258 



CASSELL'S POPULAR GARDENING. 



essential plant-food. In this state it is very soluble 

 in water, and therefore readily washed out of the 

 soil by heavy rains unless there is a vigorous crop 

 upon the ground to retain it and take it up as food. 



It is known that the most fertile soils possess a 

 great retentive power for phosphoric acid, ammonia, 

 and potash ; and these substances are consequently 

 only found in drainage waters collected from the 

 land in minute quantity, except under very special 

 circumstances. 



In the case of such ingredients, the small solvent 

 action of rain results rather in their more equable dis- 

 tribution throughout the soil than in their removal 

 from it. 



From what has been stated, we learn that the rapid 

 oxidation of organic matter in a soil, which occurs 

 imder tillage, means the production of a large amount 

 of available plant-food. The nitrates produced, how- 

 ever, while they are capable of yielding valuable 

 crops, are extremely liable to be lost by drainage ; 

 and the skill of the gardener is displayed in so ar- 

 ranging his methods of culture that the nitrates 

 shall be a source of profit instead of loss. 



Nitrates in Soils. — We wiU now proceed a 

 step further, and describe the results which have 

 been obtained at Eothamsted by actual determina- 

 tions of nitrates in soils of various history. 



The analyses of soils under bare fallow amply 

 confirm the statements set forth in previous sections. 

 It is evident that verj' large amounts of nitrates are 

 produced in soil when exposed to air and rain and 

 kept free from vegetation, and that the richness of 

 autumn drainage water is due to the gradual wash- 

 ing out of the nitrates formed in the preceding 

 summer. 



The following table gives three examples as to the 

 quantity of nitrates existing in soils which had been 

 left as bare fallow all the summer ; the samples of 

 soil were taken for analysis before loss by autumn 

 drainage had commenced. 



NiTEOGEN AS NiTBATES IN SoiL AFTER BaBE FaLLOW, 



IN Pounds peb Acre. 



of a bare faUow consist. If a diy winter follows 

 the summer fallow, the crop for which the fallow 

 has been prepared will find at its disposal an 

 amount of nitric acid equivalent to a very large 

 dressing of sodium nitrate, and, if the season be 

 favourable, a proportionately heavy crop will result. 



It is seen in two instances that the maximum 

 amount of nitrates occurred in the second 9 inches 

 of soil ; this was due to the heavy rains of August 

 in that year, which washed the nitrates formed at 

 the surface into the subsoil. And it is quite evident 

 that the quantity of niti-ates found did not repre- 

 sent the whole amount in the soU, as the lowest 

 depth analysed was still rich in plant-food. 



In the case of AgdeU Field, the samples of soil 

 were taken in September, 1882. During the pre- 

 ceding summer the rainfaU had been insufficient to 

 occasion any considerable drainage ; the nitrates were 

 therefore chiefly found in the surface soil where 

 they were produced. 



The capacity for producing nitrates possessed by 

 a fertile garden soil far exceeds the results obtained 

 under ordinary agricultural conditions. In the fol- 

 lowing table will be found the quantities of nitro- 

 gen as nitric acid existing in the first, second, and 

 third nine inches of soil in selected plots of the 

 Eothamsted experimental Wheat-field when sampled 

 in October, 1881, in lbs. per acre. It will be ob- 



There can be no doubt that it is in this very con- 

 siderable production of nitrates that the advantages 



served that the nitrates ai'e most abundant in the 

 first nine inches of depth ; the mean proportion at 

 the three depths being, in fact, as 100, 59, and 31. 

 The unmanured soil of Plot 4 yielded the lowest 

 amount of nitrates— namely, 15 lbs. ; while Plot 19, 

 manured during the three preceding seasons with 

 Eapo-cake alone, gave 34-2 lbs. of nitrogen as nitrates. 

 As Eape-cake only slowly decomposes in the soil, a 

 part of the nitrates found will in this case be due to 

 the nitrification of a residue of the manure. A still 

 more striking example of the production of nitrates 

 from organic manures is afforded by Plot 2, which 

 receives annually fourteen tons of farmyard manure; 



