Asian Journal of Soil Science and Plant Nutrition

Nitrogen (N) is an essential nutrient required for photosynthesis, growth, yield, quality, and biomass production in rice. Zinc (Zn) is also a crucial micronutrient for the growth and development of rice; its deficiency can result in reduced yield and quality. To determine the optimal levels of N and Zn for enhancing the yield and yield components of Sin Thu Kha rice, an experiment was conducted using a split-plot design with four replications. The main plot factor consisted of four levels of N: (1) 0% of the recommended N rate (N0), (2) 75% of the recommended N rate (76.5 kg N ha⁻¹) (N75), (3) 100% of the recommended N rate (102 kg N ha⁻¹) (N100), and (4) 125% of the recommended N rate (127.5 kg N ha⁻¹) (N125). All plots received equal amounts of phosphorus (27 kg P₂O₅ ha⁻¹) and potassium (117 kg K₂O ha⁻¹). The subplot factor included three levels of Zn: (1) control (Zn₀), (2) 20 kg Zn ha⁻¹ as a basal application (Zn₂₀), and (3) 40 kg Zn ha⁻¹ (which included 20 kg Zn ha⁻¹ as a basal application plus 20 kg Zn ha⁻¹ as two foliar sprays during the heading and grain-forming stages) (Zn₄₀). The results indicated that plant height, tiller number, SPAD value, and leaf area in rice were maximised with the application of N125, followed by N100 and N75. Additionally, grain yield, harvest index, and yield components (including the number of panicles hill^-1, panicle length, number of spikelets panicle^-1, filled grain percentage, and 1000-grain weight) were highest in the N125 treatment. Regarding the effects of Zn on growth and yield, the best results were observed with the Zn40 treatment, followed by Zn20 and Zn0. The N, P, K, and Zn contents of the soil increased in all treatments compared with those before the experiment. The combination of N125 and Zn40 resulted in the best growth characteristics and yield for the Sin Thu Kha rice variety, particularly when Zn was applied to the soil and by foliar spray. In conclusion, the combined application of N and Zn significantly improved rice growth and yield, as well as the nutrient content of the soil.