Analysis of the Correlation between Middle-season Rice Yield and Meteorological

Bingyu YANG, Zhengyou WANG, Min GAO, Baofeng HUANG

1. Data Section of Yunnan Meteorological Information Center, Kunming 650034, China; 2. Jingdong Meteorological Bureau, Jingdong 676299, China; 3. Pu’er Coffee Meteorological Service Center, Pu’er 665000, China; 4. Mojiang Meteorological Bureau, Mojiang 654800, China

Abstract Middle-season rice is an important food crop in southern rice areas of China, especially in Yunnan, the main rice-producing region. However, due to the impact of low temperature at the seedling stage and high or low temperature at the booting and heading stage of middle-season rice, the yield is not stable. Based on the data of yield factors of different middle-season rice varieties planted in the same ecological site in Jingdong County from 2009 to 2016, average development period was calculated using the data of development period measured in field during 2009-2016, and the average of meteorological factors (daily average temperature, daily maximum temperature, daily minimum temperature, and sunshine hours) and total precipitation were calculated. The correlation between meteorological factors in different development periods of each year and corresponding per unit area yield was analyzed. The results show that temperature is the most important factor affecting rice yield. Sufficient light is beneficial to the increase in the number of grains per spike and thousand seed weight at the sowing-seedling emergence stage and milk maturity-maturity stage. Excessive precipitation will reduce the number of grains per spike at the booting-heading stage. Excessive precipitation decreases the number of filled grains per spike at the jointing-booting stage, and proper drainage helps increase the formation rate of ears. This study provides scientific reference for rice production and management in this county in future.

Key words Jingdong County, Middle-season rice yield, Meteorological factors, Correlation analysis

1 Introduction

Rice is China’s main food crop. In recent years, because of climate change, China’s rice production has been damaged to varying degrees. Affected by meteorological factors in different years or in different regions, China’s rice output is low in stability and fluctuates frequently. Middle-season rice is an important food crop in southern rice areas of China, especially in Yunnan, the main rice-producing region. However, due to the impact of low temperature at the seedling stage and high or low temperature at the booting and heading stage of middle-season rice, the yield is not stable.

Rice, an annual herb, belongs to the genusOryza, the family Gramineae, and is widely distributed in the tropics and subtropics[1]. Jingdong County is located at the northern end of Pu’er City in the southwestern part of Yunnan Province, and has a large temperature difference between day and night, fertile land, and convenient irrigation. The good combination of soil, light and heat, as well as typical subtropical climate create unique advantages of Jingdong agriculture. Rice is one of the main food crops cultivated in Jingdong County and the staple food of people in the county. The county is mainly planted with middle-season rice. It is generally sown in late February and matured in late July and early August. During this period, rice will go through the main growth and development processes such as tillering, booting, heading and blooming, and grain filling. During these critical growth periods, adverse environmental conditions will impair the number of ears per unit area, the number of grains, the seed setting rate, and the thousand-grain weight. At present, it is generally believed that temperature is the most important meteorological factor affecting rice yield, and high temperature or low temperature during the growth period of rice will reduce rice yield[2-5]. Studies have found that environmental temperature affects the occurrence of rice tillering through its effect on gene expression, and low temperature slow down the occurrence of rice tillering[6]; the low temperature of 3-6 d has a significant inhibitory effect on rice tillering[7]. So far, there have been few reports on the impact of other meteorological factors other than temperature and light on rice yield.

In most of previous studies on the impact of climate change on crops, only the relationship between meteorological factors and crop yield was studied, and there is no in-depth analysis of impact of meteorological factors on yield factors[8-11]. In addition, these studies were generally carried out under experimental conditions, in which only the impact of meteorological factors on crops in a small range in a short period was studied. There are rare reports on meteorological data and rice yield factors for consecutive years under the conditions of field production. In this study, based on the data of yield factors of different middle-season rice varieties planted in the same ecological site in Jingdong County from 2009 to 2016, the main meteorological factors affecting rice yield are analyzed to provide scientific reference for rice production and management in this county in future.

2 Materials and methods

2.1 Data of middle-season rice fieldThe data of rice development period and yield during 2009-2016 are obtained from Jingdong Meteorological Bureau, and the observation site is on the outskirts of Xiaoheqiaoshe, Douge Village, Jinping Town, Jingdong County. It is located at 24°25′30″ N, 100°52′26″ E, and has an altitude of 1 192 m. The terrain is flat and open. The area has three crops a year, that is, rice, beans, and wheat are planted in rotation, and the preceding crop is wheat. The groundwater level is less than 2 m, and the soil of the plot is loam (provided by the county soil survey team), with a pH of 6.5 and (acidic) neutral fertility. It belongs to mountain stream, so water sources are sufficient. Field is divided into rice seedling bed and field, and annual cultivation and management methods are basically the same. The variety is indica hybrid rice, and the maturity is medium maturity, while the cultivation method is transplanting. The main varieties are Lianxiang 8 in 2009, Q You 6 in 2010, Wanyou 2 in 2011, Zhongyou 18 in 2012, Nei 2 You 6 in 2013, and Diyou 20 in 2014, Q You 1 in 2015, Neixiang 8518 in 2016.

2.2 Measured data of the growth period of middle-season riceThe development period of rice is generally divided into 12 periods: sowing, seedling emergence, three leaves, transplanting, turning green, tillering, jointing, booting, heading, flowering, milk maturity, and maturity. According to the development period of rice inSpecifivationsforAgrometeorologicalObservation, there is no observation and record in the flowering period.

2.3 Meteorological dataMeteorological data of daily average temperature, daily maximum temperature, daily minimum temperature, precipitation and sunshine hours from 2009 to 2016 are all observation data of Jingdong National Basic Meteorological Station, and are provided by Yunnan Meteorological Information Center.

2.4 Research methodJingdong County’s main food crop middle-season rice is as the research object. Average development period was calculated using the data of development period measured in field during 2009-2016, and the average of meteorological factors (daily average temperature, daily maximum temperature, daily minimum temperature, and sunshine hours) and total precipitation were calculated. The correlation between meteorological factors in different development periods of each year and corresponding per unit area yield was analyzed, and the regression equation of meteorological factors and yield was established. In the regression analysis, the meteorological factors that affect yield factors were used as the independent variables, and yield was the dependent variable. The stepwise regression method of SPSS 13.0 was used to establish the regression equation between yield and meteorological factors in different periods. The selection criteria for the variables are as follows: when the probability ofFvalue is less than 0.05, it is introduced; when the probability is greater than 0.10, it is removed.

3 Results and analysis

3.1 Separation of meteorological yieldRice yield can be decomposed into trend yield determined by socio-economic factors, meteorological yield determined by meteorological factors, and random yield caused by accidental factors, namelyy=yb+ym+δ, whereyis actual yield;ybis trend yield;ymis meteorological yield;δis random yield (usually ignored). In this study, the 3-year moving average was used to calculate trend yieldyb, thereby separating meteorological yieldym. The per unit area yield and meteorological yield of middle-season rice in each year are shown in Table 1.

Table 1 Per unit area yield and meteorological yield of middle-season rice from 2009 to 2016

3.2 Correlation between meteorological yield and meteorological factorsThe combination of multiple meteorological factors that are conducive to yield formation in rice production areas is the decisive condition for the expression of rice yield potential. These meteorological factors include sunshine, temperature, precipitation,etc[12-13]. The data of the meteorological yield of middle-season rice and meteorological factors (average daily temperature, daily maximum temperature, daily minimum temperature, sunshine hours, and total precipitation) during each development period from 2009 to 2016 in the agricultural meteorological experimental station of Jingdong County were used for correlation analysis. Fig.1 and Fig.2 only show the meteorological factors that are significantly correlated to meteorological yield. It can be seen from Fig.1 that at the booting-heading stage, daily average temperature has a significant positive correlation with meteorological output. Studies have shown that temperature is the most important factor affecting rice yield. For the middle-season rice in Jingdong, the average temperature at the booting-heading stage has a greater impact on rice yield. As shown in Fig.2, there is a significant negative correlation between the maximum temperature and meteorological yield in the milk maturity-maturity period of middle-season rice. The results show that if the temperature is too high during this period, the yield of middle-season rice will be reduced.

3.3 Correlation between meteorological factors and yield structure in the development period of middle-season rice

3.3.1Correlation between main meteorological factors and number of grains per spike. Seen from Fig.3, the minimum temperature in the sowing-seedling emergence period of middle-season rice has an extremely significant negative correlation with the number of grains per spike. The number of sunshine hours has a significant positive correlation with the number of grains per spike in the sowing-seedling emergence period. In the seedling emergence-three-leaf period, there is a significant negative correlation between the minimum temperature and the number of grains per spike. In the booting-heading period, precipitation has a significant negative correlation with the number of grains per spike.

Note: ** indicates significant correlation at the 0.01 level (bilateral); * indicates significant correlation at the 0.05 level (bilateral), the same below.

Fig.2 Relationship between meteorological factors and meteorological yield in the milk maturity-maturity period of middle-season rice

Note: a.b. Sowing-seedling emergence period; c. Seedling emergence-three-leaf period; d. Booting-heading period.

3.3.2Correlation between main meteorological factors and the number of filled grains per spike of middle-season rice. As shown in Fig.4, the minimum temperature is significantly negatively correlated with the number of filled grains per spike in the sowing-seedling emergence period of middle-season rice, and precipitation is significantly negatively correlated with the number of filled grains per spike at the jointing-booting stage. The results show that in the sowing-seedling emergence period, the too high minimum temperature will affect the emergence rate of seedlings and reduce the number of filled grains per spike. Besides, at the jointing-booting stage, in the event of low temperature and rain, the spikelets formed by the differentiation of rice panicles will degenerate, so that the total number of spikelets per spike (the number of grains after maturity) will reduce.

3.3.3Correlation between main meteorological factors and the thousand seed weight of middle-season rice. At the booting-heading stage, average temperature is significantly negatively correlated with the thousand seed weight of middle-season rice. At the milk maturity-maturity stage, the maximum temperature and sunshine hours are significantly positively correlated and extremely significantly positively correlated with the thousand seed weight of middle-season rice (Fig.5). Studies show that the grain weight of rice is determined by the volume of rice husks and the development of the endosperm[14]. In this study, it is found that the sensitive periods for the impact of meteorological factors on the thousand seed weight are mainly booting-heading and milk maturity-maturity periods. Before the initial heading stage, the husks of inner and outer glumes are formed, and appropriate low temperature is beneficial to the accumulation of carbohydrates during the development of young ears, so that the volume of the husks increases to enhance the storage capacity. After the initial heading stage, the grains are in the peak filling period, and meteorological factors mainly affect the grain filling rate, thereby influencing the fullness of the grains. If light is sufficient in this period, photosynthesis will be increased, and lower temperature can reduce respiratory consumption, thereby increasing net photosynthetic capacity, promoting its transport to the grains on rice ears, and then increasing the grain weight.

Note: a. Sowing-seedling emergence period; b. Jointing-booting period.

Note: a. Booting-heading period; b,c. Milk maturity-maturity period.

3.3.4Correlation between main meteorological factors and the formation rate of ears of middle-season rice. The minimum temperature in the sowing-seedling emergence period and seedling emergence-three-leaf period, as well as the precipitation in the jointing-booting period have a significant positive correlation with the formation rate of ears of middle-season rice (Fig.6). It shows that the sowing-three-leaf period and jointing-booting period are the sensitive periods for the impact of meteorological factors on the formation rate of ears of middle-season rice. In these periods, daily minimum temperature and precipitation are the most important meteorological factors affecting the formation rate of rice ears. During these periods, if temperature is low and light is insufficient, the photosynthesis of rice will be weakened, and the net photosynthetic efficiency will decrease. Nutrients cannot meet the needs for the differentiation of young panicles and prolong nutrient growth, and it is easy to cause rice seedlings to grow excessively. Meanwhile, the irrigation and drainage management at the jointing-booting stage should be strengthened.

Note: a. Sowing-seedling emergence period; b. Seedling emergence-three-leaf period; c. Jointing-booting period.

4 Conclusions

The results show that (i) the main meteorological factor affecting rice at the tillering stage is the maximum temperature, and the total number of rice seedlings will be affected if there is low temperature and rain after transplantation; (ii) tillering and panicle formation change mutually at the late tillering stage, and during this period, daily average temperature is higher, which is conducive to the formation of tillers and to photosynthetic production and nutrient accumulation, and then promotes tillering into ears[15]; (iii) the temperature condition and sunshine hours after transplantation are the main factors affecting the formation rate of ears, and the formation rate of ears rises with the increase of temperature and sunshine hours; (iv) the maximum temperature in the milk maturity-maturity period mainly influences the grain filling rate, thereby affecting the fullness of grains. If light is sufficient in this period, photosynthesis will be increased, and lower temperature can reduce respiratory consumption, thereby increasing net photosynthetic capacity, promoting its transport to the grains on rice ears, and then increasing the grain weight.