THE CHEMISTRY OF THE SOIL. 75 



The ioii in which this crop was grown was a light loam with about 25 per 

 cent. ciay. The clay is of a tenacious character, and has a tendency to cake 

 hard on drying. The soil is low in humus, containing only about 4 per 

 cent, of this ingredient. It is fairly rich in potash and satisfactorily sup- 

 plied with lime, but rather low in nitrogen and phosphates. It is, conse- 

 quently, just the type of soil in which green-manuring should be effective, as 

 the effect of ploughing under the crop will be to break it up and render it 

 more friable, and to supply the deficiencies in humus and nitrogen. Its effi- 

 cacy is, of course, dependent upon conditions as to rainfall being favourable 

 to its decomposition in the soil. The climate of Wagga is not very favourable 

 to the growth of these crops. 



At Bathurst, and at the Hawkesbury College, where conditions are more 

 favourable, the benefits of green-manuring were even more striking. Mr. 

 Allen obtained similar samples of tops and roots, representing the produce of 

 one square yard from crops grown at these places, and they gave the follow- 

 ing figures:— 



At Bathurst, the tops weighed IT lb. and the roots 2 lb. 5 oz. per square 

 yard, or 36 tons 14 cwt. tops and 5 tons of roots per acre, giving a total of 

 dry matter to be ploughed under of 4 tons 15 cwt. from the tops and 16 cwt. 

 from the roots. Assuming the same nitrogen content in tops and roots as 

 was found in the Wagga plants, this would give when ploughed under 411 lb. 

 nitrogen per acre from the tops and 22 lb. nitrogen from the roots. 



At Hawkesbury the produce was 21 tons 12 cwt. tops and 4 tons 14 cwt. 

 roots per acre. When ploughed under, this would yield 2 tons 16 cwt. dry 

 matter from the tops and 16 cwt. dry matter from the roots. With -5 per 

 cent, nitrogen in the tops and -2 per cent, in the roots," the soil would be en- 

 riched in nitrogen by 242 lb. per acre from the tops and 22 lb. from the 

 roots. 



The Plant's Supply of Nitrogen. 



The question of the plant's supply of nitrogen is one of the most interest- 

 ing of the problems presented to the agriculturist ; it is also one of the most 

 obscure and least understood. A large proportion of the dry matter of all 

 plants consists of nitrogenous material, and this portion of its structure is 

 of fundamental importance to the plant. Further, it is upon the nitrogenous 

 matter of plants that animals depend for their proteid material — blood, 

 flesh, &c. — since animals can . only utilise for this purpose nitrogenous 

 material already elaborated in the tissues of plants or other animals. 



The ultimate source of all this nitrogenous matter is the free nitrogen in 

 the atmosphere. It is the study of the different methods by which this 

 element is brought (naturally or artificially) into combinations in which 

 it can be utilised by the plant that will form the subject of the present 

 discussion. 



The plant may absorb its nitrogen in two ways, either by means of its 

 leaves from the free nitrogen or from the ammonia or the nitric acid in the 

 air, or by means of its roots. 



With regard to the first of these, the absorption of nitrogen by means of 

 the leaf, the question cannot be said to be definitely settled at the present 

 time; the consensus of opinion, however, is that if such absorption takes 

 place, it does so to a very limited extent, and is insufficient to constitute part 

 of the economic functions of the plant. 



