In his excellent book Creating a Forest Garden, Martin Crawford says "as a general rule a total of about 25-30 per cent area of nitrogen fixers is enough, though if you have mostly heavily cropping plants with a high nitrogen demand then this may rise to 40 per cent" (p58).

About urine he says "you can pee in situ - this is ideal" and "urine does not need diluting before applying" (p55-6)

However, Patrick Whitefield in his "How to make a Forest Garden" book says of liquid manures:

"A healthy soil will support healthy plants, whereas plants which are fed directly with highly soluble nutrients are sappy and vulnerable. What is more, a high level of soluble nutrients in the soil is actually harmful to the soil microbes which are t he power-house of natural fertility. Liquid manures contain highly soluble nutrients, so their place in forest gardening is rather limited"

"The plus side of being highly soluble is that they are quick-acting, so they can be useful as a tonic for sick plants. If the weather is very wet, vegetables can get seriously short of nitrogen and other soluble nutrients, especially if they are growing on a sandy soil. Urine, diluted two to one, can bring back their colour and vigour and get them growing again. If used when the soil is dry it should be diluted more, down to ten to one in soil so dry that the plants need watering anyway. If should be used sparingly on clay soils, as its salt content can harm the soil structure." (p66)

I think I'm going to email Martin and Patrick to get more clarification on this issue... will try to remember to report back here...

I got a pretty swift response from both Martin and Patrick...

Martin says:

"It all depends of the scale of use. A little used here and there will be fine used neat – although of course leaves can be burnt by neat urine – this is what happens in nature. If you are intending to use a lot then it is probably best used diluted and/or composted with straw etc."

And Patrick adds:

"I think the distinction here is between a mature forest garden and a typical vegetable garden consisting of annual plants, which for most of the growing season are immature. The former has a very robust, diverse and mature ecology, well equipped to deal with the neat piss of mammals, which, as Martin says, is just what happens in nature. Very different from a veg garden, both from the point of view of plant damage and that of working within natural cycles. When I wrote my book Martin's garden didn't even exist and I was writing about something I still hadn't experienced first hand (Robert Hart's garden was very much a prototype). I was transposing from my experience of annual vegetable gardening.

"Even so, if I had a garden like Martin's I'm not sure whether I would piss in it willy nilly - no pun intended."