It is by way of nationally recognized organic standards. Otherwise governments tend to be in bed with agrochemical and agribusiness companies.

Relevant section of Canadian organic standards:

5.4.2 Where appropriate, the soil fertility and biological activity shall be maintained or increased, through: a) crop rotations that are as varied as possible and include plough-down crops, legumes, catch crops and deep-rooting plants; b) incorporation of plant and animal matter in compliance with this standard and with Table 4.2 (Column 1) of CAN/CGSB-32.311, including the following:

1. composted animal and plant matter;
2. non-composted plant matter, specifically legumes, plough-down crops or deep-rooting plants within the framework of an appropriate multiyear rotation plan; and
3. unprocessed animal manure, including liquid manure and slurry, subject to the requirements of 5.5.1