UC Davis

Two of the most important agricultural practices aimed at improving soil properties are crop rotations and no-tillage, yet relatively few studies have assessed their long-term impacts on crop yields and soil greenhouse gas (GHG) emissions. The objective of this study was to determine the influence of tillage and crop rotation on soil GHG emissions and yields following 15 years of treatment implementation in a long-term cropping systems experiment in Illinois, USA. The experimental design was a split-plot RCBD with crop rotation as the main plot: (continuous corn [Zea mays L.] (CCC), corn-soybean [Glycine max (L.) Merr.] (CS), continuous soybean (SSS), and corn-soybean-wheat [Triticum aestivum L.] (CSW); with each phase of each crop rotation present every year) and tillage as the subplot: chisel tillage (T) and no-tillage (NT). Tillage increased the yields of corn and soybean. Tillage and crop rotation had no effect on methane (CH₄) emissions (p = 0.4738 and p = 0.8494 respectively) and only rotation had an effect on cumulative carbon dioxide (CO₂) (p = 0.0137). However, their interaction affected cumulative nitrous oxide (N₂O) emissions significantly (p = 0.0960); N₂O emissions from tilled CCC were the greatest at 6.9 kg-N ha⁻¹-yr⁻¹; while emissions from NT CCC (4.0 kg-N ha⁻¹-yr⁻¹) were not different than both T CS or NT CS (3.6 and 3.3 kg-N ha⁻¹⁻yr⁻¹, respectively). Utilizing just a CS crop rotation increased corn yields by around 20% while reducing N₂O emissions by around 35%; soybean yields were 7% greater and N₂O emissions were not affected. Therefore results from this long-term study indicate that a CS rotation has the ability to increase yields and reduce GHG emissions compared to either CCC or SSS alone, yet moving to a CSW rotation did not further increase yields or reduce N₂O emissions.