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

The 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-10, −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 (PDM) at the end of the first regrowth cycle (31 days). Ryegrass PDM 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 PDM production was not influenced by N rate or soil water potential. Carry-over fertiliser N caused increased (P=0.05) ryegrass residual dry matter (RDM) 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 RDM 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 RDM production, a response not observed in clover. Total dry matter (TDM) 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 TDM 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 TDM production at the lower (0, 30 and 60 kg N ha−1) fertiliser N application rates. Clover TDM production was not influenced by the treatments applied.