Well I am a skeptic. Can anyone find a published study that provides evidence that these biodynamic preparations have a greater effect on crop yields than, say, applications of compost or even green manuring? I sure can't.
For example, this study
examined affects of biodynamic preparations on potato yield. It found that biodynamic preparations increased potato yields by 0%, 6%, and 33%, depending on variety. That is an average of 13% yield increase compared with the control. It is not clear whether the control was sprayed with water lacking biodynamic preparations or not.
In contrast, this study
found that applications of compost improved potato yield by 50% at 7,344 kg compost/ha and by 89% at double that rate over the control treatment.
Similarly, this study
found that green manure applications increased potato yield by 24% over mineral fertilizers and 56% over the control treatment.
1) compost applications improved potato yields 37%-76% more than biodynamic preparations, compared with controls
2) green manure applications improved potato yields 43% more than biodynamic preparations, compared with controls
3) Mineral fertilizers (without compost or green manure application) improved potato yields 11% more than biodynamic preparations, compared with controls.
I picked potatoes because the first legit study I came across examining affects of biodynamic preparations on crop yields studied potatoes. Could other crops react differently? Sure. But we have to start somewhere.
However, this isn't the whole story. The ultimate question for a farmer is which treatment is most cost effective? Based on real world costs and percent yield increases from studies cited above these work out to:
Compost: I can get good compost for $30/cubic yard, delivered. 7,344 kg/ha equals 6,552 lbs/acre, roughly 6 cubic yards per acre, worth $180. A skilled operator can spread that much in about 2 hours, costing $3 for fuel and 2 labor hours @$13/hour = $29. $219 total, or $4.18 per percentage increase in yield over the control
Green Manure: Net costs of cover cropping run around $25-$30 per acre. That amounts to $0.53 per percent increase in yield over the control.
Biodynamic preparations: According to this study
, 2 applications each of BD500 and BD501 cost $79/acre, or $6.07 per percent increase in mean yield over the control
. Note that in the biodynamic study, BD501 was applied three times, but I won't waste more time accounting for that.
Thus the biodynamic preparations have the smallest effect on, and the highest cost per unit of, yield increase compared with doing nothing. If I could only afford to do one thing to my field, application of biodynamic preparations would not be my choice. I challenge the BD folks out there to convince me otherwise.