Evaluation of Soil Water Management Difference in Mango Orchards between Thailand and Japan

The objective of this study is to evaluate the difference of the soil water management in mango orchards between the varieties of “Irwin” in Japanand “Nam Dok Mai” inThailand. Field observations were conducted in mango orchards in Okinawa, Japan and Phrao, Thailand to clarify the water management practices. Measurement of the hourly soil water content in Phrao indicated that the irrigation was scarce and the volumetric water content in the soil was maintained almost constant. in the flowering season. This can be the farmers’ practice for flower induction. After the flowering season, irrigation was frequent in order to produce the large fruit. In the harvest season, the soil water content was relatively high because of frequent irrigation and rainfall. In Okinawa, the volumetric water content was maintained at the same level in a relatively deep layer. The result at the5 cmdepth indicated that the farmer carefully controlled the soil water content. In the flowering season, the soil water content was relatively low. While the orchard was managed empirically, the volumetric water content near the soil surface was maintained over 25% during the harvest season. This result indicates that the farmer performed the good soil water management to enhance mango fruit quality even without technical measurement. A numerical model describing the soil water and heat transfers was introduced to predict the farmer’s empirical soil water management in Okinawa. Using the meteorological data in March 2010, the irrigation regime was predicted using the simulated soil water content. In the flowering season, the farmer irrigated when the soil surface water content reached 14%. Based on this criterion for the empirical soil water management, the simulation result indicated that the farmer irrigated four times in this period. The numerical model presented here can be useful for evaluating the differences in water management practices of local farmers.

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.

Monitoring physiological responses to water stress in two maize varieties by infrared thermography

Water stress is one of the main causes of yield reductions in crops,especially in arid and semi-arid regions where the water supply is limited.Plant water status is frequently assessed by pre-dawn leaf water potential(ΨPD)or leaf stomata conductance(gL)measurements,in support of advanced irrigation scheduling.However,both methods are time and labour consuming.A non-invasive approach to water status detection is the use of infrared thermography(IRT).This experiment was conducted in a greenhouse on two potted maize varieties under irrigated and non-irrigated conditions,and the measurements began when the crop had reached its twelve leaf stage.In order to establish the IRT measurements for detecting the water status of maize,an IRT-based crop water stress index(CWSI)was calculated and compared with simultaneously measuredΨPD and gL data.Good correlations were found between CWSI and gL data(r2=0.71&0.81),as well between CWSI andΨPD data(r2=0.53&0.81).These results highlight the appropriateness of infrared thermal imagery to detect and differentiate between the crop water statuses of different genotypes.