14 On the Chemical Properties of Soils. 



It is worthy of notice that the sterile sandy soil absorbed as 

 much ammonia as the calcareous clay, and even rather more than 

 the heavy clay soil, thus proving that the property of absorbing 

 ammonia is not confined to clay soils, but that it is shared by 

 light sandy soils. 



It has been too generally assumed that sandy soils do not possess 

 the power of retaining any ammonia ; but the preceding experi- 

 ments show unmistakably that this opinion is not founded on 

 fact. If soluble manuring matters were indeed very readily washed 

 out of sandy soils, it is certain top-dressing with nitrate of 

 soda, or sulphate of ammonia and other soluble manures, in nine 

 cases out of ten, would produce little or no effect upon them ; 

 for these top-dressings are usually applied at a period of the year 

 when rain falls in abundance, and every facility is afforded 

 for the removal of these soluble matters. Experience, how- 

 ever, teaches us that such top-dressings are particularly valu- 

 able on sandy soils, which could not be the case if these did not 

 possess a power ascribed by many persons solely to clay soils. 

 Although it is no doubt the case that heavy rains wash into the 

 drains useful manuring matters, and that clay soils possess in a 

 higher degree the power of retaining fertilizing substances than 

 sandy soils, nevertheless we need not, on the approach of a 

 heavy thunderstorm, be apprehensive that all the sulphate of 

 ammonia or guano which may have been applied to some light 

 sandy land only a few days ago, will be entirely washed away. 



Again it may be noticed that the soil taken from the pasture, 

 which abounds in vegetable matter, absorbed the least ammonia. 

 The question naturally arises, Is the cause of this difference 

 due to the presence of organic matter, or to any other pecu- 

 liarity in this soil? I am unable to answer this question 

 at present, but think it possible that the presence of a large 

 quantity of organic acids in a soil may be unfavourable to the 

 retention of ammonia. Future and extended experiments are 

 needed to confirm or refute this supposition. In the mean time 

 I may direct attention to the well-known fact, that on certain old 

 pasture land ammoniacal manures produce little effect, whereas 

 these manures generally increase the produce of grass in a re- 

 markable manner. In all specimens of soil taken from old 

 pastures, upon which ammoniacal manures have little or no 

 effect, I find a large excess of organic matter. It is just possible 

 that this excess of organic matter prevents the retention of 

 ammonia by the soil ; but I have no opinion at present as to the 

 precise mode in which this is effected. 



I would also notice specially that the soil employed in the third 

 experiment was the same heavy clay soil which Mr. Mechi 

 kindly sent to me for experimental purposes, and with respect to 



