Long-term Tillage and Soil CO2 Fluxes

Long-term Tillage and Soil CO2 Fluxes February 13, 2018

Moldboard plowing
Figure 1. Moldboard plowing at an experimental site in eastern Nebraska.

Ivori Schley, Student at North Carolina A&T State University and 2017 University of Nebraska-Lincoln Integrated Agronomic Systems Intern
Sabrina Ruis, Post-Doctoral Research Associate, Department of Agronomy and Horticulture
Humberto Blanco, Soil Specialist, Department of Agronomy and Horticulture
Paul Jasa, Extension Engineer, Department of Biological Systems Engineering

Tillage is an important agricultural practice to manage crop residues, control weeds, and prepare the soil for planting, among others (Figure 1). However, the use of tillage can stimulate loss of soil organic carbon (C) to the atmosphere as carbon dioxide (CO2). Losses of CO2 may depend upon the degree of soil disturbance. The loss of soil carbon can reduce soil productivity, increase the need for fertilizer inputs, and reduce farm profits. Thus, it is important to understand how different types of tillage may affect soil CO2 fluxes in the long term.

How Do Soil CO2 Fluxes Occur?

Carbon dioxide is the most abundant soil gas and is the result of a natural process called soil respiration. Soil respiration occurs through microbial metabolic processes that decompose soil organic matter. Tillage systems affect soil CO2 fluxes by directly affecting soil properties. Tillage breaks down soil aggregates that keep soil organic matter inaccessible to microbes and incorporates crop residues, exposing the darker soil that readily absorbs rather than reflects solar radiation (Figure 2).

Chisel plowing
Figure 2. Moldboard plow incorporating crop residues. Note the darker soil surface after plowing that leads to warmer soil temperature and greater evaporation.

This means greater soil temperatures, reduced soil moisture, and potentially greater soil gas fluxes. In addition, a system under intensive tillage practices may result in increased CO2 fluxes due to increases in soil aeration and disruption of soil aggregates. The alternative method to tilling soil is to use reduced till or no-till systems. Reduced tillage methods usually consist of minimal soil disturbance and allow residue accumulation at the soil surface, which can lead to soil moisture retention and reduced fluctuations in soil temperature, potentially lowering CO2 fluxes. Depending on the environment, no-till ideally mitigates soil gas emissions from the soil, which in turn preserves soil quality.

Effects of Tillage System On CO2 Fluxes

Previous research has shown that tillage effects on CO2 fluxes may depend on tillage type and timing. Greater tillage intensity generally results in greater CO2 fluxes (Table 1), and effects of tillage are often confined to the days or seasons when tillage occurred. Tillage generally decreases soil bulk density and increases soil porosity by loosening the soil. Changes in these soil properties are not, however, permanent as they tend to return to pre-tillage state due to natural reconsolidation, wetting and drying cycles, and other factors.

Table 1. Two previous studies on soil gas fluxes in the Corn Belt.
LocationSoil TextureDuration of Study (years)Tillage TypesCropKey FindingsReference
Indiana Silty clay loam 30 Moldboard, Chisel, No-till Corn and Corn-Soybean Tillage effects confined to immediately after tillage (Chisel>Moldboard>No-till) Tillage effects through growing season were minimal Omonode et al., 2007
Ohio Silt loam 43 Moldboard, Chisel, No-till Corn Tillage did not affect CO2 fluxes in winter and spring, but summer and fall fluxes were: No-till<Moldboard<Chisel Ussiri and Lal, 2009

Case Study in Nebraska

Few have studied long-term tillage impacts on soil gas fluxes in the western Corn Belt. From fall 2016 through summer 2017, soil CO2-C flux was monitored from a long-term tillage experiment (35 years) with six tillage treatments (chisel, plow, disk, disk with rye cover crop, no-till, and no-till with rye cover crop) on a silty clay loam at Rogers Memorial Farm near Lincoln. The cropping system was a corn-soybean rotation and soil CO2 fluxes were monitored beginning after the soybean phase. Soil samples for analysis of particulate organic matter (POM), which is easily decomposed organic matter, were collected seasonally. Soil gas fluxes were collected immediately following tillage, after one week, and then monthly.

High-C charFigure 3. The influence of tillage system on CO2-C flux by season in a long-term tillage experiment in eastern Nebraska. Bars denote standard deviation of the mean. NT = no-till, CC = cover crop
Chart
Figure 4. The influence of tillage system on spring particulate organic matter fractions in a long-term tillage experiment in Nebraska. Bars denote standard deviation of the mean. NT = no-till, CC = cover crop

Results showed that tillage system did not affect seasonal cumulative CO2-C flux (Figure 3). However, within the season when tillage occurred (fall for moldboard plow and chisel, spring for disk, chisel, and moldboard plow), fluxes tended to be greater with tillage than with no-till. Fluxes tended to be greater in summer compared to winter and spring, likely due to warmer soil temperatures. Particulate organic matter, the easily degraded portion of organic matter, may show significant impacts due to tillage. In winter, particulate organic matter concentrations were lowest with the plow compared to less intensive tillage treatments (Figure 4). In spring, particulate organic matter concentrations were lowest in chisel and moldboard plow treatments compared to disk or no-till treatments, potentially due to soil disturbance and oxidation of soil organic matter. The reduction in particulate organic matter concentration with moldboard plow or chisel plow can lead to reductions in soil organic matter concentration compared with no-till although CO2-C fluxes were generally not greater under plow or chisel treatments compared to no-till.

Previous studies suggest that soil moisture and soil temperature affect soil gas fluxes, depending on season and tillage. Results from the Nebraska case study showed that cumulative CO2-C fluxes calculated by season tended to be greater with greater tillage intensity, particularly during the season in which the tillage occurred. Further, the losses of easily decomposable organic matter with high-intensity tillage compared to no-till indicate that high-intensity tillage may be detrimental to soil biological activity and thus nutrient cycling.

References

Omonode, R.A., T.J. Vyn, D.R. Smith, P. Hegymegi, and A. Gal. 2007. Soil carbon dioxide and methane fluxes from long-term tillage systems in continuous corn and corn-soybean rotations. Soil Tillage Research 95:182-195.

Ussiri, D.A.N. and R. Lal. 2009. Long-term tillage effects on soil carbon storage and carbon dioxide emissions in continuous corn cropping system from an alfisol in Ohio. Soil Tillage Research. 104:39-47.

Ivory Schley
Ivori Schley

About the Lead Author

Ivori Schley is one of seven undergraduate students completing an Integrated Agronomic Systems Fellowship at UNL this summer.

She returned to school at North Carolina A&T State University, where she is an environmental studies student.

Support

Support for this project was provided by the USDA NIFA Agriculture and Food Research Initiative: Education and Literacy Initiative—Undergraduate Experiential Learning Fellowship Program and the University of Nebraska-Lincoln Department of Agronomy and Horticulture.