Nitrogen, Phosphorus and Potassium Concentrations in the Grains of Selected Rice Varieties in Sri Lanka

Abstract

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.