The nitrogen balance of three long-term agroecosystems on a boreal soil in western Canada

Agriculture, Ecosystems and Environment 127 (2008) 241–250

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The nitrogen balance of three long-term agroecosystems on a boreal soil in western Canada S.M. Ross a, R.C. Izaurralde b,*, H.H. Janzen c, J.A. Robertson d, W.B. McGill e a

University of Alberta, Edmonton, Alta., Canada T6G 2E1 Joint Global Change Research Institute, 8400 Baltimore Avenue, Suite 201, College Park, MD 20740-2496, USA c Lethbridge Research Centre, Agriculture and Agri-Food Canada, 5403 1st Avenue South, Lethbridge, Alta., Canada T1J 4B1 d Department of Renewable Resources, 4-42 ESB, University of Alberta, Edmonton, Alta., Canada T6G 2E3 e College of Science and Management, 3333 University Way, University of Northern British Columbia, Prince George, BC, Canada V2N 4Z9 b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 7 September 2007 Received in revised form 14 February 2008 Accepted 15 April 2008 Available online 6 June 2008

Nitrogen (N) budgets can be used to quantify the flows of N in agroecosystems and to account for differences in losses and retention of N. The objective of our study was to develop 24-year N budgets for three diverse cropping systems on a boreal soil at Breton, Alberta, Canada: AER – an agroecological 8-year rotation, with N inputs from legumes [fababean (Vicia faba L.), red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.)] and manure; CF – a continuous perennial grass–legume forage system, with N inputs from fertilizer (18 kg N ha1 yr1) and white clover (Trifolium repens L.); and CG – a continuous annual grain system, with N fertilizer (90 kg N ha1 yr1). We were able to compile detailed N budgets, demonstrate accumulation of soil N, and attribute differences in N flow and permanence to treatment effects. For AER and CG, net inputs almost exactly matched gains in soil N. The AER system had the highest N flow and the largest net N accumulation. Soil total N mass to 30 cm depth increased in all systems during 1980–2005, but increases were smaller in CG (0.59 Mg N ha1) than in AER (1.90 Mg N ha1) and CF (1.63 Mg N ha1), showing the effect of legumes, perennial species, and manure in the latter systems. The proportion of total N inputs retained as soil N with organic N inputs in AER (44%) was about twice that with synthetic N fertilizer in CG (23%). The CF system had the lowest productivity and the least N loss to the environment (4 kg N ha1 yr1, compared to 28 for AER and 24 for CG). The proportion of N inputs lost to the environment was 16% for AER and 24% for CG. In CF, gains of soil N exceeded apparent net N inputs, perhaps because we under-estimated N inputs from clover. Estimate of legume N input was one of the larger sources of uncertainty. The study affirmed the value of N budgets in evaluating agroecosystem performance, and identified AER and CF as productive and sustainable systems due to their minimal reliance on external N inputs and small N losses to the environment. ß 2008 Elsevier B.V. All rights reserved.

Keywords: Nitrogen budget Nitrogen balance Long-term experiments Cropping systems Soil nitrogen Biological nitrogen

1. Introduction The management of N in agroecosystems involves a delicate balance: adding enough N to optimize yields, but avoiding costly surpluses that ‘leak’ into air and water. Globally, the efficiency of fertilizer N is about 50% (Smil, 1999; Eickhout et al., 2006) and in Canada, too, fertilizer efficiency is often not more than 50–60% (Janzen et al., 2003). Nitrogen budgets are sensitive indicators of agroecosystems performance and environmental influence (Watson and Atkinson, 1999; Oenema et al., 2003), especially when applied to long-term sites, which allow the slow changes in soil N to be measured

* Corresponding author. Tel.: +1 301 314 6751; fax: +1 301 314 6760. E-mail address: [email protected] (R.C. Izaurralde). 0167-8809/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2008.04.007

(Campbell and Zentner, 1993; Nyborg et al., 1995a,b). More results from long-term experiments are needed to understand how surpluses of N may be partitioned between N losses and soil N gains, or how deficits of N may impact soil N reserves. The long-term Hendrigan experiments on a boreal soil in Alberta, Canada offer a valuable resource for the study of N balances. These plots were named for Lou Hendrigan, a farmer who pioneered forage production and forage-livestock systems in the Breton region. Hendrigan, who advocated that boreal soils be used primarily for perennial forages, is said to have advised beginning farmers: ‘‘Don’t spend money on expensive equipment – put power in the soil not on it’’ (Provincial Archives of Alberta, 1978). The Hendrigan Plots were established in 1980 to compare crop productivity and changes in soil properties among three cropping systems: continuous perennial forage, continuous annual cash cropping, and an 8-year agroecological rotation with N provided by

1-cut of hay; fall plough down

Brome-alfalfa forage

Brome-alfalfa forage 2-cuts of hay

7

8

legumes and manure. After 9 years, there was evidence of increased total soil N, available N, microbial biomass, and counts of fungi and mycorrhizas in the agroecological rotation compared with the continuous barley (Hordeum vulgare L.) system (Wani et al., 1991a,b, 1994a,b). As well, mean barley yields were 16–19% higher in the agroecological rotation than in the continuous barley system (Wani et al., 1994b). These plots provide an opportunity to assess how the N dynamics of a system are affected by factors such as biological or synthetic sources of N, annual or perennial cropping, and crop diversity. Thus, the objective of our study was to use N budgets to discover how 24 years of continuous management of three diverse boreal agroecosystems affected their N-yield productivity, soil-N balance, and impact on the environment.

Brome-red clover forage 1-cut of hay; fall plough downc

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250

Brome-red clover forage 2-cuts of hay

242

d

Grain harvest Management

Barley in Years 1–4 was harvested for grain, with straw returned and incorporated into soil. Year 5 barley was removed without return of straw. Fababean whole-plant biomass was ploughed down as green manure. In Year 8, forage is allowed to regrow after first cut of hay, then it is terminated with herbicide and ploughed down at the end of the growing season. Fababean was ploughed down in 2000, and harvested as silage in 2001–2005. c

b

Grain harvest Plough down or silaged Grain harvest

Barley

Grain harvest Management

Crop 2000–2005

a

Brome-alfalfa forage 2-cuts of hay Barley under-seeded to forage Harvest as silage Barley Fababean Barley

Plough down

Barley 1980–1999

Crop

a

Fababean

b

Grain harvest

Plough down

Barley under-seeded to forage Grain harvesta Fababean

4 3 2 1

Year of rotation Years

Table 1 Description of the 8-year agroecological rotation (AER) at Breton, Alberta for 1980–2005

The Hendrigan Plots, established in 1980, include three cropping systems: (i) CF: a continuous perennial grass–legume forage system, (ii) CG: a continuous grain (barley) system, and (iii) AER: an agroecological 8-year rotation. The systems were chosen to augment the Breton Classical Plots (Izaurralde et al., 2001), to allow for testing of five distinctly different cropping systems. The long-term cropping systems at Breton differ in use of annual and perennial crops, sources of N, inclusion of legumes, and use of fallow. The Hendrigan Plots include 15 plots (each 31.6 m  8.53 m – three of CG, four of CF and eight of AER rotation) in a completely randomized design. Annual crops are planted with conventional tillage methods, with plots generally cultivated once in spring and once in fall. Lime was added periodically when pH fell below 6.0. The area was part of the fiveyear cereal–forage rotation of the Breton Classical Plots from 1939 to 1971. During that period, it received essentially no N fertilizer and, depending upon the particular plot, low amounts of P (5 kg ha1) and moderate amounts of S (8 kg ha1). From 1972 to 1979, the area was mainly in commercial barley production or bare fallow (twice), with varying fertilizer applications averaging approximately 10 kg N ha1 yr1, 5 kg P ha1 yr1, and 3 kg S ha1 yr1, over the 8 years. In the CF system, developed by L. Hendrigan, plots were seeded to a mixture of creeping red fescue (Festuca rubra L.), tall fescue (Festuca arundinacea Schreb.) and white Dutch clover (Trifolium repens L.) in 1981. Plots annually received fertilizer of NPS at 18–9–16 kg ha1 and periodic broadcasts of white clover seed (1 kg ha1). The forage was cut twice annually for hay. The CG system received fertilizer N at 90 kg N ha1 yr1 along with PKS at 22–46–5.5 kg ha1. After harvest of grain, the straw was returned and incorporated into the soil. The 8-year rotation of the AER system, described in Table 1, included barley, fababean (Vicia faba L.), red clover (Trifolium pratense L.), bromegrass (Bromus inermis Leyss.), and alfalfa (Medicago sativa L.). This system was designed to have N inputs from biological sources of legumes and manure rather than synthetic N fertilizer. Rates of cattle manure N additions, listed in Table 2, were based on a conceptual loop where the grain and

5

2.1. Experimental design

Barley

6

The Hendrigan Plots, of the University of Alberta, are located near Breton, Alberta (538070 N, 1148280 W)(long-term means (1951–1980) – annual precipitation: 547 mm; annual temperature: 2.1 8C; frost free days: 80; degree days >5 8C: 1060 (Canadian Climate Program, 1982)). The soil, with slope of 0–3%, is an Orthic Gray Luvisol (Albic Luvisol in FAO Soil taxonomy; Typic Cryoboralf in US Soil Taxonomy) developed on glacial till parent material under boreal forest vegetation. Gray Luvisols have low fertility status and may have excess acidity (Robertson and McGill, 1983).

Brome-red clover forage 2-cuts of hay

2. Materials and methods

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250 Table 2 Rates of cattle manure N (kg N ha1) added to the agroecological rotation (AER) at Breton, Alberta from 1980 to 2005a Year

Manure N added

Year

Manure N added

Year

Manure N added

1980 1981 1982 1983 1984 1985 1986 1987 1988

24.6 30.6 29.7 55.7 63.0 61.9 65.3 50.2 42.3

1989 1990 1991 1992 1993 1994 1995 1996 1997

23.8 44.0 36.6 42.9 44.0 52.2 – 49.8 14.4

1998 1999 2000 2001 2002 2003 2004 2005 Mean

42.0 16.9 27.6 27.6 121.6 74.5 48.1 76.9 46.6

a

Rates of N applied are based on the total area of the rotation.

forage from the plots would be fed to livestock and 70% of the N would be returned in manure (Haynes and Williams, 1993). Additions of manure were made to the following plots (‘‘Year’’ = rotation phase): Years 1, 3 and 8 in fall 1980; Year 8, following plough down of the forage, in fall 1981–1994; Year 1 (barley following forage) in spring 1996–2005; and Years 2, 4 and 5 in spring 2002–2005. Changes to the AER system in 2000 (reduced legume inputs and increased manure inputs) were intended to simulate better an integrated grain–forage–livestock agricultural ecosystem. All AER plots received PKS fertilizer at 22–46– 5.5 kg ha1 yr1. 2.2. Data collection and analysis Annual crop yields were derived from hand-harvesting of four to six 1 m2 areas in each plot. Hay and silage yields were determined using a small forage harvester to cut an area of approximately 6 m2 in each plot. The percentage of grass, legume and weeds in mixtures, by dry weight, was determined by handsampling of Cut 1. Legume content was not measured in Cut 2 of forages. All forage and crop yields are expressed on a dry-weight basis determined at 60 8C. The extent of plant sample analysis varied over 1982–2005, but plant N data was available for most treatments in most years. Generally, dried plant material was ground, digested in concentrated H2SO4 and H2O2 and analyzed for total N content using a Technicon Autoanalyzer (Technicon, 1977). Where gaps occurred in plant N data, treatment means

243

were used in calculations. Analysis of variance was performed on yield data with Proc Mixed of SAS (Statistical Analysis Systems Institute Inc., Cary, NC), using repeated measures and assumed linear trends for treatment means across time (Loughin, 2006). Significant differences were determined at a = 0.05 level of probability. Soil samples for three depths were analyzed for N, with two samples per plot for 1980 and one composite sample per plot for 2005. Each 2005 composite sample was from four soil cores, 6.5 cm diameter, collected between rows. Analysis of soil total N concentration was by combustion gas chromatography (Carlo Erba Inc., Milan, Italy), and expressed on the basis of equivalent mass (Ellert and Bettany, 1995), using bulk density determined by the core method at sampling. The reference soil mass used was 195 kg m2 for depth to 15 cm and 423 kg m2 for depth to 30 cm, based on mean mass values in 1980. The N concentration of the adjusted mass was assumed equal to the average of the N concentration above and below the selected depth. Analysis of variance was performed using SAS Proc Mixed. 2.3. Approach to N budget The N budget approach used in this study is a plant–soil system balance (Fig. 1). All of the N inputs and losses listed in Fig. 1 were estimated for three cropping systems by using 25 years of data and literature-based assumptions. The N inputs from fertilizer, manure, and seeds, and N removals from harvest were from methods and data. Estimates of N inputs from symbiotic N-fixation in legumes were based on data for above-ground biomass yields, percentage of legumes in mixtures, and N content of legumes, together with assumptions for the proportion of N derived from the atmosphere and below-ground plant N. Assumed values for N budget calculations were based on other research at Breton, studies in Canada, and other relevant literature (Table 3). Assumed annual atmospheric N deposition was based on estimates for sites remote from industrial activity. Below-ground N inputs of fababeans in AER were based on the research of Khan et al. (2002, 2003). They recommended using 34% as a default for the amount of below-ground N of fababeans, based on a number of detailed studies. Amounts of below-ground N of fababean, as a proportion of total N, were 11% by soil 15N dilution, 13% by physical recovery, 30% by mass N balance, 33% by 15N balance, and 39% by shoot 15N labelling. The relatively low estimates of below-ground

Fig. 1. Schematic representation of the components of the plant–soil system and inputs and outputs of N (solid lines with arrows) for the N budget of the Hendrigan Plots. The boundary line represents an arbitrary soil depth of 30 cm for the system. Dotted lines represent transfers among components within the system.

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250

244

Table 3 Literature-based assumptions for nitrogen (N) budgets for three cropping systems at Breton, Alberta N budget parameters

Value used

N additions N deposition from atmosphere (kg N ha1 yr1)

5

Probable range

Method a

Location/ scope

Notes/relevance

Reference

LR

Canada-wide

Average for Canadian farms remote from industrial activity

Janzen et al. (2003)

5–10 1–2 8 12 15

LR M M LR LR

NW Alberta Breton SE Norway NE Scotland NE USA

65–80 85 60–90

M M LR

Breton S Alberta Europe

N isotope dilution method N isotope dilution method Predictive software for fababean N fixation

Gu (1988) Rennie and Dubetz (1986) Reining (2005)

80

LR

Global

70–90 65–85 70–95 95

M LR M LR

Breton NW Alberta West Canada Temperate climate

Average for perennial forage legumes Red and white clover Red clover Alfalfa in mixtures with brome Modelling, clovers with grasses for hay

Carlsson and Huss-Danell (2003) Ross (1999) Soon and Clayton (2003) Chen et al. (2004) Hogh-Jensen et al. (2004)

11–39

M

Greenhouse experiments

Several methods including labelling

43

LR

Canada-wide

Bolinder et al. (2007)

45

LR

Temperate zones

LR

Global

Forage legumes – C to roots and rhizodeposition Red clover and alfalfa in mixtures – N below-ground Alfalfa and clovers – N to roots

43

LR

Canada-wide

Bolinder et al. (2007)

31–49

LR

Temperate zones

Forage legumes – C to roots and rhizodeposition White clover – below-cutting height N

LR LR LR

NE Scotland NE USA

Watson and Atkinson (1999) Drinkwater et al. (1998) Paustian et al. (1990)

<0.8

LR

SE Norway

Assumed for local area Assumed for local area Suggested for temperate regions Assumed negligible

10 7 9 13

LR LR LR LR

Canada-wide SE Norway NE Scotland Global

Average for Canadian farmland Assumed losses from fertilizer Assumed losses from manure Estimated average for fertilized soils

Janzen et al. (2003) Korsaeth and Eltun (2000) Watson and Atkinson (1999) Barton et al. (1999)

5

LR

Canada-wide

5% of fertilizer N, 30% of soluble manure N

Janzen et al. (2003)

0+

M

Breton

Izaurralde et al. (1995b)

10

LR

Canada-wide

Nitrate-N to 390 cm depth in Hendrigan Plots Average for Canadian farmland

20–24

LR

Global

Crews and Peoples (2005)

14–54

M

West Canada

24

M

West Canada

<15

M

Central Sweden

Means for legume residues – irrigated and dryland Losses from legume green manures Lentil green manure losses over 6 weeks Losses from alfalfa

M

SE Norway

Comparable cropping systems and environment

Korsaeth and Eltun (2000)

Values in literature

2–10 5

Legumes: N derived from the atmosphere (%) Fababean 75

Clovers and alfalfa

80

Soon and Clayton (2003) Nyborg et al. (1995b) Korsaeth and Eltun (2000) Watson and Atkinson (1999) Drinkwater et al. (1998)

N in precipitation Dry and wet deposition

65–90 15 15

70–95

Legumes – below-cutting-height N as % of total plant N (%) Fababean 34 30–39

Red clover and alfalfa

40

45

5

Non-symbiotic N fixation (kg N ha1 yr1)

10

Volatilization from fertilizer and manure (%)

5

Leaching from manure and fertilizer (%)

0–10

Gaseous and leaching from legume residue inputs (%)

10–20

1

Surface run-off losses (kg N ha

1

yr

)

0–1.5

LR, literature review; M, measured.

Hogh-Jensen et al. (2004) Carlsson and Huss-Danell (2003)

Hogh-Jensen et al. (2004)

0–7

Korsaeth and Eltun (2000)

5–15

2–10

0–15

Janzen et al. (2003)

10–30

Janzen et al. (1990) Bremer and VanKessel (1992) Paustian et al. (1990)

0–3 1.5–2.2

a

Khan et al. (2002, 2003)

30–50

5 5 <10

N losses Denitrification from manure and fertilizer (%)

N

30–45

6–64

White clover

15

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250 Table 4 Annual biomass yields of above-cutting-height DM and N for three cropping systems at Breton, Alberta (mean 1982–2005)a Cropping system AER Total biomass DM yield (Mg ha1 yr1) Total N yield (kg N ha1 yr1)

7.40 (0.30) a

CF 3.60 (0.33) b

Table 5 Sources of variation for soil total N concentration, bulk density, and total N mass for three cropping system treatments (TRT) and two sampling years (YR) of 1980 and 2005 at Breton, Alberta Soil parameter

CG

Source

7.05 (0.35) a Total N concentration

142 (4.7) a

62 (5.5) c

91 (6.1) b Bulk density

Values within a row followed by different letters are significantly different at p < 0.05. a AER, agroecological rotation; CF, continuous fescue-clover; CG, continuous grain; DM, dry matter; N, nitrogen; standard error of mean in parentheses.

245

Total N equivalent mass

Depth

TRT

YR

TRT  YR

0–15 15–30 0–15 15–30

*** ns ns ns

*** *** * t

** ns ns ns

0–15 0–30

*** **

*** ***

** *

ns, not significant; *, **, ***, significantly different at p < 0.05, 0.01 and 0.001, respectively; t, p value = 0.06.

N based on physical recovery of roots were consistent with findings by Gu (1988) for fababeans at Breton of 18–22 kg N ha1 in roots and 183–199 kg N ha1 in above-ground growth. The assumption of negligible leaching losses in the continuous perennial system (CF) was based on research by Izaurralde et al. (1995b). Their measured total mass of NO3–N (kg N ha1) in soil sampled to 390 cm depth in 1993 was 0 in CF, 29 in AER and 40 in CG. Surface run-off N losses from CF were also assumed negligible due to perennial cover and minimal additions of fertilizer N. Korsaeth and Eltun (2000) reported less N run-off from forage systems than from annual crop systems. Surface run-off N losses from AER and CG were based on those reported by Korsaeth and Eltun (2000), but somewhat less due to reduced slope and N input. 3. Results and discussion 3.1. Productivity The AER system, which relied on legumes and manure for N, had the highest above-cutting-height biomass and N yield (protein yield) of the three systems (Table 4). Yields in the CF system were lowest – about half those in the other systems. The CG system had DM yields similar to AER, but lower N yields because of the high N yields of fababeans and grass–legume hay in the latter.

3.2. Soil changes The effects of cropping system treatment (TRT) and time period from 1980 to 2005 (YR) were significant for soil total N content (Table 5). Effects of YR were significant for soil bulk density. Effects of TRT and TRT  YR interaction on soil total N concentration were significant for 0–15 cm soil depth but not for 15–30 cm depth. Data from 1980 provided the baseline for measuring changes in soil (Table 6). Soil bulk density, total N concentration and total N mass varied somewhat among plots in 1980, but differences were not significant. In 2005, the concentration and mass of soil total N at depth 0–15 cm were greater in AER than in CF or CG, and the mass of total N to depth 30 cm was greater in AER than in CG. In all treatments, the increase in soil total N mass was greater in the 0– 15 cm layer than in 15–30 cm. From 1980 to 2005, bulk density decreased by 3–9% in 0–15 cm and 6–9% in 15–30 cm depth, while total N concentration increased by 21–68% in 0–15 cm and 38–61% in 15–30 cm depth. Nitrogen concentrations in the subsoil (below 30 cm) changed little, perhaps increasing slightly. In 1980, soil N concentrations at about 30–55 cm averaged 0.46 g N kg1 with mean bulk density of 1.53 Mg m3 (data not shown). In 2005, N concentrations

Table 6 Soil bulk density, total N concentration, total N equivalent mass, and increase in total N mass over 25 years for three cropping systems at Breton, Albertaa Soil parameter

Depth (cm)b

Year

Cropping system AER

Bulk density (Mg m3)

0–15 15–30

Total N concentration (g N kg1)

0–15 15–30

Total N equivalent mass (Mg N ha1)c

0–15 0–30

Significance CF

CG

p value

1980 2005 1980 2005

1.30 1.18 1.54 1.40

(0.03) (0.02) (0.06) (0.01)

1.30 1.20 1.49 1.40

(0.04) (0.03) (0.08) (0.01)

1.31 1.27 1.52 1.44

(0.04) (0.03) (0.10) (0.02)

0.940 0.080 0.880 0.160

1980 2005 1980 2005

1.43 2.41 0.55 0.84

(0.07) (0.10) a (0.02) (0.06)

1.33 1.97 0.53 0.86

(0.10) (0.14) b (0.03) (0.08)

1.34 1.62 0.52 0.72

(0.12) (0.16) b (0.03) (0.09)

0.620 0.003 0.580 0.470

1980 2005 1980 2005

2.89 4.54 4.34 6.24

(0.13) (0.17) a (0.14) (0.25) a

2.72 3.76 3.94 5.57

(0.19) (0.24) b (0.20) (0.36) ab

2.75 3.13 4.13 4.73

(0.22) (0.27) b (0.23) (0.41) b

0.730 0.002 0.290 0.020

1.65 (0.10) a 1.90 (0.19) a

0.39 (0.17) c 0.59 (0.32) b

<0.001 0.010

Increase in N mass over 25 years (Mg N ha1)

0–15 0–30

1980–2005

Annual increase in N mass (kg N ha1 yr1)

0–15 0–30

1980–2005

66.1 (4.1) 75.9 (7.8)

1.04 (0.15) b 1.63 (0.27) a 41.7 (5.8) 65.0 (11.0)

15.4 (6.8) 23.6 (12.6)

Values within a row followed by different letters are significantly different at p < 0.05. a AER, agroecological rotation; CF, continuous fescue-clover; CG, continuous grain; N, nitrogen; standard error of mean in parentheses. b Soil depths are approximate: samples taken in 1980 were by horizon; calculation of total N mass was by equivalent mass not equivalent depth. c Reference soil mass for calculation of total N equivalent mass was 195 kg m2 for depth 0–15 cm and 423 kg m2 for depth 0–30 cm, based on average mass values in 1980.

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250

246

Table 7 Annual inputs and outputs of N for three cropping systems at Breton, Alberta over 24 years (mean 1982–2005)a Cropping system AER (kg N ha1 yr1) N inputs Deposition from atmosphere

5.0

Legume symbiotic N fixation – in biomass above-cutting-height Fababeans Forage legumes – clover and alfalfa Legume symbiotic N fixation – below-cutting-height Fababeans Red clover and alfalfa White clover Non-symbiotic N fixation Manure Fertilizer Seed

CF (kg N ha1 yr1)

5.0

CG (kg N ha1 yr1)

5.0

b

33.3 36.5

14.6

c

17.2 24.4 11.9 5.0 47.6 0 2.8

5.0 0 17.5 ngb

5.0 0 91.1 1.7

171.8

53.9

102.8

70.2

30.8

58.2

Gaseous losses Denitrification from manure and fertilizer Volatilization from manure and fertilizer Gaseous losses of fixed N from legume residues

4.8 2.4 7.5

1.7 0.9 1.2

9.1 4.6

Leaching lossesf Leaching from manure and fertilizer Leaching losses of fixed N from legume residues

4.8 7.5

ngb ngb

9.1

Surface run-off lossesg

1.0

ngb

1.5

Total N outputs

98.0

34.6

82.5

Totals N balance: inputs minus outputs Increase in total soil N in 0–30 cm depth Difference/unaccounted for N

73.8 75.9 2.1

19.3 65.0 45.7

20.3 23.6 3.3

Total N inputs N outputs (removed or lost) N exported in product/crop d e

a

AER, agroecological rotation; CF, continuous fescue-clover; CG, continuous grain; N, nitrogen; ngb, negligible. Assumptions used in calculations are listed in Table 3. Assumes 75% of N was derived from the atmosphere for fababeans and 80% for clover and alfalfa. c Below-cutting-height legume N could include bases of stems, stolons, roots and exudates. Estimate assumes that below-cutting-height N as percentage of total plant N was 34% for fababeans, 40% for red clover and alfalfa, and 45% for white clover. d Assumes incomplete removal of crop N: 85% for AER, 50% for CF and 95% for CG, based on potential crop N exports of 83, 62 and 61 kg N ha1 yr1, respectively. e Gaseous losses assume: 10% denitrification loss from manure and fertilizer, 5% volatilization loss from manure and fertilizer, and 10% loss of fixed N from legume residue inputs. f Leaching losses assume: CG > AER > CF, with negligible for CF, with maximum of 10% of N applied in manure & fertilizer, and 10% of fixed N from legume residue inputs. g Surface losses assume: CG > AER > CF, with negligible for CF. b

(g N kg1) at 30–45 cm were 0.53 for AER, and 0.50 for CF and CG (mean bulk density = 1.44 Mg m3), while at >45 cm, they were 0.48 for AER, 0.45 for CF and 0.46 for CG. The soil N increases in AER and CF were higher than in many studies of long-term experiments, but less than increases of 90 kg N ha1 yr1 over 10 years reported by Poudel et al. (2001) for an organic 4-year rotation in California with legumes and additions of manure. Soil N increases in CG were comparable to those of Nyborg et al. (1995a), but contrasted with declines in soil N for some conventional systems of continuous annual cropping fertilized with synthetic N (Campbell and Zentner, 1993; Drinkwater et al., 1998). Changes in soil N are influenced by crop management, but also by the initial N-status of soils. It is more difficult to increase the N levels of soils that are already high in N, than soils with low-N status such as those at Breton. Soil N increases in AER and CF demonstrated the benefits of organic N inputs and extended soil-cover. Findings were consistent with other studies showing positive impacts on soil N stores and system N balances with additions of: forage legumes (Paustian et al., 1990), fall-seeded cereals (Campbell and Zentner, 1993), manure additions (Rasmussen and Parton, 1994), reduced tillage and grass cover (Rasmussen et al., 1998), organic N inputs from

legumes and manure (Drinkwater et al., 1998; Poudel et al., 2001; Kramer et al., 2002), forages (Korsaeth and Eltun, 2000), legume green manure (Soon and Clayton, 2003), and some grasses (Al-Kaisi et al., 2005). Izaurralde et al. (1993) tested the relationship between soil N (0–15 cm) and various management factors for cropping systems at Breton, including the Hendrigan Plots. Use of legumes, manure and fertilizer N all affected soil N, but the most important factor was the fraction of a rotation occupied by a legume crop. 3.3. N budget Detailed accounting of N inputs and N removals/losses was compiled in the form of N budgets for AER, CF and CG cropping systems (Table 7). The inputs from symbiotic N fixation by legumes largely reflected biomass yields and percentage of legumes in forage mixtures. For red clover, alfalfa and white clover grown in mixtures with grasses, the mean percentage of legumes in Cut 1 of mixtures was 62% for AER and 15% for CF, by dry weight. The same legume content was assumed for Cut 2 of forages. The N yield of the above-cutting-height DM, for the total area of the rotation, was 46 kg N ha1 yr1 for red clover and alfalfa, and 18 kg N ha1 yr1

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for white clover in CF (though the latter may be an under-estimate because sampling excluded the low-growing leaves). Fababeans in the AER rotation had mean above-cutting-height biomass DM yields of 8.02 Mg ha1 with N yields of 203 kg N ha1. For the total area of the AER rotation, the above-cutting-height fababean N yields averaged 44 kg N ha1 yr1 for 1982–2005. Annual inputs of N from seeds were mainly from fababean (4.7% N, assumed) and barley seeds (1.9% N), at seeding rates of 200 kg ha1 for fababeans and 90 kg ha1 for barley. The seeds of bromegrass, red clover and alfalfa seeded in Year 5 of the AER rotation added about 1 kg N ha1. Potential crop N exports (kg N ha1 yr1) were 83 for AER, 62 for CF and 61 for CG, based on subsample yields. Crop exports included: barley grain (not straw) from AER and CG, barley silage in AER, fababean silage from AER in 2001–2005, two cuts of hay from CF and Years 6 and 7 of AER, and one cut of hay in Year 8 of AER. Estimated crop N exports were based on yield data, and assumed actual removal of 85% of grain, forage and silage in AER, 50% of forage in CF, and 95% of barley grain in CG. Differences between subsample yields and actual removals were assumed to be greatest for the cloverfescue forage in CF. Field-scale mowers, used to remove forage overages, had higher cutting height and less effective cutting than occurred with subsampling of CF forage. Hay removal would also be affected by losses from swaths and spoilage. The low-growth habit of white clover in CF could lead to incomplete removal of forage, since much of its growth may be below mower height. Even if cut, the small size and multiple stems of white clover leaves and flowers make them prone to losses from hay swaths. Estimated total leaching losses from AER of about 12 kg N ha1 yr1 compared well with leaching losses measured by others in similar systems: Drinkwater et al. (1998) measured leaching losses averaging 13 kg N ha1 yr1 from two legume-based cropping systems; Korsaeth and Eltun (2000) reported leaching losses of >15 kg N ha1 yr1 for forage-based systems. For AER and CG, increases in soil N to 30 cm were almost equal to the difference between inputs and outputs (Table 7), implying reasonably robust accounting of additions, exports and losses, based on a combination of measured data and literature-grounded assumptions. For the CF system, the N budget was not resolved: the increase in soil N to 30 cm exceeded the difference between total N inputs and outputs by 46 kg N ha1 yr1, indicating that: (i) inputs were under-estimated, (ii) outputs were over-estimated, and/or (iii) soil N increase was over-estimated. Estimates of soil N increase appear to be reasonably sound, given the balanced N budgets for AER and CG. Also, 2003 data for soil N concentrations in CF plots (data not shown) were comparable with the 2005 data used to calculate soil N increases. Plotting soil total N concentration against bulk density appears to fit with an exponential relationship. Over-estimation of the outputs in CF appears unlikely, given their small magnitude. We suspect, therefore, that the N inputs were under-estimated. For example, our estimate of clover yield was likely conservative because of its low-growth habit which prevented effective recovery during sampling. Also, the CF system might be the only one developing an N-litter layer, which was not quantified. The N account for CG was similar to other research at Breton in the observed accumulation of soil N in continuous barley fertilized with synthetic N (Nyborg et al., 1995a,b). Nyborg et al. (1995b) estimated N balances for barley systems with tillage, straw and N fertilizer treatments from 1979 to 1990. Predicted soil N values agreed closely with the difference between fertilizer N inputs and crop N removals, suggesting that other losses and gains must have been in balance. Our estimates in CG, however, suggested that losses from denitrification, leaching and volatilization exceeded gains from non-symbiotic fixation and atmospheric deposition.

247

The N balance for AER differed from N deficits reported in another experiment at Breton for cropping systems relying on organic N (Izaurralde et al., 1995a). In their study of N balances of selected systems from 1989 to 1992, two legume-based rotations had N deficits, with N exported in crops exceeding N imported by legumes. They recommended that further study of such systems should include manure incorporation. Similar to our findings for AER, Drinkwater et al. (1998) and Poudel et al. (2001) reported N surpluses (inputs minus exports) for cropping systems with N provided by legumes and manure. The N surpluses in these systems were mainly accounted for by increases in soil N. They also reported N surpluses for conventional cropping systems fertilized with synthetic N, but soil N had small increase, no increase, or decreased. Few other studies have attempted a comprehensive accounting of N inputs and outputs, with measured changes in soil N. Some N budget studies have predicted changes in soil N, but were unable to substantiate estimates with soil data (Paustian et al., 1990; Korsaeth and Eltun, 2000; Karlsson et al., 2003). Paustian et al. (1990) predicted soil N increases of 30 kg N ha1 yr1 for an alfalfa system and decreases of 10–90 kg N ha1 yr1 for three systems with barley or fescue. No significant differences in total soil N were detected in five years, as the estimated changes were small in relation to the total soil N pool. Korsaeth and Eltun (2000) calculated N balances of 12 to 45 kg N ha1 yr1 for five of six systems, suggesting that crop production occurred at the expense of soil organic N. Changes in soil N were not detectable after 8 years. Karlsson et al. (2003) used simulated changes in soil N ranging from 36 to +45 kg N ha1 yr1 to estimate N budgets for two long-term experiments. They commented that available soil data were too variable to be used in budgets and models. Our study contains a more detailed accounting of N than is found in other cropping system studies with measured soil N changes and interpretation of N balances (Campbell and Zentner, 1993; Rasmussen and Parton, 1994; Nyborg et al., 1995b; Drinkwater et al., 1998; Poudel et al., 2001). In constructing our N budgets, we drew upon a wide range of sources to estimate the component inputs and outputs. Measured changes in soil N served a valuable role in validating the estimates of N inputs, losses and balances for the AER and CG systems. Unlike most previous studies, we were able to compile detailed N budgets, demonstrate conclusively the accumulation of soil N, and ascribe treatment differences to differences in N flow and permanence. The measurable effects reflect, in part, the long duration of the study, and the responsiveness of the Luvisol soil to management influence. Low initial soil N content, lack of major climatic and physical limitations to crop growth, and high yields when adequately nourished, contribute to a high potential for soil N increase at Breton (Janzen et al., 1998). 3.4. The fate of N The estimated total N losses (kg N ha1 yr1) to the environment of about 28 for AER, 24 for CG and 4 for CF were comparable to losses of 9–21 kg N ha1 yr1 measured by Paustian et al. (1990), but were lower than losses reported in some other studies (Watson and Atkinson, 1999; Korsaeth and Eltun, 2000; Berry et al., 2003). The AER system had the highest N flow and largest net accumulation. This system, with N inputs mainly from legumes and manure, had a greater proportion of N retained in soil (44%) and a smaller proportion of N lost to the environment (16%) than CG, which retained 23% of N in soil and lost 24%. Janzen et al. (1990) and Crews and Peoples (2005) also concluded that relative retention of organic N inputs (legumes) as soil N was approximately twice that of synthetic N fertilizer. Greater relative losses to

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Table 8 Nitrogen (N) budget estimates of additions, losses, balances and soil N changes, with high and low range of estimates, for three cropping systems at Breton, Albertaa N budget parameters

AER

CF

CG

Estimate

High

Low

Estimate

High

Low

Estimate

High

Total N additions (kg N ha1 yr1) Difference (kg N ha1 yr1) Difference (%)

172

212 40 23

139 32 19

54

69 15 28

38 16 30

103

110 7 7

95 8 8

Total N removed/lost (kg N ha1 yr1) Difference (kg N ha1 yr1) Difference (%)

98

122 23 24

81 17 17

35

44 9 27

32 3 7

82

98 15 18

69 13 16

N balance – additions minus removals (kg N ha1 yr1)

74

90

58

19

25

6

20

12

26

Increase in total soil N to 30 cm depth  S.E. (kg N ha1 yr1) Difference (kg N ha1 yr1) Difference (%)

76

84 8 10

68 8 10

65

76 11 17

54 11 17

24

36 13 53

11 13 53

Low

a AER, agroecological rotation; CF, continuous fescue-clover; CG, continuous grain. High and low values for N additions: removals and balances were calculated using the highest and lowest values in the probable range for assumptions in Table 3. Soil N data is from Table 5.

the environment from synthetic N fertilizer (CG) than from organic N inputs (AER) was also consistent with Crews and Peoples (2005), who reported mean losses of 33% from fertilizer N and 24% from legume N under dryland conditions. Perennial species would have favoured retention of N in the CF and AER systems. Compared to annual species, perennials maintain deeper, more extensive root systems and have a greater ability to take up soil N over time and space (Entz et al., 2001; Crews and Peoples, 2005). Izaurralde et al. (1995b) concluded that N leaching was negligible in CF, and that AER had less potential for N leaching, as only 35% of the NO3–N occurred below the root zone (below 90 cm), compared with 87% in CG. Paustian et al. (1990) reported that meadow fescue (Festuca pratensis Huds.) fertilized with 200 kg N ha1 showed little evidence of N loss by leaching. Tillage and fallow in association with annual cropping also increases N losses (Rasmussen et al., 1998; Soon and Clayton, 2003). 3.5. Uncertainty associated with N budget calculations Any N budget calculation is subject to the combined effect of all its constituent flows (Watson and Atkinson, 1999; Oenema et al., 2003); thus, the higher the number of estimated parameters, the greater may be the uncertainty (Watson and Atkinson, 1999). In our study, uncertainty did not increase with higher numbers of estimated parameters. The AER system was the most complex of the three systems, and its N budget contained the largest number of estimated parameters, yet the relative uncertainty of the N budget for AER was not greater than that for CF. Using the highest and lowest values in the range of assumed values (Table 3) for N budget calculations produced differences of up to 30% in total additions or removals (Table 8). Legume N inputs in AER and CF constituted a large part of the variation in estimates for those systems. The measure of soil N increase in CG had relatively high uncertainty of 23.6  12.6 kg N ha1 yr1. Making reliable estimates of N losses from systems is difficult because small errors in determining soil total N result in large uncertainties in absolute N amounts (Van Faassen and Lebbink, 1994). Our N budget for the CF system raised questions about N inputs from clover and incomplete removal of hay. The low-growth habit of white clover likely contributed to under-estimation of legume yields. Forage mixtures are inherently variable, and sampling procedures for forage composition were not extensive. Composition data were generally based on one sample per plot, using a hand-grab sample from a swath. The CF data for the legume proportion of Cut 1 ranged from 0% to 57%. Estimates of N fixed by legumes may be the largest source of error in N budgets (Berry

et al., 2003). Our findings, which appear to have under-estimated legume-derived N in CF, may support that contention. Data are commonly available for agronomically-important parameters (e.g., yield) but not usually for soil processes (e.g., mineralization, immobilization and gaseous losses) that, despite their ecological importance, are more difficult to measure (Watson and Atkinson, 1999). Oenema et al. (2003), in a review of nutrient budgets, suggested three classes of uncertainties – Class 1: items with less than 5% uncertainty (e.g., mineral fertilizer); Class 2: items with 5–20% uncertainty (e.g., manure N inputs, atmospheric N deposition and N harvest); and Class 3: items with more than 20% uncertainty (e.g., losses via leaching, run off, volatilization and denitrification). Our assumptions of 5–10% uncertainty for N leaching and gaseous losses would put them in Class 2. It appeared that our N budgets were most sensitive to uncertainty associated with N inputs of legumes and N harvest of forage crops. Modelling exercises could increase understanding of the uncertainties and sensitivities of the various components of budgets. Further research on the N budgets of AER, CF and CG, will be conducted with the EPIC (Environmental Policy Integrated Climate) model, as has been done with other long-term data from Breton (Izaurralde et al., 2006). 4. Conclusions In our study of three cropping systems for the period of 1980– 2005, we were able to compile detailed N budgets, demonstrate accumulation of soil N, and attribute differences in N flow and permanence to treatment differences. Of the diverse systems, CF had the lowest productivity and the lowest amount of N loss to the environment; AER had the greatest production of biomass N. Increases in soil total N mass were: AER = CF > CG. Soil N increases in AER and CF demonstrated the impact of using legumes, perennial species, and manure additions. For AER and CG, net N inputs almost exactly matched gains in soil N, indicating reasonably robust accounting of additions, exports and losses. In CF, gains of soil N exceeded apparent net N inputs, perhaps because we under-estimated N inputs from clover. The AER system (with N from legumes and manure) retained a larger proportion of N inputs in soil and lost a smaller proportion of N to the environment than the CG system (with N from synthetic fertilizer). The AER and CF systems were productive and sustainable, due to minimal reliance on external N inputs and small losses of N to the environment. The Hendrigan Plots provided a number of advantages in the study of N balances: longevity; distinctly different cropping systems; different types of N sources; good records of data;

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archived soil samples; and measurable changes in soil N. The study also benefitted from the wealth of soils and cropping system research that has been conducted in other experiments at the Breton site since 1930. Such long-term studies, emphasizing reliable, repeated soil C and N measurements, with few but clearcut treatments, and consistent analyses of soil samples (Karlsson et al., 2003), are urgently needed to support future modelling efforts that seek to understand how our farm ecosystems respond to management and to coming global changes. Long-term experiments are crucial ‘‘listening places’’ to detect the ecosystem’s pulse, and to help steer us towards permanence (sustainability) (Janzen, 2007). This N budget study highlighted the value of long-term experiments and affirmed the foresight of those who founded and guided the Hendrigan Plots experiment from its inception in 1980. Acknowledgements We are grateful for the contributions of many University of Alberta technical staff who have worked on the Hendrigan Plots over the years, with particular appreciation for Dick Puurveen’s work on the database. We acknowledge the soils data collected by Eric Bremer in 2005, and funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) Postdoctoral Fellowships Program. RC Izaurralde acknowledges the support of the US DOE Office of Science. References Al-Kaisi, M.M., Yin, X.H., Licht, M.A., 2005. Soil carbon and nitrogen changes as influenced by tillage and cropping systems in some Iowa soils. Agric. Ecosyst. Environ. 105, 635–647. Barton, L., McLay, C.D.A., Schipper, L.A., Smith, C.T., 1999. Annual denitrification rates in agricultural and forest soils: a review. Aust. J. Soil Res. 37, 1073–1093. Berry, P.M., Stockdale, E.A., Sylvester-Bradley, R., Philipps, L., Smith, K.A., Lord, E.I., Watson, C.A., Fortune, S., 2003. N, P and K budgets for crop rotations on nine organic farms in the UK. Soil Use Manage. 19, 112–118. Bolinder, M.A., Janzen, H.H., Gregorich, E.G., Angers, D.A., VandenBygaart, A.J., 2007. An approach for estimating net primary productivity and annual carbon inputs to soil for common agricultural crops in Canada. Agric. Ecosyst. Environ. 118, 29–42. Bremer, E., VanKessel, C., 1992. Plant-available nitrogen from lentil and wheat residues during a subsequent growing-season. Soil Sci. Soc. Am. J. 56, 1155– 1160. Campbell, C.A., Zentner, R.P., 1993. Soil organic matter as influenced by crop rotations and fertilization. Soil Sci. Soc. Am. J. 57, 1034–1040. Canadian Climate Program, 1982. Canadian climate normals: 1951–1980. Atmospheric Environment Service, Environment Canada, Downsview, Ontario. Carlsson, G., Huss-Danell, K., 2003. Nitrogen fixation in perennial forage legumes in the field. Plant Soil 253, 353–372. Chen, W., McCaughey, W.P., Grant, C.A., 2004. Pasture type and fertilization effects on N-2 fixation, N budgets and external energy inputs in western Canada. Soil Biol. Biochem. 36, 1205–1212. Crews, T.E., Peoples, M.B., 2005. Can the synchrony of nitrogen supply and crop demand be improved in legume and fertilizer-based agroecosystems? A review. Nutr. Cycl. Agroecosyst. 72, 101–120. Drinkwater, L.E., Wagoner, P., Sarrantonio, M., 1998. Legume-based cropping systems have reduced carbon and nitrogen losses. Nature 396, 262–265. Eickhout, B., Bouwman, A.F., van Zeijts, H., 2006. The role of nitrogen in world food production and environmental sustainability. Agric. Ecosyst. Environ. 116, 4– 14. Ellert, B.H., Bettany, J.R., 1995. Calculation of organic matter and nutrients stored in soils under contrasting management regimes. Can. J. Soil Sci. 75, 529–538. Entz, M.W., Bullied, W.J., Forster, D.A., Gulden, R., Vessey, J.K., 2001. Extraction of subsoil nitrogen by alfalfa, alfalfa-wheat, and perennial grass systems. Agron. J. 93, 495–503. Gu, J., 1988. Carbon and nitrogen assimilation, dinitrogen fixation in fababean (Vicia faba L.) and microbial biomass in soil-plant systems (fababean, canola, barley, summer fallow) on a Gray Luvisol. MSc Thesis, University of Alberta, Edmonton, Alta. Canada. 138 pp. Haynes, R.J., Williams, P.H., 1993. Nutrient cycling and soil fertility in the grazed pasture ecosystem. Adv. Agron. 49, 119–199. Hogh-Jensen, H., Loges, R., Jorgensen, F.V., Vinther, F.P., Jensen, E.S., 2004. An empirical model for quantification of symbiotic nitrogen fixation in grass-clover mixtures. Agric. Syst. 82, 181–194.

249

Izaurralde, R.C., Robertson, J.A., McGill, W.B., Juma, N.G., 1993. Effects of crop rotations, nutrient additions, and time on organic C, total and mineralized N, and total P in Breton loam. In Report of the progress of the sustainable cropping systems research study, Alberta Agricultural Research Institute, Canada-Alberta Soil Conservation Initiative, for April 1, 1992 to March 31, 1993. Edmonton, Alta., Canada, pp. 152–163. Izaurralde, R.C., Choudhary, M., Juma, N.G., McGill, W.B., Haderlein, L., 1995a. Crop and nitrogen yield in legume-based rotations practiced with zero tillage and low-input methods. Agron. J. 87, 958–964. Izaurralde, R.C., Feng, Y., Robertson, J.A., McGill, W.B., Juma, N.G., Olson, B.M., 1995b. Long-term influence of cropping systems, tillage methods, and N sources on nitrate leaching. Can. J. Soil Sci. 75, 497–505. Izaurralde, R.C., McGill, W.B., Robertson, J.A., Juma, N.G., Thurston, J.J., 2001. Carbon balance of the Breton Classical Plots over half a century. Soil Sci. Soc. Am. J. 65, 431–441. Izaurralde, R.C., Williams, J.R., McGill, W.B., Rosenberg, N.J., Quiroga Jakas, M.C., 2006. Simulating soil C dynamics with EPIC: model description and testing against long-term data. Ecol. Model. 192, 362–384. Janzen, H.H., 2007. Greenhouse gases as clues to permanence of farmlands. Conserv. Biol. 21, 668–674. Janzen, H.H., Bole, J.B., Biederbeck, V.O., Slinkard, A.E., 1990. Fate of N applied as green manure or ammonium fertilizer to soil subsequently cropped with spring wheat at 3 sites in western Canada. Can. J. Soil Sci. 70, 313–323. Janzen, H.H., Campbell, C.A., Izaurralde, R.C., Ellert, B.H., Juma, N., McGill, W.B., Zentner, R.P., 1998. Management effects on soil C storage on the Canadian prairies. Soil Till. Res. 47, 181–195. Janzen, H.H., Beauchemin, K.A., Bruinsma, Y., Campbell, C.A., Desjardins, R.L., Ellert, B.H., Smith, E.G., 2003. The fate of nitrogen in agroecosystems: an illustration using Canadian estimates. Nutr. Cycl. Agroecosyst. 67, 85–102. Karlsson, L.O.T., Andren, O., Katterer, T., Mattsson, L., 2003. Management effects on topsoil carbon and nitrogen in Swedish long-term field experiments – budget calculations with and without humus pool dynamics. Eur. J. Agron. 20, 137– 147. Khan, D.F., Peoples, M.B., Chalk, P.M., Herridge, D.F., 2002. Quantifying belowground nitrogen of legumes. 2. A comparison of N-15 and non isotopic methods. Plant Soil 239, 277–289. Khan, D.F., Peoples, M.B., Schwenke, G.D., Felton, W.L., Chen, D.L., Herridge, D.F., 2003. Effects of below-ground nitrogen on N balances of field-grown fababean, chickpea, and barley. Aust. J. Agric Res. 54, 333–340. Korsaeth, A., Eltun, R., 2000. Nitrogen mass balances in conventional, integrated and ecological cropping systems and the relationship between balance calculations and nitrogen runoff in an 8-year field experiment in Norway. Agric. Ecosyst. Environ. 79, 199–214. Kramer, A.W., Doane, T.A., Horwath, W.R., van Kessel, C., 2002. Short-term nitrogen15 recovery vs. long-term total soil N gains in conventional and alternative cropping systems. Soil Biol. Biochem. 34, 43–50. Loughin, T.M., 2006. Improved experimental design and analysis for long-term experiments. Crop Sci. 46, 2492–2502. Nyborg, M., Solberg, E.D., Malhi, S.S., Izaurralde, R.C., 1995a. Fertilizer N, crop residue, and tillage alter soil C and N contents after a decade. In: Lal, R., Kimble, J., Levine, E., Stewart, B.A. (Eds.), Advances in Soil Science: Soil Management and Greenhouse Effect. Lewis Publishers, CRC Press, Boca Raton, FL, pp. 93–100. Nyborg, M., Solberg, E.D., Izaurralde, R.C., Malhi, S.S., Molina-Ayala, M., 1995b. Influence of long-term tillage, straw and N fertilizer on barley yield, plant N uptake and on the soil-N balance. Soil Till. Res. 36, 301–310. Oenema, O., Kros, H., de Vries, W., 2003. Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies. Eur. J. Agron. 20, 3–16. Paustian, K., Andren, O., Clarholm, M., Hansson, A.C., Johansson, G., Lagerlof, J., Lindberg, T., Petterson, R., Sohlenius, B., 1990. Carbon and nitrogen budgets of four agro-ecosystems with annual and perennial crops, with and without N fertilization. J. Appl. Ecol. 27, 60–84. Poudel, D.D., Horwath, W.R., Mitchell, J.P., Temple, S.R., 2001. Impacts of cropping systems on soil nitrogen storage and loss. Agric. Syst. 68, 253–268. Provincial Archives of Alberta, 1978. Accession Number 83.413. Government of Alberta. Department of Agriculture. Alberta Agriculture Hall of Fame nominations. File 1978 Lou Hendrigan. Rasmussen, P.E., Parton, W.J., 1994. Long-term effects of residue management in wheat-fallow. I. Inputs, yield, and soil organic matter. Soil Sci. Soc. Am. J. 58, 523–530. Rasmussen, P.E., Albrecht, S.L., Smiley, R.W., 1998. Soil C and N changes under tillage and cropping systems in semi-arid Pacific Northwest agriculture. Soil Till. Res. 47, 197–205. Reining, E., 2005. Assessment tool for biological nitrogen fixation of Vicia faba cultivated as spring main crop. Eur. J. Agron. 23, 392–400. Rennie, R.J., Dubetz, S., 1986. Nitrogen-15-determined nitrogen fixation in field-grown chickpea, lentil, fababean, and field pea. Agron. J. 78, 654– 660. Robertson, J.A., McGill, W.B., 1983. New directions for the Breton Plots. University of Alberta Agric. For. Bull. 6, 36–41. Ross, S.M., 1999. Clovers in cropping systems. M.Sc. Thesis. University of Alberta, Edmonton, Alta., Canada, 155 pp. Smil, V., 1999. Nitrogen in crop production: an account of global flows. Global Biogeochem. Cycl. 13, 647–662.

250

S.M. Ross et al. / Agriculture, Ecosystems and Environment 127 (2008) 241–250

Soon, Y.K., Clayton, G.W., 2003. Effects of eight years of crop rotation and tillage on nitrogen availability and budget of a sandy loam soil. Can. J. Soil Sci. 83, 475–481. Technicon, 1977. Individual/simultaneous determination of nitrogen and/or phosphorus in BD acid digests. Industrial Method No. 334–74 w/Bt. Technicon Industrial Systems, Tarrytown, New York. Van Faassen, H.G., Lebbink, G., 1994. Organic matter and nitrogen dynamics in conventional versus integrated arable farming. Agric. Ecosyst. Environ. 51, 209–226. Wani, S.P., McGill, W.B., Robertson, J.A., 1991a. Soil N dynamics and N yield of barley grown on Breton loam using N from biological fixation or fertilizer. Biol. Fertil. Soils 12, 10–18.

Wani, S.P., McGill, W.B., Tewari, J.P., 1991b. Mycorrhizal and common-root rot infection, and nutrient accumulation in barley grown on Breton loam using N from biological fixation or fertilizer. Biol. Fertil. Soils 12, 46–54. Wani, S.P., McGill, W.B., Haugen-Kozyra, K., Juma, N.G., 1994a. Increased proportion of active soil N in Breton loam under cropping systems with forages and green manures. Can. J. Soil Sci. 74, 67–74. Wani, S.P., McGill, W.B., Haugen-Kozyra, K., Robertson, J.A., Thurston, J.J., 1994b. Improved soil quality and barley yields with fababeans, manure, forages and crop rotations on a Gray Luvisol. Can. J. Soil Sci. 74, 75–84. Watson, C.A., Atkinson, D., 1999. Using nitrogen budgets to indicate nitrogen use efficiency and losses from whole farm systems: a comparison of three methodological approaches. Nutr. Cycl. Agroecosyst. 53, 259–267.