RESEARCH ARTICLE

Minimizing nitrogen losses from a corn–soybean–winterwheat rotation with best management practices

Susantha Jayasundara Æ Claudia Wagner-Riddle ÆGary Parkin Æ Peter von Bertoldi Æ Jon Warland ÆBev Kay Æ Paul Voroney

Received: 5 February 2007 / Accepted: 24 March 2007 / Published online: 17 April 2007

� Springer Science+Business Media B.V. 2007

Abstract Best management practices are recom-

mended for improving fertilizer and soil N uptake

efficiency and reducing N losses to the environment.

Few year-round studies quantifying the combined

effect of several management practices on environ-

mental N losses have been carried out. This study was

designed to assess crop productivity, N uptake from

fertilizer and soil sources, and N losses, and to relate

these variables to the fate of fertilizer 15N in a corn

(Zea mays L.)-soybean (Glycine max L.)-winter

wheat (Triticum aestivum L.) rotation managed under

Best Management (BM) compared with conventional

practices (CONV). The study was conducted from

May 2000 to October 2004 at Elora, Ontario, Canada.

Cumulative NO3 leaching loss was reduced by 51%

from 133 kg N ha�1 in CONV to 68 kg N ha�1 in

BM. About 70% of leaching loss occurred in corn

years with fertilizer N directly contributing 11–16%

to leaching in CONV and <4% in BM. High soil

derived N leaching loss in CONV, which occurred

mostly (about 80%) during November to April was

attributable to 45–69% higher residual soil derived

mineral N left at harvest, and on-going N mineral-

ization during the over-winter period. Fertilizer N

uptake efficiency (FNUE) was higher in BM (61% of

applied) than in CONV (35% of applied) over corn

and wheat years. Unaccounted gaseous losses of

fertilizer N were reduced from 27% of applied in

CONV to 8% of applied in BM. Yields were similar

between BM and CONV (for corn: 2000 and 2003,

wheat: 2002, soybean: 2004) or higher in BM

(soybean: 2001). Results indicated that the use of

judicious N rates in synchrony with plant N demand

combined with other BMP (no-tillage, legume cover

crops) improved FNUE by corn and wheat, while

reducing both fertilizer and soil N losses without

sacrificing yields.

Keywords Best management practices � Corn �Crop rotations � Nitrate leaching � Over-winter N

losses � 15N tracer

Introduction

Nitrogen is a key input for sustaining high yields in

cereal crops, but the fertilizer N uptake efficiency

(FNUE—percentage of fertilizer N recovered in

aboveground plant biomass during the growing

season) in these crops is relatively low (<50%) with

conventional production practices (Cassman et al.

2002; Balasubramanian et al. 2004; Krupnik et al.

2004). Part of the applied N is incorporated into soil

organic matter and inorganic N pools, but N not taken

up by crops may be vulnerable to losses during the

S. Jayasundara � C. Wagner-Riddle (&) �G. Parkin � P. von Bertoldi � J. Warland �B. Kay � P. Voroney

Department of Land Resource Science, University of

Guelph, Guelph, ON, CanadaN1G 2W1

e-mail: cwagnerr@uoguelph.ca

123

Nutr Cycl Agroecosyst (2007) 79:141–159

DOI 10.1007/s10705-007-9103-9

growing season and after crop harvest. Consequences

of low FNUE include reduced water quality due to

NO3�, enhanced greenhouse effect and stratospheric

ozone depletion due to N2O, and tropospheric ozone

production due to NOx (Galloway et al. 1995). In

addition, low FNUE in cropping systems represents a

significant economic loss to farmers.

Many alternative management practices have been

proposed to improve FNUE in agro-ecosystems (Din-

nes et al. 2002; Crews and Peoples 2005). Commonly

known as best management practices (BMP), these are

practical and affordable ways to minimize the envi-

ronmental risks without sacrificing economic produc-

tivity. Some examples are: optimizing N fertilizer rates

by the use of soil tests and accounting of N credits from

legumes and manures, matching N supply to crop N

demand by timing of application, adoption of conser-

vation tillage practices, and the use of cover crops to

intercept residual soil NO3. These BMPs focus on

ensuring adequate available N when required by plants

and preventing ‘excess-asynchrony’, i.e. N availability

exceeding plant N demand (Crews and Peoples 2005).

Prevention of excess NO3�N accumulation in the soil,

especially in the presence of excess water, such as in

the fall and over winter, is critical in minimizing

environmental N losses since leaching and denitrifica-

tion are the most dominant N loss mechanisms in many

agroecosystems.

Positive impacts of BMPs on reducing NO3

leaching and improving water quality are evident

from a number of previous studies. Pre-side-dress

nitrate test (PSNT) based N applications for corn

have significantly reduced post-harvest residual soil

NO3 (Durieux et al. 1995), flow-weighted average

NO3 concentrations in drainage water and total NO3

leaching (Guilard et al. 1999; Sogbedji et al. 2000),

when compared with the conventional yield-goal

based N applications. Similarly, conservation tillage

practices have resulted in reduced NO3 leaching

when compared with conventional tillage (Randall

and Iragavarapu 1995; Weed and Kanwar 1996). In

other studies, the use of cover crops during the inter-

growing season has led to lower residual soil NO3

and reduced leaching in corn and other field crops

(McCracken et al. 1994; Justes et al. 1999; Strock

et al. 2004). Applying N according to available soil N

reserves and matching the time of application to crop

uptake, has also been suggested as a means of

reducing N2O emissions (Mosier 1994).

The majority of studies have considered individual

BMPs separately, mainly in addressing water quality,

without considering the interactive effects of multiple

BMPs and other environmental N losses such as N2O

emissions. Mechanisms of N loss are interlinked in

the N cycle and influenced differentially by soil–

plant–water relations, thus measures to address one

loss mechanism may lead to increasing losses from

another. For example, the use of cover crops may

reduce NO3 leaching by sequestering excess NO3 into

biomass (Ritter et al. 1998; Justes et al. 1999), but

their plough-down can provide a flush of C and N,

leading to increased N2O emissions during spring

thaw (Wagner-Riddle and Thurtell 1998). Similarly,

through their influence on soil structure and water,

conservation tillage may create conditions favorable

for increased N2O emissions. Some studies have

shown increased N2O emissions (MacKenzie et al.

1998; Choudhary et al. 2002), while others indicated

no difference or lower emissions under conservation

compared to conventional tillage (Lemke et al. 1999).

These results highlight the necessity of investigating

interactive effects of multiple BMPs in mitigating

environmental N losses in agroecosystems using a

holistic agronomic management approach.

The objectives of this study were: (1) to asses the

combined effects of multiple BMPs on crop produc-

tivity, N uptake, and NO3 leaching losses in a corn–

soybean–winter wheat rotation, and (2) to relate these

variables to the fate of fertilizer 15N applied to corn

and winter wheat under conventional management

practices compared with BMPs. The results presented

here form part of an experiment conducted from May

2000 to April 2005 to study the intra- and inter-

annual variations in N2O emissions, NO3 leaching

and water balance in an agroecosystem managed

under BMPs compared with conventional practices.

Nitrous oxide emissions were reported in Wagner-

Riddle et al. (2007), and water balance components

were presented in McCoy et al. (2006).

Materials and methods

Experimental site and management history

The experiment was conducted at the Elora Research

Station, Ontario, Canada (438390 N 808250 W, 376 m

elev.). The soil type is an imperfectly drained Guelph

142 Nutr Cycl Agroecosyst (2007) 79:141–159

123

silt loam (Morwick and Richards 1946). Initial

chemical characteristics of the 0–15 cm soil layer

were pH: 7.6 (water), organic carbon: 26.9 g kg�1,

total N: 2.4 g kg�1, available P: 24 mg kg�1 and

available K: 146 mg kg�1. Textural analysis indi-

cated: 29% sand, 52% silt and 19% clay in the 0–

15 cm soil layer. Previous crops at the site were corn,

soybean, and cereals (winter wheat or barley) grown

in rotation for at least 8 years prior to the start of the

experiment. During that period, fertilizer N was

applied to corn and cereals at the general yield goal

recommendations for the area (150, 70, and

90 kg N ha�1 for corn, barley, and winter wheat,

respectively). Additionally, solid beef manure was

applied at a rate of 16 Mg ha�1 following the harvest

of winter wheat or barley (last applied in 1998). In

1999, corn was grown at the site, and the experi-

mental area was demarcated following the corn

harvest in October.

Experimental plan and management practices

The experiment consisted of two management sys-

tems, (1) conventional management system (CONV),

and (2) best management system (BM) compared

over May 2000 to October 2004. Four fields were

monitored, each 150 m by 100 m (1.5 ha) in size, two

fields for each system. The size of the fields was

determined by the requirements of micrometeorolog-

ical N2O flux measurements (Wagner-Riddle et al.

2007). The crop sequence during the experiment was

common for both systems: corn (2000), soybean

(2001), winter wheat (2002), corn (2003) and

soybean (2004) (Table 1). In the CONV system,

intensive tillage was practiced by moldboard plough-

ing in the fall to a depth of 15 cm followed by spring

disking. Fertilizer N was applied according to general

recommendations for the area (OMAFRA 2002). For

corn, fertilizer N was supplied as granular urea

broadcasted and incorporated by disking just prior to

planting at a rate of 150 kg N ha�1 (Table 1). For

winter wheat, fertilizer N was applied as granular

urea broadcasted before the start of stem elongation

(Zadock scale 25–30, Zadocks et al. 1974) at a rate of

90 kg N ha�1. Fertilizer N was not applied to

soybean. In the BM system, a combination of BMPs

was performed: no-tillage; side-dress application by

injection of liquid fertilizer 28% N for corn at 6-leaf

stage with the rate of N (50 and 60 kg N ha�1,

respectively, in 2000 and 2003) based on a soil NO3-

N test (OMAFRA 2002) and consideration of N

credits from soybean when N was applied to

succeeding winter wheat (60 kg N ha�1, allowing

for 30 kg N ha�1 N credit from soybean); use of

cover crops when possible (red clover - Trifolium

pretense L. under-seeded to winter wheat) (Table 1).

Soil and plant sampling from the main plot area

Soil samples were taken every two weeks during the

growing season (May to October) and every three to

4 weeks during the non-growing season (November

to April). On each sampling date, soil was taken from

0 to 15 and 15 to 30 cm depths from five sampling

sites selected at 25 m intervals along a transect in

each 1.5 ha field. At each sampling site, 4 soil cores

(2 cm id) were taken within 1 m2 and bulked to form

one sample. Soil samples were stored in a refrigerator

(48C) overnight and exchangeable NH4+-N and

NO3�-N were extracted with 2 M KCl (Keeney and

Nelson 1982).

Plant sampling was done at physiological maturity

of each crop to determine grain yield and stover dry

mass. For corn, 4.5 m2 were hand-harvested from five

sampling sites per field. For soybean and winter

wheat, total biomass was determined by hand

harvesting 1 m2 from five randomly selected sites

per field. All stover and grain samples were weighed,

oven dried at 708C for 72–96 h and re-weighed to

determine the moisture and dry matter contents. Sub-

samples from all dried plant materials were ground

twice, first in a Wiley mill with a 1-mm screen and

then Retsch ball mill shaker grinder to pass 150-mm

sieve (100 mesh screen) for the analysis of total N

concentration.

15N fertilizer application and sampling for 15N

analysis

When corn and winter wheat were grown, 15N

labeled fertilizer was used to differentiate N uptake

from soil and fertilizer N and to study the fate of

fertilizer N applied. Labeled fertilizer was applied to

a new set of confined mini-plots in each year. In

2000, confined mini-plots (2.5 m · 1.75 m) were

established within each 1.5-ha field (two mini-plots

per field) in opposite corners of the field, 20 m inside

Nutr Cycl Agroecosyst (2007) 79:141–159 143

123

the plot border. A 4 m · 3 m area was covered with a

plastic sheet while applying N fertilizer in the main

field, and mini-plots were established afterwards by

inserting a rigid 20 cm tall plastic frame into the soil.

The plastic frame protruded 2 cm above the soil

surface; it prevented any runoff or run-on water from

removing or adding N fertilizer. After establishing

each mini-plot, the rest of the area that had been

covered with plastic was manually fertilized with

unlabelled fertilizer.

Table 1 Dates of management practices performed in the conventional and best management systems during the experimental

period (May 2000 to October 2004)

Date Conventional system Best management system

2000 (corn)

5 June Urea broadcasted and incorporated by

disking (150 kg N ha�1)

Corn (Pioneer 3901) no-till planted

Corn (Pioneer 3901) planted –

6 June – Soil sampling for NO3 test

4 July – Urea-ammonium-nitrate solution (28% N) injected

as side-dress (50 kg N ha�1)

25 October Corn harvested Corn harvested

2001 (soybean)

24 April Moldboard plowinga –

4 May Disking –

5 May Soybean (First Line 2701R) planted Soybean (First Line 2701R) no-till planted

1 October Soybean harvested Soybean harvested

2 October Disking and winter wheat (25R37) planted Winter wheat (25R37) no-till planted

2002 (winter wheat)

23 April Urea broadcasted and incorporated

(90 kg N ha�1)

Urea broadcasted and incorporated (60 kg N ha�1,

allowing for 30 kg N ha�1 credit from soybean)

– Red clover under-seeded

1 August Winter wheat harvested Winter wheat harvested

9 October Moldboard plowing –

2003 (corn)

30 April – Red clover killed with Glyphosate

5 May Disking –

15 May Corn (Pioneer 39K40) planted Corn (Pioneer 39K40) no-till planted

Urea broadcasted and incorporated

(150 kg N ha�1)

–

20 June – Soil sampling for NO3 test

2 July – Urea-ammonium-nitrate solution (28% N) injected

as side-dress (60 kg N ha�1)

28 October Corn harvested Corn harvested

10 November Moldboard plowing –

2004 (soybean)

17 May Disking –

18 May Soybean planted Soybean no-till planted

1 October Soybean harvested Soybean harvested

a Ploughing was postponed due to unfavorable weather in the previous fall

144 Nutr Cycl Agroecosyst (2007) 79:141–159

123

For mini-plots in the CONV system, the required

quantity of 15N labeled granular urea (4.634% 15N

atom excess) was mixed with 200 g of clean dry sand

(to increase the volume of the fertilizer and facilitate

uniform spreading), sprinkled on the soil surface

uniformly and incorporated using a hand rake. Corn

was hand-planted within the mini-plot and in a 1-m

wide buffer area on the same day. The application of

labeled fertilizer to mini-plots in the BM system was

done at the 6-leaf stage of corn as per the main BM

plots. The required quantity of 15N labeled urea and

ammonium nitrate mixture was dissolved in 200 ml

de-ionized water and this solution was injected to

5 cm depth on a slit, made using a shovel with

straight blade, along the mid way between two corn

rows in the mini-plot. The differences in the method

of 15N application were to simulate the differences in

the method of fertilizer N application to corn in the

two management systems. Within each 15N labeled

mini-plot, there were 10 corn plants (excluding the

plants in a *38 cm buffer strip) which received 15N

fertilizer, and sampling for soil and plant analysis

within the mini-plot was done in the center 1.5 m2.

At physiological maturity, four corn plants from

the center sampling area were cut at the soil surface.

Soil particles adhered to the base of the stalk were

washed off with de-ionized water. Plants were

separated into stalk, leaves, cob and grain. Empty

cobs were added to the stalk and leaf portion to form

one stover sample. Dry stover and grain were

prepared for total N and 15N analysis as described

above. After harvest, two soil cores per each 15N

mini-plot were taken using a hydraulic soil probe and

segmented into 0–15, 15–30, 30–60, and 60–90 cm

depth increments. The sampling hole was then back-

filled using soil from 30 cm to 60 cm sampled

elsewhere. Each soil sample was passed through a 2-

mm screen and divided into two sub-samples. One

sub-sample was used to determine exchangeable NH4

and NO3-N, and the other sub sample was air dried

and ground for total N and 15N analysis. Soil

sampling from the 15N mini-plots was repeated

following spring thaw in April of the next year.

Ceramic-cup soil solution samplers were installed

in each 15N mini-plot at 80 cm depth for sampling

drainage water. The construction and installation of

solution samplers were similar to that described by

Lord and Shepherd (1993). Soil solution was sampled

every 1 to 2 weeks during the drainage periods. At

each sampling, a suction of 50 kPa was applied to

solution samplers using a hand-held vacuum pump.

The suction was maintained for about 2 h and water

collected in the ceramic cup was retrieved using pre-

evacuated vacutainers. Soil solution samples were

stored frozen until analyzed.

In 2001, when soybean was grown in the rotation,

a non-nodulating soybean cultivar (Glycine max L.

Merr. ‘Evans’) was planted within 15N mini-plots in

alternative rows with the same soybean cultivar

planted in the main plot. This was done to estimate

the contribution of N from biological fixation

according to the 15N isotope dilution method (Fried

and Middleboe 1977). At physiological maturity,

both nodulating and non-nodulating soybean from the

center 1.5 m2 were hand-harvested separately at the

soil surface. Soybean plants were divided into grain

and stover, dried at 708C, weighed and sub samples

were ground for total N and 15N analysis. Soil

samples (0–90 cm) from the 15N mini-plot were

taken after soybean harvest in October 2001 as

described before.

New confined 15N plots were established in

October 2001 after winter wheat planting following

the soybean crop. Solution samplers were installed in

these mini-plots in October 2001 the same way as

described earlier. When fertilizer N was applied to

winter wheat in the main plots on April 23, 2002 the

mini-plots were covered with plastic covers, followed

by application of 15N labeled urea as per description

above. At maturity, wheat plants from the center

1.0 m2 were harvested and separated into grain and

straw and analyzed for total N and 15N analysis.

After harvest and after spring thaw in April 2003, soil

profile (0–90 cm) in the 15N mini-plot was sampled

as described for corn.

For the 2003 growing season, new 15N mini-plots

were established following the procedure described

for 2000. The same protocol, as described for 2000,

was followed for soil, drainage water and plant

sampling in 2003.

Chemical analysis and 15N based calculations

The concentrations of NH4 and NO3-N in soil KCl

extracts and soil solution samples were determined by

a colorimetric technique (Keeny and Nelson 1982)

using a TRAACS 800 autoanalyzer. Soil KCl extracts

and drainage water samples were also processed for

Nutr Cycl Agroecosyst (2007) 79:141–159 145

123

15N analysis according to the diffusion technique

(Brooks et al. 1989). The 15N atom % excess of the

samples was determined using a Tracemass1 Isotope

Ratio Mass Spectrometer (Europa Scientific, Crewe,

UK) interfaced to a Roboprep CN analyzer at the

Isotope Analytical Laboratory, University of Sas-

katchewan, Saskatoon, Canada. Immobilized 15N in

the soil organic pool was calculated by subtracting

15N content in the soil mineral pool from total 15N

content (Bremner and Mulvaney 1982). This method

may be compounded by the inclusion of some clay-

fixed 15NH4-N in the immobilized fraction, but soil

at our experimental has a low NH4 fixation capacity

(Drury et al. 1991).

The fraction of N derived from fertilizer (fndff) in

plant, soil and drainage water was calculated accord-

ing to Barraclough (1995). The amounts of N derived

from fertilizer in plant or soil were calculated by

multiplying fndff for plant (or soil) by total plant (or

soil) N. The amount of N derived from atmosphere

(ndfa) in soybean was calculated according to Fried

and Middleboe (1977).

Estimates of nitrate leaching

Nitrogen loss by leaching was calculated from NO3-

N concentrations in the drainage water at 80 cm depth

and estimates of drainage volume. Drainage for the

two management systems was estimated using a

water budget approach as described in McCoy et al.

(2006). The amount of NO3-N loss was calculated by

using the estimate of deep drainage for 2 week

periods multiplied by the mean NO3-N concentration

of solution samples for that period, according to Lord

and Shepherd (1993). The amount of N leaching

derived from fertilizer N was calculated by multiply-

ing fndff for soil solution samples at successive

sampling dates by total NO3-N loss due to leaching

for the corresponding period.

Statistical analysis

This experiment consisted of two management sys-

tems (treatments) applied to two 1.5-ha fields. For

variables such as mineral N (NO3 and NH4), crop

biomass and N uptake, there were five observations

per field, or 10 replicate observations per treatment.

For variables related to the 15N study (fraction and

amount of N derived from fertilizer in crops, soil and

drainage water, and fraction and amount of biological

N fixation by soybean), there were four replicate

observations per treatment. Means were compared

using a Student t test using SAS software.

Results and discussion

Weather conditions during the experiment

The 2000 growing season experienced the highest

precipitation during the experiment (Table 2). The

start of the season was extremely wet, with May and

June precipitation exceeding normals by over 85%,

significantly delaying planting (Table 1). In addition,

below average temperature from July to September

resulted in substantially lower crop heat units in 2000

compared with the long-term value for the area

(Table 2). The weather conditions for most of 2001

growing season were normal, except for July when

monthly precipitation was 50% lower. This dry

period, which extended up to mid-August, coincided

with R4 to R6 growth stages of soybean, which are

crucial stages in terms of final seed yield (Ritchie

et al. 1997). The growing season of 2002 was dry,

particularly from July to September with warmer

temperatures and lower precipitation, while in 2003

values were close to normal in terms of precipitation,

but May and October temperatures were below

normal.

Weather conditions during the non-growing season

also indicated considerable variations during the

experiment (Table 2). The highest precipitation for

the non-growing season was experienced in 2003/

2004, while the other 3 years received less precip-

itation compared to long-term normals (Table 2). The

non-growing season in 2002/2003 received the least

cumulative precipitation. Average monthly tempera-

ture for the non-growing season ranged from 0.48C in

2001/2002 to �3.48C in 2002/2003.

Grain yield, N uptake and contribution of

different N sources to plant N

Grain yields of corn and winter wheat were not

significantly different between the two management

systems (Table 3). Average corn grain yield was

4.1 Mg ha�1 in 2000, about 50% lower than that in

2003 (8.7 Mg ha�1). Yield in 2003 was comparable

146 Nutr Cycl Agroecosyst (2007) 79:141–159

123

with average corn yield for this area, and the lower

yield in 2000 was mainly due to the unfavorable

weather during that year. Average grain yield for

winter wheat was 7.2 Mg ha�1 in 2002. The yield of

soybean was significantly higher in the BM

(3.5 Mg ha�1) than in the CONV system

(2.4 Mg ha�1) in 2001, but in 2004 there was no

difference in soybean yield averaging 3.7 Mg ha�1

for the two management systems (Table 3). The

difference in the soybean yield in 2001 may be

attributable to the differences in soil moisture stress.

Soil moisture content was significantly higher under

the BM compared to the CONV system during the

critical soybean growth stage (R4 to R6) in August

2001 (McCoy et al. 2006).

Nitrogen uptake in corn was significantly higher in

the CONV than in the BM system in 2000, while

there was no significant difference in 2003 (Table 3).

The result in 2000 appears to be due to the significant

difference in soil N contribution to corn, as the

amount of fertilizer N uptake was similar for both

systems. Soil N constituted the major fraction (over

70%) of corn N uptake in both management systems

(Table 3). It is possible that soil N supply was

limiting in the BM system in early 2000 growing

season due to limited soil N mineralization under

cool soil temperatures and/or significant soil mineral

N loss under excessive wet conditions. Surface soil

temperature under zero tillage can be significantly

lower than under conventional tillage (Cox et al.

1990), and these differences and their effect on soil N

mineralization may be more critical under colder

conditions than under normal weather conditions. It

appears that these limitations did not occur in 2003

for BM, as soil N contribution to corn uptake was

considerably higher than in 2000. Interestingly, the

amount of N uptake from fertilizer by corn under

CONV system in 2003 was significantly larger than

under BM system (60 vs. 35 kg N ha�1), but this did

not result into a difference in plant N uptake because

contribution from the soil N pool was higher in BM

system (80% of the plant N uptake vs. 67% in the

CONV) (Table 3). Total N uptake, as well as the

amount of N contributions from soil and fertilizer

Table 2 Average monthly temperature and monthly precipitation at Elora Research Station during the experimental period (May

2000 to April 2004) compared with climate normals (1971–2000) for the area

Month Daily average temperature (8C) Monthly precipitation (mm)

Normalsa 2000/

2001

2001/

2002

2002/

2003

2003/

2004

Normalsa 2000/

2001

2001/

2002

2002/

2003

2003/

2004

May 12.5 13.1 13.3 9.2 10.8 78.3 118 92 90 102

June 17.3 17.1 17.9 17.5 16.9 81.3 180 75 84 79

July 19.8 18.0 18.2 21.1 19.1 91.8 108 47 78 54

August 18.7 17.4 20.1 19.4 19.3 86.3 60 91 34 113

September 14.3 13.2 14.0 17.3 14.3 85.8 76 89 70 76

October 8.2 9.0 8.5 6.8 6.9 65.6 27 139 55 94

November 2.3 1.4 5.3 1.1 3.2 82.7 65 84 91 113

December �3.8 �9.1 �0.5 �4.3 �2.3 73.6 66 53 32 56

January � 7.1 �5.7 �2.8 �10.1 �11.0 64.4 24 23 11 92

February �6.4 �5.5 �3.8 �9.2 �6.8 51.5 104 54 41 31

March �1.2 �2.9 �1.6 �2.6 �0.4 69.9 33 61 55 87

April 5.8 6.4 5.7 4.5 4.9 76.9 86 108 77 60

GS 15.1 14.6 15.3 15.2 14.5 489.1 569 533 411 518

NGS � 1.7 �2.6 0.4 �3.4 �2.1 419.0 378 383 307 437

CHU 2682 2522 2640 2819 2646

Average temperature and cumulative precipitation for the growing season (GS, May to October) and non-growing season (November

to April of following year), and crop heat units (CHU) are also showna Environment Canada Waterloo Wellington A weather station (latitude: 438270 N, longitude: 808220 W, elevation: 317 m)

Nutr Cycl Agroecosyst (2007) 79:141–159 147

123

sources to plant N in winter wheat in 2002, were not

significantly different between the two management

systems (Table 3). As with corn, over 70% of plant N

in wheat was contributed by soil N sources.

Biological N2 fixation was the major N source for

soybean in the BM system in 2001 with 61%

(117 kg ha�1) of the total plant N originating from

this source. In contrast, the contribution of biologi-

cally fixed N2 to soybean was 42% (63 kg N ha�1) in

the CONV system and significantly lower compared

with that in the BM system. Soybean N2 fixation has

been found to be very sensitive to drought (Sinclair

and Serraj 1995), and dry soil conditions during July

to August 2001 might have severely affected soybean

N2 fixation in the CONV system. Sources of plant N

for soybean in 2004 were not determined and there

was no significant difference in the plant N in

soybean between the two systems in that year

(Table 3).

The FNUE ranged from 24% to 40% of applied N

for corn and 45% of applied N for winter wheat in the

CONV system (Table 3). These values are compara-

ble with FNUE values reported (usually below 50%)

for major cereal crops under conventional fertiliza-

tion practices (Cassman et al. 2002; Krupnik et al.

2004). Conventional fertilization usually involves N

recommendations based on average yields on a

regional basis and often assumes fertilizer is the

major N source for plant uptake (Havlin 2004).

Moreover, with conventional practices the recom-

mended amount of fertilizer N is supplied in a single

application, often at planting in early spring when soil

moisture levels are usually high. This practice results

in periods of greatest asynchrony between N supply

and plant N uptake (Fig. 1) and therefore periods of

greatest risk of N loss depending on weather condi-

tions, leading to low FNUE. In our study the lowest

FNUE (24% of 150 kg N ha�1 applied) was observed

Table 3 Grain yield, total plant N uptake and contribution of

different sources (fertilizer, soil and biological N fixation,

BNF) to plant N in corn, soybean and winter wheat in different

years of the experiment as affected by conventional and best

management practices

Crop (year) Conventional system Best management system P value

Grain yielda (Mg ha�1)

Corn (2000) 4.33 3.86 0.277

Soybean (2001) 2.38 3.54 <0.0001

Winter wheat (2002) 6.81 7.61 0.128

Corn (2003) 8.98 8.40 0.085

Soybean (2004) 3.82 3.59 0.284

Plant N uptake (kg ha�1)

Corn (2000) 133.7 109.2 0.045

Soybean (2001) 149.7 190.7 0.042

Winter wheat (2002) 134.9 144.3 0.642

Corn (2003) 184.4 176.4 0.585

Soybean (2004) 228.4 231.9 0.810

Source of plant N (kg ha�1)

Corn (2000) Fertilizer 35.8 (24%)b 32.4 (65%) 0.173

Soil 97.9 76.8 0.046

Soybean (2001) BNF 63.3 117.0 0.008

Soil 86.4 73.6 0.292

Winter wheat (2002) Fertilizer 40.3 (45%) 36.5 (61%) 0.525

Soil 94.6 107.8 0.392

Corn (2003) Fertilizer 60.4 (40%) 34.5 (58%) 0.004

Soil 124.0 142.0 0.249

Note that sources of plant N were not measured for soybean in 2004a Yields were expressed at moisture contents 15% for corn, 14.5% for winter wheat and 13% for soybeanb Fertilizer N uptake efficiency: percentage of fertilizer N recovered in the aboveground crop biomass during the growing season

148 Nutr Cycl Agroecosyst (2007) 79:141–159

123

in conventionally fertilized corn in 2000 when

excessive wet conditions followed the fertilizer

application. In 2003, a normal growing season,

FNUE for corn in the CONV system improved only

up to 40%. In comparison, BMPs, which involved

application of fertilizer N rates based on soil NO3 test

and synchronizing fertilizer N supply with the crop N

demand, led to a substantial increase in FNUE (58–

65%) without sacrificing yields (Table 3).

Mineral N in the surface soil

Mineral N (NH4 + NO3-N) content in the 0–30 cm

soil indicated considerable variations in response to

different management practices (Fig. 1). The most

conspicuous changes occurred during the growing

seasons of 2000 and 2003, when corn was grown in

the rotation. Application of 150 kg N ha�1 (as per

general yield goal based N rate) to corn at planting

increased soil mineral N content in the CONV system

to 130–160 kg N ha�1 when the rate of N uptake by

corn was less than 0.3 kg N ha�1 d�1, leading to a

period of surplus mineral N in the surface soil

(Fig. 1). Such periods of excess mineral N were not

seen in the BM system in 2000 and 2003 as the rate of

N applied was less (50–60 kg N ha�1) as well as N

was applied at a time (at 6-leaf stage) when the N

uptake rate by corn was high (*3 kg N ha�1 d�1).

Changes in soil mineral N content in response to

fertilizer N application to winter wheat were not as

distinct, probably due to comparatively low N rates

applied to winter wheat in the two systems (60 vs.

90 kg N ha�1), and due to the fact that N was applied

at the stem elongation phase when the rate of plant N

uptake was high (*2 kg N ha�1 d�1).

Mineral N content in the surface soil decreased to

<40 kg ha�1 for both systems in the latter half of the

growing season, when maximum crop N uptake had

occurred, in all years except in 2000, when corn N

uptake was reduced due to poor growth. The high

residual mineral N in the fall of 2000 was still

persistent in both systems at soybean planting in

spring 2001, but lower contents were present follow-

ing the relatively larger plant N uptake of 2003

(Fig. 1) and throughout 2004 (data not shown).

Residual N in the soil profile (0–90 cm)

In each year, significantly higher amounts of residual

mineral N were present in the soil profile in the

CONV than in the BM system at crop harvest

(Table 4). Almost all the residual mineral N present

after winter wheat in both systems and over 95% of

the residual mineral N after corn in the BM was

derived from soil organic matter mineralization. In

contrast, fertilizer derived mineral N constituted 11–

24% of the residual mineral N after corn in the

CONV system. However, the differences in total

residual mineral N in the soil profile between the two

systems were mainly due to differences in soil

0

40

80

120

160

200

00-yaM

00-peS

10-naJ

10-yaM

10-peS

20-naJ

2 0-yaM

20-peS

30-naJ

30-yaM

3 0-peS

40-naJ

4 0-yaM

Date of Sampling

ah

N gk

1-

SMN (CONV) SMN (BM) Plant N (CONV) Plant N (BM)

CornSoybeanWinter wheat

Red clover (in BM only)

Corn

A B A B

Fig. 1 Temporal variations in soil mineral N (SMN) content in

the 0–30 cm soil layer and N uptake by corn and winter wheat

in two management systems. CONV: conventional and BM:

best management. Vertical bars represent the standard error of

the mean (n = 10), upward arrows on the X axis indicate times

of fertilizer N application (for corn, A: fertilizer application for

CONV and B: fertilizer application for BM)

Nutr Cycl Agroecosyst (2007) 79:141–159 149

123

derived mineral N present after harvest (Table 4).

Mineralization from soil organic matter can release

significant amounts of mineral N into the plant

available pool during the growing season (Shen et al.

1989). In our experiment, soil derived mineral N was

the major source for corn, reaching up to

142 kg N ha�1 (80% of the plant N) in the BM

system in 2003 (Table 3). In contrast, the contribution

from soil N to corn in the CONV system was 67% of

the plant N uptake. A similar trend can be seen for

winter wheat in 2002. These differences likely did not

occur due to reduced N mineralization in the CONV

system, but more likely due to a lower uptake of soil

derived mineral N by corn and winter wheat. This

probably led to accumulation of unutilized soil

derived mineral N in the CONV system but not in

the BM system. In a study where different rates of

15N fertilizer were applied to corn, Stevens et al.

(2005) observed that high fertilizer N rates beyond an

optimum led to decreased uptake of soil derived

mineral N by corn resulting in an increased accumu-

lation of unutilized mineral N in the soil at crop

harvest. Increasing fertilizer N additions may

alter root architecture of corn by encouraging increased

root growth in the surface soil as well as decreased

root:shoot ratio (Anderson 1988; Bonifas et al. 2005),

and may reduce the ability of the root system to acquire

soil N efficiently (Cassman et al. 2002).

Higher soil derived mineral N present in the

CONV system, where a higher rate of fertilizer N was

applied, may also be attributable to the added N

interaction (Jenkinson et al. 1985). Added nitrogen

interaction (ANI) may arise due to immobilization

driven pool substitution where part of added fertilizer

N takes place of inorganic soil N that would

otherwise be removed during the immobilization

(Jenkinson et al. 1985; Azam et al. 1994). With ANI,

an increased addition of fertilizer N may lead to

increased immobilization of fertilizer N (Azam et al.

1994), as was the case in our study in 2000 and 2003,

evidenced by significantly higher amounts of fertil-

izer N in the immobilized pool after corn in the

CONV compared to BM system (Table 4). In both

years the additional amounts of fertilizer N immobi-

lized (37 and 22 kg fertilizer N ha�1 in 2000 and

2003, respectively) were approximately the same as

Table 4 Soil-derived mineral N and fertilizer-derived N present in the soil profile (0–90 cm) at crop harvest in different years of the

experiment under conventional (CONV) and best management (BM) systems

Management System Fertilizer-derived N Soil-derived Total

Organic N

(kg N ha�1)

Mineral N

(kg N ha�1)

Mineral N

(kg N ha�1)

Mineral N

(kg N ha�1)

2000 (Corn)

CONV 45.5 33.8 108.6 142.4

BM 8.6 3.7 74.7 78.4

P value 0.0007 0.007 0.047 0.024

2001 (Soybean)

CONV –a – 53.2 53.2

BM – – 28.9 28.9

P value – – 0.045 0.045

2002 (Winter wheat)

CONV 23.6 0.6 35.7 36.4

BM 18.1 0.4 21.1 21.5

P value 0.139 0.097 0.004 0.004

2003 (Corn)

CONV 40.3 8.3 63.9 72.3

BM 18.4 2 42.7 44.7

P value 0.011 0.024 0.019 0.039

a Fertilizer was not applied to soybean

150 Nutr Cycl Agroecosyst (2007) 79:141–159

123

the additional amounts of soil derived mineral N

remaining in the CONV system (34 and 21 kg N ha�1

in 2000 and 2003, respectively) (Table 4).

Of the fertilizer derived mineral N remaining in

the profile at harvest, over 95% was recovered from

0 cm to 60 cm depth, indicating less likelihood of

fertilizer N loss by leaching during the growing

season (Figs. 2a, 3a). This same trend was evident in

the profile distribution of the soil derived mineral N

at corn harvest (Figs. 2c, 3c). When the soil profile

was sampled in the following spring, 77 and 41% of

the fertilizer derived mineral N present in the CONV

system at harvest, in 2000 and 2003 respectively,

were not recovered in the profile (Figs. 2b, 3b).

Similarly, the amount of soil derived mineral N

potentially lost from the profile during the winter

period ranged from 20% to 40% of the amount

measured at corn harvest in the preceding fall

(Figs. 2d, 3d).

Nitrogen leaching losses

The pattern and amounts of drainage in the two

management systems were similar; about 80%

occurred in the non-growing season (Fig. 4a, Table 5).

This pattern is typical for southern Ontario climatic

conditions, due to low evapotranspiration relative to

precipitation during these months, and water surplus

0 5 10 15 20

0-15

15-30

30-45

45-60

60-75

75-90

)mc(

htpe

D l io

S

a

0 5 10 15 20

0-15

15-30

30-45

45-60

60-75

75-90

CONV

BM

b

0 10 20 30 40

0-15

15-30

30-45

45-60

60-75

75-90

)mc(

htpe

D l io

S

c

0 10 20 30 40

0-15

15-30

30-45

45-60

60-75

75-90

CONV

BM

d

Fertilizer Derived Mineral N (kg ha -1)

Soil Derived Mineral N (kg ha -1 )

Fig. 2 Distribution of fertilizer

derived mineral N (NH4 + NO3)

and soil derived mineral N

(NH4 + NO3) in different soil

depths at crop harvest (a, c) in

2000 and after the next spring-

thaw (b, d) in 2001

Nutr Cycl Agroecosyst (2007) 79:141–159 151

123

associated with snow melt (Parkin et al. 1999; Tan

et al. 2002). Among non-growing seasons, the

amount of drainage was highest in 2003/2004, which

received the highest cumulative precipitation, while it

was lowest in 2002/2003, which received the lowest

cumulative precipitation (Tables 2, 5). Over the

complete study period, there was only a slight

difference in the cumulative drainage between the

two management systems with CONV indicating 9%

more drainage than BM (McCoy et al. 2006).

Nitrate N concentration in drainage water varied

considerably over the different crop phases of the

rotation (Fig. 4b), closely following variations in

mineral N content (Fig. 1). During fall 2000 and

spring 2001 and from June 2003 to April 2004, NO3-

N concentration was significantly higher in the

CONV than in the BM system. The first period

followed the corn crop in 2000 and indicated the

highest concentrations of NO3-N in drainage water in

the CONV system (26–36 mg NO3-N l�1), compared

0 2 4 6 8 10

0-15

15-30

30-45

45-60

60-75

75-90

)mc(

htpe

D lio

S

a

0 10 20 30

0-15

15-30

30-45

45-60

60-75

75-90

)mc(

htpe

D l io

S

c

0 2 4 6 8 10

0-15

15-30

30-45

45-60

60-75

75-90

CONV

BM

b

0 10 20 30

0-15

15-30

30-45

45-60

60-75

75-90

CONV

BM

d

Fertilizer Derived Mineral N (kg ha-1)

Soil Derived Mineral N (kg ha -1)

Fig. 3 Distribution of

fertilizer derived mineral N

(NH4 + NO3) and soil

derived mineral N

(NH4 + NO3) in different

soil depths at crop harvest

(a, c) in 2003 and after the

next spring-thaw (b, d) in

2004

152 Nutr Cycl Agroecosyst (2007) 79:141–159

123

to 15 to 21 mg NO3-N l�1 for BM. These values are

considerably higher than the accepted Canadian

drinking water standards of 10 mg NO3-N l�1 and,

can be related to high total residual mineral N left in

the soil after a poor corn crop in 2000 (Table 4). The

impact of the fertilizer derived mineral N on drainage

water NO3-N concentration in the CONV system is

evident during this period, as the 15N atom % excess

in the drainage water was significantly higher in the

CONV compared to the BM system (Fig. 4c). These

high levels of NO3-N concentrations following corn

in 2000 persisted well into the subsequent soybean

0

5

10

15

20

25

30

35

40

45

00-yaM

00-peS

10-naJ

10-yaM

10-peS

20- naJ

20-yaM

20-peS

30-naJ

30-yaM

30-peS

40 -naJ

40-yaM

ON

3L

gm(

noitart

necn

ocN-

1-)

CONV

BMCorn Soybean Winterwheat

Red clover (in BM only)Corn

A Bb

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

00-yaM

00-p eS

10-naJ

10-yaM

10 -peS

2 0-naJ

20-yaM

20- peS

30- naJ

30-yaM

30- peS

4 0-naJ

40-yaM

51s secx

E%

mot

AN

CONV

BM

Corn Soybean Winterwheat

Red clover (in BM only)

Corn

A B

c

0

20

40

60

80

100

120

00-yaM

00-peS

10-naJ

1 0-yaM

10-peS

2 0-naJ

20-yaM

20-peS

30-n aJ

3 0-yaM

30-peS

40-n aJ

40-yaM

)m

m(e

ganiar

Dyl

htn

oM

CONV

BM

a

Fig. 4 Monthly drainage

(a), NO3-N concentration

(b), and 15N atom % excess

(c) of drainage water

sampled from ceramic cup

solution samplers placed at

80 cm depth during

different phases of the

rotation. CONV:

conventional system, BM:

best management system,

vertical bars represent the

standard error of the mean

(n = 4), downward arrows

indicate the time of

fertilizer application.

Drainage was not measured

during the growing season

of 2000

Nutr Cycl Agroecosyst (2007) 79:141–159 153

123

phase of the rotation in both systems (Fig. 4b).

However, for most of January 2002 to April 2003

(winter wheat phase of the crop rotation), NO3-N

concentration in solution decreased to <10 mg NO3-

N l�1 in both management systems (Fig. 4b). Atom %

excess 15N was generally low and not significantly

different between the two systems, indicating low

potential risk from fertilizer N contributions to NO3-

N leaching during the winter wheat phase. Nitrate N

concentration in the CONV system during May 2003

to April 2004 (second corn phase of the rotation) was

not as high as the levels observed during the 2000/

2001 season, but exceeded 10 mg NO3-N l�1

(Fig. 4b), an indication of the impact of higher rate

of N fertilizer application to corn in the CONV

system. This is confirmed by the significantly higher

atom % excess of 15N in the drainage water in the

CONV system (Fig. 4b). In comparison, drainage

water NO3-N levels remained below 10 mg NO3-

N l�1 in the BM system through out this period.

The amounts of NO3-N leaching losses were

closely related to the amount of drainage in different

periods (Table 5). Nitrate leaching losses were high

during the periods that followed corn, the highest

observed during the non-growing season of 2000/

2001 in both management systems. A total loss of

58 kg N ha�1, with 16% (9.5 kg N ha�1) of that

resulting from fertilizer N for CONV system, but

28 kg N ha�1 with only 2% (<1 kg N ha�1) of that

derived from fertilizer in 2000/2001 non-growing

season (Table 5). The amounts of NO3-N leaching

loss during the 2003/2004 non-growing season

following the second corn phase were still substantial

(35 and 18 kg N ha�1 for the CONV and BM

systems, respectively) but lower compared to the

losses in 2000/01. Of the total NO3-N leaching losses

observed in 2003/2004 non-growing season, 11% in

CONV and 4% in the BM system originated from

residual fertilizer N (Table 5).

Leaching losses of N during the growing season in

2000, when above normal precipitation occurred in

May to June (Table 2), were not quantified due to

delays in equipment installation. During the second

corn crop (in 2003), which was more normal in terms

of weather conditions, there was evidence of down-

ward movement of fertilizer derived N within 2 to

3 weeks after fertilizer application to corn in the

CONV system (Fig. 4b, c). However, due to low

drainage in the early growing season (Fig. 4a,

Table 5), significant losses of NO3-N leaching were

not observed (Table 5). Considerable amounts of

NO3-N leaching losses (26 and 16 kg N ha�1 in

CONV and BM systems, respectively) were also

observed during the soybean phase (May 2001 to

April 2002) which followed the first corn crop

(Table 5). This could be attributed to carry-over

effects of the high residual soil mineral N from the

previous corn, given that fertilizer N was not applied

to soybean. The amounts of total NO3-N leaching loss

during the winter wheat phase were the lowest

Table 5 Cumulative drainage and NO3-N leaching losses from

soil-derived N and fertilizer-derived N during the growing

season (GS, May to October) and non-growing season (NGS,

November to April) in different phases of the experiment as

affected by the management system (CONV, conventional, and

BM, best management)

Year Season Drainage

(mm)

NO3-N leached from soil derived N

(kg ha�1)

NO3-N leached from fertilizer derived N

(kg ha�1)

CONV BM CONV BM P value CONV BM P value

2000/2001 NGS 171 159 48.4 27.2 0.0096 9.5 0.6 0.0036

2001/2002 GS 31 41 8.4 6.1 0.1136 – –

NGS 164 157 18.0 9.7 <0.0001 – –

2002/2003 GS 44 23 2.5 0.7 0.0019 0.1 0.02 0.0025

NGS 154 112 8.2 3.3 0.0005 0.3 0.1 0.0029

2003/2004 GS 16 29 2.0 1.9 0.6652 0.1 0.03 0.0002

NGS 270 260 31.2 17.2 <0.0001 4.0 0.7 <0.0001

Cumulative 850 781 118.7 66.2 13.9 1.4

Measurements were not carried out during GS of 2000

154 Nutr Cycl Agroecosyst (2007) 79:141–159

123

(12 kg N ha�1 vs. 4 kg N ha�1 in CONV and BM,

respectively), less than 3% of this originating from

fertilizer N (Table 5).

Over the entire period (4 year), the total NO3-N

leaching loss in the CONV system was

133 kg N ha�1, of which *90% (119 kg N ha�1)

originated from soil derived mineral N (Table 5). In

contrast, total NO3-N leaching loss in the BM system

was 68 kg N ha�1 for the entire period, about 50%

lower compared to that in the CONV system. All of

this was soil derived mineral N, as fertilizer derived

N consisted of only 2% of the leaching loss in the BM

system.

Previous studies in Ontario have shown that

drainage water originating from corn fields fertilized

with N rates considered to be economically optimum

(around 130 kg N ha�1) often exceeds the accepted

safe limit for drinking water (Patni et al. 1996; Tan

et al. 2002). Annual average NO3-N leaching losses

in these studies ranged from 26 to 33 kg NO3-N ha�1

for continuous corn cultivated either under conven-

tional or no-tillage (Patni et al. 1996) or for rotation

corn (with oats and 2 years of alfalfa) under

conventional tillage (Tan et al. 2002). Annual aver-

age NO3-N leaching loss measured in the CONV

system in our study (33 kg N ha�1) was in the same

magnitude. With the use of 15N labeled fertilizer, we

observed that the direct contributions from fertilizer

N to NO3 leaching was low (11–16% of the total

NO3-N leached, and 3–6% of N applied in the CONV

system) and the majority of the NO3-N leached

originated from soil organic matter mineralization.

There are two explanations for low fertilizer N

contributions to NO3-N leaching in our study. First,

although some downward movement of fertilizer N

occurred in the first few weeks after fertilizer N

application, deep drainage ceased by June (Fig. 4a),

thus preventing significant losses of fertilizer N by

leaching during the growing season. Second, by the

start of the active drainage period in November, much

of the fertilizer N had been removed from the

available N pool in the soil by plant uptake, microbial

immobilization or by other unaccounted losses

(Table 6, discussed in the next section) leaving

relatively little fertilizer derived N in the residual

pool for leaching. However, it appears that high rates

of fertilizer N did promote leaching losses of soil

derived NO3-N in the CONV system indirectly,

through increased mineralization from soil organic N

due to added N interaction (Cookson et al. 2000),

and/or by reducing the uptake efficiency of soil

derived mineral N by the crop due to over-fertiliza-

tion (Stevens et al. 2005), leading to more residual

mineral N remaining in the soil and available for

leaching during the non-growing season. On-going N

mineralization from the large soil organic matter pool

may continue to add NO3-N to the mineral pool

during the over winter period (Ryan et al. 2000) and

this NO3-N may also contribute to leaching during

the non-growing season. This may explain the higher

soil derived NO3-N leaching loss measured during

the non growing season (Table 5) comparative to the

apparent mass loss of soil derived mineral N from

0 cm to 90 cm profile between harvest and after

spring thaw for 2000/2001 and 2003/2004 non-

growing seasons (Fig. 2c vs. d, Fig. 3c vs. d).

Unaccounted losses of fertilizer N

The combined recovery of fertilizer N in the above

ground biomass and in the soil (0–90 cm) at harvest

ranged from 72% to 77% of the applied N in the

CONV system (Table 6). Fertilizer N loss through

leaching was negligible during two growing seasons

(2002, 2003). Our soil sampling strategy did not

account for fertilizer N present in the root biomass at

crop harvest. However, an estimate of fertilizer N

recovery in the root biomass obtained using a root to

shoot ratio of 0.145 for corn (Anderson 1988) and

0.229 for winter wheat (Bolinder et al. 1997), and

measured total N% and fndff in corn stalk and wheat

stubble in each year, indicated that around 2–4% of

fertilizer derived N may be accounted in the root

biomass in the CONV system (Table 6). Thus, about

22% (33 kg N ha�1) of applied N for corn and 24%

(22 kg N ha�1) of applied N for winter wheat were

unaccounted at the end of each growing season in the

CONV system (Table 6). In comparison, unaccounted

fertilizer N loss during the growing season in the BM

system was 2–6% of applied N (1–3 kg N ha�1) for

corn and winter wheat. Unaccounted losses of

residual fertilizer N during the non-growing season

were on average about 5% of the fertilizer N applied

to the preceding crop (Table 6).

Reviewing 15N labeled fertilizer N studies,

Peoples et al. (1995) reported unaccounted losses in

the range of 14–58% of applied N to corn and 7–40%

of applied N to wheat in a wide range of environ-

Nutr Cycl Agroecosyst (2007) 79:141–159 155

123

Table 6 Fertilizer nitrogen (FN) balance for corn and winter wheat phases of the experiment under conventional (CONV) and best

management (BM) systems

Year (crop) CONV BM

kg ha�1 % of applied kg ha�1 % of applied

2000/2001 (corn) GSa FN input +b 150.0 50.0

Uptake in corn above ground biomass – 35.8 23.9 32.4 64.8

Residual FN at harvest (mineral) � 33.8 22.5 3.7 7.4

Residual FN at harvest (organic) � 45.5 30.3 8.6 17.2

Estimated FN recovery in root biomassc � 3.5 2.3 2.5 5.0

Unaccountedd � 31.4 21.0 2.8 5.6

NGS Residual FN at harvest (mineral) + 33.8 3.7

Residual FN at harvest (organic) + 45.5 8.6

Residual FN after spring thaw (mineral) � 7.8 5.2 1.2 2.4

Residual FN after spring thaw (organic) � 49.2 32.8 6.1 12.2

Loss by leaching � 9.5 6.3 0.6 1.2

Unaccounted � 12.8 8.5 4.4 8.8

2002/2003 (winter wheat) GS FN input + 90.0 60.0

Uptake in wheat above ground biomass � 40.3 44.8 36.5 60.8

Residual FN at harvest (mineral) � 0.6 0.7 0.4 0.7

Residual FN at harvest (organic) � 23.6 26.2 18.1 30.2

Estimated FN recovery in root biomass � 3.6 4.1 3.1 5.1

Loss by leaching � 0.1 0.1 0.0 0.0

Unaccounted � 21.8 24.1 1.9 3.2

NGS Residual FN at harvest (mineral) + 0.6 0.4

Residual FN at harvest (organic) + 23.6 18.1

Residual FN after spring thaw (mineral) � 0.5 0.6 0.5 0.8

Residual FN after spring thaw (organic) � 19.6 21.8 15.2 25.3

Loss by leaching � 0.3 0.1 0.1 0.2

Unaccounted � 3.8 4.2 2.7 4.5

2003/2004 (corn) GS FN input + 150.0 60.0

Uptake in corn above ground biomass � 60.4 40.2 34.5 57.5

Residual FN at harvest (mineral) � 8.3 5.5 2.0 3.3

Residual FN at harvest (organic) � 40.3 26.9 18.4 30.7

Estimated FN recovery in root biomass � 5.7 3.8 4.0 6.7

Loss by leaching � 0.1 0.1 0 0.0

Unaccounted � 35.2 23.5 1.1 1.8

NGS Residual FN at harvest (mineral) + 8.3 2.0

Residual FN at harvest (organic) + 40.3 18.4

Residual FN after spring thaw (mineral) � 4.9 3.3 2.2 3.7

Residual FN after spring thaw (organic) � 37.7 25.1 16.1 26.8

Loss by leaching � 4.0 2.7 0.7 1.2

Unaccounted � 2.0 1.3 1.4 2.3

a GS: growing season (May to October), NGS: non-growing season (November to April)b Positive and negative symbols indicate inputs and outputs, respectively, for the fertilizer N balance for the period consideredc FN recovery in root biomass was estimated using a root : shoot ratio of 0.145 for corn (Anderson 1988) and 0.229 for winter wheat

(Bolinder et al. 1997) and total N% and fdnff for corn stalk and wheat stubble in each yeard Nitrate leaching was not measured in 2000 growing season. Unaccounted FN during this period may include leaching losses

156 Nutr Cycl Agroecosyst (2007) 79:141–159

123

ments. Our values for unaccounted losses during the

growing season fall within these estimates. In studies

cited by Peoples et al. (1995), labeled fertilizer

derived N pools in the soil and plant had been

determined and the unaccounted fertilizer N was

attributed to leaching, NH3 volatilization and deni-

trification. Leaching losses of fertilizer N were

accounted in our experiment, therefore unaccounted

losses can be attributed to losses through gaseous N

forms. Measurements of N2O emissions were carried

out for the entire experimental period in this exper-

iment using micrometeorological methods (reported

in Wagner-Riddle et al. 2007). Although, the sources

of N2O fluxes (fertilizer N vs. soil derived N) were

not determined, annual mean N2O emissions were

decreased significantly from 2.43 kg N ha�1 in the

CONV system to 1.82 kg N ha�1 in the BM system in

the first phase of corn and from 2.68 kg N ha�1 in the

CONV system to 2.18 kg N ha�1 in the BM system in

the second phase of corn (Wagner-Riddle et al. 2007).

During the winter wheat phase, total N2O emissions

were decreased from 3.32 kg N ha�1 in the CONV

system to 0.89 kg N ha�1 in the BM system. Of the

total gaseous losses associated with denitrification,

only a small proportion (<0.1–7% of fertilizer N

applied) is generally detected in the form of N2O

(major proportion being N2 gas) (Mosier et al. 2002).

Assuming measured N2O emissions represented

approximately 5% of total denitrification loss gives

an estimate of N2 loss ranging from 46 to

63 kg N ha�1, suggesting denitrification could be

the dominant mechanism for fertilizer N loss in our

study.

Conclusions

BMPs that involved applying fertilizer N according to

soil N reserves and matching N supply with crop

demand by timing of application, combined with no-

tillage led to equal or greater grain yields in a corn–

soybean–winter wheat rotation comparative to con-

ventional management practices that involved inten-

sive tillage and application of general yield goal

based N rates for corn and wheat.

Nitrogen mineralized from soil organic matter

contributed the majority of plant N uptake in corn and

winter wheat, with BM system indicating relatively

higher utilization of N (70–80%) from this source

comparative to CONV system (67–70%). Use of

judicious N rates in synchrony with crop N demand

resulted in considerable improvement in FNUE in the

BM system (61% of applied vs. 35% of applied in the

CONV system) over corn and wheat years, with

concurrent reductions in unaccounted gaseous losses

of fertilizer N, from 27% of applied in the CONV to

8% of applied in the BM system. Averaged over corn

and wheat years, BM led to 40% reductions in N2O

emissions compared with emissions under CONV

practices.

Cumulative NO3-N leaching loss over a 4-year

period was decreased by about 50%, from

133 kg N ha�1 in the CONV system to

68 kg N ha�1 in the BM system. About 70% of the

total NO3 leaching loss occurred during corn years

with fertilizer N directly contributing 11–16% of

leaching in the CONV system and less than 4% in the

BM system. Higher soil derived N leaching loss in

the CONV system, which occurred mostly (about

80%) in the non-growing season (November to April)

was due to significantly higher (45–69%) soil derived

mineral N left in the soil at crop harvest, and due to

on-going N mineralization during the period from

crop harvest to soil freeze-up.

Acknowledgements Primary funding for this research was

provided by the Ontario Ministry of Agriculture and Food

(OMAF) and the Canadian Foundation for Climate and

Atmospheric Sciences (CFCAS). Sean Shaw, J.P. Bezeau,

and Karen Clark provided invaluable field and laboratory

assistance.

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