moving feed fences located between the bed area and the concrete feeding area.

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Fig. 2. (a) Schematic diagram of tipping buckets for effluent collection and measurements and (b) four woodchip sizes used as top bedding on the ExpOWPs.

2.1.3. Experimental design This experiment comprised four consecutive periods of 6–7 weeks; with a total duration of 6 months (4 study periods). A Graeco-Latin Square experimental design (Federer, 1955) was used to investigate the interaction between three factors (see Section 2.1.5) which were randomised across the pads at the beginning of each period (Table 1). 2.1.4. Cattle Thirty-four (34) Charolais Cross Friesian steers of average weight 470 kg (ranging from 420 to 535 kg) and average ages of 18 months were distributed between the pads in four groups. The animals remained on the pads for 24 h d−1 and were fed silage ad libitum (12% DM crude protein) and concentrates (2 kg steer−1 d−1 , 16% DM crude protein). Steers were weighed and scored for body condition (BCS) at the beginning and end of each period. The difference in weight per steer from start to end on every period provided the gained weight per period (GW) and was used to calculate daily live weight gain (DLWG) per steer. Animal welfare (data shown in Chadwick et al., 2009; Chadwick, 2009) was assessed measuring two main parameters: (i) behaviour (ruminating pattern; eating behaviour; standing/laying; position of head and ears) and (ii), appearance (lameness; cleanliness; body condition score). 2.1.5. Treatments This study comprised of three treatments: woodchip size, feeding management, and area allowance (Table 1).

2.1.5.1. Woodchip size. Four woodchip sizes (chipped Douglas Fir round wood) were used and classified according to woodchip length: (i) a coarse irregular-shape flat woodchip measuring from 5 cm to 10 cm; (ii) a long-shape woodchip from 2 cm to 4 cm; (iii) a dice-shape woodchip from 1 cm to 2 cm; (iv) sawdust (manufactured from Pallet), measuring from 0.1 cm to 1 cm. 2.1.5.2. Feeding management. In this study this term refers to the feeding location for steers on each of the four OWPs, depending if they had access (Off-pad) or not (On-Pad) to the concrete feeding area. Fed “On-Pad” implied steers eating from the woodchip bed. 2.1.5.3. Area allowance. This is the space available to each steer within the pad-measured dividing total pad area by total animals allocated on each pad (woodchip bed + concrete), expressed in m2 steer−1 . Four area allowances were included within this experiment: 11.1, 11.8, 14 and 18.6 m2 steer−1 , these representing the range found in the UK by Smith et al. (2010). 2.1.6. Samples collection, measurements and analysis 2.1.6.1. Effluent leachate. The flow of effluent from each pad was monitored using tipping buckets and sampled manually, twice per week. A total of c.500 ml was collected from each pad from its corresponding tipping bucket (Fig. 2a). Samples were kept at 4 ◦ C and analysed for total N; total P; total solids; nitrate-N; ammonium-N. 2.1.6.2. Beef cattle slurry. Samples of slurry (c.500 ml), scraped from the concrete feeding area of each pad (except where animals

Table 1 Statistical design on the ExpOWPs. Period/duration

Treatments

Pad 1

Pad 2

Pad 3

Pad 4

1/7 weeks

No. of steers Woodchip size cm Feed. management Area allowance m2 steer−1

7a 5–10 Off 18.6

9 2–4 On 11.1

7b 1–2 Off 18.6

11 Sawdust Off 11.8

2/6 weeks

No. of steers Woodchip size cm Feed. management Area allowance m2 steer−1

9 1–2 Off 14

7a Sawdust Off 18.6

11 2–4 Off 11.8

7b 5–10 On 14

3/6 weeks

No. of steers Woodchip size cm Feed. management Area allowance m2 steer−1

11 5–10 Off 11.8

7b 2–4 Off 18.6

9 Sawdust Off 14

7a 1–2 On 14

4/6 weeks

No. of steers Woodchip size cm Feed. management Area allowance m2 steer−1

7a Sawdust On 14

11 1–2 Off 11.8

7b 2–4 Off 18.6

9 5–10 Off 14

Letters “a” and “b” are to differentiate between groups with equal number of steers (7) considering they had to be kept together during the course of the experimental trial.

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were fed On-Pad) were taken manually two or three times per week directly from the bucket of a front-lift tractor. Samples were stored at 4 ◦ C until analysed for total N (Bradstreet, 1965) and dry matter (DM) content. 2.1.6.3. Ammonia emissions. Vertical profiles of NH3 -N concentrations in air were measured at 13 locations around the ExpOWPs (Fig. 1) using passive diffusion samplers (Willems, 1990) mounted on masts at heights of 0.5, 1.0, 2.0 and 3.5 m on eight occasions (two occasions per period) over the four experimental periods, with exposure times of approximately 24 h. An additional concentration measurement was made at 1.0 m height, very close to the downwind edge of each pad. Measurements were made when wind direction was predicted to be perpendicular to the line of the 4 pads and stable for at least 24 h. Emissions were then estimated using a short-range dispersion model (ADMS 4.1) with NH3 -N concentrations, hourly meteorological data and locations and dimensions of all potential NH3 -N sources as input (Hill et al., 2008). Derived emission rates were expressed, both on a unit area and per animal basis, according to the area and number of animals present on each pad for the relevant measuring period. Cumulative emissions from each pad for each of the four monitoring periods were estimated using the mean emission rate derived from the two measurements within each period multiplied by the relevant total pad area and total number of days within the period. 2.1.6.4. Silage. Periodic sampling of silage refusals (silage not eaten by the steers) was collected manually twice or three times per week. A total of c.1 kg of silage refusals was collected from different parts of the refused heaps of each pad and stored at 4 ◦ C. Dry matter contents were determined by drying c.0.5 kg sub-samples for 36 h at 80 ◦ C. Each sample was then ground and a sub-sample taken (c.10 g) for total N and total C analysis using a total elemental analyser (Carlo Erba NA1500N/C). Silage refusals were recorded for estimation of silage intake, calculated by the difference in weight with total silage offered. It was also assumed that the Total N content of the silage refusal remained unchanged from that offered. 2.1.6.5. Other measurements. At the end of each period, representative samples of dirty woodchip, or “spent timber residue” (STR, woodchip mixed with slurry and solids) were taken manually after being scraped from each pad (for each chip size). A total of c.3 kg of STR were collected from each pad and a sub-sample taken and analysed for total N, total P, nitrate-N, ammonium-N, dry matter (DM), and C:N ratio. Pad performance was visually monitored on a daily basis, especially after extreme weather (heavy rain, dry periods or frost) to observe the condition of the surface of the woodchip. When conditions of the pad surface were inappropriate for steers to lie down (standing water or excessive accumulation of dung and solids) stock were removed from the pad into a barn and the bedding cleaned before returning the stock to the pads (situation that occurred once – on one pad – during the 6 month trial). Cattle producers could equally move their stock to another area of the pad or to a nearby field if cleaning of the bedding is necessary. 2.1.7. Statistical analysis Using the statistical programme Genstat 10th Edition (GenStat, 2007), residual maximum likelihood (REML) analyses were used to determine differences between treatments comparing them to leachate composition, body condition scoring and daily live weight gain. REML estimates the treatment effects and variance components in a linear mixed model with both fixed and random effects. It can be used in situations where ANOVA might be considered appropriate but provides efficient estimates of treatment effects in unbalanced designs (Payne et al., 2007).

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2.1.8. Nitrogen balance A nitrogen (total N) balance was carried out by adapting the methodology described by Oenema and Pol-van Dasselaar (1999). This modification considered including a record of atmospheric deposition (rainfall N) as an additional input and ammonia volatilisation and denitrification processes as additional outputs. This nitrogen balance was carried out accounting for all nitrogen inputs and all outputs across the four periods. 2.1.8.1. Inputs. Feeds (silage and concentrates): Silage nitrogen input was calculated from the average protein content in silage consumed across the whole experiment (average 2.0% N of DM, see Section 2.1.6.4) and the total silage intake by the 34 steers, across the whole period. Nitrogen input in the concentrates was calculated from its protein content (16% crude protein) and the total intake by the 34 steers across the whole experiment, and adjusting for N in protein (16% N) (National Research Council, 2001). Steers: Nitrogen inputs within the steers were calculated by multiplying the average N content of steers estimated at 2.73% of live weight for 470 kg (Garret, 1968; Anrique, 1976) (beginning of period 1) by the total weight across the 34 steers at the beginning of the experiment. In other words, initial steers weight × N content of steers = steers N input. Woodchip (clean chipped timber): Nitrogen content of each clean woodchip size, analysed once at the beginning of the experiment (1.4, 0.8, 0.6 and 14.4 kg t−1 fresh weight, for the 5–10, 2–4, 1–2 and 0.1–1 cm, respectively) was multiplied by the total weight used at the beginning of each period as top bedding. The base layer of the 5–10 cm woodchip size was only applied once on all the pads (it was reused in each period). Drinking water: Samples were taken from drinking water at the experimental site and analysed for total N. The average total N concentration of 0.134 mg l−1 was multiplied by an estimated water consumption of 21 l d−1 steer−1 during the winter (Betteridge et al., 1986; Arias and Mader, 2007) and increased (to almost double) during the drier periods to balance cattle water-intake requirements due to lower silage intake of a lower dry matter supplied during spring (Betteridge et al., 1986; Arias and Mader, 2007). Rainfall: Nitrogen concentration on rainfall was determined using data provided by The Environmental Change Network (TECN, 2010) which shows average ammonium and nitrate concentrations on rainfall from 1993 to 2009 for the North Wyke site, consisting of weekly data summarised monthly. Both averaged concentrations (0.41 mg l−1 for ammonium and 0.27 mg l−1 for nitrate) were added together and multiplied by the total rainfall deposited on the four woodchip beds (400 m2 ) throughout the whole experiment. Deposited excreta: This parameter was not included as an input of the current N balance, but was estimated for nitrogen partitioning purposes only. Deposited excreta on the woodchip bed were calculated by estimating a ratio of time that the steers spent on the woodchip bed/concrete feeding area. This was done by accounting the volume of slurry scraped from the concrete feeding areas from all the pads across the whole experiment, then this value estimated as a proportion of the typical daily production of excreta by beef cattle (DEFRA, 2010). 2.1.8.2. Outputs. Spent timber residue (STR): The total amount of N from STR was calculated from the N content in STR samples analysed for each pad (top bedding) at the end of each period (varying from 1.5 to 7.9 kg t−1 fresh weight) and the total STR scraped from the pads across the four periods. Steers: Nitrogen composition of steers (670 kg live weight, ranging from 555 to 780 kg) was determined multiplying their average N content of 2.49% of live weight (Garret, 1968; Anrique, 1976) by the total weight across the 34 steers at the end of period 4. In other

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Table 2 Average (four periods) effluent qualitya from the ExpOWPs. Comparison by woodchip size. Woodchip size (cm

Total N (Kjeldahl) (mg l−1 )

Ammonium (NH4 + -N) (mg l−1 )

Nitrate (NO3 − -N) (mg l−1 )

Total P (mg l−1 )

Total solids (g l−1 )

5–10 2–4 1–2 Sawdust

1130 (124–7340) 1217 (198–7640) 1019 (80–4250) 1014 (76–6230)

883 (1–7225) 864 (1–5650) 723 (1–4568) 757 (5–4596)

2.2 (0–33) 2.1 (0–25) 1.4 (0–13) 5.3 (0–44)

45 (0–279) 50 (0–289) 45 (0–332) 64 (0–671)

8.7 (3–13) 9.6 (3–17) 10.5 (4–44) 8.2 (2–12)

Average s.e.

1095 48.75

806 39.37

2.7 0.87

51 4.61

a

9.3 0.51

Values correspond to simple means of original data with log-natural distribution.

words, final steers weight × N content of finishing steers = steers N output. Effluent drainage: Nitrogen in the effluent was determined from the average N concentration in the effluent (per sampling interval) and the total volume (per sampling interval), added together across the four periods. Ammonia emissions: Nitrogen outputs via ammonia emissions were calculated multiplying the mean daily emission rate per period by total days on each period, then cumulatively for the four periods. Scraped slurry: Nitrogen in the slurry scraped up from the concrete feed pads was calculated by multiplying its N content (2.7–3.2 kg t−1 ) by the total mass collected across the pads. Denitrification: Nitrogen losses through denitrification processes were determined assuming a value of 0.01% of deposited excretal N on the woodchip bed (Luo and Saggar, 2008), corresponding to emissions of N2 O-N, as described by the authors. This value was applied to the total estimated excretal N deposited on all the pads across the whole experiment. 2.2. Commercial out-wintering pads (ComOWPs) 2.2.1. Identification and location of sites For the selection of suitable ComOWPs the sites had to conform to the following criteria: the OWPs to be impermeably based or lined; an existing appropriate design of the drainage system for suitable effluent collection; pads to be stocked during 2008/2009; and, importantly, good farmer co-operation was considered essential. Four ComOWPs were identified as suitable for the monitoring across the UK and Ireland: • Co.Cavan OWP (Ireland) was completed in November 2008, and comprised a pad area of 1080 m2 (60 m × 18 m), with 120 m2 of concrete standing and 90 m2 of concrete feed area; stocking with up to 90 dairy cows, including heifers, at c.12 m2 steer−1 area allowance. • Powys OWP (Wales) was completed in November 2008; pad area of 1155 m2 (33 m × 35 m) stocking 40 organic beef finishers at 29 m2 steer−1 . • Leicestershire OWP (England) was completed in January 2009. The pad area of 1368 m2 (38 m × 36 m) stocking 100 beef cattle at 13 m2 steer−1 was divided into three independently drained sections. • Shropshire OWP (England) was completed in 2004, and comprised an irregular quadrilateral shape of approximately 600 m2 stocking on average 40 adult dairy cows (non-lactating) at an area allowance of 15 m2 steer−1 . 2.2.2. Effluent sampling Effluent flow was monitored at the Co. Cavan, Powys and Leicestershire ComOWPs over two out-wintering period, via (i) effluent sump emptied by pump and flow meter; (ii) overshot waterwheel; (iii) tipping bucket, respectively. Samples were collected on a

flow-proportional basis at the Powys and Leicestershire sites, for analysis of total N, total P, total solids, K, NH4 + -N and COD. Results for the initial monitoring period, only, are presented here.

2.2.3. Ammonia emissions Ammonia emissions were estimated from Powys, Leicestershire and Shropshire ComOWPs using the same methodology as for the ExpOWPs, with concentration measurements being made at 0.5, 1.0, 2.0, 3.5 and 4.5 m height on four masts deployed around the perimeter of each site with exposure periods of 48 h. A background mast was also placed approximately 50 m away from the OWP at each site according to the layout of adjacent buildings, livestock and manure storage. In total, 10 measurements were made at Powys and 7 at Leicestershire and Shropshire.

2.2.4. Additional measurements Records at each farm were made of pad design and construction, animal numbers, the time stock spent on the pad and feeding practices (pad management), animal dirty score and surface soiling of the woodchip bed was also assessed. Rainfall and temperature data were also recorded.

3. Results and discussion 3.1. Effluent quality 3.1.1. Experimental OWPs—effluent quality Woodchip size, feeding management and area allowance showed no significant effect (P > 0.05) on effluent quality, with average concentrations being closer to those typical of dirty water than beef cattle slurry (Table 2). The proportion of effluent leaving the pads is presented in Table 3. During the first, wetter period, the effluent represented 100% of the inputs (rainfall and excreta). However, during subsequent drier-periods the effluent represented only 17–45% of the inputs. This reduction of effluent volume (periods 2, 3 and 4) might have been due to significant evaporative losses from the surface of the pads (dry-windy periods) and/or due to absorption and retention of water in the woodchip matrix. French and Hickey (2003) found that effluent volume outputs from OWPs during a winter period can represent up to 100% of the inputs. Cumulative effluent (CE) and cumulative rainfall (CR) data from the ExpOWPs (Fig. 3b) showed that CE was higher than CR for the first 4 months (end of period 3), as a result of the high rainfall in period 1, Table 3. Although CR increased significantly in period 4, CE did not. At the end of each period, the liquids/solids retention was assessed. On average each pad retained in the woodchip nearly a third (33%) of their weight in liquids/solids. It was found that steers spent on average 65% of their time on the woodchip bed and 35% on the concrete feeding area; this 65:35 ratio was similar to the 66:33 ratio described in the Irish guidelines for OWPs (DAF, 2007).

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Table 3 Total effluent volumes from the ExpOWPs. Average litres per pad thousand litres

Winter

Spring

Period 1 (1) Total rainfall Rainfall per pad (2) Total excretal watera Excretal water per pad (3) Total effluent Effluent per pad Effluent as % of (1) and (2)

Period 2

52,600 13,150 27,300 6825 79,700 19,925 100%

Period 3

31,800 7,950 23,500 5875 24,700 6175 45%

Period 4

30,800 7700 22,900 5725 9100 2275 17%

28,800 7200 23,500 5875 9700 2425 19%

a Excretal water was estimated considering a daily production of excreta per steer of 26 l, of which 13 l correspond to urine (100% moisture) and 13 l correspond to dung (90% moisture). Therefore, the daily contribution from excretal water per steer was 24.7 l d−1 (13 l of urine plus 11.7 l from dung).

Table 4 Average effluent quality from the ComOWPs, ExpOWPs and literature. Site/reference/source (fresh weight basis)

Area (m2 steer−1 )

Total N (mg l−1 )

NH4 + -N (mg l−1 )

Total P (mg l−1 )

Total solids (g l−1 )

Co. Cavan Powys Leicestershire Shropshire Average farms Average ExpOWPs Augustenborg et al. (2008)a McDonald et al. (2008)b Vinten et al. (2006)c Dirty waterd Dirty watere Dirty waterf Dairy cow slurryd Beef cattle slurryd

22 29 13 15 21 14 – 4–12 12–24 – – – – –

665 229 175 – 356 1095 97–810 214–589 – 500 825 500 3000 4200

157 142 72 – 124 806 24–518 76–399 443–1056 300 457 300 1200f 1850

104 38 28 – 57 51 18–101 38–247 – 44 135 100 1200 785

3.4 3.4 4.5 – 3.8 9.3 – – – 5.0 10.7 5.0 60.0 60.0

a b c d e f

COD (g l−1 ) – 3.4 3.3 – 3.4 – – – – – 13.8 – – –

BOD (g l−1 ) 1.4 – – – 1.4 – – – – – 6.6 – – 10–20

Average eight OWPs. Average four OWPs. Average nine OWPs. Chambers and Nicholson (2004) and DEFRA (2010). Cumby et al. (1999). DEFRA (2010).

3.1.2. Commercial OWPs—effluent quality Concentrations of N and P from the three ComOWPs were lower than those reported as typical in dirty water (Table 4). Nitrogen concentrations were lower than those obtained on the ExpOWPs. However, similar results were reported by Augustenborg et al. (2008) and McDonald et al. (2008). As for ammonium-N concentrations, these were lower than those obtained by Vinten et al. (2006). The data summarised in Table 4 present average effluent concentrations from a total of 28 OWPs, showing clearly that the OWP effluent is rather closer in content to dirty water than dairy or beefcattle slurry. The differences in leachate concentrations between the three ComOWPs are likely due to a combination of factors, including weather conditions, pad design/size, stocking density or

stock/feeding management. Sampling and analyses of the surface layers of the woodchip (as shown in the N balance data—Table 6) indicate that a high level of slurry-nutrients were retained within the woodchip residue and confirming a rationale for the relatively low nutrient content of the OWP effluent (Table 4). Similar to the studies at the ExpOWPs, the volume of effluent flow represented a variable proportion of the total pad inputs (rainfall + dung and urine); e.g., at Powys, about 40% from July to December, 2009 and at the Leicestershire site (Fig. 3a), 21% for the period March–December, 2009, but then 73% for January–February, 2010, inclusive. The cumulative rainfall and effluent flow volumes for March–December, 2009 period are shown in Fig. 3a. Studies on water retention capacity have shown that a 1–2 cm woodchip can absorb nearly three times (300%) its dry weight (Darch,

Fig. 3. (a) Cumulative effluent flow and cumulative rainfall from the ComOWP at Leicestershire over a period of 9 months. (b) Cumulative effluent flow and cumulative rainfall from the ExpOWPs over a period of 6 months. Units are expressed as millimetres per square metre of woodchip bed.

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Table 5 Ammonia emission factors (g d−1 NH3 -N) from the ExpOWPs and ComOWPs. ExpOWP

Mean Minimum Maximum St. Dev. No. obs.

Powys

Leicestershire

Shropshire

Per m2

Per steer

Per m2

Per steer

Per m2

Per steer

Per m2

Per steer

2.5 0.2 6.7 2.0

25.7 1.6 84.1 25.9

0.8 0.3 2.9 0.7

26.5 8.2 106.1 28.8

0.7 0.2 1.4 0.4

24.1 6.1 47.2 14.3

1.6 1.2 2.1 0.4

21.4 13.8 32.2 5.8

8

10

7

7

Table 6 Nitrogen balance on the ExpOWPs. Total inputs and outputs across the four periods (6 months). Inputs

kg N

Silage Woodchip Steers Concentrates Drinking water Rain

931 450 437 310 <0.01 0.1

Outputs

44 21 21 15 <0.01 <0.01

STR Steersa Effluent Ammonia Scraped slurry Denitrification

2128

Total

a

% of inputs

663 568 257 213 81 2

Total

1784

N accounted for Surplus kg N retained on bottom woodchip layer over 6 months, kg N t−1

84% −344 14.3

% of outputs 37 32 14 12 5 0.1

N gain of steers can be obtained by the difference between steers outputs and steers inputs.

2009) and wood-shavings (3–7% moisture) nearly 400% (Ward et al., 2000).

3.2. Ammonia emissions

Ammonia-N emission (g m d )

3.2.1. Experimental OWPs—ammonia emissions From measurements on the ExpOWPs, there was no significant impact of woodchip size, area allowance or feeding management on NH3 -N emissions expressed on a per animal basis or per area basis (P > 0.05), with overall mean emission rates of 35.7 g animal−1 d−1 NH3 -N and 2.5 g m−2 d−1 NH3 -N, respectively. A positive correlation was found between NH3 -N emission rate and wind speed (Fig. 4), which might be expected from the results of studies on ammonia emissions from surface sources (e.g., Sommer et al., 2003; Misselbrook et al., 2005). This implies that controlling wind speed over the pad surface (e.g., for animal welfare benefit) may also provide a means of reducing NH3 -N emissions. Temperature might also be expected to have an influence, but wind speed accounted for much of the variability seen in emission rates (r2 = 0.83).

3.2.2. Commercial OWPs—ammonia emissions Ammonia emission rates from the ComOWPs, expressed on a per area basis, unsurprisingly due to the relatively low stocking rates on these pads, were lower than those derived for the ExpOWPs (Table 5), with a mean value across the commercial sites of 1.0 g m−2 d−1 NH3 -N. These values are lower than those reported by Misselbrook et al. (2006) for beef cattle on concrete yards (mean of 4.5 g m−2 d−1 NH3 -N). However, expressed on a per animal basis, emission rates from the ComOWPs were of a similar magnitude to those reported by Misselbrook et al. (2006), with mean emission rate across the commercial sites of 24.0 g animal−1 d−1 NH3 -N (Table 5), reflecting the larger area allowance for cattle on the outwintering pads than on concrete yards. Reductions in emissions compared with concrete surfaces may not be as great as expected due to retention of urine in an absorbent surface layer, as shown by Misselbrook and Powell (2005); also the impact of wind speed on ammonia emissions is noted and should be taken into account when comparing emissions from different systems. It is important to note also that comparison with alternative housing methods need to be made at a whole system level, including the emissions from manure management (storage and spreading). 3.3. Nitrogen balance on the experimental OWPs

8

-2

-1

kg N

6

y = 0.85x -0.73 R² = 0.83

4

2

0 0

2

4

6

8

10

-1

Wind speed (m s ) Fig. 4. Relationship between ammonia emission and wind speed for the ExpOWPs.

Results from the “farm-gate type” N balance calculations are shown in Table 6, and correspond to the total N inputs and outputs over the 6 month experiment. Total N inputs were 2128 kg N, while the outputs were 1784 kg N, thereby accounting for 84% of total N Inputs. The major N input were silage, representing 44%; woodchip with 21%; steers, 21%; and concentrates, representing 15%. The major nitrogen outputs were spent timber residue (STR) (37%); steers (32%); effluent (14%); and ammonia emissions (12%). French and Hickey (2003) found that N in the effluent represented nearly 10% of the total inputs, whereas on the ExpOWPs the effluent represented 14% of total inputs. The negative value of surplus (−344 kg N) represent the total kilograms of N retained within the pads across the whole experiment, and may reflect sampling variability especially of STR, or N retention in the bottom layers (20–50 cm depth)

P.A. Dumont et al. / Agriculture, Ecosystems and Environment 160 (2012) 82–90

89

Table 7 Average silage dry matter intake and daily live weight gain on the ExpOWPs. Source

DM intake (kg d−1 steer−1 )

DLWG

Area allowance (m2 steer−1 )

ExpOWPs Boyle et al. (2008) Earley and Prendiville (2008) Hickey et al. (2002) French et al. (2004) French and Hickey (2005)

7.9 5.0 10.1 10.2 10.9 11.0

1.33 0.77 1.11 1.22 1.40 1.42

14 8 12 18 18 11

of the 5–10 cm woodchip size which was never removed. A value a 14.3 kg N t−1 was estimated as retained on the bottom woodchip layer after the 6 month experiment. It was observed that the average NO3 − -N concentration in the leachate across all treatments was low (2.7 mg l−1 ), suggesting that very little nitrification occurred within the woodchip layers, as also reported by Luo et al. (2008) and Luo and Saggar (2008), supporting the reduced losses of nitrogen via denitrification in the woodchip bedding. Luo et al. (2008) found that both accumulative N in the woodchip and ammonia emissions accounted for 94% of the total deposited excretal N, whilst on the ExpOWPs, these represented 66%. 3.4. Animal production No significant differences (P > 0.05) in silage intake were observed between treatments on the ExpOWPs. Average daily silage intake of 7.9 kg DM steer−1 was higher than the 5.0 kg DM steer−1 reported by Boyle et al. (2008) for dairy heifers on OWPs, but lower than the 10.9 kg DM steer−1 found by French et al. (2004) for steers accommodated on OWPs. Earley and Prendiville (2008) observed that beef cattle on OWPs had a daily silage intake of 10.1 kg DM (Table 7). The greatest daily live-weight gain (DLWG) on the ExpOWPs was obtained on the finest grade surface layer (sawdust) with 1.44 kg steer−1 d−1 , while the lowest was on the 5–10 cm woodchip with 1.17 kg steer−1 d−1 (Table 7). Overall average DLWG was 1.33 kg d−1 steer−1 , which compares favourably with animal performance on OWPs reported elsewhere, although DM silage intake was lower on the ExpOWPs (7.9 kg d−1 steer−1 DM) than for other studies on beef cattle, e.g., by Earley and Prendiville (2008) and Hickey et al. (2002) (10.1 and 10.2 kg d−1 , respectively). 4. Conclusions Effluent quality data from both the experimental out-wintering pads and the farm-based out-wintering pads were consistent with findings in the literature. The nutrient content of the out-wintering pad effluent was, throughout these studies, consistent with dirty water rather than cattle slurry and appeared unaffected by the experimental treatments. Nonetheless, these effluents must be contained and carefully recycled to land, to avoid environmental pollution. Data from the ExpOWPs showed that these facilities provided animal welfare and production benefits (average daily live weight gain of 1.33 kg d−1 steer−1 ). Ammonia emission rates from the ExpOWPs were unaffected by the experimental treatments. The average emission rates from the ExpOWPs and the ComOWPs (2.5 and 1.0 g NH3 -N m−2 d−1 , respectively) was lower than that previously reported for beef cattle on concrete yards (4.5 g NH3 -N m−2 d−1 ). There was evidence of a strong relationship between ammonia emission and wind speed, suggesting that design features to minimise wind speed across OWPs may be an effective mitigation method. Significant retention of effluent volume by the woodchip was observed, indicating that a substantial reduction in the volume of effluent drainage from OWPs is to be expected. This should have a significant impact on OWP effluent storage and management

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