The Canberra track put some 'organic material' down a couple of years back. At least some of it was woodchips (or something similar - never really stopped to have a good look...).
From a rider's point of view, it worked really well - seemed to make the surface quite grippy and consistant (ie: it stayed damp without too much effort on race day, unlike the original stuff that always seemed to be either too dry or too wet).
Everybody loves the moist, dark loam, esp if you find it under nice fresh grass. Can't say that I've seen that very often, esp lately...
