Assessment of plant-extractable soil water in castor beans (Ricinus communis L.) using infrared thermometry

Abstract Assessment of plant-extractable soil water from experimental plots using infrared thermometer was carried out through a field experiment on rainfed castor beans (Ricinus communis L.) conducted for 2 years (1992–1993) at Hyderabad, India. The castor beans (cultivar: Aruna) were planted on three different dates in both years. Attempts were made to normalize canopy temperature and stress degree days (SDD) for environmental variability to accurately assess the plant-extractable soil water (PESW) using an Infrared thermometer. Normalization of SDD for variability of temperature and saturation deficit (division of SDD by air temperature and saturation deficit), greatly improved the predictability of the soil water status (PESW), than that based on SDD. The coefficients of determination (R2 values) of the relationship between PESW and SDD after normalization were 0.65 and 0.61 in the years 1992 and 1993, compared to 0.19 and 0.08 before normalization, in respective years. This simple method of normalization of SDD (the division of SDD with weather parameters), which seems to be a promising technique for assessing the soil water status through remote sensing techniques in semi-arid tropics (SAT) needs to be further tested in other environmental conditions and also in other crops, for realising the long-felt objective of assessing soil moisture status with the help of infrared thermometry.

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