Biodynamic (BD) farming is an alternative form of agriculture, which aims to manage the biological system to avoid the input of inorganic mineral fertilisers, pesticides and herbicides.  Despite the growing consumer interest in organic and BD agricultural products, little objective information is available to assess the productivity and sustainability of BD management of irrigated dairy farms in Australia.

Ten paired irrigated dairy farms under BD and conventional (CV) management were compared over 4 years.  The paired farms were matched for soil type, climate and farm area.  Biodynamic farms had been practising BD principles for an average of 16 years prior to the study commencing and had not received phosphorus (P) fertiliser for 17 years.  The study examined the effects of farm management on soil and pasture P concentrations and farm P budgets.

Soil Olsen extractable P concentrations were consistently 2-3 times higher (P<0.05) under CV management (mean = 22 mg/kg) at a sampling depth of 10cm, whereas under BD management, soil Olsen P concentrations were generally marginal for pasture growth (mean = 8.5 mg/kg).  Low soil Olsen P concentrations were also reflected in consistently lower mean pasture P concentrations (P<0.05) under BD management (0.25 compared to 0.35 % of dry matter on CV farms).  Lower soil Olsen and pasture P concentrations under BD management, were explained by a large negative P balance of -17 kg P/ha.year across the 10 paired farms.  This negative P balance under BD management, was a consequence of low P imports (2 kg P/ha.year) in comparison to large quantities of P (19 kg P/ha.year) effectively lost from the farming system in forms such as animal products, estimated losses in water runoff and slowly reversible soil P reactions.  These results suggest that greater P imports are required to ensure the future sustainability of BD dairy pasture farming systems in Australia.  In contrast, the inorganic P fertiliser applied to CV farms resulted in a small positive P balance averaging 2 kg P/ha.year, despite measuring mean soil test P concentrations within the desired range for productive pasture growth.  This indicates that careful P management is required on these farms to avoid unnecessary increases in soil P concentrations over time.

Table 5. Comparing an average phosphorus budget for 10 paired biodynamic and conventional irrigated dairy farms located in south-eastern Australia.

Data averaged for the 3 year study and mean area of BD farms was 62.3 ha compared to 61.7 ha under CV management

	Biodynamic	Conventional
	Imports (kg P/ha)
P fertiliser A	0	27.0
Purchased supplementsB	1.7	3.4
Total imports	1.7	30.4
	Losses (kg P/ha)
MilkC	6.5	10.1
Animals sold off D	2.3	2.5
P lost in surface runoffE	1.9	7.5
Soil P sorptionF	8.0	8.0
Total losses	18.7	28.1
Balance	-17.0	+2.3

^A  CV farms = 302 kg of SSP/ha.year containing 9% P, ^B  BD farms = 38 t DM/year, CV farms = 74 t DM/year containing 2.8 kg P/t (Standing Committee on Agriculture - Ruminants Subcommittee 1990), ^C  BD farms = 402,096 L/year, CV farms = 620, 178 L/year containing 0.10% P (Standing Committee on Agriculture - Ruminants Subcommittee 1990), ^D  BD farms = 17 cows and 84 calves/year, CV farms = 18 cows and 99 calves/year containing 8 kg P/t of live weight (Standing Committee on Agriculture - Ruminants Subcommittee 1990), ^E  Estimate based on de Boer (2003) and Austin (1998), ^F  Estimate based on Gourley et al. (2001).