Exploring maize grain yield response to boron fertilization in Mollisols: Critical thresholds and predictive models

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Background There are no extractable boron (B) thresholds for maize ( Zea mays L.) in Mollisols determined by field calibrations. Aims Our objectives were to: (1) explore maize grain yield response to B fertilization, (2) calibrate the soil hot water extractable B (HW‐B) as a predictor of maize response to B fertilization under field conditions, and (3) assess the contribution of clay, pH, and soil organic matter (SOM) as predictive variables of maize response to B fertilization. Methods We conducted 53 field trials with 2 treatments: with and without B fertilization. At all sites, we measured clay, SOM, pH, and HW‐B at a 0–20 cm depth. Results Maize grain yield ranged from 5.34 to 17.35 Mg ha −1 . Grain yield response to fertilization was observed in 6 out of 53 sites (11.3%). In responsive sites, average grain yield response was 1.0 Mg ha −1 . Multiple regression models to predict yield response to B addition that included soil, pH, and SOM only explained 19% of the variability. The critical soil HW‐B concentration threshold was 0.78 mg kg −1 , correctly diagnosing 79% of the site‐years. Conclusion The critical threshold for maize B levels resulting from our field study is the first of its kind in Mollisols. This threshold will improve the identification of soils deficient in B.