Abstract
This experiment was performed to examine the chamber method which is a means for measurment of photosynthesis in forage plant population or a sward. Perennial ryegrass (Lolium perenne L.) was used as material in this experiment. Plant was sown on field at early May in 1971 and grown under ordinary fertilizer and soil moisture conditions till late June in 1971. The assimilation chamber made of transparent acryl resin (light transmissibility of 90%) 50cm in lenght, 50cm in width and 40cm in height was designed, and was set on the metallic frame buried in the ground surface of a sward during the measurement. The regulation of the environmental conditions inside the chamber was conducted by controlling the volume of running water on the chamber and of supplying air into the chamber by means of compressor. The measurement of photosynthesis in population was carried out continuously for 6 days from June 30(12:00) to July 6(12:00) by keeping the atomospheric conditions, e.g., temperature, relative humidity, and CO_2 concentration, inside the assimilation chamber similar to those in the sward surrounding the chamber. On the other hand, the amount of dry matter production in the same sward was measured on June 30 and July 6. The examination and the evaluation of the chamber method were made comparing the amount of dry matter production calculated from CO_2 balance with that obtained by direct field measurment during the experimental period (6 days). The following results were obtained. 1) Tne results of this experiment showed that calculated value approximately agreed with observed value of the amount of dry matter production in perennial ryegrass sward. 2) As to the reason why calculated and observed values of the amount of dry matter production were approximately the same, it may be considered that the atomospheric conditions inside the chamber were maintained similar to the sward conditions outside the chamber, that is, the differences of air temperature, relative humidity and CO_2 concentration inside the chamber and those in the sward were -0.66±1.47℃, 7.1±4.3% and 0.85±7.41ppm, respectively. 3) The results mentioned above indicate that the chamber method will be appropriate for measurement of photosynthsis in forage plant population or a sward and that the value measured by the chamber method will be reliable, if the conditions of temperature, relative humidity and CO_2 concentration inside the assimilation chamber were maintained similar to the sward conditions.
