740 



Manurial Effect of Bone-Meal. [march, 



in by far the greater number of experiments sandy soils, or, at 

 any rate, soils poor in humus, had been used. The phosphoric 

 acid in bone-meal, however, is best employed by plants in soils 

 rich in humus, a fact which is usually explained by the state- 

 ment that the acid properties of the humus make bone-meal 

 more easily available. This explanation is not altogether satis- 

 factory, as there are several reasons for supposing that one is 

 dealing here with a somewhat more complicated process than 

 the simple one of making soluble a substance insoluble in 

 water, in a way similar to that which occurs in treating basic 

 slag with a 2 per cent, solution of citric acid. 



A higher proportion of humus, it must be remembered, 

 implies an entire modification both of the physical as well as 

 of the chemical properties of the soil ; for example, in a soil 

 rich in humus, the nutrient plant materials, as well as other 

 substances, exist in different proportions, and particularly in 

 other combinations than is the case in a soil poor in humus. 

 This applies in the first place to nitrogen. Whilst in artificially 

 manured soils poor in humus nitrogen occurs largely in 

 one form, most frequently in the form of nitrate, the soils 

 rich in humus contain their nitrogen partly as nitrate, 

 partly as ammonia, and partly as organic combinations of 

 various kinds. It is not altogether unlikely that the form in 

 which nitrogen is present in the soil, as well as the more or less 

 acid reaction of humus, may influence the availability of the 

 phosphoric acid in bone-meal. Some experiments by Pria- 

 nischnikow are referred to as bearing on this point, in which it 

 was shown that sulphate of ammonia when partially substituted 

 for nitrate of soda acted very favourably when used with raw 

 mineral phosphate, and gave results equal to those obtained 

 from superphosphate and nitrate of soda. When the nitrate 

 of soda was replaced by nitrate of ammonia, similar results 

 were obtained, and the latter was found to be equivalent to a 

 mixture of nitrate of soda and sulphate of ammonia. If, how- 

 ever, the nitrate of soda were entirely replaced by sulphate of 

 ammonia, an opposite effect, curiously enough, occurred, and 

 the development of the plants under experiment was seriously 

 retarded. These experiments were all made in combination 

 with mineral phosphate. W 7 hen an easily soluble phosphate, 



