THE PARTIAL STERILIZATION OF SOILS. 



Some of the weights of tomatos obtained were : — 





Nursery No. r. 



Nursery No. 2. 





I9i7. 



1918. 



1917. 



1918. 



Untreated ..... 



IOO 



IOO 



IOO 



IOO 



Steam ..... 



95 



112 



126 



109 



Hot water ..... 



96 



109 



96 



109 



Carbolic acid .... 



107 



105 



III 



112 



Formaldehyde .... 



103 



113 



92 





Tons per acre : 100 represents 



34'4 



35-8 



27*1 



35 



Further experiments have thrown considerable light on the apparent 

 discrepancy in results. It has been shown that tomatos in pots are 

 liable to suffer from nitrogen starvation and therefore respond to the 

 additional nitrogen supply resulting from partial sterilization. Tomatos 

 grown in borders, however, are far less liable to nitrogen starvation ; 

 indeed, at the Cheshunt Experiment Station they show no response 

 to nitrogenous fertilizers, but rather the reverse ; in soils more remote 

 from the virgin condition a more pronounced effect might be obtained, 

 but probably not as marked as would be given by a nitrogen-loving 

 plant such as wheat. The manure supplied in the borders suffices 

 for the less exacting tomato plants and little is gained by the additional 

 nitrogen nutrients resulting from partial sterilization. 



But although the actual yields are not much improved there is a 

 notable increase in vigour and healthiness of the plant, and a corre- 

 sponding increase in the certainty of the crop. Insect and fungus 

 diseases are checked or even suppressed ; the roots are clean, especially 

 on the steamed plots. The benefit becomes more and more marked 

 as the amount of disease increases, and in badly diseased houses the 

 crop is greatly improved as the result of sterilization. Figures are 

 difficult to obtain, but Mr. Lister gives me the following, showing 

 yields of tomatos in badly infested houses, before and after 

 treatment : — 







Nursery A. 



Nursery B. 



Number of 

 clubbed 

 roots in 

 house of 

 3000 plants. 



Nursery 

 No. 2. 







lb. a 

 plant. 



tons 

 an 



acre. 



lb. a 

 plant. 



tons 

 an 



acre. 



tons an 

 acre. 



Before treatment 



1916 



2'75 



22 











After treatment with 



1917 







4-54 



30-9 



500 



35 



steam 



,, second treatment 

 „ carbolic acid . 



1917 

 1918 



5'25 

 5'2 



42 

 41-6 



5-64 



38-0 



55 



40 



Steam is so effective that it would invariably be adopted if questions 

 of cost and convenience never arose. It not only kills animal pests, 

 ova and larvae of eelworms, wireworms, woodlice, &c, and reduces 

 fungi, but in addition it brings about a certain amount of decompo- 



