21 



The distribution at the various depths is shown in the follow 

 int;- table of percentages of the total in each group : — 



The vast majority of soil organisms w ere found at a depth not 

 exceeding 3 mches. Wireworms are exceptional in that they 

 attain their maximum numbers at a depth of 5 inches^to 7 inches. 

 Manuring increases the total number of soil organisms to the 

 extent of about 200%, but exercises no very aj^preciable influence 

 upon the niunber of wireworms present. 



IHK POSSIBILI TV OF THK CONTROL OF THE SOIL 

 POPUL.VriON. 



Previous investigations have shown that healing the soil or 

 treatment with certain poisons not only rids it of pests but actually 

 improves its productiveness, increasing the amount of bacterial 

 activity. This has been applied in glasshouse practice in the Lea 

 Valley. Steaming has proved effective and so have certain chemi- 

 cals, but their action is complicated by the fact that some poisons 

 such as phenol, cresol, naphthalene, et(.\, are destroyed in the soil 

 before they have iieen able to kill those organisms to which they 

 are fatal. It is foimd that certain soil bacteria have the power of 

 attacking or feeding on these particailar poisons : they are being 

 further studied in the bacteriological laboratory. The introduction 

 of a chlorine atom stabilises the poison and the further introduc- 

 tion of a nitro-group adds considerably to its toxicity (p. 58). 

 Much work has been done to find a suitable agent for the control of 

 wireworms (p. 43). 



INVESTIGATIONS ON THE WEED FLORA. 



The accumulated data on the weed flora of arable and grass 

 land has been worked up by Dr. Brenchley and published in book 

 form. Connections have been traced between various groups of 

 weeds on the one hand and soils and crops on the other, and in 

 some cases slight changes in manurial or cultural treatment may 

 prove efficacious in the reduction of bad weed pests. Arrange- 

 ments are being made for gathering together more information 

 from different parts of the country in order to extend the practical 

 application of the work. 



THE PHYSICAL CONDITIONS OF THE SOIL. 

 Much of the agricultural value of the soil depends on physical 

 conditions, such as the ease of cultivation, the supply of air and 

 moistiue, temperature, etc. These factors, which largely deter- 

 mine its suitability for the growth of crops and micro-organisms, 



