Decision support tools for non-destructive estimation of rice crop nitrogen (N) status (e.g., chlorophyll meter [SPAD] or leaf color chart [LCC]) are an established technology for improved N management in irrigated systems, but their value in rainfed environments with frequent abiotic stresses remains untested. Therefore, we studied the effect of drought, salinity, phosphorus (P) deficiency, and sulfur (S) deficiency on leaf N estimates derived from SPAD and LCC measurements in a greenhouse experiment. Linear relations between chlorophyll concentration and leaf N concentration based on dry weight ( ) between SPAD values adjusted for leaf thickness and and between LCC scores adjusted for leaf thickness and could be confirmed for all treatments and varieties used. Leaf spectral reflectance measurements did not show a stress-dependent change in the reflectance pattern, indicating that no specific element of the photosynthetic complex was affected by the stresses and at the stress level applied. We concluded that SPAD and LCC are potentially useful tools for improved N management in moderately unfavorable rice environments. However, calibration for the most common rice varieties in the target region is recommended to increase the precision of the leaf N estimates. 1. Introduction For more than a decade, considerable efforts have been made to develop and establish improved nutrient management options for rice (Oryza sativa L.). The goals were concepts and tools allowing site- and season-specific (i.e., real-time) adaptation of nutrient management recommendations [1]. These efforts resulted in technologies contributing considerably to increased productivity of Asian rice farmers, improved use efficiency of scarce and expensive resources, and reduced detrimental environmental effects [2]. However, these developments are mostly limited to irrigated systems because the improved nutrient management technologies did not target rainfed rice systems. But recent developments show that, because of the increasing availability of input responsive varieties for rainfed lowlands [3], these environments are characterized by the fastest yield growth rates, often enabled by increasing fertilizer use. Therefore, improved fertilizer technologies are also needed for rainfed lowlands in order to increase the productivity of rice farming in these environments to maximize the efficiency of fertilizer use and to minimize negative environmental side effects of such practices. Nitrogen (N) as the most commonly used fertilizer element and the one limiting growth in the majority of
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