It's all in the fertiliser.

Tests done by Far North Envirolab Ltd.

Lower Phosphate Leaching.

Studies showed phosphate leaching through soil samples of farms or orchards using natural fertilisers, compared with neighbouring conventional farms using artificial chemical fertilisers.Showed leaching of phosphate in soil depths of 400 mm on farms that used artificial chemical fertilisers were between 31.6% to 168.3% higher than with natural rok fertilisers. It also found Farms and orhards using natural fertilisers leaching was reduced and the waterways less polluted.
In a sediment soil the results showed a 31.6 % less phosphate leaching when natural fertilisers had been used.
In a sandy soil with little top soil it was 74 % less phosphate leaching.
In a day soil with a small layer of top soil it was 168 % less phosphate leaching.
In a mixture of sandy and clay it was 35 % less phosphate leaching.
In very rich, nearly compost soil it was 75 % less.