Agricultural practices,
earthworm abundance and soil
organic matter
- Examining the effects of five different
field treatment methods on two trial sites
Tord Ranheim Sveen
Uppsats för avläggande av kandidatexamen i naturvetenskap
15 hp
Institutionen för biologi och miljövetenskap
Göteborgs universitet
Abstract
Uppsats/Examensarbete: 15 hp Program och/eller kurs: ES1510 Examensarbete i miljövetenskap I Nivå: Grundnivå Termin/år: VT 2015 Handledare: Lennart Bornmalm Examinator: Bengt Gunnarsson Rapport nr: xx (ifylles ej av studenten/studenterna Nyckelord:
xx Abstract: Soil Organic Matter (SOM) and earthworm abundances are essential
parameters of soil health and soil quality. In two long-term field trial
sites located in Skåne, southern Sweden, five different field treatments
have been ongoing since 1987. The field treatments were divided in two
broad categories of animal keeping vs. non-animal keeping and organic
vs. conventional practices and subsequently tested on SOM levels and
earthworm abundance and biomass. The results indicate a significantly
higher earthworm abundance in the category of animal keeping practices
on one of the trial sites, whereas SOM levels, along with the category of
organic vs. conventional practices failed to display any significant
differences. The results were discussed in relation to previous research
on the reciprocal interaction of agricultural practices and earthworm
presence.
1 Table of contents
1. Introduction ............................................................................................................................ 3 2. Previous research .................................................................................................................. 4 3. Aim .............................................................................................................................................. 5 4. Research questions ............................................................................................................... 5 5. Method ...................................................................................................................................... 6 5.1. Earthworm abundance in Bollerup ........................................................................... 6 5.2. Earthworm abundance in Önnestad ......................................................................... 6 5.3. Loss on Ignition ................................................................................................................ 7 5.4. Statistical treatment ....................................................................................................... 7 5.5. Method limits and potential sources of error………………………………………......8 6. Background ............................................................................................................................. 8 6.1. The Önnestad and Bollerup field trial project ...................................................... 8 6.2. Soil degradation and Soil Organic Matter ............................................................. 10 6.3. Earthworms ..................................................................................................................... 12 7. Results ..................................................................................................................................... 15 7.1. Earthworm abundance ................................................................................................ 15 7.2. Earthworm abundance and wormholes: correlation ........................................ 17 7.4. Organic Content ............................................................................................................. 19 7.5. Correlations of earthworm abundance and SOM ............................................... 20 8. Discussion .............................................................................................................................. 22 8.1. General discussion ........................................................................................................ 22 8.2. Animal keeping and non-­‐animal keeping practices .......................................... 23 8.3. Organic vs. conventional practices .......................................................................... 24 9. Conclusion .............................................................................................................................. 25 References .................................................................................................................................. 26 Appendix ..................................................................................................................................... 30 2 1. Introduction Although food and food security is, and certainly has been, an important issue and a
concern for many governments, the question of food production (i.e. agricultural
production) has received comparatively little attention (Charles, Godfray & Garnett
2012). However, the fundamental importance of food production is increasingly
subject to a bisected focus, with the heightened awareness of the ties between food
production and climate changing greenhouse gases (GHG) on the one side, and a
fluctuating global food security on the other.
The latest IPCC report (2014) thus concludes with robust evidence that the category
Agriculture, Forestry and Other Land Use (AFOLU) is responsible for around 25 per
cent of total anthropogenic GHG emissions, and stresses that a leverage of the
mitigation potential in the category is extremely important in adequately confronting
climate change (IPCC 2014; 816). On the other hand, modern agricultural practices
have resulted in a widespread degradation of soil, and thus diminishing soil fertility
(Gardiner & Miller 2004).
The soil and soil organic content (SOC) – interchangeably used with soil organic
matter (SOM) - plays a vital role in fusing these two perspectives. SOM is the central
indicator of soil quality and health, and is in its turn strongly affected by agricultural
management (Liu et al 2006; 532). A declining of SOC-contents in agro-ecosystems
brings a corresponding increase in GHG-emissions (Fuentes et al 2011), and it is thus
critical for a sustainable agriculture to manage both to protect the natural resource
base – the soil – but also to prevent a further degradation of arable land (Lobry de
Bruyn 1997; 168; Maeder et al 2002).
The scientific literature corpus imposes no clear common definition on the
implications on either the being or the practices of a sustainable agriculture.
However, intrinsic in the debate is the alternative of organic farming to the
conventional intensive farming (Maeder et al 2002).
When discussing the challenge of how to adequately produce enough food for a
growing population globally, and maintain – if not increase – soil fertility and thus
also tackling GHG-emissions from agriculture, some often-recurring perspectives are
worth mentioning:
3 -
Although highly contextually varying, there’s a “yield gap” between organic and
intensive farming generally ranging from a 5-35 % yield deficit in organic
farming (Seufert et al 2012), with a typical figure set at 20 % (Maeder et al 2002;
de Ponti et al 2012).
-
However, although contextually varying, organic farming management typically
show to be richer in biodiversity, bioactivity and soil fertility (Maeder et al 2002;
Bengtsson et al 2005; Herencia et al 2007; Gabriel et al 2013).
-
The “yield gap” between organic and intensive agriculture is somewhat
compensated by lower energy input per unit of land area and crop dry matter unit
(Maeder et al 2002).
2. Previous research Several studies have been carried out on assessing the importance of earthworms for
agricultural practices, soil properties and ecosystems (Basker, Macgregor & Kirkman
1992; van Groeningen et al 2014; Pelosi et al 2014), whereas various reports have
indicated that different agricultural management practices such as tilling, ley, manure
addition and usage of herbicides affect earthworm abundance (Lofs-Holmin 1983;
Larsson 2003; Kukkonen et al 2004; Kukkonen et al 2006; Lagerlöf, Pålsson &
Arvidsson 2012; Pelosi et al 2014). Further, earthworm abundance also plays an
important role in the forming of organic colloids due to the decomposing of animal
matter (Burden & Sims 1999).
Although it seems impossible to accurately predict what kind of agricultural
practices would increase the abundance of earthworms, a general conclusion made by
Lofs-Holmin (1983) is that practices resulting in the entering of organic material to
the soil favour earthworm abundance, whereas practices that extract organic material
from the soil (i.e. soil-degrading practices) have the opposite effect.
Earthworms have been widely acknowledged as a useful indicator for soil
biodiversity (Paoletti 1999; Bispo et al 2009), and have been adopted by the EU Soil
Framework Directive (SFD) as such. Earthworms have also, albeit with some
4 reservation, been suggested as a useful indicator for soil health (Lobry de Bruyn
1997).
Previous research on the impact on soil fertility and crop yield of different
agriculture practices through long-term field trials indicate an increase in biodiversity
and biological activity in organically and biodynamically managed farming systems
(Maeder et al 2002), leading to the conclusion that more biodiverse farming systems
exhibit a greater resource-utilization efficiency (Tilman et al 1997; Maeder et al
2002), albeit a varyingly but significant lower crop yield, than intensive agriculture
(Stanhill 1990; Maeder et al 2002; de Ponti et al 2012).
Assessment on earthworm abundance by means of counting wormholes is a technique
previously used in agricultural soils in Sweden, as is described in Båth & Ögren
(1995).
3. Aim The aim of this thesis is to investigate whether different agricultural practices affects
important soil properties on a long-term basis. The parameters chosen for indication
of soil properties are earthworm abundance - in individuals and biomass (g/m2) – as
well as SOM. These are chosen on the basis of previous research suggesting their
respective suitability as soil health indicators.
4. Research questions With the background of the previous research stated above, the different field
treatments were divided up in the following two categories for examination of their
respective impact on SOM and earthworm abundance:
-
The categories of animal-keeping field practices, and non-animal keeping
practices.
-
The categories of conventional agricultural field practices as opposed to organic
field practices.
5 5. Method 5.1. Earthworm abundance in Bollerup An investigation area of 1×1m was randomly chosen on each different management
practice field, where the topsoil layer subsequently was removed to a depth of 10 cm
by the use of a shovel. The removed soil was thoroughly searched for earthworms,
which were placed in plastic beakers for subsequent weighing, whereas the surface
soil exposed on a 10 cm depth was searched for wormholes. Finally, the next 10 cm
of topsoil was removed and searched for earthworms by the same procedure as the
upper 10 cm soil layer.
The procedure was repeated three times on the same trial field, with the examination
of wormholes only, resulting in the data of four measurements of wormholes and one
establishment of the actual abundance of earthworms in the soil layers of 0-10 cm and
10-20 cm respectively, for each of the five different trial fields.
Soil samples were collected from each trial field and sent to lab analysis with the
purpose of establishing the SOM.
5.2. Earthworm abundance in Önnestad The procedure concurred with the procedure described regarding Bollerup above,
with the following notable exceptions:
-
Two areas of 1×1m were examined on the first two trial fields (B2 & D8), and
three areas (1×1m) were examined on the three remaining trial fields (A14, C20
& E26).
-
The actual abundance of earthworms was established in both topsoil layers (0-10
cm as well as 10-20 cm) in all of the investigation areas. The abundance of
wormholes was examined in each investigation area on a 10 cm depth.
-
Soil samples were collected from both topsoil layers and consequently examined
for organic content by loss on ignition (LOI).
6 All earthworms encountered in Önnestad and Bollerup were carefully counted and
weighted, using a Precisa 1600C scale (precision: one decimal digit).
5.3. Loss on Ignition The Total Organic Content (TOC) of soil samples collected in Önnestad was
established through LOI, according to the following standard procedures stated by the
Department of Geography, University College London (UCL 2015):
-
All samples were put to drying for 12 hrs. in a temperature of 105 °C.
-
A 10-15 gr. subsample of each sample was transferred to a porcelain crucible,
carefully weighted, and placed in a furnace for subsequent burning on 550°C
during 2 hrs.
-
The subsamples were then removed from the furnace and weighted.
Calculations on the organic content of the samples were established through the
formula of:
LOI % = (W1 – W2) X 100
W1
5.4. Statistical treatment Single-factor variance analysis (ANOVA) was used when comparing more than two
groups, and the function t-test was used when comparing two groups.
All statistical analysis of data was carried out with StatPlus:mac v5.
5.5. Method limits and potential sources of error Data obtained from the Bollerup field treatment sites were collected prior to the
carrying out of this study, and entailed no data on SOM. As a result, all indications
and conclusions involving the SOM-parameter are restricted to the Önnestad field
treatment sites.
7 Previous research established LOI/gravimetric method as the least secure of a range
of methods used for establishing the SOM-content in Brazilian savannah soils due to
its relatively large variation in mass loss (Sato et al 2014; 304). However, the usage of
stronger analyse methods such as element analysis were not available at the time of
this study’s execution.
6. Background 6.1. The Önnestad and Bollerup field trial project In 1987, the rural economy and agricultural society of Skåne initiated a long-term trial
project where five different typeset agricultural management practices were set up on
two trial fields in Skåne, southern Sweden, under the project label of “different
environmentally friendly and sustainable agricultural management practices”
(Hushållningssällskapet Skåne 2015). The aim was to provide a foundation for valid
and objective comparisons between the different management practices on a wide
range of parameters (Ibid). All management practices included six-year crop rotation
schemes, and were regularly updated to correspond the biological, technical and
economical developments of each practice respectively.
The trial fields were subjected to the following treatments (Gissén & Larsson 2008),
summarized in table 1:
Treatment A.
Manured, crops protected using best practice with environmental awareness. Straw
and foliage retained. Catch crops used to the greatest extent possible.
Treatment B.
Manured, crops protected using best practice with environmental awareness. Manure
brought in. Straw and sugarbeet foliage removed.
Treatment C.
For treatment C biodynamic principles were applied until the end of the fourth crop
rotation cycle 2013. Biodynamic principles imply the usage of compost manure,
biodynamic preparations and animal keeping. With the start of the fifth crop rotation
8 cycle in 2014 the C-field was converted into an animal-free organic management with
biogas production of crop residuals.
Treatment D.
In treatment D animals were kept and manure was used. No mineral fertiliser or
chemical pesticides were applied. Straw and sugarbeet foliage were removed.
Treatment E.
No soluble mineral fertiliser and no pesticides. However some phosphorus and
potassium were supplied via ash, sugar factory lime, potato juice and pig urine, in
amounts considered to be ecologically relevant and can be viewed as extended
recycling. Crop residues retained. One cropping year used for nitrogen acquisition via
a green manure ley.
Table 1: Agricultural management practices in Önnestad and Bollerup, southern
Sweden.
Field symbol
Management practice
Features
Animal-free; traditional
A
Conventional
crops; vegetables and
clover seed; sub-ploughing
of crop residuals.
Animals; traditional crops;
B
Conventional
ley; liquid manure;
removing of crop residuals
Animal-free*; traditional
crops; ley; composted
C
Organic/Biodynamic
manure; removal/biogas
production of crop
residuals
Animals; traditional crops;
D
Organic
ley; liquid manure;
removal of crop residuals
Animal-free; traditional
crops; vegetables and
E
Organic
clover seed; added
nutrients; sub-ploughing of
crop residuals
* Animals were kept until the fifth crop rotation cycle in 2014 where the management
shifted from biodynamic to animal-free organic with biogas production of crop
residuals. Consequently, the C-field will be classified as animal-free in this thesis
9 with the potential implications of previous animal keeping treated in the discussion
part.
Bollerup is characterised as a high-yielding traditionally arable soil, where the texture
classification of moderately humus-rich light clay, whereas Önnestad was
characterised as a moderately humus-rich to humus rich clayey sand, with good water
supply, presumably through capillary transport from below (Gissén & Larsson 2008).
In terms of crop yield, Önnestad has generally provided better yields than Bollerup in
all the field treatments (Gissén & Larsson 2008; 9).
6.2. Soil degradation and Soil Organic Matter Soil contains many forms of organic compounds, primarily in various stages of
decomposition. Burden & Sims (1999; 9) sketches five categories out of which SOM
is derived: (1) plant material; (2) animal matter; (3) microorganisms, both living and
dead; (4) synthesized and secreted products of living plants and microorganisms; and
(5) decomposition products of organic debris.
It is estimated that 65-75 per cent of organic matter in mineral soils consists of
humic materials (Schnitzer 1978) whereas the reminding part is composed primarily
of polysaccharides and protein-like substances (Flaig et al 1975). Humic matter plays
an important role in preserving a soils nutrients and salts by its rather organophilic
nature and contribution to the high cation exchange capacity of soils, thus preventing
cation leakage (Burden & Sims 1999; 10).
Soil formation is a long-term process relying on large-scale parameters such as
weathering of parent material and climatic conditions, as well as small-scale
processes such as biotic and abiotic incorporation of organic matter (Blouin et al
2013). However, with regards to the long-term geological processes involved in its
formation, soil is considered to be non-renewable on the human timescale (Jenny
1980), and a growing awareness of the extension and impacts of soil degradation have
10 made soil becoming an increasingly debated subject, where the UN announcement of
2015 as the year of soil being only one indication of this.
Due to erosion, soil degradation is a constantly on-going process. However, when
comparing degradation values between non-agricultural and agricultural soils, the
latter turns out to result in an annual soil loss of 45-450 t ha-1, compared with an
estimated value of 0,00045-0,45 t ha-1 for the former (Morgan 2005; 2).
There are clear indications thus, that although soil degradation is a phenomenon
encompassing wider contexts than agricultural aspects, the on-site effects on
agricultural fields are of particular importance (Ibid).
When further specifying what it is in the agriculture that result in soil degradation,
two main focuses stand out. The first is the effect of tillage and monocultural
cropping where significant soil-deteriorating effects along with the emission of GHG
stand out as a result (Liu et al 2006; Fuentes et al 2011). The second focus is the
positive effects on soil quality parameters such as SOC when applying crop rotation
along with reduced tillage and the addition of manure and fertilization (Reeves 1997).
These to aspects inevitably lead us back to the question posed in the introduction of
whether the benefit of higher crop yields stemming from applied intensive agriculture
outlast the impact of soil degradation connected to it (Squire et al 2015; 167).
11 6.3. Earthworms
One of the first to acknowledge the earthworm as an important factor responsible in
soil formation based on scientific reasoning was Darwin (1881), who among other
things showed that earthworms have an impact on chemical weathering.
Since then, much research has been performed on the importance of earthworms in
soil ecology, with the discoveries of their often tremendous positive effect on various
and wide ranging soil-related processes, leading to a often used label of earthworms
acting as the “the soil engineers” and ranking among the most important soil fauna
(van Groeningen et al 2014; 1). The recognition of the earthworms importance have
also resulted in it having a society – the Earthworm Society of Britain – dedicated to
promoting further research and spreading awareness on the positive impacts
associated with earthworms (Earthworm Society of Britain 2015).
Earthworms have been divided into the three primary ecological categories of epigeic,
anecic and endogeic. The first category - the epigeic – live off litter, are typically
bright red or reddy-brown and affect surface roughness and the distribution of
macropores through casts. Another characteristic of the epigeic earthworms is that
they don’t make burrows.
Anecic earthworms live in permanent vertical burrows. Feeding on leaves that they
drag into the burrows they typically produce casts or piles of casts around the
entrance to these. Anecic earthworms are typically darkly coloured at the head end
and have paler tails. One often-investigated worm from the anecic category is the
Lumbricus terrestris, commonly known as Common European earthworm.
The third category – the endogeic – are, along with the acecic earthworms, the ones of
most concern in the aim of this thesis. The endogeics live in and feed on the soil.
They make randomly oriented burrows that can go very deeply into the soil, and
rarely reuse these burrows. In terms of colours, they’re often pale, going from grey to
pinkish.
Among the soil-related processes earlier mentioned that are heavily impacted by
earthworm activity, are humus formation, burial of surface litter in the soil, bringing
12 of soil particles from lower soil horizons to the surface, and soil erosion (Blouin et al
2013; 163-164).
Acting as a sort of catalyst for the producing of humus from soil organics,
earthworms control humification rates through feeding, burrowing and interaction
with microorganisms (Bernier 1998), and have been shown to shorten the humus-tosoil transformation process down to the range of a few months (Blouin et al 2013;
163). The bioturbation entailed by earthworm activity resulting in soil brought from
deeper horizons to surface have been estimated to a staggering 40 t ha−1 year−1 under
temperate climate conditions in Europe (Feller et al 2003). These results are however,
likely to be somewhat overestimated (Blouin et al 2013; 164).
6.4. Impact on agroecosystems Whereas most studies centred around the impacts of earthworms mostly fall into the
perspectives of agriculture, some studies also provide knowledge on and highlight the
beneficial impacts of earthworms for ecosystem services. Edwards (2004) showed the
positive earthworm-induced effects on nutrient cycling in the soil, and Blouin et al
(2013) went on to meta-analyse the direct impacts of earthworms on various
ecosystem services including water regulation, soil structure, climate regulation,
pollution remediation and cultural services. It is the impact on primary production,
plant growth and nutrient cycling, however, that earthworms are most commonly
related to, and this for very good reasons. Earthworms constitute the most abundant
biomass factor in terrestrial ecosystems (Ibid; 170), and have been proven to
significantly increase the biomass of plants (Scheu 2003).
When scrutinizing the role of earthworms in agroecosystems a picture of mutual
affection crystalizes; for just as earthworms are shown to have a varying but
significant impact on crucial parameters such as crop yields and aboveground biomass
(van Groeningen et al 2014), so different agricultural practices are shown to have an
impact on the abundance and constitution of earthworms (Lofs-Holmin 1983;
Lagerlöf et al 2012; Pelosi et al 2013).
13 Of the factors of major effect on earthworms within agroecosystems are reduced
tilling (Lagerlöf et al 2011), crop specimen cultivated (Curry et al 2002), and
pesticide use (Pelosi et al 2013).
Seen from an economical perspective, the positive effect brought about on plant
biomass – and hence crop yields - from the presence of earthworms is in many cases
hefty. Scheu’s (2003) meta-analysis yielded that earthworm presence in agricultural
land significantly increased shoot biomass of plants, and van Groeningen et al (2014)
fixated the crop yield that could be gained from substantial earthworm presence to 25
per cent. However, earthworm presence does not automatically enhance crop yields.
Rather, the agricultural settings and soil properties in many cases governs not only the
earthworm abundance, but also the effectiveness of the earthworms for enhancing
crop yields. Consequently, the 25 per cent crop yield increase in the results of van
Groeningen et al (2014) is restricted to agricultural practices in which crop residues
are available and mineral fertilization input is low. In addition, different crop types
affect earthworms differently. Monocultural production of root-based crops such as
potato and carrot, which leaves no or little residues, can drastically decrease or even
completely deplete sound populations of earthworms in very short time (Curry et al
2002), whereas crops that leave much residues, such as wheat, stimulates earthworm
presence (Lofs-Holmin 1983; Curry et al 2002).
Accordingly, the stimulation of earthworm presence on crop yields is significant
albeit restricted to and dependent on both agricultural practices as well as soil
properties.
14 7. Results 7.1. Earthworm abundance Earthworm abundance and weight from the field trials in Önnestad and Bollerup are
shown in figure 1a and 1b. In Önnestad, the results indicate an unmatched earthworm
abundance and weight (g/m2) in connection to field treatment B, whereas field
treatment A exhibited very low total abundance and weight. In Önnestad thus,
checking for single factor variance shows a significant difference (P = 0,03) between
the groups, no statistical difference (P = 0,4) between the organic and conventional
field treatments, and a significant statistical difference (P = 0,01) between animal- and
non-animal keeping field treatments.
Earthworm abundance and weight, Önnestad 100 90 80 70 60 50 40 30 20 10 0 89 45 17 28 24 8 4 A B 28 18 16 C holes number 26 17 D 15 14 10 weight g/m2 E Field treatment Figure 1a: Earthworm abundance and weight from the field trials in Önnestad.
Abundance as in total earthworm and wormhole findings.
Noteworthy is that field treatment B exhibits the smallest weight/worm ratio, and
when considering the weight/earthworm ratio for the different field treatments the
results obtained (see table 2) show a homogenous trend in ratio difference between
the sites (E > C > A > D > B), with a larger internal heterogeneity in Önnestad. The
effect of the weight/worm ratio on the total weight/m2 in field treatment B is however
compensated for in Önnestad by the unrivalled relative earthworm abundance,
whereas it in Bollerup heavily affects the weight/m2 in a negative direction.
15 The samples from Bollerup showed less internal variation between the field
treatments than the Önnestad trial sites, and failed to yield any significant result (P =
0,10). Similarly, the comparison of organic and conventional field treatments, as well
as animal vs. non-animal keeping practices, failed to show any significant differences.
Earthworm abundance and weight, Bollerup 120 92 100 85 80 78 80 108 100 80 68 60 61 50 48 48 48 32 40 16 20 0 A B C holes number D E weight g /m2 Figure 1b: Earthworm abundance and weight from the field trials in Bollerup.
Abundance as in total earthworm and wormhole findings.
Table 2: Weight/worm ratio for the different field treatment sites in Önnestad and
Bollerup.
Field treatment Weight (g)/worm Önnestad Weight (g)/worm Bollerup
A
0,51
0,47
B
0,32
0,17
C
0,57
0,48
D
0,37
0,44
E
0,72
0,6
16 7.2. Earthworm abundance and wormholes: correlation Examining the correlations between the earthworm abundance and the amount of
wormholes show a very good correlation value for Bollerup (R2 = 0,962), and a fairly
good value for Önnestad (R2 = 0,648) (see fig. 2a and 2b). These results can be seen
as in line with previous assessment methods of earthworm abundance in agricultural
soil (Båth & Ögren 1995).
earthworm abundance Correlation of earthworm abundance and wormholes, Bollerup 30 y = 1,0584x + 3,6446 R² = 0,9623 25 20 15 Series1 10 Linear (Series1) 5 0 0 5 10 15 20 25 wormholes Figure 2a: correlation of earthworm abundance and wormholes in Bollerup. Results
show a high degree of correlation – R2 = 0,962.
earthworm abundance Correlation of earthworm abundance and wormholes, Önnestad 50,0 40,0 y = 5,2831x -­‐ 34,217 R² = 0,64843 30,0 Series1 20,0 Linear (Series1) 10,0 0,0 0,0 5,0 10,0 15,0 wormholes 17 Figure 2b: Correlation of earthworm abundance and wormholes in Önnestad. Results
indicate a correlation – R2 = 0,648 – albeit to a lesser degree than in Bollerup.
7.3. Earthworm abundance in differing topsoil depths
With regards to the low amount of samples obtained from the trial fields, testing for
significant differences in variance between groups in distinctive layer depths was
deemed inutile. However, the results – shown in the figures 3a and 3b below – can be
used as indications and show an overall higher abundance in the upper topsoil layer
(0-10 cm), with Bollerup field sites exhibiting higher abundance in all but one field
treatment site. This scenario is quite reversed in the lower topsoil layer (10-20 cm)
with three field treatment sites in Önnestad showing rather higher abundance than its
respective Bollerup sites.
Earthworm abundance 0-­‐10 cm Earthworm abundance 35 30,0 30 25 20 21 27 23 16 13,5 15 10 5 16 Bollerup 0-­‐10 Önnestad 0-­‐10 6,0 2,0 1,0 0 A B C D E Field treatment Figure. 3a: earthworm abundance in the topsoil layer 0-10 cm. Abundance as in
average of total findings.
18 Earthworm abundance 10-­‐20 cm Earthworm abundance 16 14,5 14 12 10 9 7,7 8 Bollerup 10-­‐20 6 4 3,7 4 2 1 2 2 2 0 0 A Önnestad 10-­‐20 B C D E Field treatment Figure 3b: earthworm abundance in the topsoil layer 10-20 cm. Abundance as in
average of total findings.
7.4. Organic Content SOM-levels from Önnestad are shown in fig. 4 below
The results of LOI show the highest organic content in field treatment C, and the
lowest organic content in field treatment E. Testing these two fields for single factor
variance yields a significant result (P < 0,005). However, neither animal vs nonanimal keeping practices, nor conventional vs organic practices show any significant
differences when compared for single factor variance.
19 SOM in Önnestad [ield treatments 8 7 SOM % 6 5 4 SOM % 3 SOM % 0-­‐10 2 SOM % 10-­‐20 1 0 A B C D E Field treatment Figure 4: The SOM of the different field treatments in Önnestad.
The results show high or very high SOM-contents in all fields when compared to
previous results from agricultural soils with similar soil profiles in Skåne (Larsson &
Mattsson 2005), which could be explained by differing methodological procedures
(Sato et al 2014). No results from Bollerup on SOM were obtained, but these field
treatment sites could be assumed to contain less SOM than the ones in Önnestad due
to the relatively higher humus content in the latter (Gissén & Larsson 2008).
7.5. Correlations of earthworm abundance and SOM A correlation analysis was performed with the parameters of SOM (in per cent) and
earthworm abundance (based on total amount) on the one hand, and of SOM and
earthworm weight/m2 on the other, with the figures 5a and 5b displaying the result.
The result indicates no correlation between neither SOM and earthworm abundance
nor SOM and the earthworm weight/m2in the field sites investigated, thus suggesting
that SOM was not of principal importance to the amount of earthworms in a site.
20 100 Earthworm abundance 90 B2 80 70 60 50 y = -­‐16,852x + 135,55 R² = 0,16461 40 30 20 Linear (Series1) C20 E26 10 Series1 D8 A14 0 0 2 4 6 8 SOM % Figure 5a: Correlation of total earthworm abundance and average SOM (in percent)
for each field treatment in Önnestad. There was no significant correlation.
30,0 B2 weight g/m2 25,0 20,0 y = -­‐4,2079x + 39,658 C20 R² = 0,13531 15,0 D8 Series1 10,0 Linear (Series1) E26 5,0 A14 0,0 0 2 4 6 8 SOM % Figure 5b: Correlation of earthworm weight/m2 and average SOM (in percent) for
each field treatment in Önnestad. There was no significant correlation.
21 8. Discussion 8.1. General discussion The long-term field trials in Önnestad and Bollerup constitute excellent providing for
comparisons between different agricultural field methods on a range of parameters.
Previously conducted research from the sites indicate a yield gap between organic and
conventional agriculture ranging from 13-48 per cent (Gissén & Larsson 2008; 137)
and a slightly higher exhaustion of soil potassium from organic field methods
(Andrist-Rangel et al 2007). However, the field trials also provide useful
opportunities for examining how different field methods affect essential soil-health
parameters such as earthworm presence and SOM-levels.
The results of earthworm abundance in Önnestad and Bollerup indicate a variance
exist between the different field treatments on the proneness of earthworm presence in
the agricultural practices. In Önnestad, the by far earthworm-richest field treatment
was in connection to field B, whereas fields A and E – both non-animal keeping
treatments – exhibited significantly lower earthworm abundance. The results also
indicate considerably higher earthworm abundance, in absolute numbers as well as in
g/m2, in Bollerup than in Önnestad. An assumption would be that the relatively more
fertile soils in Önnestad (Gissén & Larsson 2008; 9) also would display higher
earthworm abundance, as is stated by van Groeningen et al (2014).
No satisfying explanation to this fact is presented here, but considering the many
parameters of influence on earthworm abundance not investigated in this trial,
repeated studies allowing for comparison between the sites is recommended.
Another contrasting factor is that of SOM and earthworm abundance. Where previous
research has established a fairly close correlation between the amount of SOM and the
presence of earthworms (Lofs-Holmin 1983; Paoletti 1999), no such correlation was
found in this study (see figure 5a & 5b) in either of the categories tested. This could
be partly due to the unreliability of the SOM results obtained from the LOI, as this
procedure previously has been shown to entail a source of potential error (Sato et al
22 2014), but also due to the general complexity of the soil parameters governing the
earthworm abundance (Lofs-Holmin 1983; Paoletti 1999).
As for the abundance on differing layer depths, there was a notable demarcation line
in Bollerup with the 0-10 cm top layer exhibiting higher earthworm abundance in
connection to every field treatment. In Önnestad, however, the higher abundance was
fluctuating between the layers and field treatments.
8.2. Animal keeping and non-­‐animal keeping practices The contrasting of the field treatments into animal vs. non-animal keeping rendered
significant results on earthworm abundance in Önnestad but not in Bollerup. In
Önnestad, thus, both field treatments involving animal keeping displayed
considerably higher earthworm abundance than non-animal keeping treatments. In
Bollerup, However, both animal-keeping field treatments also displayed high
earthworm abundance, but the non-animal keeping treatment C displayed the second
highest abundance. Since no previous studies on the effects of animal keeping on
earthworm abundance were found, a common denominator distinguished was the
application of manure on the treatment sites. Kromp et al (1996) displayed how the
application of compost and organic manure had a significant positive effect on
earthworm abundance when compared to the application of mineral fertilizers or no
manure at all. Such an argument could in this context also be extended to include the
relatively high earthworm abundance in connection to field treatment C on both trial
sites. As previously mentioned, the C field treatment was managed in accordance to
biodynamical practices – with intrinsic animal keeping and addition of organic
manure on the fields - until the end of 2013, which could still affect the amount of
organic material available in the soil and would be confirmed by the Önnestad SOMlevels where the C-field indeed displayed the highest SOM. Unfortunately, the lack of
information on SOM-levels from Bollerup impedes any further certainty on this topic.
On the other side, another common denominator of the animal keeping field
treatments was the removal of crop residuals; a practice displayed to have a
decreasing effect on earthworm abundance compared to the sub-ploughing used by
23 fields A and E (Larsson & Mattsson 2005; van Groeningen et al 2014). Here, the
results contrast with previous studies, in that treatments where crop residuals were
removed also exhibited higher earthworm abundance.
The SOM levels failed to show any differences in the animal keeping vs. non-animal
keeping category. Here, previous studies emphasize the impact of tillage on topsoil
layer SOM (Liu et al 2006; Fuentes et al 2012), and crop properties (Curry et al 2002)
rather than features of an animal based agricultural practice.
In summary thus, when considering earthworm presence as an indicator for soil health
and soil quality (Paoletti 1999; Bispo et al 2009), the significantly higher earthworm
abundance in animal keeping field treatments shown by this study indicate that the
soil would benefit from such an agricultural practice. However, this result failed to
show in the SOM levels, which yielded no significant difference between animal
keeping and non-animal keeping practices. Since the LOI procedure for determining
SOM is proven to entail fluctuating reliability (Sato et al 2014), it is here suggested
that more accurate methods are used for determining SOM levels of the different field
treatments, along with additional samples of earthworm abundance, in order to
investigate the different field treatment’s effects on soil quality parameters more
thoroughly.
8.3. Organic vs. conventional practices The comparison of organic vs. conventional practices failed to exhibit any significant
differences in both earthworm abundance as well as SOM levels. Among the
distinguishing parameters assumed to have a differing impact on these categories was
the usage of pesticides. Although previous studies have suggested that the use of
pesticides entails negative effects on earthworm mortality, fecundity and growth
(Pelosi et al 2014), no such effects were exposed when comparing earthworm
abundance between organic and conventional practices. The effect of pesticides
applied in the conventional field treatments might have been duly compensated by the
fact that two of the three organic field treatments had been used for carrot crop in
24 2014 (see appendix 1 for field card of crops grown during 2014) which, according to
Curry et al (2002) has a negative impact on earthworm presence.
9. Conclusion The results of this study indicate that the long-term field trials in Önnestad entail a
higher earthworm abundance in connection to animal keeping practices, as opposed to
non-animal keeping practices. Whether this is due to effects of the practices
themselves or to soil parameters such as salinity or pH is here disregarded, as the
answer to this question would entail further studies.
No significant differences were found on the effects on earthworm abundance and
SOM levels when analysing organic vs. conventional field practices. Likewise, no
correlation could be drawn between the levels of SOM and the earthworm abundance
in Önnestad.
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29 Appendix Appendix 1: Field card showing the location and previous crop specimen of the field treatment sites in Önnestad. Fältkort för jordbruksförsök
Försöksseriens benämning
Skördeår
Olika miljömedvetna och uthålliga odlingsformer
Försöksvärd
Plan nr
L4-3410
2014
HL 4365
Jbr-omr
Gård eller by
Län
4A
133/86
Postadress
Önnestad
Naturbruksgymnasiet
Försök nr
L
Önnestad
A. Konventionell, kreaturslös trad lantbruksgrödor, grönsaker och klöverfrö (skörderesterna nedplöjes)
B. Konventionell, med kreatur, trad. lantbruksgrödor
C. Ekologisk, utan kreatur, trad lantbruksgrödor, grönsaker, biogasrötrest producerat inom systemet
D. Ekologisk, med kreatur, trad. lantbruksgrödor
E. Ekologisk utan kreatur, trad lantbruksgrödor, grönsaker och klöverfrö, inköpt växtnäring
(skörderesterna nedplöjes)
C6
D12
E18
B24
D år 4
E år 4
B år 4
A år 4
Havre
+ ins
Vårkorn
+ ins
Plantlök
Vårkorn
+ ins
Råg
+ vitklöver
E5
B11
D17
A23
C29
E år 6
B år 6
D år 6
A år 6
C år 6
Vitklöverfrö
Fodervall II
Fodervall II
Vårkorn
+ oljerättika
Biogasvall II
D4
A10
C16
E22
B28
D år 1
A år 1
C år 1
E år 1
B år 1
Rödbetor
Morötter
+ råg (fång)
Vårkorn
+ oljerättika
Vårkorn
+ oljerättika
Rödbetor
C3
E9
B15
D21
A27
C år 5
E år 5
B år 5
D år 5
A år 5
Biogasvall I
V-korn + vitkl
ersätter råg
Fodervall I
Fodervall I
Vitklöverfrö
B2
D8
A14
C20
D år 2
A år 2
C år 2
E år 2
Havre/ärt
+ rajgräs
Plantlök
+ råg (fång)
Morötter
+ råg (fång)
Morötter
+ råg (fång)
C7
E13
B19
D25
A år 3
C år 3
E år 3
B år 3
D år 3
Potatis
Plantlök
+ råg (fång)
Gröngödsling
+ oljerättika
Potatis
+ oljerättika
Potatis
+ oljerättika
Norrstreck
Försöket är beläget ca 100
12
E26
B år 2
Havre
A1
Bruttoruta
A30
C år 4
x
meter i SO
15
Plöjningsriktning
Riktning från
=
180
2
m
Berte
Skörderuta
X
=
m2
ÖVRIGA UPPGIFTER ANTECKNAS PÅ SÄRSKILT KORT FÖR RESP ODLINGSSYSTEM
Kontaktman vid Hushållningssällskapet
Per Modig, tel 044-22 99 47, 076-140 60 97
För försökets utförande ansvarig person
Telefon
Andreas Nilsson, 044/22 99 19, 0708-94 53 75
30