Directory UMM :Data Elmu:jurnal:A:Applied Soil Ecology:Vol12.Issue3.Jul1999:
Applied Soil Ecology 12 (1999) 217±225
Field assessment of soil quality as affected by compost and fertilizer
application in a broccoli ®eld (San Benito County, California)
S. Stamatiadisa,*, M. Wernerb, M. Buchananb
b
a
Goulandris Natural History Museum, Ecology-Biotechnology Laboratory, 13 Levidou Street, Ki®ssia, 14562, Greece
University of California±Santa Cruz, Center for Agroecology and Sustainable Food Systems, Santa Cruz, CA 95064, USA
Received 6 January 1999; accepted 8 February 1999
Abstract
Selected in-®eld physical, chemical and biological indicators were measured for the rapid assessment of soil quality changes
in a Sorrento silty clay loam as a result of compost and ammonium nitrate application to a broccoli ®eld (San Benito County,
CA). Plots were laid out in a randomized complete block design with four replications of 0, 22 and 44 Mg haÿ1 compost
treatments which were split to include fertilizer (165 kg N haÿ1) and no-fertilizer subplots. Soil samples were taken on 11 and
24 October 1995 during the active growth phase of the crop, and soil quality evaluation was compared to crop nutrient content
and yield which were determined at harvest in November.
Surface application of ammonium nitrate initially stimulated soil nitri®cation and acidi®cation processes in the top 7.6 cm
as evidenced by an 80-fold increase in nitrate-N and accumulation of nitrite, a 1.5-unit increase in electrical conductivity (EC)
and a 1.4-unit decrease in pH. Following irrigation, this pattern was reversed by nitrate leaching and root uptake, although
nitri®cation and acidi®cation effects remained detectable at both sampling depths (0±7.6 and 0±20 cm). Nitri®cation was
positively correlated to soil respiration and negatively correlated to soil water content. The estimated nitrate-N levels of
fertilizer-containing plots in the top 20 cm were two times higher than those reported in the literature as minimal levels for
optimal corn growth and indicated a high risk for groundwater contamination in this irrigated ®eld by taking into account the
rapid water in®ltration and low soil buffering capacity.
The detected short-term bene®cial effects of compost application were the stabilization of pH and the decrease of water
in®ltration rate. Stabilization of pH prevented acidi®cation effects due to fertilizer application at both sampling depths. The
high soil EC of plots receiving 44 Mg haÿ1 of compost at the 0±20 cm depth probably resulted from a high compost salt
content, other than nitrates, and warns against repeated use of high EC composts that may result in N depletion, reduced
nutrient cycling and impaired crop growth.
The relatively small differences among treatments in crop yield, head number and weight, leaf and petiole nutrients
indicated that there was suf®cient residual fertility to grow a crop in the absence of any amendments. However, the relevance
of selected soil quality indicators to plant productivity and health was evidenced by the strong correlation of soil nitrate-N
with leaf-N and head weight, despite the adequate-to-excessive amount of soil nitrate-N in most treatments. # 1999 Elsevier
Science B.V. All rights reserved.
Keywords: Nitri®cation; Acidi®cation; Crop yield
*Corresponding author. Tel.: +30-1-8087345; fax: +30-1-8080674.
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 1 3 - X
218
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
1. Introduction
The use of synthetic ammonium fertilizers is known
to cause a rapid shift of soil chemical properties which
are initiated by microbial nitri®cation. This shift may
result in soil acidi®cation. The magnitude of the effect
of these processes has been directly measured in soil
extracts by a rise of nitrate and electrical conductivity
(EC) and a decline of pH (Patriquin et al., 1993; Smith
and Doran, 1996). However, the slower nitri®cation of
N and the high cation exchange capacity of organic
amendments stabilize soil chemical properties by
increasing soil buffering capacity and slowly releasing
essential nutrients for more sustainable plant growth.
In order to fully assess the effects of such management practices in the soil environment, we need to
integrate chemical with physical and biological attributes that can serve as appropriate indicators of soil
functions. In this study, a basic set of soil quality
indicators (bulk density, in®ltration rate, water content, water holding capacity, pH, EC, NO3-N, soil
respiration) were measured in a broccoli ®eld subjected to compost and inorganic fertilizer inputs.
These indicators were selected in order to demonstrate
the utility of in-®eld measurements for the quick
detection of soil quality changes under organic and
chemical management practices. They comply with
the proposed selection criteria of soil quality indicators in that they are sensitive to variations in management, they de®ne major ecological processes in soil
and they re¯ect conditions as they actually exist in the
®eld under a given management system (Doran et al.,
1996). The techniques employed were relatively inexpensive, simple, and could be conducted on site by
many users such as farmers, researchers, consultants,
extension agents and resource conservationists (Liebig et al., 1996; Sarrantonio et al., 1996). Spacial and
temporal changes of soil attributes were evaluated and
compared to plant nutrient content and yield in order
to assess effects on both environmental quality and
plant productivity.
2. Materials and methods
2.1. Site description
The experimental site was a commercial broccoli
®eld located near Hollister, San Benito County. The
soil type is Sorrento silty clay loam, described as a
Mollisol. The climate is Mediterranean, with summer
drought, and cool, rainy winters. The site had been in a
lettuce/broccoli rotation (lettuce in the summer, broccoli in the fall) for at least the previous 3 years, using
conventional soil fertility and pest management practices. No organic matter inputs were made other than
crop residues. Water was provided during the cropping
season through sprinkler irrigation. The ®eld was
laser-leveled every 6 or 7 years.
At the time of the experiment, the `Sundance'
tillage system was in use. Permanent beds (45 cm
wide, 102 cm between two consecutive bed centers)
are maintained by a front and rear-mounted shank,
shovel and disk system, which can incorporate
prior residue while rebuilding the bed in one pass.
The pre-existing crop is ®rst mowed, the shanks rip the
center of the bed to 25±30 cm depth, followed by discs
which incorporate residues while moving soil back
into a rough triangular bed. Furrows remain undisturbed, thus wheel-traf®c is controlled and permanent.
The beds are cultivated by dragging a 46 cm shank
through the middle of the bed. Two passes with a
Lilliston cultivator were made to further incorporate
prior lettuce residues and compost prior to shaping the
raised beds and transplanting. Transplanting was on 10
August and broccoli was harvested on 10, 14, and 17
November 1995.
2.2. Experimental design and sampling
A longitudinal section of the broccoli ®eld, six rows
or 612 cm wide, was divided into four blocks and three
®elds of equal area in each block were randomly
assigned to receive three rates of compost (0, 22
and 44 Mg haÿ1) in a complete randomized block
design. Green wastes (30%), cow manure
(20%), spoiled hay (15%), clay soil (5%) and
various crop processing residues were reported to be
the initial sources of compost. The presence of soil
was indicated by the high ash content of compost
(Table 1). Each ®eld was partitioned into two subplots
that received a random assignment of the two levels of
fertilizer, 0 or 165 kg (NH4NO3)-N haÿ1 sprinkled
uniformly on the tops of beds by hand. Thus, the
resulting split-plot design was composed of four
blocks, three levels of compost within each block
and two levels of fertilizer within each level of com-
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 1
Chemical characteristics of compost applied to experimental field
during 1995
C (%)
Ash (%)
N (%)
C/N
NH4-N (ppm)
NO3-N (ppm)
pH
First application
(before summer lettuce)
Second application
(before fall broccoli)
10.9
77.2
1.0
11.0
10
170
8.8
11.2
n.a.
1.1
10.2
10
220
8.6
post application. Each subplot was 768 cm long and
612 cm (six rows) wide and the total number of
subplots in the experiment was 24. Broccoli is transplanted in double rows (30 cm apart) on each bed with
plants spaced approximately 20 cm apart within each
row.
Soil quality sampling was conducted on 11 and
25 October 1995, just prior to the start of budding,
with at least one irrigation event occurring within
this time interval. Top soil samples (0±7.6 cm depth)
were taken from the center row of each treatment
plot. These samples were analyzed with a ®eld soil
quality kit (Sarrantonio et al., 1996; Liebig et al.,
1996), established by Dr. J.W. Doran (USDA±ARS,
Lincoln, NE), for gravimetric water content, bulk
density, electrical conductivity and soil pH of 1 : 1
soil±water mixture using individual calibrated Hanna
pocket meters and nitrate-N estimated from ®ltered
extract of 1 : 1 soil±water mixture using AquaChek
test strips (Whatman). Soil EC and nitrate-N values
were adjusted for deviation from a 1 : 1 soil±water
mixture.
On-site water in®ltration rate was measured
within PVC in®ltration rings which were inserted
to a 7.6 cm soil depth. Soil respiration (pre-irrigation
and post-irrigation) was measured from the headspace of covered in®ltration rings for 30 min using
0.1% CO2 gas sampling tubes (National Draeger).
Post-irrigation samples of surface soil (0±7.6 cm)
from within the irrigation rings were analyzed
for soil bulk density and water holding capacity
(WHC). Further details of the ®eld soil quality
procedures used are given by Sarrantonio et al.
(1996). Post-irrigation samples could not be re-
219
trieved for the ®rst sample date due to an unexpected
pesticide application. Respiration and in®ltration
measurements were made on Control, Fertilizer, 22,
and 44 Mg haÿ1 plots only. Additional composite
cores (0±20 cm depth, 10 cores per sample) were
collected from all plots on 25 October 1995 and
analyzed for gravimetric water content, NO3-N, EC,
and pH.
Crop harvesting was performed sequentially on 10,
14, and 17 November 1995. Only market grade broccoli was cut from the inner 3.1 m length of a single
bed. The market for bunching requires a tight ¯oret of
no more than about 10 cm in diameter, cut with a stalk
of approximately 15 cm length. All harvested heads
for each plot were counted and weighed. Petiole and
leaf samples were collected from 10 plants per plot at
®rst harvest on 10 November. Plant tissue analysis was
performed by the University of California (Department of Agriculture and Natural Resources Laboratory, Davis). After oven drying and grinding, petiole
samples were extracted and analyzed for NO3-N (by
colorimetry) and K (by inductively coupled plasma,
ICP), and leaf samples for total N (dry combustion by
an elemental analyzer), P, K, Ca, Mg, Zn and Fe (by
ICP).
2.2.1. Statistical analysis
Analysis of variance using a complete randomized block design was performed on data obtained
with the soil quality kit on the ®rst sampling date
(11 October) and for in®ltration, WHC, BD and
soil respiration of the second sampling date (24
October). Split-plot ANOVA was performed on soil
pre-in®ltration data for both depths on 24 October
where the variability due to subplots (fertilizer by
block and fertilizer by compost by block interactions)
was used as the error term to test fertilizer effects. The
effect of compost was evaluated separately by an
F-test using the compost by block interaction as the
error term. All plant data was similarly analyzed based
on a split-plot randomized complete block design. In
all cases, Bonferonni multi-comparison of means was
used at the level of P < 0.05. Correlation coef®cients
were computed by standard analytical procedures
at the level of P < 0.05. All the employed procedures
are reported in the statistical analysis system (SAS
Institute, 1985).
220
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 2
Changes of top soil properties caused by fertilizer and compost application on 11 October 1995 (means for 0±7.6 cm depth, n 3)
Soil quality indicator
Control
Compost
Fertilizer
ÿ1
Soil bulk density (g/cm3)
Electric conductivity (dS/m)
Soil pH
Soil NO3-N (kg NO3-N/ha)
Soil NO2-N (kg NO2-N/ha)
Respiration (kg CO2-C/ha/d) 60%
water-filled pore space, 258C
First inch (min)
Second inch (min)
ÿ1
22 Kg ha
44 Kg ha
Pre-irrigation
1.09
0.52
8.1a
2.4b
0
[63.2ab]
1.09
0.50
8.1a
9.9b
0.04
17.1b
1.16
0.57
8.3a
2.7b
0
31.5b
1.04
2.06
6.7b
186.0a
1.65
[84.9a]
Infiltration time
0.07
0.57
0.07
0.40
0.09
0.82
0.07
0.57
Data in square brackets ([ ]): n 2.
Same letters or absence of letters within rows indicates no significant difference between means.
Means within rows followed by different letters are significantly different at P < 0.05.
3. Results and discussion
3.1. General soil properties
The control treatment of this experiment had an
acceptable soil bulk density and water holding capacity, but very rapid water in®ltration rate, low nitrate
levels, high pH and background electrical conductivity
in the top 7.6 cm (Tables 2 and 3). High pH > 8 are
usually due to the presence of Ca and Na salts (Smith
and Doran, 1996) while bicarbonate is a signi®cant
counter ion for these basic cations in alkaline soils of
low nitrate and high EC values (Patriquin et al., 1993).
High soil pH can restrict nitri®cation, result in signi®cant loss of N through ammonia volatilization and
lead to nitrite accumulation (Smith and Doran, 1996).
Soil samples to a 0±20 cm depth had higher nitrate
levels and pH < 8 (Table 4) indicating better conditions in the rooting zone for plant growth. Effects of
fertilizer or compost application were detected in all
measured soil properties of the top soil except for soil
bulk density and water holding capacity.
3.2. Fertilizer effects on soil quality
Fertilizer application caused changes of soil chemical properties, water content and respiration.
Nitrate-N and EC were increased and pH was reduced
in the top 7.6 cm at both sampling times (Tables 2 and
3). Nitrate levels were extremely high, 80 times higher
than that of the control, and nitrite accumulation was
detected at the ®rst sampling date 3 weeks after
fertilizer application (Table 2). The high nitrate levels
caused a rise in EC by 1.5 units above background
levels and resulted in a signi®cant correlation between
these two variables (Table 4). Soil acidi®cation was
produced by microbial nitri®cation during formation
of nitrate from the ammoniacal fertilizer, while the
decrease in pH by 1.4 units indicated a low soil
buffering capacity (Patriquin et al., 1993; Smith and
Doran, 1996; Table 2). Two weeks later and after
irrigation, however, nitrate and associated EC levels
dropped considerably in the top 7.6 cm of the fertilizer
treatment and soil pH increased by 1.1 units (Table 3)
although acidi®cation effects were still pronounced
(Fig. 1). These rapid chemical changes are attributed
to nitrate leaching from the soil surface after irrigation
which may explain the higher nitrate-N concentration
in all fertilizer-containing plots within the 0±20 cm
depth (Fig. 1). The absence of signi®cant correlations
between NO3-N and pH at this depth (Table 4) suggests that nitri®cation was more pronounced in the
surface soil and was followed by nitrate leaching to
greater depths.
As illustrated in Fig. 2, estimated nitrate-N levels of
fertilizer-containing plots were on average two times
higher than those needed by crops such as corn1 during
1
20±25 mg N kgÿ1 in the top 30 cm of soil or 53 kg N haÿ1 in
the top 20 cm, kg haÿ1 21 mg gÿ1 1.25 g cmÿ3 20 cm/10.
221
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 3
Comparison of mean soil properties of inorganic fertilizer and organic compost treatments on 24 October 1995 (n 3 for 0±20 cm depth and
post-irrigation data, n 4 for remainder)
Sample depth
Soil quality indicator
No fertilizer
0 Mg haÿ1
(control)
0±20 cm
0±7.6 cm
Fertilizer added
22 Mg haÿ1
44 Mg haÿ1
0 Mg haÿ1
22 Mg haÿ1
44 Mg haÿ1
14.7b
0.69b
7.7
40.9ab
1.19
0.63a
8.4a
27.9
15.0b
0.87ab
7.8
55.5a
1.08
0.52ab
8.3ab
11.8
Soil water content (g/g, %)
Electric conductivity (dS/m)
Soil pH
Soil NO3-N (mg/g)
Soil bulk density (g/cm3)
EC1:1 (dS/m)
Soil pH
Soil NO3-N (kg NO3-N/ha)
Pre-irrigation
17.3a
17.6a
0.55b
0.74ab
7.9
7.7
11.4c
19.5bc
1.15
1.13
0.43b
0.51ab
a
8.5
8.4a
4.3
6.7
17.0a
1.18a
7.8
12.3c
1.12
0.45ab
8.6a
3.1
13.7b
0.60b
7.5
39.6ab
1.15
0.45ab
7.8b
20.7
First inch (min)
Second inch (min)
Infiltration time
0.06b
0.06b
0.39ab
0.34b
0.12a
0.88a
0.06b
0.35b
Post-irrigation
0.30
0.29
1.18
1.15
8.8b
14.4ab
0.30
1.14
14.0ab
Water holding capacity (g/g)
Soil bulk density (g/cm3)
Respiration (kg CO2-C/ha/d) 60%
water-filled pore space, 258C
0.28
1.19
18.1a
±
±
±
±
±
±
±
±
±
±
Means within rows followed by different letters are significantly different at P < 0.05. Same letters or absence of letters within rows indicates
no significant difference between means.
the early growing season when crop demand is greatest (Bundy and Meisinger, 1994), although broccoli
needs differ, at least seasonally, as N uptake peaks in
the ®nal third of the seasons between the start of
budding and the formation of heads (Magni®co et al.,
1979; Stivers et al., 1993). Given these high levels of
available N, the very rapid in®ltration rates and low
buffering capacity of this soil, great potential of
leaching and ground water contamination is possible
with this management practice. Even greater rates of
Table 4
Correlation coefficients of soil NO3-N* with EC, pH and respiration
Sampling time
Sampling depth
11 October 1995
0±7.6 cm
24 October 1995
0±7.6 cm
24 October 1995
0±20 cm
*
DATA subset
All (n 12)
Control fertilizer (n 6)
Compost (n 6)
All (n 24)
Control fertilizer (n 8)
Compost (n 8)
Compost fertilizer (n 8)
All (n 18)
Control fertilizer (n 6)
Compost (n 6)
Compost fertilizer (n 6)
ppm for 0±20 cm depth and kg haÿ1 for 0±7.6 cm depth
n: 10, b n: 4, c: n 12, d: n 6
Underlined values coefficients indicate significant correlation at P < 0.05.
a
Correlation coefficient of NO3-N with
EC1:1
pH
CO2-C
0:99
0:99
0.09
0:85
0:80
0:91
0:93
0.22
0.58
0.50
0:83
ÿ0:66
ÿ0.58
ÿ0:90
ÿ0:62
ÿ0:91
ÿ0:87
ÿ0.53
ÿ0.37
ÿ0.74
ÿ0.49
ÿ0.36
0:75a
0.76b
ÿ0.50
0:67c
0.79d
0.00d
±
±
±
±
±
222
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
likely result of greater plant growth (vegetative material) and greater extraction of soil water. Such a
relationship is suggested by a signi®cant negative
correlation between water content and nitrate-N in
plots that did not contain any compost (r ÿ 0.92,
n 6).
3.3. Compost effects on soil quality
Fig. 1. Effects of fertilizer application on selected soil chemical
properties at different compost application rates and sampling
depths on 25 October 1995. Solid lines represent treatments
without fertilizer and broken lines treatments with addition of
fertilizer. Different letters indicate significant difference between
two means (P < 0.05) within each compost application rate.
Absence of letters indicates no significant difference between the
two means.
fertilization (175 to 350 kg N haÿ1) than those applied
in this experiment are reported to be typically used by
growers for lettuce, celery, broccoli and cauli¯ower in
the western US and groundwater contamination by
levels of nitrate-N above the public health drinkingwater standard is a growing problem in such agricultural areas (Stivers et al., 1993).
The higher soil respiration in the fertilizer-containing plots (Table 3) was associated with greater nitri®cation rates (Table 4). Gravimetric water content
was signi®cantly lower in all fertilizer plots, with or
without compost, at 0±20 cm depth (Table 3) as a
Compost application decreased water in®ltration
rate, increased EC at 0±20 cm depth and increased
soil buffering capacity as indicated by the unchanged
soil pH even after fertilizer application (Table 3,
Fig. 3). Increased soil buffering capacity is one of
the bene®ts of building up soil organic matter through
compost application. Ulrich (1987) found no acidi®cation effects and no relationship of pH to NO3, but
higher cation exchange capacity and base saturation,
in soil amended with compost as compared to soil
without compost. Our data show signi®cant correlations between pH and NO3-N in compost-treated plots
(Table 4), but in such narrow ranges that acidi®cation
effects were undetectable. Despite the initially high
nitrate content of compost (Table 1), nitrate levels of
compost soil were low and similar to the control
indicating net loss through leaching, root uptake
and possibly immobilization and denitri®cation processes. The addition of fertilizer to compost in combined treatments did not bring about any changes in
soil properties other than an expected increase in
nitrate-N (Table 3).
The positive relationship of soil EC to compost
application for the 0±20 cm depth (Fig. 3) shows an
excessive content of salts, other than nitrates, in this
compost. Soil EC values doubled, relative to the
control, in plots amended with 44 Mg haÿ1 compost
to levels characterized as slightly saline that may
adversely affect the growth of salt-sensitive crops
(Smith and Doran, 1996). The rise in EC warns against
continued application of high EC composts that may
lead to soil salinization and result in N depletion,
reduced nutrient cycling and impaired crop growth.
Leaching of soluble salts contained in compost
explains the low soil EC of the top 7.6 cm (Fig. 3)
and illustrates the need to sample at greater depth in
order to detect such adverse management effects
especially in soils of low buffering and cation
exchange capacity.
223
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Fig. 2. The relationship between soil nitrate-N (top 20 cm on 25 October), leaf N and head weight of broccoli harvested in November 1995.
Table 5
Broccoli yield and nutrients at harvest in response to compost and nitrogen fertilizer applications
Soil quality indicator
No fertilizer
ÿ1
Crop yield
No. of heads (heads plotÿ1)
Head weight (g headÿ1)
Head weight (Mg haÿ1)
Petiole nutrients
NO3-N (ppm)
K (ppm)
Leaf nutrients
N (%)
P (%)
K (%)
Ca (%)
Mg (%)
Zn (ppm)
Fe (ppm)
Fertilizer added
ÿ1
ÿ1
0 Mg ha
(control)
22 Mg ha
44 Mg ha
17.0
222
13.9
17.3
236
14.6
16.3
236
13.6
872
2150
5.27
0.62
2.54
2.10
0.68
28.3
70.0
985
2075
5.34
0.64
2.53
2.32
0.67
29.7
84.3
970
2175
5.33
0.67
2.77
2.19
0.60
30.3
83.0
Differences between means (n 4) within each row were not significant at P < 0.05.
0 Mg haÿ1
14.5
240
12.6
960
2200
5.52
0.66
2.84
1.93
0.61
32.7
87.3
22 Mg haÿ1
17.5
240
15.2
915
2150
5.50
0.66
2.81
2.22
0.66
30.7
84.3
44 Mg haÿ1
14.8
245
12.9
1002
2275
5.55
0.63
2.77
2.16
0.62
31.3
85.6
224
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Fig. 3. Effects of compost application on selected soil chemical
properties at two different sampling depths with and without
addition of fertilizer on 25 October 1995. Different letters indicate
significant difference between means of depths (P < 0.05) within
each compost application rate. Absence of letters indicates no
significant difference between the two means.
3.4. Crop growth and its relation to soil quality
Differences between treatments in crop yield and
number of heads were insigni®cant and relatively
small, the biggest difference being observed between
22 Mg haÿ1 compost and fertilizer plots (the former
being 20% higher than the latter, Table 5). Even
smaller differences were found in head weight, leaf
nutrients (N, P, K, Ca, Mg, Zn, Fe) and petiole
nutrients (NO3, K) and indicated that there was suf®cient residual fertility to grow a crop in the absence of
any amendments.
Although the values of these plant variables ¯uctuated within narrow ranges, a few signi®cant correla-
tions emerged. The number of broccoli heads was a
good predictor of crop yield (r 0.97, n 6) with the
chemically fertilized plants producing the smaller
number of heads which may be seen as a negative
plant response, direct or indirect, to excessive soil N
levels. Although, a similarly low number of heads in
44 Mg haÿ1 compost plots may have been caused by
high soil EC (Fig. 3), the greatest number of heads
produced by 22 Mg haÿ1 plants, without or with fertilizer added (Table 5), suggests that compost application at reasonable rates was associated with highest
yields. However, crop yield or number of heads was
not signi®cantly correlated to any measured soil attributes so that compost nutrients, other than nitrates,
might be related to the higher yield of 22 Mg haÿ1
plots. Moreover, plant elemental analysis did not show
any major differences between compost and no-compost plants, or between plants of 22 and 44 Mg haÿ1
compost (Table 5).
Broccoli head weight and leaf N content were
signi®cantly correlated to soil nitrate-N (Fig. 2), thus,
illustrating the relevance of this indicator in soil
quality assessment from plant productivity and health
perspectives. Leaf N content was directly proportional
to soil nitrate-N in the top 20 cm at the second
sampling time (r 0.97, n 6, Fig. 2) or in the top
7.6 cm at the ®rst sampling time (r 0.96, n 4).
Patriquin et al. (1993) also obtained a signi®cant
correlation between leaf and soil nitrates in organically fertilized lettuce. The lack of relationship of crop
yield with any of these variables appears to have
resulted from adequate-to-excessive levels of soil
nitrates beyond crop needs in most treatments and
from other compost-related factors that were unrelated
to N content.
Acknowledgements
This project was supported by the Fulbright Foundation in collaboration with the University of California±Santa Cruz/Center for Agroecology and
Sustainable Food Systems (USA) and the Goulandris
Natural History Museum/Gaia Environmental
Research and Education Center±Ki®ssia (Greece).
Thanks are extended to Dr. John Doran for supplying
the USDA-ARS soil quality test kit and for advice on
soil quality assessment methods.
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
References
Bundy, L.G., Meisinger, J.J., 1994. Nitrogen availability indices.
In: Weaver, R.W. et al. (Eds.), Methods of Soil Analysis, Part 2.
SSSA Book Series 5. Soil Sci. Soc. Am., Madison, WI, pp.
951±984.
Doran, J.W., Sarrantonio, M. Liebig, M.A., 1996. Soil health and
sustainability. In: Sparks, D.L. (Ed.), Advances in Agronomy,
vol. 56. Academic Press, San Diego, CA, pp. 1±54.
Liebig, M.A., Doran, J.W., Gardner, J.C., 1996. Evaluation of a
field test kit for measuring selected soil quality indicators.
Agronomy J. 88, 683±686.
Magnifico, V., Lattanzio, V., Sarli, G., 1979. Growth and nutrient
removal by broccoli. J. Am. Soc. Hort. Sci. 104, 201±203.
Patriquin, D.G., Blaikie, H., Patriquin, M.J., Yang, C., 1993. Onfarm measurement of pH, electrical conductivity and nitrate in
soil extracts for monitoring coupling and decoupling of nutrient
cycles. Biological Agric. Hortic. 9, 231±272.
Sarrantonio, M., Doran, J.W., Liebig, M.A. Halvorson, J.J., 1996.
225
On-farm assessment of soil quality and health. In: Doran, J.W.,
Jones, A.J (Eds.), Methods for Assessing Soil Quality. Soil Sci.
Soc. Am. Spec. Publication #49 SSSA, Madison, WI, pp. 83±
105.
SAS Institute, 1985. SAS User's Guide: Statistics, Version 5 edn.
Cary, NC, USA.
Smith, J., Doran, J.W., 1996. Measurement and use of pH and
electrical conductivity for soil quality analysis. In: Doran, J.W.,
Jones, A.J (Eds.), Methods for Assessing Soil Quality. Soil Sci.
Soc. Am. Spec. Publication #49. SSSA, Madison, WI, pp. 169±
185.
Stivers, L.J., Jackson, L.E., Pettygrove, G.S., 1993. Use of nitrogen
by lettuce, celery, broccoli, and cauliflower: a literature review.
California Department of Food and Agriculture, Fertilizer
Research and Education Program, Sacramento, CA, 79 pp.
Ulrich, B., 1987. Stability, elasticity and resilience of terrestrial
ecosystems with respect to matter balance. In: Schulze, E.D.,
Zwolfer, H (Eds.), Potentials and Limitations of Ecosystem
Analysis. Springer, New York, pp. 11±49.
Field assessment of soil quality as affected by compost and fertilizer
application in a broccoli ®eld (San Benito County, California)
S. Stamatiadisa,*, M. Wernerb, M. Buchananb
b
a
Goulandris Natural History Museum, Ecology-Biotechnology Laboratory, 13 Levidou Street, Ki®ssia, 14562, Greece
University of California±Santa Cruz, Center for Agroecology and Sustainable Food Systems, Santa Cruz, CA 95064, USA
Received 6 January 1999; accepted 8 February 1999
Abstract
Selected in-®eld physical, chemical and biological indicators were measured for the rapid assessment of soil quality changes
in a Sorrento silty clay loam as a result of compost and ammonium nitrate application to a broccoli ®eld (San Benito County,
CA). Plots were laid out in a randomized complete block design with four replications of 0, 22 and 44 Mg haÿ1 compost
treatments which were split to include fertilizer (165 kg N haÿ1) and no-fertilizer subplots. Soil samples were taken on 11 and
24 October 1995 during the active growth phase of the crop, and soil quality evaluation was compared to crop nutrient content
and yield which were determined at harvest in November.
Surface application of ammonium nitrate initially stimulated soil nitri®cation and acidi®cation processes in the top 7.6 cm
as evidenced by an 80-fold increase in nitrate-N and accumulation of nitrite, a 1.5-unit increase in electrical conductivity (EC)
and a 1.4-unit decrease in pH. Following irrigation, this pattern was reversed by nitrate leaching and root uptake, although
nitri®cation and acidi®cation effects remained detectable at both sampling depths (0±7.6 and 0±20 cm). Nitri®cation was
positively correlated to soil respiration and negatively correlated to soil water content. The estimated nitrate-N levels of
fertilizer-containing plots in the top 20 cm were two times higher than those reported in the literature as minimal levels for
optimal corn growth and indicated a high risk for groundwater contamination in this irrigated ®eld by taking into account the
rapid water in®ltration and low soil buffering capacity.
The detected short-term bene®cial effects of compost application were the stabilization of pH and the decrease of water
in®ltration rate. Stabilization of pH prevented acidi®cation effects due to fertilizer application at both sampling depths. The
high soil EC of plots receiving 44 Mg haÿ1 of compost at the 0±20 cm depth probably resulted from a high compost salt
content, other than nitrates, and warns against repeated use of high EC composts that may result in N depletion, reduced
nutrient cycling and impaired crop growth.
The relatively small differences among treatments in crop yield, head number and weight, leaf and petiole nutrients
indicated that there was suf®cient residual fertility to grow a crop in the absence of any amendments. However, the relevance
of selected soil quality indicators to plant productivity and health was evidenced by the strong correlation of soil nitrate-N
with leaf-N and head weight, despite the adequate-to-excessive amount of soil nitrate-N in most treatments. # 1999 Elsevier
Science B.V. All rights reserved.
Keywords: Nitri®cation; Acidi®cation; Crop yield
*Corresponding author. Tel.: +30-1-8087345; fax: +30-1-8080674.
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 1 3 - X
218
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
1. Introduction
The use of synthetic ammonium fertilizers is known
to cause a rapid shift of soil chemical properties which
are initiated by microbial nitri®cation. This shift may
result in soil acidi®cation. The magnitude of the effect
of these processes has been directly measured in soil
extracts by a rise of nitrate and electrical conductivity
(EC) and a decline of pH (Patriquin et al., 1993; Smith
and Doran, 1996). However, the slower nitri®cation of
N and the high cation exchange capacity of organic
amendments stabilize soil chemical properties by
increasing soil buffering capacity and slowly releasing
essential nutrients for more sustainable plant growth.
In order to fully assess the effects of such management practices in the soil environment, we need to
integrate chemical with physical and biological attributes that can serve as appropriate indicators of soil
functions. In this study, a basic set of soil quality
indicators (bulk density, in®ltration rate, water content, water holding capacity, pH, EC, NO3-N, soil
respiration) were measured in a broccoli ®eld subjected to compost and inorganic fertilizer inputs.
These indicators were selected in order to demonstrate
the utility of in-®eld measurements for the quick
detection of soil quality changes under organic and
chemical management practices. They comply with
the proposed selection criteria of soil quality indicators in that they are sensitive to variations in management, they de®ne major ecological processes in soil
and they re¯ect conditions as they actually exist in the
®eld under a given management system (Doran et al.,
1996). The techniques employed were relatively inexpensive, simple, and could be conducted on site by
many users such as farmers, researchers, consultants,
extension agents and resource conservationists (Liebig et al., 1996; Sarrantonio et al., 1996). Spacial and
temporal changes of soil attributes were evaluated and
compared to plant nutrient content and yield in order
to assess effects on both environmental quality and
plant productivity.
2. Materials and methods
2.1. Site description
The experimental site was a commercial broccoli
®eld located near Hollister, San Benito County. The
soil type is Sorrento silty clay loam, described as a
Mollisol. The climate is Mediterranean, with summer
drought, and cool, rainy winters. The site had been in a
lettuce/broccoli rotation (lettuce in the summer, broccoli in the fall) for at least the previous 3 years, using
conventional soil fertility and pest management practices. No organic matter inputs were made other than
crop residues. Water was provided during the cropping
season through sprinkler irrigation. The ®eld was
laser-leveled every 6 or 7 years.
At the time of the experiment, the `Sundance'
tillage system was in use. Permanent beds (45 cm
wide, 102 cm between two consecutive bed centers)
are maintained by a front and rear-mounted shank,
shovel and disk system, which can incorporate
prior residue while rebuilding the bed in one pass.
The pre-existing crop is ®rst mowed, the shanks rip the
center of the bed to 25±30 cm depth, followed by discs
which incorporate residues while moving soil back
into a rough triangular bed. Furrows remain undisturbed, thus wheel-traf®c is controlled and permanent.
The beds are cultivated by dragging a 46 cm shank
through the middle of the bed. Two passes with a
Lilliston cultivator were made to further incorporate
prior lettuce residues and compost prior to shaping the
raised beds and transplanting. Transplanting was on 10
August and broccoli was harvested on 10, 14, and 17
November 1995.
2.2. Experimental design and sampling
A longitudinal section of the broccoli ®eld, six rows
or 612 cm wide, was divided into four blocks and three
®elds of equal area in each block were randomly
assigned to receive three rates of compost (0, 22
and 44 Mg haÿ1) in a complete randomized block
design. Green wastes (30%), cow manure
(20%), spoiled hay (15%), clay soil (5%) and
various crop processing residues were reported to be
the initial sources of compost. The presence of soil
was indicated by the high ash content of compost
(Table 1). Each ®eld was partitioned into two subplots
that received a random assignment of the two levels of
fertilizer, 0 or 165 kg (NH4NO3)-N haÿ1 sprinkled
uniformly on the tops of beds by hand. Thus, the
resulting split-plot design was composed of four
blocks, three levels of compost within each block
and two levels of fertilizer within each level of com-
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 1
Chemical characteristics of compost applied to experimental field
during 1995
C (%)
Ash (%)
N (%)
C/N
NH4-N (ppm)
NO3-N (ppm)
pH
First application
(before summer lettuce)
Second application
(before fall broccoli)
10.9
77.2
1.0
11.0
10
170
8.8
11.2
n.a.
1.1
10.2
10
220
8.6
post application. Each subplot was 768 cm long and
612 cm (six rows) wide and the total number of
subplots in the experiment was 24. Broccoli is transplanted in double rows (30 cm apart) on each bed with
plants spaced approximately 20 cm apart within each
row.
Soil quality sampling was conducted on 11 and
25 October 1995, just prior to the start of budding,
with at least one irrigation event occurring within
this time interval. Top soil samples (0±7.6 cm depth)
were taken from the center row of each treatment
plot. These samples were analyzed with a ®eld soil
quality kit (Sarrantonio et al., 1996; Liebig et al.,
1996), established by Dr. J.W. Doran (USDA±ARS,
Lincoln, NE), for gravimetric water content, bulk
density, electrical conductivity and soil pH of 1 : 1
soil±water mixture using individual calibrated Hanna
pocket meters and nitrate-N estimated from ®ltered
extract of 1 : 1 soil±water mixture using AquaChek
test strips (Whatman). Soil EC and nitrate-N values
were adjusted for deviation from a 1 : 1 soil±water
mixture.
On-site water in®ltration rate was measured
within PVC in®ltration rings which were inserted
to a 7.6 cm soil depth. Soil respiration (pre-irrigation
and post-irrigation) was measured from the headspace of covered in®ltration rings for 30 min using
0.1% CO2 gas sampling tubes (National Draeger).
Post-irrigation samples of surface soil (0±7.6 cm)
from within the irrigation rings were analyzed
for soil bulk density and water holding capacity
(WHC). Further details of the ®eld soil quality
procedures used are given by Sarrantonio et al.
(1996). Post-irrigation samples could not be re-
219
trieved for the ®rst sample date due to an unexpected
pesticide application. Respiration and in®ltration
measurements were made on Control, Fertilizer, 22,
and 44 Mg haÿ1 plots only. Additional composite
cores (0±20 cm depth, 10 cores per sample) were
collected from all plots on 25 October 1995 and
analyzed for gravimetric water content, NO3-N, EC,
and pH.
Crop harvesting was performed sequentially on 10,
14, and 17 November 1995. Only market grade broccoli was cut from the inner 3.1 m length of a single
bed. The market for bunching requires a tight ¯oret of
no more than about 10 cm in diameter, cut with a stalk
of approximately 15 cm length. All harvested heads
for each plot were counted and weighed. Petiole and
leaf samples were collected from 10 plants per plot at
®rst harvest on 10 November. Plant tissue analysis was
performed by the University of California (Department of Agriculture and Natural Resources Laboratory, Davis). After oven drying and grinding, petiole
samples were extracted and analyzed for NO3-N (by
colorimetry) and K (by inductively coupled plasma,
ICP), and leaf samples for total N (dry combustion by
an elemental analyzer), P, K, Ca, Mg, Zn and Fe (by
ICP).
2.2.1. Statistical analysis
Analysis of variance using a complete randomized block design was performed on data obtained
with the soil quality kit on the ®rst sampling date
(11 October) and for in®ltration, WHC, BD and
soil respiration of the second sampling date (24
October). Split-plot ANOVA was performed on soil
pre-in®ltration data for both depths on 24 October
where the variability due to subplots (fertilizer by
block and fertilizer by compost by block interactions)
was used as the error term to test fertilizer effects. The
effect of compost was evaluated separately by an
F-test using the compost by block interaction as the
error term. All plant data was similarly analyzed based
on a split-plot randomized complete block design. In
all cases, Bonferonni multi-comparison of means was
used at the level of P < 0.05. Correlation coef®cients
were computed by standard analytical procedures
at the level of P < 0.05. All the employed procedures
are reported in the statistical analysis system (SAS
Institute, 1985).
220
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 2
Changes of top soil properties caused by fertilizer and compost application on 11 October 1995 (means for 0±7.6 cm depth, n 3)
Soil quality indicator
Control
Compost
Fertilizer
ÿ1
Soil bulk density (g/cm3)
Electric conductivity (dS/m)
Soil pH
Soil NO3-N (kg NO3-N/ha)
Soil NO2-N (kg NO2-N/ha)
Respiration (kg CO2-C/ha/d) 60%
water-filled pore space, 258C
First inch (min)
Second inch (min)
ÿ1
22 Kg ha
44 Kg ha
Pre-irrigation
1.09
0.52
8.1a
2.4b
0
[63.2ab]
1.09
0.50
8.1a
9.9b
0.04
17.1b
1.16
0.57
8.3a
2.7b
0
31.5b
1.04
2.06
6.7b
186.0a
1.65
[84.9a]
Infiltration time
0.07
0.57
0.07
0.40
0.09
0.82
0.07
0.57
Data in square brackets ([ ]): n 2.
Same letters or absence of letters within rows indicates no significant difference between means.
Means within rows followed by different letters are significantly different at P < 0.05.
3. Results and discussion
3.1. General soil properties
The control treatment of this experiment had an
acceptable soil bulk density and water holding capacity, but very rapid water in®ltration rate, low nitrate
levels, high pH and background electrical conductivity
in the top 7.6 cm (Tables 2 and 3). High pH > 8 are
usually due to the presence of Ca and Na salts (Smith
and Doran, 1996) while bicarbonate is a signi®cant
counter ion for these basic cations in alkaline soils of
low nitrate and high EC values (Patriquin et al., 1993).
High soil pH can restrict nitri®cation, result in signi®cant loss of N through ammonia volatilization and
lead to nitrite accumulation (Smith and Doran, 1996).
Soil samples to a 0±20 cm depth had higher nitrate
levels and pH < 8 (Table 4) indicating better conditions in the rooting zone for plant growth. Effects of
fertilizer or compost application were detected in all
measured soil properties of the top soil except for soil
bulk density and water holding capacity.
3.2. Fertilizer effects on soil quality
Fertilizer application caused changes of soil chemical properties, water content and respiration.
Nitrate-N and EC were increased and pH was reduced
in the top 7.6 cm at both sampling times (Tables 2 and
3). Nitrate levels were extremely high, 80 times higher
than that of the control, and nitrite accumulation was
detected at the ®rst sampling date 3 weeks after
fertilizer application (Table 2). The high nitrate levels
caused a rise in EC by 1.5 units above background
levels and resulted in a signi®cant correlation between
these two variables (Table 4). Soil acidi®cation was
produced by microbial nitri®cation during formation
of nitrate from the ammoniacal fertilizer, while the
decrease in pH by 1.4 units indicated a low soil
buffering capacity (Patriquin et al., 1993; Smith and
Doran, 1996; Table 2). Two weeks later and after
irrigation, however, nitrate and associated EC levels
dropped considerably in the top 7.6 cm of the fertilizer
treatment and soil pH increased by 1.1 units (Table 3)
although acidi®cation effects were still pronounced
(Fig. 1). These rapid chemical changes are attributed
to nitrate leaching from the soil surface after irrigation
which may explain the higher nitrate-N concentration
in all fertilizer-containing plots within the 0±20 cm
depth (Fig. 1). The absence of signi®cant correlations
between NO3-N and pH at this depth (Table 4) suggests that nitri®cation was more pronounced in the
surface soil and was followed by nitrate leaching to
greater depths.
As illustrated in Fig. 2, estimated nitrate-N levels of
fertilizer-containing plots were on average two times
higher than those needed by crops such as corn1 during
1
20±25 mg N kgÿ1 in the top 30 cm of soil or 53 kg N haÿ1 in
the top 20 cm, kg haÿ1 21 mg gÿ1 1.25 g cmÿ3 20 cm/10.
221
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Table 3
Comparison of mean soil properties of inorganic fertilizer and organic compost treatments on 24 October 1995 (n 3 for 0±20 cm depth and
post-irrigation data, n 4 for remainder)
Sample depth
Soil quality indicator
No fertilizer
0 Mg haÿ1
(control)
0±20 cm
0±7.6 cm
Fertilizer added
22 Mg haÿ1
44 Mg haÿ1
0 Mg haÿ1
22 Mg haÿ1
44 Mg haÿ1
14.7b
0.69b
7.7
40.9ab
1.19
0.63a
8.4a
27.9
15.0b
0.87ab
7.8
55.5a
1.08
0.52ab
8.3ab
11.8
Soil water content (g/g, %)
Electric conductivity (dS/m)
Soil pH
Soil NO3-N (mg/g)
Soil bulk density (g/cm3)
EC1:1 (dS/m)
Soil pH
Soil NO3-N (kg NO3-N/ha)
Pre-irrigation
17.3a
17.6a
0.55b
0.74ab
7.9
7.7
11.4c
19.5bc
1.15
1.13
0.43b
0.51ab
a
8.5
8.4a
4.3
6.7
17.0a
1.18a
7.8
12.3c
1.12
0.45ab
8.6a
3.1
13.7b
0.60b
7.5
39.6ab
1.15
0.45ab
7.8b
20.7
First inch (min)
Second inch (min)
Infiltration time
0.06b
0.06b
0.39ab
0.34b
0.12a
0.88a
0.06b
0.35b
Post-irrigation
0.30
0.29
1.18
1.15
8.8b
14.4ab
0.30
1.14
14.0ab
Water holding capacity (g/g)
Soil bulk density (g/cm3)
Respiration (kg CO2-C/ha/d) 60%
water-filled pore space, 258C
0.28
1.19
18.1a
±
±
±
±
±
±
±
±
±
±
Means within rows followed by different letters are significantly different at P < 0.05. Same letters or absence of letters within rows indicates
no significant difference between means.
the early growing season when crop demand is greatest (Bundy and Meisinger, 1994), although broccoli
needs differ, at least seasonally, as N uptake peaks in
the ®nal third of the seasons between the start of
budding and the formation of heads (Magni®co et al.,
1979; Stivers et al., 1993). Given these high levels of
available N, the very rapid in®ltration rates and low
buffering capacity of this soil, great potential of
leaching and ground water contamination is possible
with this management practice. Even greater rates of
Table 4
Correlation coefficients of soil NO3-N* with EC, pH and respiration
Sampling time
Sampling depth
11 October 1995
0±7.6 cm
24 October 1995
0±7.6 cm
24 October 1995
0±20 cm
*
DATA subset
All (n 12)
Control fertilizer (n 6)
Compost (n 6)
All (n 24)
Control fertilizer (n 8)
Compost (n 8)
Compost fertilizer (n 8)
All (n 18)
Control fertilizer (n 6)
Compost (n 6)
Compost fertilizer (n 6)
ppm for 0±20 cm depth and kg haÿ1 for 0±7.6 cm depth
n: 10, b n: 4, c: n 12, d: n 6
Underlined values coefficients indicate significant correlation at P < 0.05.
a
Correlation coefficient of NO3-N with
EC1:1
pH
CO2-C
0:99
0:99
0.09
0:85
0:80
0:91
0:93
0.22
0.58
0.50
0:83
ÿ0:66
ÿ0.58
ÿ0:90
ÿ0:62
ÿ0:91
ÿ0:87
ÿ0.53
ÿ0.37
ÿ0.74
ÿ0.49
ÿ0.36
0:75a
0.76b
ÿ0.50
0:67c
0.79d
0.00d
±
±
±
±
±
222
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
likely result of greater plant growth (vegetative material) and greater extraction of soil water. Such a
relationship is suggested by a signi®cant negative
correlation between water content and nitrate-N in
plots that did not contain any compost (r ÿ 0.92,
n 6).
3.3. Compost effects on soil quality
Fig. 1. Effects of fertilizer application on selected soil chemical
properties at different compost application rates and sampling
depths on 25 October 1995. Solid lines represent treatments
without fertilizer and broken lines treatments with addition of
fertilizer. Different letters indicate significant difference between
two means (P < 0.05) within each compost application rate.
Absence of letters indicates no significant difference between the
two means.
fertilization (175 to 350 kg N haÿ1) than those applied
in this experiment are reported to be typically used by
growers for lettuce, celery, broccoli and cauli¯ower in
the western US and groundwater contamination by
levels of nitrate-N above the public health drinkingwater standard is a growing problem in such agricultural areas (Stivers et al., 1993).
The higher soil respiration in the fertilizer-containing plots (Table 3) was associated with greater nitri®cation rates (Table 4). Gravimetric water content
was signi®cantly lower in all fertilizer plots, with or
without compost, at 0±20 cm depth (Table 3) as a
Compost application decreased water in®ltration
rate, increased EC at 0±20 cm depth and increased
soil buffering capacity as indicated by the unchanged
soil pH even after fertilizer application (Table 3,
Fig. 3). Increased soil buffering capacity is one of
the bene®ts of building up soil organic matter through
compost application. Ulrich (1987) found no acidi®cation effects and no relationship of pH to NO3, but
higher cation exchange capacity and base saturation,
in soil amended with compost as compared to soil
without compost. Our data show signi®cant correlations between pH and NO3-N in compost-treated plots
(Table 4), but in such narrow ranges that acidi®cation
effects were undetectable. Despite the initially high
nitrate content of compost (Table 1), nitrate levels of
compost soil were low and similar to the control
indicating net loss through leaching, root uptake
and possibly immobilization and denitri®cation processes. The addition of fertilizer to compost in combined treatments did not bring about any changes in
soil properties other than an expected increase in
nitrate-N (Table 3).
The positive relationship of soil EC to compost
application for the 0±20 cm depth (Fig. 3) shows an
excessive content of salts, other than nitrates, in this
compost. Soil EC values doubled, relative to the
control, in plots amended with 44 Mg haÿ1 compost
to levels characterized as slightly saline that may
adversely affect the growth of salt-sensitive crops
(Smith and Doran, 1996). The rise in EC warns against
continued application of high EC composts that may
lead to soil salinization and result in N depletion,
reduced nutrient cycling and impaired crop growth.
Leaching of soluble salts contained in compost
explains the low soil EC of the top 7.6 cm (Fig. 3)
and illustrates the need to sample at greater depth in
order to detect such adverse management effects
especially in soils of low buffering and cation
exchange capacity.
223
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Fig. 2. The relationship between soil nitrate-N (top 20 cm on 25 October), leaf N and head weight of broccoli harvested in November 1995.
Table 5
Broccoli yield and nutrients at harvest in response to compost and nitrogen fertilizer applications
Soil quality indicator
No fertilizer
ÿ1
Crop yield
No. of heads (heads plotÿ1)
Head weight (g headÿ1)
Head weight (Mg haÿ1)
Petiole nutrients
NO3-N (ppm)
K (ppm)
Leaf nutrients
N (%)
P (%)
K (%)
Ca (%)
Mg (%)
Zn (ppm)
Fe (ppm)
Fertilizer added
ÿ1
ÿ1
0 Mg ha
(control)
22 Mg ha
44 Mg ha
17.0
222
13.9
17.3
236
14.6
16.3
236
13.6
872
2150
5.27
0.62
2.54
2.10
0.68
28.3
70.0
985
2075
5.34
0.64
2.53
2.32
0.67
29.7
84.3
970
2175
5.33
0.67
2.77
2.19
0.60
30.3
83.0
Differences between means (n 4) within each row were not significant at P < 0.05.
0 Mg haÿ1
14.5
240
12.6
960
2200
5.52
0.66
2.84
1.93
0.61
32.7
87.3
22 Mg haÿ1
17.5
240
15.2
915
2150
5.50
0.66
2.81
2.22
0.66
30.7
84.3
44 Mg haÿ1
14.8
245
12.9
1002
2275
5.55
0.63
2.77
2.16
0.62
31.3
85.6
224
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
Fig. 3. Effects of compost application on selected soil chemical
properties at two different sampling depths with and without
addition of fertilizer on 25 October 1995. Different letters indicate
significant difference between means of depths (P < 0.05) within
each compost application rate. Absence of letters indicates no
significant difference between the two means.
3.4. Crop growth and its relation to soil quality
Differences between treatments in crop yield and
number of heads were insigni®cant and relatively
small, the biggest difference being observed between
22 Mg haÿ1 compost and fertilizer plots (the former
being 20% higher than the latter, Table 5). Even
smaller differences were found in head weight, leaf
nutrients (N, P, K, Ca, Mg, Zn, Fe) and petiole
nutrients (NO3, K) and indicated that there was suf®cient residual fertility to grow a crop in the absence of
any amendments.
Although the values of these plant variables ¯uctuated within narrow ranges, a few signi®cant correla-
tions emerged. The number of broccoli heads was a
good predictor of crop yield (r 0.97, n 6) with the
chemically fertilized plants producing the smaller
number of heads which may be seen as a negative
plant response, direct or indirect, to excessive soil N
levels. Although, a similarly low number of heads in
44 Mg haÿ1 compost plots may have been caused by
high soil EC (Fig. 3), the greatest number of heads
produced by 22 Mg haÿ1 plants, without or with fertilizer added (Table 5), suggests that compost application at reasonable rates was associated with highest
yields. However, crop yield or number of heads was
not signi®cantly correlated to any measured soil attributes so that compost nutrients, other than nitrates,
might be related to the higher yield of 22 Mg haÿ1
plots. Moreover, plant elemental analysis did not show
any major differences between compost and no-compost plants, or between plants of 22 and 44 Mg haÿ1
compost (Table 5).
Broccoli head weight and leaf N content were
signi®cantly correlated to soil nitrate-N (Fig. 2), thus,
illustrating the relevance of this indicator in soil
quality assessment from plant productivity and health
perspectives. Leaf N content was directly proportional
to soil nitrate-N in the top 20 cm at the second
sampling time (r 0.97, n 6, Fig. 2) or in the top
7.6 cm at the ®rst sampling time (r 0.96, n 4).
Patriquin et al. (1993) also obtained a signi®cant
correlation between leaf and soil nitrates in organically fertilized lettuce. The lack of relationship of crop
yield with any of these variables appears to have
resulted from adequate-to-excessive levels of soil
nitrates beyond crop needs in most treatments and
from other compost-related factors that were unrelated
to N content.
Acknowledgements
This project was supported by the Fulbright Foundation in collaboration with the University of California±Santa Cruz/Center for Agroecology and
Sustainable Food Systems (USA) and the Goulandris
Natural History Museum/Gaia Environmental
Research and Education Center±Ki®ssia (Greece).
Thanks are extended to Dr. John Doran for supplying
the USDA-ARS soil quality test kit and for advice on
soil quality assessment methods.
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 217±225
References
Bundy, L.G., Meisinger, J.J., 1994. Nitrogen availability indices.
In: Weaver, R.W. et al. (Eds.), Methods of Soil Analysis, Part 2.
SSSA Book Series 5. Soil Sci. Soc. Am., Madison, WI, pp.
951±984.
Doran, J.W., Sarrantonio, M. Liebig, M.A., 1996. Soil health and
sustainability. In: Sparks, D.L. (Ed.), Advances in Agronomy,
vol. 56. Academic Press, San Diego, CA, pp. 1±54.
Liebig, M.A., Doran, J.W., Gardner, J.C., 1996. Evaluation of a
field test kit for measuring selected soil quality indicators.
Agronomy J. 88, 683±686.
Magnifico, V., Lattanzio, V., Sarli, G., 1979. Growth and nutrient
removal by broccoli. J. Am. Soc. Hort. Sci. 104, 201±203.
Patriquin, D.G., Blaikie, H., Patriquin, M.J., Yang, C., 1993. Onfarm measurement of pH, electrical conductivity and nitrate in
soil extracts for monitoring coupling and decoupling of nutrient
cycles. Biological Agric. Hortic. 9, 231±272.
Sarrantonio, M., Doran, J.W., Liebig, M.A. Halvorson, J.J., 1996.
225
On-farm assessment of soil quality and health. In: Doran, J.W.,
Jones, A.J (Eds.), Methods for Assessing Soil Quality. Soil Sci.
Soc. Am. Spec. Publication #49 SSSA, Madison, WI, pp. 83±
105.
SAS Institute, 1985. SAS User's Guide: Statistics, Version 5 edn.
Cary, NC, USA.
Smith, J., Doran, J.W., 1996. Measurement and use of pH and
electrical conductivity for soil quality analysis. In: Doran, J.W.,
Jones, A.J (Eds.), Methods for Assessing Soil Quality. Soil Sci.
Soc. Am. Spec. Publication #49. SSSA, Madison, WI, pp. 169±
185.
Stivers, L.J., Jackson, L.E., Pettygrove, G.S., 1993. Use of nitrogen
by lettuce, celery, broccoli, and cauliflower: a literature review.
California Department of Food and Agriculture, Fertilizer
Research and Education Program, Sacramento, CA, 79 pp.
Ulrich, B., 1987. Stability, elasticity and resilience of terrestrial
ecosystems with respect to matter balance. In: Schulze, E.D.,
Zwolfer, H (Eds.), Potentials and Limitations of Ecosystem
Analysis. Springer, New York, pp. 11±49.