Effects of Mowing and Fertilization on Warm Season Turfgrasses

The need to maintain good quality turfgrass at relatively low costs in the face of current energy crisis and inflationary costs have led to the investigations reported in this thesis. A field experiment was conducted to investigate the effect of mowing heights and N fertilization on the commonly cultivated warm season grasses used in the tropics and subtropics. Response trends of zoysiagrass (Zoysia japonica Steud.) and seashore paspalum (Paspalum vaginatum Swartz) were also observed. A greenhouse experiment was conducted to determine the N-K levels required of carpetgrass (Axonopus affinis Chase) which is the main turfgrass used in Singapore for parks and open spaces. The objective of this experiment was to determine the optimum N-K combination required to produce acceptable turf at lowest input. Three nitrogen fertilizer levels and two mowing heights were used in the field experim.ent. N levels were recommended low, medium, and high for the individual turf species. Growth parameters used for evaluation of responses were visual ratings, clipping dry weights, and chlorophyll contents in both experiments. In addition, root depths were measured for the field experiment and dried shoots and roots were weighed at the termination of the glasshouse pot culture experiment. Tissue N analysis was carried out to relate the growth responses observed. Mowing heights affected visual ratings of all turf species. However, they differ in response to mowing height in that bermudagrass (Cynodon dactylon (L.) Pers.) and centipedegrass (Eremochloa ophiuroides (Munro.) Hack.) had higher visual ratings at low mowing height whilst carpetgrass (Axonopus affinis Chase) and St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntze) had higher visual ratings at high mowing heights. Mowing heights had different effects on different grasses in terms of clipping dry weights. The method of collecting clippings was less than desirable and led to higher experimental error for some grasses than others. Chlorophyll contents followed the same trend as visual ratings in that bermudagrass and centipedegrass had higher chlorophyll content at low mowing heights whilst centipedegrass and St. Augustinegrass were higher at high mowing heights. Root depths of St. Augustinegrass decreased significantly at low mowing height. The root depths of all other species tended to decrease with closer mowing although the effect was not significant at the 5% level. Centipedegrass was the only species that responded to N fertilizer as expected. Clipping dry weights, chlorophyll contents, and %N increased with increasing levels of N. Rooth depth decreased as N level increased. The reason for lack of response of other species to N fertilizer was probably due to insufficient differences in N levels applied. In the glasshouse experiment, increasing N levels from 6.25 ppm to 50 ppm, increased visual ratings, clipping dry weights, and chlorophyll contents, and depressed root growth. N has no effect on shoot dry weights at termination of the experiment. Average results over the experimental period showed that K had no effect on visual ratings, shoot dry weights, and root dry weights. The optimum level for K for maximum chlorophyll content was 15 ppm whereas clipping dry weights increased with increasing K above 15 ppm. Combinations within the range of 25 ppm N with 15 ppm K and 25 ppm N with 30 ppm K produced good quality carpetgrass without being over luxuriant. However, as this was based on data collected from a glasshouse experiment, it should be further tested in the field. Visual ratings was found to be a reliable parameter for evaluation of turfgrass quality, and should suffice for routine purposes. Visual ratings were correlated with clipping dry weights, chlorophyll contents, and root dry weights