Depth Distribution of Soil Organic Carbon as a Signature of Soil Quality

Transcription

1 Depth Distribution of Soil Organic Carbon as a Signature of Soil Quality a.k.a. stratification ratio of soil organic matter Alan J. Franzluebbers Raleigh NC

2 Soil quality Capacity of soil to function (Karlen et al 1997; Soil Sci Soc Am J 61, 4-10) How well soil does what we want it to do (Schjønning et al 2003; Managing Soil Quality: Challenges in Modern Agriculture, CABI Publ) 1. High water infiltration and low runoff to avoid erosion and offsite contamination 2. Sustained supply of nutrients to plants for long-term productivity 3. Root growth promotion to increase nutrient acquisition and water utilization for optimum plant production and minimal nutrient loss 4. Rich soil biological habitat, activity, and diversity for effective nutrient cycling, biodegradation capacity, and ecosystem stability

3 Soil organic carbon Cultivated Grassland Conditions / Reference g C kg -1 soil < < 22 Typic Haplorthox, Brazil, 20 yrs following Cerrado; Green et al 2007, Soil Till Res 92, Typic Haplorthox, Brazil, 3 yrs following grass; Pinheiro et al 2004, Soil Till Res 77, < < 34 Pachic Haplustoll, USA, 16 yrs following pasture; Liebig et al 2004, Soil Till Res 78, Chromic Luvisol (FAO), Australia, 20 yrs following pasture; Blair et al 2000, Soil Till Res 55, Absolute level of soil organic C (SOC) is different depending on soil and region, but relative management effects are often similar

4 Depth distribution of soil organic matter Soil Organic Carbon (g. kg -1 ) Soil Depth (cm) Management Systems at Watkinsville GA 15-yr tall fescue pasture 16-yr conservation tillage 4-yr conventional tillage In the warm-humid region of the southeastern USA and elsewhere, organic matter accumulates near the soil surface when undisturbed

5 Depth distribution of soil organic matter Soil Depth (cm) Soil Organic Carbon (g. kg -1 ) *** ** Georgia Typic Kanhapludult Tall fescue previously ** *** 3-yr conventional tillage following 20 yr-pasture 3-yr no tillage following 20-yr pasture SOC (0-30 cm) Surface residue C Soil Organic C (Mg ha -1 ) < < > > < < 0.7 Franzluebbers and Stuedemann (2008) Soil Sci. Soc. Am. J. 72:

6 Depth distribution of soil organic carbon Soil Organic C (g. kg -1 ) Soil Depth (cm) Conventional tillage No tillage Quantity of SOC (Mg. ha -1 ) 0-12 cm Distribution of SOC (0-3 / 6-12 cm) NT / CT Franzluebbers (2002) Soil Till. Res. 66,

7 Impact of soil organic carbon distribution on water infiltration CT undisturbed Time (minutes) for 2.8 cm of water to infiltrate surface CT NT 2x quantity Sieved P = x distribution Intact P < 0.01 NT undisturbed Franzluebbers (2002) Soil Till. Res. 66, Greater rate of infiltration due to stratified distribution of organic C, rather than quantity of organic C

8 Implications of stratified soil organic carbon for land managers Easier to change SOC at the surface than to change SOC deeper in the profile Greater impact from increment of change in SOC Cost per unit of effective change in SOC is reduced Increasing SOC is not easy in some environments, so faster and more effective change in SOC maximizes benefits to farmers and to society (i.e. cleaner environment)

9 Characterization of soil organic carbon depth distribution Surface residue Plow layer of soil 0-5 cm Zone most affected by management Zone relatively unaffected by management cm Stratification Ratio SOC (0-5 cm).. SOC (15-30 cm) Plowed soils tend to have values near 1 Franzluebbers (2002) Soil Till. Res. 66,

10 Why calculate stratification ratio of soil organic carbon? Soils differ in inherent stocks of organic C Basic soil properties and processes can be isolated at appropriate depths for their response to management Long-term outcomes can be predicted from shorter term studies Comparative analyses of conservation tools across soils would benefit technology transfer and adoption

11 Stratification ratio of soil organic carbon SOC = 40.0 (1 - e SR ) r 2 = 0.34 Stratification Ratio of SOC Soil Organic Carbon (Mg. ha -1 ) [0-20 cm] Pasture Conservation-tillage cropland Conventional-tillage cropland Stratification Ratio of Soil Organic C (0-5 cm / cm) Causarano et al. (2008) Soil Sci. Soc. Am. J. 72,

12 Surface soil condition is important for water quality Fraction of 0.6 Rainfall as 0.4 Runoff Well-drained silt loam soil in Indiana Wheat straw applied to bare ground 156 mm of rainfall simulated during 3 days Soil Loss (Mg. ha -1 ) Surface Crop Residue (Mg. ha -1 ) Surface cover is important for controlling runoff and soil erosion Data from Mannering and Meyer (1963) Soil Sci. Soc. Am. Proc. 27:84-86

13 Management impacts on runoff responses Small-plot rainfall simulations AL Truman et al. (2003) MS, OH Rhoton et al. (2002) PA Sharpley & Kleinman (2003) WI Andraski et al. (1985) Field-plot rainfall simulations GA Bosch et al. (2005), Endale et al. (2004) KY Seta et al. (1993) VA Ross et al. (2001) Water catchments with natural rainfall GA Endale et al. (2000), Langdale et al. (1985) MD Angle et al. (1984) OH Shipitalo & Edwards (1998) OK Sharpley & Smith (1994) TX Harmel et al. (2004)

14 Water runoff Water Runoff (% of precipitation) Assumed Stratification Ratio of SOC a 40% reduction in runoff b b 0 n = 15 n = 15 n = 2 Conventional Tillage Cropping No Tillage Cropping Perennial Pasture Data from multiple sources Reported in Franzluebbers (2008) J. Integr. Biosci. 6, 15-29

15 Soil loss Soil Loss (Mg. ha -1 ) Assumed Stratification Ratio of SOC a n = 14 Conventional Tillage Cropping >80% reduction in soil loss b n = 14 No Tillage Cropping b n = 3 Perennial Pasture Data from multiple sources Reported in Franzluebbers (2008) J. Integr. Biosci. 6:15-29

16 Nutrient loss Nutrient loss related mostly to sediment transport Loss of Phosphorus in Runoff (kg. ha -1 ) Broad impact assessments of soluble P fraction still needed Assumed Stratification Ratio of SOC a n = 6 Conventional Tillage Cropping Total b n = 5 No Tillage Cropping Dissolved P tends to be greater with NT due to surface accumulation Dissolved c n = 3 Perennial Pasture Data from multiple sources Reported in Franzluebbers (2008) J. Integr. Biosci. 6:15-29

17 Conservation of nutrients Soil Depth (cm) Soil Organic Carbon (g. kg -1 ) *** ** Soil Depth (cm) *** 3-yr conventional tillage following 20 yr-pasture 3-yr no tillage following 20-yr pasture Total Soil Nitrogen (g. kg -1 ) ** *** *** * *** *** 3-yr conventional tillage following 20 yr-pasture 3-yr no tillage following 20-yr pasture Franzluebbers and Stuedemann (2008) Soil Sci. Soc. Am. J. 72,

18 Conservation of nutrients 4 Total Soil Nitrogen (Mg. ha -1 ) 3 2 Conventional tillage No tillage 1 Effective loss of Continuation of pasture 242 kg N/ha/yr with CT compared 0 with NT Years of Management *** Franzluebbers and Stuedemann (2008) Soil Sci. Soc. Am. J. 72,

19 Nutrient acquisition by plants Cover Crop Biomass (Mg. ha -1. yr -1 ) Stratified TSN was associated with improved nutrient release to plants CT NT > CT 16% NT Rye / sorghum CT NT > CT 34% Stratification Ratio of TSN Management System NT Pearl millet / wheat Franzluebbers and Stuedemann (2007) Renew. Agric. Food Syst. 22,

20 Conclusions Quantity of soil organic carbon (SOC) is important to ecosystem functioning However, the distribution of SOC (at the surface) is even more important Soil quality and ecosystem functioning are closely associated with stratification ratio of SOC

21 Conclusions Empirical data are becoming more available to suggest that depth distribution of SOC as affected by long-term management can be used as a signature of soil quality Characterization of conservation management systems with stratification ratio of SOC is increasing, e.g. o Argentina (Quiroga et al. 2009) and Brazil (Sa & Lal 2009) o Canada (Carter & Gregorich 2010; Tiessen et al. 2010) o China (Du et al. 2010; Guo et al. 2010; Wang et al. 2010) o Italy (Tabaglio et al. 2009) and Spain (Alvaro-Fuentes et al. 2008; Hernanz et al. 2009; Lopez-Bellido et al. 2010; Madejon et al. 2009; Melero et al. 2009) o USA (Levi et al. 2010; Spargo et al. 2008; Wright et al. 2007)

22 Acknowledgements