Can topdressing with salt increase oversowing success and pasture quality on steep, south facing slopes in hill country pastures?

Abstract

Two experiments were conducted in sodium deficient (<0.03% Na in DM) pastures on steep, south facing slopes at Mt Grand, Hawea, Central Otago (600 m.a.s.l), to determine the effect of the application of coarse salt (NaCl) fertiliser on pasture composition and establishment of oversown seeds. In Experiment 1, factorial combinations of salt (0, 150 kg NaCl/ha), N (0,100 kg N/ha as urea) and sulphur superphosphate (0, 500 kg/ ha) fertilisers were applied to 30 x 8 m plots in early December 2003. Balansa clover (10 kg seed/ha) and subterranean clover (10 kg/ha) seeds were oversown into each plot in March 2004. Plots where salt was applied were grazed intensively by Merino ewes immediately after salt application creating up to 50% bare ground. In December 2004, pastures where salt had been applied one year earlier were shorter, had a lower percentage of white clover and a higher percentage of bare ground and balansa clover. In Experiment 2, factorial combinations of salt fertiliser (0, 100 kg NaCl/ha) and seed (no seed, mixture of Caucasian clover (10 kg/ha), Lotus pendunculatus (2 kg/ha) and plantain (2 kg/ha)) were applied together to 5 x 10 m plots in September 2004. In April 2005, pastures where salt was applied were shorter, had fewer grass seedheads, a lower percentage of resident grasses and litter but a higher percentage of bare ground and plantain. There were more seedlings of plantain where salt was (6.5 seedlings/m2) than where it was not applied (1.1 seedlings/m2). This small plot work indicates that salt fertiliser application to Na-deficient herbage can enhance grazing intensity. By creating soil disturbance and reducing competition from resident grasses, salt application increased the establishment of oversown seeds of plantain and balansa clover. Establishment of the slow growing species (Caucasian clover, lotus) and the large seeded subterranean clover appeared to be unsuccessful under the conditions of the experiments. Salt application is a tool for pasture management and improvement in the hill/high country that could be used together with other methods such as herbicides, seeding, sub-division, grazing management and fertiliser. Keywords: grazing, sodium, oversowing, hill country