68 TRINIDAD AND TOBAGO BULLETIN. [XVIII. 2. 



worked out might find an application in Trinidad. There are sections in 

 the Naparimas where the control of root disease requires the services 

 of an engineer rather than a mycologist, and where a steam roller 

 working on the traces would have more effect on the crop than a steam 

 plough in the fields. 



Green Dressings. 



55. The matter of green dressings is not so simple as it looks, 

 nor so well understood as it might be. There is a good deal that is 

 doubtful as to what happens to the material under various conditions 

 of soil and moisture, and as to the nature and extent of the benefit 

 derived. Decent work in India is throwing some light on these problems. 



56. The purpose of the green dressing is threefold : to supply organic 

 matter for the production of humus, to open up the soil for the access 

 of air, and, in the case of leguminous crops, to derive a supply of nitrogen 

 from the atmosphere. The first two purposes are served by any kind 

 of plant material, and where sufficient for the purpose can be produced 

 in connexion with a saleable crop, as is the case with the sweet potato 

 in Barbados, the choice of a legume may be overruled by this considera- 

 tion, nitrogen being supplied in some other form. If the full manurial 

 effect is needed a leguminous crop should be grown and turned under 

 complete, or better, its produce in the form of peas or beans used as 

 stock food and returned to the soil in this way. If the produce is sold 

 the manurial increment is by so much diminished. 



57. Where a green dressing is thickly sown and forms a dense cover 

 the protection of the soil is no small part of its value. The need for 

 aeration in the silt soils of the Colony has already been referred to, and 

 it would appear that in the choice of a green dressing for these lands its 

 effectiveness in regard to this function should be a first consideration. 

 The use of a woody, deep-rooted plant is indicated. I would suggest 

 careful trial of pigeon pea, if it is practicable to get the stems turned 

 deeply into the soil. The decay of such material leaves channels for the 

 access of air, and the results of )ueasures taken to this end in India 

 have been surprisingly good. 



Mulch. 



58. Sugar cane supplies its own mulch in the form of trash. I got 

 the impression, which may or may not be justified, that in this 

 direction as in others not so much care is taken as in the northern 

 islands to make the most of the benefits available from this material. 

 Like the conservation of pen manure, the best disposition of trash is a 

 matter well worthy of being made the subject of a careful enquirj*. 



THE CHOICE OF ROTATION CROPS. 



59. What is most to be desired for Trinidad agriculture is a rotation 

 crop with a value sufficient to secure, without a sense of sacrifice, its 

 alternation with caii'e as a general practice. No such crop is at present 

 visible. 



60. Among the crops which are available, two lines of development 

 are suggested by the imports of agricultural produce, i.e. the production 

 of stock food and of dholl, in both of which there is a trade of very 

 considerable annual value. 



