Scientific Agriculture. 



408 



To sum up. What the Home Country can supply to the Empire is :— (1) 

 cultural instructors such as are trained for the purpose at Kew ; (2) men with a 

 sound scientific training and a firm grasp of the principles underlying agricultural 

 practice of whatever kind, and for these we must look to the universities. Men who 

 are merely familiar with British agricultural conditions will be mostly of little use 

 unless they possess the flexibility of mind which will apply theory to new and 

 unfamiliar conditions. —Times of Ceylon. 



NOTES ON GREEN MANURES. 



Amongst the most effective methods of increasing the fertility of the soil is 

 the practice of green-manuring — that is, the ploughing under of a green crop. The 

 beneficial action of this operation is a two-fold one : it enriches the soil, in the first 

 place, by supplying it with a considerable proportion of readily-available plant-food ; 

 and in the second place, by adding humus, and thus improving the soil's texture and 

 its power of absorbing and retaining moisture. When such a crop is buried, the 

 surface soil becomes enriched by the nourishing materials which the crop during the 

 period of its growth has drawn from the air and from the lower portions of the sub- 

 soil, and this material is now placed within the reach of the succeeding crop. 



During the growth of the plant the soil has, in addition, been stirred up and 

 disintegrated by the development of the roots. When ploughed under, provided 

 that sufficient moisture and warmth are present, the buried mass decomposes with 

 more or less rapidity, and the succeeding crop gets the benefit of the fertilising 

 ingredients contained in the decaying mass of vegetation in a readily-available form. 

 The resulting humus is of the greatest value, not only as a source of plant-food, but 

 in improving the soil's texture, in preventing too rapid evaporation, and in enabling 

 the soil to absorb and retain water, thus rendering it less liable to suffer during dry 

 spells. 



A further important result is the formation of carbonic acid by the decom 

 position of the buried crop. Carbonic acid is given off abundantly in the fermenta- 

 tion of the mass, and assists in the disintegration of the soil and in rendering 

 available the plant-food contained in it. 



Green-manuring is effective both in sandy and on heavy clay soils, and, 

 indeed, on all soils deficient in humus. On sandy soils the effect of green-manuring 

 is to consolidate the soil, the humus formed binding the particles together. On 

 clay soils, the effect of the addition of humus and the production of carbonic acid 

 is to loosen and aerate them. When conditions as to warmth and moisture are 

 favourable, and the crop decomposes fairly rapidly, the production of soluble 

 plant-food proceeds with considerable rapidity. This is especially the case in 

 respect to nitrogen, which is the principal manurial ingredient. Nitrification (that 

 is, the conversion of the nitrogenous material of the plant into soluble nitrates 

 takes place quite rapidly. In sandy soils, green manure nitrifies more rapidly 

 than manures like dried blood, bone-dust, &c, and only less slowly than ammonium 

 sulphate ; while in stiff clay soils the green crop nitrifies very much more rapidly 

 than either sulphate of ammonia or animal manures. 



With regard to the kind of crop to be used for the purpose of green manur- 

 ing, a good deal of latitude is permissible. Any crop that is rapid and luxuriant 

 in growth, and that can be readily turned under, is suitable for the purpose, and 

 the selection will be guided by considerations such as the time of year at which 

 it is to be grown, its suitability to soil and district, &c. Amongst the most 

 effective class of crops for the purpose are leguminous plants, such as clover, 

 cow-pea, lupines, &c, since these are specially valuable on account of their power 

 of obtaining their nitrogen from the air. They are, therefore, especially suitable 



