The use of lime to alleviate high pasture manganese in Central Otago

Abstract

Rates of lime (0, 1.25, 2.5, 5.0, 7.5 and 10 t/ha) were applied to two sites (Wyuna and Routeburn Stations) near Glenorchy in Central Otago. At both these sites initial herbage manganese (Mn) concentrations (780 and 471 mg/kg dry matter (DM) respectively) were above the level (400 mg/kg DM) that has been shown to reduce lamb growth rates. Total pasture production for the three years averaged 3600 kg DM/ha/yr at Wyuna and 8400 kg DM/ha/yr at Routeburn. The application of lime to the predominately browntop (Wyuna = 72%, Routeburn = 46%) pastures in this study, did not result in significant pasture production increases in the first 2 years but in Year 3 there was a significant production increase due to lime at Wyuna (P<0.05). Significant increases in soil pH and calcium and decreases in soil Mn occurred with the application of lime. The lime application also resulted in significantly lower herbage Mn concentrations. One year following lime application at rates of only 2.5 t/ha, herbage Mn concentrations were lowered to below the 400 mg/kg DM animal health threshold at both sites. A relationship between sward dead material content (x) and herbage Mn concentration (y) was established which had different slopes at the two sites (Routeburn y=8.34x + 577; r2 = 0.683, P < 0.001: Wyuna y = 6.8x + 633; r2 = 0.640, P<0.01). This relationship, the slope of which decreased as lime application rates increased, has implications in the interpretation and likely implementation of the results. It would thus appear that improved grazing management which limits the dead material content in the sward would lessen the amount of lime required to lower herbage Mn to below the animal health threshold. Keywords: browntop, dead material, lime application, manganese