Comparison of ingrowth-core and sequential soil core methods on the belowground net primary production estimation in ryegrass-clover swards

Transcription

1 Comparison of ingrowth-core and sequential soil core methods on the belowground net primary production estimation in ryegrass-clover swards Shimeng Chen ASA, CSSA and SSSA Annual Mettings 4 th.nov. 2013,Tampa, USA Robert F.Barnes Graduate Student Competition Prof.Dr.Friedhelm Taube Institute of Crop Science and Plant Breeding Univesity of Kiel, Germany 1

2 Introduction Material and method Conclusion - Grünland und Futterbau/Ökologischer Landbau- 2

3 Introduction Soil organic matter (SOM): the largest terrestrial C pool. Temperate grassland: Inherently high SOM (Conant et al., 2001; Soussana et al., 2004) 3

4 Introduction CO 2 C sequestration in grasslands CO 2 Coefficient Belowground of variation: net 75% primary of measurements production (BNPP) BNPP: Higher than croplands Key source of C input SOM prediction?? Quantification suffers from high uncertainty. SOM 4

5 Introduction BNPP measurement in managed grasslands Method Ingrowth-core Soil core Observant Accumulation of root ingrowth Fluctuation in belowground biomass Root free 0-30 cm,ø = 4 cm 45 5

6 Material and method BNPP methods comparison: 2010 / 2011, ryegrass-clover swards Ingrowth-core Soil core 1) Sum of ST 2) Sum of MT 3) LT 4) "Max-Min" maximum BGB - minimum BGB 5) "Posi" all positive increments in BGB 6

7 Material and method Hypothesis: 1) BNPP estimates would be identical among five methods. (ST, MT, LT, Max-min, Posi) One-way ANOVA on BNPP estimates 2) Both ingrowth period and BNPP level affect the coefficient of variation (CV) of ingrowth-core method. e.g. root decay; fail to recover from disturbance Compare the CV among literatures 7

8 Annual BNPP estimates (g m -2 ) 12/20/2013 Hypothesis: 1) BNPP estimates would be identical among methods. -level: 0.05 ST/ MT: 2-3 t C ha -1 (Nitschelm et al., 1997; Garcia-Pausas et al., 2011) LT: 55% decay (Gill and Jackson, 2000) ab a c c bc Max-Min, Posi : ST MT LT Max-Min Posi Underestimates 8

9 Hypothesis: 2) ingrowth period and BNPP level affect CV. Ingrowth-core Soil Core ST MT LT Max-min Posi CV % in BNPP CV : affected by the ingrowth period? 9

10 Coefficient of variation (%) 12/20/2013 Hypothesis: 2) ingrowth period and BNPP level affect CV. Identify CV caused by a single sampling CV : affected by the ingrowth period References: present study; Boyd and Svejcar, 2009; Higgins et al., 2002; Johnson and Matchett, 2001; Niklaus et al., 2001; Schäppi and Körner, 1996; Warwick et al.,

11 Coefficient of variation (%) 12/20/2013 Hypothesis: 2) ingrowth period and BNPP level affect CV. CV affected by BNPP / ingrowth period Ingrowth period: within 6 weeks > 6 weeks Precision & Bias: Ingrowth-core fits well for productive grasslands References: present study; Boyd and Svejcar, 2009; Higgins et al., 2002; Johnson and Matchett, 2001; Niklaus et al., 2001; Schäppi and Körner, 1996; Warwick et al.,

12 Conclusion The ingrowth-core method delivers reliable carbon input estimates in productive grassland sites whereas in such sites the soil core method produces underestimates. A 4-6 weeks ingrowth period is recommended for both reliability and feasibility. Highlighted for lower CV, the ingrowthcore is promising to distinguish treatments effect with small changes. 12

13 Thank you! 13

14 Max-Min (g m -2 ) 12/20/2013 Hypothesis: 1) BNPP estimates would be identical among methods. BGB among sampling dates numdf F-value P-value Date Lack of seasonality in BGB: Precondition is violated for Max-min / Posi. (Scurlock et al., 2002) MT ingrowth (g m -2 ) Posi (g m -2 ) Both soil core calculations deliver underestimates at higher BNPP level sites. 14

15 Hypothesis: 1) BNPP estimates would be identical among methods. BNPP estimates among methods (g m -2 ) ST MT LT Max-min Posi Resown 583 A 602 A 245 A 252 A 248 A 5-years-old 338 B 359 B 172 B 341 A 370 A (Mean ± 1SE, n = 12.) 15

16 Hypothesis: 1) BNPP estimates would be identical among methods. Max-min Posi x: white clover cover y: BNPP estimates LT MT ST 16

17 Hypothesis: 2) ingrowth period and BNPP level affect CV. 17

18 Material and method Hypothesis: 3) ST and MT should be identical by among defoliations e. g. "1+1=2" Compare ST and MT: Four-way ANOVA on installation disturbance Fixed effects: Sets, Defoliation, Sward age, Slurry 18

19 BNPP among defoliations (g m -2 ) 12/20/2013 Hypothesis: 3) ST and MT should be identical by among defoliations P-value P-value M 0.18 M*Y*N 0.31 M*Y 0.71 M*Y*D 0.60 M*N 0.24 M*N*D 0.67 M*Y*N*D 0.97 Performance of ingrowth-core: independent on treatments Method * Date < D1 D2 D3 D4 *** * 19

20 BNPP (g m -2 ) 12/20/2013 Hypothesis: 3) ST and MT should be identical by among defoliations ST2: at the ryegrass booting stage Root weight: ; but ST2 failed (Garwood, 1969) Key: phenology D1 D2 D3 D4 20

21 BNPP (g m -2 ) 12/20/2013 Hypothesis: 3) ST and MT should be identical by among defoliations 9 weeks MT4: partial root decay (Waston et al., 2000; van der Krift and Berendse,2002) Key: ingrowth period D1 D2 D3 D4 21

22 BNPP (g m -2 ) 12/20/2013 Hypothesis: 3) ST and MT should be identical by among defoliations " 1+1 = 2 " D1 D2 D3 D4 Installation disturbance: non-significant (4-6 weeks) 22

23 Hypothesis: 3) ST and MT should be identical by among defoliations * * * Significance level: P <

24 Hypothesis: 3) ST and MT should be identical by among defoliations * * * * * * Comparison of weighted average SRL from ST and MT ingrowth-core Significance level: P <

25 Root growth seasonality Specific root length (SRL, m g -1 ) and root N concentration (mg g -1 ) derived from medium-term ingrowth-core on average of 2010 and 2011 among four cuts. 25

26 Root growth seasonality BNPP and specific root length (SRL, m g -1 ) dynamics. * Vertical lines indicate the silage cut 26

27 Correlation between root N concentration and root fraction (f BNPP ) sampled by medium-term ingrowth-core among the 1-year, 2-years, 5-years-old sward and permanent grassland, with 0 or 240 kg N ha -1 y -1 slurry, respectively. N0: dashed line, R 2 =0.37, P < N1: solid line, R 2 =0.32, P <

28 Introduction Direct root observation: Soil Core Ingrowth-core Rhizo-/ Minirhizotron Excavation Isotope dilution Coefficient of variation (CV): ~ 75% of BNPP estimates in perennial forages Method evaluation: Non-root observation: Nitrogen budget Carbon balance Regression model. Precision & Bias (Lauenroth, 2006; Bolinder et al., 2007 Milchunas, 2009) 28

29 Material and method MAT: 8.7 C MAP: 785 mm Sandy loam 2010 / 2011 Sward age: 1- / 5-years Slurry: 0 / 240 kg N ha -1 29

30 Material and method Mesh size: 1 mm Pre-sieved root-free soil from the same plot 0-30 cm,ø = 4 cm Key factors: Bulk density Original soil Avoid dry-wet cycles 45 30

31 Proportion of white clover in aboveground biomass (%) N0 N1 Y1: 14 c A 5 b B Y2: 44 a A 18 a B Y5: 32 b A 13 a B PG: 25 b A 12 a B Data in each row with different capital letters are significantly different at α level of Data in each column with different lower-case letters are significantly different at α level of