Relationship between Root Distribution of Upland Crops and their Yield : IV. Soil water uptake pattern in upland rice under different soil moisture levels

[摘要] The field experiments were conducted during summer in 1978 and 1979 on a field of volcanic ash soil at Kitamoto to improve a method determining the soil water uptake patterns by field crops. The amount of the evapotranspiration in upland rice was measured by the chamber method developed by KATO et al. after cutting roots horizontally by piano wire at 15, 20 and 30 cm in depth, respectively, for three soil moisture levels controlled by irrigation just before treatment. The main results obtained are as follows: 1. When soil moisture was kept at low level of pF 2.0-2.3, the cutting roots at 20 and 30 cm in depth was not effective for the evapotranspiration in case of the rate less than 0.9 mm per hour. 2. When soil moisture was kept at pF 2.8, the results obtained by cutting roots at 15 cm in depth was the same as shown in item 1. 3. Under the condition of 42% soil moisture in surface soil, the evapotranspiration of treated plot decreased to 60% of the controlled one and wilted in daytime. 4. It was suggested from these results that upland rice grew mainly by water in the layer of 0-20 cm if the moisture was at low (pF1 2.0-2.3), but, when evapotranspiration rate got higher than 0.9 mm per hour even the moisture of surface soil was kept at low level (pF 2.0-2.3) or moisture of surface soil was less than 42%, the roots above 15 cm in depth did not uptake soil water enough to support the normal evapotranspiration.

[学科分类] 农业科学（综合）