Water extraction and growth of rice (Oryza sativa L.) in relation to soil physical constraints under simulated rainfed conditions

Results of the study showed that of the two soil types, one was classified as clay loam with 30% clay; the other was clay with 54% clay content. Differences in various chemical properties between the two soil types were noted. Variations in soil volumetric moisture content at early stage of drought were insignificant. As drought progressed, the clay had higher volumetric moisture content than the clay loam soil. Prior to and during the drought, plants grown in the clay loam soil were larger than those grown in the clay under well-watered conditions. The puddled clay soil was more reduced than the clay loam soil thus, the possibility that toxic compounds were produced at higher quantities in the former than in the latter cannot be ruled out. Continuous submergence of both soil types enhanced the development of the root system within the upper 15 cm layer. Even the root system of CT9993 was limited to a shallow layer above tha artificial pan. Remarkable number of roots penetrated the soft artificial pan yet root length density below the artificial barrier was quite small. Puddling and high clay content restricted root growth under drought conditions. The volumetric soil moisture content to root dry weight ratio was quite high near the bottom of the pots. The ratio of cumulative transpiration to volumetric soil moisture content obtained in the clay was lower than those in the clay loam soil. Root dry weight, root length density, leaf area, shoot dry weight, and readily available moisture were linked to soil moisture extraction efficiency. High efficiency could be risky as it may lead to rapid soil moisture depletion and early plant dessication during a long dry spell. Plant status prior to an impending drought is very crucial. Cultural practices applied at early stages of growth are intended to enhance shoot growth, the adoption of which should consider both the benefits and associated risks