Oxalate interferes with the absorption of calcium (Ca) in livestock. However, insoluble oxalate, which presents mostly as a complex combined with Ca, is not considered to be a problem in ruminants. The objective of this study was to test the possibility of increasing insoluble oxalate content in plants by increasing Ca supply in pot-grown napiergrass (Pennisetum purpureum Schumach). The plants were cut three times at approximately 2-month intervals from summer to autumn. Four treatments (0, 30, 60 and 90 g m-2) of Ca(OH)2 were applied in three equal split doses: before transplanting and soon after the first two cuttings. At almost all of the cuttings, soluble oxalate in forage showed a decreasing trend and insoluble oxalate and Ca concentration showed a reverse trend with an increased rate of Ca(OH)2 application. Averaged over the three cuttings, the 90-g Ca(OH)2 treatment was most effective in reducing soluble oxalate by increasing insoluble oxalate, with significant (P &lt
0.05) differences between the 0- and 90-g Ca(OH)2 treatments. However, total oxalate content was not affected (P &gt
0.05) by the rate of Ca(OH)2 application. Moreover, Ca(OH)2 application did not affect dry matter yield and the concentrations of magnesium, potassium and sodium of plant material. It may be concluded that the level of soluble oxalate in plants can be partially replaced by formation of insoluble oxalate using Ca(OH)2 fertilizer. © Journal Compilation © 2009 Japanese Society of Grassland Science.