164 On the CompofrifioJi of Waters of Land-Drainof/c. 



modify the composition of the manures used, and to prepare 

 plant-food, which is neither so soluble as to injure the crop, nor 

 so insoluble as to remain inactive. 



5. Although the drainag-e-waterswere found to contain appre- 

 ciable quantities of phosphoric acid and potash, practically 

 speaking the land sustains bj drainage no appreciable loss of 

 these important mineral constituents of plants. 



6. Whilst phosphoric acid and potash, which are the most 

 valuable components of soils and manures, are retained in the 

 land almost entirely, lime, magnesia, sulphuric acid, chlorine^ 

 and soluble silica, or the less important — because more abundant 

 and widely distributed — mineral matters pass into the waters of 

 land-drainage in considerable quantities. 



7. The total amount of fertilizing matter which is carried ofT 

 the land by drainage is greater on highly manured fields than 

 on land left unmanured. 



8. The loss of fertilizing matters by drainage is greater 

 during the autumn and winter months than during the periods, 

 of active growth of plants. 



9. Nitrogenous organic matters, applied to the land in farm- 

 yard-manure, suffer decomposition, and are gradually resolved, at 

 first into ammonia compounds, which are retained by the soil 

 for a limited period, and finally osydised into nitrates. Farm- 

 yard-manure thus yields a more constant and gradual supply of 

 nitrogenous food than nitrate of soda, which, unless consumed 

 by the crop to which it is applied, is wasted to a large extent 

 by drainage. 



10. Although all soils have the power of decomposing salts of 

 ammonia, and aljsorbing and retaining the latter for a limited 

 time, the ammonia thus absorbed is rapidly oxydised in porous 

 soils ; and, in wet weather, a considerable proportion of the 

 nitrogen applied to the land in the shape of salts of ammonia 

 passes into the drains as nitrates and is lost. 



11. With each increased supply of nitrogen by ammonia- 

 salts, there was an increased loss of nitrogen in the form o-f 

 nitric acid in the drainage-water, 



12. Nitrate of soda is rapidly removed from the land by the 

 rainfall, for soils have not the power to absorb and retain either- 

 nitric acid or soda to any great extent. 



In one of the experiments the drainage from land after a 

 recent application of a heavy dressing of nitrate of soda con- 

 tained 5'83 parts of nitrogen as nitrates per 100,000 parts of 

 water. This is equivalent to a loss of about 13 lbs. of nitrogen 

 per acre for every inch of rain which then passed through the 

 soil. 



In wet seasons the loss of nitrogen by drainage is thus very 



