Evaluation and grading of climatic conditions on nutritional quality of rice: A case study of Xiaozhan rice in Tianjin
Authors: Chen Sining , Guo Jun , Zhao Yanxia , Li Xingyang , Liu Fang , Chen Yuehao 
Published: August 2021

Based on the daily meteorological monitoring data of Xiaozhan rice in Tianjin planting area from 2010 to 2020 and the observation data of nutritional quality of Xiaozhan rice in Tianjin from 2014 to 2020, comprehensive characterization parameter M of nutritional quality of Xiaozhan rice in Tianjin and the evaluation model of meteorological conditions' influence on the nutritional quality of rice was established by principal component analysis, ordered sample optimal clustering method and stepwise regression method. The climatic evaluation grades of nutritional quality of Xiaozhan rice in Tianjin were divided into four grades. The comprehensive characterization parameter (M) of nutritional quality of Xiaozhan rice can be determined using five quality factors (protein, amylose, gel consistency, amino acid and chalkiness) into three weighted sums, and the coefficients are is the proportion of the eigenvalues corresponding to the three principal components to the total variance of the original variables. The thresholds of M corresponding to the four grades of ‘general’, ‘good’, ‘excellent’, ‘extra‐superior’, in the climatic evaluation of nutritional quality of Xiaozhan rice in Tianjin were M < 0.3, 0.3 ≤ M < 0.45, 0.45 ≤ M < 0.7, 0.7 ≤ M, respectively. The results showed that M was related to 14 meteorological factors such as average temperature, minimum temperature, maximum temperature, precipitation, sunshine duration and daily range in different months of rice growth period. Among them, the temperature condition in September was the key factor affecting the nutritional quality of Xiaozhan rice, including amylose, gel consistency, protein, chalkiness and the comprehensive characterization parameter (M). September is the period from grain filling (the grain filling stage of rice refers to the period from the end of flowering to the beginning of glume closure to grain maturity) to mature harvest of Xiaozhan rice in Tianjin. That is to say, the temperature in this period has a very significant effect on the final nutritional quality of Xiaozhan rice. The correlation between the 14 factors and M is high, and all 29 pass the Pearson correlation significance test of p < 0.01. The absolute value of lowest correlation coefficient is sunshine hours in May, |R| = 0.839; and the absolute value of highest correlation coefficient was the highest temperature in June, R = 0.982. Among the 14 factors, 9 factors are related to temperature (including the day difference in June), and all of them positively correlated with climate evaluation index M of nutritional quality, 3 factors are related to sunshine hours, and 2 factors are related to precipitation, indicating that the temperature condition in the whole growth period of Xiaozhan rice is the most important climate factor to determine its nutrition quality formation. The root mean square error of the simulation results of the climate evaluation model for the nutritional quality of Xiaozhan rice is 0.0236, which indicates that the model can be used for the climate impact evaluation of the nutritional quality of Xiaozhan rice in Tianjin, so as to determine the nutritional quality grade of Xiaozhan rice and provide scientific reference for reasonably predicting the market price of Xiaozhan rice.