REFERENCE
Al-Kaisi, M. M., Archontoulis, S., & Kwaw-Mensah, D. (2016). Soybean spatiotemporal yield and economic variability as affected by tillage and crop rotation. Agronomy Journal, 108 (3), 1267-1280.

OBJECTIVE
To investigate how soybean yields and economics vary across sites, tillage systems and cropping systems, and which factor contributes the most to the year-to-year variability.

METHODOLOGY
In collaboration with Dr. Mahdi Al-Kaisi group we statistically analyzed a comprehensive long term soybean dataset (2003–2014) that included the effects of 7 sites (Sutherland, Kanawha, Nashua, Ames, Lewis, McNay and Crawfordsville) x 5 tillage systems (no-tillage, strip-tillage, chisel plow, deep rip, and moldboard plow) x 2 cropping systems (corn-soybean and corn-corn-soybean) on soybean yields and economics in Iowa. The experiments were replicated (n=4) and are still on-going and maintained by Dr. Mahdi Al-Kaisi.

KEY-FINDINGS
Soybean yields varied from 22 to 75 bu/ac and the coefficient of variation varied from 15 to 25% across years and sites (Fig. 1). Crop rotation had a greater influence on soybean yields and economics than tillage systems. The corn-corn-soybean system resulted in 9% greater soybean yields and 11% greater economic returns than corn-soybean rotation in five out of seven locations (Fig. 2). The tillage effect on soybean yield was not significant. The economic return with no-tillage exceeded that with conventional tillage due to lower input cost for the no-tillage system. A systems analysis of combined soybean (this study) and corn data (Al-kaisi et al., 2015) across years and sites showed that the economic return was higher in corn-soybean rotation, followed by corn-corn-soybean and then by the continuous corn system (Fig. 3). Read more here. 

REFERENCE
Al-Kaisi M, Archontoulis SV, Kwaw-Mensah D, Miguez FE, 2015. Tillage and crop rotation effect on corn agronomic response and economic return at seven Iowa locations. Agron J, 107: 786–798. 

OBJECTIVE
To investigate the effect of tillage and crop rotation on corn yields and economics across in Iowa and quantify the yield penalty under continuous corn.

METHODOLOGY
In collaboration with Dr. Mahdi Al-Kaisi research group we statistically analyzed a comprehensive long term corn dataset (2003–2014) that included the effects of 7 sites (Sutherland, Kanawha, Nashua, Ames, Lewis, McNay and Crawfordsville) x 5 tillage systems (no-tillage, strip-tillage, chisel plow, deep rip, and moldboard plow) x 3 cropping systems (continuous corn, corn-soybean and corn-corn-soybean) on corn yields and economics in Iowa. The experiments were replicated (n=4) and are still on-going and maintained by Dr. Mahdi Al-Kaisi.

KEY FINDINGS
Corn yields varied from 39 to 251 bu/ac across treatments with no detectable increase over time (Fig. 1). Corn yields were higher in the corn-soybean rotation, followed by the corn-corn-soybean and finally by the continuous corn system (Fig. 2). Higher corn yields and economic returns were found in northern locations compared to southern locations but there was substantial year-to year variability as indicated by the coefficient of variation (Fig. 1). The corn yield penalty, defined as yield difference between yield in corn-soybean and continuous corn, was found to be location specific and varied from 11 to 28%. Corn yields and economic penalty were greater with no-tillage than conventional tillage in the northern locations (poorly-drained soils) than locations with well-drained soils. The findings suggest a location specific adoption of tillage and crop rotation for achieving optimum yield. Read more here.