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Rasmussen_IA_et_al

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					             Organic Crop Rotation Experiments –
             short-term versus longer-term results
                        Ilse A. Rasmussen, Margrethe Askegaard, and Jørgen E. Olesen


Abstract - Danish experiments with cereal-based                            spring in R1, and ploughed in autumn before sowing
organic crop rotations have shown that the short-                          of winter cereal in R2. R1 was only represented at
term results (the first course, up to four years after
conversion) are different from those obtained in the
longer-term (the second course, fifth to eighth year                                                                 1,4




                                                                           -1
                                                                                                                                                            1997-2000




                                                                           Yield increase from manure, t DM ha
after conversion). Yield gain from use of manure                                                                                                            2001-2004
increased from the first to the second course on a                                                                   1,2

sandy soil, but decreased on loamier soils. Yield gain
                                                                                                                     1,0
from leguminous catch crops increased from the first
to the second course in a crop rotation without grass-                                                               0,8
clover. Some of these effects were caused by
                                                                                                                     0,6
buffering effects of the grass-clover, other effects
were caused by changes in soil fertility over time. 1                                                                0,4


                          INTRODUCTION                                                                               0,2

In 1997 a crop rotation experiment was initiated at                                                                  0,0
                                                                                                                            R1     R2    R2        R4   R2      R4
three sites in Denmark. The objective of the                                                                                 Jyndevad         Foulum     Flakkebjerg
experiment was to explore the possibilities for both
                                                                           Fig. 1. Yield increase (t DM ha-1) from use of manure for
short-term and long-term increases in organic cereal
                                                                           each location, rotation and course. Average of all harvested
production through manipulation of crop rotation
                                                                           crops in the rotation and catch crop treatments.
design on different soil types. The experiment
included three factors (proportion of grass-clover in
                                                                           Jyndevad, and R4 was not represented at Jyndevad.
the rotation, catch crops and manure application) in
                                                                           All crops in all rotations were represented every
a randomised factorial design. The main indicators
                                                                           year. Results are presented from the first (1997-
measured in the experiment were crop yield,
                                                                           2000) and second (2001-2004) courses of the
nutrient leaching and weeds (Rasmussen et al.,
                                                                           experiment.
2006).

                                                                                                                                         RESULTS
                     EXPERIMENTAL DESIGN
                                                                           Use of manure increased yields (Olesen et al.,
The Danish organic crop rotation experiment was                            2002). The yield gain caused by the use of manure
designed as a factorial experiment (Olesen et al.,                         as a mean of the rotation increased from the first to
2000). The experiment was carried out at three sites                       the second course of the experiment at the sandy
representing different soil types (Jyndevad: coarse                        soil, but decreased or was unchanged at the more
sand, Foulum: loamy sand, and Flakkebjerg: sandy                           loamy soils, with the largest tendency for decrease
loam) and climate regions in Denmark. The
experimental factors were 1) crop rotation (fraction
                                                                                                                     1,0
of grass-clover green manure in the rotation), 2)
                                                                           -1
                                                                           Yield increase from catch crop, t DM ha




                                                                                                                                                              1998-2000
catch crop (with: +CC and without: -CC catch crop)                                                                   0,8                                      2001-2004
and 3) manure (with: +M and without: -M animal
manure applied as slurry).                                                                                           0,6

   The rotations differed with respect to the use and
                                                                                                                     0,4
duration of a grass-clover green manure crop. This
crop was present in rotations R1 and R2, but not in                                                                  0,2
rotation R4. The grass-clover crop was ploughed in
                                                                                                                     0,0


                                                                                                                     -0,2
Ilse A. Rasmussen is with the Danish Institute of Agricultural Sciences,
Department of Integrated Crop Protection, DK-4100 Slagelse,
Denmark (ilsea.rasmussen@agrsci.dk).                                                                                        R1      R2    R2      R4      R2       R4
    Margrethe Askegaard is with the Danish Institute of Agricultural                                                          Jyndevad      Foulum         Flakkebjerg
Sciences, Department of Agroecology, DK-8830 Tjele, Denmark                Fig. 2. Yield increase (t DM ha-1) from use of catch crop for
(margrethe.askegaard@agrsci.dk).
    Jørgen E. Olesen is with the Danish Institute of Agricultural          each location, rotation and course. Average of all harvested
Sciences, Department of Agroecology, DK-8830 Tjele, Denmark                crops in the rotation and manure treatments. 1997 is not
jorgene.olesen@agrsci.dk).
included, because there was no effect of previous catch crop                                                     rotation than in the first. Here the positive effect of
this year.                                                                                                       the leguminous catch crop on the yield of the
                                                                                                                 succeeding crop
Proportion of clover in grass-clover (% of DM)


                                         100
                                                                                                                                                           6.0




                                                                                                                 Grain yield in winter wheat (t DM ha-1)
                                                                                                                                                                        Jyndevad
                                                 80                                                                                                        5.5          Foulum
                                                                                                                                                                        Flakkebjerg
                                                                                                   r2=0.96                                                 5.0
                                                 60
                                                                                                                                                           4.5          r2=0.40
                                                                                                       r2=0.24
                                                 40
                                                                                                                                                           4.0

                                                 20                                                                                                        3.5
                                                           Jyndevad
                                                           Foulum                                      r2=0.48                                                             r2=0.69
                                                                                                                                                           3.0
                                                           Flakkebjerg
                                                  0                                                                                                                                           r2=1.00
                                                      0        1             2              3             4                                                2.5
                                                                                                                                                                 0          20           40             60           80
                                                            Grain yield in spring barley (t DM ha-1)
                                                                                                                                                                 Clover proportion at the first cut in grass-clover (% of DM)
Fig. 3. Proportion of clover in grass-clover (% of DM) in the
                                                                                                                 Fig. 4. Average annual yields of winter wheat (1998-2004 at
first cut in 2000 as a function of spring barley grain yield (t
                                                      -1
                                                                                                                 Foulum and Flakkebjerg, 1998-2000 at Jyndevad) as a
DM ha ) in each plot in the previous year.
                                                                                                                 function of the clover proportion in the first cut of the grass-
                                                                                                                 clover in the previous year.
in R2 (Fig. 1). Use of catch crops resulted in both
yield increases and decreases, depending on crop
                                                                                                                 was larger than the negative effect of high yields on
and position in the rotation (Askegaard et al.,
                                                                                                                 the clover content of the catch crop.
2005b). As a mean of the rotation there was hardly
                                                                                                                    Conclusions based on the results from the first
any effect on the yield except for R4 in the second
                                                                                                                 course of the experiment would have been different
course (Fig. 2).
                                                                                                                 from those based on the second course of the
   In both cases, this development may be
                                                                                                                 experiment. This underlines the importance of
explained by a buffering effect of the clover in the
                                                                                                                 carrying out longer-term studies in organic farming,
grass-clover crop. The clover content of the grass-
                                                                                                                 where interactions between the studied factors
clover decreased with increasing grain yields of the
                                                                                                                 might develop over time.
spring barley, in which the ley was undersown (Fig.
3). The winter wheat yield increased with increasing
                                                                                                                                                                               ACKNOWLEDGEMENT
clover content in the grass-clover green manure at
the more loamy soils (Fig. 4). At the sandy soil there                                                           The study was funded by the Danish Research
was practically no response of grain yield in winter                                                             Centre for Organic Farming through the Danish
wheat to the clover proportion in the grass-clover.                                                              Directorate for Development under the Ministry of
This is most likely because of large nitrate leaching                                                            Food, Agriculture and Fisheries.
losses during winter (Askegaard et al., 2005a).
                                                                                                                                                                                     REFERENCES
                                                            DISCUSSION & CONCLUSION
The buffering effect of the grass-clover seems to                                                                Askegaard, M., Olesen, J.E. and Kristensen, K.
work like a seesaw: with a large yield in the crop                                                               (2005a). Soil Use and Management 21:181-188.
where the grass-clover is undersown, the clover
proportion is decreased, and the yield of the crop                                                               Askegaard, M., Olesen, J.E. and Rasmussen, I.A.
after grass-clover is also decreased. And with a low                                                             (2005b). In 'Researching Sustainable Systems –
yield in the crop before grass-clover, the yield of the                                                          Proceedings of the First Scientific Conference of the
succeeding crop is increased. The same effect occurs                                                             International  Society    of    Organic    Agriculture
with leguminous catch crops, although to a lesser                                                                Research', pp. 198-201, eds. U. Köpke et al.
extent: high yield in the cover crop decreases yield                                                             (ISOFAR: Bonn, Germany).
in the succeeding crop and vice-versa.
    At the sandy soil, the soil fertility decreased over                                                         Olesen, J.E., Askegaard, M. and Rasmussen, I.A.
time in the system without manure. Thus yield                                                                    (2000). Acta Agriculturae Scandinavica, Sect. B, Soil
increases from use of manure were larger in the                                                                  and Plant Science 50:13-21.
second course of the rotation than in the first. At the
more loamy soils, the soil fertility produced by the                                                             Olesen, J.E., Rasmussen, I.A., Askegaard, M. and
use of grass-clover and catch crops resulted in a                                                                Kristensen, K. (2002). Journal of Agricultural Science
tendency for smaller yield increases from use of                                                                 139:361-370.
manure in the second course of the rotation than in
the first.                                                                                                       Rasmussen, I.A., Askegaard, M., Olesen, J.E. and
    In the rotations with grass-clover, the yield                                                                Kristensen, K. (2006). Agriculture, Ecosystems &
effects from catch crops were much smaller than                                                                  Environment 113:184-195.
those for use of manure, and did not change over
time. In the rotation without grass-clover, the yield
increases were larger in the second course of the

				
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