Abstract
Many studies have been carried out on N sources effect on fragrant rice; however, their impact on rice grain quality is largely unclear. In this study, we evaluated the effects of different types of N sources on rice growth, yield, 2-acetyl-1-pyrroline (2AP), amylose and cooked rice elongation. Two indica rice cultivars, Basmati 385 (B385), Xiangyaxiangzhan (XYXZ) and two japonica cultivars, Yunjingyou (YJY), Daohuaxiang (DHX) were grown in experimental pots with six replications under four N sources: Potassium nitrate (KNO3), ammonium bicarbonate (NH4HCO3), urea (H2NCONH2) and sodium nitrate (NaNO3) in 2019 and 2020 early seasons. Our results showed that N dynamics regulated the number of panicles, 1000-grain weight, grain yield, 2-acetyl-1-pyrroline, amylose and cooked rice elongation across all the four treatments. The NH4HCO3 treatment significantly increased the number of panicles and grain yield across the four rice varieties compared with KNO3, H2NCONH2 and NaNO3 N sources in both 2019 and 2020 early season, The KNO3 treatment significantly showed higher 1000-grain weight in B-385, YJY, XYXZ and DHX compared to other N sources. Compared with other N sources treatment, the NH4HCO3 treatments significantly increased the 2AP contents in heading stage leaves, matured leaves and grains of B-385, YJY, XYXZ and DHX respectively. Cooked rice elongation percentage also showed significant difference in all treatments studied with KNO3 recorded the highest across the four varieties. Analysis of major enzymes and compounds such as P5C, P5CS, PDH, Pyrroline, proline and Methylglyoxal showed remarkable differences in each cultivar at heading and maturity stages with higher activity in NH4HCO3 and H2NCONH2 treatments. Similarly, in all treatments, we also observed significant increase in amylose content percentage, with NH4HCO3 having greater percentage of amylose.
Highlights
The main concern today on a global scale, is to minimize the use of nitrogen in the crops production under climate change condition and the efficient use of nitrogen is recognized as an important production factor for rice [1]
Many studies have shown that nitrogen affects rice in various ways, for instance [36] demonstrated that, application of nitrogen at the booting stage affects the 2-acetyl-1-pyrroline, proline and total nitrogen contents of aromatic rice; Different rice genotypes differed in their rice growth, development and grain yield in response to different nitrogen application rates and nitrogen types [37,38,39,40,41,42,43]
There is a significant difference between nitrogen sources for the 1000-grain weight and KNO3 showed the best result in each rice cultivar: 18.92 g, 24.25 g, 21.64 g, and 26.52 g for Basmati 385 (B385), YJY, XYXZ and DHX respectively
Summary
The main concern today on a global scale, is to minimize the use of nitrogen in the crops production under climate change condition and the efficient use of nitrogen is recognized as an important production factor for rice [1]. A large amount of chemical fertilizers, especially nitrogen (N) has played an important role in the advancement of rice production in the past [2]. Excess N fertilizer accompanied by low efficiency of nutrient utilization is a serious problem in rice production all over the world, as it affects yield and grain quality [3,4]. Previous studies on the effect of fertilizer application on yields, milling and quality parameters of aromatic rice have mainly focused on the role of an individual nutrient [5]. Nitrogen fertilizer application increased grain length, length: width ratio, grain length after cooking, and aspect ratio. The influences of nitrogen fertilizers on the quality of the grain are due to the effects on the activity of the biosynthetic carbohydrate enzymes. The NO3 form is mobile, less toxic and can be stored in vacuoles for most crop plants; NO3- must be reduced to NH4+ before it can be used [8]
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