SPAD dynamics in maize crop with precision nitrogen management under rain-fed and irrigated conditions

Real-time monitoring of canopy chlorophyll content is crucial for understanding crop growth and guiding precision agricultural management. The SPAD chlorophyll meter is a valuable tool for assessing nitrogen status in maize (Zea mays L.), a key cereal crop used for food, feed, and biofuels. Efficient nitrogen management is essential to maximize maize yield, particularly under varying water regimes. A study conducted over two years (2020-2021) utilized a strip plot design to investigate the spatiotemporal dynamics of SPAD readings and their correlation with maize yield under rainfed (M1) and irrigated (M2) conditions. Eight precision nitrogen management practices were implemented, including SPAD at sufficiency index and Green Seeker at response index, achieving ranges of 86-100% and 1.11-1.41, respectively. The findings revealed that irrigated maize produced significantly higher grain yields (6347 kg ha^-1) compared to rainfed maize (5262 kg ha^-1). The highest yield (9508.2 kg ha^-1) was achieved when nitrogen was applied at a sufficiency index of 96-100%. The correlation between SPAD values and grain yield was strongest at reproductive stages (VT and R4), with R² values of 0.99 and 0.98 under rainfed conditions. In irrigated conditions, R² values ranged from 0.95 to 0.96 for earlier growth stages (V10, V12, VT, and R4). Multivariate analysis indicated critical management stages for optimizing yields in both conditions. Overall, SPAD-based nitrogen management strategies have the potential to enhance maize yields and resource efficiency while informing the development of sophisticated monitoring tools for real-time crop management.