Chlorophyll meter-based nitrogen management of rice grown under alternate wetting and drying irrigation

• Published in: Field crops research 2011-02, Vol.121 (1), p.136-146
• Main Authors: Cabangon, R.J., Castillo, E.G., Tuong, T.P.
• Format: Article
• Language: English
• Subjects: alternate wetting and drying irrigation; anaerobic conditions; chlorophyll; deficit irrigation; economic analysis; field experimentation; grain yield; irrigation rates; irrigation systems; leaf color chart; leaves; nitrogen; nitrogen content; Nitrogen-use efficiency; nutrient management; nutrient use efficiency; Oryza sativa; plant nutrition; remote sensing; rice; soil water content; SPAD; Water balance; Water productivity; Water saving; water use efficiency
• ISSN: 0378-4290; 1872-6852
• DOI: 10.1016/j.fcr.2010.12.002

▶ A good correlation between leaf N content per unit leaf area versus SPAD reading and SPAD readings versus LCC readings was observed for continuously flooded and AWD treatments. ▶ A combination of AWD −10 and SPAD-based N management, using critical value 38, can save irrigation water and N fertilizer while maintaining high yield as in CF conditions with fixed time and rate of nitrogen application of 180 kg ha −1. ▶ The findings show that SPAD can be used under AWD conditions and that LCC can also be a practical tool for N-fertilizer management of rice grown under AWD, but this needs further field validation. Farmers have adopted alternate wetting and drying (AWD) irrigation to cope with water scarcity in rice production. This practice shifts rice land away from being continuously anaerobic to being partly aerobic, thus affecting nutrient availability to the rice plant, and requiring some adjustment in nutrient management. The use of a chlorophyll meter (also known as a SPAD meter) has been proven effective in increasing nitrogen-use efficiency (NUE) in continuously flooded (CF) rice, but its use has not been investigated under AWD irrigation. This study aimed at testing the hypotheses that (i) SPAD-based N management can be applied to AWD in the same way it is used in CF rice, and (ii) combining chlorophyll meter-based nitrogen management and AWD can enhance NUE, save water, and maintain high rice yield. Experiments were conducted in a split-plot design with four replications in the 2004 and 2005 dry seasons (DS) at IRRI. The main plots were three water treatments: CF, AWD that involved irrigation application when the soil dried to soil water potential at 15-cm depth of −20 kPa (AWD −20) and −80 kPa (AWD −80) in 2004, and AWD −10 and AWD −50 were used in 2005. The subplots were five N management treatments: zero N (N 0), 180 kg N ha −1 in four splits (N 180), and three SPAD-based N-management treatments in which N was applied when the SPAD reading of the youngest fully extended leaf was less than or equaled 35 (N SPAD35), 38 (N SPAD38), and 41 (N SPAD41). In 2005, N SPAD32 was tested instead of N SPAD41. A good correlation between leaf N content per unit leaf area and the SPAD reading was observed for all water treatments, suggesting that the SPAD reading can be used to estimate leaf N of rice grown under AWD in a way similar to that under CF. SPAD readings and leaf color chart (LCC) values also showed a good correlation. There were no water × nitrogen in