258 



CASSELL"S POPULAR GAKDEXIXG. 



essential plant-food. In this state it is A'ery soluble 

 in water, and therefore readily washed out of the 

 soil by heavy rains unless there is a %-igorous 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 

 onlv 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 theii- more equable dis- 

 tribution throughout the soil than in their removal 

 fi'om it. 



From what has been stated, we learn that the rapid 

 oxidation of organic matter in a soil, which occurs 

 under tillage, means the production of a large amount 

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

 ever, while they ai'e capable of yielding valuable 

 crops, are extremely liable to be lost by di-ainage ; 

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

 ranging his methods of crdtm-e that the nitrates 

 shall be a source of profit instead of loss. 



Nitrates in Soils. — ^Ve will now proceed a 

 step further, and desciibe 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 

 confiiTn the statements set forth in previous sections. 

 It is evident that very large amounts of nitrates are 

 produced in soil when exposed to air and i-ain and 

 kept free from vegetation, and that the lichness of 

 autumn drainage water is due to the gi'adual wash- 

 ing out of the niti-ates formed in the preceding 

 summer. 



The following table gives thr-ee 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. 



XiTEOGEX AS Nitrates ix Soil .ifterBahe Faxlow, 

 IN PorxDS PEK Ache. 



Depth. 



Clav Croft 

 Field. 



Foster" s 

 Field. 



Aedell 

 Field. 



First 9 inclie? . 

 Second 9 inclies 

 Third 9 laches 



lbs. 

 16-4 

 26-0 

 15-9 



lbs. 

 14-6 

 24-6 

 17 3 



lbs. 

 40-1 

 14-3 



Total 27 inches 



58-8 



56-5 



59-9 



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

 siderable production of nitrates that the advantages 



of a bare fallow consist. If a dry 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 

 di-essing of sodium nitrate, and, if the season be 

 favourable, a proportionately heavj- crop will result. 



It is seen in two instances that the maximum 

 amount of nitrates occuiTed 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 sm-face into the subsoil. And it is quite evident 

 that the quantity of nitrates found did not rej^re- 

 sent the whole amount in the soil, as the lowest 

 depth analysed was stiU. 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 rainfall had been insufiicient to 

 occasion any considerable drainage : the niti-ates 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 agricultm-al conditions. In the fol- 

 lowing table will be found the quantities of nitro- 

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

 thii'd nine inches of soil in selected plots of the 

 Eotliamsted experimental "VMieat-field when sampled 

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



Depth of Soil. 



is i 



il 



I'lol, 19. I<np(!- 

 (;ii,ko. 



1-1 . 

 .2 S = 



S 5 £ f 



lis - 



=' " i z 

 ^ = ~ - 



1 i g = 



_ 



First 9 inches 

 Second 9 inches 

 Third 9 inches 



Total 27 inches 



lbs. 

 9 2 

 40 

 1-S 



lbs. 

 14-1 

 13 

 71 



lbs. 

 19-7 

 10-0 



lbs. 

 22-S 

 11-3 

 57 



lbs. 

 211 

 13-9 

 7-8 



Ibs- 



m-0 



15-4 



15-0 



:34-2 



3S-0 



39-8 



42-S 



=;o ■ o 



served that the nitrates are most abundant in the 

 fu-st nine inches of depth ; the mean proportion at 

 the thi'ee depths being, in fact, as 100, 59. and 31. 

 Tlie uomanured soil of Plot 4 yielded the lowest 

 amoxmt of nitrates — namely. 15 lbs. : while Plot IP. 

 manui-ed dui-ing the three preceding seasons with 

 Eape-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 niti-ates 

 from organic manva-cs is affe^rded by Plot 2, which 

 receives annually fouiteen tons of faiTuyard manure ■, 



