Quantifying soil carbon change in a long‐term tillage and crop rotation study across Iowa landscapes

Abstract

AbstractThe dominant cropping system of corn and soybean in the midwestern United States, coupled with use of conventional tillage (CT), has contributed to soil organic carbon (SOC) loss since the conversion of grassland to row crops. This study, conducted at seven sites in Iowa from 2002 to 2014, included five tillage systems: conservation tillage (no tillage [NT], strip‐tillage [ST]) and CT (chisel plow [CP], deep rip [DR], and moldboard plow [MP]) as main treatment and three crop rotations (corn–soybean [C‐S], corn–corn–soybean [C‐C‐S], and continuous corn [C‐C]) as subtreatments in a completely randomized block design with four replications. The objective was to quantify the effect of different tillage intensities and crop rotations on SOC change in different regions in Iowa. The average SOC gain in northern Iowa with NT and ST was 0.33 Mg ha−1 yr−1 over 12 yr with C‐S and C‐C‐S and 0.28 Mg ha−1 yr−1 over 7 yr in the C‐C rotations. The average SOC loss with CP, DR, and MP was −0.34 Mg ha−1 yr−1 with C‐S and C‐C‐S and −0.36 Mg ha−1 yr−1 with C‐C over the same periods. In southern Iowa, NT and ST gained 0.36 Mg ha−1 yr−1 with C‐S and C‐C‐S and 0.33 Mg ha−1 yr−1 with C‐C, whereas CP, DR, and MP on average lost −0.36 Mg ha−1 yr−1 with C‐S and C‐C‐S and −0.34 Mg ha−1 yr−1 with C‐C. The findings also showed that most SOC change (gain or loss) occurred at the top 0–30 cm with no evidence of significant SOC translocation to lower depths.