Can Edaphic Variables Improve DTPA‐Based Zinc Diagnosis in Corn?

Core Ideas DTPA‐extractable Zn is often used to predict corn response to Zn application. Can DTPA–Zn‐based diagnosis be improved by considering other soil properties? Soil properties did not contribute to explain corn grain yield response. DTPA–Zn allowed to discriminate sites based on their response to Zn fertilization. We determined a Zn‐critical range from 0.86 to 1.30 mg kg−1 (n = 64). Current zinc (Zn) diagnostic methods for corn (Zea mays L.) are often based on soil DTPA (diethylenetriamine‐pentaacetic acid) extractable Zn (DTPA‐Zn). However, calibration of the DTPA‐Zn test may be influenced by other soil properties such as pH, organic matter (SOM) and available Bray‐P (PBray‐1). Our objective was to assess the contribution of soil properties to a DTPA‐Zn model used to predict corn response to Zn fertilization. We conducted 64 field trials with two Zn‐fertilization treatments: with and without Zn fertilization. In all sites, we measured SOM, PBray‐1, pH, and DTPA‐Zn at 0‐ to 20‐cm depth before sowing. Yield difference between Zn‐fertilized and unfertilized treatments (Ydᵢffₑᵣₑₙcₑ) was significant in 33% of the experimental site‐years. In responsive site‐years, the average Ydᵢffₑᵣₑₙcₑ was 0.98 Mg ha‐¹ (11.4%). Soil organic matter was the only property that was a significant addition to the DTPA‐Zn model for predicting the corn relative yield (Model R² including SOM = 0.27). However, the improvement was nominal (Partial R² of SOM = 0.06). Use of DTPA‐Zn alone was suitable to discriminate Zn responsiveness among site‐years based on the Ydᵢffₑᵣₑₙcₑ by correctly diagnosing 81% of the outcomes. We determined three soil DPTA‐Zn ranges with different probability of resulting in a Ydᵢffₑᵣₑₙcₑ greater than zero when fertilized with Zn: high (<0.9 mg kg‐¹), medium (0.9–1.3 mg kg‐¹), and low (>1.3 mg kg‐¹). These soil‐test‐based Zn recommendations improve the identification of Zn‐deficient soils allowing prevention of yield loss from Zn deficiency and more rational use of Zn fertilizers.