Influence of Irrigation and Application of Kaolin on Canopy Temperature of Peppers Measured by Infrared Thermography

This paper presents measurements of temperature of the above-ground parts of peppers plants using a thermal imager in order to determine the water regime. The experiment was set as a bifactorial block system, with three replications, in the open field on a carbonate chernozem soil in Stara Pazova (40 km North from Belgrade, Serbia). Three treatments of irrigation regimes, with and without the application of 5% kaolin suspension (Surround WP), were monitored. Kaolin (Surround WP) was applied by spraying of the part of the plant above the ground seven times during the vegetation seasons between April and September 2011. All the treatments that have been applied with kaolin have a sign K. Treatment with full irrigation (F, FK) when 100% is covered by ETc (evapotranspiration), a treatment with deficit irrigation (R, RK) with 80% of the ETc and a treatment with deficit irrigation (S, SK) with 70% of ETc. The measurements of plant temperature were carried out with an infrared camera (FLIR, T335) seven times during the vegetation season. From each treatment a sample of 15 measurements was taken and the measurements were used for determination of average temperature of the plant on every level of irrigation. Soil moisture was measured by gravimetric method in 7 day intervals, up to 0.6 m and every 0.2 meters. Temperature measurement data show that the F treatment plants were the coldest with the average temperature of 21.29 degrees C, followed by the R and S treatment with the average temperature of 21.79 degrees C and 22.26 degrees C, respectively. Average temperatures of FK, RK and SK treatments were as follows 21.58 degrees C, 22.11 degrees C and 22.47 degrees C. Plants treated with kaolin had higher temperatures on average, but for the precise conclusion more measurements are needed due to the variability of canopy temperature. Observing the values of soil moisture over all treatments, it can be assumed that kaolin has a role in reducing water consumption. It is also confirmed by CWSI (Crop Water Stress Index). Relationships of available soil water (ASW) and the CWSI show differences between all irrigation and kaolin treatments. The values of CWSI are the lowest and almost never more than zero in fully irrigated treatments (F and FK), in R and RK treatments they are slightly higher, and the highest in S and SK treatments. The values of CWSI are lower in the treatments without kaolin application. Obtained results show an effect of irrigation regime on the canopy temperature of peppers, while the influence of kaolin is small.