Nitro-chalk was at one time a by-product of the gas and other industries, but now that manufacturing methods have changed, it is not so plentiful or cheap.

A chemical breakdown can be achieved by the addition of any readily available nitrogen source such as sulphate of ammonia, or Nitro-chalk, but these soluble salts can inhibit bacterial action and the end-product is not so well balanced and does not produce such good results.

In the short term, nitrogenous fertilizers, by increasing grasses and clovers, can result in an increase in the earthworm population, but continuous use of superphosphate or Nitro-chalk over a long period has been shown, in trials at Rothamstead, to reduce numbers in proportion to the amount of nitrogen applied.