The effect of fertiliser N rates on growth of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) grown at high soil water levels under controlled conditions

Abstract

Accepted 10 March 2006The response of perennial ryegrass and white clover to fertiliser N rates of 0, 30, 60, 120 and 180 kg N ha-1 when grown at soil water potentials of -1 0, -20, -25 and -35 kPa were investigated. Increasing fertiliser N levels from 0 to 120 kg N ha-1 resulted in increased (P=0.05) perennial ryegrass primary dry matter production (POM) at the end of the first regrowth cycle (31 days). Ryegrass POM yield was influenced (P=0.05) by soil water potential, with higher yields recorded at the -10 and -20 kPa treatments compared to the -25 and -35 kPa treatments. White clover POM production was not influenced by N rate or soil water potential. Carry-over fertiliser N caused increased (P=0.05) ryegrass residual dry matter (ROM) yields as fertiliser N rate was increased from 0, 30, or 60 kg N ha-1 to 120 and 180 kg N ha -1, while clover ROM production increased as fertiliser N rate was increased from 0 to 180 kg N ha-1 . Higher (-10 and -20 kPa) soil water levels caused increased ryegrass ROM production, a response not observed in clover. Total dry matter (TOM) production (the accumulative dry matter production during a 60 day period following fertiliser N application) of ryegrass was significantly increased as fertiliser N rate was increased from 0 to 180 kg N ha-1 . Higher ryegrass TOM yields at -10 kPa and -20 kPa were recorded at the higher (120 and 180 kg N ha-1 ) N application rates, but water content did not influence TOM production at the lower (0, 30 and 60 kg N ha-1 ) fertiliser N application rates. Clover TOM production was not influenced by the treatments applied.

The effect of low soil temperature and fertiliser N rate on perennial ryegrass(Lolium perenne)and white clover(Trifolium repens)grown under controlled conditions

“…Although the application of fertiliser N (0-180 kg N ha -1 ) to white clover does not directly affect white clover productivity (Labuschagne & Agenbag, 2006), the N fixing Rhizobium bacteria could be negatively effected (Kessler et al, 1990). Symbiotic N fixation will also be negatively affected as soil temperatures decrease (Russell, 1988).…”