466 Mr Lawrence Balls, A Note on Leaf-Fall, etc. i 
A Note on Leaf-Fall as a Cause of Soil Deterioration. ‘By! 
W. Lawrence Batts, M.A., St John’s College. | 
[Read 4 May 1914.] 
In 1907 a portion of the cotton-breeding plot of the Khedivial | 
Agricultural Society at Giza, Egypt, was sown with Caravonica, \ 
Senaar, and Nyam-nyam Tree cottons*, the second of these in) 
particular having abundant leafage. The portion of the plot under: 
these trees was about 15 metres square. The trees stood till 1912.) 
In 1912 this land was taken over by a horticultural colleague, ! 
who in the summer of 1913 pointed out to me that one portion ; 
refused to grow anything, the immediate crop being orange : 
| 
seedlings. On referring to old plans it was found that this in-) 
fertile spot exactly coincided with the tree-cotton portion. The | 
land had been heavily manured, and the cause of its infertility | 
appeared to be the presence of some toxic substance. Analysis | 
showed 0°5°/, of NaCl as against 0°1°/, elsewhere, in the top | 
10 centimetres of soil. ; | 
Similar phenomena were shown during 1913 by soil in the 
wire-gauze cages which had been erected for the protection of | 
pure strains from natural crossing in 1912. The growth in these | 
cages during 1912 was extremely rank, though the plants were | 
prolific, and the amount of leaf shed appeared to have been 
approximately ten times that which the land would have received | 
in normal field crop. | 
In both cases the particular sites were situated above | 
patches of clay, so that no natural under-drainage existed, and | 
any salts, or other soluble bodies, once brought up to or placed | 
upon the surface, could not be washed down and away by | 
irrigation. | 
No valid explanation could be found which would apply to } 
both cases, excepting that the leaves had deposited something in \ 
the upper soil, of which NaCl was one component. The amount | 
of NaCl was, however, scarcely sufficient to produce the observed | 
effects, and possibly toxic bodies had resulted from decomposition + 
of the leaves. Some support was lent to this conclusion by the | 
unsatisfactory nature of cotton leaf-mould for potting purposes. _ 
If substantiated, this conclusion forms a strong additional 
argument against the use of tree-cottons in intensive cultivation. 
Established trees flourish in such soil, because their deep roots | 
are well below the toxic surface layer, but new sowing cannot be 
effected. | 
These episodes led to the enquiry into salinity of the cell-sap. 
* See Sir G. Watt, The Wild and Cultivated Cottons of the World. 
