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Tracking Nutrients in Outdoor Piggery Systems

Final Report

APL Project 2011/1011.416

December 2014

FSA Consulting

S.G. Wiedemann

PO Box 2175

Toowoomba QLD 4350

Australia

i

Acknowledgements

This project is supported by funding from Australian Pork Limited and the Department of Agriculture.

The authors wish to thank the contributing pig operators for their participation and assistance during

the project. Technical assistance with soil sample collection and soil sample data collation by Michael

O’Keefe and Justin Galloway was appreciated.

ii

Executive Summary

This study aimed to quantify nutrient deposition, accumulation and distribution in rotational free range

pig farming paddocks over a three year time period, coinciding with the pig farming phase or the

cropping phase. The impact of novel management practices and methods to improve nutrient

distribution, such as frequent moving of shelters, feeders and waterers, was quantified using electro-

magnetic (EM) mapping technology and spatial soil sampling based on apparent soil electrical

conductivity (ECa). Soil nutrients were found to increase significantly in the surface and sub-soil within

one year of introducing pigs. Mean soil available P levels exceeded upper environmental threshold

levels of 85 mg/kg after one year, and sub-soil (60cm depth) nitrate N levels also exceeded threshold

levels of 4 mg/kg after one year of pig farming. Nutrient distribution was improved by moving shelters,

as evidenced by the changing pattern of nutrients from year to year and the increase in minimum

nutrient levels across each outdoor area during the pig phase.

However, nutrients were still found to be distributed in a non-uniform pattern defined by the location

of shelters, feeders and waterers, and this pattern corresponded to mapped ECa. Strong regression

relationships were observed between ECa and nutrients of interest including nitrate, available

phosphorus and potassium, allowing these nutrients to be mapped. Nutrient hotspots corresponded

to the location of shelters, feeders and waterers, where nutrient levels were up to 6 times higher than

mean levels for the whole paddock.

Management strategies to improve nutrient distribution were successful in increasing the distribution

of key nutrients across the range areas. This resulted in minimum nutrient levels increasing from

deficient levels to adequate levels, providing confidence to reduce fertiliser applications in subsequent

crop phases. Soil profile nitrate, and available phosphorus levels were sufficient for subsequent crop

farming at both sites without additional fertiliser, though nitrate leaching through the soil profile may

limit the amount of nitrate available. However, nutrient levels in the hotspots were sufficient for many

years of cropping, after only one pig phase. Successful utilisation of these nutrients would require

specialist management techniques.

Considering the high nutrient accumulation rates and low levels of ground cover, further research is

required to quantify the environmental risk from these systems in different regions, and to provide

more suitable management practices that can meet minimum environmental thresholds.

iii

Table of Contents

Acknowledgements ........................................................................................................................................... i

Executive Summary .......................................................................................................................................... ii

1 Introduction ................................................................................................................................................... 1

1.1 Objectives of the Research Project ..................................................................................... 2

2 Methodology .................................................................................................................................................. 3

2.1 Farms Surveyed ........................................................................................................................ 3 2.1.1 Farm One ....................................................................................................................... 3 2.1.2 Farm Two ....................................................................................................................... 5

2.2 Nutrient Inputs and Deposition ........................................................................................... 7

2.3 Soil Monitoring – Nutrient Accumulation and Movement ............................................. 7

2.4 EM Survey and Soil Mapping .................................................................................................. 7

2.5 EM Survey and Soils Data Analysis ....................................................................................... 8

3 Results ............................................................................................................................................................. 9

3.1 Nutrient Deposition ................................................................................................................ 9

3.2 Soil Nutrient Accumulation and Movement ...................................................................... 9 3.2.1 Farm One – Monitoring Sites .................................................................................... 9 3.2.2 Farm One – Nutrient Distribution Dataset ......................................................... 10 3.2.3 Farm Two – Monitoring Sites .................................................................................. 11 3.2.4 Farm Two – Nutrient Distribution Dataset ........................................................ 12

3.3 Spatial Distribution of Nutrients ........................................................................................ 13 3.3.1 Apparent Soil Conductivity ...................................................................................... 13 3.3.2 Spatial Distribution of Nutrients – Farm One ..................................................... 16 3.3.3 Spatial Distribution of Nutrients – Farm Two .................................................... 19

4 Discussion ..................................................................................................................................................... 25

4.1 Nutrient Accumulation and Distribution ......................................................................... 25

4.2 Environmental Risk ................................................................................................................ 26

4.3 Mitigating Risk ......................................................................................................................... 27

5 Conclusions and Recommendations ...................................................................................................... 28

5.1 Conclusions ............................................................................................................................. 28 5.1.1 Pig Phase ....................................................................................................................... 28 5.1.2 Crop Phase ................................................................................................................... 28

5.2 Recommendations ................................................................................................................. 29 5.2.1 Further analysis of impacts from outdoor pig farming ...................................... 29 5.2.2 Demonstration of more effective management practices ................................ 29

6 References .................................................................................................................................................... 30

1

1 INTRODUCTION

Free range systems are often promoted on the basis of improved animal welfare and environmental

performance compared to conventional pork production. However, little scientific research has been

undertaken in relation to the environmental performance of free range piggeries in Australia,

particularly in terms of soil nutrient levels.

Pigs excrete a large proportion of the nutrients that they ingest as manure, which requires careful

management to ensure nutrients are not lost to the environment. Where stocking densities are high,

a simple assessment of nutrients added from manure typically shows additions to be well in excess of

nutrient removal (Watson et al. 2003, Zadow et al. 2010). However, simple tools such as nutrient

balances do not take into account variability in nutrient distribution within a free range area and their

appropriateness for assessing environmental impacts from these systems has been questioned

(Watson et al. 2003).

Nutrient distribution is highly variable in areas grazed by outdoor pigs (Galloway 2011, Galloway &

Wiedemann 2011, Horta et al. 2011, Quintern & Sundrum 2006, Salomon et al. 2007, Watson et al.

2003). Watson et al. (2003) demonstrated that soil nitrogen (N) and phosphorus (P) levels around

drinkers, feeders and huts could exceed saturation levels after only 15 months of outdoor housing.

Horta et al. (2011) also demonstrated that elevated soil P levels occur in specific parts of the outdoor

area, leading to elevated P losses in runoff.

Studies by Watson et al. (2003) and Salomon et al. (2007) showed that the vast majority of nutrients

are deposited in 4-24% of the area available to the pigs, corresponding to the location of feed, water

and shelter points. Variable deposition of manure nutrients has also been found in poultry (Kratz et

al. 2004) and dairy cattle systems (Fu et al. 2010).

From a review of Australian and international literature, Tucker (2011) concluded that nutrient

accumulation leads to higher risks of nutrient loss and that variable deposition must be managed to

ensure reduce this risk. Management of total nutrient deposition and variable deposition patterns

have been included in environmental guidelines for Australian rotational and outdoor piggeries (Tucker

& O’Keefe 2013) but few studies have quantified if the recommended strategies are effective in

mitigating the risk of nutrient losses. The present study investigated the impact of total nutrient

deposition and the variability of nutrient deposition on nutrient accumulation and the risk of nutrient

loss for rotational outdoor piggeries over a three year period to provide quantitative data on the

effectiveness of these management practices.

Most studies have investigated variable nutrient distribution using a stratified sampling strategy (i.e.,

Horta et al. 2011, Salomon et al. 2007, Watson et al. 2003), typically separating feeding, housing and

grazing areas. While such strategies are beneficial, establishing the correct boundaries required

detailed records of animal defecation (Salomon et al. 2007) or were based on qualitative visual

measures (Watson et al. 2003). These approaches are either highly intensive in the case of the first,

or imprecise in the case of the second.

As an alternative to these methods, electro-magnetic induction (EM) soil mapping has been proposed

as a method for rapidly assessing spatial variability of soil properties (Corwin & Lesch 2005b).

Interest in applying EM technology to agriculture began with soil salinity research (Corwin & Lesch

2003) but has since expanded to include assessment of nutrients, organic matter and physical soil

properties (Corwin & Lesch 2005a).

The diverse range of applications for EM technology stem from the range of factors driving apparent

soil electrical conductivity (ECa). These factors are highly site-specific, and it is likely that only one or

two factors are the primary drivers of ECa on a specific site (Corwin & Lesch 2005a, Johnson et al.

2

2005). Hence ECa can be used to explain the spatial distribution of the dominant driving soil property

once an association between ECa and the given soil parameter has been established. This requires

ground truthing of the surveyed field by taking soil samples across a range of ECa measurements and

chemically analysing these to determine which soil parameters provide a positive correlation.

Soil surveying using EM has been used to demonstrate non-uniformity in effluent (Woodbury et al.

2003, Woodbury et al. 2005) manure utilisation areas (Eigenberg et al. 2002 , Eigenberg & Nienaber

1998, Eigenberg et al. 2006). Eigenberg and Nienaber (2003) also applied EM soil surveying to assess

soil nutrient levels at an abandoned manure-handling site and were able to map nitrate leaching to a

considerable depth using this approach. Provided non-related parameters such as soil texture,

moisture, temperature and unrelated salinity effects are relatively constant across the sampling area,

EM soil surveying can provide strong correlations with manure and effluent reuse or dispersal, allowing

these trends to be mapped via interpolation from correlated soil analysis with measured ECa.

Australian research by Wiedemann and Zadow (2010) and Galloway and Wiedemann (2011) have

demonstrated that nutrient distribution in poultry and pig free range areas can be identified using EM

mapping and targeted soil sampling strategies. Galloway and Wiedemann (2011) showed that elevated

nutrient levels were evident around shelters, feeding and watering areas on Australian outdoor farms,

with nutrient levels exceeding recommended thresholds in the National Environmental Guidelines for

Outdoor Rotational Piggeries (Tucker & O’Keefe 2013). The results suggest that nutrient deposition

rates are too high for long-term use without paddock rotation. This study provided snap-shot results

only and did not investigate the impact of free range pig farming over an extended period of time,

where management effects could be more fully investigated.

The project reported here extends this research with the view of establishing a clear understanding

of nutrient distribution and change over time at free range piggeries under different management

practices. Specific objectives are listed below.

1.1 Objectives of the Research Project

The four objectives of the project are outlined below.

Objective 1: To collect long term data on the levels and distribution of nutrients in the soil profiles

of outdoor pig paddocks.

Objective 2: To relate data on the levels and distribution of nutrients in outdoor pig paddocks to

environmental risk.

Objective 3: To assess the impact of changed management practices on nutrient loading and

distribution over an extended period.

Objective 4: To provide outdoor piggery operators with recommended best management

practices for nutrient management in outdoor piggeries.

The outcomes of the project include:

Annual soil nutrient mapping and soil profile nutrient analysis data showing the levels and

distribution of nutrients at two outdoor piggeries over three consecutive years.

A report detailing the soil mapping and analysis results; details of land use over that time

period (pig phase/cropping phase and estimated nutrient additions and removals);

interpretation of the findings in terms of environmental risk; and recommendations

concerning best practices for managing nutrients in outdoor piggery paddocks.

3

2 METHODOLOGY

2.1 Farms Surveyed

Two outdoor piggeries located in southern NSW (piggery 1) and southwest Victoria (piggery 2) were

selected, and research was conducted over three years from 2012 to 2014. At piggery one, the

surveyed site was used for grower-finisher pigs while at piggery two, the site was used for breeder

pigs.

2.1.1 Farm One

Farm one operates an outdoor rotational grower unit, with a 1 ½ year pig phase and approximately a

five year cropping phase. Paddocks are designed in a novel ‘checker board’ pattern (see Photograph

1). Two paddocks were selected for the trial (see Photograph 2). Both paddocks were recently

established for pig farming in an area previously used for cropping. Each paddock was approximately

1 hectare and was divided into two. Each half was stocked with 100 grower pigs for a total of 17 weeks

from wean to finish, then spelled for 17 weeks while the alternative half of the paddock was stocked.

The total pig stocking phase was 68 weeks, during which each half of the paddock was stocked for 34

weeks. When averaged over the whole pig phase, the stocking rate was 50 pigs per hectare. During

the stocking period, the pigs were confined in a small run area for the first weeks, then allowed to

range until finishing.

To aid nutrient distribution, houses, feeders, waterers and wallowing areas were moved around the

paddock frequently. The trial assessed the effectiveness of this approach for improving nutrient

distribution, and assessed the impact of nutrient deposition on soil nutrient accumulation over the

whole pig phase and into the first part of the cropping phase.

Paddock Three.

Showing mosaic paddock design with the

eastern side stocked and western side

unstocked. Annual monitoring points shown.

Paddock Four.

Prior to stocking with pigs. Annual monitoring

points shown.

PHOTOGRAPH 1: PIGGERY ONE SHOWING AN AERIAL VIEW OF PADDOCK THREE AND FOUR SHOWING LONG-TERM MONITORING

POINTS

4

Paddock Three.

Top to bottom – showing first housing location

and centre fence with one side stocked (image

1) and after stocking both sides (image 2). Image

3 shows damage from wallows.

Paddock Four.

Top to bottom – showing first housing location

at bottom end of paddock (image 1). Image 2

shows new housing location in the centre of the

paddock. Image 3 shows movable shelter, water

point and feeder.

PHOTOGRAPH 2: PIGGERY TWO SHOWING PADDOCKS THREE AND FOUR OVER THE TRIAL PERIOD

5

2.1.2 Farm Two

Farm two operates an outdoor breeding facility using a traditional ‘wagon wheel’ type paddock design.

The piggery accommodates sows in outdoor pens, with weaner pigs transferred to a deep litter

housing facility at 27 days of age. The piggery comprises both farrowing and gestating paddocks.

Farrowing paddocks house six sows (one per hut) and are approximately 0.3-0.4 ha in size. The

gestating sow paddocks are set out in a wagon wheel configuration, with one wheel having eight

spokes. Stocking density is similar for both farrowing and gestating sows and is approximately

18 sows/ha.

The property has been operating as a free range farm for more than 10 years. The study was

conducted in two gestating sow paddocks, known as Paddock five and Paddock six.

Paddock five was 1.8 ha, and was at the start of the pig rotation when the trial began (Photograph 4).

The paddock was continuously stocked with 29 dry sows during the trial. Houses were moved short

distances every 6 months, and the feeding point was moved approximately each 6 months to aid

nutrient distribution.

Paddock six was 1.35 ha and was at the end of the pig rotation and the start of the crop rotation at

the start of the trial. The paddock was cropped during the trial. The first survey was immediately after

pigs had been removed from the site. After this, the site was rehabilitated using a levelling bar to

distribute top soil. Paddocks were then cultivated and sown to crops.

Photographs are shown below of the two free range farms surveyed as part of the project.

PHOTOGRAPH 3: PIGGERY TWO (PADDOCK FIVE) SHOWING LONG-TERM MONITORING POINTS

SW corner

6

Paddock Five.

South west corner (see Photograph 4). From

top to bottom, Year one (June), Year two

(January), Year two (July). Note change in feeder

type (trough in first picture, self-feeders in

second two pictures) and feeder location.

Paddock Six.

From top to bottom, Year one (June)

immediately after pigs removed. Year one

(December) with Brassica crop. Year two

(September) cereal hay crop prior to cutting.

PHOTOGRAPH 4: PIGGERY TWO – PADDOCK FIVE AND SIX

Feeder - troughs

Self-feeder – north of houses

Self-feeder – south of houses

7

2.2 Nutrient Inputs and Deposition

The mass of nutrients excreted by pigs was estimated using standard excretion rates from APL (2010)

which were derived from the mass balance model PIGBAL (Casey et al. 2000). Total nutrient

excretion was determined from standard excretion rates multiplied with records of livestock stocking

rates on each farm. Records or estimates of bedding using in the shelters were also maintained and

used to determine total nutrient inputs at each site.

2.3 Soil Monitoring – Nutrient Accumulation and Movement

Four nutrient monitoring points on each paddock were established in the first year of the trial using

points from the EM survey that provided a distribution of points across the site based on underlying

soil properties. These monitoring points were returned to and sampled in each year of the

experiment. Sampling was carried out at 0-10cm and 20-30cm in all years.

Additional soil nutrient monitoring was conducted using the soil analysis dataset collected annually for

the nutrient distribution analysis. This dataset provided 12 points selected at points determined by

the EM survey to interpret the variability in ECa across each paddock and were therefore not randomly

sampled. However, the same selection criteria was applied each year, providing a consistent strategy

for sampling to take into account the maximum variability across the site. As a result, variation in the

dataset was high, making statistical analysis difficult but mean values were deemed to be a reasonable

representation of each paddock in each year.

2.4 EM Survey and Soil Mapping

The EM soil surveys were carried out using an EM38-MK2 (Geonics Ltd) operated in the vertical plane,

mounted on a non-ferrous sled (see Photograph 5) to enable sampling at close to the soil surface when

towed behind an all-terrain vehicle (ATV). The EM38-MK2 provided measurement of ECa using dual

coil spacing’s of 0.5 m and 1.0 m concurrently. This provides sampling depths of approximately 0.75 m

and 1.5 m.

8

PHOTOGRAPH 5: GEONICS EM38-MK2 MOUNTED ON SLED

General operation protocol followed Corwin and Lesch (2005b) and O’Leary and Peters (2006). The

EM survey was conducted using an ATV at an average ground speed of approximately 10 km/hr.

Transect widths between 2 and 10 m were used depending on the size of the area surveyed. Positional

data were logged using a GPS at intervals of approximately 1 second. An Allegro data logger was used

as a data receiver for the GPS unit and EM38-MK2. Apparent conductivity data were processed using

the ESAP-RSSD program (Lesch et al. 2000) which was used to identify soil sampling points (n=12)

based on the variability of ECa across the sampling transect. Soil samples were collected at 0-10cm,

20-30cm and 50-60cm. At each soil sampling site, 2-3 soil cores were taken within a one metre radius

to minimise localised variability. Soil samples were analysed for nitrogen, nitrate-N, phosphorus,

Colwell phosphorus, Olsen phosphorus, potassium, organic matter, Cation exchange capacity (CEC),

exchangeable sodium percent, chloride, and electrical conductivity by SGS Agritech in Brisbane, a

NATA accredited laboratory. Results are presented for major nutrients only.

2.5 EM Survey and Soils Data Analysis

Apparent conductivity and soil analysis results were analysed using multiple linear regression (MLR) in

ESAP-Calibrate (Lesch et al. 2000). Based on the regression analysis, nutrient mapping was conducted

using ESAP-SaltMapper (Lesch et al. 2000). Spatial distribution maps were developed based on the

MLR of specific soil parameters and ECa on each paddock, in each year. Significant regressions with

R2 values exceeding 0.5 were mapped.

Nutrient monitoring data were analysed using analysis of variance (ANOVA) between means for each

year, and significant differences were determined using the least significant difference (L.S.D) test at

the 90% and 95% confidence level.

9

3 RESULTS

3.1 Nutrient Deposition

Predicted nutrient deposition rates based on pig production data supplied by the farms is shown in

Table 1. Nutrient deposition rates were around 2.5 times higher on farm one because of the high

stocking rate.

TABLE 1. ANNUAL NUTRIENT DEPOSITION RATES ESTIMATED FROM MANAGEMENT RECORDS

Farm One

Farm Two

Manure

Nitrogen (kg.ha.yr) 625 236

Phosphorus (kg.ha.yr) 203 88

Potassium (kg.ha.yr) 163 63

Bedding

Nitrogen (kg.ha.yr) 7 123

Phosphorus (kg.ha.yr) 1 14

Potassium (kg.ha.yr) 16 272

Total

Nitrogen (kg.ha.yr) 632 359

Phosphorus (kg.ha.yr) 204 103

Potassium (kg.ha.yr) 179 335

3.2 Soil Nutrient Accumulation and Movement

3.2.1 Farm One – Monitoring Sites

Analysis of the monitoring sites over three years at the grower site on Farm one showed significant

increases in nutrient levels for most parameters. Total P (0-10cm) and available P (0-10, 20-30cm)

increased significantly in the first year after pigs were first introduced, and levels remained elevated

into the third year, though a trend toward reducing levels (not significant) was observed between the

second and third year. The significant increase in available P at the 20-30cm depth in year two and

three demonstrates phosphorus movement through the profile, suggesting deposition rates exceed

the soil buffering capacity, though this was not directly measured.

Soil nitrogen results showed a significant increase in nitrate-N (0-10, 20-30cm) between year one and

year two. A similar, though not significant trend appeared with total nitrogen levels. In contrast to

soil P, a significant decline in nitrate-N was observed in year three at both soil depths.

10

TABLE 2. AGGREGATED MEAN NUTRIENT LEVELS MEASURED OVER THREE YEARS FROM FIXED MONITORING POINTS ON TWO FREE

RANGE PADDOCKS AT FARM ONE

SOIL SAMPLING IN YEAR ONE OCCURRED PRIOR TO THE INTRODUCTION OF PIGS. PIGS WERE STOCKED FOR 18 MONTHS AND THEN

REMOVED 3-6 MONTHS PRIOR TO SAMPLING IN YEAR THREE.

Phosphorus

(total -

mg/kg)

Colwell

Phosphorus

(available - mg/kg)

Nitrogen

(total -

mg/kg)

Nitrate N (mg/kg) Potassium (mg/kg)

0-10cm 0-10cm 20-30cm 0-10cm 0-10cm 20-30cm 0-10cm 20-30cm

Year one 285.5 45.2 5.8 892.2 22.3 4.7 263.9 242.4

Year two 421.9** 118.3** 21.4** 1106.2 67.5** 20.3** 595.2** 335.3

Year

three 384.4** 101.3** 16.5** 1109.0 25.2 10.7 450.3** 372.2

L.S.D 80.1 32.3 8.3 20.0 7.2 94.2

* Indicates significant difference compared to year one for the same depth, at the 90% confidence level

** Indicates significant difference compared to year one for the same depth, at the 95% confidence level

3.2.2 Farm One – Nutrient Distribution Dataset

The nutrient distribution soil sampling dataset (Table 3) was determined from 12 points collected

annually based on the ESAP RSSD design. This was primarily collected to determine nutrient variability,

but also provided a second dataset for determining mean total nutrient accumulation, reported here.

The change in nutrient levels between years followed the same general trend as the fixed monitor

points. Surface nutrient levels increased significantly for all indicators, with the exception of nitrate-

N at both sites, with the increase mainly being between year one and two. High nutrient levels were

sustained into the third year, after the paddocks were destocked, for most indicators. Nitrate N levels

were followed a trend towards higher levels in the sub-soil depths, but significant differences could

not be determined because of the the high variability in the dataset.

Interestingly, sparingly soluble nutrients such as P were found to increase significantly to 30 cm depth

on both paddocks, and to 60 cm depth on paddock four. Potassium levels were found to increase

significantly in the surface and 20-30 cm depths across both paddocks. In contrast to the soil

monitoring points, total P was found to decline in the third year to levels similar to year one on

paddock three. This result may have been anomalous, or may indicate P losses from the surface soil

via other pathways such as erosion and runoff.

11

TABLE 3: SOIL NUTRIENT PROPERTIES FOR PADDOCK THREE AND FOUR – FARM ONE

ANNUAL SOIL SAMPLING STRATEGY DETERMINED FROM THE ESAP RSSD DESIGN BASED ON ECA (N=12).

Soil

depth

(cm)

Nitrogen (mg/kg)

Nitrate-N

(mg/kg)

Phosphorus

(mg/kg)

Colwell Phosphorus

(mg/kg) Potassium (mg/kg)

mean S.D mean S.D mean S.D mean S.D mean S.D

Paddock three

Year

one 0-10 806.0 167.8 35.2 29.5 338.1 56.0 61.8 19.2 284.3 69.8

20-30 5.8 3.9 7.6 3.1 248.4 36.1

50-60 3.3 1.4 7.8 12.1 241.3 50.9

Year

two 0-10 1112** 202.6 56.0 37.9 436.6** 96.8 92.3** 40.9 627.4** 384.2

20-30 20.7 20.3 16.75** 7.6 340.5** 135.9

50-60 10.3 16.9 7.4 4.0 282.1 90.3

Year

three 0-10 1233.3** 323.4 32.7 39.0 316.1 47.6 49.5 22.3 364.8 52.6

20-30 17.8 24.2 11.4 4.7 319.7 50.2

50-60 12.5 9.3 5.3 1.7 258.8 60.6

Paddock four

Year

one 0-10 957.6 57.3 8.2 3.9 296.3 50.0 44.9 13.7 256.8 53.7

20-30 2.0 0.9 6.1 3.3 249.9 49.5

50-60 1.9 1.1 4.7 0.9 307.9 93.2

Year

two 0-10 1153.8** 303.5 83.6 122.0 436.6 96.8 100.7** 42.9 659.3** 398.0

20-30 23.3 41.4 16.3** 7.4 417.5** 192.7

50-60 14.1 31.6 8.5** 4.3 438.6 207.9

Year

three 0-10 1188.1** 208.1 70.5 78.3 901.7* 1101.7 96.1** 63.1 506.1** 320.0

20-30 23.1 39.6 12.9** 7.0 388.5** 203.0

50-60 7.3 6.2 7.7** 2.1 391.3 198.6

* Indicates significant difference compared to year one for the same depth, at the 90% confidence level ** Indicates significant difference compared to year one for the same depth, at the 95% confidence level

3.2.3 Farm Two – Monitoring Sites

Analysis of the monitoring sites over three years at the breeder facility on Farm two showed significant

increases in Total P (0-10cm) and available P (0-10cm).

Soil nitrogen in the surface tended to increase (P=0.07) from year one to year two, as did soil organic

matter (P=0.08). No significant changes were observed in nitrate N or potassium levels across the

three years. Mean levels of available P and nitrate-N were high compared to crop or pasture

requirements, particularly in year two and three.

12

TABLE 4. MEAN NUTRIENT LEVELS MEASURED OVER THREE YEARS FROM FIXED MONITORING POINTS ON TWO FREE RANGE

PADDOCKS AT FARM TWO

SOIL SAMPLING IN YEAR ONE OCCURRED AT THE START OF THE PIG PHASE FOR PADDOCK FIVE AND AT THE START OF THE CROPPING

PHASE FOR PADDOCK SIX

Phosphorus

(total -

mg/kg)

Colwell

Phosphorus

(available - mg/kg)

Nitrogen

(total -

mg/kg)

Nitrate N (mg/kg) Potassium (mg/kg)

0-10cm 0-10cm 20-30cm 0-10cm 0-10cm 20-30cm 0-10cm 20-30cm

Paddock five

Year one 297.8 17.3 3.8 1200.0 20.3 7.0 127.3 148

Year two 299.8 94.3 8.3 1237.5 121.5** 22.3 136.3 104.3

Year

three 359 81.8 6.3 1572.5 144.5** 19.5 261.5 138.3

Paddock six

Year one 356.8 101.3 30.0 802.5 105.5 63.8 127.3 225.5

Year two 370.5 111.8 37.3 1390.0** 84.5 28.0 136.3 193.3

Year

three 544.3** 189.5* 33.8 1079.8 55.5* 8.5 261.5 220

* Indicates significant difference compared to year one at the 90% confidence level

** Indicates significant difference compared to year one at the 95% confidence level

3.2.4 Farm Two – Nutrient Distribution Dataset

The change in nutrient levels between years followed the same general trend in the nutrient

distribution dataset (Table 5) as the fixed monitor points. On paddock five, surface nutrient levels

increased significantly in the first year for all indicators with the exception of total P, and remained

elevated into the third year for most indicators with the exception of total N. The static total P values

were unexpected considering the nutrient deposition levels, and suggest that losses may have occurred

via other pathways such as runoff or erosion. This may also explain the reduction in total N in the

third year despite continued nitrogen additions in the form of manure.

Nitrate N levels were significantly higher than the baseline year at both the 20-30cm and 50-60cm

depths in year’s two and three, indicating movement through the soil profile.

Results for paddock six followed a similar trend to the fixed monitoring point dataset. Nutrient levels

tended to decline in year two (not significant), and nitrate-N levels were observed to decline in year

three at all depths. However, in year three nutrient levels increased, with both total N and total P

being significantly higher than the baseline year.

13

TABLE 5: SOIL NUTRIENT PROPERTIES FOR PADDOCK FIVE AND PADDOCK SIX – FARM TWO

ANNUAL SOIL SAMPLING STRATEGY DETERMINED FROM THE ESAP RSSD DESIGN BASED ON ECA (N=12).

Soil

depth

(cm)

Nitrogen (mg/kg) Nitrate-N (mg/kg)

Phosphorus

(mg/kg)

Colwell

Phosphorus

(mg/kg)

Potassium

(mg/kg)

mean S.D mean S.D mean S.D mean S.D mean S.D

Paddock five

Year

one 0-10 1113.3 118.5 25.6 36.1 291.5 64.8 17.8 7.3 140.6 100.4

20-30 6.3 4.7 3.3 1.5 137.6 55.1

50-60 4.3 3.2 1.7 1.4 183.0 50.9

Year

two 0-10 1335** 311.1 124.3** 43.7 296.6 112.7 75.5** 44.4 224.1* 88.2

20-30 36.3** 33.6 10.8 15.7 173.6 39.0

50-60 12.8** 4.9 2.3 1.6 215.2** 22.8

Year

three 0-10 1016.7 127.4 119.5** 45.2 286.8 72.7 70.1** 35.5 190.8* 60.2

20-30 35.1** 17.9 4.6 2.2 111.8 37.9

50-60 13.0** 10.9 3.6 3.9 133.1** 19.7

Paddock six

Year

one 0-10 880.2 117.8 107.6 44.8 408.2 279.2 115.2 91.1 301.3 187.2

20-30 50.3 51.7 30.9 36.9 216.4 92.9

50-60 21.5 15.3 8.7 8.7 216.8 31.8

Year

two 0-10 1104.0 130.9 87.2 33.5 302.0 101.6 89.4 45.3 398.5 151.1

20-30 25.3 8.5 22.3 12.6 247.3 91.1

50-60 16.0 7.4 14.8 14.1 232.3 70.5

Year

three 0-10 1270.3* 665.5 64.3** 45.5 587.5** 435.6 191.2 180.5 432.2 268.2

20-30 16.5** 13.2 27.7 23.3 162.8 68.4

50-60 4.5** 6.5 3.9 5.8 135.3 21.5

* Indicates significant difference compared to year one for the same depth, at the 90% confidence level

** Indicates significant difference compared to year one for the same depth, at the 95% confidence level

3.3 Spatial Distribution of Nutrients

3.3.1 Apparent Soil Conductivity

Figure 1 and Figure 2 show the ECa over three years for all paddocks, together with the location of

pig shelters and soil sampling points. Because of differences in soil moisture, the scale of the ECa

levels are not equivalent between sites or between years. However, the variability in ECa is indicative

across years and typically corresponded closely with the location of shelters, water points and feeding

points, where defecation is likely to be highest.

14

Paddock Three.

Apparent Soil Conductivity. From top to bottom: 2012,

2013, 2014

Paddock Four.

Apparent Soil Conductivity. From top to bottom: 2012, 2013,

2014

Figure 1. Apparent Soil Conductivity on Paddock three and four showing soil sampling points ( ) and animal house ( )

and location– Farm One

15

Paddock Five.

Apparent Soil Conductivity. From top to bottom: 2012,

2013, 2014

Paddock Six.

Apparent Soil Conductivity. From top to bottom: 2012, 2013,

2014

Figure 2. Apparent Soil Conductivity on Paddock five and six showing soil sampling points – Farm Two

16

3.3.2 Spatial Distribution of Nutrients – Farm One

Baseline (2012) nutrient variability was not significantly correlated with ECa on either paddock at farm

one, but was dominated by natural soil characteristics, principally CEC and EC. This confirmed that

baseline nutrient conditions displayed no strong distribution pattern as a result of previous paddock

management and provided confidence that strong patterns in nutrient distribution following stocking

with pigs could be associated with pig management. Results from years two and three showed

significant regression relationships between ECa and surface available P (Figure 3), sub-soil nitrate N

(Figure 4), total soil profile nitrate (Figure 5) and potassium (Figure 6) across both paddocks. Significant

regression relationships between total nitrogen and phosphorus were only evident in some years

across the two paddocks (maps not shown). Available P levels were highest in the second year on

both paddocks (Figure 3), with around 30% of the paddocks reaching levels exceeding 100 mg/kg

Colwell P. These nutrient hotspot areas were approximately 50% higher than the mean nutrient level

for the paddock (see Table 3) with the highest measured levels being twice the paddock mean (data

not shown). Elevated levels in the second year corresponded to the first year of stocking with pigs,

before declining in the third year, particularly on paddock three. Nutrient distribution was found to

be high around the location of shelters, feed and water points, though levels were also elevated across

the whole paddock suggesting that management practices such as moving shelters, feeders and

waterers was reasonably effective in dispersing nutrients.

Paddock Three

Surface (0-10cm) sample depth. From top to bottom:

2013, 2014

Paddock Four

Surface (0-10cm) sample depth. From top to bottom: 2013,

2014

Figure 3. Distribution of Colwell P measured over two years at Farm One

17

Nitrate N levels were assessed at all depths but are shown here for the bottom of the root zone (50-

60cm – Figure 4) as an indication of environmental risk from nutrient leaching. Nitrate N levels at

depth increased significantly over the trial period, and high levels were strongly associated with the

location of housing on both sites. Nitrate-N levels exceeded 50mg/kg in hotspots on both paddocks,

or up to six times the mean levels, and large areas exceeded 25 mg/kg in paddock four. The distribution

of subsurface nitrate was found to change substantially on paddock four in particular, most likely in

response to the changed location of infrastructure over the trial. The reduction in nitrate-N levels

over some areas may also be in response to leaching below the sampling depth, considering paddock

records indicated little pasture growth during the pig stocking phase.

Paddock Three

Sub-soil (50-60cm) sample depth. From top to bottom:

2013, 2014

Paddock Four

Sub-soil (50-60cm) sample depth. From top to bottom: 2013,

2014

Figure 4. Distribution of subsoil nitrate-N over two years at Farm One showing paddock three and paddock

four

18

Total profile Nitrate N levels (to 60cm – Figure 5) ranged from below 100 kg N / ha to well above

500 kg N / ha, with levels increasing across the site over the two years. Elevated nitrate N levels

throughout the soil profile corresponded to the location of shelters, resulting in hotspots exceeding

500 kg N / ha, or approximately enough for two-three years of crop production. Considering the

high levels of nitrate N at the bottom of the root zone and the likely high levels of leaching between

year two and three, it is expected that a large proportion of this available N would be deep in the soil

profile by the subsequent cropping cycle.

Paddock Three

Surface (0-10cm) sample depth. From top to bottom:

2013, 2014

Paddock Four

Surface (0-10cm) sample depth. From top to bottom: 2013,

2014

Figure 5. Distribution of total estimated nitrate-N in the soil profile (kg/ha to 60cm) over two years at Farm One

showing paddock three and paddock four

19

Soil potassium levels (Figure 6) followed a similar distribution pattern to phosphorus and nitrogen,

with concentrated nutrient hotspots being co-located with shelters, feeders and waterers. Potassium

levels were found to increase significantly in the first year, but then appear to decline in the surface

soil over large parts of the paddocks. Analysis of the soils data at depth indicated movement of

potassium beyond the surface soil.

Paddock Three

Surface soil (0-10cm) sample depth. From top to

bottom: 2013, 2014

Paddock Four

Surface soil (0-10cm) sample depth. From top to bottom:

2013, 2014

Figure 6. Distribution of Potassium over two years at Farm One showing paddock three and paddock four

3.3.3 Spatial Distribution of Nutrients – Farm Two

At farm two, significant regression relationships were identified between nutrient levels and ECa in

the baseline year on paddock five, which corresponded to the paddocks having been stocked with pigs

some months prior to the trial being initiated. Results from years two and three showed significant

regression relationships between ECa and surface available P (Figure 3), sub-soil nitrate N (Figure 4),

total soil profile nitrate (Figure 5) and potassium (Figure 6) across both paddocks and elevated nutrient

levels corresponded to known management factors such as the location of shelters, water and feed

points. Significant regression relationships between total nitrogen and phosphorus were only evident

in some years across the two paddocks (maps not shown).

20

Distribution of available P in the surface soil over three years for paddock five is shown in Figure 7,

showing large increases in available P levels, and concentration of nutrients at towards the location

of shelters and feed/water points. Maximum nutrient levels in the first year were 63% higher than

the mean. In the second and third years, maximum levels in hotspot areas were more than twice

the mean for the paddock.

Figure 7. Distribution of Colwell P measured in the surface soil over three years on Paddock five at Farm Two

21

Distribution of nitrate N is shown in the surface soil over three years for paddock five is shown in

Figure 8. Nutrient levels contrast strongly between the two paddocks, with levels increasing across

paddock five (pig phase) and decreasing across paddock six (during the cropping phase where two

crops were grown. Nitrate levels increased across a large proportion of paddock five rapidly, and

remained elevated in the second and third year. Maximum nutrient levels were almost twice the mean

on paddock five in year three.

Paddock Five.

From top to bottom: 2012, 2013, 2014 (pig phase)

Paddock Six.

From top to bottom: 2012, 2013, 2014 (crop phase)

Figure 8. Distribution of Nitrate nitrogen measured in the surface soil over three years at Farm Two showing paddock

five and six

22

Total profile Nitrate N levels (to 60cm – Figure 9) ranged from below 100 kg N / ha across most of

the paddock (paddock five) at the start of the pig phase, increasing to between 300-500 kg N / ha in

year two and maintaining this high level in year three. Elevated nitrate N levels throughout the soil

profile were reasonably well distributed across the paddock, however, considering the high levels of

nitrate N at the bottom of the root zone and the likely high levels of leaching between year two and

three, it is expected that a large proportion of this available N would be deep in the soil profile by the

subsequent cropping cycle.

Figure 9. Distribution of total estimated nitrate-N in the soil profile (kg/ha to 60 cm) over three years at Farm Two –

paddock five

23

As expected, total profile Nitrate N levels (to 60cm) on paddock six (Figure 10) followed the opposite

trend to paddock five, as crops utilised profile nitrate during the cropping phase. Levels were

extremely high (> 500 kg N / ha) at the start of the crop phase and declined substantially during the

cropping phase. Sufficient profile nitrate remained for at least one further crop without significant

fertiliser additions.

Figure 10. Distribution of total estimated nitrate-N in the soil profile (kg/ha to 60 cm) over three years at Farm Two for

paddock six

24

Soil potassium levels on paddock five (Figure 11) followed a similar distribution pattern to phosphorus

and nitrogen, with concentrated nutrient levels at the end of the paddock closest to the shelters.

Figure 11. Distribution of surface soil (0-10cm) potassium at Farm Two – Paddock five

25

4 DISCUSSION

4.1 Nutrient Accumulation and Distribution

Nutrient deposition and distribution on free range pig farms are both high and variable, as a function

of pig stocking rates and pig behaviour. In the present study, nutrient deposition from pigs was high

compared to other farming practices, with 100-200 kg / ha.yr of phosphorus and in the order of 300-

600 kg N / ha.yr being added during the pig cycle. The high rate of nutrients added with manure

resulted in significant increases in soil nutrients, including nitrate-N, total soil nitrogen, available P,

total soil phosphorus and potassium during the pig phase. Soil phosphorus was found to increase

significantly to at least 30cm depth at some sites in a one year period, indicating significant movement

of phosphorus through the soil. Nitrate-N, which is more mobile within the soil profile, was found to

increase significantly to 60cm depth on some sites. Nutrient accumulation was a function of the high

nutrient deposition rates and the negligible nutrient removal or uptake by plants during the pig phase.

Mean levels of available P and nitrate-N at farm one showed moderate soil fertility for a cropping soil

at the start of the trial. Following the first year of stocking with pigs, nutrient levels had risen to very

high levels of available P, which are well in excess of pasture requirements ((Gourley et al. 2007) and

above threshold levels for environmental performance (Tucker & O’Keefe 2013). Excessive nutrient

build-up in a short period of time was also found by Watson et al. (2003). Elevated available P levels

remained after the paddocks were destocked, while nitrate-N levels had declined. This suggested

nitrate losses were occurring, possibly via leaching below the monitoring depths. Mean levels of

available P and nitrate-N were higher at the start of the trial on farm two, possibly in response to

prior stocking with pigs. As a consequence, levels of available P exceeded pasture requirements

(Gourley et al. 2007) at the start of the trial, and increased well above recommended threshold levels

for environmental performance (Tucker & O’Keefe 2013) in the first year. Nitrate N levels were at

high levels at the start of the trial and increased over time.

Nutrient levels were found to be variable across both sites in the first year, reflecting natural variability

in soil properties. At farm one, the minimum observed available P levels increased from 25 mg/kg in

year one (marginal) to 41 mg/kg in year three (adequate). Similarly at farm two, the minimum Colwell

P levels in year one was 14 mg/kg and four values were observed below 21 mg/kg, suggesting that a

proportion of the monitored area would be responsive to P fertiliser at the start of the trial. Minimum

levels increased to 38 mg/kg in year two and remained at this level. This finding suggests adequate

levels of available P may be present to allow zero P fertiliser applications without compromising crop

production in at least the first year of the cropping phase.

We found that nutrient levels could be mapped spatially through the established association between

ECa and soil nutrient levels of interest. Results from the EM mapping demonstrated that nutrient

levels were not distributed evenly across the free range area, but were highest in areas corresponding

to the location of shelters, feeders and water points, creating nutrient ‘hot spots’ in the range area.

This finding corresponds well with previous research (Horta et al. 2011, Salomon et al. 2007). This

finding suggests that average nutrient deposition rates reported per hectare are not sufficient for

understanding nutrient loading, as found by Watson et al. (2003), because a large proportion of the

nutrients are concentrated in areas surrounding the shelters, feeders and water points. Because this

is governed by pig behaviour, it may also be manipulated by management. On farm one, nutrient levels

were successfully dispersed across the range area by moving shelters, feeders and waterers during the

pig phase. At farm two, moving shelters and feeders was also effective in increasing nutrient

distribution, but not to the same extent because the infrastructure was moved shorter distances and

less frequently than at farm one.

While nutrient levels increased substantially and in a non-uniform fashion during the pig phase, each

of these paddocks operated in a long term rotation with cropping and the effects of the whole rotation

were not assessed because of the time frame of the project.

26

Both of the farms operated a long-term rotation, with 1.5-2 years in the pig phase and 5-6 years in the

cropping phase. The aim of this rotation is to allow sufficient time during the pig phase to capitalise

on the required infrastructure for pig farming, while allowing enough time in the cropping phase to

assimilate nutrients. Paddock five at farm two was included to investigate the impact of the start of

the crop phase on nutrients. While the results demonstrated a reduction in nitrate-N over the three

years, levels of available phosphorus remained high during the second year, possibly in response to

mineralisation after cultivation. Nutrient levels increased in the third year in response to additional

fertiliser added with cropping. This finding suggests that the cropping phase must be managed

specifically to utilise nutrients deposited during the pig phase rather than following typical agronomic

practice. For this to be successful, practices that disperse nutrients over a larger area during the pig

phase will be beneficial.

4.2 Environmental Risk

High rates of nutrient deposition and variable deposition patterns during the pig phase resulted in

excess nutrients in the soil profile and concentrated nutrient deposition in some parts of the free

range area. The recommendations of Skerman (2000), as adopted in the National Environmental

Guidelines for Piggeries (NEGP 2010) , suggest trigger levels for further investigation of Colwell

phosphorus for manure and effluent application areas. The levels are soil texture and pH specific, and

vary from 35 to 85 mg/kg for the topsoil (0-10 cm) and were exceeded in the second year of the trial

(one year after the introduction of pigs).

Nutrient levels in the sub-soil were observed to increase significantly to 60cm depth, and excess nitrate

is expected to leach beyond this depth, particularly in the nutrient hotspot areas. These hotspots are

therefore likely to result in nutrient losses exceeding the level expected from average nutrient

deposition rates or average paddock nutrient levels.

Thresholds for nitrate-N are also provided by Skerman (2000), and adopted in Tucker & O’Keefe

(2013) for soil samples collected from the bottom of the root zone (generally >60 cm). Levels

observed in the second year exceeded these thresholds across most of the free range areas,

highlighting the potential risk of nitrate leaching. Elevated subsoil nitrate levels were observed within

one year of stocking with pigs and continued into the second year. This suggests that nutrients are at

risk of leaching beyond the depth that can be utilised by crops in the later cropping phase, unless soil

depth, climatic conditions and crop species allow deep rooting depths. Further research is required

to investigate this. During the pig phase, the deposition rate of phosphorus was 100-200 kg P / ha, or

equivalent to between 1.1 and 2.2 tonnes of single superphosphate per hectare. This application rate

is equivalent to the requirements for 10-20 years of crop production, and relies on the ability of soil

to safely store phosphorus within the profile. Effective management and removal of this nutrient with

cropping is hindered by uneven nutrient distribution, because some parts of the field have large

nutrient excesses while other parts of the paddock may be deficient. Specific management techniques

will be required to improve nutrient distribution during the pig phase, and to manage nutrient

variability in the crop phase.

Considering the low levels of ground cover in the free range areas and high levels of nutrients in

surface soils, there is a high risk of nutrient losses via runoff from these systems. Nutrient losses via

this pathway were not investigated in the current study, though others have demonstrated high losses

in runoff (Horta et al. 2011). Nutrient losses via runoff or erosion may explain why total phosphorus

declined in the third year on some paddocks, though this may also have been because of nutrients

leaching deeper into the soil profile. Further research is required to understand nutrient losses via

runoff and erosion from these facilities.

27

A number of additional impacts from pig farming were observed but not quantified in the present

study. The soil analysis data suggested that salinity indicators (soil conductivity, chloride and

exchangeable sodium) all increased during the pig phase (data not shown). Further research is required

to understand these impacts. Additionally, impacts on soil health warrant further investigation.

Soil concentrations of organic matter appeared to increase in this study, though these data were not

interrogated in detail. Soil compaction and erosion potential also warrant further investigation both

in the pig phase and during the subsequent cropping phase. It is expected that impacts on soil health

will be site dependant based on soil type and management history, and further research is required to

understand the impacts and management methods required to improve soil health outcomes.

4.3 Mitigating Risk

Both farms trialled new approaches to manage the pig phase, with the aim of maximising nutrient

distribution. Results suggest that these techniques were reasonably successful in distributing nutrients,

with mean nutrient levels increasing across the whole paddock and minimum nutrient levels increasing

between years. However, the high nutrient deposition rates in small areas of the range still resulted

in excessive nutrient levels in the surface and sub-soil. This risk could be further reduced by moving

pigs more frequently over a large area to reduce the stocking rate and formation of hotspots. During

the cropping phase, variable rate fertiliser application is required to utilise nutrients contained in

hotspot areas without compromising yields in other parts of the paddock. Mapping areas expected to

have high nutrient loading (based on the location of shelters and feed/water points) would be required

to apply this approach throughout the cropping phase. This approach would lead to lower fertiliser

costs, though the capital requirements for machinery would increase in order to apply variable rate

technology.

The results suggest that excess nutrients rapidly accumulate in the surface soil during the pig phase,

presenting a risk for nutrient losses via wind and water erosion, and losses with runoff. Further

research is required to quantify this risk, but the impacts from other industries in southern Australia

such as dairy (Barlow et al. 2005) and sheep (Ridley et al. 2003) show this to be a substantial risk. The

risk of nutrient losses via erosion requires maintenance of ground cover. This is difficult to achieve

because of the rooting behaviour of pigs (Eriksen et al. 2006a, Eriksen et al. 2006b) and management

would need to focus on rotating pigs over a larger area, with short stocking periods and long plant

recovery periods. Similar practices in the sheep and cattle industries focus on very short grazing

periods of 1-2 days, up to 1-2 weeks, prior to moving the animals. This is followed by a long period

of pasture recovery (up to 90 days). Further investigation would be required to understand the

practical application and effectiveness of similar practices for the pig industry. Alternatively,

management practices may be used that focus on managing the risk of nutrients being lost from the

free range site in runoff or erosion. This may be achieved through construction of controlled drainage

areas, runoff containment dams or vegetative filter strips. Such practices would minimise the possible

off-site impacts from free range production and could be investigated by the industry.

28

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

The study determined that nutrient distribution at outdoor rotational piggeries could be improved

through better management practices, with beneficial outcomes for the crop phase. However, overall

indicators of performance suggest that new management practices are required to address the high

levels of nutrient accumulation and low ground cover during the pig phase. Conclusions relating to

the pig phase and crop phase are provided below.

5.1.1 Pig Phase

This study quantified nutrient deposition, accumulation and distribution in outdoor areas during the

pig phase over a three year period. The study demonstrated the impact of practices known to improve

nutrient distribution. High density stocking where shelters, feeders and waterers were frequently

moved (farm one) resulted in wider distribution of nutrients across the free range area. Lower density

stocking, and moving feeder location, resulted in better distribution of nutrients at farm two. However,

nutrient deposition and accumulation was still excessive at both sites, and the risk of nutrient loss

during the pig phase was high. This risk can be attributed to:

i) The high stocking rates, resulting in high nutrient deposition rates over the whole

area,

ii) Excessive nutrient deposition in small areas despite more frequent moving of

infrastructure and shorter term rotations, and

iii) The relatively long duration of stocking which resulted in very low levels of ground

cover.

While the impacts of these practices on actual nutrient loss were not determined, the thresholds for

good environmental performance were exceeded within a short period of time.

5.1.2 Crop Phase

Minimum soil nutrient levels for critical crop nutrients such as phosphorus were found to increase

significantly, from marginal to adequate levels, during the pig phase. This suggests that cropping may

be conducted with low or zero P fertiliser inputs to reduce input costs to the cropping phase and

reduce the risk of nutrient losses. High levels of nitrate N throughout the soil profile suggest that crop

nutrient requirements will be adequately met in the first year at a minimum. At farm two, cropping

for two years successfully utilised soil nitrate and reduced environmental risk. However, cropping was

not effective in reducing soil available P, most likely because mineralisation rates matched or exceeded

plant uptake in the second year. Considering the very high and uneven nutrient deposition rates

across the paddocks, specific management of the crop phase to maximise nutrient uptake is required

to achieve effective decreases in nutrient levels.

29

5.2 Recommendations

This trial confirms the findings of many others that show high levels of nutrient accumulation and

elevated risks from outdoor pig farming. Considering the results show these systems exceed relevant

environmental thresholds rapidly, further research and demonstration is required. There are two

broad directions this can take. Firstly, further research can investigate the actual likelihood of

environmental harm from these systems, via the pathway of nutrient losses and/or damage to soil

condition. Secondly, further research and demonstration can focus on alternative management

practices that can be carried out, with the aim of meeting the environmental thresholds set out in the

Australian environmental guidelines for rotational outdoor piggeries. Recommendations below

address both possible research directions.

5.2.1 Further analysis of impacts from outdoor pig farming

The study investigated the change in nutrient levels over a relatively short period, mainly covering the

pig phase or the cropping phase. It would be valuable to assess the decline of nutrient levels over the

cropping phase by resampling these sites in one or two years time. This would provide greater

evidence of the long-term impact of the rotation on nutrient levels and may show that high levels of

nutrients in the pig phase decline to acceptable levels, with appropriate management. This may show

that outdoor rotational piggeries have less impact over the longer term (5+ years) than it would appear

from this study.

While this study focussed on nutrient levels, a number of other important factors warrant further

investigation. Soil analysis data were collected for salinity indicators and organic matter, though these

data were not analysed in detail. Salinity indicators appeared to rise during the pig phase which may

negatively impact on soil condition. In contrast, soil organic matter levels may have increased during

the pig phase, supporting improved soil structure. Expanding the study to analyse these data would

provide a broader assessment of soil condition and impacts than provided here.

Pigs may result in deleterious impacts to soil structure and high stocking rates combined with long

periods of continuous stocking may result in low levels of ground cover, leaving soil susceptible to

wind and/or water erosion. Further research on multiple soil types is required to understand these

impacts. Studies that measured impacts on soil structure, erosion rates, and nutrient loss rates may

be beneficial.

5.2.2 Demonstration of more effective management practices

Trials are recommended that use short pig grazing periods and long rest periods, with high or low

stocking rates. The main aim of this would be to demonstrate methods that maximise ground cover

and reduce nutrient deposition. A dynamic management system that shifted pigs in response to ground

cover and climate (rainfall) would be beneficial, with the aim to maintaining groundcover above 70%.

Application of methods used in other grazing sectors could be explored and applied to pig farming.

Improved methods of fencing that do not restrict vehicle movement, and automated systems for

moving houses, waterers, wallows and feeders warrant investigation as part of this trial.

Trials are recommended to demonstrate the application of variable fertiliser application during the

cropping phase after pig farming. The trial demonstrated that nutrient distribution is still variable

despite improved management. By using variable rate fertiliser application during the cropping phase,

nutrient hot-spots will be more effectively drawn down, while crop yields will still be maintained on

parts of the paddock with lower (deficient) nutrient levels. This trial could demonstrate using EM

technology, field assessment methods and farm records to determine fertiliser rates each year to

quantify improvements and demonstrate this to the broader industry.

30

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