Micronized Zn Oxide on Carbonic Anhydrase Activity, Health, and Yield of Ratoon Sugarcane Under Tropical Conditions

Zinc (Zn) is one of the most important micronutrients with a direct effect on sugarcane yield. Our hypothesis is that micronized Zn oxide is an optimal Zn source to improve the zinc status, health, and yield of ratoon sugarcane. The present study assessed the effect of Zn doses, sources, and application times (foliar spraying) on sugarcane yield, carbonic anhydrase activity (CAA), and plant diseases in tropical conditions. A study was developed in three sites (Assis, Ourinhos, and Serrana, São Paulo state), Brazil, during the first ratoon cane in 2019/2020. The study tested four Zn doses (0; 639; 1039; and 1386 g ha⁻¹), two Zn sources (Zn sulfate; and micronized zinc oxide), and three application times [at plant heights of 0.5 (100% dose); 1.0 m (100% dose); and 0.5 (50% dose) + 1.0 m (50% dose)]. The results showed that Zn foliar spraying increased CAA (from 224.8 to 742.1 UE g⁻¹) and leaf Zn content (from 12 to 15 g kg⁻¹). The Zn doses reduced orange rust severity and increased yield. Application at the onset of ratoon development (0.5 m tall stems) was more efficient than the other timing formats. Based on the results obtained, it was concluded that soil fertilization micronized zinc oxide improves the Zn status of sugarcane and CAA, contributing to reducing Zn deficiency and health problems in this crop.