22. After harvesting a crop of cereals (other than maize), oil seeds or grain legumes (such as peas or beans) the controller shall ensure that from harvest to 15th January in the following year, one of the following conditions is met on the land at any time—
(a)the stubble of the harvested crop remains in the land; or
(b)the land is sown with a crop which will take up nitrogen from the soil.
23. In having regard to these Regulations, the following principles of crop management shall apply—
(a)residues of crops harvested late, such as maize and potatoes, shall be left undisturbed until immediately prior to sowing the following spring; and
(b)where grass leys are grown in rotation with arable crops the first crop should be sown as soon as possible after the grass has been ploughed.
24. In addition to the measures mentioned in regulations 22 and 23, where regulation 12 applies the controller of a derogated holding shall carry out the following measures—
(a)temporary grassland shall be ploughed in spring;
(b)ploughed grass on all soil types shall be followed immediately by a crop with high nitrogen demand; and
(c)crop rotation shall not include leguminous or other plants fixing atmospheric nitrogen except for grassland with less than 50 % clover and to areas with cereals and pea undersown with grass.