Rotation and tillage affect soybean grain composition, yield, and nutrient removal

• Soybean grain yield, and protein, K, Zn, B, and Cu concentrations were affected by rotation and tillage treatments.
• Grain K, Zn, and Fe concentration differences were attributed to differences in tillage while differences in protein and Cu were attributed to rotation.
• Grain oil, P, Ca, Mg, and Fe concentrations were not affected by rotation or tillage either study year.

Soybean (Glycine max [L.] Merr.) grain composition determines its uses, nutritional quality, value, and the amount of nutrients removed from agricultural ecosystems. Yet few studies have evaluated the effects of annual farming practices on composition. This study was conducted to determine whether soybean grain composition is altered by farming practices and how these practices impact yield and nutrient removal. The effects of long-term cropping systems (continuous soybean or soybean in rotation with corn (Zea mays L.), both tilled and no-till) on yield and concentrations of grain protein, oil, and nine mineral components, after 20 and 22 years of continuous management, were determined. Grain yield, protein, K, Zn, B, and Cu concentrations differed among cropping systems in both years while Mn concentration differed in one of two years. Oil, P, Ca, Mg, and Fe concentrations did not differ among cropping systems in either year, but across both years mean Fe concentration was affected. Differences in K, Fe, and Zn concentrations were mostly attributed to tillage each year, while those in protein and Cu concentrations were mostly attributed to rotation each year. Distinct B concentrations were attributed to tillage while distinct Mn concentrations were attributed to rotation. Grain yield differences were attributable to both rotation and tillage each year. In most instances, oil and protein yield, and mineral removal were dominated by grain yield differences and not concentration. Nonetheless, long-term tillage and rotation greatly affected soybean grain composition. Thus, rotation and tillage should be accounted for when assessing seed quality and seed composition.