Rice canopy temperature is affected by nitrogen fertilizer

Canopy temperature strongly influences crop yield formation and is closely related to plant physiological traits.However, the effects of nitrogen treatment on canopy temperature and rice growth have yet to be comprehensively examined. We conducted a two-year field experiment with three rice varieties(HD-5, NJ-9108, and YJ-805) and three nitrogen treatments(zero-N control(CK), 200 kg ha~(–1)(MN), and 300 kg ha~(–1)(HN)). We measured canopy temperature using a drone equipped with a high-precision camera at the six stages of the growth period. Generally,canopy temperature was significantly higher for CK than for MN and HN during the tillering, jointing, booting, and heading stages. The temperature was not significantly different among the nitrogen treatments between the milky and waxy stages. The canopy temperature of different rice varieties was found to follow the order: HD-5>NJ-9108>YJ-805, but the difference was not significant. The canopy temperature of rice was mainly related to plant traits, such as shoot fresh weight(correlation coefficient r=–0.895), plant water content(–0.912), net photosynthesis(–0.84), stomatal conductance(–0.91), transpiration rate(–0.90), and leaf stomatal area(–0.83). A structural equation model(SEM) showed that nitrogen fertilizer was an important factor affecting the rice canopy temperature.Our study revealed:(1) A suite of plant traits was associated with the nitrogen effects on canopy temperature,(2) the heading stage was the best time to observe rice canopy temperature, and(3) at that stage, canopy temperature was negatively correlated with rice yield, panicle number, and grain number per panicle. This study suggests that canopy temperature can be a convenient and accurate indicator of rice growth and yield prediction.

Stomatal conductivity, canopy temperature and evapotranspiration of maize (Zea mays L.) to water stress in Northeast China

The Northeast China Plain(NECP)is one of the main maize(Zea mays L.)production regions in China but is now subject to drought because of climate change and a rain-fed cultivation system.A two-year experiment was conducted in a typical maize cultivation region in the NECP to investigate the responses of plant physiological factors and evapotranspiration(ET)to water stresses at different growth stages.Results show that the responses of plant physiological factors to water stress can be divided into three levels based on soil water content(SWC)in the main root zone:when SWC was greater than 0.22 cm^(3)/cm^(3)(equivalent to 62%field capacity(FC)),stomatal conductivity(gs)and ET reached their highest values,and the canopy temperature(Tc)was close to the air temperature;when SWC was within 0.15-0.22 cm^(3)/cm^(3)(43%-62%FC),the gs and ET decreased,and Tc increased as SWC decreased;and when SWC was lower than 0.15 cm^(3)/cm^(3)(<43%FC),gs and ET reached their lowest values and Tc was greater than 1.2 times the air temperature.The ratio of canopy temperature to air temperature(RT),is closely related to stomatal conductivity and soil water content,and especially linearly related to crop water stress index(CWSI),and can be used as an alternative to CWSI for evaluating maize water stress because of easily data achieving and simple calculation processes.In a conclusion,RT of 1.2 can be used as an index to identify a severe water stress status,and maintaining SWC greater than 60%FC at the heading and grain-filling stages is important for supporting maize normal ET and growth in the study region.

The Effect of Organ Temperature on Total Yield of Transplanted and Direct-Seeded Rice(Oryza sativa L.)

The canopy temperature of rice is an important index that directly reflects the growth and physiological state of rice,and affects the yield of rice plants to a great extent.The correlation between the temperatures of different rice organs and canopy in different growth stages and the grain yield is complex.The stability and universality of these correlations must be verified.We conducted a pot experiment using two rice varieties and two temperature treatments(high temperature treatment was carried out at the beginning of heading stage for 10 days).We measured rice organ temperature during seven stages of growth using a high-precision infrared thermal imager.Results showed that the optimal observation period for the rice canopy temperature was 13:00.Although the rice variety did not significantly impact the canopy or organ temperature(p>0.05),the different organs and canopy exhibited significantly different temperatures(p<0.05).The correlations between the leaf,stem,panicle,canopy–air temperature differences and seed setting rate,theoretical and actual yields were the strongest during the milk stage.Among them,the correlation coefficient betweenΔT_(s) and theoretical and actual yields was the highest,the relationship between theoretical yield(Y)andΔT_(s)(X)was Y=−5.6965X+27.778,R^(2)=0.9155.Compared withΔT_(l),ΔT_(p) andΔTc,ΔT_(s) was closely related to the main traits of plants.ΔT_(s) could better reflect the growth characteristics of rice thanΔT_(c),such as dry matter accumulation(r=−0.931),SPAD(r=0.699),N concentration(r=0.714),transpiration rate(r=−0.722).In conclusion,stem temperature was more important indicator than canopy temperature.Stem temperature is a better screening index for rice breeding and cultivation management in the future.

Reciprocal Analysis of Sensible and Latent Heat Fluxes in a Forest Region Using Single Height Temperature and Humidity Based on the Bowen Ratio Concept

Evapotranspiration in forests has been researched for a long time because it serves an important role in water resource issues and biomass production. By applying the reciprocal analysis based on the Bowen ratio concept to the canopy surface, the sum result of sensible and latent heat fluxes, i.e., actual evapotranspiration (ET), is estimated from engineering aspect using the net radiation (Rn) and heat flux into the ground (G). The new method uses air temperature and humidity at a single height by determining the relative humidity (rehs) using the canopy temperature (Ts). The validity of the method is confirmed by the latent heat flux (lE) and sensible heat flux (H) observed by mean of eddy covariance method. The heat imbalance is corrected by multiple regression analysis. The temporal change of lE and H at the canopy surface is clarified using hourly and yearly data. Furthermore, the observed and estimated monthly evapotranspiration of the sites are compared. The research is conducted using hourly data and the validation of the method is conducted using observed covariance at five sites in the world using FLUXNET.

Challenges in using an analog uncooled microbolometer thermal camera to measure crop temperature

It has been long known that thermal imaging may be used to detect stress(e.g.water and nutrient deficiency)in growing crops.Developments in microbolometer thermal cameras,such as the introduction of imaging arrays that may operate without costly active temperature stabilization,have vitalized the interest in thermal imaging for crop measurements.This study focused on the challenges occurring when temperature stabilization was omitted,including the effects of focal-plane-array(FPA)temperature,camera settings and the environment in which the measurements were performed.Further,the models for providing thermal response from an analog LWIR video signal(typical output from low-cost microbolometer thermal cameras)were designed and tested.Finally,the challenges which typically occur under practical use of thermal imaging of crops were illustrated and discussed,by means of three cereal showcases,including proximal and remotely based(UAV)data acquisition.The results showed that changing FPA temperature greatly affected the measurements,and that wind and irradiance also appeared to affect the temperature dynamics considerably.Further,it is found that adequate settings of camera gain and offset were crucial for obtaining a reliable result.The model which was considered best in terms of transforming video signals into thermal response data included information on camera FPA temperature,and was based on a priori calibrations using a black-body radiation source under controlled conditions.Very good calibration(r^(2)>0.99,RMSE=0.32℃,n=96)was obtained for a target temperature range of 15-35℃,covering typical daytime crop temperatures in the growing season.However,the three showcases illustrated,that under practical conditions,more factors than FPA temperature may need to be corrected for.In conclusion,this study shows that thermal data acquisition by means of an analog,uncooled thermal camera may represent a possible,cost-efficient method for the detection of crop stress,but appropriate corrections of disturbing factors are required in order to obtain sufficient accuracy.

Assessing crop water stress of winter wheat by thermography under different irrigation regimes in North China Plain

Thermal imaging can be used as an indicator of water stress due to the closure of stomatal aperture.In this paper,we analyzed the robustness and sensitivity of thermography of winter wheat in the North China Plain.The seasonal and diurnal variations of Crop Water Stress Index(CWSI)were evaluated.Five treatments were applied by means of irrigation,with plots receiving 100%of ETo(DI),50%(D50),16%(D16)and no irrigation(NI).A high correlation was found between stomatal conductance(gs)and CWSI,depending on the phenological stage of the crop with R2=0.44 at pre-heading stage and R2=0.77 at post-heading stage.In addition,a high correlation between yield and CWSI at different growth stages indicates that thermography can predict yield.Hourly measurements of canopy temperature were taken to study the effect of the time of day on image acquisition and it was found that midday was the most appropriate time.These results should assist in designing precision irrigation scheduling for setting the threshold values.

Crop water stress index for off-season greenhouse green peppers in Liaoning, China

The crop water stress index(CWSI)is a complex instrument to effectively monitor the degree of water stress of crops and provides guidance for timely irrigation.In an experiment utilizing the CWSI with off-season green peppers planted in barrels in a greenhouse in Liaoning Province,Northeast China,this study monitors the sub-indexes--such as canopy temperature,environmental factors and yield--determines the changing law of each constituent,achieves an empirical model as well as a baseline formula for the canopy temperature of the peppers with a sufficient water supply,and verifies the rationality of the formula with corresponding experimental data.The results obtained by using the CWSI show that the optimal time to determine the water deficit for off-season green peppers is at noon,by measuring the diurnal variation in the peppers with different water supplies.There is a nonlinear relationship between the yield and the average CWSI at the prime fruit-bearing period;moreover,the optimal time to supply water for off-season green peppers comes when the average water stress index ranges between 0.2 and 0.4 during the prime fruiting stage,thereby ensuring a high yield.