Soil water extraction during drought in a simulated rainfed lowland environment
2002
Nieuwenhuis, P. | Lales, J.S. | Robles, R.P. | Samonte, H.P. | Amarante, S.T. | Wade, L.J. (International Rice Research Inst., DAPO Box 7777, Metro Manila (Philippines))
A greenhouse experiment was conducted at IRRI to determine the soil water extraction of rainfed lowland rice cv IR62266 in two soil types, with and without artificial hardpans, in puddled and nonpuddled soils under drought. The experimental unit was a PVC pipe of 20cm diameter petrolatum mixture installed 20 cm below the soil surface. Drought was imposed from 21 to 40 days after planting. Soil water extraction was calculated from volumetric water content determined daily by time domain reflectometry. Cummulative transpirational water loss was determined daily by gravimetric method. Shoot and root parameters were measured thrice during the drought period. Prior to the imposition of drought (20 DAP), 83-97% of the total root dry weight was recovered above the artificial pan. Significantly higher root dry weight, root length density, and leaf area were noted in the clay loam than in the clay, particularly under nonpuddled conditions. More roots penetrated the soft than the hard artificial pan, yet root length density below the artificial pan was quite low. Plants grown in the clay loam had higher cummulative transpiration than those grown in the clay. The ratio of cummulative transpiration to volumetric soil water content was higher in the clay loam, indicating a higher efficiency of water extraction. Whether this is beneficial depends upon the reserves of soil water available at depth and the likelihood of recharge. Metering of plant water loss is also important
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