SOILS AND COMPOSTS. 



473 SOILS, CHARACTER OF. 



and more watery, and full of vegetable 

 matter ; but the most important of all 

 manures is the urine from the stables and 

 drainings of the dung-heap, which is 

 wasted daily to an enormous extent, 

 "The urine of carnivorous animals," says 

 the authority we have already quoted, " is 

 rich in the principles urea and uric acid. 

 In herbivora, hippuric acid takes its place ; 

 but in all cases it is rich in nitrogen, and, 

 when allowed to putrefy, ammonia is 

 evolved. Urine is thus one of the most 

 important constituents of farmyard 

 manure." 



The composition of manure is a very 

 heterogeneous mixture. It may be broadly 

 viewed as a mixture of humic acid bodies 

 fixed in alkaline salts, and nitrogenous 

 bodies capable of yielding ammonia ; and 

 it becomes an important question how is 

 its strength best economised. Some advo- 

 cate the practice of allowing the compost 

 heap to be entirely decomposed into an 

 earthy mass thus permitting the whole of 

 the ammonia to escape ; others have gone 

 so far as not to permit of any fermentation 

 at all, stopping all action by continual 

 turning. "It must be a bad practice," says 

 Dr. Scoffern, " to allow so valuable an 

 agent as ammonia to go to waste ; and 

 this is the inevitable result of permitting 

 manure to undergo its last degree of fer- 

 mentation. In the second place, it is 

 doubtful whether the full and immediate 

 virtues of the manure can be brought into 

 play if it has not been submitted to in- 

 cipient decomposition." There are means, 

 however, of fixing the ammonia and retain- 

 ing it in all its strength, while the manure 

 containing it is reduced to a state suited 

 for assimilation as food for plants. It may 

 be absorbed by gypsum or sulphate of lime, 

 which, being cheap, is often mixed with 

 the compost heap for the purpose ; the 

 ammonical salts thus formed being after- 

 wards decomposed by the vegetable 



organism, or by its agency combined with 

 atmospheric influences. 



Soils, Character and Consti- 

 tuents of. 



Humus or Organic Matter. While 

 absolutely essential to the farmer, an 

 intimate knowledge of the characters of 

 soils is useful to the gardener. To a 

 large extent, the gardener, operating on 

 a limited scale, can prepare his soils, and 

 ameliorate their nature, by the use of 

 humus, or vegetable mould, the product 

 of decomposed animal and vegetable 

 manures. Of all the constituents o\ 

 soils that have been named, humus per- 

 forms the most important part in the 

 direct food for the nutrition of plants ; 

 but whether it combines with organic 

 matter and forms plant, or whether it 

 only exercises a beneficial influence on 

 vegetation by furnishing a continual source 

 of carbonic acid by its decomposition, or 

 by condensing ammoniac gas from the 

 atmosphere, is by no means a settled 

 question, the best chemists differing widely 

 on the point ; some of them denying alto- 

 gether the efficacy of inorganic matter in 

 soils. Recent experiments, however, show 

 distinctly the great influences that inor- 

 ganic matter exercises over the growth of 

 plants; it is taken up by the roots, and may 

 be traced in the ashes of plants ; and it 

 has been most satisfactorily proved that 

 organic matter alone is incapable of sup- 

 plying all the wants of the growing plant, 

 certain inorganic substances being required 

 by every plant, which, if not present in 

 the soil, there is a barrier to its healthy 

 growth. There can be no doubt that 

 humus supplies plants with an essential 

 part of their food ; but it acts in various 

 ways, which, as it has been said, are not 

 very clearly ascertained. 



Chemical Substances or Inorganit 

 ter. All fertile soils thus contain, 



