Evaluation of polyhalite fertilizer in varying levels and combination with chemical fertilizers on the growth and yield performance of lowland rice (Oryza sativa L.) in the Philippines

The results showed location- and season-specific variations. The growth and yield parameters improved with increasing rates of NPK applied, irrespective of the potassium source. During the dry season, grain yields varied among treatments and locations. In Oriental Mindoro, the highest yield was achieved by T4 (50% NP + 50% MOP) at 10.12 tons ha⁻¹, while the T1 (Control) produced 9.63 tons ha⁻¹. In Laguna, T10 (100% NP + 80% MOP + 20% POLY4) and T9 (100% NP + 60% MOP + 40% POLY4) recorded the highest yields at 7.76 and 7.60 tons ha⁻¹, respectively, compared to T1 with 4.46 tons ha⁻¹. In Nueva Ecija, T7 (100% NP + 100% POLY4) and T3 (100% NP + 100% MOP) produced the highest yields of 7.39 and 7.37 tons ha⁻¹, respectively, while T1 yielded 4.81 tons ha⁻¹. During the wet season, in Oriental Mindoro, T7 yielded 10.06 tons ha⁻¹, with T8 (100% NP + 40% MOP + 60% POLY4), T9, and T10 closely following (9.54, 9.49, and 9.48 tons ha⁻¹), all outperforming T1 (7.77 tons ha⁻¹). In Laguna, T8 recorded the highest yield at 8.85 tons ha⁻¹, followed by T7 (8.26 tons ha⁻¹), while T1 produced only 4.89 tons ha⁻¹. In Nueva Ecija, T8 and T7 achieved the highest yields at 9.26 and 9.17 tons ha⁻¹, respectively, significantly higher than T1 (8.30 tons ha⁻¹).