Zinc (Zn) deficiency is the most widespread micronutrient deficiency in crops, and it affects more than 160 million ha of arable land worldwide (Alloway, 2009). Maize (Zea mays L.) is one of the most susceptible crops to this nutrient deficiency (Brown et al., 1993). Zinc deficiency can be avoided by the application of Zn fertilizers. However, to achieve rational Zn fertilizer management, the development, correlation, calibration and interpretation of soil test methods to diagnose plant-available soil Zn are necessary (Dahnke & Olson, 1990). The use of an adequate diagnostic method would avert under-or over-application of Zn, thereby reducing economic losses.

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Determining soil Zn thresholds for wheat (Triticum aestivum L.) is still challenging because soil Zn tests have been poorly calibrated. Therefore, this work aimed to determine, under field conditions, the diethylenetriaminepentaacetic acid (DTPA)-Zn critical threshold for wheat grain yield (GY) response to Zn fertilization in noncalcareous Mollisols. We conducted 14 Zn-fertilization field trials in Typic Argiudolls from the Argentinean Pampas. Zinc fertilization increased GY in 6 out of 14 trials. Wheat GY response to Zn fertilization ranged from 300 to 949 kg ha -1 . Our DTPA-Zn threshold is the first one determined by field trials for wheat grown in Mollisols (1.03 mg kg −1 , with a 95% confidence interval from 0.87 to 1.23 mg kg −1 ). This threshold was greater than those previously reported for other soil types. Future studies should compare different Zn-fertilization strategies for wheat on Mollisols by combining different fertilizer rates, sources, timings, and placements.