Sustainability in Small Scale Farms- a South Gippsland Farm Perspective

Year of study:

2010-11

Lead organisation & collaborators:

Monash university

Property owners (Gil and Meredith Freeman–Tarnuk Bushfoods and Flowers, and Darryl Morris manager of the peas and grazing).

Contact:

Larissa Burns

T: 0418373629

E: lkbur5@student.monash.edu; larissa@supportnet.com.au

Best available science assessment:

Objectives

Conceptual model

Study design

Soil analysis

Production & financial

Method reporting

Data analysis

Results reporting

Publication

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Project details

Objectives:

The project sought to better understand how soil health indicators may be used to assess the sustainability of small scale farms. This analysis considered these indicators in the context of a permaculture and conventional farm setting. The primary research question was, can smallholding, natural systems farms be considered sustainable in terms of soil health?

Hypotheses:

Primary research question: Can small holding, natural systems, farms be considered sustainable in terms of soil health?

In order to investigate this, the affects of different land uses on soil health using a variety of soil properties as indicators were assessed. This highlighted soil health as a significant indicator of environmental sustainability. To achieve this goal, some secondary questions were asked:

  1. What aspects of soil health are the most important to measure?

  2. What are the most appropriate methods of measuring soil health?

  3. How can the results be interpreted in relation to land use?

  4. Is there currently an effective mechanism for [holistically and multidimensionally] comparing land use sustainability?

  5. Is soil health an effective and appropriate mechanism for comparing land use sustainability?

The hypothesis of this research is that soil health is a good indicator of environmental sustainability at the farm scale. Through soil testing and seasonal variation analysis between the conventional and permaculture farms, it is hoped that the result will provide a strong comparative basis for defining sustainability metrics.

Basis of trial:

The literature surrounding sustainability provides much information regarding what to measure in terms of soil health indicators. For this study, various physical, chemical and biological properties were selected; soil moisture, bulk density, soil texture, soil strength, pH, soil carbon, soil nitrogen, and microbial respiration. These provide a snapshot overview of the soil health status within each land use and farm system. Through this basis, this project seeks to quantify the sustainability of farms using these indicators.

Location details

Trial site details:

Kardella- near to Western Reservoir. Both sites belong to the same valley and are within a few kilometres of one another They share similar slope (15-20o), aspect (roughly North facing), climatic influence, geology (Lower Cretaceous Strzelecki Group), and soil types (Brown Dermosol).

Trial was conducted during a wet year (November 2010-April 2011)

Average annual rainfall= 1207.7mm/a (Korumburra (BoM))

  1. Permaculture site (Tarnuk Bushfoods and Flowers): organic farm, hazelnuts, mountain pepper plantation and rainforest land uses
  2. Conventional site: pea farm and some grazing

Pre-trial management:

  1. Permaculture site: previously was used for grazing- dairy farm until 1983. Property owners then bought in hazelnuts and later converted the site to permaculture (it is now an organic farm, which has done work with Landcare). Mountain pepper is irrigated.
  2. Conventional site: grow peas in rotation on site – Fertiliser mixture applied. Dairy grazing areas have used fertilisers and applied urea. Soil testing has been conducted previously (Darryl says liming recommended as the outcome).

Treatment results

Summary of key findings of trial:

Given the wet season experienced, testing found high water content in the soil.

The results showed that some, but not all, of the measured indicators of soil health were significantly different across the different land uses. The negative impacts of conventional farming on soil health were shown by several results. ‘Conventional farming practices’ led to water logging, increased bulk density and soil strength in the cattle grazing paddock leading to soil structure decline. This is due to the effect the large hoofed cattle have on the soil. The mechanical tillage in the pea paddock is exacerbating water erosion and drying of the surface layers of the soil, while fertilizer oxidation is contributing to the acidification levels in the soil. Nitrogen and carbon are also being lost due to ploughing. Positive results for the soil health of the permaculture farm include it having the most gradual decline in topsoil moisture retention over summer. However, due to the robust nature of the landscape studied, and the short period of time over which the land uses have differed, the results imply that no one land use can be stated as more sustainable in terms of soil health.

All results indicate that soils within the study location have healthy nutrient status and can support all of the land uses observed. The soil sampling conducted in this project represents a snapshot in time. These results provide a foundation for a longitudinal study of soil properties under permaculture (for this specific location), and further comparison of soil health in the future would be would be worthy of investigation to see how these properties change spatially over time.

It is important to acknowledge that these land uses have not been dissimilar for very long in terms of soil age (~30 years), so significant changes in the properties of the soil may not be found yet.

The project ultimately recognises the limitations of using key indicators of soil health in isolation as a measure of sustainability. Whilst measuring indicators of soil health can determine some aspects of environmental impact, sustainability encapsulates the system, people and the values which they hold. The issue of identifying, measuring and applying appropriate indicators of sustainability remains a significant difficulty.

In spite of the complexities of measuring sustainability and the difficulties in comparing land uses, it is still important to examine indicators of environmental condition, such as soil health. These indicators provide very relevant information about soil behaviour and response to land management, and are crucial to incorporate into any broad inference about sustainability. Measuring an indicator such as soil health provides a very good starting point when evaluating a landscape.

Variation in soil pH with time and management influence:

One off sampling

The surface pH values (0-5 cm) displayed some variation; however, statistical analysis found that these were not significantly different across the 5 land uses (P-value 0.101). The 5-10 cm depth showed a statistically significant (P-value 0.005) change in pH values between land uses, with the average pH value for grazing (4.08) at least 0.2 higher than all other land uses. The lower depths measured (15-20 cm and 25-30 cm) showed no significant different in pH measurements across land uses. No values exceeded a pH of 4.2

The results indicated that surface soils were most acidic, with a declining trend through the profile. This was most apparent for the peas and grazing land uses (oxidation of fertilizer and breakdown of organic materials), however, all soils had high organic matter content.

The measured results of testing are provided in the following tables.

RF= rainforest
PS= peas
GZ= grazing
MP= mountain pepper
NT= hazelnuts

 

GZ NT MP PS RF
% organic matter
0-5

14.1%

10.2%

13.6%

15.0%

12.6%

5-10

12.2%

9.3%

8.2%

10.5%

7.8%

15-20

9.5%

6.5%

6.3%

9.6%

6.3%

25-30

7.3%

5.7%

5.2%

7.2%

4.9%

% organic carbon
0-5

6.1%

4.4%

5.9%

6.5%

5.5%

5-10

5.3%

4.1%

3.6%

4.6%

3.4%

15-20

4.1%

2.8%

2.7%

4.2%

2.7%

25-30

3.2%

2.5%

2.3%

3.1%

2.1%

pH
0-5

4.2

4.2

3.9

3.8

4.0

5-10

4.1

3.8

3.6

3.7

3.7

15-20

3.9

3.9

3.8

3.7

3.9

25-30

3.8

3.9

3.9

3.7

3.9

 

GZ NT MP PS RF
% nitrogen
0-5

0.34

0.33

0.49

0.31

0.37

5-10

0.28

0.25

0.29

0.28

0.21

15-20

0.17

0.1

0.19

0.22

0.1

25-30

0.07

0.05

0.08

0.13

0.08

% organic carbon
0-5

4.09

4.16

6.3

3.95

4.74

5-10

2.98

3.43

3.72

3.45

2.63

15-20

2.33

1.86

2.58

2.87

1.55

25-30

1.19

1.34

1.62

1.92

1.3

Other soil treatments:

The field measurements of soil moisture clearly show seasonal variation, displaying a general decline in the amount of moisture retained in soils across summer months, both in the upper and lower depths measured. The permaculture farm had the most gradual decline in the topsoil moisture retention over the drier Summer months, a reflection of land use and the nature of water storage and use for the perennial and more mature plants. The grazing and the peas experienced the greatest variation in moisture content, with the subsoils storing more water on average, attributed to the disturbed nature of the topsoil in each location. The laboratory results showed that that at each land use and depth, the moisture content of the soil was statistically significantly different. Averages were high for all land uses except the peas. Fluctuating readings for the peas however, may not be solely due to the water holding and storage capabilities of the soil but reflective of the artificial surface of the pea paddock. Sections of this area were ploughed during the sampling timeframe, affecting the structure of the soil, and possibly skewing these results, because ploughing soil separates aggregates, drying the surface layers. This topsoil has less organic material to bind particles together and greater potential for erosion and surface runoff.

Moisture retention fluctuated most, at depth, in land uses that do not have perennial species. Interestingly, both soil structure and moisture content in the landscape appears to be attributed to land use practice.

Other measures of treatment response:

The difference in bulk density at the surface between grazing and the other land uses can be attributed to compaction by the hoofed grazing cattle. Some areas within the grazing paddock exhibited concerning visual evidence of the affect of this. Signs included the absence of vegetative cover, where it would normally be present, and pugging where cattle have intensively trampled wet soil, which breaks down soil aggregates, reducing pore spaces and slowing water infiltration. Whilst the paddock still appears healthy, in future, if high rainfall in the region continues, pugging has the potential to become a more serious problem for cattle grazing, particularly at slope breaks (even on slight inclines).

The results for bulk density were consistent with those from field measurements of soil strength. At all times of measurement, the grazing paddock exhibited much greater resistance to penetration, on average, than other land uses

Soils in the pea growing paddock experienced a consistently low average bulk density with machinery breaking apart the topsoil particles to make a seedbed. The peas were also most variable when strength was measured. After ploughing, these looser top soils are left with no surface cover to protect against erosive forces. A plough pan layer has not yet been formed, however, the paddock has only been under tillage for four years.

All other land uses experienced variation of soil strength, with readings increasing over summer months, and decreasing in other spring and autumn months

Experimental design

Treatments:

N/A. Soil sustainability research.

Trial design/layout:

Sites were based on paddocks within the farm sites and were tested over a series of land uses. These were:

  1. Permaculture site: 3 land uses tested- mountain pepper plantation, hazelnuts and rainforest area (tropical plants found in northern NSW/QLD)
  2. Conventional site: 2 land uses: peas and grazing.

Each site had a series of soil sampling:

  • Comprehensive samples in January 2011
  • Seasonal sampling in late November, mid January, mid March and April to test moisture and resistance to penetration

No prior testing in Permaculture farm so data collected in this study forms baseline measurements.

Grazing was seen generally as the ‘control’, due to history of the area broadly being grazing/ dairy.

Soil sampling method:

Comprehensive sampling (January 2011) was taken in each paddock (representing the land uses sampled) – through a randomised process a GPS was used to identify 5 points to sample (except of rainforest land use which was much smaller (0.2 acres) only had 3 points). At each of those points, 4 sets of soil samples were taken at 0-5 cm, 5-10 cm, 15-20 cm and 25-30 cm. A triplicate sample was taken at each hole and labelled A, B and C. Pits were dug using shovels, no augering.

Seasonal sampling (late November, mid January, mid March and April) tested at 50 points in each land use paddock. Points were randomised each time. Measurements of moisture were taken at 10 and 20 cm depths and resistance to penetration readings were taken at the surface.

Specific soil indicators included:

  • pH- (lab) using a probe (1:5 soil-water solution)
  • Carbon-(lab) high emission Loss on Ignition Method (furnace at 550 degrees for 2 hours)
  • Carbon and nitrogen- (lab) dry combustion method (machine auto analyser)
  • Particle size analysis- (lab and field) texture, machine
  • Bulk density- (lab) as applied by department (collected in rings of known volume, sample weighed, oven dried (overnight), and reweighed)
  • Resistance to penetration (soil strength) –(field) Hand held penetrometer (kPa)
  • Soil moisture – (field and lab) Moisture probe at 10 and 20 cm, and gravimetric (g water per 100 g oven dry soil)
  • Soil respiration figures were also taken, but were not viable in this instance.

 

Reporting:

How results have been reported:

Honours thesis

How a copy of any relevant reports can be obtained:

Larissa Burns

lkbur5@student.monash.edu

0418 373 629

Level of review of results:

Internal technical review

Next steps

Further research is recommended in this area to build on this study longitudinally, and to expand the types of tests conducted (like infiltration rate to build on moisture tests). In-depth tests regarding nutrient status can determine whether natural farming systems increase or deplete soil nutrients because of differing inputs. Further research may provide some definitive conclusions about soil health status at Tarnuk Bushfoods and Flowers, in comparison to neighbouring land uses in the valley.

It is also essential for future research to identify and measure other key indicators of sustainable practice, to fully explore the concept of agricultural sustainability in terms of natural systems farming. Such research could focus on the current challenges facing the farming industry and those who strive to identify, measure and apply knowledge of appropriate indicators sustainability, by exploring options to place monetary value on those things which are currently seen as ‘too hard’ to value, and therefore cannot be adequately measured.

Currently, it is too difficult to compare such different land uses, without taking into account that which people value, but which do not have a monetary value. In order to measure sustainability more completely, it needs to be assessed over space and time, using multiple criteria instead of just one (soil health), relating to environmental, economic and social indicators.