Chlorophyll Meter-Based Nitrogen Management in a Rice–Wheat Cropping System in Eastern India

Abstract

Sustainable crop production in sub-tropical countries is severely affected by the unscientific application of fertilizers. The SPAD based N management of the rice–wheat sequence was investigated in eastern India. Topdressing of 25 kg N ha−1 was applied at SPAD 36 and 40 (S36 and S40) for rice (Oryza sativa L.) and wheat (Triticum aestivum L.), respectively, reduced the N requirement by an average of 26.5% (33.3% in rice and 18.8% in wheat) over the fixed-time N management (FTNM) without reducing the grain yield. The 25 kg N ha−1 increased nutrient removal in the system having high agronomic N use efficiency (21.4) and nitrogen recovery efficiency (0.60) with the lower N requirement (62.5 kg N ha−1) over the FTNM. The treatment with medium SPAD (S36 for rice and S40 for wheat) under 25 kg N ha−1 increased the agronomic N use efficiency by 58% in rice and 58.5% in wheat compared to that under FTNM and recorded the highest gross (2106.1$ ha−1 Year−1) and net (1202.5$ ha−1 Year−1) returns from the rice–wheat system. The SPAD-based N management increased the water content in N-treated plots compared to that in the control plots, and the utmost moisture custody was observed when using a moderate (25 kg ha−1) N topdressing at a moderate SPAD (S36 for rice and S40 for wheat) for a given soil suction. This study suggests that using SPAD meter in rice–wheat system can cover the productive N management and profitability and can be dependably used in precision agriculture to manage the spatial variation in farmers’ field.