CANE SUGAR. 



in each case. The curve, however, shows that the production on this Plot 10 is 

 declining, notwithstanding the great reserves of mineral plant food with which the 

 soil started. At the present time also the crop on this plot presents a very unhealthy 

 appearance, is very slow to mature, and is extremely liable to rust. 



" We thus see that it is possible to grow a cereal crop like wheat, year after 

 year, on the same land for at least sixty years without any decline in the produc- 

 tiveness of the soil, provided an appropriate manure be supplied to replace the 

 nitrogen, phosphoric acid and potash removed by the crops. There is no evidence, 

 in fact, that the wheat gives a smaller yield when following a long succession of 

 previous wheat crops than when grown in rotation, although the vigour of the plant 

 does not appear to be so great. The real difficulty in continuous corn growing is to 

 keep the land clean ; certain weeds are favoured by the wheat and tend to accumulate, 

 so that the land can only be maintained clean by an excessive expenditure in 

 repeated land hoeing. Notwithstanding all the labour that is put on the plots, the 

 'Black Bent' grass, Alopecurus agrestis, has from time to time become so trouble- 

 some that special measures have had to be taken to eradicate it and to restore the 

 plots to a reasonable degree of cleanliness." 



It does not seem altogether unreasonable to attribute in part the damage 

 done by fungus and insect pests to the continual growth of cane on the same 

 soil, as in this way the pests have a continuous habitat. 



In discussing rotations it may not be out of place to refer to the toxic 

 excretion theory ; it was originally suggested by De Candolle that plants 

 excreted a toxic substance which prevented the continual growth on the same 

 soil, and in this way explained the benefits of rotations. After definite 

 abandonment this idea has been revived, mainly by Whitney and Cameron, but 

 its discussion lies altogether without the limits of the present text book. 



Pen Manure. In those countries which employ animal traction very 

 large numbers of cattle and mules are kept for transport purposes, and large 

 quantities of pen manure are produced annually, and it is remunerative to stall 

 the cattle at night with sufficient litter, such as dry cane trash, to absorb their 

 urine. In Mauritius great attention is paid to this source of manure. The 

 method adopted is as follows. 



The live stock of the estate, which may number from two to three hundred, 

 are in great part kept in 'pares,' which may be from fifty to a hundred yards 

 square ; a portion of the pare is often covered in to provide shelter in inclement 

 weather. The whole area is covered with cane trash transported from the 

 fields and used as bedding. During the whole year if the supply of labour is 

 sufficient, the soiled litter is in a continual process of renewal and removal, the 

 bedding being replaced throughout on an average once a week ; on removal it 

 is placed on stone platforms or in basins ten feet deep, both platforms and 

 basins generally being about fifty feet square. The whole mass when com- 

 pleted is continually watered with fermented molasses and water or distillery 

 refuse, and sometimes with dilute sulphuric acid; the drainings collect in 



88 



