670 



It would appear as if in a soil made from the disintegration of 

 a trap rock the potash would be found in greater proportions than 

 the lime, but it is not so, for the reason that, in the process of 

 denudation, the potash is carried away in larger proportions, by the 

 action of water and carbonic acid, either to a lower depth than the 

 soil, or into w r ater courses, where it is lost to the soil. 



It will be quite evident from the above analysis that it will be 

 very seldom found that lime will benefit to any great extent soils 

 made from the disintegration of trap rocks after they have been 

 brought into cultivation. That is what has been found in practice. 



These soils derive a certain amount of phosphoric acid from 

 the rocks that they are formed from, and it is less easily washed 

 out of the soil than potash or lime, being more insoluble and not so 

 easily acted upon by carbonic acid. The granites, including 

 syenite, gneiss, and trachyte contain from -2 to 1-5 per cent, of 

 phosphoric acid. Trap rocks and red sandstone from '5 to 1*5 per 

 cent, of phosphoric acid. Limestones and marl from 1*2 to 3*5 per 

 cent. 



\Ye have seen how soils obtain their potash and phosphoric 

 acid. The analysis of soils that I have given show the amount of 

 these plant foods. It is not only necessary to know the amount, 

 but also what is available. 



A soil containing *i per cent, of potash or phosphoric acid will 

 contain from 3,500 to 3,800 Ibs. per acre in a soil 12 inches deep. 

 Yet that soil maybe barren to a crop owing to the potash or phos- 

 phoric acid not being in a soluble enough state for the plant to ab- 

 sorb it in the time that it requires to mature in the soil. These 

 analysis show potential power in the soil. Although we cannot 

 imitate the action of the plants on the fertilisers, as we do not fully 

 understand the process at the present time, we can approximate it 

 so closely by treating the soil with very dilute acid that the results of 

 such an analysis are correct for all practical purposes. Such an 

 analysis is sometimes called a fertility analysis. The field analysis is 

 probably the best for practical purposes, and will be treated with 

 further on. It must not be understood that I place no value on these 

 analyses ; on the contrary, I place a high value on them with regard to 





