Soybean Yield Components As Influenced by Field Variability.

Many different products and practices can be managed spatially in soybean ((Glycine max (L.) Merr.) production. Yield monitoring and GPS technologies allow farmers to measure soybean yield differences within fields. However to improve spatial management in soybean, we need a better understanding of which soybean yield components are affected the most by within-field variability. In 2011, eight soybean fields were selected in central and eastern Iowa.  Ten sampling areas were selected within each field based on a range of variability in soil properties and plant growth. Soybean plants were sampled from a single row, 1 m along the row at each of the sampling area. Bean, pod, and node counts, plant population, plant height, and grain yield were measured for the main plant stems and stem branching. Also, pod and bean counts, and bean weight were measured for different (1 to 30) nodal positions.  A principal component analysis identified the bean count as the primary and bean weight as the secondary factor affecting soybean yield variation. The soybean yield for the different nodal positions varied significantly within each field.  The analyses confirmed that the different soybean yield components influenced soybean yield variation differently within fields.  The proposed sampling method can help to identify soybean yield components that might be affected by both field variability or by site-specific management practices.