A FIELD STUDY OF MAIZE YIELD ON MIXED ORGANIC AND
CONVENTIONAL DAIRY FARMS IN DENMARK IN 2001
Jozef Sowinski1, Ib Sillebak Kristensen2, and John E Hermansen2
1
Department of Crop Production, Agricultural University of Wroclaw,
Norwida 25 50-375 Wroclaw
e-mail: sowinski@ekonom.ar.wroc.pl
2
Danish Institute of Agricultural Sciences, Department of Agricultural Systems
Research Centre Foulum, P.O. Box 50, 8830 DK-Tjele
e-mail: ibs.kristensen@agrsci.dk
e-mail: john.hermansen@agrsci.dk
Precented at conference: „Scientific aspects of organic farming“. 21-22. March 2002.
Latvia University of Agriculture in Jelgava.
SUMMARY
A field study was carried out on mixed dairy farms in Denmark, five organic and five
conventional farms. The surveys were set up to identify main reasons for low yields under
practical conditions. Cob yield and quality of maize for silage as well as weeds were measured
in 34 fields with five samples per field.
Conventional maize gave a cob yield of 7,6251,922 Scandinavian Feed Units (SFU) ha-1, and
organic maize 3,6421,813 SFU ha-1. The main yield components for the conventional and
organic farms respectively were: Cob weight 83 and 49 g DM cob -1, dry matter in cobs: 42 and
32%; Maize plant number 80,000 and 66,000 plants ha-1. Other main differences were climatic
differences between North and South Jutland, where North Jutland had 5% lower T-sum
compared to South. On organic farms weeds were a problem, especially from midsummer until
harvest, a period where weed grew vigorously under the light open maize. On the organic farms
the weed content at harvest averaged 25% of the crop volume. Also, maize height was lower by
25% in organic fields, and 19% of the kernels of the cobs were unfilled, double of that of the
conventional fields. Statistical models are given to quantify importance of the above factors.
Key words: maize, organic and conventional farms, cob yield, Scandinavian Feed Unit, weed.
INTRODUCTION
With an average T-sum of 2,200-2,500 (Corn Heat Unit, (3) Denmark constitutes the northern
border for maize production. Late varieties (T-sum more than 2,500) have to be harvested with
low dry matter content in cold years.
In variety trials the yields of recommended varieties averaged 11,300 1,500 SFU ha-1 in the
years 1996-2000 measured from direct harvest of the plots (1). 1 SFU (Scandinavian Feed Unit)
corresponds to the feeding value of 1 kg barley.
On 10-16 private mixed dairy pilot farms a silage yield of 8,2002.100 SFU ha-1 was achieved
in the years 1996-2000 (2). In year 2000, 5 mixed organic dairy farms had achieved only
4,7001,300 SFU ha-1. The silage net yield is measured when fed to the dairy herd, after field
and silage losses. However a net silage yield was still only 40% of the plot yield achieved in
field trials, indicating big losses.
To investigate causes for low net yield under real life and practical conditions a survey was set
up to quantify the field yield on organic and conventional mixed dairy farms.
Document1
MATERIALS AND METHODS
The investigation was carried out on 5 conventional and 5 organic farms. Farmers were chosen
from a group of pilot farms of 30 farms cooperating with The Farming System Group in The
Department of Agricultural Systems. From each field farm records were made on all treatments
(sowing, spraying etc.). Midsummer the crop was evaluated in 3 subplots for plant density,
weed competition and pest. Again 2-20 days before harvest the crop was evaluated, and cobs
samples were taken.
The farms are all located in Jutland. At harvest in each field five subplots were chosen along the
longer diagonal of the field. Data were collected from a total of 170 subplots. Each subplot was
5 m long and 4 rows wide. Area of subplots for most fields was 15 m2 (in one field 10 m2).
In each subplot the following measurements were carried out, in order to describe yield and
quality of maize:




Number of plants
Number of developed cobs defined as cobs of more than half the normal size
Height of plant (from 3-5 measurement per subplot)
Number of missing plants (empty space)
The cob's dry matter yield was estimated from number of plants per 15 m2 (~ 120 plants),
weight of cobs (from 16 plants) and dry matter content in the cob (5 cobs). For the rest of cobs
(11 cobs) development was evaluated. Percentage of cobs with poor or unfilled grains was
evaluated as percentage of total cobs.
Volume of weeds and volume of maize were evaluated in cubic meters per 15 m2.
Calculated SFU yield in cobs were calculated in accordance to Danish standards (5), based on
analyses of dry matter, crude protein, starch, crude fibre and in vitro organic matter digestible.
20 samples was analysed by conventional chemical methods and regression to NIR-analyses
was used to estimate each sample.
Statistical analyses were made at farm and field level using multiple linear regression methods
(GLM procedure in SAS). Effects of system – organic vs. conventional farm – were tested by
the following model:
Model 1: Yijkl
where
Yijkl
Systemi
Farmj
Fieldk
Errorijkl
=
=
=
=
=
=
Systemi + Farmj (Systemi)+ Fieldk (Farmj (Systemi)) + errorijkl
SFU yield of cobs ha-1 for the individual plot within field
Organic and conventional mixed dairy farms, i = 1-2.
Farms within each system, j =1-5
Fields within each farm, k =1-8
Residual
Systems were tested against Farm(System) and farms were tested against Field(Farm(System)).
Afterwards the covariates were tested in model 2, where model 1 was extended with the
covariates: Temperature sum, precipitation, day of sowing, weed in summer and autumn,
earliness of variety, development stage at harvest, maize plants, % empty kernals.
RESULTS AND DISCUSSION
2
The climate in year 2001 was favourable for maize growth. T-sum accumulated from 15. April
to 15. October had a variation from 2420-2760 degree-day and was in average 7% higher than
20 years' average,(1). In June the maize was turning yellow during a 3 week cold and rainy
period (100C). Some herbicide inhibition was observed during this period.
In Table 1 the average treatment of the fields is described. Especially the conventional farms
had selected a field with warm microclimate for continuous maize production for 2-6 years.
Maize on organic farms had only been grown for 1-3 years. The total level of N-fertilisation was
the same within the two groups. On organic farms a bigger proportion of animal manure were
from deep litter, which only have low N-fertilizer value and a high K-content. On the
conventional farms start fertilisers (around 30 kg N & 15 kg P ha-1) were placed 5-10 cm beside
maize seeds.
Table 1. Soil type, and fertilization in organic and conventional maize fields in DK 2001,
mean + standard deviation.
System
Soil type1)
- number of fields on sand + clay
Organic manure (t per ha)
Total amount of:
- N2)
-P
-K
- Mg
-S
1)
2)
Organic
Conventional
7+ 3
44 17
17 + 7
50 13
147 +20
38 10
321 78
10 1
7 16
147 +19
47 8
185 54
18 5
11 5
Sandy = % clay < 10% and fine sand <40% (20-200 m), clay = % clay > 5% and fine sand >40%
Animal N is calculated as artificial N-fertiliser equivalent
In average the organic farmers were weed harrowing 5 times beginning with blind harrowing
before maize could be seen above ground, 2-4 weed harrowing in May/June and ending with 13 row harrowing in June until maize height of 0.5 m.
In conventional farms the maize were sprayed 2-3 times in average. Frit flies and weed were
treated in average low doses was used with average 0.4 standard doses per treatment.
In table 2 the characteristic of the maize fields is shown. On some of the organic farms false
seedbeds were prepared 1-4 weeks before sowing in order to stimulate weed germination, which
could be killed during seedbed preparation. This is probably the main reason for later sowing
among the group organic farms. Eleven days later sowing among organic farms could explain
lower T-sum from sowing to 1. August. The conventional fields had 70 mm higher precipitation
however no drought occurred in year 2001.
3
Table 2. Characteristic of maize fields. Average + standard deviation.
System
Observation (fields)
Day of sowing
T-sum
PrecFert_June,mm
Plants_ha, 1000 ha-1
“Germination”2), % of sown
WeedSummer, soil cover
WeedHarvest, soil cover
WeedHarvest, % vol. of maize
Maize_m
% empty cereals in cobs
Pct. sideshoot
% DM in cobs
g DM cob-1
Cob-yield, 1000 kg DM ha-1
Cob-yield, 1000 SFU ha-1
Organic
50 (10)
8. May +10
1262 +89
82 +27
66 +151
66 +15
30 +15
59 +30
25 +181
1.7 +0.4
19 +14
1 +1
32 +7
49 +21
3.4 +1.7
3.6 +1.8
Conventional
120 (24)
28. April +9
1307 +61
153 +28
80 +121
89 +10
8 +9
40 +36
4 +61
2.3 +0.2
9 +8
5 +6
42 +8
83 +19
7.1 +1.7
7.6 +1.9
1) Mean of the standard deviation within fields
2) “Germination” = Full developed maize plants at harvest as percentage of sown seeds
The number of maize plants in organic fields was only 66,000 varying from 51-81,000 maize
ha-1. The recommended number in Denmark is 80-100,000 maize ha-1. The low maize number
could be caused by lower germination and physical damage during weed harrowing in organic
fields. Weed harrowing was difficult during June in period with slowly maize growth (10 0C in 3
week and raining) and a lot of weed survived in the maize rows. In warmer years this weed can
be killed when covered by thin soil layer from weed harrowing, but when maize were not
growing the small maize would also be covered. In average the organic fields had 30% weed
cover in July and only 3 fields had less than 25% weed cover at harvest. After 1. July when
weed harrowing were not longer possible the weed spread vigorous and at harvest the weed
covered 59% soil in organic field and were tall, so 25% of the maize volume were covered by
weed. In conventional fields the soil cover were also 40%, but the weed were low and
accumulated to only 4% of the maize volume.
In organic fields dominating weed were: Chenopodium album L. ssp. Album (20.8% soil cover),
Elytrigia repens (L.) Nevski (5% soil cover), Solanum nigrum L. (4.2% soil cover), Stellaria
media (L.) Vill. (3.1% soil cover).
In conventional fields dominating weed were: Poa annua L. (17.4% soil cover), Elytrigia
repens (L.) Nevski (5.5% soil cover), Solanum nigrum L. (5.2% soil cover).
The organic maize were 0.6 m shorter than conventional and the cob-yield were lower because
of 24% lower dry matter content in cobs, 41% lower cob weight and double proportion of empty
cereals in cobs. Unfavourable conditions during later growth stages of maize growth may have
reduced number of silks resulting in poor pollination and restricting the number of developed
cereals (10).
Weed probably is the main course of the low yield. In Table 3 the correlation between cob yield
and main characteristics is shown.
4
Table 3. Correlations between cob-yield and covariates of 34 maize fields (n = 34).
Cob-yield
BBCH
Plants_ha
Height_m
% EmptyCereals
Volume weedHarv
BBCH
Plant_ha Height_m
%EmptyCereals
0.7***
0.7***
0.3
-0.6***
-0.5**
-0.2
-0.4*
Earlines
PrecFert_Ju PLN_ha
0.7***
0.2
0.6***
ne
Cob-yield
BBCH
Plants_ha
Maize_m
% EmptyCereals
Volume weedHarv
T-sum
Earlines
PrecFert_June
PLN_ha
Volume weedSummer
Covariates at farm level:
T-sum
PrecFert_June
Day of sowing
WeedSummer
Earlines
BBCH
Covariates at plot level:
Plant_ha
% empty kernals
WeedHarv
-0.1
0.0
0.2
0.0
-0.2
-0.2(*)
-0.3
0.5**
0.1
0.6***
0.7***
-0.2
-0.4**
-0.1
0.0
0.0
0.0
0.0
-0.1
-0.4*
0.2
0.4*
-0.4
0.1
Volume
weedSummer
-0.6***
-0.3(*)
-0.5**
-0.7***
0.4*
0.6***
-0.1
-0.1
-0.6***
0.2
=
=
=
=
=
=
T-sum from sowing to 1. August. (3)
Accumulated precipitation from first fertilisation to 1. July
Day number after 1. January 2001 of maize sowing.
Soil cover of weed in July
Earliness of each variety (5)
Stage of development on harvest date, BBCH scale 75-85(6).
=
=
=
Number of maize plants ha-1
% unfilled kernals of total cob
m3 weed per m3 maize just before harvest
Volume
weedHarv
-0.5**
-0.3
-0.2
-0.6***
0.5**
T-sum
0.5**
0.7***
0.1
-0.2
-0.2
0.0
Day of
sowing
0.6***
0.7***
0.2*
0.0
-0.3***
-0.2*
0.9***
-0.3***
0.1
0.3***
-0.2*
A correlation matrix based on the individual plots (n=170) showed the same overall picture as
Table 3.
The cob yield was positively correlated with development stage in the interval 75-85 BBCH;
with maize plants ha-1; with maize height; with T-sum between sowing and 1. August; with
precipitation and with day of maize sowing. The weed in midsummer (soil cover) and % empty
cereals in cobs had negative correlation with cob-yield. However from the correlation matrix it
can be seen that several of the covariates were correlated making the estimates in linear
statistical analysis dependent. In the following only covariates with lower correlation than + 0.5
are included in the linear regression model at the same time.
There was a significant effect of growing system and of farm within growing system on cob
yield, the expected cob-yield being 7,656 SFU ha-1 in the conventional system and 3,709 SFU
ha-1 in the organic system (Table 4). Farm 81-1 and 82-1 had lower yield than 40-1, 41-1 and
42-1. Explanation for this can be that 81-1 and 82-1 were situated in North Jutland. The fields
were sown 10-20 days later in the same period as the organic fields, also in North Jutland 44
mm extra surplus precipitation in June could have leached some N out of the root zone, at least
the maize turned yellow in June because of cold rainy weather during 3 weeks (100C and up to
100 mm precipitation).
5
Table 4. Analysis of variance of maize cob-yield (SFU ha-1) on five organic and five
conventional mixed dairy farms in year 2001 and LS-mean cobs for system and farm.
Variable
DF
System
1
Farm (System)
Field (farm (system))
Residual
Organic
Conventional
Farms
Organic
30-9
31-9
62-9
63-9
35-5
Conventional
40-1
41-1
42-1
81-1
82-1
Sum of square Mean square
560
8
227
24
230
136
144
Estimates for cob yield
3,709
7,656
560
Pr > F
R2
0.003
0.88
28
0.019
9
0.0001
1
Standard Error
166
100
3,387
3,688
4,746
3,426
3,299
325
231
461
326
461
7,466
9,748
8,815
6,610
5,642
163
231
231
231
231
In order to investigate how much of the variation in cob yield between fields that could be
explained by the measured state variates, maize plants per ha, weed, earliness of variety, T-sum
from sowing to 1. August, precipitation from fertilization to 1. June, N-application, maize plant
height, maize stage of development at harvest were includes as co-variates. Only co-variates
with interdependence lower than +0,5 correlation were included in the model at the same time
(Table 3).
Table 5. Analysis of variance of maize cob-yield (SFU ha-1) on 5 organic and 5
conventional mixed dairy farms in year 2001.
Variable
Plants_ha
Weedharv
T-sum
Residual
DF
1
1
1
30
Sum of square
64
65
42
32
Mean square
64
65
42
1
Estimate
1.05
-82
-43
Pr > F
< 0.0001
< 0.0001
< 0.0001
R2
0.84
From Table 5 the significant variables of above mentioned are shown. This difference in cobyield of 4000 SFU ha-1 between organic and conventional fields could be explained by maize
plants ha-1 and weed volume at harvest. A difference of 14,000 plants ha-1 (80,000-66,000 plants
in conventional and organic fields, see Table 2) could explain 1,469 cob SFU ha-1 (= 14,000 x
1.05). Weed difference of 21% of maize volume could explain 1,721 SFU ha-1 (21 * 82) and Tsum 726 SFU ha-1.
In figure 1 the relationship between SFU and predicted cob yield by the model in Tabel 5 are
shown. Symbols are shown for system, altitude (north/south) and fields with higher than 25%
weed soil cover mid summer (=weedy). From the figure a tendence can be seen for stronger
relationship between measured and predicted yields in conventional fields compared with
organic fields indicating that the yield potential are better utilized in clean conventional fields
compared to weedy organic fields.
6
Excluding environmental variables, yield losses in maize are caused mainly by competition
from weeds (9, 11). Importance of weed competition is described for critical periods. For maize
the critical period ranges from 1 to 8 weeks after maize emergence (4, 8, 11, 12). Weed
competition in early growing stage was the main problem and depressed yield of cobs on
organic farms.
Focus should also be paid to weed control especially in the maize rows. From trial results it
should be possible to control weed better than 15-45% weed soil cover midsummer. But
between 30-cm maize height and harvest it can be difficult to control weed competition. So
fields with low seed bank of weeds should be selected for maize production even through
quickly weed enrichment should be expected in these fields.
Weed competition and probably nutrient uptake by weeds were related to a high percentage of
empty cobs in organic group.
Probably an effect of weather conditions (temperature at early growth stages of maize) or wrong
types of varieties where main indicators of lower yield of maize cobs from the northern part of
Denmark.
CONCLUSIONS
Maize cob yield in 24 conventional and 10 organic fields in year 2001 could be predicted from
maize density, weed and T-sum (R2 = 84%).
Weed volume at harvest explaining 44% of the yield difference between the group of organic
and conventional fields; maize number per ha 37% and the T-sum between sowing and 1.
August 18% of the yield difference. Many other variables had significant correlation to the
covariates and with this survey set up it is not possible to distinguish between importances of
each because of bias.
Practical implications could be to recommend organic farmers to have a higher seeding rate or
to be more careful protecting the maize plants during weed harrowing.
AKNOWLEGEMENTS
The authors wish to thank K.R. Hansen, N.H. Thomsen, O. Nielsen, and H.K. Andersen for their
technical assistance. Danish Institute of Agricultural Sciences supported this work.
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