Campbell, C.A.

Grant, B.

Lemke, R.

McConkey, B.G.

Smith, W.

VandenBygaart, A.J.

Zentner, R.P.

English

eCommons@USASK

Quantitative changes in soil organic C over 37 years under conventional tillage - effect of crop rotations and fertilizers

University of Saskatchewan Research Archive

 Quantitative Changes in Soil Organic C over 37 years under Conventional Tillage - Effect of Crop Rotations and Fertilizers   C.A. Campbell1*, R.P. Zentner2, A.J. VandenBygaart1,  B.G. McConkey2, B. Grant1, R. Lemke2 and W. Smith1  1 Agriculture and Agri-Food Canada - Eastern Cereal and     Oilseed Research Centre, Ottawa, ON 2 Agriculture and Agri-Food Canada - Semiarid Prairie            Agricultural Research Centre, Swift Current, SK.   INTRODUCTION  • Scientists and the agricultural community require methods of quantifying C sequestration in soils. This is important re "C Trading". • Measuring changes in soil organic C (SOC) is tedious because such changes are small, slow and field variability high. • Quantification using models may be a more effective mode of assessing SOC changes. • A 37-yr crop rotation experiment, being conducted at Swift Current, Saskatchewan, in which SOC is regularly monitored, provided an opportunity to test three models for their effectiveness in quantifying SOC changes.  MATERIALS AND METHODS  The rotation experiment was initiated in 1967 on land that was in fallow-wheat (F-W) for the previous 60 years. • Ten cropping systems (Table 1) in which SOC was measured in the 0-15cm depth in 1976, 1981, 1984, 1990, 1993, 1996 and 2003, were assessed. • The three models tested were Century (Parton et al. 1987), the Introductory C Balance Model (ICBM) (Andren and Katterer, 1997) and the Campbell et al. model (Campbell et al. 2000). • All three models require estimates of C inputs from crop residues. We estimated these Inputs for ICBM and the Campbell et al. model from measured grain yields, using Straw/grain ratios and root/straw ratios we had developed. Century used its simulated Yields. We assumed 45% C in residues. • The regressions for converting grain yields to C inputs used in this study are shown in Table 2.  RESULTS AND DISCUSSION  TRENDS IN SOC  • Large standard errors are evidence of large variability usually encountered in measured SOC (Fig. 1). • SOC in fallow-containing systems was generally constant till about 1990 then tended to increase thereafter (Fig. 1). • SOC in extended rotations increased in first decade (Fig. 1), tended to level off in droughty 1980's, then increased after 1990 due to above-average precipitation (Fig. 2) which led to greater C inputs (Fig. 3). • The Campbell et al. model simulated SOC trends fairly well (Fig. 1), but tended to overestimate the lower SOCs and underestimate the higher values (Fig. 4a). • ICBM also simulated SOC well (Fig. 1), but also tended to underestimate higher SOCs (Fig. 4b). • Century simulated SOC trend in Cont W (N + P) but underestimated SOC quite markedly, especially for F-W and F-W-W (Fig. 1). This inaccuracy was related to its underestimate of soil water conserved during summerfallow, which then depressed N mineralization, resulting in low yields (Fig. 5) and C inputs, and poor simulation of SOC (Fig. 4c).  GAIN IN SOC (1967-2003) TABLE 1  • SOC gain between 1967 and 2003 in the 0 - 15cm depth ranged between 3.04 Mg ha-1 in F-W-W (+P) and 11.18 Mg ha-1 in W-Lent (N + P). • On average, F-W-W (N + P) gained 140 kg C ha-1yr-1, about 25 kg ha-1yr-1 more than for F-Flx-W (N + P), and 50-60 kg ha-1yr-1 more than F-W-W without N or without P, but about 45 kg ha-1yr-1 less than for F-Rye-W (N + P). • Cont W (N + P) gained 236 kg C ha-1yr-1, i.e., 130 kg ha-1yr-1 more than Cont W (+ P) and 65 kg ha-1yr-1 less than W-Lent (N + P). • These rates of gain were much less than obtained in a 6-yr study in a Brown Chernozem at Lethbridge (Bremer et al. 2002) where Cont W gained 250 kg C ha-1yr1 more than F-W and 130 kg ha-1yr-1 more than F-W-W.  EFFICIENCY OF CONVERSION OF RESIDUE C TO SOC  • We used regressions relating grain yield to straw yield, and root yield to straw yield to estimate C inputs (Table 2). • We calculated efficiency of conversion of C inputs to SOC gained (%) (Table 1). • Efficiencies were lowest for poorly fertilized systems (6 -7%), intermediate for well-fertilized fallow-containing systems (9 - 12%), and highest for well-fertilized continuous cropping systems (12 - 17%). • We can make first estimates of the influence of crop management on SOC gains for degraded soils in the semiarid prairies by using estimates of C inputs (Table 2) and efficiencies of conversion (Table 1).  CONCLUSIONS  • Using SOC measured periodically during 37 years in a crop rotation experiment in the semiarid prairies at Swift Current, we tested the effectiveness of 3 models in estimating SOC changes and trends. • The ICBM and Campbell et al. models performed reasonably well and better than Century, perhaps because their yield (C inputs) do not have to be modelled as is the case for Century. • In any event, results with Century were less convincing and this model requires further work.   REFERENCES Andren, O. and Katterer, T. 1997.  ICBM: The introductory carbon balance model for exploration of soil carbon balances. Ecological Applications 7: 1226-1236.  Bremer, E, Janzen, H.H., and McKenzie, R.H. 2002.  Short-term impact of fallow frequency and perennial grass on soil organic carbon in a Brown Chernozem in southern Alberta. Can.J. Soil Sci. 82: 481-488.  Campbell, C.A., Zentner, R.P., Liang, B.-C., Roloff, G., Gregorich, E.C. and Blomert, B. 2000.  Organic C accumulation in soil over 30 years in semiarid southwestern Saskatchewan. Effect of Crop rotations and fertilizers. Can. J. Soil Sci. 80: 179-192.  Parton, W.J., Schimel, D.S., Cole, C.U., and Ojima, D.S. 1987.  Analysis of factors controlling soil organic matter levels in great plains grasslands. Soil Sci. Soc. Am. J. 51: 1173-1179.   Table 1.  SOC gain, C input and efficiency of conversionz of C input to                       SOC (%) (1967-2003) ________________________________________________________________________   SOC gain SOC gain Mean C Total C Efficiency of Treatmenty (Mgha-1) per year input  input  conversion of      (kgha-1yr-1) (kgha-1) (Mgha-1)       input C to  SOC(%)   _______________________________________________________________________ F-W-W(+ P)      3.04       82               1421                 51.2                    5.9 F-W-W(N+P)       5.15                 140              1611                58.0                     8.9 F-Flx-W(N+P)      4.31               116              1162                41.8                   10.3    F-Rye-W(N+P)     6.87                 185              1634                58.8                   11.7  F-W-W(+N)          3.39                  92               1397                50.3                     6.7  Cont W(N+P)        8.75                 236              1983     71.4                    12.3 F-W (N+P)            4.71                 127              1379                49.6                     9.5 Cont W (+P)          3.90                 105              1504                54.1                     7.2 W-Lent(N+P)x      11.18                302              1840                66.2        16.9 F-W-W-W-W-Ww   9.21                250               ndv                    ndv                      ndv      (N+P) ________________________________________________________________________ z SOC gain (1967 - 2003) ÷ total C inputs (1967-2002). We assume starting SOC in    0-15cm depth in 1967 for all plots was 30.5 Mgha-1 (Campbell et al. 2000a). y  F = fallow, W = spring wheat, Flx = flax, Rye = fall rye, Lent = grain lentil,    Cont = continuous. N and P applied based on soil test (N) and general recommendation    (P). x  This rotation was constructed in 1979 from two extra Cont W (N+P) rotations. w  This rotation was established in 1985 from an Oat hay-W-W and Flx-W-W rotations     receiving N + P. v   nd = not determined.  Table 2.  Regressions for converting grain yields (y)z to C       inputsy __________________________________________________________________________________ Crop            Regression ________________________________________________________________________ Hard Red spring wheat  C input       =   1.20 Y +   64  Fall rye    C input       =   0.86 Y + 794  Flax     C input        =  1.39 Y  +  36  Grain lentil                                  C input       =  0.88 Y  + 746 ________________________________________________________________________ z  Units = kgha-1 y  Calculated from regressions relating straw yield to grain yield; assuming root/straw     ratio = 0.59 and C in residues = 45%.           Swift Current F-W-W (+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM F-W-W (+P)Measured MeanCampbell ModelCentury Model Swift Current F-W-W (+N+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM F-W-W (N+P)Measured MeanCampbell ModelCentury Model Swift Current F-Flx-W (+N+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2) ICBM F-Flx-W (N+P)Measured MeanCampbell Model Swift Current F-Rye-W (+N+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM F-Rye-W (N+P)Measured MeanCampbell Model Swift Current F-W-W (+N)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM F-W-W (+N)Measured MeanCampbell ModelCentury Model Swift Current Cont W (+N+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM ContW (N+P)Measured MeanCampbell ModelCentury Model Swift Current Cont W (+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM ContW (+P)Measured MeanCampbell ModelCentury ModelSwift Current F-W (+N+P)25272931333537394143451965 1970 1975 1980 1985 1990 1995 2000 2005YearSOC (kg m-2)ICBM F-W (N+P)Measured MeanCampbell ModelCentury Model Figure 1. Trends in SOC in 0-15 cm depth, 1967-2003, as measured and modeled by ICBM, Campbell et al. 2000, and Century. Vertical bars on measured points are standard error of the mean.  y = 0.009x - 8.00; R2 = 0.66**y = 0.007x - 6.75; R2 = 0.86***y = 0.005x - 1.32; R2 = 0.94***0.03.06.09.012.015.01000 1200 1400 1600 1800 2000 2200Mean C Inputs (kg ha-1)Net SOC Gain (Mg ha-1)MeasuredCampbellICBM              Figure 2. Accumulated departure from the long-term mean growing season (1 May to 31 August) precipitation at Swift Current for the period 1886 - 2003. (Long-term mean = 210 mm). (Note: Only slopes are meaningful. Positive slopes denote period of above average precip; negative slopes denote period of drought; zero slope denotes period of average precip.).                        Figure 3. Relationship between net SOC gain in 0-15cm depth (measured and modeled) between 1967 and 2003 and C inputs. [Note: SOC in 1967 assumed to be 30.5 Mg ha-1 in all plots as measured in F-W (N+P) in 1976, Campbell et al. 2000]. a.Campbell et al. (2000a )Modely = 0.32x + 22.63R2 = 0.47***25.027.029.031.033.035.037.039.041.043.045.025.0 27.0 29.0 31.0 33.0 35.0 37.0 39.0 41.0 43.0 45.0Measured SOC (Mg ha-1)Simulated SOC (Mg ha-1)F-W-W (+P) F-W-W (N+P)F-Flx-W (N+P) F-Rye-W (N+P)F-W-W (+N) ContW (N+P)F-W (N+P) ContW (+P)W-Lent (N+P) 1:1Linear (Regression) b.ICBM Modely = 0.43x + 19.50R2 = 0.40***25.027.029.031.033.035.037.039.041.043.045.025.0 27.0 29.0 31.0 33.0 35.0 37.0 39.0 41.0 43.0 45.0Measured SOC (Mg ha-1)Simulated SOC (Mg ha-1)F-W-W (+P) F-W-W (N+P)F-Flx-W (N+P) F-Rye-W (N+P)F-W-W (+N) ContW (N+P)F-W (N+P) ContW (+P)W-Lent (N+P) 1:1Linear (Regression) c. Century Modely = 0.21x + 24.15R2 = 0.21**25.027.029.031.033.035.037.039.041.043.045.025.0 27.0 29.0 31.0 33.0 35.0 37.0 39.0 41.0 43.0 45.0Measured SOC (Mg ha-1)Simulated SOC (Mg ha-1)F-W-W (+P) F-W-W (N+P)F-W-W (+N) ContW (N+P)F-W (N+P) ContW (+P)1:1 Linear (Regression) Figure 4. Relationship between simulated SOC in 0-15 cm depth and measured SOC for the a) Campbell et al. (2000a) model, b) ICBM model, and c) Century model.      a.b.c.FWW (N + P)0.00.51.01.52.02.53.03.54.01964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004YearCrop Yield (Mg ha-1)CenturyMeasuredr = 0.26, n = 24ContW (N + P)0.00.51.01.52.02.53.03.54.01964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004YearCrop Yield (Mg ha-1)CenturyMeasuredr = 0.62**, n = 36F-W (N + P)0.00.51.01.52.02.53.03.54.01964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004YearCrop Yield (Mg ha-1)CenturyMeasuredr = 0.62**, n = 18                     Fig. 5. Measured and estimated crop yield by Century on the a) F-W (N + P) (only one phase estimated), b) F-W-W (N + P), and c) ContW (N + P) treatments at Swift Current SK. 

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Quantitative changes in soil organic C over 37 years under conventional tillage - effect of crop rotations and fertilizers

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