SOIL CARBON AND CLIMATE CHANGE NEWS

 

From Kansas State University's:

Consortium for Agricultural Soils Mitigation of Greenhouse Gases (CASMGS)

http://soilcarboncenter.k-state.edu

 

Charles W. Rice, K-State Department of Agronomy, National CASMGS Director

(785) 532-7217 cwrice@ksu.edu

Scott Staggenborg, K-State Department of Agronomy (785) 532-7214 sstaggen@ksu.edu

Steve Watson, CASMGS Communications (785) 532-7105 swatson@ksu.edu

 

 

April 24, 2009

No. 66

 

Effect of single tillage operation

on carbon sequestration in a no-till system

 

No-till crop production systems have been found to increase soil carbon sequestration in most situations. But sometimes circumstances arise in which a one-time tillage operation becomes necessary in an otherwise continuous no-till system. What effect will such a single low-intensity tillage operation have on stored soil carbon? Would a single low-intensity tillage operation reverse years of carbon accumulation in no-till?

 

To answer this question, Chuck Rice, professor of agronomy at Kansas State University, and K-State graduate student Chad Asmus, conducted research at three locations in western Kansas. The crop rotation at two of the sites was wheat/corn/fallow. At the other site, the field was in continuous wheat. All sites were dryland. The three locations had all been under continuous no-till cropping for at least five years. Three types of low-intensity tillage operations were then performed at each site:

 

* Disk plow

* Chisel plow

* Sweep plow

 

One plot was kept in no-till production. In the tillage plots, the land was returned to no-till after the one-time tillage operation was performed. The soil was sampled at three depths (0-5 cm, 5-15 cm, and 15-30 cm) for total carbon, aggregate distribution, and bulk density pre-tillage, then at 9 and 12 months after the tillage treatment.

 

Key Findings

 

* A single tillage pass with a disk, sweep, or chisel did not affect soil organic carbon (SOC) stocks compared to uninterrupted no-till under dryland cropping in a semi-arid environment. At the Wallace County site, there was a slight increase in SOC concentration when averaged over the 0-30 cm depth with the disk plow treatment, but no significant increase in soil C mass (which takes bulk density into account) to a depth of 30 cm. The increase in soil C concentration after tillage at this one location can be attributed to the shallow incorporation and decomposition of surface residue. Although most of the residue-C and some of the SOC is respired as CO₂ following tillage, there can be a net increase in soil C concentration if a sufficient amount of surface residue is introduced into the soil. 

 

Whole soil C mass by tillage and depth, 12 months after treatment

 

Wallace Co., Kansas (Wheat/corn/fallow)

 

Spearville, Kansas (Continuous wheat)

 

Tribune, Kansas (Wheat/corn/fallow)

 

 

 

* Aggregation was not significantly affected by a single tillage operation. There were some changes in aggregation due to cropping sequence and changes in soil moisture, but not due to the single tillage operation. At all three sites there was a general trend for the amount of large microaggregates to decrease and small microaggregates to increase over time. 

 

* The greatest mass of aggregate-associated C existed in the large microaggregate fraction for all three soils. It is this aggregate size fraction that had the greatest influence on whole soil C for these locations. However, other pools of organic C contributed to the net accumulation or loss of whole soil organic C besides aggregate-protected C. 

 

* Tillage did not significantly affect bulk density at any location.

 

Other Similar Studies

 

The results of this study are similar to those of several studies involving more intensive one-time tillage operations, such as:

 

1. Michigan. In this study, plowing a no-till field one time had no effect on SOC mass at the 0-30 cm depth 5 years later. Kettler, T.A., D.J. Lyon, J.W. Doran, W.L. Powers, and W.W. Stroup.  2000. Soil quality assessment after weed-control tillage in a no-till wheat-fallow cropping system.  Soil Sci. Soc. Am. J. 64: 339-346.

 

1. Michigan. In this study, one-time plowing of a long-term no-till plot did not affect SOC mass in the top 20 cm of soil, although it did redistribute the C so that less was in the upper surface layer. Pierce, F.J., M.-C. Fortin, and M.J. Staton. 1994. Periodic plowing effects on soil properties in a no-till farming system. Soil Sci. Soc. Am. J. 58: 1782-1787.

 

2. Nebraska. This study of rainfed systems in western Nebraska had findings similar to the Michigan study above. A one time tillage operation redistributed C within the top 30 cm of soil, but did not affect the total amount of SOC in the soil. Quincke, J.A., C.S. Wortmann, M. Mamo, T. Franti, and R.A. Drijber. 2007. Occasional Tillage of No-Till Systems: Carbon Dioxide Flux and Changes in Total and Labile Soil Organic Carbon. Agron. J. 99(4): 1158 - 1168.

 

3. Nebraska. In this study, plowing a no-till field one time had no effect on SOC levels at the 0-30 cm depth 5 years later. Kettler, T.A., D.J. Lyon, J.W. Doran, W.L. Powers, and W.W. Stroup.  2000. Soil quality assessment after weed-control tillage in a no-till wheat-fallow cropping system.  Soil Sci. Soc. Am. J. 64: 339-346.

 

4. Ontario, Canada. Plowing a no-till field one time had no effect on SOC mass on most soils 18 months later, except for a sandy loam soil with low initial organic matter levels. VandenBygaart, A.J. and B.D. Kay. 2004. Persistence of soil organic carbon after plowing a long-term no-till field in southern Ontario, Canada. Soil Sci. Soc. Am. J. 68(4):1394-1402.

 

Some other studies on this topic have had slightly different findings for soil the effects of a one-time tillage on soil aggregation, however. In a Michigan study, plowing a no-till field one time immediately and substantially reduced soil aggregation, and that this condition persisted for several years. Soil carbon mass remained unchanged averaged over the 0-20 cm depth. Grandy, A.S. and G. P. Robertson. 2006. Aggregation and organic matter protection following tillage of a previously uncultivated soil. Soil Sci. Soc. Am. J. 70(4): 1398 - 1406.

 

Summary

 

In the arid environment of western Kansas, the K-State team found that a single tillage event did not have a deleterious effect on sequestered carbon or aggregation as long as the land is immediately returned to no-till.

 

 

-- Steve Watson, CASMGS Communications

swatson@ksu.edu