What is the meaning of 'keq' in keq/ha/year?

Keq stands for kiliequivalent. This helps to distinguish between the amount of a certain element within a whole molecule. For example, the nitrogen in ammonia, NH₃.

The unit known as equivalent, eq (a keq is 1000 eq), refers to the molar equivalent of e.g. sulphur, oxidised and reduced nitrogen, as well as base cations. For example:

1 keq N ha-1 yr-1 is equal to 14 kg N ha-1 yr-1 and

1 keq S ha-1 yr-1 is equal to 16 kg S ha-1 yr-1.

When converting compounds the valency is important and is connected with the charge on the ion. For example: NH₄⁺ or NO₃^- have a valency of 1.

For sulphur, the prevalent ion is sulphate SO₄^2-, which has a double charge (valency). The full process is to convert kg to kmoles, then kmoles to keq. The 'equivalent' refers to the ionic charge on an ion. 1 kmole SO₄^2- is 2 keq, (because of the double - charge) and 1 keq SO₄ is 32/2 or 16 kg S.