ROT ATI OX OF CROPS 47 



principle of alternating crops should he practised. The question 

 of a practical system of rotation to replace the wasteful method of 

 chena cultivation in Ceylon (by which virgin land is cleared, culti- 

 vated for a season or two and then abandoned for a number of 

 years) has yet to be satisfactorily solved. Rotation of a kind is some- 

 times applied to rice cultivation in the tropics, though seldom in 

 Ceylon. Rotation also exerts a beneficial mechanical effect on the 

 soil, owing to the more or less different mode of preparation of the 

 land required for different products, as well as by the quantity of 

 roots, etc., left in the ground by successive crops. Certain roots 

 penetrate the ground deeper than others ; these aerate the subsoil 

 and, when the crop is removed, remain in the ground to rot. 

 Proper rotation is also claimed to be an excellent preventive against 

 fungoid diseases and insect pests, these dying of starvation when a 

 crop intervenes that on which they live or feed. Weeds, too, are 

 checked (sometimes exterminated) by means of crop rotation. 

 It will generally be noticed that when plants of one kind are grow- 

 ing together in great numbers and for many succeeding years, they 

 are liable to be attacked by insect pests and fungoid diseases. 

 Any system of rotation adopted must, of course, vary according to 

 the variety of crops that are desirable to grow ; thus different systems 

 are used in different countries. DR. WILLIS recommended the 

 following system for chena lands in Ceylon : 



First Year. Tobacco, Indian-corn or Maize, Cotton, Citronella 

 or Lemon grass (these last may be left on for about three 

 years) ; all fairly exhausting crops. Pen cattle on the land between 

 crops, and dig in green-manures, e.g., Pila leaves, etc. 



Second Year. Root crops, e.g.. Cassava, Sweet- Potatoes, 

 Yams, Arrowroot, Onions, Ginger, Turmeric, etc., Pen cattle, etc. 



Third Year. Dry grains e.g. (Kurrakan), Chillies, Gingelly, 

 Gourds, small fruits, Castor-oil plants, grasses for fodder. Mustard, 

 Murunga. Pen cattle, etc. 



Fourth Year. Gram, Ground-nuts, Peas or Dhal, or other 

 leguminous crop to enrich the soil in nitrogen. 



Fifth Year. As first year, and so on. 



For Tobacco land, MR. C. DRIEBERG recommends a 3-course 

 rotation, thus: (1) Tobacco, (2) Leguminous crop, e.g., beans, 

 grams, ground-nuts etc. (3) Grain-crop, e.g., paddy, kurrakan. amu. 

 maize, etc. 



For gardens, the following rotation is recommended: (1) 

 Cabbage, (2) Carrots or Beet, (3) Peas, (4) Celery, (5) Potatoes. 



