Richard Newlands, of Wellington, asks :-

What are the main chemicals in urine? Is daily peeing under a lemon tree beneficial (as implied in the film "The World's Fastest Indian") or detrimental (as a nursery man told me - they die)?

Keith Cameron, a soil scientist at Lincoln University, responded.

Typical chemical composition of human urine is: water 95%; urea 9.3 g/l; chloride 1.87 g/l; sodium 1.17 g/l; potassium 0.750 g/l; creatinine 0.670 g/l.

Although urine will add some nitrogen and potassium to a lemon tree, I would recommend using toilet facilities rather than peeing on the tree. The urine would probably not damage the tree but the student could end up being prosecuted for indecent exposure! Be better to buy some fertiliser or compost.

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