Grain quality attributes of different rice varieties affected by different rates of nitrogen

Abstract

The study was conducted at the Rice Research and Development Centre, Bombuwala, to evaluate the effects of varying nitrogen fertilizer rates on the grain quality of rice. Three nitrogen levels (0, 50 and 100 kg N/ha) were applied to seven rice varieties (Bw 372, Bw 367, Bw 363, Bg 359, Bw 312, Bg 300 and Bw 272-6b) using a split plot design with three replicates. Physical, biochemical, nutritional and functional quality attributes of rice grains were assessed in response to nitrogen application. Results showed that the interaction between rice variety and nitrogen level significantly influenced grain quality traits. Increased nitrogen rates improved several grain quality attributes, including brown rice percentage, thousand seed weight, hardness, protein content, phenol content, flavonoid content and gelatinization temperature. However, iron (Fe) content decreased with higher nitrogen application while ash content remained unchanged. Among the rice varieties, Bg 300 exhibited the highest brown rice percentage (81.80 ± 0.37 %) and thousand seed weight (26.923 ± 1.43g) at all nitrogen levels tested. Variety Bw 272-6b” was identified as the most protein-rich variety across all the treatments, with 9.613±0.02 %. Bw 312 demonstrated the highest hardness (64.433 ± 1.78N), while Bw 372 and Bw 363 consistently showed high gelatinization temperatures (fscore value = 1). BW 312 also recordedthe highest phenol content (160.266±13.71mg Gallic Acid Equivalent/100g). Notably, Bg 300 had the highest total flavonoid content (132.566 mg Quercetin Equivalent/100 g extract) at 100 kg N/ha, while Bg 367 showed the highest antioxidant content (69.166 Trolox mM/g) under no nitrogen application. In conclusion, applying nitrogen fertilizer, particularly at 100 kg N/ha, significantly enhances several physical and biochemical traits, although it may reduce iron content. The findings support the use of appropriate nitrogen levels to optimize rice grain quality depending on the variety and desired quality attributes.