Rhizobial inoculation and fertilizer rates as factors in the establishment of subterranean clover in South Australia

Abstract

The rate of application of phosphatic fertilizer was found to be the most important single factor influencing first year establishment of sown pastures of subterranean clover. In soils of low fertility in South Australia, increases in the rate of application of superphosphate were accompanied by decreases in the number of unthrifty plants and increases in herbage yield. A minimum rate of superphosphate was found to be necessary to ensure a satisfactory establishment. The use of lime in the form of basic superphosphate was accompanied by increase in yield and decrease in the number of poor plants, but current theories are inadequate to explain its mode of action. Use of a trace element mixture containing copper, zinc, manganese, and molybdenum produced significant increases in yield, but did not decrease the number of poor plants.Heavy dressings of artificial nitrogenous fertilizers or inoculation by effective strains of Rhizobium trifolii Dang. produced increases in yield, but did not produce significant reduction in the number of poor plants. Untreated, control plants showed regular nodulation, and it was found that an indigenous population of strains of Rh. Trifolii apparently efficient in nitrogen fixation already existed in these soils. Increases in herbage yield of as much as 50% were obtained in the first year; this justifies recommending rhizobial inoculation as a commercial practice, but the effect was not sustained in subsequent years. There was no evidence to indicate that lack of artificial inoculation would jeopardize establishment of sown pastures in these soils.