Calibration of leaf colour chart for need-based nitrogen management in Rabi maize under varied planting density in rainfed agriculture

Efficient nitrogen management is critical to improving maize (Zea mays L.) productivity and sustainability under rainfed conditions, where excessive or untimely N use can result in environmental degradation and low nitrogen use efficiency (NUE). Two years of field studies were conducted during consecutive Rabi seasons (2017-18 and 2018-19) at the wetland Farm of S.V. Agricultural College, Tirupati, to calibrate the lead colour chart (LCC) for increasing grain yield, NUE and nutrient uptake under varied planting densities. The study intended to establish threshold leaf greenness values as practical guides for in-season, need based nitrogen top dressing in maize. A split-split plot design was used with three planting densities (66666, 83333 and 111111 plants ha-1), three nitrogen levels (30, 35 and 40 kg N ha-1) and three LCC thresholds (4, 4.5 and 5). Results showed that highest planting density (111111 plants ha-1) combined with 40 kg N ha-1 applied in splits based on LCC 5 significantly improved plant growth parameters, chlorophyll content, dry matter accumulation and kernel yield (5.36 t ha-1), along with enhanced nitrogen uptake (114.1 kg ha-1) and NUE (31.4 kg grain per kg N). Regression analysis revealed that dry weight (R² = 0.96), LAI (R² = 0.84) and NUE (R² = 0.70) were the strongest predictors of yield. LCC based nitrogen scheduling synchronized N supply with crop demand, minimized losses and improved soil N balance. These findings validate that LCC is an effective, ow cost tool for enhancing maize productivity and nutrient efficient under rainfed conditions.