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SUMMARY. 



1. Conclusions which are easily derived from the above data are that 

 the soil is not merely dead, inert matter, but, on the contrary, in the 

 highest degree a living organism. It contains numerous ferments which 

 in their activity either favour or restrain the growth of crops. It is the 

 part of scientific agriculture to determine, in so far as possible, the law* 

 which govern the evolution of both of these forms of bacteria for the pur- 

 pose of securing the greatest activity of the beneficial organisms and the 

 least activity of the inimical ones. 



2. The bacteria which provide niirogenous food for plants are of three 

 great classes. One of these exerts its activity only on organic nitrogen 

 contained in the humus of the soil. The second class is developed sym- 

 bietically with the growing plants, herding in colonies upon their 

 rootlets, and securing in their vital activity an oxidation of the free nitrogen 

 of the atmosphere. The third class of organism and the one least known 

 appears to have the ability, in an independent form of life and without 

 the aid of plant vitality, to secure the oxidation of atmo-pheric nitrogen. 

 The first of the classes mentioned above is itself separated into three divi- 

 sions comprising the organisms which produce ammonia, nitrous and 

 mitric acids, respectively. 



3. Many crops, such as the cereal, have no ability in themselves to 

 increase the stores of nitrogen in the soil. Such crops may be grown 

 for many years upon the same field, in which case the nitrogenous supply 

 of the field will at first be rapidly diminished, with a cot responding decrease 

 in the crop itself. Finally a time will come when a certain minimun 

 crop will be produced apparently for an indefinite time, varying only 

 under seasonal influences. 



4. Other plants especially leguminous plants, favour the develop- 

 ment of the organisms which are capable of oxidising free nitrogen and 

 thereby tend to increase the supply of available nitrogenous matter. 

 These crops, however, together with certain root crops, cannot be grown 

 successfully without rotation, and all crops are benefited by a judicious 

 succession. 



5. Thesummerfallowingof land is highly injudicious, and especially if 

 thefieldbe left bare through the winter The nitrates whieh areformedby 

 the activity of the nitrifying organism in such cases are easily washed out 

 by heavy rains and lost to agricultural uses perhaps for thousands of years. 



6. Late autumnal ploughing, after the activity of the nitrifying organ- 

 isms has practically ceased, may prove beneficial, especially to some crops, 

 by exposing the soil to the decomposing effects of the frosts of winter. 



7. In past geological ages vast quantities of nitrogenous matters have 

 been oxidised and stored, in the form of nitrates, and these stores are now 

 available for the uses of agriculture 



Nitric acid, in the form of nitrates, should be employed only as a tem- 

 porary fertiliser in order to improve the fertility of the soil to such an 

 extent as to make profitable the growing leguminous crops. The con- 

 tinued use of nitrates for fertilising purposes deprives the nitrifying 

 organism of their functional activity, and hence tends to diminish th» 

 numbers and to enfeeble their work. Nitrates should only be applied in 

 small quantities at a time, sufficient to meet the demands of the crop. It 

 is better to apply the dressing of nitrates at two or three different timea 

 during the growth of the crop, rather than to use it all at once. 



