Effect of Zinc Application on Maize Dry Matter, Zinc Uptake, and Soil Microbial Community Grown Under Different Paddy Soil pH

Zinc (Zn) is often of deficient in paddy soils, and optimizing its application is crucial for improving maize productivity in intensive rice–maize cropping systems. This study aimed to develop practical Zn fertilizer strategies suitable for paddy soils with varying pH levels, thereby improving nutrient management and understanding of soil microbial responses. Field experiments were conducted during the 2020–2021 dry seasons at three sites: Chon Daen (pH 5.8), Noen Maprang (pH 6.7), and Lom Sak (pH 7.8). A two-factorial randomized complete block design with four replications was used, including four ZnSO4·H2O rates (0, 1.5, 3, and 6 times the DTPA-extractable Zn in soil) and two hybrid maize varieties, Suwan 5731 and Suwan 5819. Results showed that at Chon Daen, Zn application significantly enhanced shoot Zn uptake and soil Zn concentration, with SW5819 exhibiting greater Zn efficiency and biomass production. At Noen Maprang, Zn application did not significantly affect dry matter, while, at Lom Sak, Zn responses were moderate, though SW5819 maintained better growth and Zn uptake. Across sites, maize Zn efficiency was highest under acidic conditions and in SW5819. Soil microbial communities remained largely unaffected by Zn fertilization and were primarily influenced by soil pH, with Proteobacteria, Crenarchaeota, and Ascomycota dominating bacterial, archaeal, and fungal groups, respectively. These findings support the feasibility of Zn fertilization strategies to enhance both crop productivity and nutritional quality without altering the microbial community composition.