July, 1908: 



SCIENTIFIC AGRICULTURE. 



THE EFFECTS OF LONG-CONTINUED 

 NITROGENOUS MANURING. 



By Professor J. B. Harrison, 



M.A., C.M.G., f.i.c. 



[From the Progress Report on Agri- 

 cultural Experiments at the Botanic 

 Gardens, 1906-1907.] 



In 1901-1905 attempts were made by 

 some persons interested in the sugar- 

 industry of the colony but non-resident 

 therein, to explain the marked falling 

 off in the productive power of some of 

 the cane fields which has been uoticeable 

 of late years by reference to the ex- 

 traordinary effects of long-continued 

 repeated manurings with sulphate of 

 ammonia which have occurred at the 

 Woburn Experimental Farm of the 

 Royal Agricultural Society, and to a less 

 extent on certain of the Experimental 

 Fields at Rothamsted. The soil of the 

 former place is a light sandy one, but 

 the latter is a clay loam. Where 

 sulphate of ammonia has been used con- 

 tinuously at Woburn for between 20 

 and 30 years, the soil has been rendered 

 absolutely barren for economic plants, 

 whilst the evil effects of the long con- 

 tinued manuring (for 50 years and over) 

 at Rothamsted with the same salt are 

 now perceptible. Both these Experimen- 

 tal Farms were visited by me in May 

 and June of this year, and their results 

 carefully examined. 



Advantage was taken in 1905 of the 

 mode in which the experiments have 

 been conducted on the northern part of 

 South Field to arrange trial-fields for 

 examining into the question whether 

 the use of sulphate of ammonia from 

 1892 to 1905 had been injurious to the 

 soil of the experimental field, and whether 

 better results would not be obtained by 

 the institution, as recommended by the 

 non-resident authorities, of nitrate of 

 soda for sulphate of ammonia. 



The previous manuring of the field 

 allowed the following comparisons to 

 be made with three varieties of canes 

 on not-limed and on limed land : — 



Sulphate of Ammonia after 



Sulphate of Ammonia (14 years) 



Sulphate of Ammonia after 



Nitrate of Soda „ 

 Nitrate of Soda after Sulphate 



of Ammonia 

 Nitrate of Soda after Nitrate 



of Soda j, 



The following were the mean results 

 in tons of canes per acre : — 









Mean, 









not-Limed. 





Not Limed. 



Limed. 



and Limed. 



No Nitrogen 



.. 10-1 



12-9 



11*5 



Sulphate of Ammonia 









after 









Sulphate of Ammonia 



... 22-2 





23'6 



Nitrate of Soda (con- 









tinuously) 



... 19'3 



)9'1 



19-2 



Nitrate of Soda, 









after 









Sulphate of Ammonia 



... 2i-4 



20-9 



207 



Nitrate of Soda (con- 









tinuously) 



... 187 



19-] 



18-9 



The results of the experiments show 

 that the substitution of nitrate of soda 

 for sulphate of ammonia on the not- 

 limed land continuously manured with 

 the latter has been attended by a reduc- 

 tion of the increased yield, due to the 

 nitrogenous dressing, from 12"1 tons to 

 10 3 tons, whilst the substitution of 

 sulphate of ammonia or nitrate of soda 

 on the nitiate fields has increased the 

 yield from 8 - 6 tons to 9-2 tons. 



On the limed land, the substitution of 

 nitrate of soda for sulphate of ammonia 

 has reduced the yields due to nitro- 

 genous manuring from 11*8 tons to 8 

 tons per acre, whilst the change from 

 nitrate of soda to sulphate of ammonia 

 on the nitrate fields practically has not 

 affected the yield. 



The apparent ill-effects of long-con- 

 tinued nitrogenous manurings are far 

 more noticeable where nitrate of soda 

 has been continuously used than where 

 sulphate of ammonia has been, thus the 

 mean increase on the fields long-manured 

 with the former was 7 5 tons of canes 

 per acre as against 10'6 tons where the 

 latter had been similarly applied. On 

 the not-limed land the increases were at 

 the rates of 8'9 and 11*2 tons respectively, 

 whilst on the limed land they were only 

 at the rates of 6'2 and 9 - 9 tons. 



These are the results of only one 

 series of experiments and hence require 

 confirmation, but in my opinion they 

 clearly indicate that on very heavy clay- 

 soils, such as that of the Experimental 

 Field, and under tropical meteorological 

 conditions, the de-flocculation of pud- 

 dling caused by long-continued dressings 

 of nitrate of soda is likely to prove more 

 injurious to the soil than is the souring- 

 action of sulphate of ammonia. The 

 results also suggest that the injurious 

 effects of the nitrate of soda are more 

 marked on limed land than on not-limed 

 land, and, as it is known that the de- 

 flocculation caused by nitrate of soda is 

 due to alkali set free from it in the soil, 

 this is in accordance with what would 

 be expected. 



