Why do pastures respond to lime?

Abstract

Lime responses in pasture have been attributed to amelioration of aluminium (Al) and manganese (Mn) toxicity, increased plant availability of nitrogen (N), phosphorus (P) and molybdenum (Mo), and increased soil moisture. Methods of assessing the occurrence of each of these mechanisms are given, illustrated using results from two contrasting lime trials where mechanisms of lime response were determined. The results indicate that lime responses on the Mangatea soil could be attributed to lime increasing N, P, and Mo availability, and to the amelioration of Al toxicity allowing better access to soil moisture over summer. In contrast, on the Matapiro soil lime responses were owing to enhanced N mineralisation. The results show that the occurrence and size of a pasture response owing to a given mechanism are owing to interactions between soil factors, plant species and climate. Hence more complex pasture models than are currently available are required before predictions of the size and duration of lime responses can be improved. Keywords: aluminium, lime, manganese, nitrogen, phosphorus, pasture response