Transpiration Rate Changes in Response to Soil Dry of Five Warm-Season Turfgrass Species.

Water availability is increasingly limited for use on landscapes, particularly in urbanized areas, where water use restrictions are often imposed. Knowledge regarding transpiration changes in response to soil drying could provide important information when selecting turfgrass species. The objective was to determine the changes in the transpiration rate of 19 genotypes of five warm season turfgrass species during soil drying. The species evaluated were:  Zoysia japonica, Z. matrella, Cynodon dactylon var. dactylon, C. transvaalensis, and Stenotaphrum secundatum. Transpiration response to drying soil was tested using clonally propagated plugs grown in pots in a controlled temperature room in Gainesville, FL. Each genotype was represented by 10 pots arranged in a completely randomized design. Four pots of each were maintained as well-watered pots and six were subjected to a controlled dry down for 18 days. To obtain transpiration rate for a period of ≈ 24 h, the weight of each pot was recorded at ≈1300 h each day. After each dry down cycle the fraction of transpirable soil water (FTSW) was recorded. The FTSW break point (BP) was estimated as the point at which transpiration begins to decline. There were not significant differences in BP between species. Differences between genotypes were significant (P < 0.0001) with the lowest BP for genotype 336 (Z. matrella BP = 0.25), and the highest BP for genotype 5269-24 (Z. japonica BP = 0.41). The r² were higher than 97% in all data obtained. The number of days to reach BP showed significant differences between species.  St. Augustinegrass reached BP the soonest at 7d and Z. matrella the slowest at 8 d. Transpirational responses do differ between genotypes and some may be more suited for use where the use of irrigation for landscapes is restricted.