Corn response to composting and time of

MANURE MANAGEMENT
Corn Response to Composting and Time of Application of Solid Swine Manure
Terrance D. Loecke, Matt Liebman,* Cynthia A. Cambardella, and Tom L. Richard
ABSTRACT

social impacts of doing so have some producers and
scientists searching for alternative forms of management
in which manure is handled as a solid (Honeyman, 1996).
One option involves swine production in deep-bedded
hoop structures. In Iowa, nearly one million head of swine
are finished per year in these hoop structures (Leopold
Cent. for Sustainable Agric., 2001). Swine hoop structures are typically bedded with corn stalks or cereal
straw, which absorb urine and feces throughout the fourto six-month production cycle. During this time, some
in situ composting occurs although the extent of this
unmanaged decomposition varies widely. Swine manure
from hoop structures can be spread on fields immediately after animals are removed from the buildings, or it
can be piled for additional composting (Tiquia et al.,
2000).
Composted manure has a number of potential advantages over fresh manure, including reductions in viable
weed seed content (Wiese et al., 1998; Eghball and Lesoing, 2000), improvements in handling characteristics
(by reducing manure volume and associated transportation costs), and a reduction in particle size leading to

increased uniformity of field application (Rynk, 1992).
Compost-amended soils can increase crop growth beyond levels explainable by nutrient effects (Valdrighi
et al., 1996), provide protection from plant pathogens
(Hoitink and Kuter, 1986), and suppress weed seedling
emergence (Menalled et al., 2002). Phytotoxic substances
contained in fresh solid swine manure, such as high
concentrations of NH4⫹–N, decrease with time of composting (Tiquia and Tam, 1998) and time following soil
application. Disadvantages of composting are potentially large losses of C and N and labor and capital
costs associated with extra manure handling and space
requirements for the compost piles. Losses of N measured during composting of animal manure have ranged
from 20 to 70% (Martins and Dewes, 1992; Rao Bhamidimarri and Pandey, 1996; Eghball et al., 1997; Tiquia
et al., 2002). Garrison et al. (2001) estimated that 41%
of total N contained in fresh swine hoop manure was lost
during two months of intensively managed composting.
Synchrony of plant-available soil nutrients and crop
nutrient demand is essential for optimum crop performance and environmental protection (Magdoff, 1995).
If plant-available N (NO3⫺ and NH4⫹) is not supplied in
synchrony with crop demand, then substantial N losses
can occur before or after periods of crop demand. The
quantity of plant-available N is dynamic and reflects the

balance between N mineralization, N immobilization, and
removal of inorganic or organic N from the soil rooting
zone (e.g., via leaching, volatilization, denitrification,
soil erosion, and plant uptake). Soil physical conditions,

Swine production in hoop structures is a relatively new husbandry
system in which a mixture of manure and bedding accumulates. This
manure/bedding pack can be applied to crop fields directly from a hoop
structure or piled for composting. During 2000 and 2001, field experiments were conducted near Boone, IA, to determine the effects of
form of solid swine manure (fresh or composted) and time of manure
application (fall or spring) on corn (Zea mays L.) nutrient status and
yield. Fresh and composted manure were applied at 340 kg total N
ha⫺1. Urea N fertilizer treatments of 0, 60, 120, and 180 kg N ha⫺1
were used to determine N fertilizer equivalency values for the manure.
In 2000, but not in 2001, fresh manure decreased corn emergence by
9.5% compared with the unamended, nonfertilized control treatment.
No corn yield differences due to the form or the time of manure application were detected in 2000, but all treatments receiving manure
produced more corn grain than the unamended control. In 2001, fall
application of manure increased corn grain yield more than spring
application, and composted manure increased yield more than fresh

manure, with spring-applied fresh manure providing no yield response
beyond the unamended control. Mean N supply efficiency, defined
as the N fertilizer equivalency value as a percentage of the total N
applied, was greatest for fall-applied composted manure (34.7%),
intermediate for fall-applied fresh manure (24.3%) and spring-applied
composted manure (25.0%), and least for spring-applied fresh manure (10.9%).

O

ver one billion metric tons of N are excreted in
swine (Sus scrofa L.) manure in the United States
annually (NRCS, 2000). Swine manure applied to crop
fields can be an important source of plant nutrients and
organic matter, which can improve soil quality (Khaleel
et al., 1981). Nevertheless, current practices for management and utilization of swine manure can potentially
contribute to degradation of water and air quality
(Sharpley et al., 1998; Zebarth et al., 1999). Better management options are needed.
Most swine manure in the USA is handled and stored
as a liquid (NRCS, 2000), but the environmental and
T.D. Loecke, Dep. of Crop and Soil Sci., Michigan State Univ., 539

Plant and Soil Sciences Bldg., East Lansing, MI 48824-1325; M. Liebman, Dep. of Agron., 3405 Agronomy Hall, Iowa State Univ., Ames,
IA 50011-1010; C.A. Cambardella, USDA-ARS, 310 Natl. Soil Tilth
Lab., Ames, IA 50011-3120; and T.L. Richard, Dep. of Agric. and
Biosyst. Eng., 3222 Natl. Swine Res. and Inf. Cent., Iowa State Univ.,
Ames, IA 50011-3080. Partial funding for this work was provided by
the Leopold Center for Sustainable Agriculture (Project 2000-42),
the Iowa Department of Natural Resources (Project 00-G550-01CG),
and Chamness Technology (Project 1221). We thank J. Ohmacht, D.
Sundberg, and R. Vandepol for technical assistance in the field and
laboratory. Received 5 Dec. 2002. *Corresponding author (mliebman@
iastate.edu).
Published in Agron. J. 96:214–223 (2004).
 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

214

LOECKE ET AL.: FORM OF SWINE MANURE AND APPLICATION TIME AFFECT CORN YIELD

including temperature, water status, and aeration, and

the C/N ratio and C constituents (especially lignin quantities) of organic materials are the primary factors affecting mineralization rates (Jenny, 1980; Swift et al., 1979).
In previous investigations, corn yield responses to
composted and fresh manure have been similar when
these amendments were applied at the same time (Reider
et al., 2000; Eghball and Power, 1999; Brinton, 1985;
Ma et al., 1999; Xie and MacKenzie, 1986). However,
N use efficiencies observed in these studies indicate
that plant-available N from manure-derived compost is
typically equal to or less than that from fresh manure.
Timing of amendment application can influence crop
responses but often interacts with weather conditions
(Warman, 1995; Talarczyk et al., 1996; Sanchez et al.,
1997).
Currently, no guidelines are available for when and
in what form (composted or fresh) swine hoop manure
should be field-applied to best utilize it as a nutrient
resource and to minimize potential negative environmental impacts. The objective of this study was to determine first-year corn response to season of application
(fall vs. spring) and form of swine hoop manure (composted or fresh).
MATERIALS AND METHODS
Field Site and Experimental Design

Field plot research was conducted at the Iowa State University Agronomy and Agricultural Engineering Research Farm
near Boone, IA (42⬚1⬘ N, 93⬚45⬘ W), during 2000 and 2001 on
Clarion loam (fine-loamy, mixed, superactive, mesic Typic Hapludolls) and Nicollet loam (fine-loamy, mixed, superactive,
mesic Aquic Hapludolls) soils. Soil samples taken from the
surface 20 cm before fall application of amendments indicated
adequate P and K fertility levels in both years (Table 1).
The field used for the 2000 experiment was cropped with oat
(Avena sativa L.) in 1999; the field used for the 2001 experiment was cropped with soybean [Glycine max (L.) Merr.] in
2000. Neither field had received animal manure for at least
the previous 8 yr. Annual and long-term weather data were
collected from an automated weather station located ⬍1 km
from the field sites (Fig. 1).
The core of the experiment consisted of a factorial treatment design that crossed season of application (fall or spring)
with form of manure (fresh or composted hoop manure). An
additional set of treatments (0, 60, 120, and 180 kg N ha⫺1 urea)
was applied to plots not receiving manure and was used to
estimate N fertilizer equivalency of the manure. Treatments
were arranged in a randomized complete block design with
four replications. Plot size was 3.8 m (five rows with a 0.76-m
row spacing) by 10.7 m in 2000 and 12.2 m in 2001. Manure

treatments were applied by hand in the fall (22 Oct. 1999 and
24 Oct. 2000) and spring (25 Apr. 2000 and 25 Apr. 2001) at
a rate of 340 kg N ha⫺1 based on moisture and total N content
of samples taken 2 wk before application (Table 2). Amendments were incorporated with a disk into the surface 15 cm
within 6 h of application. Application rates were chosen based
on the assumption that one-third of the total applied N (i.e.,
110 kg N ha⫺1) would be available during the first year after
application, as was observed by Eghball and Power (1999).
This expected quantity of available N is approximately equal
to the N harvested in 9.0 Mg of corn grain, the long-term
average yield per hectare from the experiment site.

215

Table 1. Characteristics of the surface 20 cm of soil in experiment
fields before treatment applications.
Soil parameter
cm⫺3

Bulk density, g

Total organic C, Mg ha⫺1
Total organic N, Mg ha⫺1
Nitrate N, kg ha⫺1
Ammonium N, kg ha⫺1
Mehlich-1 P, kg ha⫺1
Mehlich-1 K, kg ha⫺1
pH
Electrical conductivity, S m⫺1

14 Oct. 1999

28 Sept. 2000

1.3
43.5
3.8
13.0
4.0
115
381

6.6
0.0155

1.2
46.7
4.1
19.3
1.8
113
270
6.4
0.0178

All of the fresh and composted hoop manure was produced
on the Iowa State University Rhodes Research Farm in Marshall County, IA, except for the fresh manure applied in the
spring of 2001, which came from a commercial farm in Story
County, IA. Urea N was side-dressed in plots that did not receive manure at corn growth stage V6 (Hanway, 1963) (9 June
2000 and 18 June 2001) and was incorporated within 24 h of
application using an interrow cultivator. Corn (‘Pioneer 35P12’)
was planted at 68 000 seeds ha⫺1 on 4 May 2000 and 74 000 seeds

ha⫺1 on 9 May 2001. Weed control was achieved with a preplantincorporated application of metolachlor [2-chloro-N-(2-ethyl-6methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] at 1.5
kg a.i. ha⫺1, interrow cultivation at plant growth stage V6, and
hand weeding.

Plant, Soil, and Amendment Sampling and Analysis
A 4-L composite sample of each amendment (fresh or composted manure) was collected immediately before materials
were applied to plots, generating one sample per plot and
four replicates per treatment. Samples were stored at ⫺20⬚C
in plastic freezer bags, then thawed, homogenized, separated
for various analyses (total P, K, NH4⫹–N, NO3⫺–N, moisture,
ash content, pH, and electrical conductivity), and then refrozen until individual parameters were analyzed. Amendment
total C and N were determined after acidification with 0.5 M
HCl (1:2 sample/solution ratio), air drying, grinding, and dry
combustion in a Carlo-Erba NA1500 NCS elemental analyzer
(Haake Buchler Instruments, Paterson, NJ) as described by
Cambardella et al. (2003). Total P and K were determined on
dried ground samples by USEPA method 3051 at a commercial
laboratory (Midwest Laboratory, Omaha, NE) following a protocol given by Dancer et al. (1998). Ammonium N and nitrate
N were determined using 2 M KCl extracts (1:80 amendment/
solution ratio) and Lachat flow analysis (Lachat Instruments,

Milwaukee, WI) (Keeney and Nelson, 1982). Amendment
moisture content was determined by drying at 70⬚C for 48 h,
ash content was determined by ignition at 550⬚C, and pH and
electrical conductivity were determined using a 1:5 amendment/water slurry.
To monitor plant and soil N status throughout the growing
season, late-spring soil NO3⫺–N concentration, ear leaf N and
chlorophyll contents, and fall stalk NO3⫺–N concentration were
measured. All plant and soil parameters were measured from
the center three rows of each plot. Soil NO3⫺–N samples, consisting of a composite of ten 2-cm-diam. soil cores from the
surface 30 cm, were collected from each plot on 3 June 2000
and 4 June 2001 and were processed according to procedures
described by Blackmer et al. (1989).
Thirty leaf chlorophyll meter readings were taken in each
plot using a Minolta SPAD-502 chlorophyll meter (Minolta,
Ramsey, NJ) as others have done (Piekielek and Fox, 1992).
Readings were taken 1.5 cm from the leaf edge of the center
(lengthwise) of the topmost fully expanded leaf or the same
location on the ear leaf, when developed.

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AGRONOMY JOURNAL, VOL. 96, JANUARY–FEBRUARY 2004

Fig. 1. (a) Monthly average daily temperature and (b) total precipitation for 2000, 2001, and the 50-yr average at a weather station located
⬍1 km from the field sites.

Ten ear leaves were collected in each plot at growth stage
R1 (Hanway, 1963) for nutrient analysis. Ear leaf samples
were dried at 60⬚C for 4 d, ground to pass a 0.85-mm screen,
and analyzed for total Kjeldahl N. Ear leaf P concentrations
were determined by nitric acid plus peroxide digestion followed by inductively coupled plasma mass spectrometry (Harris Laboratory, Lincoln, NE). Grain was harvested with a
combine from 9.8 and 10.7 m of the center three rows of each
plot in 2000 and 2001, respectively. Reported grain yields are
adjusted to a moisture content of 155 g kg⫺1. Fifteen stalk
samples (20 cm in length) were collected 15 cm above the soil

surface from each plot at grain harvest, dried at 60⬚C for 4 d,
ground to pass a 0.85 mm screen, and analyzed for NO3⫺–N
(Binford et al., 1992).

Statistical Analysis
Analysis of variance (ANOVA) was conducted using the
PROC GLM routine of SAS (SAS Inst., 1999) to test for main
and interaction effects, with blocks, years, and treatments in
the model. Single degree-of-freedom contrasts were used to
test specific hypotheses and main and interaction effects. Stalk

217

LOECKE ET AL.: FORM OF SWINE MANURE AND APPLICATION TIME AFFECT CORN YIELD

Table 2. Composition of organic amendments.
Total
Time of application
1999

Fall

2000

Spring

2000

Fall

2001

Spring

Form
Fresh manure
Composted manure
Fresh manure
Composted manure
Fresh manure
Composted manure
Fresh manure
Composted manure

H 2O
624
340
631
313
389
317
613
534

Ash
406
624
302
726
284
608
418
595

P
g
11.5
11.7
11.0
8.8
11.3
7.4
5.2
6.7

K

C

N

C/N

␮g

21.7
20.6
24.7
15.4
20.5
12.9
13.0
16.6

323
181
343
144
323
199
316
206

28.6
16.9
30.0
12.8
24.8
17.2
22.3
16.3

11.3
10.7
11.5
11.2
13.0
11.6
14.2
12.7

NO3⫺–N

NHⴙ4 –N

kg⫺1‡

pH†

EC†

8.8
8.0
8.2
8.1
8.5
7.4
8.3
8.3

S m⫺1
0.46
0.59
0.57
0.55
0.70
0.50
0.23
0.51

g⫺1

3500
500
2770
730
910
360
1560
940

15
820
78
750
18
750
96
140

† Electrical conductivity (EC) and pH were determined using a 5:1 water/amendment slurry.
‡ Moisture content is expressed on a wet weight basis, and all other concentration parameters are expressed on a dry matter basis.

nitrate concentrations were square-root–transformed before
statistical analysis to meet the ANOVA assumption of homogeneity of variances. Correlations between soil and plant parameters were made on an experimental unit basis using PROC
CORR in SAS. PROC REG of SAS was used to fit quadratic
equations to the relationship between grain yields and urea
N fertilizer rates.

RESULTS AND DISCUSSION
Weather Conditions
The period from amendment application in October
1999 until corn planting in May 2000 was warmer and
drier than the 50-yr average (Fig. 1a and 1b) whereas
the 2000–2001 winter was colder and wetter than the
50-yr average (Fig. 1a and 1b). Mean monthly temperatures during the 2000 and 2001 growing seasons were
typical compared with the 50-yr average (Fig. 1a). Both
growing seasons had lower-than-normal total precipitation (Fig. 1b), but the precipitation patterns differed
between years. The 2000 growing season began with dry
soil conditions followed by timely but limited precipitation. In contrast, the 2001 growing season was drier than
normal from mid-June until September but began with
moist soil conditions in May following the wet winter
season (Fig. 1b).

Amendment Composition and Application
Carbon/N ratios of the applied amendments ranged
from 10.7:1 to 14.2:1 with means of 12.5:1 and 11.6:1 for
fresh and composted manures, respectively (Table 2).
Materials with C/N ratios of less than 20:1 are generally
thought not to immobilize soil N (Mathur et al., 1993)
although short-term immobilization with partially composted hoop manure (C/N ratios of 12:1 to 15:1) has been
observed (Cambardella et al., 2003). The amendments
applied in the spring of 2001 had the highest C/N ratios,
perhaps due to the cool and wet conditions of the fall–
winter–spring period of 2000–2001, which may have
slowed decomposition in the compost windrows. These
weather conditions also likely increased the bedding
requirement and/or altered the bedding management
on the commercial farm from which the fresh manure
applied in the spring of 2001 was obtained.
The ratio of NH4⫹–N to NO3⫺–N has been used as an
indicator of compost maturity (Mathur et al., 1993), with
lower ratios indicative of greater decomposition. The

NH4⫹–N to NO3⫺–N ratios observed here suggest that the
composted manure generally was more decomposed than
the fresh manure; the exception being the manure
applied in the spring of 2001, which had a more similar NH4⫹–N/NO3⫺–N ratio than at all other application
times (Table 2).
Each of the applied amendments contained a substantial quantity of total P (Table 2). Annual applications
of livestock manure to fields in corn–soybean rotations
at rates sufficient to meet corn N requirements have
the potential to accumulate soil P (Jackson et al., 2000)
due to higher P application rates than grain P removal
rates. In our study, the P application rate ranged from
79 to 242 kg P ha⫺1 (Table 3), with mean P application
rates of 121 and 188 kg P ha⫺1 for fresh and composted
hoop manure, respectively, and 167 and 142 kg P ha⫺1
for fall- and spring-applied amendments, respectively
(Table 3). During 2000–2001, corn and soybean yields
in Boone County, IA, averaged 9.7 and 2.7 Mg ha⫺1
(NASS, 2002), respectively, which would have removed
an estimated 28 kg P ha⫺1 yr⫺1 for corn and 16 kg P
ha⫺1 yr⫺1 for soybean (Voss et al., 1999). The combined
P removal rate from one cycle of a corn–soybean rotation therefore would have been 44 kg P ha⫺1. A comparison of the P applied in this study with the estimated P
grain removal indicates that one application of either
fresh or composted hoop manure per rotation cycle
would lead to soil P accumulation. It should be noted,
however, that fresh hoop manure had a higher N/P ratio
(Table 3), which would slow soil P accumulation compared with composted hoop manure if P removal rates
for grain were equal in the two management systems.
Table 3. Loading rates of organic amendments.
Application rate†
Time of application
Fall

1999

Spring

2000

Fall

2000

Spring

2001

Form
Fresh manure
Composted manure
Fresh manure
Composted manure
Fresh manure
Composted manure
Fresh manure
Composted manure

N
kg
340
340
340
340
340
340
340
340

P
ha⫺1
130
240
120
230
150
140
80
140

C

DM‡

Mg ha⫺1
3.66
11.3
3.74
20.7
3.85
11.2
3.76
26.1
4.38
13.6
3.89
19.5
4.77
15.1
4.24
20.6

† Application rates of total N, P, and C contained within each manure.
‡ DM, dry matter.

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AGRONOMY JOURNAL, VOL. 96, JANUARY–FEBRUARY 2004

Table 4. Treatment means, analysis of variance, and correlation to yield for plant population and late-spring soil nitrate concentration
during 2000 and 2001.
Plant population
Time of application
None
Side-dressed (at V6)
Side-dressed (at V6)
Side-dressed (at V6)
Fall
Fall
Spring
Spring

Form
None (control)
Urea
Urea
Urea
Fresh manure
Composted manure
Fresh manure
Composted manure
Standard error (SE)

Total rate
kg N ha⫺1
0
60
120
180
340
340
340
340

Source of variation
Treatment contrasts
Forms (F)
Urea fertilizer linear response
Urea fertilizer quadratic response
Urea fertilizer cubic response
Control vs. all organic amendments
Among amendments (fresh vs. composted)
Time of application (A)
Amendments (fall vs. spring)
F⫻A
Amendments (fresh vs. composted) ⫻ (fall vs. spring)
Correlation to yield (r )

2000

Soil nitrate

2001

2000

Plants ha⫺1
65 900
63 300
67 400
65 200
61 000
63 500
58 300
64 000
1 050

2001

⫺1
NO⫺
3 –N, ␮g g
8.3
3.3
7.8
3.2
8.5
4.6
8.9
3.5
10.7
5.8
15.8
5.3
9.1
5.2
19.6
5.8
1.1
0.5

72 800
72 700
73 300
72 900
72 800
72 700
72 500
73 800
910
P⬎F

ns
ns
*
**
***

ns
ns
ns
ns
ns

ns
ns
ns
***
***

ns
ns
ns
***
ns

ns

ns

ns

ns

ns
⫺0.20ns

ns
⫺0.11ns

*
0.47*

ns
0.18ns

* Significant at the P ⬍ 0.05 probability level.
** Significant at the P ⬍ 0.01 probability level.
*** Significant at the P ⬍ 0.001 probability level.

Corn Emergence
In 2000, corn emergence was negatively affected by
fresh manure applied in both fall and spring (Table 4).
We believe these plant emergence effects were likely
caused by a combination of physical and chemical influences of the fresh manure. In the spring of 2000, freshmanure clods were visible on the soil surface despite
tillage. Combined with dry soil surface conditions, which
required a deeper-(8–10 cm)-than-normal (4–6 cm) planting depth for seed to soil moisture contact, the physical
and/or chemical effects of the fresh-manure clods on
the soil surface over the plant row prevented consistent
emergence. Fall-applied fresh manure tended to reduce
plant emergence less than spring-applied fresh manure
in 2000 (Table 4). This was probably due to degradation
and/or dispersion of any potential phytotoxic substances
and physical degradation of the fresh manure clods that
occurred during the winter following fall application of
manure. Tiquia et al. (1996) found NH4⫹–N concentration (ranging from ⬍500 to 4200 ␮g g⫺1) to be the most
important chemical component of solid swine manure
in predicting phytotoxic effects on vegetable seedlings.
Despite the stand reductions observed in the present
study, plant population densities were not correlated
with grain yields (Table 4).
In 2001, plant emergence was not affected by manure
treatments (Table 4). Moist soil conditions throughout
the spring of 2001 allowed for adequate reductions of
fresh-manure clod size during tillage and thus eliminated the plant emergence problems observed in 2000.

Late-Spring Soil Nitrate Concentration
The NO3⫺–N concentration in the surface 30 cm of soil
when corn is 20 to 30 cm tall has been used in the

midwest and northeast USA to predict corn yield response to N fertilizer (Blackmer et al., 1989; Magdoff,
1991). Although this method has been calibrated for
synthetic N fertilizer sources and to a limited extent for
soils amended with liquid swine manure (Hansen, 1999),
it has not been calibrated for soils receiving solid livestock manure. In an evaluation of corn yield responses
to variations in soil NO3⫺–N concentration, Blackmer et
al. (1989) set the maximum soil NO3⫺–N concentration
in the surface 30 cm at which to expect a yield response
from applications of synthetic N fertilizer at 25 ␮g g⫺1
for unmanured soils in years with normal or belownormal spring precipitation, at 20 to 22 ␮g g⫺1 for unmanured soils in years with wet springs, and at 11 to
15 ␮g g⫺1 for manured soils.
In both years of our study, soil NO3⫺–N concentrations
were higher in plots receiving manure than in the unamended fertilizer-free control (Table 4). A significant
manure form ⫻ application time interaction was detected for soil NO3⫺–N concentrations in 2000 (Table 4),
with the highest soil NO3⫺–N concentrations found in
plots treated with spring-applied composted manure
and the lowest found in plots amended with springapplied fresh manure. The lower soil NO3⫺–N concentrations observed in 2001 compared with 2000 (Table 4)
may have reflected the high soil moisture conditions
before sampling (Fig. 1b), which could have caused nitrate leaching or denitrification losses.

Ear Leaf Nitrogen and Phosphorus
Concentrations and Chlorophyll Meter Readings
Chlorophyll meter readings of corn ear leaves at growth
stage R1 responded positively to urea application in both
years (Table 5). A significant quadratic response to in-

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LOECKE ET AL.: FORM OF SWINE MANURE AND APPLICATION TIME AFFECT CORN YIELD

Table 5. Treatment means, analysis of variance, and correlation to grain yield for SPAD chlorophyll meter readings and corn ear leaf
N and P concentrations at growth stage R1, and fall stalk nitrate concentrations in 2000 and 2001.
SPAD
Time of application
None
Side-dressed (at V6)
Side-dressed (at V6)
Side-dressed (at V6)
Fall
Fall
Spring
Spring

Form
None (control)
Urea
Urea
Urea
Fresh manure
Composted manure
Fresh manure
Composted manure
Standard error (SE)

Rate
kg N ha⫺1
0
60
120
180
340
340
340
340

Source of variation
Treatment contrasts
Forms (F)
Urea fertilizer linear response
Urea fertilizer quadratic response
Urea fertilizer cubic response
Control vs. all organic amendments
Among amendments (fresh vs. composted)
Time of application (A)
Amendments (fall vs. spring)
F⫻A
Amendments (fresh vs. composted) ⫻ (fall vs. spring)
Correlation to yield (r )

2000
55.7
60.4
61.2
61.8
58.0
60.1
57.2
60.0
0.53

Ear leaf N
2001
52.6
54.6
56.2
58.0
57.5
58.3
50.7
55.1
0.81

2000
20.5
24.5
26.5
27.0
24.1
24.6
23.1
25.5
0.9

Ear leaf P

2001
25.2
25.1
26.7
27.9
26.2
26.3
23.2
25.5
0.7

2000

g kg⫺1
2.5
2.9
3.1
3.3
3.5
3.0
3.4
3.4
0.1

Fall stalk nitrate

2001
2.0
2.2
2.1
2.2
2.2
2.2
2.1
2.2
0.1

2000
NO⫺
3 –N,
4.5 (20)
4.5 (20)
26.0 (815)
77.7 (6123)
10.1 (135)
9.6 (119)
5.3 (31)
7.1 (58)
3.2

2001
␮g g⫺1†
4.9 (38)
4.3 (25)
23.3 (566)
37.9 (1491)
18.3 (402)
6.5 (52)
8.0 (66)
5.0 (36)
2.4

P⬎F
***
***
ns
***
***

***
ns
ns
**
**

***
‡
ns
***
ns

**
ns
ns
ns
‡

***
ns
ns
***
ns

‡
ns
ns
*
ns

***
***
ns
ns
ns

***
**
ns
ns
**

ns

***

ns

**

ns

ns

ns

*

ns
0.70***

*
0.51*

ns
0.44*

‡
0.55**

‡
0.25ns

ns
0.35*

ns
0.54**

‡
0.37*

* Significant at the P ⬍ 0.05 probability level.
** Significant at the P ⬍ 0.01 probability level.
*** Significant at the P ⬍ 0.001 probability level.
† Analysis of variance conducted on square-root–transformed data. Data in parentheses are means of raw data.
‡ Significant at the P ⬍ 0.1 probability level.

creasing rates of urea fertilizers ( p ⬍ 0.001) was found
in 2000, suggesting that N was not limiting in the higher
urea application rates (120 and 180 kg N ha⫺1) at this
point in the season (Table 5). However, because chlorophyll meters are useful for indicating N deficiencies, but
not for determining excessive soil N availability (Schepers et al., 1992), this issue remains unresolved.
Eghball and Power (1999) found similar chlorophyll
meter reading results when comparing composted and
noncomposted beef feedlot manure to unamended controls throughout the growing season. In 2000 of our study,
composted manure treatments (fall- and spring-applied)
had higher chlorophyll readings than fresh manure (falland spring-applied), and the mean of all manure treatments was greater than the no-amendment control (Table 5). A significant interaction was detected in 2001
between form of manure and timing of application (Table 5). Spring-applied fresh-manure plots in 2001 had
the lowest chlorophyll readings among the manure treatments whereas fall-applied fresh and composted manure
had the highest readings and the spring-applied composted manure gave an intermediate value (Table 5).
Corn ear leaf N concentration at growth stage R1 responded positively to urea application in both years (Table 5) although the intensity of the response was greater
in 2000 than in 2001. The mean ear leaf N concentration
of all manure treatments was higher than that of the
control in 2000, but no difference between manure treatments and the control was detected in 2001 (Table 5).
The season of manure application was important for the
2001 corn crop; fall-applied manure generated higher
ear leaf N concentrations than did spring-applied manure (Table 5).
Both the corn ear leaf N concentrations and chloro-

phyll meter readings at growth stage R1 correlated well
with final corn grain yield (Table 5). Eghball and Power
(1999) also found a strong correlation (r ⬎ 0.71) between chlorophyll meter readings and grain yield, except
in a season of low precipitation. In our study, ear leaf
N concentration and chlorophyll readings at R1 were
also well correlated with each other (2000: r ⫽ 0.54,
P ⬍ 0.01; 2001: r ⫽ 0.64, P ⬍ 0.0001).
Corn ear leaf P concentrations increased linearly with
increasing rates of urea application in both years (Table 5). This may indicate that plants in the higher urea
treatments foraged for soil P more efficiently and/or
that the hydrolysis of urea lowered soil pH, thus making
more soil P available to plants (Miller and Ohlrogge,
1958; Olson and Dreier, 1956). Differences in ear leaf
P between years may have been due to differences in
early-season soil moisture although many fertility and
environmental factors can interact to influence ear leaf
P concentrations (Voss et al., 1970). In 2001, there were
minimal differences between treatments with regard to
ear leaf P concentration (Table 5).

Corn Grain Yield
Corn grain yields increased in both years in response
to increasing rates of urea application (Fig. 2; Table 6).
The highest yields in response to urea application were
similar in both years, but the yield of the control treatment was lower in 2000 than in 2001. This pattern was
similar to that observed for the ear leaf N concentration
at plant growth stage R1 and may reflect the influence
of the previous year’s crop on the quantity and quality
of organic matter added to the soil and its N mineralization rate (Green and Blackmer, 1995). At 0 kg N ha⫺1,

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AGRONOMY JOURNAL, VOL. 96, JANUARY–FEBRUARY 2004

Fig. 2. Grain yield from urea N rates side-dressed at plant growth stage V6 and fresh manure and compost treatments from 2000 and 2001.
Error bars represent plus/minus one standard error. Grain yields were adjusted to a moisture content of 155 g kg⫺1. Treatment contrasts are
presented in Table 6.

the 2000 corn crop, which followed oat, had a lower
yield than the 2001 corn crop, which followed soybean
(6.7 vs. 8.1 Mg ha⫺1).
The mean grain yield from manure treatments was
greater than the control in both years (Table 6; Fig. 2).
In 2000, no grain yield differences were detected due
to the time of application or the form of manure (composted or fresh manure) (Table 6). In contrast, in 2001,
grain yields from composted manure treatments were
Table 6. Analysis of variance of corn grain yields in 2000 and 2001.
Source of variation
Treatment contrasts
Forms (F)
Urea fertilizer linear response
Urea fertilizer quadratic response
Urea fertilizer cubic response
Control vs. all organic amendments
Among amendments (fresh vs. composted)
Time of Application (A)
Amendments (fall vs. spring)
F⫻A
Amendments (fresh vs. composted) ⫻ (fall vs. spring)
** Significant at the P ⬍ 0.01 probability level.
*** Significant at the P ⬍ 0.001 probability level.

P⬎F
2000

2001

***
ns
ns
***
ns

***
ns
ns
**
***

ns

**

ns

ns

greater than those from fresh-manure treatments (10.3
vs. 8.8 Mg ha⫺1). Additionally, fall-applied manure produced higher yields than did spring-applied manure
(10.1 vs. 8.9 Mg ha⫺1) (Table 6).
The poor yield response to spring-applied fresh manure was more pronounced in 2001 when early-season
soil conditions were moist and cool relative to 2000. In
Wisconsin, similar results were found in wet-cool springs
if fresh solid dairy manure was applied immediately before corn planting (Talarczyk et al., 1996). Talarczyk et al.
(1996) attributed this result to a pattern of manure N
mineralization that was slower than normal. Fall application of solid manure in their study and in our study
resulted in more consistent yield benefits than did spring
applications. This may be due to more timely net N
mineralization relative to plant N demand with fall application vs. spring application.

Nitrogen Fertilizer Equivalency and
Nitrogen Supply Efficiency
A quadratic equation was fit to the yield data of urea
N treatments for each year (Fig. 2). Although only the

LOECKE ET AL.: FORM OF SWINE MANURE AND APPLICATION TIME AFFECT CORN YIELD

Table 7. Calculated N fertilizer equivalency values and N supply
efficiencies of amendments, based on corn yield response to urea
fertilizer side-dressed at corn growth stage V6, in 2000 and 2001.
Time of
application
Fall
Fall
Spring
Spring

N fertilizer
equivalency value
Form
Fresh manure
Composted manure
Fresh manure
Composted manure

N supply
efficiency†

2000 2001 Mean 2000 2001 Mean
103
96
79
97

kg N ha⫺1
60
82
137
117
⫺6
37
71
84

%
30.7 17.9
28.6 40.8
23.5 ⫺1.8
28.9 21.1

24.3
34.7
10.9
25.0

† N supply efficiency defined as the N fertilizer equivalency value expressed
as a percentage of the total N applied (340 kg N ha⫺1).

linear trend was statistically significant (Table 6), the
quadratic function produced a better fit to the data and
thus allowed for a more realistic extrapolation between
the yield data of urea N fertilizer and manure treatments
(see Blevins et al., 1990). Based on each quadratic urea
response curve, N fertilizer equivalency values were calculated for each manure treatment mean (Table 7). Nitrogen supply efficiencies for the different manure treatments were calculated by dividing N fertilizer equivalency
values by the total amount of N applied in each manure
(Table 7). On average, fall application of manure gave
higher N fertilizer equivalency values and higher N supply efficiencies than did spring application, and composted manure provided more consistent N benefits than
did fresh manure. At the application rate used in this
experiment, spring-applied fresh manure produced inconsistent N benefits.
It is not surprising that fall application of manure
tended to be more effective in supplying N to corn, given
the longer time and greater number of accumulated heat
units associated with fall, rather than subsequent spring,
application. Nevertheless, monitoring of soil N losses
and net N mineralization in response to the timing of
manure application would help to clarify whether the
observed N fertilizer equivalencies and N supply efficiencies were due to patterns of N transformation and
release or other non-N-related factors. More research
is needed to address this question.

Fall Stalk Nitrate Concentration
Nitrate concentration in the lower portion of a corn
stalk (the section between 15 and 35 cm above the soil
surface) at plant maturity has been used as an indicator
of late-season soil NO3⫺–N concentrations and/or environmental stress (Binford et al., 1992). A stalk NO3⫺–N
concentration of ⬎2000 ␮g g⫺1 indicates excessive soil
NO3⫺ or stress whereas concentrations ⬍200 ␮g g⫺1 indicate insufficient inorganic soil N for maximum economic
grain yield (Binford et al., 1992).
In our study, urea application resulted in positive
stalk NO3⫺ responses in both years (Table 5). The significant quadratic responses that were observed typically
occur as plant-available soil N becomes greater than the
plant’s ability to assimilate NO3⫺ into amino acids (Binford et al., 1992). In both years, all manure treatments
resulted in stalk NO3⫺–N concentrations ⬍500 ␮g g⫺1,
and the mean stalk NO3⫺–N concentration of manure
treatments was not different from the control treatment

221

(Table 5). In 2001, fresh-manure applications resulted
in higher stalk NO3⫺–N concentrations than compostedmanure applications, and fall applications gave higher
stalk NO3⫺–N concentrations than did spring-applied
manure. The relationship of stalk NO3⫺–N concentration
to grain yield in 2000 followed closely the relationship
described by Binford et al. (1992), but this pattern was
not as distinct in 2001 (figure not shown). It is unclear
if this was due to limited available soil N or increased
NO3⫺ assimilation efficiencies. For example, in 2001, despite having similar yields, the fall-applied compostedmanure treatment resulted in lower stalk NO3⫺–N concentrations than did the 120 and 180 kg N ha⫺1 urea N
treatments. This suggests that factors other than N effects may have contributed to the grain yield response
to manure.

SUMMARY
At the rates used in this study, spring application of
fresh hoop manure resulted in problems with corn emergence, lower N use efficiencies, and inconsistent yields.
Although treatment effects were not always significant,
measurements of soil NO3⫺–N concentrations at plant
growth stage V6 and apparent ear leaf chlorophyll and N
concentrations at growth stage R1 indicated that springapplied fresh manure supplied less N to the plants before
and during flowering than did the other manure treatments. Thus, N deficits may have contributed to lower
yields in the spring-applied fresh-manure treatment compared with the other manure treatments. Increasing
spring-applied fresh hoop manure application rates to
meet crop N demands may be detrimental to plant emergence and may increase soil N immobilization.
In 2001, stalk NO3⫺–N concentrations in the manure
treatments were low (⬍500 ␮g g⫺1) compared with the
stalk NO3⫺–N concentrations of urea N treatments despite similar grain yields (Tables 5 and 6; Fig. 2). A
similar pattern was observed in the soil NO3⫺–N concentrations in the late spring of 2001 relative to grain yield
where manure treatments resulted in soil NO3⫺–N concentrations below levels predicted to provide for optimal yield despite similar yields to urea N treatments.
This finding supports the concept that soils freshly
amended with biologically active organic materials have
different N dynamics than those amended with mineral
N fertilizers (Magdoff, 1991; Cambardella et al., 2003).
A more detailed examination of the seasonal N mineralization and crop N uptake patterns in response to fresh
or composted hoop manure is needed to determine
when and if supplemental N fertilizers may increase N
use efficiencies.
Although we observed similar mean N supply efficiencies for fall-applied fresh manure (24.3%) and
spring-applied compost (25.0%) (Table 7), the potential
for large N losses during composting of fresh hoop manure (Garrison et al., 2001) suggests that fall-applied
fresh manure may be more desirable than spring-applied
compost for whole-farm N conservation. However, nitrate leaching potential could be relatively high with
fall-applied fresh manure, which might result in negative
impacts on water quality. The multiple pathways through

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AGRONOMY JOURNAL, VOL. 96, JANUARY–FEBRUARY 2004

which N may be lost following fall application of manure
need to be studied for a more complete whole-farm N
budget that considers both production and environmental endpoints.
In cases where producers remove fresh manure from
hoop structures in the spring, composting the material
for subsequent fall application appears to be a better
strategy than spreading it immediately before planting
corn since mean N supply efficiency was higher for the
former management system (34.7%) than for the latter
(10.9%) (Table 7). However, economic comparisons of
manure management alternatives are needed to examine possible tradeoffs between composting costs, hauling
distance to the field with the associated reduction in
compost volume, and crop yield benefits. Economic and
environmental analyses will complement the agronomic
results presented here as all play critical roles in assessing the suitability and sustainability of solid manure
management alternatives.
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