Critical Sulfur Dilution Curve and Sulfur Nutrition Index in Maize.

Record grain yields and increased awareness of climate variability have more producers considering intensive (i.e., high-input) wheat (Triticum aestivum L.) management. This study investigated soft winter wheat response to several agronomic inputs across intensive and traditional (i.e., low-input) management systems. Sulfur (S) deficiency can severely limit maize (Zea mays L.) yield. This deficiency could be predicted by quantifying the S concentration (S_C) in the shoot biomass (BM) and by calculating the S nutrition index (SNI = observed S_C/critical S_C). However, as shoot S_C determination is laborious, alternative S diagnostic methods should be developed in maize. Thus, the objectives of our study were to: (i) determine and validate a critical S dilution curve, (ii) quantify the critical SNI, and (iii) explore the use of S_C and chlorophyll meter reading (CMR), both determined in the uppermost developed leaf at vegetative growth stages, to predict SNI and for diagnosing S status in maize. Six field studies evaluating fertilizer S rates were executed, collecting maize shoot and uppermost developed leaf samples and determining S_C, CMR, yield, and SNI parameters. The main outcomes from our study were: (i) a maize critical S dilution curve was fitted (S_C = 2.13BM-0.23) and validated with an independent dataset; (ii) a critical SNI threshold of 0.79 adequately diagnosed S status at ~V6 stage; (iii) at V6, SNI was linearly related to S_C (R² = 0.65) and CMR (R² = 0.85). As a result, a threshold value of 2.0 g S kg-1 for S_C, 47.5 units for CMR, and 0.94 units for relative CMR can be used to successfully diagnose S deficiencies at early vegetative (~V6) maize stages. Future studies testing S diagnostic tools for maize should be performed in environments with severe S deficiency and nutrient co-limitations. [ABSTRACT FROM AUTHOR]