Our ADAS Crop Physiologists just debated Compost Tea and our views were varied. A key aspect of our debate was balancing our respect for practice with our trust in science – something very much at the heart of FarmPEP. Farmers using Compost Teas claim BIG effects e.g. "up to 50% increase in yield", and then offer 'scientific' explanations e.g. "The presence of active fungi is essential for effective nitrogen and phosphorous absorption in crops" and “spray Compost Tea in the evening” because "most plant growth occurs between 3am and 8am". Each of these reasons is patently wrong according to our training as crop physiologists – crops can take up N and P quite happily from sterile media, so without any fungal help, and crops grow by photosynthesis, which is driven by sunlight, something that is not strong from 3am to 8am! Justifying a product with incorrect science surely can't help its cause? But using Compost Tea for the wrong reasons doesn't make Compost Tea mistaken. So how do we decide whether Compost Tea (or any other promoted elixir) is a trustworthy notion?

If the science is uncertain our answer must come from testing, but lots of it!  No single crop experiment, even a good one, can provide a sufficiently trustworthy answer (because errors inherent in all crop experiments are larger than the cost of Compost Tea). So, we need lots of experiments across multiple conditions, firstly to see whether Compost Tea works at all or, if not always, what conditions suit its use.

Compost Tea could be invaluable on farms, and could even change our scientific beliefs, but farmers could waste lots of money and effort if they are persuaded to rely on ineffective Compost Teas, and whatever happens, Compost Tea is unlikely to show us that fungi are essential to crops, or that crops grow mostly in the dark!  Journalists surely have a duty to say and double-check when they are reporting such controversial claims. And as scientists, if we can’t say whether Compost Tea works, we can at least say when the underlying reasoning is wrong.