Manures and Fertilizers. 23 



tute of them. On the contrary, the upper six or eight inches 

 of soil even in the poorest field usually contains sufficient of 

 these materials to provide for a hundred crops, and yet, as 

 we know, the yield is unsatisfactory unless manure is added. 

 The reason for this is that although the soil already contains 

 these food materials they are present in such a form that the 

 plant cannot immediately make use of them; it can absorb 

 them only as they become soluble. When they are in this con- 

 dition they become dissolved in soil-water and are then drawn 

 into the plant's system by the fine root-hairs. The condition 

 of solubility is brought about very slowly by the action of the 

 atmosphere, by the carbonic acid contained in soil-water, by 

 the acid sap exuded from the root-hairs of plants, and by the 

 work of soil bacteria. 



Therefore, the elements of plant food in the soil may be re- 

 garded as so much locked-up capital, only a small portion of 

 which is available at any given time, and it should be the object 

 of the cultivator to so handle this capital that some of it, and 

 a larger quantity of it, can be brought into immediate use, and 

 by manuring to supplement such available foods as are insuffi- 

 cient in quantity for a full and paying crop. 



When proper means are taken, by maintaining the soil in a 

 sweet, friable, and deeply-pulverized condition, to increase the 

 available plant foods less manure is needed and better crops 

 are grown. Manure can never take the place of cultivation ; 

 indeed its full effect will only be obtained where it enters into 

 combination with good cultivation. Additional plant foods 

 should be given freely, as required, but it must be constantly 

 borne in mind that they are only part of a complete whole. 



NITROGEN is the most important element in plant nutrition. 

 Its function is to build up the vegetable part of the plant. 

 When the supply is insufficient for the plant's requirements 

 growth is stunted and the leaves are of a pale and sickly 

 colour. If nitrogen in a readily available form is supplied to 

 a plant presenting this appearance its growth, which before 

 was almost at a standstill, will speedily increase ; the plant will 

 show greater vigour and will produce larger leaves of a darker 

 green. This result must not lead cultivators to suppose that 

 the application of nitrogen will always be beneficial. There 



