Conventional agricultural practices that rely heavily on blanket fertilizer recommendation, eventually leading to deteriorated partial factor productivity and N use efficiency. We investigated the effect of SPAD-based N-management on productivity and N use efficiency of rice and wheat in eastern India. Here, in the experiment three SPAD thresholds (34, 36 and 38 in rice and 38, 40 and 42 in wheat) using three N levels (15, 25 and 35 kg N ha −1 ) in split were incorporated as real-time N management (RTNM), one fixed-time N management (FTNM), farmers' fertilizer practice (FFP) and control (No fertilizer) were introduced in wet and dry seasons for rice and wheat, respectively, during the years 2010 to 2012. Topdressing with 25 kg N ha −1 at medium SPAD (S 36 in rice and S 40 in wheat) increased soil N availability, leaf N content and grain yield of rice (5215 kg ha −1 ) and wheat (4483 kg ha −1 ) over the grain yield recorded under a low rate of N topdressing at low SPAD. While saving 33.3% N in rice and 18.8% N in wheat, the agronomic N use efficiency (58.5% in both rice and wheat) and nitrogen recovery efficiency (32.2% in rice and 15.1% in wheat) can be increased when compared with conventional FTNM. The SPAD-based management strategy showed great promise in efficient management of N fertilizer, and we estimated the optimal SPAD threshold for rice and wheat as 37.5 and 41.8, respectively.
N management must be based on crop demand and supply capacity of the soil. A field experiment was conducted to analyze the effect of chlorophyll meter (SPAD meter) based N management on growth, productivity and agronomic N use efficiency of rice (cv. IR 36) in lateritic soil of India during the wet season of 2010 and 2011. The Experiment contained twelve N management treatments such as farmers' fertilizer practice, one fixed time N management (FTNM), nine treatments of real time N management (RTNM), and one control. The RTNM is the combination of three SPAD threshold (SPAD: 34, 36 and 38) and three N levels (15, 25 and 35 kg ha -1 ) for top dressing when the SPAD value of rice leaf falls below the threshold. The grain yield of RTNM was in the range 93 to 105% as that of FTNM, but with lower N application rate. Among RTNM treatments, SPAD 36 with 35 and 25 kg N ha -1 top-dressing could save N fertilizer by 20 to 35% compared to FTNM without reducing grain yield. Agronomic N use efficiency can be increased at high yield level using SPAD meter based N management.
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