36 COMPOSTS 



injurious to plants ; all such are, therefore, best applied as mixtures. 

 For potting plants, valuable composts are prepared by mixing loam 

 or ordinary soil, leaf-mould, well-decomposed manures, and a 

 small proportion of fine sand and charcoal ; the proportions used 

 should vary according to the nature of the plants for which they 

 are intended and the texture of the ingredients. While many arti- 

 ficial fertilisers may be mixed together with advantage, certain 

 others are quite unsuited for combination. Thus, kainit may be 

 mixed with basic slag, sulphate of ammonia with superphosphate, 

 but neither of the latter should be mixed with basic slag, nor 

 superphosphate with nitrate of soda. Neither should sulphate of 

 ammonia come in contact with lime. 



THREE GUIDING PRINCIPLES IN MANURING 



PROFESSORS WILFARTH and WIMMER have found that the 

 appearance of plants will sometimes afford an indication of what 

 food they are most in need of. Thus : 



Nitrogen. When the plants want nitrogen the leaves are 

 said to lose their normal green colour, and take on a clear green 

 or a yellowish tint, and to dry finally \vith a clear brownish-yellow 

 colour. Nitrate increases the colour and vigour of foliage. So 

 powerful is this influence, that the energies of a fruit- bearing plant 

 may be diverted to the production of foliage by too liberal an 

 application of nitrate. 



Phosphoric acid. When phosphoric acid is deficient, the 

 leaves become a deep clear green, almost blue-green colour. With 

 a greater scarcity there appear on the leaves (first at the margin and 

 later on the whole leaf) dark-spots, and the leaf dries with a dark- 

 brown to a black-green colour. Phosphates promote fruitfulness 

 and early ripening of fruit crops. 



Potash. A scarcity of potash is said to be coincident with 

 spotted leaves, the spots appearing in the margin, and later becom- 

 ing distributed over the whole leaf, the stalk, mid-rib and veins 

 retaining their green colour. The leaf also curves or curls \vith its 

 convex side upwards, and finally dries up. Potash also improves the 

 quality of fruits and flowers, increasing the sugar contents of the 

 former, and the scent and quantity of the latter. 



