Evaluation of the effect of K fertilization rate on soybean yield and soybean looper (Chrysodeixis includens ) development

Inorganic fertilizers increase yields.  However, these same fertilizers can stimulate insect outbreaks.  To reduce insect pest outbreaks, we must understand the specific interactions between fertilizers and herbivores.  Understanding these complex interactions between host/herbivore/nutrient inputs is key to maintaining a balance between productivity and control.  Soybean is often rotated with high input crops of corn, wheat, rice, and sugarcane; utilizing leftover nitrogen.  In this study, we evaluated the effect of potassium fertilization rates on soybean yield and soybean looper, Chrysodeixis includens (Walker), development.  Potassium (K₂O) was applied at planting at 6 different rates: 0, 30, 60, 90, 120, and 150 lb/A, and treatments were arranged in a RCBD with four replications.  Leaf tissue was taken for nutrient testing and soybean looper life table bioassays at R1, R3, R5, and R6.  Soybean yield increased at 90 and 150 lb/A.  At 120 and 150 lb/A, soybean looper consumed more tissue and pupal weights increased at the 150 lb/A rate.  However, no significant interaction was observed between K fertilization rate and egg hatch rate as well as mortality.  This study suggested that higher potassium fertilization rates led to higher soybean yield and resulted in soybean plants being more suitable for soybean looper population growth.