Growth of Kikuyugrass (Pennisetum clandestinum) Under Clipping. II. Regrowth Characteristics in Relation to Nitrogen Fertilization and Climate

A better understanding of the response of kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) to management and climate is needed in order to best exploit this important forage grass. The objective of this study was to describe kikuyugrass regrowth under a variety of conditions and to relate regrowth performance to N-nutrition, environment, and sward characteristics. Kikuyugrass swards at two locations (Kula, 945 m elevation, and Makawao, 660 m elevation) were trimmed and fertilized with three levels of N (22, 56, and 168 kg/ha) at 10-week intervals. During alternate 10-week periods, plots were cut sequentially after 4, 6, 8, and 10 weeks of regrowth. Regrowth began slowly after a 10-week period, especially at Kula during the cool season. Changes in the area: dry weight ratio of the forage indicated that this may have been due to retarded leaf development under low temperatures. At other times, regrowth at both locations was normally rapid after the 4th week and continued at a high rate through the 10th week. About 600 kg/ha of harvestable green vegetation (DM basis) were required support subsequent near-maximum growth rates. This was equivalent to 8 cm harvestable height, 30% interception of blue light, and a leaf-plus-stem area index of 1.0. Crude protein (CP) yields tended to level off after weeks, especially during the warmer months. Percent CP in the low and moderate N treatments declined during the regrowth period from approximately 16 to 18% at 4 weeks to 8% at 10 weeks. Percent CP in the high-N treatment was higher but more seasonally variable; 4-week regrowth contained over 30% CP equiv, during the cooler months. Some of this N was present as NO₃ which ranged from 20 ppm NO₃-N (low or moderate N-level, 8 weeks regrowth) to over 2000 ppm (high N-level, 2 to 6 weeks growth at Makawao). Nitrate levels thus approached potentially toxic concentrations for ruminants in some cases. Multiple regression analysis identified several factors as being significantly associated with growth rate: nitrogen nutrition of the sward, temperature (air or soil), and position on the growth curve. Unidentified site factors were also determinants.