Organic Farming | 2016 | Volume 2 | Issue 1 | Pages 1–16
DOI: 10.12924/of2016.02010001
ISSN: 2297–6485
Organic
Farming
Research Article
Management Options for Organic Winter Wheat Production
under Climate Change
Ralf Bloch
1,2,
*, J
¨
urgen Heß
3
and Johann Bachinger
1
1
Leibniz Centre for Agricultural Landscape Research (ZALF), Institute of Land Use Systems, M
¨
uncheberg, Germany
2
Eberswalde University for Sustainable Development, University of Applied Sciences, Eberswalde, Germany
3
University of Kassel, Witzenhausen, Department of Organic Farming and Cropping Systems, Witzenhausen, Germany
* Corresponding author: E-Mail: bloch@zalf.de; Tel.: +49 3343282423; Fax: +49 3343282387
Submitted: 25 September 2015 | In revised form: 16 March 2016 | Accepted: 19 March 2016 |
Published: 19 April 2016
Abstract:
An effective adaptive strategy for reducing climate change risks and increasing agro-system resiliency
is broadening cropping system diversity, heightening the flexibility of cultivation and tillage methods. Climate
change impacts on standard cultivation practices such as mineralisation and nitrate leaching due to mild and
rainy winters, as well as frequent drought or water saturation, not only limiting fieldwork days, but also restricting
ploughing. This calls for alternative methods to counteract these propensities. From 2010 to 2013, a farming
system experiment was conducted on a distinctly heterogeneous organic farm in Brandenburg, Germany. With
the intention of devising a more varied and flexible winter wheat cultivation method, standard organic farming
practices (winter wheat cultivation after two years of alfalfa-clover-grass and ploughing in mid-October) were
compared to four alternative test methods, which were then evaluated for their robustness and suitability as
adaptive strategies. Two of the alternative methods, early sowing and catch crop, entailed moving up the
date for alfalfa-clover-grass tilling to July. Instead of a plough, a ring-cutter was used to shallowly (8 cm) cut
through and mix the topsoil. In the early sowing test method, winter wheat was sown at the end of August, after
repeated ring-cutter processing. With the catch crop method, winter wheat seeding followed a summer catch
crop and October tillage. The two oat methods (oat/plough; oat/ring-cutter) entailed sowing winter wheat in
September, following oat cultivation. Overall, the cultivation methods demonstrated the following robustness
gradation: standard practice = catch crop
early sowing
>
oat/plough
>
oat/ring-cutter. When compared to
standard procedures, the catch crop and early sowing test methods showed no remarkable difference in grain
yields. Measured against early sowing, the catch crop test method was significantly more robust when it came to
winterkill, quality loss, and weed infestation (40% lower weed-cover). High N
min
-values (up to 116 kg N ha
1
)
in autumn could have caused the chamomile and thistle infestation in both oat/plough and oat/ring-cutter test
methods, which led to crop failure in the hollows. Compared to standard practices, the oat ring-cutter test method
brought in over 50% less grain yield. This was attributed to ring-cutter processing, which reduced N mineralisation
and caused high weed infestation. However, the ring-cutter effectively regulated alfalfa-clover-grass fields in both
exceedingly wet and very dry weather; a temporal flexibility which increases the number of fieldwork days. The
catch crop and early sowing test methods contributed most to boosting future agronomic diversity.
Keywords: Adaptive capacity; cropping systems; on-farm research; reduced tillage; winter wheat
c
2016 by the authors; licensee Librello, Switzerland. This open access article was published
under a Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/).
librello
1. Introduction
Farmers today face the challenge of adapting their crop
cultivation methods to climatic changes. In the near fu-
ture, farms with a high adaptive capacity will have a dis-
tinct advantage. The adaptive capacity of a farm is estab-
lished first and foremost by expanding diversity and flexi-
bility [
1
]. Between 2009 and 2014, strategies to increase
the adaptive capacity of organic farms were developed
within the interdisciplinary project Innovation Network of
Climate Change Adaptation Brandenburg Berlin (INKA BB;
http://www.inka-bb.de/). Addressing practical issues re-
garding climate change adaptation, farmers and scientists
worked together to develop modification measures, which
were then tested on-site [
2
]. This paper illustrates a farming
system experiment probing test methods for adapting winter
wheat cultivation to climate change. The experiment was
carried out from 2010 to 2013 in northeast Germany on the
stockless organic farm Wilmersdorf.
1.1. Problem Description
Winter wheat provides the economic foundation for the
Wilmersdorf organic farm and has, thus far, been culti-
vated solely according to standard procedures. These stan-
dard organic farming procedures entail sowing winter wheat
on fields prepared with a two-year multispecies legume-
grass (LGS), which is mulched two to four times a year and
ploughed under in autumn of the second harvest year. Di-
rectly following this virgin tillage (i.e. ploughing the sward
without prior shallow soil processing), winter wheat is sown
in mid-October. The subsequent crop is usually winter rye.
This standard cultivation practice is practiced on large, rolling
fields averaging 40 hectares, interspersed with hills and
hollows. Such small-scale heterogeneity with varying soil
types (see Section 2.2), further complicates ploughing and
seedbed preparation. Poor soil contact and uneven germina-
tion are common problems. Particularly during dry periods,
a common occurrence at Wilmersdorf (Section 2.3), hilltops
are low yield (problem) areas and ploughing the shallow
topsoil there is limited. In contrast, the hollows are often
waterlogged, particularly in spring and in years with heavy
precipitation, which also severely limits ploughing. The farm
manager reports an annual fluctuation in winter wheat yields,
between
0.9–5.8 t ha
1
(Ø 3.5 t ha
1
)
. Therefore, to attain
high winter wheat yields with the standard practice, the nitro-
gen (N) supply from LGS residuals and the N-up-take vital
to winter wheat development must occur synchronously [
3
].
This process is closely linked to the water supply and the
soil’s microbial activity, which could be strongly influenced
by climate changes projected for Brandenburg [
4
]. Such
climatic developments include frequent mild and wet winters,
increasing spring and summer droughts, recurrent extreme
weather events (heavy rainfall and drought), and a rise in the
average annual temperature [
5
]. Figure 1 depicts projected
climatic changes from 2062 to 2092, illustrating their effects
on the Wilmersdorf organic farm.
In view of these projected climate changes, the current
standard cultivation practice reveals several weaknesses:
LGS virgin tilling in mid-October, followed by a mild and
rainy winter, may lead to N-mineralisation, nitrate leach-
ing and erosion, as the low development of winter wheat
mass is unable to take up sufficient nitrogen at this time
[
6
]. On the other hand, increasing drought in early spring
reduces microbial nitrogen release [
7
]. This can result in
an N-deficiency during developmental phases, when winter
wheat has high nitrogen requirements (Stem elongation;
Zadoks scale 30–32) [
8
]. Furthermore, ploughing in au-
tumn heightens erosion susceptibility and the risk of plough
sole compression [
9
]. As a result, root depth and infiltration
can be retarded, hindering the soil’s buffering capacity in
extreme weather events (heavy rain and drought).
These issues are compounded by the influence dry pe-
riods and increased precipitation in late autumn and winter
has on the number of suitable fieldwork days for ploughing
and sowing. In the future, winter crop sowing conditions
could deteriorate in direct proportion to the instability of
appropriate fieldwork days [10].
Since LGS processes great quantities of water via tran-
spiration, increasing temperatures can potentially lead to a
water shortage in the soil, inhibiting subsequent crop growth
[
9
]. Despite uncertainties in climate predictions, the above
listed weaknesses illustrate how strongly climatic changes
may influence growth, site and weather conditions, and so
of course crop yields. The question is, which strategies and
measures can minimise yield risk in future winter wheat
cultivation on the Wilmersdorf organic farm?
Figure 1.
Monthly temperatures and precipitation observed
from 1978 to 2008 and projected for 2062–2092 by the
Angerm
¨
unde Climate Station; Climate data modeled on the
regional statistics model STARS [11].
1.2. The Central Issue
The extent of climate risks can be offset by increasing diver-
sification within an agricultural ecosystem. This means not
only introducing a greater diversity in crops and varieties,
but also more flexibility in cultivation and tillage methods
[
12
,
13
]. Such alternative tilling and/or seeding methods
help farmers more effectively adapt to changing weather
conditions, extending the number of available fieldwork days.
2
To date, the Wilmersdorf organic farm has used only one
method for producing winter wheat.
This work is therefore dedicated to the following ques-
tions: In addition to the standard practice, which winter
wheat cultivation methods are most effective in offsetting
climate change influences? Which methods contribute most
to diversification on a specific farm?
1.3.
Alternative Test Methods for Winter Wheat Cultivation
In collaboration, the Wilmersdorf farm manager and the
INKA BB field trial project a) developed new cultivation tech-
niques and, b) tested the viability of these methods as alter-
natives to standard procedures. When evaluating various
courses of action, i.e. cultivation methods, for their adapt-
ability to uncertain climate change conditions, robustness
is an important criterion [
14
]. Robustness is a system’s
immunity to a wide range of influences [
15
]. In this case,
the robustness of a new cultivation method is measured
by its yield stability over a three-year period under varying
field conditions. Hallmarks of these new cultivation meth-
ods are reduced tillage and alternative crop rotation. They
should be able to improve the N and water supply to winter
wheat. These alternative cultivation methods, (Figure 2),
and the reduced tillage agricultural tool, the ring-cutter, will
be described in detail.
A new agricultural tool, the ring-cutter, was used for the
first time during the field tests in Brandenburg. This agricul-
tural instrument has cutting rings running diagonally to the
driving direction, allowing for an overall, non-turning, shallow
tillage (see: http://www.heko-landmaschinen.de). The spe-
cial ring-cutter construction is intended for soil processing
when dryness or sogginess renders ploughing unsuitable.
As opposed to the plough, the ring-cutter could be applied to
both the dry hilltops and damp hollows on Wilmersdorf farm.
The tool should also enable unploughed LGS processing, so
that grain mulch seeding (early sowing and oat/ring-cutter
test methods) or catch crops can be seeded directly follow-
ing ring-cutter processing. If ring-cutter processing proves
successful, summer crops and early sowing can stay on
schedule, despite wet or dry soil. At the same time, shallow
processing can reduce the water loss caused by evaporation
in ploughed soil. Reduced tillage with the ring-cutter should
also retard N-mineralisation, reducing the risk of N-leaching
in winter (see test method oat/ring-cutter) [16].
1.3.1.
Early Sowing of Winter Wheat and a Summer Catch
Crop
In the cultivation methods early sowing and catch crop, the
LGS processing date is moved forward to mid-July (summer
processing). This early treatment of LGS can either move
winter wheat seeding forward or prepare a better seedbed
than virgin tillage and an autumn furrow do. Instead of the
plough, the ring-cutter is used for early, mechanical LGS
killing. The early sowing test method repeats ring-cutter
processing two or three times between mid-July and mid-
August, creating a mulched summer fallow. This fallow
protects the soil from water loss that would otherwise occur
in living LGS crop transpiration [
9
]. The mulch also protects
from evaporation, reducing water loss from the soil surface
(evaporation fallow) [
17
], while seasonal heavy rains are
buffered by the mulch (erosion protection) [
18
]. At the end
of August, the catch crop mixture (50% summer vetch, Vicia
sativa; 28% buckwheat, Fagopyrum esculentum; 16% flax,
Linum usitatissimum; and 5% Phacelia) is sown directly
into the summer fallow (mulch seeding). Not turning the
earth protects soil life, keeping vertical earthworm chan-
nels (macropores) intact and improving infiltration [
19
21
].
Since it has a longer and stronger plant growth until its dor-
mant season, early sown winter wheat should better absorb
the nitrogen mineralised from late summer to early autumn
[
22
,
23
]. The catch crop mixture should suppress weed
growth and prevent an overly lush development of the early
sown winter wheat [
24
]. Furthermore, in autumn the catch
crop absorbs any potential nitrogen surplus, conserving it
in its biomass throughout the winter. In spring, the frozen
catch crop vegetal material mineralizes the soil, supplying
the winter wheat with the required nitrogen. Early sown
winter wheat develops more profusely in spring, creating
better rooting in the subsoil. This is conducive to the nitro-
gen and water supply in the event of a spring drought. Also,
early sowing pre-dates winter wheat primary water needs
(stem elongation) to a time when the soil should still have
enough winter moisture. Furthermore, the early seeding
head-start in growth should assure the plants are no longer
subjected to drought stress during the grain filling phase
[
25
,
26
]. The unploughed early sowing test method should
primarily improve crop establishment and the subsequent
grain yield on dry hilltops.
Figure 2.
Winter wheat (WW) test methods with plough and
ring-cutter in the cultivation field tests on the farm Wilmers-
dorf (2010–2013). Sp: standard practice (plough); ESr:
WW early sowing (ring-cutter); CCp: winter wheat follow-
ing catch crop (plough); Op: winter wheat following oat
(plough) and Or: winter wheat following oat (ring-cutter);
LGS: Legume-grass swards; personal compilation.
3
In contrast to early sowing, the catch crop test method
does not have summer fallow. Instead, after repeated pro-
cessing with the ring-cutter, the same catch crop mixture
as in early sowing is sown at the end of July. The aim of
the catch crop is to bind nitrogen mobilised by the early
LGS tilling in summer, and to convert it into organic material
which will have a narrow C/N ratio the following spring [
27
].
This material activates soil life, improving N resources for
winter wheat. Coinciding with the standard autumn furrow,
the catch crop is ploughed immediately before winter wheat
late seeding (mid-October).
1.3.2. Winter Wheat Following an Oat Crop
In the oat/plough and oat/ring-cutter test methods, LGS
tillage takes place in late March. The advantage of spring-
time tillage over autumn tillage is that the pre-winter min-
eralisation from LGS residuals, and so nitrate leaching, is
nearly non-existent [
6
]. Compared to autumn tillage, spring
tillage usually allows for a better balance between the N
release from LGS residuals and N crop up-take [
27
]. Due
to the generally cooler temperatures and a high C/N LGS
residual ratio, tillage in spring can also go hand in hand
with delayed N mineralisation [
6
,
27
]. Since the mineralisa-
tion process following spring tillage begins later and lasts
longer, often only the second subsequent crop profits from
the N provided by multi-annual LGS [
6
]. For this reason,
the oat/plough and oat/ring-cutter test methods switch crop
rotation, growing oats prior to winter wheat. By inserting
oats, the N-deployment from organic plant matter (decom-
posed LGS residuals, straw and oat root residues) is more
in sync with winter wheat N up-take the following spring.
The advantages of oat as an LGS subsequent crop are
its extensive root system and high nutrient up-take [
28
],
while as a winter wheat preceding crop, oat’s vegetative
growth suppresses weeds. As a recovery crop, oat pre-
vents the spreading of fungal pathogens, such as black
root rot (Gaeumannomyces graminis) [
29
,
30
]. At the same
time, the increased winter moisture resulting from climate
change should be used productively for early oat cultivation,
extending the cultivation period in the future. An earlier
vegetation period grants a surplus of available fieldwork
days for seeding spring grains [10,31].
To keep future seeding on schedule despite higher winter
precipitation (see Figure 1) saturating the soil, the oat/ring-
cutter test method foregoes ploughing, working the oats with
the ring-cutter to establish mulch-till. After harvesting the
oats, the stubble is worked with the ring-cutter. The oat straw
remains on the field, as its broad C/N ratio helps prevent ex-
cessive LGS-residue N release in autumn and subsequent
nitrate leaching in winter. In contrast to standard procedure
virgin tillage, prior oat cultivation improves the winter wheat
seedbed preparation and allows for a more flexible seeding
schedule. In both oat test methods, winter wheat is sown
at the end of September. In test method oat/ring-cutter,
seeding follows reworking the soil with the ring-cutter—
unploughed mulch-till—while test method oat/plough en-
tails renewed ploughing. All unploughed test methods are
designed to improve dry hilltop yields.
1.3.3. Hypotheses
The robustness of each cultivation method is tested based
on the following hypotheses:
(1)
The ring-cutter effectively cuts and regulates LGS in
both damp and dry soil conditions, where ploughing is
restricted.
(2)
Compared to the standard practice, winter wheat
test methods ploughed in autumn, catch crop and
oat/plough, produce equivalent annual grain yields, on
hilltops as well as in hollows.
(3)
The unploughed winter wheat test methods early sow-
ing and oat/ring-cutter are particularly suitable for dry
hilltop sites, where, when compared to hollows, the an-
nual grain yields of these test methods come closer to
those of standard practices.
2. Materials and Methods
2.1. Farm Location and Characteristics
The stockless organic farm Wilmersdorf (Bioland growers’
association member) is located in the north German low-
lands in the northeast of Brandenburg (Uckermark; com-
munity Angerm
¨
unde, district of Wilmersdorf: 53.11431
N;
13.90660
E). The farm has over 1,108 hectares of arable
land and 5 hectares of grassland. Almost half of the arable
land is used to grow legumes. Forage legume cultivation
accounts for the main area (surface area 29%), followed
by grain legume cultivation (19%). The remaining half of
the arable land is reserved for growing grains, winter rye
(28%) and winter wheat (20%), spelt (16%) and spring
wheat (15%), as well as winter and spring barley (12% and
9%, respectively). Wilmersdorf has predominately sandy
loamy soil and implements the following crop rotation: Al-
falfa clover-grass / winter wheat / winter rye / field peas /
spelt under sown with alfalfa clover-grass.
2.2. Soil Characteristics
Wilmersdorf, located in the upper moraine region, is domi-
nated by a hilly to undulating landscape of hills and hollows
(40 to 75 meters above sea level) [
32
]. Sub-glacial till,
lime-free loam or loamy sand prevail [
32
]. The topsoil is
characterised by soil erosion and a low decalcification depth.
Predominant is calcite luvisol/gley luvisol (brown soil fam-
ily), known for both its fertility and its tendency to compress
the topsoil foundation [
32
]. Typical, indigenous catena se-
quences are, from the hilltop to hollow, calcarite regosol
>
eroded calcite luvisol
>
gley luvisol
>
eutric gley [
33
]. In dry
years, exposed hilltops are prone to yield reductions, while
in wet years the loss occurs on the lower slopes and in the
hollows [
32
]. At the same time, the eroded peaks exhibit
higher pH values than the hollow depressions (Table 1).
4
Sandy loam was the predominant soil type in all sub-plots
of the pilot facility. Considering a main root zone of 100 mm,
sandy loam has a field capacity of 110 mm. In contrast to
the hollows, the hilltops are carbonaceous, and average
a higher proportion of clay and higher pH values (Table
1). The carbonate level indicates the initial till substrate
which topsoil erosion has brought close to the surface. Soil
samples found compressed topsoil foundation (soil depth
20–25 cm) on the shallow calcarite regosol hilltops (Ah/C
soil). In the samples taken in 2011, the above-mentioned
soil conditions were particularly pronounced. Ploughing
was limited on the hilltops due to the shallow topsoil and
the initial substrate’s proximity to the surface.
2.3. Climatic Conditions
The Wilmersdorf climate is characterised by low annual
rainfall and frequent dry periods in early summer and au-
tumn. With 517 mm annual rainfall and an average annual
temperature of 8.8
C, it is one of the driest regions in Ger-
many [
32
]. The three experiment years (2010–2013) were
partially influenced by extreme weather patterns and high
annual precipitation that exceeded the long-term average
in all three years (Figure 3).
In 2010, high precipitation in summer (August: 117 mm;
annual rainfall: 640 mm), made most fields impassable dur-
ing both harvest and autumn sowing. 2011 was marked by
a very warm and dry April and heavy rains in July
(203 mm)
.
Annual rainfall was 693 mm. Winter 2012 brought black
frost and a succession of frost/thaw cycles, leading to con-
siderable winterkill. The early sowing test method plots
were so badly damaged by winterkill that they had to be re-
established with spring wheat. After a warm and a partially
dry spring, above average precipitation fell in July (annual
rainfall 626 mm). A prolonged and snowy 2012/2013 win-
ter was followed by a pre-summer drought in April, then a
dry and warm July and August. With an annual rainfall of
583 mm, 2013 was the driest project year.
2.4. Test Plots and Implementation
The field trial was designed as a three-year serial experi-
ment. Complying with crop rotation, the experiments were
carried out on a different field each year. Two homogeneous
fields (one hilltop, one hollow) were selected on each of
these fields by interfacing digital plot, soil and yield maps.
The trial cultivation systems were set upon the two sites in
fully randomised blocks. Each block contained four plots
divided into five sub-plots (20 sub-plots per site/40 sub-plots
total). Except for reaping, the 15 m long by 5 m wide plots
were worked with the customary combine harvester. The in-
dividual steps, deadlines and applied techniques are listed
in Table 2. The selected ring-cutter tool had a three-meter
working width, six cutting rings and a leaf spring roller for
reconsolidating the soil. After the winter wheat harvest, the
trial plots were completely ploughed and winter rye was
cultivated.
Table 1. Soil attributes of the experiment plots.
Trial No. Plot No. pH
KCL
C
org
% CaCO
3
% Gravel % Sand % Silt % Clay% Field Cap.% Vol.
+
Texture class*
5 401-405 7.07 2.27 4.2 60.2 29.6 10.2 18.8 SaL
406-410 6.91 2.54 2.3 60.3 28.3 11.4 19.6
411-415 6.95 2.5 5.7 60.7 27.9 11.4 19.6
416-420 6.99 2.89 4 56.9 29.7 13.4 21.7
6 421-425 7.43 3 3.9 52.1 28.2 19.7 26.2 SaL
426-430 7.4 2.82 3.51 4 57.6 28 14.4 22.4
431-435 7.13 2.71 1.3 59.9 28 12.1 20.3
436-440 7.5 3.51 2.16 1.4 52.8 26.9 20.3 26.6
245 481-485 6.72 2.64 3.3 55.9 33.8 10.3 20.9 SaL
486-490 7.03 2.97 1.6 54.3 33.8 11.9 22.1
491-495 6.01 2.39 1.6 58.7 27.5 13.8 21.2
496-500 6.69 2.84 1.5 57 31.6 11.4 20.7
246 501-505 7.49 2.89 7.41 1.9 53.6 31.8 14.6 23.6 SaL
506-510 7.56 3.14 4.86 2.7 51.8 30.8 17.4 24.6
511-515 7.73 2.65 6.97 3.1 55.2 31.6 13.2 21.8
516-520 7.59 2.69 7.92 4.3 54.6 29.9 15.5 22.9
253 5101-5105 7.32 2.39 2.5 64.9 23.9 11.2 18.7 SaL
5106-5110 7.44 2.83 2.7 56.8 30.5 12.7 21.5
5111-5115 7 3.07 1.7 58 29.9 12.1 21.7
5116-5120 7.38 3.23 1.7 55 29.1 15.9 22.1
254 5121-5125 7.5 3.24 4.11 2.7 56.8 29.2 14 22.4 SaL
5126-5130 7.64 2.86 7.35 2.5 52.5 33.4 14.1 23.2
5131-5135 7.62 2.27 9.19 3.7 56.1 29.5 14.4 21.6
5136-5140 7.57 2.8 4.73 2.2 60.2 26.6 13.2 21
* estimated with the soli texture triangel USDA;
+
estimated with the soil water characteristics programm USDA.
5
Figure 3.
Temperature and precipitation regime at Wilmersdorf project location from 2010 to 2013 (project term) and
1971–2000 (long-term average).
Table 2.
Steps and schedule for the Sp (standard practice; plough), ESr (winter wheat early sowing; ring-cutter), CCp
(winter wheat following catch crop; plough), Op (winter wheat following oat; plough) and Or (winter wheat following oat;
ring-cutter) test methods of winter wheat cultivation following LGS.
Year 2010 2011 2012
Variant Sp ESr CCp Op Or Sp ESr CCp Op Or Sp ESr CCp Op Or
Ploughing
*
04-04 28-03 26-03
Ring-cutter
+
30-03 24-03 23-03
04-04 28-03 26-03
Oat sowing
+
05-04 29-03 05-04
Oat harvest
06-08 04-08 20-08
Mulching LGS-Mixture
◦◦
31-05 31-05 31-05 15-06 15-06 15-06 24-05 24-05 24-05
09-07 09-07 09-07 22-07 22-07 22-07 06-07 06-07 06-07
09-08 23-08
14-10
Ring-cutter
+
13-07 13-07 12-08 30-03 26-07 26-07 17-08 17-08 09-07 09-07 23-08 23-03
16-07 16-07 17-09 04-04 28-07 28-07 29-08 29-08 12-07 12-07 17-09 26-03
19-07 19-07 12-08 17-08 24-09 03-08 23-08
12-08 17-09 29-08 23-08 17-09
02-10
Catch crop sowing
22-07 02-08 16-07
Ploughing
*
19-10 19-10 20-09 24-10 24-10 24-09 16-10 16-10 02-10
Winter wheat sowing
19-10 26-08 19-10 22-09 22-09 25-10 31-08 25-10 27-09 27-09 18-10 23-08 18-10 18-10 18-10
Intercrop sowing
26-08 31-08 23-08
Year 2011 2012 2013
Winter wheat harvest 04-08 20-08 01-08
Winter rye sowing
05-10 05-09 20-09
Winter rye harvest - 01-08 24-07
*
Lemken Opal 90: Mounted reversible plough with four bodies (working depth 25 cm);
+
Ring-cutter (working width 3 m; working depth 6-8 cm);
V
¨
aderstad Drill Rapid 300 C (working width 3 m);
◦◦
Mulching dates depending on the crop height.
6
2.5. Data Compilation and Analysis
The yields of oat, winter wheat, and subsequent winter rye
(2012 and 2013) were assessed by documenting the num-
ber of ears per square meter, the thousand kernel weight
and the grain yield. The crude protein content in winter
wheat, an indication of grain quality, was measured as well
as the oat hectolitre weight. The development and structure
of crops were determined by visually appraising cultivated
plants, weeds and catch crop mixture coverage [
34
]. Weed
appraisal focused on pre-eminent weeds displaying a high
degree of both consistency and coverage.
Biomass growth was compiled by taking manual cuts
(
0.5 m
2
) from LGS, the oat crop and the summer catch crop.
Depending on the test method (Figure 2), two manual LGS cuts
were taken from plots of the early sowing and the catch crop
method, and three cuts were taken from standard practice plots.
All LGS cuts were taken independently, either before the usual
mulching dates or prior to using the ring-cutter for the first time,
respectively (Table 2). The LGS cuts from oat fields (Zadok
scale 69) and from the summer catch crop were taken after
buckwheat bloom [
8
]. To determine the respective yield share,
the LGS and oats samples were sorted by hand. The N-input
of the second harvest year was determined by calculating LGS
biomass yield, leguminosae and N-content. With the N-balance
calculator the N-input count was taken from N
2
-fusion minus
gaseous N-losses that arise from mulching [
35
]. Soil samples to
determine Nmin- content were extracted as weather conditions
allowed (P
¨
urkhauer drills, soil layer 0–60 cm), i.e. in autumn after
winter wheat seeding, at the beginning of vegetation in spring
and after the winter wheat harvest. For the extraction of the soil
mineral nitrogen, NH
4
-N and NO
3
-N 2M KCl solution was used.
In 2010, due to drought, one shallower sample (0–30 cm soil
layer) was taken after the oat harvest in late summer. The sta-
tistical variance analysis was carried out with MIXED procedure
(SAS 9.1 statistical software) and subsequently compared to
the mean values (Tukey HSD test).
3. Results
3.1. Preceding Crops—Alfalfa-Clover-Grass and Summer
Catch Crops
In accordance with test method design, the same LGS seed
mix was sown on all plots over all three years. Over all three
years, no substantial differences in the quantity of biomass
growth on hilltops and hollows could be discovered (Table
3). However, there was a great difference in growth quality
regarding which species grew on which site. On the hilltops,
LGS growth regularly exhibited a higher percentage of al-
falfa; in the hollows, more grasses, herbs, white clover and
weeds (Table 4).
In 2010 and 2011 until mid-October, catch crop test plots
achieved growth between 2.5 and 3.9 t DM ha
1
, (N up-take
from 72 to 100 kg N ha
1
). In contrast, in 2012, low rainfall
in August and unevenly distributed precipitation in September,
caused summer catch crop plots to fail (Table 3).
Table 3.
LGS dry mass yields as well as CCp method catch
crop dry mass yields (t DM ha
1
). Sp: Standard practice
(plough); ESr: Early sowing of winter wheat (ring-cutter);
CCp: Winter wheat following catch crop (plough); CC: Catch
crop.
Site Year Test method Cut 1 Cut 2 Cut 3 CC
Hollow 2010 SP 4.1 3.3 2.2
ESr 4.7 4
CCp 4.5 3.3 3.7
HSD 2.2 0.9
p-value 0.7179 0.0947
2011 SP 5.7 5.3 4.1
ESr 5.4 5.9
CCp 5.7 5.9 2.8
HSD 1.3 1.4
p-value 0.7125 0.3542
2012 SP 5 2.4 4.4
ESr 4.8 2.5
CCp 5.1 2.7
HSD 1.4 1.1
p-value 0.8631 0.7744
Hill 2010 SP 4.7
a
4.3 2.5
ESr 4.7
a
3.5
CCp 5.8
b
4.6 3.9
HSD 1 2.3
p-value 0.0318 0.3774
2011 SP 4.9 4 3
ESr 5.2 3.6
CCp 5.7 4.5 2.5
HSD 2.1 3.3
p-value 0.571 0.6816
2012 SP 4 1.7
a
2
ESr 4 2.3
a
CCp 4.7 2.4
b
HSD 1.5 0.5
p-value 0.3866 0.0067
HSD (honestly significant difference);
Different letters indicate significant differences (α 0.05).
Table 4.
Yield shares in % of alfalfa, white clover, red clover,
grass and herbs in the LGS mixture. Alfal: alfalfa; WC:
white clover; RC: red clover; herb.: herbs.
Site Year Alfal. WC RC Grass/herb.
Hollow 2010 9 66 25
2011 49 4 47
2012 38 15 47
Hill 2010 62 23 14
2011 76 1 23
2012 63 5 1 32
3.2. Preceding Crop Oats
In 2010 and 2012, oat yields were 21% and 54% higher
in the oat/plough test method than in the oat/ring-cutter
test method, respectively (Table 5). In each trial year, the
yield difference between the two test methods was more
pronounced in the hollows than on the peaks. Only on the
hilltops in 2011, where ploughing was limited, (see Section
2.2), did the unploughed oat ring-cutter method achieve a
17% higher oat grain yield.
7
Table 5.
Oat yield structure—Op and Or methods. Op:
Oat variant with plough; Or: Oat variant with ring-cutter;
tkw: thousand kernel weight.
Site Year Test Ears tkw Grain yield Hectolitre
method (m
2
) (g) (t ha
1
) weight (kg)
Hollow 2010 Op 270 36.2 5.1
a
45.8
Or 211 35.8 2.9
b
45.9
HSD 76 12 1.5 0.7
p-value 0.0829 0.5128 0.0214 0.1001
2011 Op 307 47.3 5.3 51.5
Or 280 49.1 4.6 51.4
HSD 41.7 4.2 2.4 2.1
p-value 0.1266 0.2744 0.4132 0.8299
2012 Op 145 41.4 3.9
a
48.2
Or 178 39.9 1.8
b
48.1
HSD 76 2.9 0.2 3.5
p-value 0.2612 0.2177 <.0001 0.9349
Hill 2010 Op 243
a
36.2 4.2
a
43.9
Or 181
b
36.1 3.3
b
45.2
HSD 21.4 3.2 0.4 3.8
p-value 0.0027 0.9624 0.0076 0.3451
2011 Op 285 46.1 3.6 49.5
Or 274 48 4.1 50.3
HSD 73.8 6.2 1.6 0.9
p-value 0.668 0.3883 0.3302 0.0657
2012 Op 209 41.2 4.2 47.8
Or 165 41.6 2.3 48.2
HSD 61.8 2.3 2.3 1.6
p-value 0.1082 0.6804 0.0882 0.4824
HSD (honestly significant difference);
Different letters indicate significant differences (α 0.05).
3.3. Winter Wheat
Among test methods, the winter wheat grain harvest varied
considerably. This variance was most pronounced in the
years with extreme weather conditions (2011 and 2012; see
Section 2.3.).
In 2011 and 2012, winter wheat on the oat/plough and
oat-ring-cutter test plots could not be harvested due to fre-
quent heavy precipitation and a rampant weed infestation
(Tripleurospermum perforatum). In all years and on all test
plots, when harvesting was possible, winter wheat grown with
the oat/ring-cutter test method produced the lowest grain
yield of all test methods—significantly lower on hilltops in
2012 and 2013; and in hollows in 2013 (Table 6). In addition,
the hilltop winter wheat in oat/ring-cutter test methods exhib-
ited decidedly lower crude protein in 2011 and 2012. There
was no great difference in grain yields between the standard
procedure and early sowing and catch crop test methods.
Compared to standard practices, however, the early sowing
method had consistently lower grain yields. In 2011, the crude
protein content in early sowing was markedly lower than in
standard and catch crop methods. In contrast, in the dry year,
2013, early sowing exhibited a much higher thousand kernel
weight than standard and catch crop methods. The catch
crop method came closest to matching the standard practice
in yield and quality. With the exception of catch crop in 2013,
none of the alternative test methods were able to achieve a
higher yield than the standard practice.
3.4. Subsequent Crop Winter Rye
In 2012 and 2013, winter rye was a subsequent crop to
winter wheat, bringing in high grain yields, especially in the
hollows. With the exception of the thousand kernel weight
in the hollows in 2013 there was no discernible difference
between the test methods (Table 7).
Table 6.
Winter wheat yield and quality. Sp: Standard
practice (plough); ESr: Early sowing of winter wheat
(ring-cutter); CCp: Winter wheat following catch crop
(plough); Op: Winter wheat following oat (plough); Or:
Winter wheat following oat (ring-cutter); tkw: thousand
kernel weight.
Site Year Test Ears tkw Grain yield Crude
method (m2) (g) (t ha-1) protein (%)
Hollow 2011 SP 256 41.9 4 13.6
a
ESr 262 41.3 3.6 11.0
b
CCp 243 43.7 3.8 12.4
a
Op - - - -
Or - - - -
HSD 84.3 3.4 2 1.3
p-value 0.7886 0.1727 0.807 0.0025
2012 SP 197 46.6 3.1 13.9
ESr * * * *
CCp 189 47 2.9 13.9
Op - - - -
Or - - - -
HSD 127.4 5.4 2.4 1.7
p-value 0.8544 0.8314 0.7934 0.9942
2013 SP 166 43.9
a
2.8
a
13
ESr 185 48.2
b
2.8
a
12.6
CCp 191 42.9
a
2.8
a
12.7
Op 187 42.2
a
2.3
a
12.7
Or 181 38.4
c
1.0
b
12.7
HSD 74.1 3.3 0.8 1
p-value 0.851 <.0001 <.0001 0.7514
Hill 2011 SP 270 43.9
ab
4.6
a
12.8
a
ESr 237 41.1
a
3.5
ab
10.3
b
CCp 250 45.8
b
4.5
a
11.4
a
Op 176 41.8
a
3.6
ab
9.9
c
Or 158 42.5
a
1.9
b
9.9
c
HSD 157.3 2.9 2 1.5
p-value 0.1647 0.0018 0.0078 <.0001
2012 SP 170
a
42 2.6
a
13.6
a
ESr * * * *
CCp 153
ab
40 2.5
ab
13.7
a
Op 93
b
40 1.3
ab
12.6
ab
Or 85
b
44.7 1.2
b
11.6
b
HSD 68.6 7.5 1.3 1.1
p-value 0.0082 0.359 0.0172 0.0009
2013 SP 218 41.7
a
2.6
ab
11.5
ESr 177 47.1
c
2.6
ab
11.9
CCp 188 42.6
a
2.9
a
11.7
Op 234 40.5
ab
2.2
b
11.6
Or 171 37.5
b
1.2
c
11.4
HSD 87 3.1 0.4 0.8
p-value 0.1562 <.0001 <.0001 0.3644
*Winterkill damage; HSD (honestly significant difference);
Different letters indicate significant differences (α 0.05).
8
Table 7.
Yield structure—subsequent winter rye crop.
Sp: Standard practice (plough); ESr: Early sowing of
winter wheat (ring cutter); CCp: Winter wheat follow-
ing catch crop (plough); Op: Winter wheat following oat
(plough) and Or: Winter wheat following oat (ring cutter);
tkw: thousand kernel weight.
Site Year Test Ears tkw Grain
method (m
2
) (g) yield (t ha
1
)
Hollow 2012 SP 400 34.1 6.2
ESr 403 33.4 6
CCp 351 35 6.4
Op 370 33.9 5.9
Or 426 35.3 6.2
HSD 111.3 2.6 2.2
p-value 0.2842 0.2873 0.9548
2013 SP 438 31.9
a
4.9
ESr 438* 34.1*
ab
6.0*
CCp 485 32.2
a
5
Op 476 32.3
a
6.3
Or 430 35.4
b
5.3
HSD 152.2 2.3 2.4
p-value 0.6883 0.0015 0.2964
Hill 2012 SP 294 35.4 5.2
ESr 357 33.4 5.1
CCp 306 34.7 4.8
Op 244 34.9 4.1
Or 278 35.1 4.6
HSD 124.9 3.2 2.2
p-value 0.1238 0.3836 0.5357
2013 SP 244 35 3.7
ESr 223* 37.3* 2.9*
CCp 269 36.8 4.2
Op 221 36.2 2.5
Or 269 34.7 3.3
HSD 180.37 5.3 5
p-value 0.8397 0.6058 0.8433
*Preceding crop summer wheat;
HSD (honestly significant difference);
Different letters indicate significant differences (α 0.05).
3.5. N-dynamic
The N-dynamic in cultivation methods was estimated based
on the LGS N-input, N-up-take in the grains and N
min
-
contents in the soil. Interdependent on tilling date, biomass
yield and the leguminous crop, the LGS provided an N-input
from 145 to 352 kg N ha
1
in the second harvest year (Ta-
ble 8). Oats attained the highest nitrogen up-take after LGS
tillage and ploughing, taking up more than 100 kg N ha
1
in the hollows in 2010 and 2011.
In late summer 2010 (Table 9), N
min
sampling from
the early sowing and catch crop test plots at the hollow
exhibited significantly higher N
min
values than the other
test methods. Prior to sampling, the LGS plots of both test
methods were killed in July via root separation with the
ring-cutter (see Table 2).
In the autumn of 2011 and 2012, oat/plough and
partly oat/ring-cutter wheat plots exhibited significantly
higher N
min
-values than those of the standard practice
(Ø +45 kg N ha
1
; Table 10). Oat plough had the highest
N
min
-values of all test methods. In spring, the highest
N
min
-values were always observed on standard practice
and catch crop wheat plots, which had been ploughed at
a later date. Compared to the standard practice, oat/ring-
cutter and oat/plough methods had significantly lower N
min
-
values in the spring (Hollow 2011–2013). There were no
remarkable differences in N
min
-values in samples taken
from beneath the subsequent winter rye crop (08.11.2011,
22.10.2012), or taken immediately after the winter wheat
harvest (08.02.2013; Table 11). The five highest N
min
-
values of all sampling dates were found in the subsequent
winter rye crop (max. value,
148 kg Nha
1
; oat/ring-cutter
test method).
Table 8.
N-input and N-uptake in the crop sequence (N kg
ha
1
). Sp: Standard practice (plough); ESr: Early sowing
of winter wheat (ring cutter); CCp: Winter wheat follow-
ing catch crop (plough); Op: Winter wheat following oat
(plough); Or: Winter wheat following oat (ring cutter).
Site Year Test Input Uptake Uptake Uptake Balance
method LGS Oat WW WR
Hollow 2010–2012 SP 259 83.8 83.7 0.32
ESr 191 59.5 78.2 0.31
CCp 180 71.2 80.3 0.4
Op 105.8
a
74.6
Or 56.2
b
76.2
HSD 43.7 43.5 26.5
p-value 0.0447 0.3031 0.8273
2011–2013 SP 267 65.4 52 0.24
ESr 184 66
CCp 211 60.3 54.4 0.29
Op 100.4 66.6
Or 83 54.4
HSD 40.4 47.5 25
p-value 0.2642 0.7571 0.2373
2012–2013 SP 206 55.4
a
0.27
ESr 145 53.2
a
0.37
CCp 146 54.6
a
0.37
Op 73.2 a 43.4
a
Or 31.7 b 18.8
b
HSD 9.2 14.3
p-value 0.0007 <.0001
Hill 2010–2012 SP 352 87.4
a
69.2 0.25
ESr 265 54.2
bc
65 0.2
CCp 278 77.8
ab
60.2 0.28
Op 79.0
a
53.8
bc
49.5
Or 59.0
b
29.1
c
57.5
HSD 10.53 32.3 27.4
p-value 0.0091 0.0008 0.255
2011–2013 SP 222 52.9 a 47.9 0.24
ESr 228 37.6
CCp 226 52.3
a
55.5 0.23
Op 66.2 24.8
b
29.7
Or 78 20.6
b
38.5
HSD 32 25.7 64.2
p-value 0.3229 0.0047 0.7404
2012–2013 SP 149 45.1
ab
0.3
ESr 156 46.0
ab
0.29
CCp 145 51.3
a
0.35
Op 69.8 37.6
b
Or 39.1 20.6
c
HSD 43.4 7.4
p-value 0.1094 <.0001
HSD (honestly significant difference);
Different letters indicate significant differences (α 0.05).
9
Table 9.
N
min
-values of mulched LGS (Sp), of LGS after ring-cutter root separation (ESr), of catch crop mixture (CCp)
and of oat stubble (Op und Or)—soil layer 0–30 cm. Sp: Standard practice (plough); ESr: Early sowing of winter wheat
(ring-cutter); CCp: Winter wheat following catch crop (plough) Op: Winter wheat following oat (plough); Or: Winter wheat
following oat (ring-cutter); HSD (honestly significant difference).
N
min
kg ha
1
(0–30 cm)
Date of sampling Site Sp ESr CCp Op Or x HSD p-value
11-08-2010 Hollow (2010) 35.8
b
109.8
a
96.9
a
42.4
b
22.5
b
61.4 28.1 <.0001
Hill (2010) 34.6
b
89.5
a
73.5
ac
43.0
bc
20.0
b
52.1 32.9 <.0001
Different letters indicate significant differences (α 0.05).
Table 10.
N
min
-values, (soil layer 0–60 cm) beneath winter wheat after autumn seeding and at the onset of spring
vegetation. Sp: Standard practice (plough); ESr: Early sowing of winter wheat (ring-cutter); CCp: Winter wheat following
catch crop (plough); Op: Winter wheat following oat (plough); Or: Winter wheat following oat (ring-cutter).
N
min
kg ha
1
(0–60 cm)
Date of sampling Site Sp ESr CCp Op Or x HSD p-value
05-04-2011 Hollow (2010) 79.7
a
36.7
bc
48.6
c
25.0
b
22.2
b
42.4 22.4 <.0001
Hill (2010) 48.7
a
16.9
b
36.0
a
15.4
b
15.6
b
26.5 15.4 <.0001
01-11-2011 Hollow (2011) 66.9
a
73.9
a
77.5
a
115.6
b
90.3
a
84.8 39.5 0.0153
Hill (2011) 49.0
a
79.2
ac
53.0
a
106.6
c
98.7
c
77.3 38.5 0.0262
24-04-2012 Hollow (2011) 99.5
a
* 114.7
a
42.9
b
42.0
b
74.8 51.5 0.0003
Hill (2011) 101.8
ab
* 119.3
ab
78.3
ab
73.7
b
93.3 55 0.0258
22-10-2012 Hollow (2012) 46.4
a
61.1
ab
33.7
a
77.4
b
54.1
a
54.5 22.8 0.0007
Hill (2012) 34.0
a
48.1
ab
39.7
a
74.2
b
59.0
ab
51 26.4 0.0029
06-03-2013 Hollow (2012) 76.1
a
38.8
b
47.3
b
38.6
b
34.0
b
46.9 21.7 0.0003
Hill (2012) 51.6 41.5 52.6 37.3 36.2 43.8 21.8 0.0897
*Winterkill damage; Different letters indicate significant differences (α 0.05).
Table 11.
N
min
-values (soil layer 0–60 cm) under WR subsequent to WW (08.11.2011; 22.10.2012) and shortly after
WW harvest (02.08.2013). Sp: Standard practice (plough); ESr: Early sowing of winter wheat (ring-cutter); CCp: Winter
wheat following catch crop (plough); Op: Winter wheat following oat (plough); Or: Winter wheat following oat (ring-cutter);
HSD (honestly significant difference).
N
min
kg ha
1
(0–60 cm)
Date of sampling Site Sp ESr CCp Op Or x HSD p-value
08-11-2011 Hollow (2010) 120 94.5 84.0 125.7 148.5 114.5 111.5 0.4086
Hill (2010) 130.4 99.7 137.3 96.3 122.5 117.2 82.9 0.4461
22-10-2012 Hollow (2011) 97 70.6 87.3 50.3 66.2 74.2 64.5 0.2293
Hill (2011) 104.1 121.3 116.8 66.5 97.1 101.1 75.3 0.2184
02-08-2013 Hollow (2012) 41.1 35.3 40.5 38 33.4 37.6 12.3 0.2672
Hill (2012) 28.5 29.9 30.2 31.1 24.6 28.8 9.8 0.306
10
3.6. Weeds
Weed distribution varied on the different sites and test
method plots. In all experimental years, the weed pop-
ulation in oats and winter wheat was more pronounced in
the hollows than on the hilltops.
On average, the standard practice and catch crop test
method (autumn ploughing and late seeding) had the low-
est weed dockage, the weed coverage ratio (WCR) in both
methods being nearly identical. In comparison, the early
sowing WCR was from distinctly to significantly higher in
each year. On the oat/ring-cutter plots there was usually
a higher WCR (Table 12) and/or a higher weed biomass
(Table 13) in established oat and winter wheat cultures than
on the oat/plough (Op) test plots. In addition to these quan-
titative differences, specific differences were found in weed
group composition on the varying sites and in the varying
test methods.
The prior LGS crops generated weed flora—alfalfa (Med-
icago sativa L.), red and white clover (Trifolium repens L.
and Trifolium pratense L.) as well as perennial ryegrass
(Lolium perenne L.) and couch grass (Agropyron repens
L.)—on all locations and test methods. Comparing stan-
dard practices and ploughed test methods (catch crop,
oat/plough) to the unploughed test methods (early sow-
ing and oat/ring-cutter ) (Table 13), alfalfa did not regrow
in ploughed methods, neither in the preceding oat crop
nor or in winter wheat. In 2011, however, alfalfa did re-
grow on standard practices and catch crop hilltop plots
because the plough could not optimally turn the soil in au-
tumn. Besides alfalfa, the weed population was dominated
by, in descending order, creeping thistle (Cirsium arvense
L.), scentless chamomile (Tripleurospermum perforatum),
poppy (Papaver rhoeas L.), common chickweed (Stellaria
media L.), larkspur (Consolida regalis Gray) and veronica
(Veronica chamaedrys L.). These species varied within
sites and procedures. In the hollows and in the unploughed
test methods, creeping thistle was much more dominant
(Table 14), particularly in the oat/ring-cutter winter wheat.
In the hollows and on one hilltop, scentless chamomile
dominated, mainly in the early sowing, oat/ring-cutter and
oat/plough winter wheat test methods (cover ratio, 75–90%).
In 2011 and 2012, a rampant odourless chamomile infes-
tation caused winter wheat crop failure in oat/plough and
oat/ring-cutter hollows.
4. Discussion
The experimental cultivation methods were carried out
from 2010 to 2013 and were at times subject to extreme
weather conditions. Only 2013 came close to long-term av-
erages and predicted climate changes, such as pre-summer
drought (see Figure 3). With this in mind, the following dis-
cussion addresses the extent to which the tests provide a
practical alternative to standard practices and if they can
contribute to diversifying winter wheat cultivation.
4.1. Reduced Tillage With the Ring-Cutter
The hypothesis that the ring-cutter can effectively kill and
regulate LGS in both wet (spring) and dry (summer) soils
was confirmed—LGS secondary growth coverage on un-
ploughed oat and wheat plots was the same height as on
ploughed plots. The tool’s cutting technique - a shallow, ver-
tical undercutting of the upper topsoil - separates the alfalfa
sprout shaft below the root crowns, effectively impeding re-
growth. In contrast to the plough, ring-cutter tractive power
requirements are low and operating speed (
11 km h
1
) is
remarkably fast. Nonetheless, the tool required two to four
working cycles to prepare the plots for mulch seeding after
the two-year LGS cultivation. Further drawbacks to the
ring-cutter were much lower grain yields in two of the three
years on oat/ring-cutter and winter wheat plots and less
N-availability than oat/plough plots. Ring-cutter implemen-
tation only reached higher oat yields than oat/plough on the
shallow hilltop in the 2011 test method. Numerous other
studies substantiate that reduced tillage in organic farm-
ing results in lower yields and lower N-availability [
19
,
36
39
]. Reduced tillage limits N-availability by delaying soil
organic matter (SOM) mineralisation, due to minimal aer-
ation [
19
] and poor soil warming in the spring, particularly
when densely mulched [
40
]. Especially in spring, unpro-
cessed earth is often cooler and soggier than ploughed
soil, hindering both germination and the initial growth of
summer grains [
41
]. Reduced soil processing can also
lead to increased compression in untreated layers [
18
,
39
]
and to accumulated SOM in the upper soil layer [
42
], as
confirmed by ring-cutter processing research conducted at
the ZALF M
¨
uncheberg experimental station where much
higher soil compression limited root penetration of winter
grains [
43
]. Limited N, compressed soil and thwarted root
growth impede a plant’s ability to absorb nutrients, which
may have caused the much lower oat and winter wheat
harvests [
37
]. In addition to these factors, the ring-cutter
plots displayed dense weed growth (Tables 12 and 13); typ-
ical for reduced tillage in organic farming [
19
,
44
]. Shallow
ring-cutter processing causes weed seeds to remain close
to the surface, providing excellent germination conditions.
Perennial species such as couch grass and creeping thistle
thrive under reduced tillage [45].
Bearing all this in mind, it becomes clear that the re-
sults of reduced tillage are highly dependent on the time
of ring-cutter processing, on crop rotation selection and
on weather conditions, as confirmed by the completely un-
ploughed oat/ring-cutter and early sowing test methods [
18
].
While oat/ring-cutter did not generate stable oats or winter
wheat grain yields, the early sowing wheat yields of two
trial years did not deviate greatly from standard procedure
yields. Hence, reduced soil processing can be successful
when applied to pertinent sites and adapted to the entire
cultivation system, i.e. alterations in crop rotation, seeding
and the catch crop [19].
11
Table 12.
Percentage weed coverage in all winter wheat cultivation methods (Sp, ESr, CCp Op and Or). Sp: Standard
practice (plough); ESr: Early sowing of winter wheat (ring-cutter); CCp: Winter wheat following catch crop (plough); Op:
Winter wheat following oat (plough); Or: Winter wheat following oat (ring-cutter); HSD (honestly significant difference).
Weed coverage %
Date Site Zadoks scale Sp ESr CCp Op Or x HSD p-value
27-04-2011 Hollow (2010) 30–37 11
a
71
b
16
a
71
b
94
b
53 29.7 <.0001
Hill (2010) 32–39 19
a
64
b
19
a
26
a
75
b
41 32.8 0.0002
28-06-2011 Hollow (2010) 77–83 34
a
64
b
48
ab
91
c
99
c
67 25.5 <.0001
Hill (2010) 77–83 29 50 34 24 50 37 49.1 0.3428
03-05-2012 Hollow (2011) 30–34 51
a
* 48
a
97
b
93
b
72 36.1 <.0001
Hill (2011) 30–34 12
a
* 11
a
8
a
54
b
21 39.4 0.0036
16-07-2012 Hollow (2011) 83–87 73
a
* 71
a
95
b
90
ab
83 21.5 0.0021
Hill (2011) 83–87 49 * 40 45 43 44 42.1 0.5208
23-04-2013 Hollow (2012) 29–31 12
a
73
b
6
a
8
a
34
c
26 15.9 <.0001
Hill (2012) 29–31 9
ac
71
b
5
a
6
a
21
c
22 15.4 <.0001
24-05-2013 Hollow (2012) 41–49 31
a
68
b
38
a
36
a
59
b
46 24.5 0.0017
Hill (2012) 41–49 20
ac
66
b
17
ac
10
a
33
c
29 21.3 <.0001
*Winterkill damage; Different letters indicate significant differences (α 0.05).
Table 13.
Weed biomass in oats (at blossoming), Op and Or methods. Op: Oat (plough); Or: Oat (ring-cutter); HSD
(honestly significant difference).
Weed DM t ha
1
Date Site Op Or HSD p-value
30-06-2010 Hollow (2010) 1.2
a
2.5
b
1.8 1.2 0.0491
Hill (2010) 0.7 1.6 1.2 0.7 0.1373
09-06-2011 Hollow (2011) 0.9 1.3 1.1 1.4 0.4211
Hill (2011) 0.7 0.3 0.5 0.7 0.216
12-06-2012 Hollow (2012) 1.8 2.2 2 0.7 0.2211
Hill (2012) 0.8 1 0.9 1.2 0.4896
Different letters indicate significant differences (α 0.05).
Table 14.
Dominance (dom.; %) and frequency (freq.; %) of Cirsium avense (Ca) and Medicago sativa (Ms) in oat and
winter wheat (SP, ESr, CCp, Op and Or test methods). Sp: Standard practice (plough); ESr: Early sowing of winter wheat
(ring cutter); CCp: Winter wheat following catch crop (plough); Op: Winter wheat following oat (plough); Or: Winter wheat
following oat (ring cutter).
Sp ESr CCp Op Or
Ca Ms Ca Ms Ca Ms Ca Ms Ca Ms
Oat
n Site dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq.
32 Hollow (2010) 12 38 29 84
32 Hill (2010) 16 100 20 34 23 20
12 Hollow (2011) 5 8 12 100 12 58 8 100
12 Hill (2011) 19 100 13 100
4 Hollow (2012) 8 25 25 75 4 75
4 Hill (2012) 2 75 22 50 5 100
Winter Wheat
n Site dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq. dom. freq.
20 Hollow (2010) 5 20 5 5 7 45 6 10 14 75 9 45 25 85
20 Hill (2010) 13 20 14 35 22 20 6 20 12 55 8 20 4 15 4 20 10 45 7 20
8 Hollow (2011) 13 25 15 25 * * 17 88 5 13 6 13 25 100
8 Hill (2011) 20 100 * * 14 100 3 25 8 13
8 Hollow (2012) 8 13 6 50 15 38 8 25 19 63 9 38 13 25 33 100 4 13
8 Hill (2012) 8 75 9 25 6 25 12 13 8 88 12 63 8 13
12
4.2. Winter Wheat Early Sowing and Summer Catch Crop
Test Methods
In the test methods early sowing and catch crop, LGS pro-
cessing takes place in the summer. The ring-cutter was
used to sever LGS roots by shallowly working the topsoil,
even in dehydrated soil (i.e. in June 2010). August 2010
N
min
-samples proved that early ring-cutter processing re-
leases significant N-quantities in late summer (up to 109
kg N ha
1
) for early sowing and summer catch crops (see
Table 9). Heavy rains in August and November 2010 and
in July 2011 caused above average precipitation, possibly
leading to nitrate leaching and loss in late summer and
autumn, especially in 2010, in these two test methods. Fur-
ther indication of such losses is the significantly lower N
min
-
value in early sowing and partly in catch crop in spring 2011,
when compared to standard practices.
On the other hand, in 2010 and 2011, catch crop plots
developed vigorous cover crops that were able to absorb
a portion of the mineralised nitrogen by October (up to 86
kg N ha
1
). Other studies came to similar results with an
early catch crop after clover-grass tilling [
6
]. Compared to
standard procedures, the summer catch crop organic mate-
rial provided a slightly improved N-supply for winter wheat
in spring. This is supported by increased N
min
-values on
catch crop plots in spring 2012. Despite the possible catch
crop nitrate transfers, yields were comparable to standard
yields, confirming the hypothesis that the catch crop winter
wheat test method ploughed in autumn produces equivalent
annual grain yields, on hilltops as well as in hollows, where
the other test methods reported yield losses. As to location
and weather conditions, the catch crop test method proved
the hardiest.
Although the early sowing test method yields did not dif-
fer greatly from standard practices, compared to catch crop,
early sowing yield was characterised by low stability and
robustness. In 2012, early sown winter wheat was particu-
larly susceptible to winterkill and in 2011, contained a much
lower crude protein. The early sowing test method also
had a high weed content despite the catch crop mixture,
which is typical in early sown crops [
46
]. In 2013, with an
early drought in April and dry summer months, early sowing
came closest to matching standard practice yields. Possibly
the more abundant pre-winter growth, followed by a cold
and snowy winter in 2012/2013, allowed early sowing winter
wheat to exploit the winter moisture and take up nitrogen
early, as confirmed by much higher N
min
-values on early
sowing plots the previous autumn and decidedly lower ones
in spring 2013. Due to the developmental advantage of
early sowing, winter wheat was perhaps less affected by
water shortages in April (stem elongation) and drought in
July during the grain-filling phase [
25
,
26
]; an idea supported
by the significantly higher thousand kernel weight in this
year (Table 6). Overall, the early sowing test method shows
how heavily grain yields depend on cultivation procedure
and weather conditions throughout the year, and that un-
ploughed early sowing is not necessarily synonymous with
minimal yield. The only early sowing location effect was
weed pressure. This was less pronounced on hilltops and
therefore advocates unploughed processing. Based on the
grain yield, the early sowing test method is not particularly
suitable for dry knoll locations, as was otherwise proposed
in hypothesis 3.
4.3. Winter Wheat Following Oat
Studies suggesting oat as a good LGS exploiter are con-
firmed by their results [
28
]. Especially in the oat/plough test
method and in the damp hollows, oats were able to take
up high levels of mineralised LGS nitrogen in spring (up to
105 kg N ha
1
). With a high N-supply, oat/plough strongly
suppressed weed growth [29].
Oat/plough and oat/ring-cutter test methods showed
high N
min
-values (up to 115.6 kg N ha
1
on oat/plough;
98.7 kg N ha
1
on oat/ring-cutter) at the beginning of
November 2011 and the end of October 2012 despite high
N-deprivation and an early winter wheat sowing date in
2011. In contrast to standard practice and catch crop,
oat/plough and oat/ring-cutter exhibited lower N
min
-content
in the spring than in autumn, which points to nitrate leaching
into deeper soil layers after rainy and cold winter months.
In both winters, 2011/2012 (205 mm) and 2012/2013
(
149 mm
), rainfall from November to February was above
field capacity (110 mm; see Section 2.2.).
Despite summer crop cultivation after springtime LGS
tilling, there may be an increased risk of nitrate leaching
the following winter [
27
]. This risk can be offset by es-
tablishing a second subsequent crop in early autumn, en-
suring a high and rapid N-up-take. Winter wheat N-up-
take (
10–30 kg N ha
1
) in autumn is less pronounced than
other grains (for example, winter rye with 30–50 kg N ha
1
)
[
47
]. Consequently, winter wheat sown on oat/plough and
oat/ring-cutter plots at the end of September (2010 and
2011) and in mid-October 2012 only minimally prevented
nitrate leaching.
In the spring, oat/plough and oat/ring-cutter winter
wheat plots were unable to compete against odourless
chamomile. This multiyear species has a fibrous and deep-
reaching root system, asserting its dominance especially
on wet and compacted terrain [
48
]. Without weed control,
odourless chamomile can overrun a winter wheat grain yield
by up to 90% [
48
]. In the wet years 2011 and 2012, this was
irrefutably confirmed in the hollows, locations particularly
vulnerable to crop failure [
32
]. In summary, despite spring
tillage and an oat insertion, the nitrogen supply for winter
wheat was not improved. Also, the oat/plough and oat/ring-
cutter test methods were highly susceptible to weeds. Only
on the hilltops and in the dry year 2013 was oat/plough
winter wheat yield comparable to standard practices, con-
trary to hypothesis 2. In each trial year and compared to
standard practice, the oat/ring-cutter winter wheat hilltop
harvests produced a smaller deficit margin than harvests in
the hollows did. According to hypothesis 3, the oat method
is more suitable for hilltops. However, it is not a viable al-
13
ternative to standard cultivation practices as its yield levels
are much lower.
5. Conclusion and Outlook
When it comes to adapting cultivation methods to climate
changes, greater diversity is an effective risk management
strategy for agricultural enterprises [
12
]. Practically applied,
cultivation and soil processing methods must nurture crop
robustness. The unpredictable influences of our changing
climate demand crops that are insensitive to a broad spec-
trum of influences [
15
]. The field test cultivation methods
revealed distinctly variable degrees of robustness when it
came to growth sites and weather conditions. In every field
test year, the standard practice and the catch crop test
method produced relatively hardy grain and stable crops
on all plots. Waiving LGS virgin tilling in autumn as well
as improving work-cycle peaks make catch crop a viable
alternative, contributing to winter wheat diversification. As-
suming that future climate changes lead to less winter frosts
and therefore less risk of winterkill, the early sowing test
method could be an equally feasible option for winter wheat
diversification [
5
]. This is clearly shown in early sowing yield
levels which were comparable to standard practice yields
during the dry year 2013. The oat/plough and oat/ring-
cutter test methods were far more precarious than standard
practices or the early sowing and catch crop test methods.
Both oat test methods are highly site and weather sensitive,
which resulted in two years of failed winter wheat crops in
the soggy hollows. Assuming that climate change brings an
increase in heavy rainfall [
5
], the weaknesses of oat/ring-
cutter and oat/plough (saturated hollows and rampant weed
infestation) make this test method impracticable.
Ring-cutter processing proved to be overall practical,
and particularly suited to organic farming needs (multiple-
year LGS tillage). However, the denser weed growth, lower
N mineralisation and lower grain yields, clearly proves it
cannot replace the plough. Nonetheless, as a flexible, man-
ageable tool, the ring-cutter is indeed an alternative on fields
where site or weather conditions create severe ploughing
risks, such as ploughing depth compaction and hilltop ero-
sion. Climate changes are also changing the customary
ploughing and/or soil processing dates [
4
]. The ring-cutter
can help to increase the number of fieldwork days, allowing
for LGS processing on both wet and dry soil. The field
tests made evident, however, that reduced ploughing must
go hand in hand with adjusting cultivation methods and
scheduling. The ploughing in spring and autumn resulted
in severely reduced oat and winter wheat yields, which was
not the case when ploughing in summer. This confirms
observations in organic farming that timing is often more
decisive than method when it comes to N-supply and weed
regulation [
49
]. If an appropriate moment is not seized, the
ensuing consequences cannot be offset by turning to short-
term resources, as is the case in conventional farming [
9
].
This is a distinctive issue and climate change adaptation is
a unique and demanding process for organic farmers [
2
].
There are no universally applicable measures for increasing
diversification and robustness on organic farms. A farm’s
individual site and operating needs must be taken into ac-
count to bring robustness to the entire system [
50
]. In order
to identify and develop specific measures for adapting or-
ganic farms to climate changes, on-site projects such as
this one are indispensable.
Acknowledgments
This work was funded by the Federal Ministry of Education
and Research (BMBF), Germany, by the Federal Ministry of
Food, Agriculture and Consumer Protection (BMELV), Ger-
many and by the Ministry of Science, Research and Culture
(MWFK), Brandenburg. We thank Mr. Stefan Palme, or-
ganic farmer, for his expert advice and for allowing the
experiments to be conducted on Wilmersdorf.
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