Leaf Chlorophyll Readings as an Indicator for Spinach Yield and Nutritional Quality with Different Nitrogen Fertilizer Applications |
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Authors: | Yan-Ju Liu Yi-Ping Tong Yong-Guan Zhu Hui Ding F Andrew Smith |
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Institution: | 1. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing, China;2. Beijing Center for Physical and Chemical Analysis , Beijing, China;3. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing, China;4. Beijing Center for Physical and Chemical Analysis , Beijing, China;5. Soil and Land System, School of Earth and Environmental Sciences, The University of Adelaide , Adelaide, Australia |
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Abstract: | The objective of this study was to investigate the possibility of predicting the concentrations of total nitrogen (N), nitrate-nitrogen, and ascorbic acid in spinach (Spinacia oleracea) leaves using the pocket chlorophyll meter SPAD-502 (Minolta, Japan) in a pot experiment in a greenhouse. Spinach plants were grown in plastic pots filled with 0.5 kg of brown soil per pot with urea as N fertilizer at 0, 30, 60, 120, and 240 mg N/kg soil. SPAD readings of the two uppermost fully expanded leaves were recorded 18, 25, and 32 d after sowing and at harvesting (34 d). Dry-matter biomass and total N concentrations in leaves and roots, and NO3-N, and ascorbic acid concentrations in leaves, were measured after harvesting. SPAD readings showed continuous reduction with increasing growth period irrespective of N applications. SPAD readings at harvest were significantly correlated with total N, leaf dry weight (DW), and NO3-N concentration. However, this correlation did not exist between SPAD readings and ascorbic acid concentrations in leaves. The above results suggest that it is possible to apply SPAD readings to estimate NO3-N concentrations in spinach plants, and that they may be applied for field assessments in decision-making and operational nutrient-management programs for the plant. Furthermore, the SPAD method may also be useful for ascertaining the harvest time. The results suggest that treatment with 120 mg N/kg significantly improved both leaf yields and leaf quality (i.e., leaf nitrate-N concentration and ascorbic acid). Too little and too much N fertilizer was not good for yield or spinach quality. |
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Keywords: | SPAD readings chlorophyll meter nitrogen nitrate-N ascorbic acid |
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