114 



he is usually aware. In Jamaica very little imoortance seems to be 

 attached to the subject of forestry, or more especially the iufliience of 

 trees on the natural water supply a id the coiiserv^ation of soilmoistu e. 

 It is usually vaguely understood that the raiaf ill is grea'er ia well 

 wooded districts than on open tracts, bat the fact that the mere plant- 

 ing of a fringe or belt of trees — known as a " wind-break" — is instru- 

 mental in saving a 1 irge amount of soil water by preventing evapora- 

 tion, is seldom propndy appreciated. 



The subject of the artificial supply of water for irrigation is t )o 

 wide to be more than just touched upoa here It is slowly being rea- 

 lised that it is not necessarily only the dry rainless districts that require 

 to be irrigated. For irrigation if practised with reason and intelligence 

 enables the planter to do what the natural rainfall may of tea fail to 

 accomplish — that is, supply the crops with sufficient water at the right 

 time. 



If, however, the land is irrigated without due regard to the require- 

 ments of the individual crop, not only will there be a great waste of 

 water but also, in all probability, considerable damage done to the soil. 

 Further, irrigation must not be overdone. 



Over irrigation will result in : — (i.) The loss of m'lch ava^ilable plant 

 /c>^?^^ which will be washed out of the soil. The water will dissolve much 

 more of the soluble salts than the crop is capable of absorbiag. 

 Naturally the most soluble salts will be washed out in the largest 

 quantity, and it is for this reason that an over-irrigated soil is so easily 

 robbed of its nitrates — so yaluable on account of their being the SDurce 

 of the plant nitrogen. 



(ii.) Over-cropping y which will permanently damage the soil unless 

 proper return be mide by means of fertilizers. The growth of the 

 erop is so rapid that the process of converting dormant into active 

 plant food is unable to keep pace with it. 



(iii.) Coldnetsofthetoil. — A certain amount of heat will not increase 

 the temperature of a given bulk of water to the same extent as it will 

 an equal bulk of soil, consequently a wet soil requires more heat to 

 warm it than a dry soil -in other words — the wetter the soil the colder. 

 G-ermination is often retarded by the coldness of a soil. 



(iv.) Stagnation and consequent sourness. — It must be borne in mind 

 that no land should be irrigated unless properly drained, either 

 naturally, or by means of pipes or ditches. The irrigation of undrained 

 land would most certainly lead to the badly ventilated condition of the 

 land such as is found in water logged soils. 



The drainage of a soil must always be closely connected with the 

 water supply, although the existing climatic and geological conditions 

 tend to lessen its importance in Jamaica. 



The impetus lately given to banana cultivation by the establishment 

 of the Direct Fruit Line must mean that more and more land will be 

 brought under irrigation, and consequently the practical agriculturi-st 

 will find himself face to face with the necessity for drainage. 



The chief object of drainage is to aerate the soil, and any operation, 

 that helps to ventilate the soil must increase its fertility. In a water- 

 logged soil all the interspaces are filled with water to the exclusion of 

 air, with the result that the plant-roots rot, owing to being deprived of 

 the necessary supply of oxygen. 



