SOIL FERTILITY.

Waipa Post, Volume 48, Issue 3470, 24 May 1934, Page 2

SOIL FERTILITY.

ENRICHING WITH NITROGEN,

Green manuring benefits the soil in ' two ways. It enriches the soil in the first place, by suppling it with a considerable amount of readily available, plant food, and in the second place, by adding humus, and thus improving the soil's texture and its, power of absorbing and retaining moisture. When a manure, crop is. buried, the surface soil becomes enriched by the nourishing materials which the crop during the per,iod of its growth has.

drawn from the air and from the lower portions of the subsoil, and this material is now placed within the reach of the succeeding crop.

During the growth of the plant the soil has, in addition, been stirred up and disintegrated by the development of the roots. When ploughed under, provided sufficient moisture and warmth are present, the buried mass decomposes with more or less rapidity. A further important result is the formation of carbonic acjd by the decomposition of the buried crop. Carbonic acid is given off abundantly in the fermentation of the mass, and assists in the disintegration of the soil and in rendering available the plant, food contained in it. With regard to the kind of crop to be used for the purpose of green manuring, a good deal of latitude impermissible. Any crop that is rapid and luxuriant in growth, and that can be readily turned under, is suitable for the purpose, and the selection will be guided by considerations such as time of the year at which it is to be grown, its suitability to soil and district, etc. Among the most, effective crops for the purpose are leguminous plants such as clover, velvet beans, peas, etc., since these are specially valuable on account of their power of obtaining their nitrogen from the air. They are, therefore, specially suitable for soils poor in nitrogen, and are of high virtue in enriching the soil with, this ingredient.

It is a not uncommon fallacy that if a luguminous crop is removed from the land and the roots with their nodules remain, the soil is thereby enriched in nitrogen. The nitrogei taken from the air by legumes it association with certain bacteria ii the soil does not, however, exist in the nodules, but is made up of and

distributed throughout the plant, and the removal of the above-ground portion of the plant from the land therefore means the removal of a large amount, of nitrogen.' An increase in the nitrogen content of the soil can only result from the growing of leguminous crops when they are ploughed in, or when they are fed off or soiled to stock, and the resultant manure from the stock is returned to the soil.