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NITROGEN MANAGEMENT

Using Leaf Color Charts to Estimate Leaf Nitrogen Status of Rice

^a Rice Cultivation Res. Div., Natl. Crop Exp. Stn., Rural Dev. Administration, 209 Seodundong, Suwon 441-100, Republic of Korea
^b Crop, Soil, and Water Sci. Div., Int. Rice Res. Inst. (IRRI), DAPO Box 7777, Metro Manila, Philippines

* Corresponding author (s.peng{at}cgiar.org)

Received for publication April 4, 2002. Leaf color charts (LCCs) have substituted for chlorophyll meter (SPAD) to estimate leaf N status of rice (Oryza sativa L.) and to properly time N fertilizer application. The objectives of this study were to (i) compare three different types of LCC in estimating leaf N status, (ii) determine if specific leaf weight (SLW) affects the estimation of dry weight–based N concentration (N_dw) by LCC, and (iii) determine the relationship between LCC scores and SPAD values. Two field experiments were conducted in the Philippines with different N rates and cultivars grown during 2000 wet season and 2001 dry season. The LCC score and SPAD reading were taken on uppermost fully expanded leaves at three growth stages, and SLW was calculated as the ratio of dry weight to leaf area. Nitrogen content was determined by micro-Kjeldahl procedure and expressed as N_dw and leaf area–based N content (N_a). There was a linear relationship between LCC scores and N_dw at each growth stage (R² range of 0.25–0.97) and across growth stages (R² range of 0.46–0.62). Adjusting LCC scores for SLW (LCC/SLW) greatly improved the prediction of N_dw across growth stages (R² range of 0.84–0.92), suggesting that leaf thickness affects LCC scores. Leaf color chart estimated N_a better than N_dw across growth stages. Leaf color chart scores were closely related to SPAD values (R² range of 0.62–0.98). Strong correlations existed among the scores of the three types of LCC (r range of 0.93–0.99). They are all suitable for use by rice farmers in timing N topdressing.

Abbreviations: DS, dry season • FL, flowering • IRRI, International Rice Research Institute • LCC, leaf color chart • MT, midtillering • N_a, leaf area–based nitrogen content • N_dw, dry weight–based nitrogen concentration • PI, panicle initiation • SLW, specific leaf weight • SPAD, chlorophyll meter • UCD, University of California, Davis • WS, wet season • ZAU, Zhejiang Agricultural University

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