_Nitrate of soda_, or cubical nitre, which is found in South America, consists of soda and nitric acid. It furnishes both soda and nitrogen to plants, and is an excellent manure. LIME. The subject of _lime_ is one of most vital importance to the farmer; indeed, so varied are its modes of action and its effects, that some writers have given it credit for every thing good in the way of farming, and have gone so far as to say that _all_ permanent improvement of agriculture must depend on the use of lime. Although this is far in excess of the truth (as lime cannot plow, nor drain, nor supply any thing but _lime_ to the soil), its many beneficial effects demand for it the closest attention. [Do all soils contain enough lime for the use of plants? What amount is needed for this purpose? What is its first-named effect on the soil? Its second? Third? Fourth? Fifth? How are acids produced in the soil?] As food for plants, lime is of considerable importance. All plants contain lime--some of them in large quantities. It is an important constituent of straw, meadow hay, leaves of fruit trees, peas, beans, and turnips. It constitutes more than one third of the ash of red clover. Many soils contain lime enough for the use of plants, in others it is deficient, and must be supplied artificially before they can produce good crops of those plants of which lime is an important ingredient. The only way in which the exact quantity of lime in the soil can be ascertained is by chemical analysis. However, the amount required for the mere feeding plants is not large, (much less than one per cent.), but lime is often necessary for other purposes; and setting aside, for the present, its feeding action, we will examine its various effects on the mechanical and chemical condition of the soil. 1. It corrects acidity (sourness). 2. It hastens the decomposition of the organic matter in the soil. 3. It causes the mineral particles of the soil to crumble. 4. By producing the above effects, it prepares the constituents of the soil for assimilation by plants. 5. It is _said_ to exhaust the soil, but it does so in a very desirable manner, the injurious effects of which may be easily avoided. [How does lime correct them? How does it affect animal manures in the soil?] 1. The decomposition of organic matter in the soil, often produces acids which makes the land _sour_, and cause it to produce sorrel and other weeds, which interfere with the healthy growth of crops. Lime is an _alkali_, and if applied to soils suffering from sourness, it will unite with the acids, and neutralize them, so that they will no longer be injurious.