132 



THE GARDENER'S ASSISTANT. 



From the quantities of marine shells that are 

 found inland, and at considerable elevations, it 

 would appear that the sea must at some remote 

 period have rolled over the low-lying parts of 

 Great Britain, and swept before it different sub- 

 stances and various kinds of soil. The land 

 may have sunk, for some time, considerably 

 below the level of the sea, or the latter may 

 have been elevated above the surface of the 

 land; in either case the soil and the looser 

 portions of rocks would be moved by the over- 

 whelming force of the mass of water. To this 

 fact must be attributed the formation of those 

 numerous apparently water-formed eminences i 

 which diversify the general level of the low j 

 parts of the country, and present aspects more 

 or less inclined to the sun, and consequently 

 better adapted for the growth of a greater 

 variety of vegetable productions than a level 

 plain. Were it not for the soil being thrown 

 into a diversified surface we should not, in our j 

 latitude, have a country so capable of drainage 

 and improvement, nor one-half so productive, 

 as it can now be made. 



The Soil as a source of Plant-food. — In order to j 

 start with definite notions about the inherent j 

 fertility of soils, let us take as an example an 

 ordinary arable clayey soil in fair condition of 

 productiveness. "When all vegetable roots have 

 been removed such land will contain in the first 

 9 inches of the surface soil a quantity of organic 

 matter containing about 3000 lbs. of nitrogen 

 and 30,000 lbs. of carbon per acre. This nitro- 

 genous organic matter of the soil has been 

 derived either entirely from the decay of vege- 

 table growth left in the land by preceding gene- 

 rations of plants, or possibly to some extent 

 also from past applications of organic manures. 

 When we remember, therefore, that full crops 

 of many of our garden plants only need from 

 100 to 150 lbs. of nitrogen per acre for their 

 successful growth, it is somewhat surprising to 

 learn that with the large store of organic nitro- 

 gen in the soil the gardener finds it necessary 

 to add nitrogenous manures at all, yet the 

 efficiency of even small quantities of nitrate of 

 soda, guano, or ammonium-salts, as fertilizers, 

 has long ago been abundantly proved. 



Boussingault showed that the nitrogenous 

 organic matters of ordinary soils are usually 

 inert and inactive for plant-life, their oxidation 

 and nitrification, or in plainer language their 

 decay, being too slow to subserve the require- 

 ments of the multitudinous individuals that 

 make up the crops of our gardens and horti- 

 cultural establishments. Hence the soil left to 



its own resources is unable to satisfy the de- 

 mands made upon it. And even with an abun- 

 dant dressing of farmyard or stable manure, 

 certain soils may still remain unproductive, 

 owing to the non-nitrification of its organic 

 matter. This may be due to sourness and to 

 a lack of available lime or potash. 



We get a fairly correct idea of what takes 

 place in a soil in regard to nitrification from 

 an analysis of the drainage water percolating 

 through it. Professor Deherain found in 1891 

 that various soils that had received a copious 

 manuring with about 24 tons of farmyard dung 

 per acre, allowed the following quantities of 

 nitrogen, as nitric acid, to drain away. For 

 comparison is also given the amount of nitrogen 

 as nitric acid percolating through an unmanured 

 soil : — 



Nitrogen as Nitrates in Drainage Water. 



Seasons. 



Quantities of Nitrogen per Acre. 



Dunged Soil. 



Unmanured Soil. 



Spring, 



Summer, 



Autumn, 



Winter, 



Yearly total, 



lbs. 



461 

 22-6 

 38-2 

 17-4 



lbs. 



19-5 

 13-5 

 28-3 

 13-5 



124-3 



74-8 



The quantity of nitrogen as nitrates formed 

 in the soil and liable to be washed away is thus 

 seen to be very considerable, ranging from a 

 yearly total of nearly 75 lbs. in the unmanured 

 land to more than 124 lbs. per acre in the 

 dunged soil, the latter being more open and 

 porous and thus more accessible to the oxygen 

 of the air. It is seen that in the dunged soil 

 the greatest loss of nitrogen occurred during 

 the spring months ; this was probably owing to 

 the oxidation of the organic matter that had 

 taken place in the winter, and on the approach 

 of spring, there being no growing crop to assimi- 

 late it, this very soluble substance was washed 

 into the drainage. There was also a considerable 

 loss in the dunged soil during the autumn, 

 whilst the greatest loss of nitrogen in the un- 

 manured soil occurred in the autumn, the result 

 of the summer nitrification. 



Some invaluable experiments of Sir John 

 Lawes and Sir Henry Gilbert, conducted at 

 Rothamsted, Hertfordshire, afford another ex- 

 ample of a similar kind. Three drain gauges 

 of unmanured and uncropped soil have been in 

 operation since September, 1870, that is, for 

 twenty-six harvest years to the end of August, 

 1896. 



