| Heat stress is one of the common agrometeorological disasters in the rice production in the middle and lower reaches of the Yangtze River in China.To mitigate the effect of heat stress on rice growth,irrigation with pond or well water was usually adopted,and which is considered to be an effective measure.In order to explore the effects of irrigation pond water and well water on rice paddy temperature during high temperature and heat damage,The rice variety Liangyoupeijiu was the study objects,a field experiment was conducted at the Agricultural Meteorological Experiment Station of Nanjing University of Information Science and Technology(32.2°N,118.7°E)in 2016-2017,and three daily irrigation treatments: T1: pond water was used for the irrigation,the irrigation started from 8:00 and stopped when the height of water layer reached about 10 cm.the paddy water was drained out at 18:00,lasts 7 days,the average temperature was about 30.5℃ in 2016,the average temperature was about 30.9℃ in 2017;T2: well water was used for the irrigation,the irrigation started from 8:00 and stopped when the height of water layer reached about 10 cm.the paddy water was drained out at 18:00,lasts 7 days,the average temperature was about 18.2℃ in 2016,the average temperature was about 19.6℃ in 2017;CK: pond water was used for the irrigation,the water was kept with a height between 5 and 10 cm,lasts 7 days,the average temperature was about 27.2℃ in 2016,the average temperature was about 27.4℃ in 2017.The temperature and humidity within the rice canopy at four different heights(40cm(at 1/3 of the height of rice plants),80cm(at 2/3 of the height of rice plants),120cm(at the height of rice plants)and 130 cm),leaf temperature at the canopy top,and solar radiation above the canopy were measured.The diurnal variation of each energy balance component in the paddy field was calculated using the Penman-Monteith stratification model,and the photosynthesis characteristics,senescence characteristics,dry matter accumulation and distribution of rice were measured at the initial filling stage,milk maturity stage and maturity stage,the yield and the yield components were analyzed.Combined with rice field microclimate,rice field energy balance and rice physiology,the mechanism of different irrigation water sources on high temperature damage in rice fields was systematically studied.The main findings are as follows:1.In 2016 and 2017,the air temperature and soil temperature of rice fields showes T1?CK?T2 after irrigation,and the air temperature decreased with the increase of air temperature,and the soil temperature decreased with the increase of soil depth,the relative humidity shows T2?CK?T1,and the difference between treatments decreases with the increase of height.Pond water irrigation increases the air temperature and the soil temperature of the rice field,and decreases the relative humidity,which aggravated the high temperature heat damage of the rice field.Well water irrigation reduces the air temperature and the soil temperature of the rice field,and increases the relative humidity,which is beneficial to mitigate the high temperature damage of rice fields.At night,the temperature of rice fields shows CK?T1?T2.This is because the water layer absorbs a lot of heat during the day,and water layer becomes a heat source in the field at night,indicating that drainage at night will reduce the air temperature of the rice fields and help the rice fields to cool down.2.In 2016 and 2017,the sensible heat flux,latent heat flux and soil heat flux of the paddy showes T1?CK?T2,and the heat flux in water showed T2?CK?T1.Pond water irrigation warms up the rice fields and strengthens energy dissipation such as sensible heat flux,latent heat flux and soil heat flux in paddy fields,while high water temperature hinders the absorption of heat by water bodies and reduces the heat flux in water.In contrast,well water irrigation reduces the sensible heat flux,latent heat flux,and soil heat flux in rice fields,and the energy is absorbed by the water body,which enhances the heat flux in water.The latent heat flux accounts for the largest proportion of net radiation,indicating that rice fields are mainly based on latent heat exchange.In each treatment,the heat flux in the water body accounts for the largest difference in the proportion of net radiation,indicating that different irrigation water sources mainly cause differences in rice field temperature by affecting the change of the heat flux in water.3.In 2016 and 2017,the SPAD value,net photosynthetic rate,SOD activity,POD activity,CAT activity and soluble protein content of rice flag leaves after the irrigation treatment at the initial filling stage,milk maturity stage and maturity stage showes T2?CK?T1,MDA content shows T1?CK?T2.It indicated that well water irrigation enhanced the photosynthetic capacity of rice leaves and delayed the senescence process of rice.Pond water irrigation weakened the photosynthetic capacity of rice leaves and accelerated the senescence process of rice.Dry matter accumulation of rice,material transport rate and contribution rate,root activity,seed setting rate,grain number per ear,and yield spikes all showed T2?CK?T1.In summary,in the case of high temperature damage,high temperature pond water irrigation will cause water body exotherm to increase rice field temperature,and the high temperature damage of the rice will be strengthened,which will reduce the yield of rice.Low temperature well water irrigation will cause water to absorb heat,which enhances the heat flux in water,reduces the temperature of the rice field,and effectively improves the physiological status of the rice,resulting in a significant increase in rice yield. |
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