S Michael Gove’s staff look at the environment v. Farming, they might do woerse than to read this series of posts on N fertilisers.
When ammonium nitrate hits the soil moisture, it forms two “ions”. The ammonium carries a positive charge and is an “anion”. The nitrate carries a negative charge and is a “cation”. Sands have a very low ability to hold onto nutrients whether they be anions or cations.. Clays have some useful colloidal capacity which has some ability to hold onto anions (so it will hold some ammonium ion) but not much ability to hold cations (so it will hold very little nitrate).
“Humus” is a very complex and variable black tarry material made up of large, Carbon-based chain molecules (so in chemists’ language they are “organic Carbon” molecules) forming hydrocarbons, carbohydrates and proteins. The proteins carry one or more Nitrogen molecules. These molecules are insoluble in water. So this humus-N will not leach out in rain or irrigation. More than that, humus is very colloidal, so it will hold both ammonium and nitrate ions and reduce the leaching of synthetic N.
So, pushing up the organic matter in soils is a real economic and environmental plus.
See the next post on this blog for how organic N storage work sand promotes crop growth.
Bill Butterworth, Land Research Ltd, May 2018