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Nitrogen Management

Calibrating the Leaf Color Chart for Nitrogen Management in Different Genotypes of Rice and Wheat in a Systems Perspective

^a Y. Singh, Project Directorate for Cropping Syst. Res. (PDCSR), Modipuram, Meerut-250110, India
^b Int. Rice Res. Inst., DAPO Box 7777, Metro Manila, Philippines
^c Rice–Wheat Consortium for IGP, CIMMYT-RWC, CG Block, NASC Complex, DPS Marg Pusa Campus, New Delhi-110012, India
^d Indian Agric. Res. Inst., New Delhi, India
^e Natl. Agric. Technol. Project, Krishi Anusandhan Bhawan-II, New Delhi 110012, India

^* Corresponding author (J.K.Ladha{at}cgiar.org)

Received for publication October 22, 2003. Low N use efficiency (NUE) continues to be a problem in the rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system. The leaf color chart (LCC)–based real-time N management can be used to optimize/synchronize N application with crop demand or to improve existing fixed split N recommendations. We conducted a field experiment during 2001–2003 at Modipuram, India, to determine the threshold LCC values for N application in rice and wheat, assess the need for basal N application, calibrate the LCC with a chlorophyll meter (SPAD), and work out the economics of rice–wheat systems. Treatments consisted of LCC scores of 2 to 5 for different cultivars of rice and wheat and were compared with the zero-N control and a recommended fixed-time N splitting. In rice, LCC 3 for ‘Basmati-370’, 4 for ‘Saket-4’, and 5 for ‘Hybrid 6111/PHB-71’ produced higher yield and NUE than recommended N splits. In wheat, maintenance of LCC 4 required 120 kg N ha^–1, which produced higher grain yield, N uptake, and NUE than that of recommended N splits. Chlorophyll meter reading and crop growth rate (g m^–2 day^–1) at 15 d after transplanting in rice and 21 d after seeding in wheat were not significantly different with or without basal N application, indicating that basal N application in rice and wheat was not necessary in soils having relatively high indigenous N supply. Both LCC and SPAD readings (r = 0.84 to 0.91) were highly correlated in rice and wheat. Net returns were 19 to 31% higher in LCC-based N management than in fixed-time N application for rice–wheat cropping.

Abbreviations: AE_N, agronomic efficiency of nitrogen • CRI, crown root initiation • DAS, days after sowing • DAT, days after transplanting • INS, indigenous nitrogen supply • LCC, leaf color chart • N_a, leaf nitrogen content on leaf area basis • N_dw, leaf nitrogen content on dry weight basis • NR, net return(s) • NUE, nitrogen use efficiency • PI, panicle initiation • RE_N, recovery efficiency of nitrogen • SLW, specific leaf weight • SPAD, soil plant analysis development • TCC, total cost of cultivation

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