THE MANURING OF THE CANE. 



able conditions are the reverse of those aiding nitrification, that is to say, it 

 proceeds in the absence of air, and in the presence of an excess of water and of 

 organic matter ; hence it occurs in badly tilled, unaerated waterlogged soils, 

 Dentrification has also been noted to occur when fresh stable manure, new 

 dung or even finely chopped straw is added to the soil, so much so as to depress 

 the yield below that obtained when no manure is added to the soil. In 

 addition, the combined use of stable manure and of the readily available forms 

 of nitrogen has been contraindicated ; this action is perhaps due to the intro- 

 duction of large numbers of denitrifying organisms, and to the inhibiting effect 

 of large amounts of organic matter on the nitrifying organisms. However r 

 the experiments of Wagner and others, from which these conclusions were 

 drawn, were not made under conditions consonant with ordinary agricultural 

 practice, and contain nothing to warrant any fear of harm resulting from the 

 well-advised return to the soil of well -rotted stable, &c., manure as usually 

 practised as a standard agricultural process.* 



Green Manuring. Green soiling or green manuring is a practice 

 which has been carried on for generations past. In Europe the method 

 employed is to sow a catch crop of some quickly growing plant between the 

 harvest of the one and the seed time of the succeeding crop ; the catch crop 

 is ploughed into the soil and acts as a green manure to the following crop. 

 The principles of this practice are as follows. It had been known for a large 

 number of years that leguminous crops (beans, peas, clover, &c.), although 

 they contained large amounts of nitrogen, did not respond to nitrogenous- 

 manurings, and even frequently gave a smaller crop when manured with 

 nitrogen than when unmanured. It was eventually established by Atwater in 

 America, Marshall Ward in England, and Hellriegel and Wilf arth in Germany,, 

 about 1886, that leguminous plants are able to absorb nitrogen from the air. 

 The absorption is not made directly by the plant, but by the agency of bacteria. 

 If the roots of a leguminous plant be examined, there will be found attached 

 to its rootlets a number of wart-like excrescences the size of a pin's head and 

 upwards. These bodies, which are termed nodules, on being crushed and 

 examined under the microscope, are found to consist of countless numbers of 

 bacteria ; these bacteria, living in symbiosis or commensalism with the host 

 plant, supply it with, at any rate, a part of its nitrogen. 



If then leguminous plants be sown and allowed to reach maturity, and 

 then be ploughed into the soil, there is placed in the soil a large amount of 

 nitrogen obtained from the air. 



Green manuring as an integral part of cane cultivation is practised most 

 intensively in Louisiana and Mauritius, and to a limited extent in Hawaii. 



*For more detailed discussions reference may be made to Hall's The Soil, and Hilgard's 

 Soils, which the writer considers the best books, in English, that deal with general agriculture^ 



83 



