Nitrogen management of irrigated rice based on tillering dynamics
2000
Sanico, A.L. | Peng, S. | Visperas, R.M. | Laza, M.R.C. (International Rice Research Inst., MCPO Box 3127, 1271 Makati City (Philippines). Agronomy, Plant Physiology and Agroecology Div.)
Cultivar IR72 was grown at IRRI {Los Banos, Laguna, Philippines] farm in the dry (DS) and wet season (WS) of 1999 at a 20-x 20- cm spacing. Nitrogen rate (kg/ha) of fix-schedule N management was 150 and 225 in the DS and 0, 60 and 120 in the WS, applied as basal and topdressed at midtillering, panicle initiation, and flowering. The SPAD-based and tiller-based N management were included as N treatments in both DS and WS. Weekly SPAD measurements and tiller counting were conducted 2 weeks after transplanting up to flowering. Threshold levels of tiller number at a given growth stage were determined from previous experiments where a maximum yield of IR72 was achieved. In SPAD-based N treatment, 20-45 kg N/ha was applied when SPAD value was below 35. When tiller number per sq m was below the threshold level and when daily tillering rate was smaller than 30 sq m, 20-45 kg N/ha was applied in the tiller-based N treatment plots. The SPAD and tiller-based N treatments received N three times at the same growth stages with a total input of 105 kg N/ha is the DS and 60 kg N/ha in the WS. Because amount and timing of N topdressing in both SPAD and tiller-based N treatments were the same, the grain yield and N use efficiency were comparable in the two treatments. However, the SPAD and tiller-based N management resulted in a significantly higher N use efficiency than the fix-schedule N management. The results suggest that tiller counting can substitute for the chlorophyll meter in determining the correct timing of N topdressing in irrigated rice
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