Nitrogen use efficiencies using leaf colour chart in rice (Oryza sativa)-wheat (Triticum aestivum) cropping system

A field experiment was conducted at Project Directorate for Cropping Systems Research, Modipuram, Meerut during 2001-02 and 2002-03 to determine the threshold leaf colour chart values for N application in rice (Oryza sativa L.) and wheat (Triticum aestivum L. emend. Fiori & Paol.) for increasing fertilizer N use efficiency, reducing nitrate-N leaching and work out economics of leaf colour chart-based N management in rice-wheat cropping system. Combinations of 3 rice-wheat cultivars ('Basmati 370' followed by 'PBW 343', 'Saket 4' followed by 'HD 2687' and 'Hybrid 6111/PHB-71' followed by PBW 226) were grown in main plot and 6 N management practices under a split-plot design with 3 replications. Leaf colour chart threshold values of 3 for 'Basmati 370', 4 for 'Saket 4' and 5 for 'Hybrid 6111/PHB-71' gave higher grain yield (14.7, 15.6 and 12.4% respectively) with greater N use efficiencies (AE(N), 35-54% and REN, 22-38%) than recommended N use, ie 120 kg N/ha in 3 splits. In wheat, leaf colour chart threshold value <= 4 gave higher grain yield (0.45 to 0.70 tonnes/ha), N uptake and N use efficiency than with 120 kg N/ha applied in 3 fixed time splits. A significant positive effect of N management through leaf colour chart on different yield attributing parameters, viz particles/ m(2), fertile grains/panicle and grain weight/panicle of rice and wheat was noticed. In addition, results showed that nitrate N content in lower layer (beyond 60 cm depth) was less under leaf colour chart based N management vis-a-vis recommended N split. The net returns in leaf colour chart-based N management were 16-33% higher than recommended N application..