Moldboard plow tillage depth and short-term carbon dioxide release

Agricultural ecosystems can play a significant role in the production and consumption of greenhouse gases, specifically, carbon dioxide (CO2). Intensification of agricultural production is an important factor influencing greenhouse gas emission, particularly the relationship between intensive tillage and soil carbon (C) loss. Information is needed on the mechanism and magnitude of greenhouse gas generation and emission from agricultural soils with specific emphasis on tillage operations. The specific objective of this work was to evaluate the short-term effects of moldboard plowing depth on CO2 loss from a Barnes loam (Udic Haploboroll, fine loamy, mixed) in west central Minnesota, U.S.A. Experimental treatments were weed-free replicated plots, moldboard plowed to depths of 0.102, 0.152, 0.203, and 0.280 m using two passes of a four-bottom conventional moldboard plow (MP) following harvest of a spring wheat (Triticum aestivum L.) crop that was compared with an undisturbed area (no-tillage). The CO2 flux was measured immediately after the tillage with a large, portable chamber commonly used to measure crop canopy gas exchange and continued intermittently for several hours after the initial tillage and at 24 and 48 h and periodically to 500 h after tillage. To cope with the weather-induced temporal variability, the flux data at each tillage depth was fitted to the same two-part exponential function for smoothing temporal trends and statistical analysis. The CO2 release immediately following tillage increased with plow depth, and in every case was substantially higher than that from the no-tillage treatment. Expressing the results relative to no till (NT) showed the relative cumulative CO2 loss for plowed depths were 3.8, 6.7, 8.2, and 10.3 times larger than NT for the MP 0.102 m, MP 0.152 m, MP 0.203 m and MP 0.280 m, respectively. The smaller CO2 loss with shallow tillage was significant and suggests progress is being made in understanding the effect of tillage intensity on soil C management. Any effort to decrease tillage depth and maximize crop residue return to the soil surface should result lower in fuel consumption and increase soil C sequestration for enhanced environmental quality.