Effect of POLY4 (polyhalite) and different nutrient levels on growth and productivity of groundnut under irrigated conditions

India is the world’s second largest groundnut producer, accounting for 30 % of global production with 119.42 lakh tonnes from 57.62 lakh hectares. Despite its economic significance, the national productivity (2073 kg ha-1) remains low due to sub-optimal nutrient management practices and soil compaction during the pegging stage. In this connection, this study evaluated the efficacy of POLY 4 (polyhalite), a multi-nutrient fertiliser (potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S)), as both a soil amendment and a potential alternative to gypsum for groundnut cultivation. A field experiment was carried out at SRM College of Agricultural Sciences (SRMCAS), SRM Institute of Science and Technology (SRMIST), India during the rabi season of 2025–26 under irrigated conditions. The trial was laid out in a randomised block design (RBD) with 10 treatments and 3 replications on clay loam soil. The groundnut variety GG7 was sown with a spacing of 30 cm × 10 cm. The results revealed that the application of 100 % recommended dose of fertiliser (RDF-nitrogen and phosphorus (NP)- 25:50 kg ha-1) with POLY4 (applied in two splits: 50 % basal and 50 % at 45 days after sowing (DAS)) recorded the highest growth and physiological attributes viz., plant height (45.7 cm), dry matter production (6573 kg ha-1), number of branches plant-1 (13.2), leaf area index (4.20), total chlorophyll content (50.5 µmol m-2) and root nodule count plant-1 (273.2), alongside yield and yield attributes such as number of flowers plant-1 (36), number of pegs plant-1 (76), number of pods plant-1 (47), filling percentage (77), number of single seeded pods plant-1 (2.6), number of double seeded pods plant-1 (32.2), number of matured pods plant-1 (34.8), pod yield (2026 kg ha-1), haulm yield (5096 kg ha-1) and harvest index (0.30). Heatmap analysis further confirmed that treatment T5 (100 % RDF (N and P) + 100 % POLY4 (polyhalite) at 50 % basal and 50 % at 45 DAS) produced strong positive normalised values for growth, physiological and yield parameters, indicating enhanced vegetative growth and reproductive efficiency. The results suggest that polyhalite can improve the yield, leading to higher groundnut productivity under irrigated conditions.