Effects of soil modification and treading on pasture growth and physical properties of an irrigated red-brown earth

Abstract

Lemnos loam, a red-brown earth used extensively for pasture production in northern Victoria, and its exposed subsoil (topsoil removed) were both subjected to surface cultivation and total profile modification. Total profile modification consisted of excavating and mixing the top 1.1 m of soil and incorporating gypsum (10 t ha-1), superphosphate (4.5 t ha-1) and ammonium nitrate (0.5 t ha-1) . A white clover-perennial ryegrass pasture was established. Treading by cattle was superimposed over these soil treatments. Exposure of the subsoil, as often occurs with laser landforming, reduced pasture growth by 30% compared with a normal soil profile. Modification of the exposed subsoil negated this effect. Modification of the normal soil profile had little effect on pasture production but did influence pasture composition. Treading had a cumulative effect with time, reducing pasture production by 6, 9 and 12% in 1981, 1982 and 1983, respectively. This occurred despite the precaution of allowing grazing only when the soil was dry. Profile modification resulted in increased pore space and root growth, and lowered bulk density and penetrometer resistance at depth. Treading increased surface soil bulk density, with penetrometer studies showing that this effect was confined to the top 0.15 m.