CONTEIBUTIONS FROM THE WISLEY LABORATORY. 611 



garden crops up to the present, but if the supply diminishes largely 

 other sources will have to be tapped. The large number of other organic 

 substances commonly used for manure are mostly waste products, and 

 their supply cannot be expected to respond to a growing demand. 

 Greater attention will necessarily be paid to the use of chemical manures, 

 and green manuring for the supply of nitrogen. 



Until the introduction of the two manures in question practically 

 the only available chemical manures containing nitrogen were nitrate of 

 soda and sulphate of ammonia. The supply of the latter depends 

 largely upon other manufactures, and is not directly connected in any 

 way with plant-industry, though special sources may be developed 

 before long. Estimates have been made leading to the conclusion that 

 the nitrate deposits in South America (and no other deposits of large 

 extent are likely to become available) are within measurable distance of 

 extinction. Whether these estimates are based on accurate information 

 or not, agriculturists and horticulturists alike will welcome the advent 

 of two new manures, like nitrate of lime and calcium cyanamide, com- 

 parable in their effects upon plants with nitrate of soda and sulphate of 

 ammonia respectively. 



It may not be out of place to allude to the fact that the value of sub- 

 stances added to the soil as manures depends not only on the essential 

 chemical elements they supply the plants, but also upon the influence 

 they have upon the " reaction " of the soil and upon its physical con- 

 dition. It is well known, for instance, what a remarkable effect farm- 

 yard and similar organic manures have upon the physical condition of 

 a soil, and what an important part lime plays (though we fear this is 

 often lost sight of) in the maintenance of good physical conditions and 

 the prevention of soil acidity. It is not likely therefore that bulky 

 manures can be completely replaced by chemical fertilizers, but the 

 latter wisely used in combination with the former will economize both 

 and lead to the production of better and healthier crops. 



That other sources of combined nitrogen may be made available as 

 time goes on is not at all improbable. The bacterial fixation of 

 nitrogen is continually utilized in practical farming by the cultivation 

 of leguminous crops and the use of their residues as manure, while 

 no doubt some form of green-manuring " will be made to take the 

 place of the heavy dressings of farmyard manure now in vogue. The 

 interesting paper by Mr. W. D. Scott-Moncribff in this Journal 

 (vol. xxxiv. pp. 462-468) opens up a method of preventing enormous 

 economic loss by making use of the nitrifying power of bacteria upon 

 sewage matter. 



The trials detailed below were carried out to ascertain how calcium 

 cyanamide and nitrate of lime compared in their effects upon growth 

 and development with sulphate of ammonia and nitrate of soda. 



The site of the trials was varied in each of the three years covered 

 by the experiment, so that no accumulated effects interfered with the 

 results. The land used in 1908 was poor land in fair condition of 

 tilth ; in 1909 it was poor and not in good condition, and the plants 



s s 2 



