Predicting Boron Availability for Soybean: Field Calibration of Soil and Plant Analyses

Background Boron (B) deficiency can negatively affect the physiological processes of soybean ( Glycine max (L.) Merr.). However, little is known about using soil or plant tissue tests as predictors of soybean seed yield response to B fertilization. Aim To evaluate the ability of soil and plant analyses to predict soybean seed yield response to B fertilization. Methods Field studies were conducted between 2004 and 2022 across 30 site‐years. Two treatments were evaluated: with or without foliar B fertilization. Soil samples (0–20 cm) were collected at sowing, and B was extracted with CaCl 2 (CaCl 2 ‐B) or ammonium acetate (NH 4 Ac‐B) and quantified by the azometine‐H method. Total B concentration was also determined in seed samples and trifoliate leaves collected at the vegetative (V 7 –V 8 ) and reproductive (R 2 ) growth stages. Results Boron fertilization increased seed yield by 5%–6% and generally did not increase leaf or seed B concentrations. Soil testing for B availability predicted soybean seed yield response to fertilization. The critical B thresholds for CaCl 2 ‐B and NH 4 Ac‐B were 0.72 and 0.66 mg kg −1 , respectively. However, NH 4 Ac‐B showed a greater proportion of correctly diagnosed cases than CaCl 2 ‐B. Neither the early nor the late‐stage leaf or seed‐tissue analysis of B total concentration provided an accurate diagnosis of B response to B fertilization. Conclusions Under field conditions, NH 4 Ac‐B proved more accurate than CaCl 2 ‐B for identifying B deficiency. Plant tissue B analyses did not demonstrate significant predictive value. We recommend soil testing with NH 4 Ac for predicting seed yield response to B fertilization in soybean.