Mineral Fertilizers and Green Mulch in
Chinese Cabbage [Brassica pekinensis
(Lour.) Rupr.]: Effect on Nutrient
Uptake, Yield and Internal Tipburn
Magnusson, M. (Department of Agricultural Research for Northern
Sweden, Swedish University of Agricultural Sciences, Box 4097, SE-904
03 UmeaÊ , Sweden). Mineral fertilizers and green mulch in Chinese cabbage [Brassica pekinensis (Lour.) Rupr.]: effect on nutrient uptake, yield
and internal tipburn. Accepted February 20, 2002. Acta Agric. Scand.,
Sect. B, Soil and Plant Sci. 52: 25– 35, 2002. © 2002 Taylor &
Francis.
Large applications of mineral fertilizers in Chinese cabbage [Brassica
pekinensis (Lour.) Rupr.] increased growth, total nitrogen and nitrate
concentrations at harvest, and increased the occurrence of internal
tipburn. Green mulch, as the only fertilizer or in combination with
small amounts of mineral fertilizers, resulted in slower growth and
lower total nitrogen and nitrate concentrations at harvest, and also
prevented the occurrence of internal tipburn. No visible symptoms of
nutrient deŽ ciencies were detected, but plant analyses showed that the
concentrations of magnesium, zinc, manganese and copper were below
the estimated sufŽ ciency limits in all fertilizer regimes. High soil pH,
6.4 – 6.8, and large amounts of calcium in the soil decreased the
availability of these elements. The results demonstrate the importance
of simultaneous analyses of several elements in revealing suboptimal
concentrations and:or imbalances that depress yield and quality but
do not result in visible symptoms. The results also indicate that organic fertilizers such as green mulch may be more suitable than mineral fertilizers in preventing the occurrence of physiological disorders
such as tipburn.
Introduction
Chinese cabbage [Brassica pekinensis (Lour.) Rupr.]
is a very productive crop with a potential for yields
of 100 t ha ¼ 1. Increasing nitrogen (N) applications
usually increase total fresh weight production, increase total N and nitrate (NO3) concentrations in
the plants, and decrease dry matter content (Venter,
1983; Liebhard & Holzerbauer, 1985; Kraxner et
al., 1988; Guttormsen, 1996). These are all factors
reported to increase the risk of the physiological
Margareta Magnusson
Department of Agricultural Research
for Northern Sweden, Swedish
University of Agricultural Sciences,
Box 4097, SE-904 03 UmeaÊ , Sweden
Key words: calcium, copper,
magnesium, manganese, nitrate, PLS,
soil pH, zinc.
disorder internal tipburn, which can make a whole
crop unmarketable. Internal tipburn is a necrotic
breakdown of the marginal tissue of leaves in the
heads, usually attributed to localized calcium (Ca)
deŽ ciency; its occurrence is believed to be related to
the weather (Balvoll, 1995). Large applications of
easily available N at the time of planting are
known to increase shoot:root ratios, and thus to
increase the susceptibility to physiological disorders
later in the season (Brumm & Schenk, 1993;
Marschner, 1995). Restricted root growth is an
25
M. Magnusson
important factor shown to reduce Ca uptake and
induce tipburn (Aloni, 1986). Tipburn is often reported to be promoted by factors inducing fast
growth, e.g. high temperature and large N applications (Zhao et al., 1982; Brumm & Schenk, 1993;
Balvoll, 1995; Guttormsen, 1996). According to
Balvoll (1995), internal tipburn of Chinese cabbage
in Norway often occurs some weeks after a period
with similar transpiration rates by day and by night,
whether low or high. Saure (1998) cites con icting
reports concerning the in uence of light intensity,
photoperiods, temperature, humidity, growth rate
and Ca supply on the incidence of tipburn, and
states that although tipburn has been known for
about 100 years, it is still poorly understood and its
occurrence cannot be predicted. Saure (1998) concludes that tipburn seems to be a stress-related disorder and that mild stresses, below a level that would
cause damage, may reduce the risk of tipburn by
increasing tolerance to stress.
The optimum N addition for marketable yield in
Chinese cabbage has often been reported to be below 200 kg ha ¼ 1 (Balvoll, 1995; Guttormsen, 1996)
or, in some cases, between 200 and 300 kg ha ¼ 1
(Kraxner et al., 1988; Goodlass et al., 1997). The
actual optimal N applications for marketable yield
can be expected to depend on difference between
soils in availability of several other nutrient elements. Few investigations have studied the importance of N and Ca in relation to other nutrient
elements and there have been few efforts to estimate
optimal concentrations of essential elements in Chinese cabbage. Often only some of the major elements are varied, and it is assumed that all other
nutrients are at optimal level. Usually, neither soil
nor plants are analysed for more than the elements
studied, and deŽ ciencies are probably overlooked
unless some explicit deŽ ciency symptoms appear. It
is well known that a deŽ ciency of a nutrient element
can decrease yield to a considerable extent without
any visible symptoms. This situation may be much
more common in Ž eld experiments than has been
recognized. Multielement studies in cauli ower
(Brassica oleracea L. var. botrytis) and broccoli
(Brassica oleracea L. var. italica) revealed several
latent nutrient deŽ ciencies [i.e. magnesium (Mg),
boron (B), manganese (Mn), zinc (Zn), iron (Fe) and
copper (Cu)] and it was concluded that the often
recommended soil pH of at least 7.0 for brassica
crops is far too high, especially when organic fertilizers are applied (Magnusson, 2000).
The objective of this work was to study the uptake
of a large number of nutrient elements in Chinese
cabbage, grown with different fertilizer regimes,
and its relation to marketable yield and internal
tipburn.
26
Material and methods
Field experiments
During 1996 and 1997, Ž eld experiments with Chinese cabbage (Brassica pekinensis [Lour.] Rupr.) cv.
TG2003 were performed at the agricultural research
station Röbäcksdalen (63°49Æ N, 20°17Æ E). The
transplants were propagated in a glasshouse in trays
(21 ml volume per plug). Sowing dates were 24 May
1996 and 21 May 1997. The planting dates were 12
June 1996 and 10 June 1997. Peak harvest was 6 – 14
August 1996 and 4 – 12 August 1997. All plots were
on  at ground on a sandy soil (Table 1); the size of
the plots was 32.4 m2 in 1996 and 31.5 m2 in 1997.
The distance between rows was 0.5 m, with 0.3 m
between plants. There were 216 plants in each plot
in 1996 and 210 plants in 1997. Four fertilizer
regimes, F1– F4 (changed slightly between the years),
were compared (Table 2). There were four replicates.
No control without fertilizer addition was included
as no normal growth of unfertilized Chinese cabbage
can be expected and analyses of such plants would
be a waste of money. To protect the plants from
insects, a transparent cover (Agryl 17 g m ¼ 2) was
put on at the time of planting and removed 4 weeks
later. In 1997, irrigation was applied immediately
after planting but in 1996 no irrigation was needed.
Soil samples were taken from each plot seven times
during the season, every 14 days, beginning on 10
June before any fertilizer was added. Plant samples
were taken from the transplants at the time of planting and thereafter from each plot four times during
the season (every 14 days, beginning 14 days after
planting). The experiments were located in the same
Ž eld, a few metres apart.
Sample preparation and analyses
The soil samples were taken to a depth of 30 cm. For
each sample, 10 subsamples were carefully mixed,
and about 0.5 l of soil was put in plastic bags. The
samples were kept in a freezer and sent frozen to the
laboratory. The following soil factors were deterTable 1. Organic matter, particle size distribution and
average soil pH on the experimental sites (% of dry
matter)
Parameter
1996
1997
Organic matter
Clay (B 0.002 mm)
Silt (0.002–0.02 mm)
Fine sand (0.02–0.2 mm)
Sand (0.2–2 mm)
Soil pH before fertilizing
4
2
6
68
20
6.4
4
6
16
63
11
6.8
Mineral fertilizers in Chinese cabbage
Table 2. The four fertilizer regimes applied each year
Fertilizer
regime
Application before
planting
F1
F2 1996
F2 1997
F3 1996
NPK 1000 kg ha¼1
NPK 300 kg ha¼1
NPK 500 kg ha¼1
NPK 300 kg ha¼1»
Green mulch 50 t ha¼1
NPK 300 kg ha¼1
Green mulch 50 t ha¼1
F3 1997
F4 1996
F4 1997
Application 2 weeks after
planting
Application 4 weeks after
planting
NPK 300 kg ha
Calcium nitrate 450 kg ha¼1
Calcium nitrate 300 kg ha¼1
Calcium nitrate 300 kg ha¼1
¼1
Green mulch 40 t ha¼1
Green mulch 40 t ha¼1
The NPK used was 11–5–18 micro and the calcium nitrate was with boron (15.5% N and 0.15% B). The green
mulch was grass ley.
mined at the soil laboratory LMI in Helsingborg: pH
(1 : 4 soil : deionized H2O, 15 min), NO3 – N, NH4 –
N, phosphorus (P), potassium (K), Mg, sulfur (S),
Ca, sodium (Na), chlorine (Cl), Mn, aluminium (Al),
B, silicon (Si), strontium (Sr), nickel (Ni) and cadmium (Cd) (modiŽ ed Spurway Lawton method: 1 : 6
soil : HAc 0.1%, 30 min), and Fe, Zn, Cu and molybdenum (Mo) (1 : 10 soil : NaEDTA in deionized H2O,
60 min). NO3 – N, NH 4 – N and Cl were detected with
ion-selective electrodes in an autoanalyser; all other
elements were detected with ICP-OES. The results
were expressed as mg l ¼ 1 soil.
Ten randomly chosen plants were cut above
ground in each plot at each sampling. At peak harvest, the plants were divided into yield (head) and
residue (the plant material remaining above ground
after the heads had been cut and removed). The
plants were washed in cold running tap water to
remove contamination before being cut into pieces
and dried. The samples were dried at 70°C for 24 h
plus 105°C for 1 h. The plant material was analysed
at Biospectron (TaÊ garp, Sweden) for the total concentrations in the dry matter of Al, B, barium (Ba),
carbon (C), Ca, Cd, cobalt (Co), Cu, Fe, K, Mg, Mn,
Mo, N, Na, Ni, P, lead (Pb), rubidium (Rb), S,
selenium (Se), Si, tin (Sn), Sr and Zn. C and N in the
dry matter were analysed in a Carlo Erba-instrument:
NA-1500 (Milan, Italy) (Dumas principle). For all
other elements digestion was with perchloric acid and
nitric acid, and detection with ICP-OES and ICPMS. The plant samples were also analysed at the
Cereal Laboratory (Svalöv, Sweden) for total concentration in the dry matter of Cl (AACC Method
40 – 31). The samples of the green mulch were
analysed for the same elements as the plants.
Statistical evaluation
Plant development during the season is presented as
descriptive statistical graphs created in the technical
graphics and data analyses program Origin 6.0.
Statistical measures used are arithmetic mean and
SEM (¾SD: n). PLS (Partial Least Squares Projection to Latent Structures) analyses were performed in
the multivariate program SIMCA-P 8.0 (UMETRI,
UmeaÊ , Sweden). For a description and discussion of
the method with applications in plant nutrition, see
StaÊ hle & Wold (1988, 1990), Wold (1991, 1995),
Eriksson et al. (1995) and Magnusson (2000). The
usual practice, adopted in this paper, is to normalize
the data to zero mean and unit variance. The statistical parameters used are R 2Y ¾variance in Y explained and Q 2 ¾ variance predicted. The latter is a
measure of the validity of the model, estimated by
means of cross-validation . R 2Y(cum) and Q 2(cum)
are the accumulated values for all signiŽ cant components in a model. Both parameters can have values
between 0 and 1; larger values indicate a stronger,
more valid model. However, a PLS model with a high
degree of explanation in Y, but a low Q 2, has low
validity and must be interpreted cautiously. Ideally,
Q 2 should not be more than 5– 20% lower than R 2Y.
The PLS regression coefŽ cients used correspond to
centred and scaled X, and scaled but uncentred Y
(CoeffCS).
Results
Fresh weight accumulation and dry matter content
The temperature was lower and the precipitation was
slightly greater in 1996 than in 1997 (Fig. 1). There
were fewer sunny days in 1996 and the transpiration
was lower; the soil and air moisture was constantly
relatively high. At the time of planting the transplants
had an average fresh weight of 2.9 g plant ¼ 1 in 1996
(19 days after sowing) and 2.4 g plant ¼ 1 in 1997 (20
days after sowing). In general, the growth was faster
and the accumulated fresh weight at harvest was
larger in 1997 than in 1996 (Fig. 2). The plants in F1
27
M. Magnusson
Fig. 3. Marketable yield, incidence of internal tipburn, dry matter
content (DM%) and nitrate in the heads at harvest. Means and SE
bars (n ¾ 4).
Fig. 1. Air temperature (top) and precipitation (bottom) during the
growing seasons.
and F4 in 1997. In 1996, the marketable yield corresponded to the total growth as there was no major
incidence of quality disorders (Fig. 3). However, in
1997 there was a severe incidence of internal tipburn
in F1 and F2, with a consequent large reduction in
marketable yield.
Soil analyses
After 2 weeks in the Ž eld, soil pH was more depressed in F1 and F2 than in F3 and F4 (Fig. 4). This
was accompanied by a strong increase in electrical
conductivity (Ec), N, K and S, especially in F1. The
concentration of chloride in the soil increased
strongly in F3 and F4 in 1996. On the two last
sampling occasions (after harvest) the concentration
of elements in the soil increased in the majority of
plots.
Fig. 2. Accumulated fresh weight (FW) and changes in dry matter
content (DM%) in the whole plant above ground at harvest.
Means and SE bars (n ¾4).
and F2 were growing the most rapidly and the difference was large from the beginning. After 2 weeks in
the Ž eld the weight had increased to 80.4 g plant ¼ 1 in
F1 and 86.0 g in F2 in 1997, compared with 33.0 g
and 24.3 g, respectively, in 1996. The corresponding
Ž gures for F3 were 11.7 g ha ¼ 1 in 1996 and 76.6 g in
1997, and for F4 6.9 g ha ¼ 1 in 1996 and 47.0 g in
1997. The dry matter content was high at transplanting and decreased in all treatments after a few weeks
in the Ž eld. The largest decrease was in F1, which had
both the lowest dry matter content and the largest
fresh weight accumulation in both years. The concentrations of total N and of NO3 were very low in F3
28
Nutrient uptake
The total uptake of 16 elements in the whole crop
above ground was compared with the amounts added
with the fertilizers (Tables 3, 4). In F1 and F2,
where no green mulch was added, the uptake of K,
N, Ca, Cl, Na, Fe, Mo and Ni was more than the
amounts added. In the combined NPK and green
mulch treatment, F3, the uptake of the majority of
elements was less than the amounts added. In F4,
where only green mulch was applied, the uptake of
the majority of elements was less than the addition in
1996, while in 1997 the uptake of several elements
was more than the addition. The harvest index, expressed as per cent of total weight above ground
removed with the crop (the heads), was 72% for fresh
weight and 71% for dry matter (Fig. 5). The harvest
index for the 16 elements, expressed as per cent of
Mineral fertilizers in Chinese cabbage
strongly in the green mulch treatments, F3 and F4, in
1996, but less in 1997. The NPK fertilizer used contained 10.4% S and the S concentration in the plants
increased with the amounts applied. The Mg concentration decreased successively during the season in all
treatments, but most in F4 and least in F1. The
concentration of Na, Zn and Mn decreased strongly
after transplanting and remained low during the rest
of the season. The concentration of Mo in the transplants was more than twice as high in 1997 as in
1996. The concentration in F4 was much larger than
in the other treatments.
PLS models
Fig. 4. Soil pH (H2O), electrical conductivity (Ec) and HAc-extracted nitrogen (NO3 – N »NH4 – N), potassium, sulfur and chloride in the soil (0 – 30 cm). Means and SE bars (n ¾ 4).
total uptake above ground removed with the crop,
varied from 31% for Ca to 83% for Zn.
Element concentrations
The changes in dry matter concentration of 16 elements in the whole plant above ground during the
season were similar in the two years for the majority
of elements (Fig. 6). Both K and N increased strongly
after transplanting into the Ž eld and then decreased
at harvest. F1 had the highest N concentration
throughout the season, especially in 1997. The Ca
concentration increased strongly after transplanting
in all treatments in 1997, but returned to the initial
level at harvest. The Cl concentration increased very
A PLS model was created with the total fresh weight
above ground at harvest as response (Y) variable.
The descriptor (X) variables were the concentration
in the plants of the elements analysed on each of the
Ž ve sampling occasions and the mean values for the
soil analyses taken from the Ž rst Ž ve samplings. The
model has three signiŽ cant components with
R 2Y(cum) ¾ 0.820 and Q 2(cum) ¾ 0.649. The Ž rst
component explained 60.5% of the variation in Y and
the second explained 11.2%. The object plot (Fig. 7)
shows that F1 dominates in the upper right part,
which is associated with high total fresh weight, while
F4 dominates in the lower left part, associated with
low total fresh weight. The scatter plot for the soil
variables (Fig. 8) shows that high total fresh weight
was associated with high concentrations of NH4 – N
and NO3 – N, high Ec and high concentrations of Zn,
P and S in the soil. The scatter plots for the plant
variables measured at different stages during the season (Fig. 9) show that high fresh weight was associated with high concentrations of N, S, Zn, Mg, Mn,
Cu and Rb in the plants. Low fresh weight was
associated with high soil pH, high concentrations of
Si, Cl, K and Ca in the soil, high dry matter content
and high concentrations of Mo, Cl and Ba in the
plants.
Separate PLS models for Mg, Zn, Mn and Cu were
created. The regression coefŽ cients are shown in Fig.
10. The values for R 2Y(cum) and Q 2(cum) show that
all models have a high degree of explanation and a
high validity. The strongest negative correlation to
Mg and Zn in the plants was for soil pH and Ca in
soil and plants. The strongest negative correlation to
Mn and Cu in the plants was for Mo and C in the
plants.
Discussion
The transplants looked perfectly healthy in both
years, although the high dry matter content together
with the low N concentration suggest that growth
29
M. Magnusson
Table 3. Calculated addition of macroelements with fertilizers, uptake in the whole crop above ground, and
difference between addition and uptake (kg ha¼1)
1996
Element
Fertilizer regime
Potassium
Nitrogen
Calcium
Chlorine
Sulfur
Phosphorus
Magnesium
Sodium
Fertilizer regime
Potassium
Nitrogen
Calcium
Chlorine
Sulfur
Phosphorus
Magnesium
Sodium
Fertilizer regime
Potassium
Nitrogen
Calcium
Chlorine
Sulfur
Phosphorus
Magnesium
Sodium
Fertilizer regime
Potassium
Nitrogen
Calcium
Chlorine
Sulfur
Phosphorus
Magnesium
Sodium
1997
Addition
Uptake
Addition – uptake
Addition
Uptake
Addition – uptake
180
184
86
356
221
118
40
51
44
9.8
1.8
¼176
¼37
¼32
¼40
53
2
7.2
¼1.8
180
184
86
332
209
108
43
57
43
9.2
2.2
¼152
¼25
¼22
¼43
47
3
7.8
¼2.2
292
173
107
34
43
37
7.6
1.2
¼184
¼58
¼50
¼34
19
¼9.6
2.6
¼1.2
90
104
57
274
137
97
31
42
37
7.4
1.2
¼184
¼33
¼40
¼31
10
¼14
1.1
¼1.2
393
335
93
142
54
52
20
0.3
309
161
106
77
39
38
7.3
0.9
84
174
¼12
65
14
13
13
¼0.6
260
173
34
123
44
37
14
0.3
257
107
89
66
32
34
6.5
0.7
3.0
65
¼55
57
12
3.0
7.0
¼0.5
339
300
93
142
22
38
15
0.3
241
122
83
64
24
31
5.6
0.6
99
178
10
78
¼2.0
7.3
9.4
¼0.3
206
138
34
123
13
23
8.5
0.3
281
113
107
65
26
38
7.0
0.6
¼75
25
¼73
58
¼14
¼15
1.5
¼0.3
1
104
46
17
2
108
115
57
62
28
10.2
52
23
8.5
3
4
was restricted. The fertilizer additions made during
the last week before planting probably could not fully
compensate the fast-growing plants for the small soil
volume of the pots. The incidence of internal tipburn
in F1 and F2 in 1997 can be explained by factors
already known to increase the risk of this disorder,
i.e. high salt and N concentrations in the soil, fast
growth, high total N and NO3 concentrations and
low dry matter content of the plants. The absence of
internal tipburn in F3 and F4 is also in agreement
with the observation that salt and N concentrations
do not usually increase as much early in the season
when organic fertilizers are applied as with mineral
fertilizers. The decrease in soil pH 2 weeks after
30
104
46
17
applications of mineral fertilizers was related both to
the direct acidifying effect and to the increased salt
concentration in the soil. As the pH was measured in
the bulk soil, pH in the vicinity of a dissolving
fertilizer granule may be much lower. This acidifying
effect often increases the availability of several nutrients in high pH soils (Magnusson, 2000).
The removal in the crop of a large proportion of
the Zn, N, P and Cu could be expected, as the
concentrations of these elements are known to be
large in young, actively growing parts of plants.
However, higher concentrations of Zn, Mg and Mn
in the residues than in the heads would be expected
when the plants are well supplied with these elements,
Mineral fertilizers in Chinese cabbage
Table 4. Calculated addition of microelements with fertilizers, uptake in the whole crop above ground and
difference between addition and uptake (g ha¼1)
1996
Element
Fertilizer regime
Iron
Zinc
Boron
Manganese
Copper
Molybdenum
Nickel
Cobalt
Fertilizer regime
Iron
Zinc
Boron
Manganese
Copper
Molybdenum
Nickel
Cobalt
Fertilizer regime
Iron
Zinc
Boron
Manganese
Copper
Molybdenum
Nickel
Cobalt
Fertilizer regime
Iron
Zinc
Boron
Manganese
Copper
Molybdenum
Nickel
Cobalt
Addition
1997
Uptake
Addition – uptake
362
184
213
85
26
32
16
1.2
¼362
116
762
915
474
¼12
¼16
18.8
12
298
141
187
64
21
31
13
1.0
¼298
39
443
536
279
¼19
¼13
11
1450
373
221
915
233
44
22
7.6
319
139
172
55
19
53
13
0.8
1450
283
131
615
83
40
22
1.6
246
106
136
31
15
59
11
0.6
Addition
Uptake
Addition – uptake
503
200
173
125
31
28
8.7
1.3
¼503
100
802
875
469
¼7.8
¼8.7
18.7
10
316
146
154
65
23
36
6.7
9.4
¼316
4.0
446
435
227
¼26
¼6.7
9.4
1131
234
49
860
214
¼9.3
8.3
6.8
1967
249
123
844
191
31
10
7.2
245
121
133
63
19
36
5.5
0.5
1722
128
¼11
781
172
¼5.0
4.9
6.7
1204
176
¼5.0
584
68
¼22
11
¼1.0
1967
159
33
544
41
25
10
1.2
262
122
155
50
21
71
6.6
0.4
1706
36
¼123
494
20
¼46
3.8
0.8
1
300
975
1000
500
20
20
300
975
1000
500
20
20
2
180
630
600
300
12
150
600
500
250
10
3
4
Fig. 5. Harvest index, expressed as % of total amount above
ground removed with the crop at harvest for 16 elements, fresh
weight (FW) and dry matter (DM). Means and SE bars (n ¾32).
and the large harvest index indicates deŽ ciency of
these elements (Magnusson, 2000). When only mineral fertilizers are used, the K requirement is difŽ cult
to satisfy without adding too much of some other
elements, such as S or Cl. Where only green mulch is
applied, the amounts of S and B added are most
likely to be insufŽ cient. However, members of the
Leguminosae (Fabaceae) are known to contain higher
concentrations of both S and B than the Gramienae
(Poaceae) (Berger, 1949; Gupta et al., 1985;
Marschner, 1995), and a green mulch other than
grass ley would probably be more suitable. The ability of legumes to acidify the rhizosphere and thus
increase the uptake of several micronutrients can also
31
M. Magnusson
Fig. 6. The concentration in dry matter (DM) of 16 elements during the season in the whole plants above ground. Means and SE bars
(n ¾ 4).
be expected to have a favourable effect. It has been
shown that green mulch gives better results in brassicas on soils with a relatively low soil pH, below 6.0
(Magnusson, 2000). On high pH soils, the large N
32
application with green mulch often resulted in too
vigorous plants and smaller marketable yield. On low
pH soils, however, the N was balanced by better
availability of several micronutrients which increased
Mineral fertilizers in Chinese cabbage
Fig. 7. Object plot for the PLS model with the total fresh weight at
harvest as response (Y) variable. The descriptor (X) variables were
the concentration in the plants of the elements analysed on each of
the Ž ve sampling occasions and the mean values for the soil
analyses taken from the Ž rst Ž ve samplings. F1 – F4 refer to the
different fertilizer regimes.
Fig. 8. Scatter plot for soil variables in the PLS model with the
total fresh weight at harvest as response (Y) variable. The Y-variable is represented by a grey square. Ec: electrical conductivity as
a measure of the total salt concentration in the soil.
marketable yield and caused a dilution of N concentrations in the crop at harvest.
The large application of N with the green mulch
compared with the uptake in the crop in 1996 was the
reason for decreasing the amount of green mulch
from 50 to 40 t ha ¼ 1 in 1997. As the material had a
considerably smaller content of all elements in 1997,
the reduction in addition of nutrients was larger than
expected. However, the total addition of Cl in F3 and
F4 was only slightly more in 1996 than in 1997. The
main reason for the much higher concentration in soil
and plants in 1996 is probably related to the higher
precipitation, which caused more chloride to leach
into the soil from the green mulch. The high concentrations of chloride may have depressed growth.
Large amounts of S in the soil are known to decrease
Mo uptake by the crop. This, together with the
decrease in soil pH also caused by the NPK fertilizer,
resulted in much lower Mo concentrations in the
Fig. 9. Scatter plots for plant variables and soil pH of the PLS
model with the total fresh weight at harvest as response (Y)
variable. From top: sampling 2, 4, 6 and 8 –9 (at harvest) weeks
after planting. The response (Y) variable is represented by a grey
square. Fw: fresh weight; dm%: dry matter content in the whole
plant at harvest. NO3: nitrate concentration in the heads at harvest.
plots where NPK was applied than in F4 where only
green mulch was applied. However, the Mo concen33
M. Magnusson
Fig. 10. PLS regression coefŽ cients of the models with Mg, Zn,
Mn and Cu, respectively, in the whole plant at harvest as response
(Y) variables. The tags 1 – 5 refer to the sampling occasions (1: at
planting; 5: at harvest); tag s refers to the concentration in the soil.
R 2Y: variance in Y explained; Q 2: variance predicted. The latter is
a measure of the validity of the model. Only the X-variables with
the strongest correlation to the Y-variable are included and sorted
in descending order.
trations were well above the estimated sufŽ ciency limits
in all treatments and were very high in F4. The strong
decrease in Zn and Mn concentrations after transplanting indicates that the availability in the soil of these
elements was too low. In general, F1 had the highest
concentrations of all elements except for Cl and Mo,
although the differences were small for several elements. For N and S the difference was related mainly
to the larger amounts of the elements applied in an
34
easily available form. However, the decrease in soil pH
caused by the NPK fertilizer probably increased the
availability of the other elements in the soil.
There are several reports of the normal dry matter
concentrations in whole plants of Chinese cabbage at
harvest (Pevná, 1976; Venter, 1983; Liebhard & Holzerbauer, 1985; Kraxner et al., 1988; Guttormsen, 1996;
Gajc-Wolska & Skapski, 1998; Kim & Kim, 1998;
Markov & Marinova, 1999). They can be summarized
as: N 2.7 – 4.6%, K 3.3 –4.6%, Ca 1.8 – 2.2%, Mg
0.25– 0.40%, P 0.28 – 0.58%, S 0.75%, Na 0.17 – 0.59%,
Fe 100 – 150 mg kg ¼ 1, Zn 44 – 86 mg kg ¼ 1, Mn 25– 42
mg kg ¼ 1 and Cu 8– 12 mg kg ¼ 1. Compared with the
general sufŽ ciency limits for other brassicas
(Bergmann, 1992; Mills & Jones, 1996; Magnusson,
2000) the concentrations of K, P, Ca and Mo in the
present study were well above the estimated sufŽ ciency
levels in all objects. The concentrations of N and S were
below the estimated sufŽ ciency levels in some objects.
The concentrations of Mg, Zn, Mn and Cu were below
the estimated sufŽ ciency levels in the majority of
objects. Supplemented with the PLS models, it is
concluded that the elements Mg, Zn, Mn and Cu
limited growth in all fertilizer regimes. High soil pH
and large amounts of Ca in the soil decreased the
availability of these elements. The ratio Ca:Mg in the
soil varied between 10.3 and 23.5, which is much larger
than the reported optimal ratio of 4 – 6 (Jacoby, 1961;
Jokinen, 1981; Magnusson, 2000). The average soil pH
before fertilizing in this study was 6.4 in 1996 and 6.8
in 1997; this is below the recommended pH values of
7.0 – 7.5 for brassicas, which is partly motivated by the
wish to prevent the serious disease club root (Plasmo diophora brassicae). However, a more advisable
method to prevent this disease would be a proper crop
rotation.
The results of this study show that organic fertilizers
such as green mulch may be more suitable than mineral
fertilizers in preventing the occurrence of physiological
disorders such as tipburn. However, in this study,
neither the composition of the mulching material nor
the soil conditions were optimal. The results demonstrate the importance of simultaneous analyses of
several elements in revealing suboptimal concentrations and:or imbalances that depress yield and quality
but do not result in visible symptoms. Better knowledge of nutrient availability in the soil and nutrient
composition of different organic fertilizers is a prerequisite of optimization of nutrient applications in organically grown vegetable crops.
Acknowledgement
The Swedish Council for Forestry and Agricultural
Research is gratefully acknowledged for Ž nancing the
analyses.
Mineral fertilizers in Chinese cabbage
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