Effects of Nitrogen and Potassium on Wear Mechanisms in Perennial Ryegrass. I. Wear Tolerance and Recovery

Fertility may influence wear tolerance and recovery, but its effects on perennial ryegrass (Lolium perenne L.) are unknown. Our objective was to evaluate the effects of nitrogen (N) and potassium (K) on wear tolerance and recovery in perennial ryegrass. Field studies were conducted in 2006 and 2007 to evaluate five rate levels of N (49, 147, 245, 343, and 441 kg ha–1 yr–1) with three rate levels of K (49, 245, and 441 kg ha–1 yr–1). Wear was applied using differential slip wear (DSW) and grooming brush wear (GBW). Injury was assessed using visual ratings and a relative chlorophyll index from spectral readings measured on wear-treated and nontreated plots. Grooming brush wear was ineffective for assessing recovery. Wear tolerance ratings between GBW and DSW were correlated with r-values as high as 0.93 (P 0.001). Reflectance readings were correlated with GBW and DSW ratings. Nitrogen influenced wear tolerance and recovery. Wear tolerance decreased linearly as N increased, and N accounted for as much as 95% of the treatment variation. Reductions in wear tolerance with increasing K were observed with GBW, while significant gains in recovery from DSW were observed with K at 2 wk after treatment (2WAT). Nitrogen in excess of 245 kg ha–1 yr–1 promoted reductions in wear tolerance but faster recovery. The 245 kg N ha–1 yr–1 rate afforded full recovery in the shortest interval as early as 8WAT. Optimum N for maximum wear tolerance and recovery for perennial ryegrass is 245 kg N ha–1 yr–1.