Long-Term Tillage and Crop Rotation Effects On Soil Carbon and Soil Productivity.

Tillage practices and crop rotations can greatly alter agronomic performance and physical and biological properties of the soil. The effects on agronomic performance are greatly influenced by the type of landscape, soil characteristics (i.e., drainage class, slope, soil texture, etc.), crop rotation, and type of tillage practices. Conservation tillage systems and crop rotations offer an alternative to minimize the negative effect of conventional tillage systems or mono-cropping systems such as continuous corn on yield and soil quality. Changes in soil physical and biological properties can be very slow and gradual. In many studies, changes in soil carbon or physical properties in response to no-till for example was very slow and insignificant in the short-term (<10 years).

This study was conducted on seven Iowa State University Research and Demonstration Farms starting in 2002, and continuing to the present. Treatments include five tillage systems (no-till, strip-tillage, chisel plow, deep ripper, and moldboard plow) and three crop rotations of corn-corn-soybean, corn-soybean, and corn-corn across the five tillage systems and several soil associations. Baseline soil samples were collected in 2002 prior to implementing the tillage treatments. Soil samples were periodically collected for each site, with the most recent samples taken in 2010. The soil samples were collected from all sites for depths of 0-6, 6-12, 12-18, and 18-24 inches and were analyzed for total carbon, total nitrogen, and bulk density.  Grain yield was also collected yearly for each tillage treatment and rotation.  The experimental design was a randomized complete block design with four replications. 

Regardless of the crop rotation, average corn yields from across the state show that both strip-tillage and conventional tillage generally over preformed no-till.  However, the amount of difference in yields between tillage treatments depends on the soil and drainage conditions of the site.  Comparing the corn yield of each tillage system shows that second year corn in a C-C-S rotation was lower than that for corn after soybean in all tillage systems.  Soybean yields are affected by yearly variability within all tillage systems, but no differences in yield were observed between tillage systems within each year.  The lack of significant soybean yield differences between different tillage systems was observed at all sites across the state.