BUILDING UP A SOIL.

Otago Witness, Issue 3414, 20 August 1919, Page 10

BUILDING UP A SOIL.

Every farmer should realise the importance of an abundant supply of organic matter of humus in the soil. He knows that sandy soils cannot be compared with a loam soil in regard to its humus content till a considerable amount of green stuff or the like has been added over a lengthy period. The soil is alive with organisms which feed on the vegetable and animal matter added, and in an open sandy soil it is found that conditions are so favourable that the added material is quickly destroyed, while on heavier soils the action 'of bacteria is slower 1 , and residues of organic matter are available for storing up food for crops. It is a problem the farmer has to, deal with on a farm which has been carelessly worked—just how to build up the soil again. If a crop or portion of it is ploughed under the soil will be improved, although it is not generally regarded as profitable to turn under a full crop. So some modification of this method must be adopted, such as harvesting the crop, feeding it to stock, and returning the manure to the land. It is slow but sure. Some ingredients required by crops must be purchased. Phosphorus, potash, and nitrogen are required by grasses and cereals. If such crops are returned to the soil we increase the organic matter, but not the amount of these substances. In respect to the nitrogen, our southern lands are fairly well stocked, and we can call upon Nature per medium of the legumes (clover, lucerne, peas, beans, etc.), which, helped by the bacteria nodules in their roots, will draw upon the unlimited store of • nitrogen in the air and add it to the soil. If a leguminous crop on the roots of which tubercles are abundant is ploughed under not only is the organic content of the soil increased, but the expensive nitrogen will be added, a detail which is not effected when ploughing under a cereal straw crop. It is a reasonable and good farming proposition to build up a thin soil by growing wellinoculated legumes, harvesting, and feeding off, etc. There is one point in this legume-growing which deserves to be emphasised, and that is this: a legume, viewed as a legume, simply cannot draw nitrogen from the air until it is linked up with the proper bacteria, and this must be supplied if not in possession already. In an acid and light soil it is very probable that the bacteria will have died out if in the absence of the necessary legume. Some soils do not require inoculating. Quite so; but, generally speaking, _it would be -wise before sowing a new kind of legume to provide the proper bacterial seed. This seed, if it may be so_ termed, can be obtained from any field in which the legume has been recently growing freely. A farmer can readily ascertain whether the legumes have nodules on the roots or not. If the latter, he must go further afield for his soil. Generally speaking, it is considered that each legume has its own special bacteria; but if the soil conditions are favourable they seem to "fraternise" —at least the clovers (red, white, alsike, and crimson) "do" with the same bacteria, although sweet clover and lucerne would reap no benefit from them, nor are the bacteria which favour lucerne and sweet clover of much use to peas and beans. In a bulletin issued by the Wisconsin County it is i-ecommended that in order to build up a light soil it is best to sell butter-fat and milk and pigs rather than beef or grain or hay, because it means that you will keep more of the potassium, phosphorus, and nitrogen you now own on the farm. Grow legumes as much as possible, and see that the roots are always thickly studded with nodules. If they are not, inoculate the seed when you next sow that legume on that field. By growing legumes properly inoculated it is possible to take dollars' worth of nitrogen from the air and put it into your soil, and probably double or treble the yield and increase its feeding value. There is .the chance of getting something in the "way of riches for next to nothing, that you are likely to meet. The most valuable possession you have is the soil, and its future should be considered in the interests of the nation.