SECTION virr. — factors influencing blight prevalence. 10.") 



In all questions of rainfall in connection with agriculture it must be 

 remembered that it is the available moisture rather than the total 

 precipitation that is important. The former depends on the state of the 

 soil and drainage, both of which will be discussed below. In addition 

 the rainfall is not the only source of moisture, as in many parts of 

 Trinidad in the dry season there are heavy dews and ground mists each 

 night, which condense on leaves of the plants and supply them witli 

 much of the moisture necessary for growth at this time of the year. 



Rainfall records have been kept at about a hundred stations in 

 Trinidad for many years, but up to the present no attempt has been 

 made to study the records or to produce rainfiall maps. In view of the 

 importance of an accurate survey of the rainfall in the study of agriculture, 

 plant diseases, and. last but not least, the water supply of towns, it is 

 to be hoped that funds will be made available for such work without delay. 



CONTOUR. 



There appear to be certain districts in the Island more liable to frog- 

 hopper attack and others less liable. The low-lying parts of Harmony 

 Hall Estate in the Naparimas, the Waterloo group of estates in the 

 Couva district, and the estates in the Northern Section are particularly 

 liable to attack, while those in the Princes Town district are particularly 

 free. Some of these differences are due to differences in the soil, others 

 to differences in the rainfall (e.g. Princes Town district) but as a general 

 rule it seems that the low-lying flat districts are more liable to attacks 

 than the hilly parts. 



In individual fields a similar effect is sometimes seen between the 

 part of a field on the top of a slope and that at the foot, but the 

 difference is not always in the same direction and in some fields it is the 

 upper part that is damaged and in others the lower part. A close 

 examination almost always reveals some change in the soil which will 

 account for the difference in infestation. Some examples of each are 

 given below. 



Damage Worse at top of Slope. 



Brecliin Castle. Mr. Arbuckle says that some years ago he had a 

 field with a small hill in it and that the top of the hill was destroyed 

 while the lower surroundings were untouched. 



Tarouha. Field E. "better at N.W. corner at top of slope ivhere 

 soil is distinctly better". (20. i. 19.) 



Union Hall. Field 6 N. damaged at top of slope, 10. ix. 19. Visible 

 difference in soil, ivliich is heavier red clay at top. 



Corinth. Field 6. 10. ix. 19, "Worst part of field is on slope, 

 especially near the top." 



Wellington. Field 43. 16. viii. 18 "Damage chiefly at top of hill 

 wh re soil is redJ'^ 



Hermitage (19. xii. 17) "In several spots damage is at top of hill and 

 not lower down." 



La Fortunee. Field 6, 16 & 17 BS. Damage much worse at top of 

 hill in 1918. Analysis showed much poorer soil, {see p. 110). 



La Fortunee. Field 33 k 48 BS. Worse at top of hill than at 

 bottom, 11. ix. 17. 



