Effects of phosphorus and nitrogen on growth of pasture plants and VAM fungi in SE australian soils with contrasting fertiliser histories (conventional and biodynamic)

The soil biological community has been reported to differ between conventional and alternative (organic and biodynamic) farming systems. However, few studies have investigated whether this results in substantial differences in the biological pathways controlling major ecosystem processes, such as plant nutrient uptake. This paper describes a glasshouse experiment conducted using a red-brown earth (Natrixeralf) soil sampled from three conventional and three biodynamic irrigated dairy pastures located in the Goulburn River Valley, Victoria, Australia. The biodynamic soils had not had organic or inorganic fertilisers applied for, on average, 17 years, while the conventional soils had received regular inputs of fertilisers containing soluble phosphorus (P) and nitrogen (N). The experiment examined whether the contrasting fertiliser histories had resulted in different pathways of plant nutrient uptake through assessing the response of white clover (Trifolium repens L.), perennial rye grass (Lolium perenne L.) and the indigenous vesicular-arbuscular mycorrhizal (VAM) fungi to addition of four levels of soluble P and N. The response to added P and N did not differ between the conventional and biodynamic soils, although, plants in the biodynamic soils had a slower growth rate and a higher level of colonisation by VAM fungi due to lower initial soil P and N concentrations. Overall, there was no indication that the biodynamic and conventional soils had developed substantially different processes to enhance plant nutrient uptake or that the indigenous VAM fungi differed in their tolerance to applications of soluble nutrients.