ABSTRACT
Paddy Field ........................................................... 305 II. Characteristics of Water Flow in Upland
Agricultural Fields....................................................... 307 A. Water Flow in Unsaturated Subsoil in an
Upland Field ......................................................... 307
B. Tillage Effects on Water Flow in Upland Fields.................................................................... 310
C. Drainage Efficiency in an Upland Field in Japan ............................................................... 310
III. Water Balance in Fields with Vegetation.................. 312 IV. Evapotranspiration..................................................... 315
A. Factors Affecting Evapotranspiration ................ 315 B. Soil Water Availability......................................... 317
V. Soil Water Uptake by Plant Roots ............................. 318 A. Mechanism of Soil Water Uptake ....................... 318
1. Driving Forces of Soil Water Uptake ........... 318 2. Definition of Hydraulic Resistance............... 320 3. Factors Affecting Hydraulic Resistances ..... 322
B. Equation of Soil Water Uptake ........................... 325 C. Distribution of Crop Roots .................................. 327 D. Water Uptake Rate and Water Extraction
Pattern................................................................. 331 1. Water Uptake Rate........................................ 331 2. Water Extraction Pattern ............................. 332 3. Prediction of Water Extraction Pattern ....... 334
E. Water Uptake by Roots in Cracks....................... 336 1. Estimation of Daily Water Uptake ............... 336 2. Soil Water Content Profiles Toward
Cracks with Roots ......................................... 338 VI. Effects of Vegetation on Soil Water Regime .............. 340 References............................................................................ 346
I. CHARACTERISTICS OF WATER FLOW IN PADDY RICE FIELDS
A. Water Flow in Unsaturated Subsoil in a Paddy Field
It is sort of amazing that, in paddy rice fields covered with surface irrigation water, the subsoils are continuously kept in unsaturated conditions, even when the downward water flows last for months.
