10 



in bacterial numbers, but a permanent depression in soil protozoa. 

 The rate of ammonia production also shows the usual increase. 

 Thus quicklime owes part of its effect to its sterilising action. This 

 discovery throws important light on the behaviour of lime in soil 

 and clears up much that has long been obscure. Other effects of 

 lime on the soil of a chemical and physical nature were observed 

 and investigated. 



The usual demonstrations have been continued showing the 

 improvement in productiveness brought about by partial sterilisation. 

 Several large scale trials have been made in commercial glasshouses. 

 The new Experiment Station in Lea Valley, now in course of 

 formation, will in future take over much of this demonstration 

 work. The laboratory work has been continued in conjunction with 

 Mr. Buddin, who has been investigating the effect of certain typical 

 organic antiseptics with a view to devising some general schemes 

 of classification of substances suitable for practical application. 



An investigation by Dr. Hutchinson and Mr. Goodey of the 

 samples of soil collected from our plots at various periods and stored 

 in dry condition has further illustrated the close parallelism estab- 

 lished in earlier papers between the soil protozoa and the factor 

 detrimental to bacteria. Samples collected and bottled in 1874 

 behaved normally on moistening — the bacteria developed, but not to 

 any very great extent — amoebae and flagellates were found ; on 

 partial sterilisation the protozoa were killed and the bacterial 

 numbers rose in the usual way. Samples of soil collected and 

 bottled in 1846 and dried in 1880, however, behaved like soil 

 already partially sterilised: on moistening, the bacterial numbers 

 rose considerably, no protozoa were found, and no further change 

 was produced by partial sterilisation. Thus long storage in dry 

 condition causes the soil to lose the factor detrimental to bacteria, 

 and it also loses its protozoa. 



Besides the detrimental organisms already referred to, another 

 factor influencing the soil decompositions has been revealed this 

 year. Determinations of the nitrate content of our arable soils have 

 shown that there is always less accumulation of nitrate on our 

 cropped than on our fallow plots, even after allowing for the nitrate 

 taken up by the plant. Examination of the data obtained here and 

 elsewhere indicates that the growing crop in some way interferes 

 with the process of ammonia and nitrate formation. It does not 

 appear that the effect is merely accidental and due to some climatic 

 factor, for Lyttleton Lyon has already obtained a similar result at 

 Ithaca. Field experiments alone are not sufficient to solve the 

 problem ; a proper series of pot experiments is required. There are, 

 however, several important consequences of such an interaction 

 between the growing plant and the soil bacteria, should it be proved 

 to exist. If the growing crop interferes with the process of ammonia 

 and nitrate formation it is obvious that one crop may be expected 

 adversely to affect another. Mr. Pickering's grass growing experi- 

 ments afford evidence that such an interference does take place : 

 there is, moreover, a strong opinion to this effect among practical 

 men and the American Bureau of Soils has accepted it, and put for- 

 ward a hypothesis in explanation, one, however, which we were 

 unable to confirm at Rothamsted. 



Dr. Hutchinson's experiments suggest that the Pickering effect is 



