Soil acidification, chlorsulfuron application and Rhizobium meliloti as factors in lucerne yield decline

Paddock sampling and subsequent pot experiments have identified a number of factors which may contribute to low lucerne yields in the mid-north of South Australia. Soil acidification appears to be a significant factor as soil pH(w) (1:5, soil-water) ranged from 5.0 to 6.8 in the surveyed paddocks, 0.9-1.7 units below the fenceline values for these paddocks; 80% were below pH(w) 6.0. In all cases, soil from these lucerne paddocks also had low Rhizobium meliloti populations with paddock values ranging from