Root growth of rice (Oryza saliva L.) is frequentlyinhibited by an adverse physical environment resulting from high moisture stress and strength of soilunder upland conditions, and the effects are often reflected in poor performance of the crop. This necessitates a critical understanding of rice root growth under varying soil physical conditions.
The growth responses of the rice root system to the interaction between moisture regime and bulk density of soil as well as to the induced soil physical characteristics were assessed under controlled glasshouse conditions. Four moisture regimes: 0 (M1), 0–20 (M2), 0–350(M3), and 350–10000 (M4) mb, were superimposed on low, medium and high bulk density treatments in clay, loam and sandy loam soils. The soil physical environment was characterized by measurements of moisture distribution, penetrationenergy and oxygen diffusion rate in soils as functions of depth.
A low moisture stress of 20 mb in low density soils favoured rice root growth. In low density soils, even though the number of roots at the base (proximal end) was maximum under M1, the depth of penetration, volume and dry weight of root were significantly more underM2 than under M1; M3 and M4. Irrespective of bulk density, even though oxygen diffusion rates in soils under M3 and M4 were greater than those under M1 and M2, the number of roots at the base, volume and dry weight of the root system decreased under M3 and M4 owing to low moisture content and high penetration energy in the surface layer (0–5 cm) of all the soil types. Lower moisture content and higher penetration energy at higher bulk densities of the soil types significantly reduced the root growth and especially the depth of penetration.