56 



It is commonly held that soils in hot countries, especially in tropical 

 climates, contain more organic matter than those of our latitudes : but 

 it is evident from the above analyses that such is not the case for cane 

 soils. The figure which includes organic matter and combined water 

 owes a great deal to the latter, which is driven off by heat with the 

 organic matter. In fact, putting aside soils of a peaty nature, it is 

 rare that we meet with cane soils yielding more than from 2 to 4 per 

 cent, of humus or " vegetable mould and the loss of this organic 

 matter has been proved a source of sterility in Java by causing a want 

 of porosity, of nitrogen, and of carbonic acid. Hence the danger of ap- 

 plying lime to these soils, much as most of them require it, since it 

 tends to destroy the humus in a very short space of time. In our own 

 climates lime is always "backed up," if I may use the expression, by a 

 liberal supply of organic manure ; and this is even more essential in 

 Demerara than with us. 



V. 



The Java and Demerara clays when properly drained and worked 

 will, from the moment they are put under cultivation, yield good crops 

 of canes without manure for at least ten or twelve years. In Jamaica 

 the same kind of clay will yield well for about fifteen years, and the red 

 porous clay of South Australia for fifteen or twenty years. After this 

 period the yield will become less and less each season ; and for some 

 years past it has been customary to dose the soils with sulphate of 

 ammonia or Peruvian guano, which will usually raise the produce for 

 the next two or three seasons ; but after this their stimulating effect 

 will cease almost completely, and the soil will be then in a worse con- 

 dition than before. It is preferable in most cases to endeavour by a 

 rational system of culture to restore these partially exhausted soils 

 before they have gone too far, rather than to take in new land farther 

 and farther from the boiling-houses. 



When a soil has got into this partially exhausted state, no manure 

 hitherto known, with the exception of good stable manure, well- 

 fermented farmyard dung, or the urban manure made from excreta, can 

 restore the equilibrium in favour of the planter. The reason of this 

 appears to reside in the fact that these manures are natural products, 

 and not only contain all that the pi ant requires, as is shown by analysis, 

 but in the proper state for assimilatio)t. 



Anyone who will take the trouble of perusing the accounts of the old 

 experiments made by Griobert, Lampadius, and others, will soon be con- 

 vinced that very little practical knowledge has been added to what was 

 perfectly well-known prior to the year 1820 regarding the effects of 

 manures upon the soil. Giobert mixed together silica, alumina, 

 magnesia, and lime, in the proper proportions, as he thought, to con- 

 stitute a fertile soil : he planted vegetables therein, and watered them, 

 but none of them grew until he moistened his artificial ?oil with water 

 from a dunghill. Lampadius varied the experiment by forming several 

 compartments, which he filled each with a different substance. The 

 plants which he caused to grow in these extraordinary soils " did so 

 because he watered with the liquor which exuded from a dunghill." 



These are some of the oldest experiments on manures, and were made, 

 as we see, with the most perfect manure yet known — stable manure. 

 Centuries before this the natives of Peru used guano, and the manner 



