Water movement across plant bed and water use of chinese cabbage (Brassica campestris L. ssp. pekinensis)

Findings of the study were as follows. The upper limit of the soil water availability was the water content at matric potential of -0.05x10 (exp.5) Pa. The available water capacity of 80 cm. soil profile ranged from 0.14 to 0.31 cubic meter/cubic meter with the value for the root zone of 0-30 cm. depth as 0.175 cubic meter/cubic meter. Specific water capacity of high value covered a rather narrow span from near soil saturation to water content at a matric potential of -0.5x10 (exp.5) Pa, indicating that Kamphaeng Saen soil series should be irrigated frequently to maintain high water content in the soil which can be readily available for plant use. The upper 20 cm. of soil had a moderately rapid level of saturation hydraulic conductivity of 23-29 mm./h. The values fell sharply to 2.8-6.7 mm./h. in the lower depth, resulting in an averaging value of 6.7 mm./h. for the 50 cm. soil profile. The unsaturated hydraulic conductivity varied from 10 (exp.-6) to 10 (exp.-11) m./s., over the volumetric water content of 0.4 to 0.1 cubic meter/cubic meter. In summary, the Kamphaeng Saen soil series had a high available water capacity of 0.165 cubic meter/cubic meter, The growth of the shallow root Chinese cabbage, which could have a high water consumptive use of 6.3 mm./day was best under sprinkler irrigation. Sprinkler application, which distributes water uniformly to the plot, and helps lower the leaf temperature, gave the highest yield and rate of head formation, but also the highest rate of tipburn incidence. The highest irrigation efficiency was obtained under the twice-a-week sprinkler scheme. However, sprinkler irrigation at the rate of 145 % of PET was found to be insufficient for optimum growth of Chinese cabbage during summer season.