Responses in three species of summer type turfgrasses to different regimes of underground water level and solar radiation

Abstract

Manillagrass (K), Japanese lawngrass (J), and Bermudagrass (B) are all summer type turfgrasses used commonly in warm regions of Japan. To compare sensitivity to soil moisture and solar radiation regimes, sod materials of these grass species were each grown under three levels of underground water level and solar radiation (Fig. 1, Tables 1, 2, 5) .
The experiments consisted of two parts, springsummer and summer-autumn-tests in 1983. In the former test, the effects of underground water levels on aboveground yields were examined by two cuttings——1st (July 25) and 2nd (August 30) . The effects of solar radiation on aboveground yields were examined in the latter test also by two cuttings—3rd (September 27) and 4th (December 2) . Dry weight of regenerated aboveground organs was measured throughout 4 cuttings. In addition to this, plant height and dry weight of the residual stocks (including the basal part of stems, rhizomes and roots) were measured in the 3rd and 4th cuttings, respectively.
Responses of each species to the underground water levels were clearly shown in the summertest (2nd cut.) rather than the spring (1st cut.) by way of the decrease in dry weight with increasing water levels. A significant interaction between grass species and water levels in variance analysis indicated that the sensitivity to the water levels differed with the species in the order of B>>J>K (Tables 3, 4) .
Responses of each species to the solar radiation were clearly shown also in the summer-test (3rd cut.) by both the increase in plant height and decrease in dry weight in relation to the reduction of solar radiations. Sensitivity to solar radiation, as a significant interaction between grass species and solar radiation shows, also differed with the species in the order of B>>J>K (Tables 6, 7, 8) .
Dry weight of the residual stocks (exclusive of roots) decreased conspicuously with the reduction of solar radiation. Sensitivity of this part to solar radiation measured in terms of reducing dry weight also differed with species showing a tendency of K>J>B (Tables 9, 10) . This suggests that the growth of each species in the following year may be restricted in the same order describedabove.
From the results mentioned above, the present authors considered that the Japanese lawngrass possesses both plasticity and constancy (nonplasticity) to some extent in response to soil moisture and solar radiation. Consequently, the species appears to be more convenient to practical use than the other two, at least under poor intensive management.