Research Publications

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Open Access
Nitrogen, Phosphorus and Potassium Concentrations in the Grains of Selected Rice Varieties in Sri Lanka
(SLIIT, 2022-02-11) Neththasinghe, N. A.S. A; Chandrasekara, E. D. C.T; Ekanayake, E. M.S; Madushan, N. D.R; Rathnayake, W. M. U. K; Sirisena, D. N; Suriyagoda, L. D. B
Rice (Oryza sativa L.) is the staple food for Sri Lankans, and it serves as a key source of essential mineral elements. The variation of grain nutrient concentrations as affected by genetic factors (variety, grain color and age group) are not known, and those were tested in the current study. Total of 200 rice grain samples were collected using a stratified random sampling approach, representing all agro-climatic zones in Sri Lanka. Grain nitrogen (N), phosphorus (P) and potassium (K) concentrations were measured using Kjeldahl, Colorimetric, and General methods, respectively. Grain N P and K concentrations were significantly different among rice varieties (P<0.1). Grain N concentration varied between 4-19 mg g−1 . The highest grain N concentration was recorded in Bg 307 (14 mg g−1 ) while the lowest (i.e., < 10 mg g−1 ) in Bg 367, Bg 374, Bg 358, Bg 310 and Bg 379-2. Grain P concentration varied in the range 0.6- 1.7 mg g−1 . Grain P concentration in At 406 was the highest (1.6 mg g-1), followed by Bg 307, Bg 94-1, Bg 367 i.e., >1.3 mg g-1 and the lowest in Bg 403, Ld 365 and Bg 310 i.e., < 1 mg g−1 . Bg 357, Ld 365, Bg 406, Ld 368 and Bg 310 rice varieties showed significantly lower P concentration than other varieties (P<0.1) Grain N, P and K concentrations were similar among different age classes of rice varieties (P>0.05). Moreover, grain N and P concentrations between the red and white grain varieties were similar (P>0.05). However, varieties with white color grains had higher K concentration than in red rice varieties. There was a significant correlation between grain P and K concentrations (r =0.496, P<0.001). This information would be useful when selecting rice varieties with high and low nutritional qualities and implementing sustainable nutrient management practices in rice-based cropping systems in Sri Lanka.
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Seasonal fluctuations in live and dead biomass of Phragmites australis as described by a growth and decomposition model: implications of duration of aerobic conditions for …
(Elsevier, 2002-07-01) Asaeda, T; Hietz, P; Tanaka, N; Karunaratne, S
We developed a model of Phragmites australis growth and decomposition to evaluate the material budget and nutrient cycles of a reed stand in Neusiedlersee, Austria. The model describes the growth of each organ of P. australis, the collapse of standing dead shoots, the decomposition of leaves and stalks, and nutrient uptake and release during these processes. The model was calibrated using growth and decomposition data from the literature, and subsequently applied to predict the effects of P. australis stands on a marsh ecosystem. From the start of its decomposition in water, the litter was assumed to stay in the aerobic water layer for 6, 12 or 24 months before entering the anaerobic sediment layer. Because decomposition increases with increasing oxygen and temperature, the aerobic decomposition rate (before the litter was transferred to the anaerobic substrate) increased markedly, especially from spring to autumn. The model predicted that between 33 (6 months aerated) and 48% (24 months aerated) of the annual aboveground production would decompose within 1 year, while the rest would remain in the anaerobic substrate. Rates of nitrogen and phosphorus release were 1.4 times higher between late spring and the end of summer than during autumn and winter. A higher proportion of phosphorus than nitrogen was expected to remain trapped in the anaerobic layer. The uptake of nitrogen and phosphorus during the growing season exceeded release during decomposition 4–6 and 5–7-fold, respectively. The model is useful for quantifying the nutrient cycles of reed-dominant marshes.

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