INTRODUCTION. xxxvii 



wheat-straw, alkaline silicates in short, none of the ash-constituents of plants had any effect. But 

 wherever ammonia was used there was obtained an increased yield, and, within certain limits, the 

 increase of wheat was in proportion to the quantity of ammonia supplied. 



But here a new and important fact was brought to light. Though the increase of wheat was in 

 proportion to the quantity of ammonia supplied, in no single case out of many hundreds of experiments 

 which have been made during the last twenty years, was as much ammonia (or, rather, nitrogen) 

 obtained in the increase of the wheat and straw as was furnished to the soil in manure. 



There was evidently a loss of ammonia by the, growth of wlieat. Professor Way lias advanced the 

 hypothesis that the large quantity of silica found in the straw of wheat and other grains is taken up 

 by the roots of the plants as an ammonia-silicate the silica being deposited on the straw, and the 

 ammonia evaporated into the atmosphere. This mayor may not be the true explanation ; but that 

 there \s, practically, a great loss &amp;lt;,f ammonia by the growth of wlieat there can be no doubt. The 

 same, it is believed, is true of barley, oats, rye, and Indian corn, as well as of herds-gross, rep-top, rye- 

 grass, and other grasses grown for fodder. We rest this belief on the indications of experiments, and 

 on the experience of practical farmers, and not on Way s hypothesis in regard to the absorption of 

 silica as an ammonia-silicate. 



But if that hypothesis is correct, it follows, as a matter of course, that the plants we have named, 

 and all others having silicious stems and stalks, belong to this class, and their growth involves a great 

 loss of ammonia to the farm. 



On the other hand, Mr. Lawes s experiments on clover, beans, peas, and tares, indicate that there 

 is no loss of ammonia during the growth of these plants. If we apply fifty pounds of ammonia to a crop 

 of wheat, (which is equal to three hundred weight of the best Peruvian guano,) the increased growth of 

 the wheat and straw will not give us back more than twenty or twenty-five pounds of ammonia; the 

 remaining twenty-five or thirty pounds has been evaporated into the atmosphere. If, on the other hand, 

 we apply fifty pounds of ammonia to clover or other leguminous plants, or to turnips, it is all, or nearly 

 all, retained. There is little or no loss. 



Ammonia, or nitrogen, exists in all soils, but usually in a condition unavailable to plants except in 

 small quantity. If it existed in an available condition, it would long ago have been washed away; but 

 it lies there inert and insoluble. It is rendered active and available by tillage. Hence the advantages 

 of summer fallows on clay soils. Such soils frequently .abound in nitrogen and other elements of plants, 

 but they arc in an insoluble condition. The soil is so compact that light, heat and air the three 

 grand agents of decomposition are excluded, and it is only by tillage by stirring the soil, by exposing 

 it io the sun, and letting in the air that these inert substances can be rendered available as food for 

 plants. 



On light and sandy soils, which admit the air more readily, there is not that accumulation of 

 organic matter and other food of plants which exists in the clays, and consequently mere tillage is not 

 so beneficial. 



Ammonia and nitric acid (which probably has the same effect as ammonia) exist in the atmos 

 phere. A well-pulverized soil, especially of a somewhat clayey nature, attracts ammonia from the air 

 and retains it. And here we may allude to one of the most important discoveries which have been 

 made in scientific agriculture during the past ten years. Professor Way, at the time chemist to the 

 Royal Agricultural Society of England, made a series of investigations on what has since been called 

 the &quot;absorptive powers of soils,&quot; which resulted in throwing new light on the processes of vegetable 

 nutrition, and opening up a new field for future investigations, which have since been made, in regard 

 to the manner in which plants take up food from the soil through their roots. In the course of these 

 investigations he found that ordinary soils possessed the power of separating from solution in water the 

 different earthy and alkaline substances presented to them in manure. Thus, when solutions of salts 

 of ammonia, of potash, magnesia, &c., were made to filter slowly through a bed of dry soil five or six 

 inches deep, arranged in some suitable vessel, it was observed that the liquid which ran through no 



