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Samson, B.K.1, L.J. Wade2 and M Hasan1
1: Rajshahi Regional Station, Bangladesh Rice Research Institute,
Bangladesh
2: Agronomy Plant Physiology and Agroecology Division, IRRI, Philippines
Introduction
Rice roots are commonly shallow in rainfed lowland conditions. Mechanical impedence is one factor that may resist access of roots to deeper soil layers, thereby reducing the capacity of the root system to extract water from depth during late season drought (Wade 1996, Samson et al. 1997).
Methods
We examined the capacity of rice roots to penetrate restriction zones by conducting experiments at Rajshahi, Bangladesh, in the 1994 wet season. Eight lines (CT9993, IR52561, IR58821, IR62266, KDML105, Mahsuri, Namsagui19, and IR20) were grown in three environments (irrigated, early-planted rainfed, and late-planted rainfed), with each location comprising a randomized complete block design with five replications.
Results and Discussion
As drought intensified during grain filling, soil penetration resistance increased dramatically in both rainfed locations, especially at 20 cm depth. Most roots remained shallow in all three environments. Lines differed in the capacity of their root systems to penetrate a hardpan with greater root diameter associated with enhanced penetration to depth. Roots that penetrated a hardpan were thicker than roots of the same variety at lower impedance. Some lines, eg IR58821, were able to increase root length density in deeper soil layer as soil strength further increased on drying.
References