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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Soil Management and Sugarbeet Research » Research » Publications at this Location » Publication #332050
Title: Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

Author
item Stewart, Catherine
item HALVORSON, ARDELL - Former ARS Employee
item Delgado, Jorge

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2017
Publication Date: 4/26/2017
Citation: Stewart, C.E., Halvorson, A.D., Delgado, J.A. 2017. Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn. Soil & Tillage Research. 171:9–18. doi:10.1016/j.still.2017.04.003.

Interpretive Summary: No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but the effects deeper in the soil profile are uncertain. We followed a long-term tillage and N rate study near Fort Collins, CO after 11 years of continuous NT and report residue yields, SOC, and particulate organic matter C (POM-C). Conversion from CT to NT resulted in surface SOC accumulation and subsurface (7.5-15 and 15-30 cm) SOC loss of 30-50% of POM over the study as previously buried residues decomposed. N fertilization increased surface SOC stocks and reduced SOC loss in the 7.5-15 and 15-30cm layers, through a doubling of stover returned to the soil. In contrast to surface effects, when evaluated through the 0-120cm profile, there was no overall effect of tillage or N on SOC stocks. Long-term NT with and without N addition redistributed SOC to the surface, with previously buried C decomposing and an overall loss of SOC from the profile. Conservation practices can promote sustainable production and build surface SOM, but did not promote SOC sequestration throughout the soil profile in this irrigated system.

Technical Abstract: No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but the effects deeper in the soil profile are uncertain. Subsequent tillage could counter SOC stabilized through NT practices by disrupting soil aggregation and promoting decomposition. We followed a long-term tillage and N rate study near Fort Collins, CO after 11 years of continuous NT and report residue yields, SOC, and particulate organic matter C (POM-C). Six years of strip till (ST) after 5 years of NT increased corn grain yields, but only compared to the initial phase of the experiment; in the later 7 years of the experiment, there was no difference in yields or stover biomass between NT and ST. Conversion from CT to NT resulted in surface SOC accumulation and subsurface (7.5-15 and 15-30 cm) SOC loss of 30-50% of POM over the study as previously buried residues decomposed. ST after the initial 5 years of NT completely negated surface (0-7.5 cm) SOC gain, which was only partially explained by a loss of POM-C (25-33%). N fertilization increased surface SOC stocks and reduced SOC loss in the 7.5-15 and 15-30cm layers, through a doubling of stover returned to the soil. In contrast to surface effects, when evaluated through the 0-120cm profile, there was no overall effect of tillage or N on SOC stocks. Long-term NT with and without N addition redistributed SOC to the surface, with previously buried C decomposing and an overall loss of SOC from the profile. Conservation practices can promote sustainable production and build surface SOM, but did not promote SOC sequestration throughout the soil profile in this irrigated system.